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Urban evaporation rates for water-permeable pavements.
In urban areas the natural water balance is disturbed. Infiltration and evaporation are reduced, resulting in a high surface runoff and a typical city climate, which can lead to floods and damages. Water-permeable pavements have a high infiltration rate that reduces surface runoff by increasing the groundwater recharge. The high water retention capacity of the street body of up to 51 l/m(2) and its connection via pores to the surface lead to higher evaporation rates than impermeable surfaces. A comparison of these two kinds of pavements shows a 16% increase in evaporation levels of water-permeable pavements. Furthermore, the evaporation from impermeable pavements is linked directly to rain events due to fast-drying surfaces. Water-permeable pavements show a more evenly distributed evaporation after a rain event. Cooling effects by evaporative heat loss can improve the city climate even several days after rain events. On a large scale use, uncomfortable weather like sultriness or dry heat can be prevented and the urban water balance can be attenuated towards the natural. PMID:20818060
Starke, P; G—bel, P; Coldewey, W G
Soil water management implications during the constant rate and the falling rate stages of soil evaporation
Desorptivity is a soil physical term used to describe the ability of soil to lose water by evaporation. Theoretically, it has been established that evaporation of water from soil during the falling rate stage, when water becomes limiting, is proportional to the square root of time. The proportionality constant is called desorptivity. Using ten soils with different textures from different
Mensah Bonsu
Estimating steady-state evaporation rates from bare soils under conditions of high water table
A procedure that combines meteorological and soil equations of water transfer makes it possible to estimate approximately the steady-state evaporation from bare soils under conditions of high water table. Field data required include soil-water retention curves, water table depth and a record of air temperature, air humidity and wind velocity at one elevation. The procedure takes into account the relevant atmospheric factors and the soil's capability to conduct 'water in liquid and vapor forms. It neglects the effects of thermal transfer (except in the vapor case) and of salt accumulation. Homogeneous as well as layered soils can be treated. Results obtained with the method demonstrate how the soil evaporation ratesñdepend on potential evaporation, water table depth, vapor transfer and certain soil parameters.
Ripple, C. D.; Rubin, J.; Van Hylckama, T. E. A.
Evaporation Rates for Liquid Water and Ice Under Current Martian Conditions
NASA Technical Reports Server (NTRS)
A number of studies have been concerned with the evaporation rates under martian conditions in order to place limits on the possible survival time of both liquid water and ice exposed on the surface of Mars. Such studies also aid in assessing the efficacy of an overlying layer of dust or loose regolith material in providing a barrier to free evaporation and thus prolong the lifetime of water in locations where its availability to putative living organisms would be significant. A better quantitative understanding of the effects of phase changes of water in the near surface environment would also aid the evaluation of the possible role of water in the formation of currently observed features, such as gullies in cliff walls and relatively short-term changes in the albedo of small surface areas ('dark stains'). Laboratory measurements aimed at refinement of our knowledge of these values are described here. The establishment of accurate values for evaporation rates and their dependence on the physical conditions of temperature, pressure and energy input, is an important benchmark for the further investigation of the efficacy of barriers to free evaporation in providing a prolonged period of survival of the water, particularly as a liquid.
Sears, D. W. G.; Moore, S. R.; Meier, A.; Chittenden, J.; Kareev, M.; Farmer, C. B.
Effect of Thickness of a Water Repellent Soil Layer on Soil Evaporation Rate
NASA Astrophysics Data System (ADS)
A water repellent soil layer overlying wettable soil is known to affect soil evaporation. This effect can be beneficial for water conservation in areas where water is scarce. Little is known, however, about the effect of the thickness of the water repellent layer. The thickness of this layer can vary widely, and particularly after wildfire, with the soil temperature reached and the duration of the fire. This study was conducted to investigate the effect of thickness of a top layer of water repellent soil on soil evaporation rate. In order to isolate the thickness from other possible factors, fully wettable standard sand (300~600 microns) was used. Extreme water repellency (WDPT > 24 hours) was generated by 'baking' the sand mixed with oven-dried pine needles (fresh needles of Pinus densiflora) at the mass ratio of 1:13 (needle:soil) at 185¯C for 18 hours. The thicknesses of water repellent layers were 1, 2, 3 and 7 cm on top of wettable soil. Fully wettable soil columns were prepared as a control. Soil columns (8 cm diameter, 10 cm height) were covered with nylon mesh. Tap water (50 ml, saturating 3 cm of a soil column) was injected with hypoderm syringes from three different directions at the bottom level. The injection holes were sealed with hot-melt adhesive immediately after injection. The rate of soil evaporation through the soil surface was measured by weight change under isothermal condition of 40¯C. Five replications were made for each. A trend of negative correlation between the thickness of water repellent top layer and soil evaporation rate is discussed in this contribution.
Ahn, S.; Im, S.; Doerr, S.
An experimental investigation on the effects of surface gravity waves on the water evaporation rate in different air flow regimes
NASA Astrophysics Data System (ADS)
Estimating rate of evaporation from undisturbed water surfaces to moving and quiet air has been the topic a vast number of research activities. The obvious presence of various shapes of gravity waves on the water body surfaces was the motivation of this experimental investigation. In this investigation experimental measurements have been done to quantify evaporation rate from wavy water surfaces in free, mixed and forced convection regimes. The effects of a wide range of surface gravity waves from low steepness, round shaped crest with slow celerity, to steep and very slight spilling crest waves, on the water evaporation rate have been investigated. A wide range of was achieved by applying different air flow velocities on a large heated wave flume equipped with a wind tunnel. Results reveal that wave motion on the water surface increase the rate of evaporation for all air flow regimes. For free convection, due to the effect of wave motion for pumping rotational airflows at the wave troughs and the dominant effect of natural convection for the air flow advection, the maximum evaporation increment percentage from wavy water surface is about 70 %. For mixed and forced convection, water evaporation rate increment is more sensitive to the air flow velocity for the appearance of very slight spilling on the steep wave crests and the leeward air flow structures.
Jodat, Amin; Moghiman, Mohammad; Shirkhani, Golshad
Habitat-mediated shifts and plasticity in the evaporative water loss rates of two congeneric pit vipers (Squamata, Viperidae, Agkistrodon)
Question: Are increased rates of total evaporative water loss (TEWL) associated with evolutionary transitions from terrestrial to aquatic habitats? Do individuals acclimated to wet conditions demonstrate higher TEWL rates than those acclimated to dry conditions? Organisms: Individuals of the snake species Agkistrodon piscivorus (Viperidae; semi-aquatic) and Agkistrodon contortrix (terrestrial) collected from the Savannah River Site, Aiken, SC, USA. Methods: We
Daniel S. Moen; Christopher T. Winne; Robert N. Reed
NSDL National Science Digital Library
In this activity, learners conduct an experiment to measure the temperature of a dry cotton ball versus a wet one. Explore water evaporation and investigate why swimming and drinking water keeps your body cool. This activity guide includes a step-by-step instructional video.
Center, Saint L.
A Wind Tunnel Investigation of the Rate of Evaporation of Small Water Drops Falling at Terminal Velocity in Air
An experimental study of the effect of ventilation on the rate of evaporation of small water drops falling at terminal velocity in air has been carried out in a wind tunnel where water drops could he suspended freely in the tunnel airstream. For Reynolds numbers NRe2 it was found that the Sherwood number NSh was linearly related to NRe1\\/2NI, in
K. V. Beard; H. R. Pruppacher
A previously published kinetic model for evaporative rates of substances into air leads to the estimation of the dependence of solute transfer coefficients on turbulence applied to the system. The ratios of the transfer coefficients of all solutes become insensitive to air turbul...
NASA Technical Reports Server (NTRS)
A water membrane evaporator (WME) has been conceived and tested as an alternative to the contamination-sensitive and corrosion-prone evaporators currently used for dissipating heat from space vehicles. The WME consists mainly of the following components: An outer stainless-steel screen that provides structural support for the components mentioned next; Inside and in contact with the stainless-steel screen, a hydrophobic membrane that is permeable to water vapor; Inside and in contact with the hydrophobic membrane, a hydrophilic membrane that transports the liquid feedwater to the inner surface of the hydrophobic membrane; Inside and in contact with the hydrophilic membrane, an annular array of tubes through which flows the spacecraft coolant carrying the heat to be dissipated; and An inner exclusion tube that limits the volume of feedwater in the WME. In operation, a pressurized feedwater reservoir is connected to the volume between the exclusion tube and the coolant tubes. Feedwater fills the volume, saturates the hydrophilic membrane, and is retained by the hydrophobic membrane. The outside of the WME is exposed to space vacuum. Heat from the spacecraft coolant is conducted through the tube walls and the water-saturated hydrophilic membrane to the liquid/vapor interface at the hydrophobic membrane, causing water to evaporate to space. Makeup water flows into the hydrophilic membrane through gaps between the coolant tubes.
Ungar, Eugene K.; Almlie, Jay C.
Sheet Membrane Spacesuit Water Membrane Evaporator
NASA Technical Reports Server (NTRS)
A document describes a sheet membrane spacesuit water membrane evaporator (SWME), which allows for the use of one common water tank that can supply cooling water to the astronaut and to the evaporator. Test data showed that heat rejection performance dropped only 6 percent after being subjected to highly contaminated water. It also exhibited robustness with respect to freezing and Martian atmospheric simulation testing. Water was allowed to freeze in the water channels during testing that simulated a water loop failure and vapor backpressure valve failure. Upon closing the backpressure valve and energizing the pump, the ice eventually thawed and water began to flow with no apparent damage to the sheet membrane. The membrane evaporator also serves to de-gas the water loop from entrained gases, thereby eliminating the need for special degassing equipment such as is needed by the current spacesuit system. As water flows through the three annular water channels, water evaporates with the vapor flowing across the hydrophobic, porous sheet membrane to the vacuum side of the membrane. The rate at which water evaporates, and therefore, the rate at which the flowing water is cooled, is a function of the difference between the water saturation pressure on the water side of the membrane, and the pressure on the vacuum side of the membrane. The primary theory is that the hydrophobic sheet membrane retains water, but permits vapor pass-through when the vapor side pressure is less than the water saturation pressure. This results in evaporative cooling of the remaining water.
Bue, Grant; Trevino, Luis; Zapata, Felipe; Dillion, Paul; Castillo, Juan; Vonau, Walter; Wilkes, Robert; Vogel, Matthew; Frodge, Curtis
Water evaporation in silica colloidal deposits.
The results of an experimental study on the evaporation and boiling of water confined in the pores of deposits made of mono-dispersed silica colloidal micro-spheres are reported. The deposits are studied using scanning electron microscopy, adsorption of nitrogen, and adsorption of water through attenuated total reflection-infrared spectroscopy. The evaporation is characterized using differential scanning calorimetry and thermal gravimetric analysis. Optical microscopy is used to observe the patterns on the deposits after evaporation. When heating at a constant rate and above boiling temperature, the release of water out of the deposits is a two step process. The first step is due to the evaporation and boiling of the surrounding and bulk water and the second is due to the desorption of water from the pores. Additional experiments on the evaporation of water from membranes having cylindrical pores and of heptane from silica deposits suggest that the second step is due to the morphology of the deposits. PMID:23928488
Peixinho, Jorge; LefÒvre, GrÕgory; Coudert, FranÓois-Xavier; Hurisse, Olivier
NSDL National Science Digital Library
This three-part activity consists of an activity that groups of learners develop themselves, a given procedure, and an optional demonstration. First, learners discuss examples of evaporation and then design and conduct their own test to find out whether heating water has an effect on the rate of evaporation. While waiting for their results, learners conduct another evaporation activity using single drops of water on 2 paper towels, one of which is heated. The optional demonstration compares the rate of evaporation of hot and cold water using a sensitive scale or balance. In each of these experiences with evaporation, learners will identify variables, consider how to best control them, and use their observations to conclude that heating water increases the rate of evaporation.
Kessler, James H.; Galvan, Patricia M.
Rate of runaway evaporative cooling
NASA Astrophysics Data System (ADS)
Evaporative cooling is a process that is essential in creating Bose-Einstein condensates in dilute atomic gasses. This process has often been simulated based on a model using a truncated Boltzmann distribution. This model assumes that the energy distribution up to the threshold energy can still be described by a Boltzmann distribution: it assumes detailed balance up to the threshold energy. However, the evolution of the distribution function in time is not taken into account. Here we solve the kinetic Boltzmann equation for a gas undergoing evaporative cooling in a harmonic and linear trap in order to determine the evolution of the energy distribution. The magnitude of the discrepancy with the truncated Boltzmannmodel is calculated by including a polynomial expansion of the distribution function. We find that up to 35% fewer particles are found in the high-energy tail of the distribution with respect to the truncated Boltzmann distribution and up to 15% more collisions are needed to reach quantum degeneracy. Supported by a detailed investigation of the particle loss rate at different energies, we conclude that the limited occupation of high-energy states during the evaporation process causes the lowering of the evaporation speed and efficiency.
van de Groep, J.; van der Straten, P.; Vogels, J. M.
Computation of hypersonic flows with finite rate condensation and evaporation of water
NASA Technical Reports Server (NTRS)
A computer program for modelling 2D hypersonic flows of gases containing water vapor and liquid water droplets is presented. The effects of interphase mass, momentum and energy transfer are studied. Computations are compared with existing quasi-1D calculations on the nozzle of the NASA Langley Eight Foot High Temperature Tunnel, a hypersonic wind tunnel driven by combustion of natural gas in oxygen enriched air.
Perrell, Eric R.; Candler, Graham V.; Erickson, Wayne D.; Wieting, Alan R.
The influence of organic coatings on water evaporation rates from aqueous ammonium sulphate aerosols
An open issue related to organic aerosol components is their ability to form films around atmospheric particles, i.e. if and how aqueous particles get coated with water-insoluble material. Organic aerosol formation resulting from ozonolysis of alpha-pinene, myrcene and sabinene was investigated in a large aerosol chamber in the presence of aqueous seed aerosols. The partitioning of oxidation products into the
A. Kiendler-Scharr; T. F. Mentel
Repeatability and individual correlates of basal metabolic rate and total evaporative water loss in birds: A case study in European stonechats
Basal metabolic rate (BMR) and total evaporative water loss (TEWL) are thought to have evolved in conjunction with life history traits and are often assumed to be characteristic features of an animal. Physiological traits can show large intraindividual variation at short and long timescales, yet natural selection can only act on a trait if it is a characteristic feature of
Maaike A. Versteegh; Barbara Helm; Niels J. Dingemanse; B. Irene Tieleman
Evaporation Rates of Brine on Mars
NASA Technical Reports Server (NTRS)
While Mars is now largely a dry and barren place, recent data have indicated that water has flowed at specific locations within the last approx. 10(exp 6) y. This had led to a resurgence of interest in theoretical and experimental work aimed at understanding the behavior of water on Mars. There are several means whereby the stability of liquid water on Mars could be increased, one being the presence solutes that would depress the freezing point. Salt water on Earth is about 0.5M NaCl, but laboratory experiments suggest that martian salt water is quite different. We recently began a program of laboratory measurements of the stability of liquid water, ice and ice-dust mixtures under martian conditions and here report measurements of the evaporation rate of 0.25M brine.
Sears, D. W. G.; Chittenden, J.; Moore, S. R.; Meier, A.; Kareev, M.; Farmer, C. B.
Quantifying nonisothermal subsurface soil water evaporation
NASA Astrophysics Data System (ADS)
Accurate quantification of energy and mass transfer during soil water evaporation is critical for improving understanding of the hydrologic cycle and for many environmental, agricultural, and engineering applications. Drying of soil under radiation boundary conditions results in formation of a dry surface layer (DSL), which is accompanied by a shift in the position of the latent heat sink from the surface to the subsurface. Detailed investigation of evaporative dynamics within this active near-surface zone has mostly been limited to modeling, with few measurements available to test models. Soil column studies were conducted to quantify nonisothermal subsurface evaporation profiles using a sensible heat balance (SHB) approach. Eleven-needle heat pulse probes were used to measure soil temperature and thermal property distributions at the millimeter scale in the near-surface soil. Depth-integrated SHB evaporation rates were compared with mass balance evaporation estimates under controlled laboratory conditions. The results show that the SHB method effectively measured total subsurface evaporation rates with only 0.01-0.03 mm h-1difference from mass balance estimates. The SHB approach also quantified millimeter-scale nonisothermal subsurface evaporation profiles over a drying event, which has not been previously possible. Thickness of the DSL was also examined using measured soil thermal conductivity distributions near the drying surface. Estimates of the DSL thickness were consistent with observed evaporation profile distributions from SHB. Estimated thickness of the DSL was further used to compute diffusive vapor flux. The diffusive vapor flux also closely matched both mass balance evaporation rates and subsurface evaporation rates estimated from SHB.
Deol, Pukhraj; Heitman, Josh; Amoozegar, Aziz; Ren, Tusheng; Horton, Robert
Turkish Undergraduates' Misconceptions of Evaporation, Evaporation Rate, and Vapour Pressure
NASA Astrophysics Data System (ADS)
This study focused on students' misconceptions related to evaporation, evaporation rate, and vapour pressure. Open-ended diagnostic questions were used with 107 undergraduates in the Primary Science Teacher Training Department in a state university in Turkey. In addition, 14 students from that sample were interviewed to clarify their written responses and to further probe their understandings of the questions asked in the test. The findings revealed a number of misconceptions, many of which have not been previously documented. The results have implications for tertiary level teaching suggesting that a substantial review of teaching strategies is needed.
Canpolat, NurtaÓ
Analytical solution for soil water redistribution during evaporation process.
Simulating the dynamics of soil water content and modeling soil water evaporation are critical for many environmental and agricultural strategies. The present study aims to develop an analytical solution to simulate soil water redistribution during the evaporation process. This analytical solution was derived utilizing an exponential function to describe the relation of hydraulic conductivity and water content on pressure head. The solution was obtained based on the initial condition of saturation and an exponential function to model the change of surface water content. Also, the evaporation experiments were conducted under a climate control apparatus to validate the theoretical development. Comparisons between the proposed analytical solution and experimental result are presented from the aspects of soil water redistribution, evaporative rate and cumulative evaporation. Their good agreement indicates that this analytical solution provides a reliable way to investigate the interaction of evaporation and soil water profile. PMID:24355839
Teng, Jidong; Yasufuku, Noriyuki; Liu, Qiang; Liu, Shiyu
Condensation and evaporation of water vapor in mixed aerosols of liquid droplets and ice: numerical comparison of growth rate expressions
We compare four different H2O mass flux descriptions in simulations of the evolution of mixed water\\/ice aerosol populations undergoing condensational growth. It is shown that the Maxwellian description, ignoring condensation heat release, overestimates the growth rates severely when compared with an exact numerical description. The well-known Mason equation predicts the growth rates somewhat better, but still in an inadequate manner
Jukka Hienola; Markku Kulmala; Ari Laaksonen
Dynamics of water evaporation fronts
NASA Astrophysics Data System (ADS)
The evolution and shapes of water evaporation fronts caused by long-wave instability of vertical flows with a phase transition in extended two-dimensional horizontal porous domains are analyzed numerically. The plane surface of the phase transition loses stability when the wave number becomes infinite or zero. In the latter case, the transition to instability is accompanied with reversible bifurcations in a subcritical neighborhood of the instability threshold and by the formation of secondary (not necessarily horizontal homogeneous) flows. An example of motion in a porous medium is considered concerning the instability of a water layer lying above a mixture of air and vapor filling a porous layer under isothermal conditions in the presence of capillary forces acting on the phase transition interface.
Il'ichev, A. T.; Shargatov, V. A.
Water Purification by Evaporation and Condensation
NSDL National Science Digital Library
This demonstration illustrates how the water cycle helps to purify water. Students are introduced to the key terms, which are evaporation and condensation. They discover that evaporation is defined as the process through which a liquid becomes a vapor, while condensation is simply the reverse. Students also learn that in the case of water, the main mechanisms for evaporation and condensation are heating and cooling, respectively.
Spatial distributions of expansion rate, cell division rate and cell size in maize leaves: a synthesis of the effects of soil water status, evaporative demand and temperature
extent. Conversely, cell size of epidermis and mesophyll were reduced by water deficit in mature The spatial distributions of leaf expansion rate, cell parts of the leaf. division rate and cell size was examined under con-
Francois Tardieu; Matthieu Reymond; Philippe Hamard; Christine Granier; Bertrand Muller
Evaporative cooling of speleothem drip water
This study describes the first use of concurrent high-precision temperature and drip rate monitoring to explore what controls the temperature of speleothem forming drip water. Two contrasting sites, one with fast transient and one with slow constant dripping, in a temperate semi-arid location (Wellington, NSW, Australia), exhibit drip water temperatures which deviate significantly from the cave air temperature. We confirm the hypothesis that evaporative cooling is the dominant, but so far unattributed, control causing significant disequilibrium between drip water and host rock/air temperatures. The amount of cooling is dependent on the drip rate, relative humidity and ventilation. Our results have implications for the interpretation of temperature-sensitive, speleothem climate proxies such as ?18O, cave microecology and the use of heat as a tracer in karst. Understanding the processes controlling the temperature of speleothem-forming cave drip waters is vital for assessing the reliability of such deposits as archives of climate change.
Cuthbert, M. O.; Rau, G. C.; Andersen, M. S.; Roshan, H.; Rutlidge, H.; Marjo, C. E.; Markowska, M.; Jex, C. N.; Graham, P. W.; Mariethoz, G.; Acworth, R. I.; Baker, A.
Evaporative cooling of speleothem drip water.
This study describes the first use of concurrent high-precision temperature and drip rate monitoring to explore what controls the temperature of speleothem forming drip water. Two contrasting sites, one with fast transient and one with slow constant dripping, in a temperate semi-arid location (Wellington, NSW, Australia), exhibit drip water temperatures which deviate significantly from the cave air temperature. We confirm the hypothesis that evaporative cooling is the dominant, but so far unattributed, control causing significant disequilibrium between drip water and host rock/air temperatures. The amount of cooling is dependent on the drip rate, relative humidity and ventilation. Our results have implications for the interpretation of temperature-sensitive, speleothem climate proxies such as ?(18)O, cave microecology and the use of heat as a tracer in karst. Understanding the processes controlling the temperature of speleothem-forming cave drip waters is vital for assessing the reliability of such deposits as archives of climate change. PMID:24895139
Cuthbert, M O; Rau, G C; Andersen, M S; Roshan, H; Rutlidge, H; Marjo, C E; Markowska, M; Jex, C N; Graham, P W; Mariethoz, G; Acworth, R I; Baker, A
Contaminated Water Evaporation System Design for the Tailing Facility
NASA Astrophysics Data System (ADS)
The treatment and disposal of contaminated water is a major issue for the mining industry. A common approach to this issue is through the process of evaporation and evapotranspiration. This process is commonly done simply by spreading the contaminated water over a given area and exposing it to the sun. This causes the water to evaporate and be returned into the hydrological cycle as clean water, leaving the contaminants behind. Evaporation systems are based on the continuity principle for conservation of mass, so that the rate of evaporation is greater than the inflow. Evaporation systems are by no means a new method, but the design criteria, procedures, and methodology have not been documented. Without design criteria there are no guidelines to creating a successful evaporation system for water treatment. This paper describes the methodology of designing a water evaporation system based on the continuity principle and conservation of mass. This paper also presents how incorporating a time series model can utilize historical data to predict future requirements for the evaporation area and contaminated water storage. With this methodology, the mining industry can have guidelines and design standards to follow for a sustainable alternative for the treatment of contaminated water.; ;
Langer, J. M.; Cheng, J.
Water evaporation and conformational changes from partially solvated ubiquitin.
Using molecular dynamics simulation, we study the evaporation of water molecules off partially solvated ubiquitin. The evaporation and cooling rates are determined for a molecule at the initial temperature of 300?K. The cooling rate is found to be around 3?K/ns, and decreases with water temperature in the course of the evaporation. The conformation changes are monitored by studying a variety of intermediate partially solvated ubiquitin structures. We find that ubiquitin shrinks with decreasing hydration shell and exposes more of its hydrophilic surface area to the surrounding. PMID:21188070
Thirumuruganandham, Saravana Prakash; Urbassek, Herbert M
Black Hole Evaporation Rates without Spacetime
NASA Astrophysics Data System (ADS)
Verlinde recently suggested that gravity, inertia, and even spacetime may be emergent properties of an underlying thermodynamic theory. This vision was motivated in part by Jacobsons 1995 surprise result that the Einstein equations of gravity follow from the thermodynamic properties of event horizons. Taking a first tentative step in such a program, we derive the evaporation rate (or radiation spectrum) from black hole event horizons in a spacetime-free manner. Our result relies on a Hilbert space description of black hole evaporation, symmetries therein which follow from the inherent high dimensionality of black holes, global conservation of the no-hair quantities, and the existence of Penrose processes. Our analysis is not wedded to standard general relativity and so should apply to extended gravity theories where we find that the black hole area must be replaced by some other property in any generalized area theorem.
Braunstein, Samuel L.; Patra, Manas K.
Black hole evaporation rates without spacetime.
Verlinde recently suggested that gravity, inertia, and even spacetime may be emergent properties of an underlying thermodynamic theory. This vision was motivated in part by Jacobson's 1995 surprise result that the Einstein equations of gravity follow from the thermodynamic properties of event horizons. Taking a first tentative step in such a program, we derive the evaporation rate (or radiation spectrum) from black hole event horizons in a spacetime-free manner. Our result relies on a Hilbert space description of black hole evaporation, symmetries therein which follow from the inherent high dimensionality of black holes, global conservation of the no-hair quantities, and the existence of Penrose processes. Our analysis is not wedded to standard general relativity and so should apply to extended gravity theories where we find that the black hole area must be replaced by some other property in any generalized area theorem. PMID:21902381
Braunstein, Samuel L; Patra, Manas K
Experimental investigation of evaporation-induced convection in water using laser based measurement techniques
Recent studies have shown that the evaporation of water can induce surface tension gradients along the water surface that ultimately lead to a surface driven flow, known as Marangoni convection. To visualize and characterize the Marangoni convection in water, this study generated evaporation driven convection in pure water with a vacuum pump to control and increase the evaporation rate of
Xudong Song; David S. Nobes
Advances in Sensible Heat Balance Characterization of Soil Water Evaporation
NASA Astrophysics Data System (ADS)
Soil water evaporation intimately couples the hydrological cycle with the land-surface energy balance, making it an important driver for a wide range of terrestrial processes. To date, few methods have been available characterize soil water evaporation in detail, which has, in turn, limited capability to predict soil water evaporation processes in local and large scale models. Recent work has developed a measurement-based soil sensible heat balance (SHB) approach, capable of quantifying evaporation time and depth dynamics at a vertical scale of millimeters, near the soil surface. The SHB approach does not require detailed characterization or estimation of soil hydraulic properties, which has been a limitation in previous work. Rather it utilizes detailed measurements of the soil temperature profile and soil thermal properties from heat-pulse sensors in order to derive evaporation front dynamics. Laboratory experiments indicate that the SHB approach is precise to within <10% of independent mass balance measurements. Field tests indicate that the SHB is well correlated to lysimeter and Bowen ratio measurement approaches for bare surface conditions. Using SHB, laboratory and field experiments have characterized migration of the soil water evaporation front during multi-day drying events, and linked the shift between potential evaporation and falling rate evaporation to changes in soil surface albedo and soil moisture.
Heitman, J.; Xiao, X.; Deol, P. K.; Horton, R.; Ren, T.
Evaporative Recovery of Chromium Plating Rinse Waters.
National Technical Information Service (NTIS)
This demonstration project documents the practicality of a new evaporative approach for recovering chromic acid from metal finishing rinse waste waters, as well as the economics of the system under actual operating conditions. The six-month study of chrom...
L. N. Elicker R. W. Lacy
Spreadsheet and short-cut methods have been developed for predicting evaporation rates and evaporation times for spills (and constrained baths) of chemical mixtures. Steady-state and time-varying predictions of evaporation rates can be made for six-component mixtures, includ...
Evaporation from soil in relation to residue rate, mixing depth, soil texture and evaporativity
The role of crop residues as a surface mulch on evaporation has been widely studied. But information on evaporation and its reduction by crop residues mixed in surface soil to different depths particularly in relation to soil texture and evaporativity (Eo) is lacking. We studied the effect of four rates of paddy straw, viz. 0, 2, 4 and 8 Mg
B. S. Gill; S. K. Jalota
Estimating soil water evaporation using radar measurements
NASA Technical Reports Server (NTRS)
Field studies were conducted to evaluate the application of radar reflectivity as compared with the shortwave reflectivity (albedo) used in the Idso-Jackson equation for the estimation of daily evaporation under overcast sky and subhumid climatic conditions. Soil water content, water potential, shortwave and radar reflectivity, and soil and air temperatures were monitored during three soil drying cycles. The data from each cycle were used to calculate daily evaporation from the Idso-Jackson equation and from two other standard methods, the modified Penman and plane of zero-flux. All three methods resulted in similar estimates of evaporation under clear sky conditions; however, under overcast sky conditions, evaporation fluxes computed from the Idso-Jackson equation were consistently lower than the other two methods. The shortwave albedo values in the Idso-Jackson equation were then replaced with radar reflectivities and a new set of total daily evaporation fluxes were calculated. This resulted in a significant improvement in computed soil evaporation fluxes from the Idso-Jackson equation, and a better agreement between the three methods under overcast sky conditions.
Sadeghi, Ali M.; Scott, H. D.; Waite, W. P.; Asrar, G.
Thermal effects of the substrate on water droplet evaporation.
We experimentally investigate the behavior of a pinned water droplet evaporating into air. The influence of the substrate temperature and substrate thermal properties on the evaporation process are studied in both hydrophilic and hydrophobic conditions. Our objective is to understand the effect of thermal mechanisms on the droplet evaporation process. The experimental results are compared with the quasisteady, diffusion-driven evaporation model, which is implemented under the influence of the temperature; the model assumes the isothermia of the droplet at the substrate temperature. The results highlight a favorable correlation between the model and the experimental data at ambient temperatures for most situations considered here. The model works to qualitatively describe the influence of the substrate temperature on the evaporation process. However, with an increase in the substrate temperature, the role of the thermal-linked mechanisms becomes increasingly important; this experiment highlights the need for more accurate models to account for the buoyant convection in vapor transport and the evaporative cooling and heat conduction between the droplet and the substrate. Finally, the experimental data reveal the modification of contact angle evolution as the temperature increases and the crucial role played by the nature of the substrate in the evaporation of a sessile droplet. The influence of the substrate thermal properties on the global evaporation rate is explained by the parallel thermal effusivity of the liquid and solid phases. PMID:23005772
Sobac, B; Brutin, D
Membrane-Based Water Evaporator for a Space Suit
NASA Technical Reports Server (NTRS)
A membrane-based water evaporator has been developed that is intended to serve as a heat-rejection device for a space suit. This evaporator would replace the current sublimator that is sensitive to contamination of its feedwater. The design of the membrane-based evaporator takes advantage of recent advances in hydrophobic micropore membranes to provide robust heat rejection with much less sensitivity to contamination. The low contamination sensitivity allows use of the heat transport loop as feedwater, eliminating the need for the separate feedwater system used for the sublimator. A cross section of the evaporator is shown in the accompanying figure. The space-suit cooling loop water flows into a distribution plenum, through a narrow annulus lined on both sides with a hydrophobic membrane, into an exit plenum, and returns to the space suit. Two perforated metal tubes encase the membranes and provide structural strength. Evaporation at the membrane inner surface dissipates the waste heat from the space suit. The water vapor passes through the membrane, into a steam duct and is vented to the vacuum environment through a back-pressure valve. The back-pressure setting can be adjusted to regulate the heat-rejection rate and the water outlet temperature.
Ungar, Eugene K.; McCann, Charles J.; O'Connell, Mary K.; Andrea, Scott
The technical conununity has only recently addressed the role of atmospheric temperature variations on rates of air-water vapor phase toxicant exchange. The technical literature has documented that: 1) day time rates of elemental mercury vapor phase air-water exchange can exceed ...
Evaporation rates of pasture-mesquite vegetation in central Mexico
NASA Astrophysics Data System (ADS)
The semiarid highlands of Queretaro, in central Mexico, are characterized by booming urban and industrial developments with increasing demand for water. Agriculture takes place in the valleys and the surrounding hills have different types of xeric to subtropical rangeland. Hills are unfit for agriculture and usually are managed for cattle production and fuelwood. However, recent studies suggest that some hill areas are important for groundwater recharge and if they are not protected, important water shortages are envisioned. A critical question involves the effects of land management practices on rangeland hydrologic processes. Evaporation (E), which includes plant and soil evaporation is the largest water loss from rangelands and few data are available for central Mexico. The objective of this study was to estimate E from a mesquite (Prosopis sp.) dominated vegetation using the eddy correlation and the Pennman-Monteith models. Measurements were made during 24 summer days of 2004 at a piedmont site at Amascala, Queretaro (1919 m, 20¯ 41' N, 100¯ 16' W). Long term annual rainfall is 568 Ý 137 mm. Shrub density was 770 plants per hectare and mean height was 1.8 m. The understory was composed by a mixture of annual and perennial grasses but their biomass was negligible. Agroforestry was the current land use of the site. Shrubs were pruned every 2 or 3 years to maintain its height and promote leafty regrowth. Goats usually browsed the mesquite canopy, but during the time of the study they were excluded from the area.The rainy season started on 15 May and measurements initiated on 1 June, five days after a severe hail storm. Although the mesquite canopy had a full developed canopy with leaf area index of 3.2 by this time, they lost approximately 70% of leaf area. May and June rainfall was 146 mm and 46 mm occurred during the measuring period. Throughout the measurement period E was coupled to global radiation and total evaporation was 73.8 mm. On cloudy days E ranged from 1.1 to 2.0 mm d-1, maximum E was 4.3 mm d-1 on sunny days and the average E was 3.1 mm d-1. Average daily E increased during the measuring period at a rate of 0.05 mm d-1 (r2=0.2, p<0.05). Data suggest that evaporation from a pasture-mesquite vegetation is an important component in the water balance considering the limited rainfall occurring.
Sosa, E. G.; Escobar, A. G.
Hollow-Fiber Spacesuit Water Membrane Evaporator
NASA Technical Reports Server (NTRS)
The hollow-fiber spacesuit water membrane evaporator (HoFi SWME) is being developed to perform the thermal control function for advanced spacesuits and spacecraft to take advantage of recent advances in micropore membrane technology in providing a robust, heat-rejection device that is less sensitive to contamination than is the sublimator. After recent contamination tests, a commercial-off-the-shelf (COTS) micro porous hollow-fiber membrane was selected for prototype development as the most suitable candidate among commercial hollow-fiber evaporator alternatives. An innovative design that grouped the fiber layers into stacks, which were separated by small spaces and packaged into a cylindrical shape, was developed into a full-scale prototype for the spacesuit application. Vacuum chamber testing has been performed to characterize heat rejection as a function of inlet water temperature and water vapor back-pressure, and to show contamination resistance to the constituents expected to be found in potable water produced by the wastewater reclamation distillation processes. Other tests showed tolerance to freezing and suitability to reject heat in a Mars pressure environment. In summary, HoFi SWME is a lightweight, compact evaporator for heat rejection in the spacesuit that is robust, contamination- insensitive, freeze-tolerant, and able to reject the required heat of spacewalks in microgravity, lunar, and Martian environments. The HoFi is packaged to reject 810 W of heat through 800 hours of use in a vacuum environment, and 370 W in a Mars environment. The device also eliminates free gas and dissolved gas from the coolant loop.
Bue, Grant; Trevino, Luis; Tsioulos, Gus; Mitchell, Keith; Settles, Joseph
Nonideal statistical rate theory formulation to predict evaporation rates from equations of state.
A method of including nonideal effects in the statistical rate theory (SRT) formulation is presented and a generic equation-of-state based SRT model was developed for predicting evaporation rates. Further, taking the Peng-Robinson equation of state as an example, vapor phase pressures at which particular evaporation rates are expected were calculated, and the predictions were found to be in excellent agreement with the experimental observations for water and octane. A high temperature range (near the critical region) where the previously existing ideal SRT model is expected to yield inaccurate results was identified and predictions (for ethane and butane) were instead made with the Peng-Robinson based SRT model to correct for fluid nonidealities at high temperatures and pressures. PMID:18954106
Kapoor, Atam; Elliott, Janet A W
Sheet Membrane Spacesuit Water Membrane Evaporator Thermal Test
NASA Technical Reports Server (NTRS)
For future lunar extravehicular activities (EVA), one method under consideration for rejecting crew and electronics heat involves evaporating water through a hydrophobic, porous Teflon(Registered Trademark) membrane. A Spacesuit Water Membrane Evaporator (SWME) prototype using this membrane was successfully tested by Ungar and Thomas (2001) with predicted performance matching test data well. The above referenced work laid the foundation for the design of a compact sheet membrane SWME development unit for use in the Constellation System Spacesuit Element Portable Life Support System (Vogel and et. al., ICES 2008). Major design objectives included minimizing mass, volume, and manufacturing complexity while rejecting a minimum of 810 watts of heat from water flowing through the SWME at 91 kg/hr with an inlet temperature of 291K. The design meeting these objectives consisted of three concentric cylindrical water channels interlaced with four water vapor channels. Two units were manufactured for the purpose of investigating manufacturing techniques and performing thermal testing. The extensive thermal test measured SWME heat rejection as a function of water inlet temperatures, water flow-rates, water absolute pressures, water impurities, and water vapor back-pressures. This paper presents the test results and subsequent analysis, which includes a comparison of SWME heat rejection measurements to pretest predictions. In addition, test measurements were taken such that an analysis of the commercial-off-the-shelf vapor pressure control valve could be performed.
Trevino, Luis A.; Bue, Grant C.
Evaporation of water droplets on soft patterned surfaces.
The evaporation process of a sessile drop of water on soft patterned polydimethylsiloxane (PDMS) substrates is investigated in this study. Different softness of a regular pillar-like patterned PDMS substrate can be achieved by controlling the mixing ratio of a PDMS's prepolymer base and a curing agent at 10?:?1, 20?:?1 and 30?:?1. The receding contact angle is smaller for softer pillar-like patterned substrates. Consequently, the evaporation rate is faster on softer pillar-like substrates. A sessile drop on the regular pillar-like PDMS substrates, prepared at the mixing ratio of a base to a curing agent of 10?:?1 and 20?:?1, is observed to start evaporating in the constant contact radius (CCR) mode then switching to the constant contact angle (CCA) mode via stepwise jumping of the contact line, and finally shifting to the mixed mode sequentially. During the evaporation, a wetting transition from the Cassie to the Wenzel state occurs earlier for the softer substrate because softer pillars relatively cannot stand the increasingly high Laplace pressure. For the softest regular pillar-like PDMS substrate prepared at the mixing ratio of the base to the curing agent of 30?:?1 (abbreviated by PDMS-30?:?1 substrate), the pillars collapse irreversibly after the sessile drop exhibits the wetting transition into the Wenzel state. Furthermore, it is interesting to find out that the initial stage of evaporation of a sessile drop on the PDMS-30?:?1 substrate in the Cassie state is in the CCR mode followed by the CCA mode with stepwise retreatment of the contact line. Further evaporation would induce the wetting transition from the Cassie to the Wenzel state (due to the collapse of pillars) and resume the CCR mode followed by the CCA mode again sequentially. PMID:24643481
Chuang, Yu-Chen; Chu, Che-Kang; Lin, Shih-Yao; Chen, Li-Jen
Numerical Evaluation of Heat Pulse Technology for Estimation of Evaporation Rates from a Subsurface Drying Front
NASA Astrophysics Data System (ADS)
Soil water evaporation plays a crucial role for both the soil surface energy balance and the hydrologic cycle. Recently introduced heat pulse probes (HPP) allow in-situ measurements of subsurface soil water evaporation. The sensible heat component is calculated from soil heat flux densities measured at two depths and the change in sensible heat storage between these depths is measured by the HPP. The latent heat component detectable during stage 2 evaporation is then estimated from the heat balance residual. Although the accuracy of the estimated evaporation rate depends on many factors (i.e., location of sensor needles, soil texture), the theoretical limits of the HPP method have not been thoroughly evaluated. In the study presented, numerical simulations of the soil water evaporation process were conducted for a heat pulse line source to evaluate the capabilities of the HPP method using a high resolution grid (i.e., mm scale). Calculated temperatures at the depths of virtual sensor needles were used for the HPP method and measured subsurface evaporation rates were compared with simulated ones. The impacts of sensor needle depths were also evaluated for tri-needle (THPP) and penta-needle (PHPP) heat pulse probe configurations. Furthermore, the impact of soil texture was evaluated using coarse- and fine-textured soils. Numerical simulations including liquid water, soil water vapor flux and heat transport were conducted using the HYDRUS-1D code.
Sakai, M.; Jones, S. B.; Tuller, M.
Ultra-high cooling rate utilizing thin film evaporation
This research introduces a cell cryopreservation method, which utilizes thin film evaporation and provides an ultra-high cooling rate. The microstructured surface forming the thin film evaporation was fabricated from copper microparticles with an average diameter of 50??m. Experimental results showed that a cooling rate of approximately 5æ104?¯C/min was achieved in a temperature range from 10?¯C to ?187?¯C. The current investigation will give birth to a cell cryopreservation method through vitrification with relatively low concentrations of cryoprotectants.
Su, Fengmin; Ma, Hongbin; Han, Xu; Chen, Hsiu-hung; Tian, Bohan
Ultra-high cooling rate utilizing thin film evaporation.
This research introduces a cell cryopreservation method, which utilizes thin film evaporation and provides an ultra-high cooling rate. The microstructured surface forming the thin film evaporation was fabricated from copper microparticles with an average diameter of 50??m. Experimental results showed that a cooling rate of approximately 5[Formula: see text]10(4)?¯C/min was achieved in a temperature range from 10?¯C to -187?¯C. The current investigation will give birth to a cell cryopreservation method through vitrification with relatively low concentrations of cryoprotectants. PMID:23093807
Su, Fengmin; Ma, Hongbin; Han, Xu; Chen, Hsiu-Hung; Tian, Bohan
Ultra-high cooling rate utilizing thin film evaporation
NASA Astrophysics Data System (ADS)
This research introduces a cell cryopreservation method, which utilizes thin film evaporation and provides an ultra-high cooling rate. The microstructured surface forming the thin film evaporation was fabricated from copper microparticles with an average diameter of 50 ?m. Experimental results showed that a cooling rate of approximately 5æ104 ¯C/min was achieved in a temperature range from 10 ¯C to -187 ¯C. The current investigation will give birth to a cell cryopreservation method through vitrification with relatively low concentrations of cryoprotectants.
Su, Fengmin; Ma, Hongbin; Han, Xu; Chen, Hsiu-hung; Tian, Bohan
Long Duration Testing of a Spacesuit Water Membrane Evaporator Prototype
NASA Technical Reports Server (NTRS)
The Spacesuit Water Membrane Evaporator (SWME) is a heat-rejection device that is being developed to perform thermal control for advanced spacesuits. Cooling is achieved by circulating water from the liquid cooling garment (LCG) through hollow fibers (HoFi?s), which are small hydrophobic tubes. Liquid water remains within the hydrophobic tubes, but water vapor is exhausted to space, thereby removing heat. A SWME test article was tested over the course of a year, for a total of 1200 cumulative hours. In order to evaluate SWME tolerance to contamination due to constituents caused by distillation processes, these constituents were allowed to accumulate in the water as evaporation occurred. A test article was tested over the course of a year for a total of 1200 cumulative hours. The heat rejection performance of the SWME degraded significantly--below 700 W, attributable to the accumulation of rust in the circulating loop and biofilm growth. Bubble elimination capability, a feature that was previously proven with SWME, was compromised during the test, most likely due to loss of hydrophobic properties of the hollow fibers. The utilization of water for heat rejection was shown not to be dependent on test article, life cycle, heat rejection rate, or freezing of the membranes.
Bue, Grant C.; Makinen, Janice; Cox, Marlon; Watts, Carly; Campbell, Colin; Vogel, Matthew; Colunga, Aaron
Long Duration Testing of a Spacesuit Water Membrane Evaporator Prototype
NASA Technical Reports Server (NTRS)
The Spacesuit Water Membrane Evaporator (SWME) is a heat-rejection device that is being developed to perform thermal control for advanced spacesuits. Cooling is achieved by circulating water from the liquid cooling garment (LCG) through hollow fibers (HoFi s), which are small hydrophobic tubes. Liquid water remains within the hydrophobic tubes, but water vapor is exhausted to space, thereby removing heat. A SWME test article was tested over the course of a year, for a total of 600 cumulative hours. In order to evaluate SWME tolerance to contamination due to constituents caused by distillation processes, these constituents were allowed to accumulate in the water as evaporation occurred. A test article was tested over the course of a year for a total of 600 cumulative hours. The heat rejection performance of the SWME degraded significantly--below 700 W, attributable to the accumulation of rust in the circulating loop and biofilm growth. Bubble elimination capability, a feature that was previously proven with SWME, was compromised during the test, most likely due to loss of hydrophobic properties of the hollow fibers. The utilization of water for heat rejection was shown not to be dependent on test article, life cycle, heat rejection rate, or freezing of the membranes.
Bue, Grant C.; Makinen, Janice; Cox, Marlon; Watts, Carly; Campbell, Colin; Vogel, Matthew; Colunga, Aaron; Conger, Bruce
Studies on the evaporation of crude oil and petroleum products: I. the relationship between evaporation rate and time
The time dependance of evaporation was studied for several crude oils and petroleum oil products. Evaporation was determined by weight loss measured on a balance and recorded constantly on a computer. Examination of the data shows that most oil and petroleum products evaporate at a logarithmic rate with respect to time. This is attributed to the overall logarithmic appearance of
Merv F. Fingas
Measurement of spray droplet evaporation rate constant by laser diffraction
A technique for measuring the droplet evaporation rate constant for a spray is shown, and a novel laser diffraction technique is applied to the investigation of spray vaporizations. Local spatial size and distribution were measured in volume elements within a quasi two dimensional spray injected from the fan spray nozzle. The diffracted total light energy and its relative diffracted light
M. Nakayama; T. Arai
Evaporation of forsterite in the primordial solar nebula; rates and accompanied isotopic fractionation
Evaporation rates of forsterite in the primordial solar nebula were modeled. There are 3 evaporation regimes expected: 1. free evaporation-dominated (FED) regime, where forsterite evaporates as free evaporation, 2. hydrogen reaction-dominated (HRD) regime, where the evaporation is affected by H2 gas, and 3. H2O\\/H2 buffer-dominated (HBD) regime, where the evaporation is controlled by redox states buffered by the H2O\\/H2 ratio
Akira Tsuchiyama; Shogo Tachibana; Toshio Takahashi
The continuous similarity model of bulk soil-water evaporation
NASA Technical Reports Server (NTRS)
The continuous similarity model of evaporation is described. In it, evaporation is conceptualized as a two stage process. For an initially moist soil, evaporation is first climate limited, but later it becomes soil limited. During the latter stage, the evaporation rate is termed evaporability, and mathematically it is inversely proportional to the evaporation deficit. A functional approximation of the moisture distribution within the soil column is also included in the model. The model was tested using data from four experiments conducted near Phoenix, Arizona; and there was excellent agreement between the simulated and observed evaporation. The model also predicted the time of transition to the soil limited stage reasonably well. For one of the experiments, a third stage of evaporation, when vapor diffusion predominates, was observed. The occurrence of this stage was related to the decrease in moisture at the surface of the soil. The continuous similarity model does not account for vapor flow. The results show that climate, through the potential evaporation rate, has a strong influence on the time of transition to the soil limited stage. After this transition, however, bulk evaporation is independent of climate until the effects of vapor flow within the soil predominate.
Clapp, R. B.
Dynamics of soil water evaporation during soil drying: laboratory experiment and numerical analysis.
Laboratory and numerical experiments were conducted to investigate the evolution of soil water evaporation during a continuous drying event. Simulated soil water contents and temperatures by the calibrated model well reproduced measured values at different depths. Results show that the evaporative drying process could be divided into three stages, beginning with a relatively high evaporation rate during stage 1, followed by a lower rate during transient stage and stage 2, and finally maintaining a very low and constant rate during stage 3. The condensation zone was located immediately below the evaporation zone in the profile. Both peaks of evaporation and condensation rate increased rapidly during stage 1 and transition stage, decreased during stage 2, and maintained constant during stage 3. The width of evaporation zone kept a continuous increase during stages 1 and 2 and maintained a nearly constant value of 0.68?cm during stage 3. When the evaporation zone totally moved into the subsurface, a dry surface layer (DSL) formed above the evaporation zone at the end of stage 2. The width of DSL also presented a continuous increase during stage 2 and kept a constant value of 0.71?cm during stage 3. PMID:24489492
Han, Jiangbo; Zhou, Zhifang
17Oexcess in evaporated desert waters and vapor from evaporation experiments
NASA Astrophysics Data System (ADS)
Oxygen and hydrogen isotopes are classical proxies for the investigation of climatic effects in hydrological processes. The combination of the isotopic ratios 17O/16O and 18O/16O in water allowed the determination of mass dependent processes and enabled differentiation between equilibrium and kinetic fractionation (Barkan and Luz, 2007). In analogy to d-excess, deviation in ?17O from the global average trend of meteoric water is defined as: 17Oexcess = ?'17O - 0.528 æ ?'18O 17Oexcess depends on the impact of diffusive evaporation into air and thus reflects relative humidity conditions. The isotope ratios of water ?17O and ?18O were determined by isotope ratio gas mass spectrometry in dual inlet mode on a ThermoFinnigan MAT 253. The oxygen was extracted by water fluorination with CoF3. Our average measurement precision for ?17O is æ0.03 , for ?18O æ0.05 and for 17Oexcess approximately æ7 per meg (1?). We compared 17Oexcess in natural waters from the highly arid deserts of Sistan (East Iran) and Atacama (Chile) with data obtained from evaporation experiments. In these experiments, water was evaporated into a stream of dry nitrogen and vapor collected cryogenically. The data show a systematic depletion of 17Oexcess in water with increasing degree of evaporation in the residual water body. Most negative 17Oexcess were determined for samples from ponds (Sistan) and salars (Atacama). These strongly evaporated samples indicate an evaporation development, following a fractionation trend (?) of approximately 0.523. The evaporation experiment shows a ? of 0.525 and is in agreement with water data from an experiment by Barkan and Luz (2007). The difference between natural and experimental evaporation suggests either different evaporation kinetics in the natural environment, variable proportion of kinetic and equilibrium fractionation, or additional diffusive processes during ground water seepage. References: Barkan, E. and Luz, L. (2007). Diffusivity fractionations of H216O/H217O and H216O/H218O in air and their implications for isotope hydrology. Rapid Commun. Mass Spectrom., Vol. 21, pp. 2999-3005.
Surma, J.; Assonov, S.; Staubwasser, M.
Evaporation estimates from the Dead Sea and their implications on its water balance
NASA Astrophysics Data System (ADS)
The Dead Sea (DS) is a terminal hypersaline water body situated in the deepest part of the Jordan Valley. There is a growing interest in linking the DS to the open seas due to severe water shortages in the area and the serious geological and environmental hazards to its vicinity caused by the rapid level drop of the DS. A key issue in linking the DS with the open seas would be an accurate determination of evaporation rates. There exist large uncertainties of evaporation estimates from the DS due to the complex feedback mechanisms between meteorological forcings and thermophysical properties of hypersaline solutions. Numerous methods have been used to estimate current and historical (pre-1960) evaporation rates, with estimates differing by 100%. Evaporation from the DS is usually deduced indirectly using energy, water balance, or pan methods with uncertainty in many parameters. Accumulated errors resulting from these uncertainties are usually pooled into the estimates of evaporation rates. In this paper, a physically based method with minimum empirical parameters is used to evaluate historical and current evaporation estimates from the DS. The more likely figures for historical and current evaporation rates from the DS were 1,500-1,600 and 1,200-1,250 mm per annum, respectively. Results obtained are congruent with field observations and with more elaborate procedures.
Oroud, Ibrahim M.
Analysis of evaporative water loss in the Skylab astronauts
NASA Technical Reports Server (NTRS)
Daily evaporative water losses (EWL) during the three Skylab missions were measured using the indirect mass and water balance techniques. A mean inflight EWL of 860 ml/day-m 2 was obtained for nine men who averaged one hour of daily exercise. Although it was expected the EWL would increase in the hypobaric environment of Skylab (1/3 atmosphere), an average decrease from preflight sea level conditions of 11 percent was measured. The results suggest that weightlessness may have been a factor in modifying EWL primarily by decreasing sweat losses during exercise and possibly by reducing insensible skin losses as well. The weightless environment apparently promotes the formation of a sweat film on the skin surface both directly, by reducing heat and mass convective flow and sweat drippage, and perhaps indirectly by inducing measurable biochemical changes resulting in high initial sweating rates. It is proposed that these high levels of skin wettedness favor sweat suppression by a previously described mechanism.
Leonard, J. I.
Modeling of over Lake Wind Profile for Estimating Water Surface Evaporation Using Land-based meteorological Data
NASA Astrophysics Data System (ADS)
Evaporation from reservoirs and small lakes plays an important role in water management. Estimating the evaporation from surface water resources such as small lakes and reservoirs requires extensive data. Evaporation is difficult and expensive to measure experimentally over the water surface. For operational purposes it would be attractive if evaporation from a lake could be estimated with acceptable accuracy from standard meteorological data taken at nearby land-based stations. Several techniques and models have been suggested and used to estimate evaporation from open water bodies. One of the most commonly used methods is the aerodynamic mass transfer method which gives reliable results for water bodies if suitable data are available. With the aerodynamic approach, evaporation rate is modeled as the product of a vapor pressure deficit between the water surface and upwind air and a wind function that depends on the wind profile over the water surface. As measuring wind speed, and other meteorological data, over a water surface is not easy, most literature uses land-based meteorological measurements. Using land-based meteorological stations data in estimating evaporation introduces significant errors in estimated values of evaporation. On the other hand, the aerodynamic method should account for the size or fetch of a desired water body as evaporation rate decreases with distance downwind from the land-water edge due to increased entrainment of water vapor. Neglecting the fetch effects in this method introduce errors in estimated evaporation values. In this paper, we use a CFD model (RANS Model) to simulate the wind profile over the water surface that utilizes land-based measurements. The modeled wind profile is used to estimate evaporation from water surface using the aerodynamic approach. This proposed model is tested for small lakes and reservoirs in arid and semi-arid regions. Results show a good agreement with the experimental measurements and can be used in water management plans to estimate evaporation from reservoirs and small water bodies.
Abbasi, Ali; van de Giesen, Nick
Evaporative rate model for a natural convection glazed collector\\/regenerator
In this paper, a numerical method has been applied to model the water evaporation rate of a glazed collector\\/regenerator component of an open-cycle absorption refrigeration system. This two-dimensional model calculates local heat and mass-transfer coefficients as part of the solution. The air flow in the glazed channel is driven by the combined buoyancy of both heat and mass transfer (water
D. J. Nelson; B. D. Wood
Oxygen isotopic composition of soil water: Quantifying evaporation and transpiration
The oxygen isotopic composition of soil water provides an extra quantitative dimension in water balance analysis which allows separation of evaporation from transpiration. Spatial and temporal variations in water content and oxygen isotopic composition in soils along an arid to humid transect in Hawaii reflect the processes of recharge by rain, mixing with antecedent moisture, and evapotranspiration. Rainwater is always
Jean C. C Hsieh; Oliver A Chadwick; Eugene F Kelly; Samuel M Savin
Evaporation of J13 water: laboratory experiments and geochemical modeling
We report results from experiments on the evaporative chemical evolution of synthetic J13 water, representative of water from well J13, a common reference water in the Yucca Mountain Project. Data include anion and cation analysis and qualitative mineral identification for a series of open system experiments, with and without crushed tuff present, conducted at sub-boiling temperatures. Ca and Mg precipitated
M. J. Dibley; K. G. Knauss; N. D. Rosenberg
Silica scale technology and water conservation. [Recirculating evaporative cooling
Conservation of water at the Los Alamos Scientific Laboratory (LASL) has been accomplished by recirculating evaporative cooling waters. Because of high silica concentration (80 mg\\/l) in Los Alamos groundwater, the concentration of recirculating water must be carefully controlled to prevent scaling. The most troublesome scale at Los Alamos has been identified as colloidal silica bound in a crystalline matrix of
W. S. Midkiff; H. P. Foyt
Evaporation rate from square capillaries limited by corner flow viscous losses
NASA Astrophysics Data System (ADS)
High evaporation rates from soil surfaces are sustained by capillary flows drawing water from the receding drying front along liquid pathways in crevices of the pore space. With increasing depth of the drying front viscous losses add to growing gravitational head and at a certain depth overcome capillary drive and disrupt liquid pathways. Viscous losses are significant in fine textured media resulting in earlier capillary failure than predicted by gravity-capillary force balance. To reproduce limitations of viscous corner flow on evaporation rates from angular pores (capillaries) we imaged drying dynamics from a square shaped glass capillary using a high speed camera, to provide for detailed record on receding menisci and thickness of liquid corner films including detachment dynamics at the top of the capillary. Additionally, deposition patterns of dye delineated regions of high rates of phase change (evaporation) showing a decrease in drying rate with recession of menisci and films into the capillary due to increasing diffusive path and reduced gradients. Effects of viscous losses on evaporation dynamics were systematically evaluated by varying ratio of viscous, gravity and capillary forces using different liquids (water, ethanol and octane), capillary geometry (0.5 and 1.0 mm width), and flow rate and direction with respect to gravity (horizontal and vertical arrangement). Experimental results were compared with analytical solutions for corner flow considering viscous losses. Preliminary results indicate that the maximum (main) meniscus depth supporting corner flow is not only dependent on the effective conductivity behind the interfaces, but also on interfacial processes taking place at the very top of the capillary. The pore scale findings will be incorporated into macroscopic models for determining viscous losses from soils and for estimating elapsed times for transition from high capillary-sustained evaporation rates to diffusion limited rates.
Hoogland, F.; Lehmann, P.; Yiotis, A.; Or, D.
Selective Adsorption of Ions to Aqueous Interfaces and its Effects on Evaporation Rates
NASA Astrophysics Data System (ADS)
By exploiting the strong UV charge-transfer-to-solvent (CTTS) resonances of selected anions in aqueous electrolytes, their interfacial adsorption properties are measured by UV-SHG spectroscopy. Temperature and concentration dependences are determined, with the goal of establishing a molecular description of selective ion adsorption. A study of prototypical chaotrope thiocyanate reveals that its strong adsorption is driven by enthalpic forces and impeded by entropy. A study of nitrite indicates even stronger adsorption as an ion pair with sodium. Evaporation rates are measured by combining liquid microjet technology and Raman thermometry. The relationship between surface propensities of ions and evaporation rates is investigated. A detailed molecular mechanism for aqueous evaporation is sought. W. S. Drisdell, R. J. Saykally, R. C. Cohen Effect of Surface Active Ions on the Rate of Water Evaporation, J. Phys. Chem. C 114, 11880-11885 (2010). D.E. Otten, R. Onorato, R. Michaels, J. Goodknight, R. J. Saykally "Strong Surface Adsorption of Aqueous Sodium Nitrite as an Ion Pair," Chem. Phys. Lett. 519-520, 45-48 (2012). D.E. Otten, P. Shaffer, P. Geissler, R.J. Saykally "Elucidating the Mechanism of Selective Ion Adsorption to the Liguid Water Surface," PNAS 109 (3), 701-705 (2012).
Saykally, Richard J.
The desorptivity model of bulk soil-water evaporation
NASA Technical Reports Server (NTRS)
Available models of bulk evaporation from a bare-surfaced soil are difficult to apply to field conditions where evaporation is complicated by two main factors: rate-limiting climatic conditions and redistribution of soil moisture following infiltration. Both factors are included in the "desorptivity model', wherein the evaporation rate during the second stage (the soil-limiting stage) of evaporation is related to the desorptivity parameter, A. Analytical approximations for A are presented. The approximations are independent of the surface soil moisture. However, calculations using the approximations indicate that both soil texture and soil moisture content at depth significantly affect A. Because the moisture content at depth decreases in time during redistribution, it follows that the A parameter also changes with time. Consequently, a method to calculate a representative value of A was developed. When applied to field data, the desorptivity model estimated cumulative evaporation well. The model is easy to calculate, but its usefulness is limited because it requires an independent estimate of the time of transition between the first and second stages of evaporation. The model shows that bulk evaporation after the transition to the second stage is largely independent of climatic conditions.
Clapp, R. B.
Numerical study of heat and mass transfer of ammonia-water in falling film evaporator
NASA Astrophysics Data System (ADS)
To investigate the performance of the heat and mass transfer of ammonia water during the process of falling film evaporation in vertical tube evaporator, a mathematical model of evaporation process was developed and solved based on stream function. Then an experimental study of falling film evaporation was carried out in order to validate the mathematical model. A series of parameters, such as velocity, film thickness and concentration, etc., were obtained from the mathematical model. The calculated results show that the average velocity and the film thickness change sharp at the entrance region when x < 100 mm, while they vary slightly in the fully developed region when x > 100 mm. The film thickness depends largely on the flow rate of solution. It is observed that the heating power and mass flow of solution significantly affect the concentration difference between the inlet and outlet of evaporation tube. The calculated results reveal that the tube length has a significant impact on the amounts of ammonia vapor evaporated. It is suggested that the roll-worked enhanced tube should be used in order to decrease the concentration gradient in the film thickness direction and enhance the heat and mass transfer rate. Furthermore, the experimental and calculated results indicate that the inlet solution concentration has a great influence on the heat exchange capacity, the amounts of ammonia vapor evaporated and the evaporation pressure.
Bu, Xianbiao; Ma, Weibin; Huang, Yuanfeng
A simulation model for evaporation of defrosted water in household refrigerators
This paper presents a simple dynamic simulation model for predicting the evaporation rates of defrosted water from water trays in domestic refrigerators. The model was successfully tested for one domestic refrigerator. The model was used to investigate the effect of different variables (ambient temperature, relative humidity, air velocity, compressor heat, auxiliary condenser) by comparing eight different arrangements with each other
P. K. Bansal; G. Xie
Fractionation of oxygen and hydrogen isotopes in evaporating water
Variations in oxygen and hydrogen isotope ratios of water and ice are powerful tools in hydrology and ice core studies. These variations are controlled by both equilibrium and kinetic isotope effects during evaporation and precipitation, and for quantitative interpretation it is necessary to understand how these processes affect the isotopic composition of water and ice. Whereas the equilibrium isotope effects
Boaz Luz; Eugeni Barkan; Ruth Yam; Aldo Shemesh
Long Duration Testing of a Spacesuit Water Membrane Evaporator Prototype.
National Technical Information Service (NTIS)
The Spacesuit Water Membrane Evaporator (SWME) is a heat-rejection device that is being developed to perform thermal control for advanced spacesuits. Cooling is achieved by circulating water from the liquid cooling garment (LCG) through hollow fibers (HoF...
A. Colunga B. Conger C. Campbell C. Watts G. C. Bue J. Makinen M. Cox M. Vogel
Development and Evaluation of Improved Films for Suppressing Water Evaporation.
National Technical Information Service (NTIS)
A small water-wind tunnel with an air passage 0.24 m high by 0.22 m wide and 6.5 m long over a water layer 7 cm deep has been used for the dynamic testing of surface films for evaporation control. Differences in the entering and exit humidity were determi...
C. O. Reiser T. J. Ruhoff
Evaporative water loss in the new-born baby
1. Measurements of total evaporative water loss (EWL) were made on sixty-three premature and full-term babies 0-65 days after birth within a closed Perspex chamber under varied environmental conditions by measuring the flow and absolute humidity of air entering and leaving the chamber. Control experiments suggested that the method underestimated loss by about 5%. Measurements of O2 consumption were made concurrently by recording the volume change of the closed gas circuit. 2. The total basal EWL averaged 10ñ8 g H2O/m2.hr in infants 2-10 days old when ambient water vapour pressure (PH2O) was 18 mm Hg; basal EWL was correlated with basal metabolic rate at all ages studied and evaporative heat loss accounted for ? 23% of basal heat production. 3. Respiratory water loss was measured by detecting the water added to air at 33¯ C passed across the face of eight infants in a trunk plethysmograph. Respiratory water loss was inversely related to the water vapour content of the inspired air; gas appeared to leave the nose ? 95% sat. at 35ñ6¯ C. 4. Measurements of total EWL were obtained when humidity was varied and skin loss was calculated by subtracting estimated respiratory loss from total loss; changing PH2O from 7 to 25 mm Hg appeared to decrease basal skin water loss by only 1ñ5 g/m2.hr. 5. No consistent changes in EWL were obtained when environmental temperature (TE) was varied between 28 and 34¯ C. Active sweating occurred in infants 0-10 days old born within 3 weeks of term when TE exceeded 34-35¯ C and rectal temperature (TR) rose above 37ñ2¯ C. The threshold rectal temperature at which sweating was detected fell significantly in the first 10 days of life; EWL increased two to fourfold when TR rose to between 37ñ5 and 37ñ8¯ C. 6. In infants of less than 215 days post-conceptual age (term ? 268 days) EWL increased less than 50% at TR 37ñ7-37ñ8¯ C; it is concluded that the sweating mechanism is defective in these infants.
Hey, E. N.; Katz, G.
On the remote measurement of evaporation rates from bare wet soil under variable cloud cover
NASA Technical Reports Server (NTRS)
Evaporation rates from a natural wet soil surface are calculated from an energy balance equation at 0.1-hour intervals. A procedure is developed for calculating the heat flux through the soil surface from a harmonic analysis of the surface temperature curve. The evaporation integrated over an entire 24-hour period is compared with daily evaporation rates obtained from published models.
Auer, S.
Gas scavenging of insoluble vapors: Condensation of methyl salicylate vapor onto evaporating drops of water
NASA Astrophysics Data System (ADS)
We have observed the evaporation of acoustically levitated water drops at 0 and 32% relative humidity in a moving gas stream which is nearly saturated with methyl salicylate vapor. The initial evaporation rate is characteristic of a pure water drop and gradually slows until the evaporation rate becomes that of pure methyl salicylate. The quantity of condensed methyl salicylate exceeds its Henry's law solubility in water by factors of more than 30-50. This apparent violation of Henry's law agrees with the concentration enhancements in the liquid phase found by glotfelty et al. (1987, Nature235, 602-605) during their field measurements of organophorus pesticides in fog water. Under our conditions, visual evidence demonstrates the presence of two liquid phases, thus invalidating the use of Henry's law. A continuum evaporation-condensation model for an immiscible two-component system which accounts for evaporative self-cooling of the drop correctly predicts the amount of methyl salicylate condensed onto the water drops.
Seaver, Mark; Peele, J. R.; Rubel, Glenn O.
ABSTRC?.--Allometry, the study of the consequences of body size on form and function, has been a powerful investigative tool in avian biology. Comparison of phenotypic data with allometric reference equations permits the identification of possible adaptations and the formulation of hypotheses for testing. The standard allometric equation that relates total evaporative water loss (TEWL) to body mass in birds, published
Dynamics of Water Absorption and Evaporation During Methanol Droplet Combustion in Microgravity
NASA Technical Reports Server (NTRS)
The combustion of methanol droplets is profoundly influenced by the absorption and evaporation of water, generated in the gas phase as a part of the combustion products. Initially there is a water-absorption period of combustion during which the latent heat of condensation of water vapor, released into the droplet, enhances its burning rate, whereas later there is a water-evaporation period, during which the water vapor reduces the flame temperature suffciently to extinguish the flame. Recent methanol droplet-combustion experiments in ambient environments diluted with carbon dioxide, conducted in the Combustion Integrated Rack on the International Space Station (ISS), as a part of the FLEX project, provided a method to delineate the water-absorption period from the water-evaporation period using video images of flame intensity. These were obtained using an ultra-violet camera that captures the OH* radical emission at 310 nm wavelength and a color camera that captures visible flame emission. These results are compared with results of ground-based tests in the Zero Gravity Facility at the NASA Glenn Research Center which employed smaller droplets in argon-diluted environments. A simplified theoretical model developed earlier correlates the transition time at which water absorption ends and evaporation starts. The model results are shown to agree reasonably well with experiment.
Hicks, Michael C.; Dietrich, Daniel L.; Nayagam, Vedha; Williams, Forman A.
Drizzle and Sub-cloud Evaporation in Marine Stratocumulus and Implications for Water and Energy Budgets
NASA Astrophysics Data System (ADS)
Drizzle and its evaporation below the cloud layer are important to the water and energy budgets of the stratocumulus-topped marine boundary layer (MBL). Here, we report in situ aircraft observations of the cloud drop size distribution (DSD) of near-coastal marine stratocumulus clouds, and thereby derive drizzle and sub-cloud evaporation rates. Measurements were obtained using the Artium Flight Phase Doppler Interferometer during two field projects: the Marine Stratus Experiment (MASE) in July 2005 in the northeastern subtropical Pacific, and the VAMOS Ocean-Cloud-Atmosphere-Land Study -Regional Experiment (VOCALS-REx) from October to November 2008 in the southeastern subtropical Pacific. Using examples from both VOCALS and MASE, we investigate drizzle and sub-cloud evaporation across a range of stratocumulus conditions (e.g. liquid water path, stability, aerosol, and shear). The VOCALS cases were generally characterized by higher cloud tops, stronger temperature inversions, higher aerosol concentrations and lower drizzle rates than the MASE cases. Combining these projects in our analysis yields a broader perspective on the impact of drizzle on the cloud-topped MBL. The rate of drop evaporation after drizzle falls below cloud base into the sub-cloud layer is dependent on the DSD at cloud base, as well as the sub-cloud relative humidity and temperature profiles. In turn, such evaporation can be an important for the dynamics within the boundary layer and, via feedbacks, impact the cloud layer itself. For example, sub-cloud evaporative cooling can alter boundary layer turbulence and buoyancy production by increasing the stability of the MBL and promote the decoupling of the mixed layer. The generation of cold pools may also influence mesoscale circulations in the cloud-topped MBL. Understanding how the evaporation of drizzle quantitatively affects the MBL system is therefore important in predicting its properties and evolution.
Rossiter, D. L.; Small, J. D.; Chuang, P. Y.
Numerical study of the influence of water evaporation on radiofrequency ablation
Background Radiofrequency ablation is a promising minimal invasive treatment for tumor. However, water loss due to evaporation has been a major issue blocking further RF energy transmission and correspondently eliminating the therapeutic outcome of the treatment. Method A 2D symmetric cylindrical mathematical model coupling the transport of the electrical current, heat, and the evaporation process in the tissue, has been developed to simulate the treatment process and investigate the influence of the excessive evaporation of the water on the treatment. Results Our results show that the largest specific absorption rate (Q SAR ) occurs at the edge of the circular surface of the electrode. When excessive evaporation takes place, the water dehydration rate in this region is the highest, and after a certain time, the dehydrated tissue blocks the electrical energy transmission in the radial direction. It is found that there is an interval as long as 65 s between the beginning of the evaporation and the increase of the tissue impedance. The model is further used to investigate whether purposely terminating the treatment for a while allowing diffusion of the liquid water into the evaporated region would help. Results show it has no obvious improvement enlarging the treatment volume. Treatment with the cooled-tip electrode is also studied. It is found that the cooling conditions of the inside agent greatly affect the water loss pattern. When the convection coefficient of the cooling agent increases, excessive evaporation will start from near the central axis of the tissue cylinder instead of the edge of the electrode, and the coagulation volume obviously enlarges before a sudden increase of the impedance. It is also found that a higher convection coefficient will extend the treatment time. Though the sudden increase of the tissue impedance could be delayed by a larger convection coefficient; the rate of the impedance increase is also more dramatic compared to the case with smaller convection coefficient. Conclusion The mathematical model simulates the water evaporation and diffusion during radiofrequency ablation and may be used for better clinical design of radiofrequency equipment and treatment protocol planning.
Analysis of condensation and evaporation of ammonia\\/water mixtures in matrix heat-exchangers
A theoretical analysis is carried out for the condensation and evaporation of water\\/ammonia mixtures in matrix heat-exchangers. A set of equations is formulated and a calculation algorithm is developed to predict the local rate of heat and mass transfer for binary-component systems. A thermodynamic property model is developed for ammonia\\/water mixtures on the basis of the Peng-Robinson equation of state.
C. B. Panchal; B. Arman
Impact of groundwater levels on evaporation and water-vapor fluxes in highly saline soils
NASA Astrophysics Data System (ADS)
In aquifers of arid and hyper-arid zones, such as those occurring in the Chilean Andes high plateau, it is important to determine both the quantity and location of water discharges at the temporal scales of interest to close the basin's water budget and thus, to manage the water resource properly. In zones where shallow aquifers are the main source of water, overexploitation of the water resource changes the dynamics of water, heat and solute transport in the vadose zone. As aquifers are exploited, fluctuations in depth to groundwater are exacerbated. These fluctuations modify both soil structure and evaporation from the ground, which is typically the most important discharge from the water budget and is very difficult to estimate. Therefore, a correct quantification of evaporation from these soils is essential to improve the accuracy of the water balance estimation. The objective of this study was to investigate the evaporation processes and water-vapor fluxes in a soil column filled with a saline soil from the Salar del Huasco basin, Chile. Water content, electrical conductivity and temperature at different depths in the soil profile were monitored to determine the liquid and vapor fluxes within the soil column. The results showed that evaporation is negligible when the groundwater table is deeper than 1 m. For shallower groundwater levels, evaporation increases in an exponential fashion reaching a value of 3 mm/day when the groundwater table is near the surface of the ground. These evaporation rates are on the same order of magnitude than the field measurements, but slightly lower due to the controlled conditions maintained in the laboratory. Isothermal fluid fluxes were predominant over the non-isothermal fluid and water vapor fluxes. The net flux for all the phreatic levels tested in the laboratory showed different behaviors, with ascending or descending flows as a consequence of changes in water content and temperature distribution within the soil. It was found that evaporation from bare soils occurs as a consequence of vapor transport due to the thermal gradients. This vapor transport was also influences by the salinity of the soil.
Munoz, J. F.; HernÃndez, M. F.; Braud, I.; Gironas, J. A.; Suarez, F. I.
Measurements and simulations of the near-surface composition of evaporating ethanol-water droplets.
The evolving composition of evaporating ethanol-water droplets (initially 32.6 or 45.3 microm radius) is probed by stimulated Raman scattering over the period 0.2 to 3 ms following droplet generation and with a surrounding nitrogen gas pressure in the range 10 to 100 kPa. The dependence of the evaporation rate on the relative humidity of the surrounding gas phase is also reported. The measured data are compared with both a quasi-steady state model and with numerical simulations of the evaporation process. Results from the numerical simulations are shown to agree closely with the measurements when the stimulated signal is assumed to arise from an outer shell with a probe depth of 2.9+/-0.4% of the droplet radius, consistent with a previous determination. Further, the time-dependent measurements are shown to be sensitive to the development of concentration gradients within evaporating droplets. This represents the first direct measurement of the spatial gradients in composition that arise during the evaporation of aerosol droplets and allows the influence of liquid phase diffusion within the condensed phase on droplet evaporation to be examined. PMID:19727484
Homer, Christopher J; Jiang, Xingmao; Ward, Timothy L; Brinker, C Jeffrey; Reid, Jonathan P
Distribution of evaporation rate on human body surface.
Relative humidity (R. H), vapour pressure (Psk) and evaporation rate (Esk) of the human skin surface were measured at 29 points by an evaporimeter at 25 degrees C, 28 degrees C, 31 degrees C, 34 degrees C and 37 degrees C of air temperature (Ta), with 35 +/- 10 % R. H and air velocity of less than 0.2 m/s. The skin temperatures and the body weight loss were also measured by thermography and electronic balance. Ten healthy female subjects aged 22-34 years, wearing brassiere and shorts, took a supine and a prone posture during experiment. Comparisons of the obtained Esk with the previous results of other studies showed that there were no definite differences among the measuring methods of Esk, while it is ascertained that the calibration of the results to some standard values such as weight loss were more important to get accurate values of Esk. Distribution patterns of Esk were almost the same in the insensible zone but they remarkably changed in the sweating zone. According to the regression analysis of Esk and Ta, 29 regions were classified into the following 9 groups which showed similar values and changes of Esk with the air temperature: 1) face, 2) front upper trunk, 3) back upper trunk, 4) front lower trunk, 5) back lower trunk, 6) arm, 7) leg, 8) hand and foot and 9) palm, sole and axilla. These results were discussed in relation to the contributing factors such as the number and the capacity of the sweat gland, the regional skin temperature and the pressure-sweat response and also in relation to the skin wettedness. PMID:1476561
Park, S J; Tamura, T
Spacesuit Water Membrane Evaporator Development for Lunar Missions
NASA Technical Reports Server (NTRS)
For future lunar extra-vehicular activities (EVA), one method under consideration for rejecting crew and electronics heat involves evaporating water through a hydrophobic, porous Teflon membrane. A Spacesuit Water Membrane Evaporator (SWME) prototype using the Teflon membrane was tested successfully by Ungar and Thomas (2001) with predicted performance matching test data well. The above referenced work laid the foundation for the design of the SWME development unit, which is being considered for service in the Constellation System Spacesuit Element (CSSE) Portable Life Support System (PLSS). Multiple PLSS SWME configurations were considered on the basis of thermal performance, mass, volume, and performance and manufacturing risk. All configurations were a variation of an alternating concentric water and vapor channel configuration or a stack of alternating rectangular water and vapor channels. Supporting thermal performance trades mapped maximum SWME heat rejection as a function of water channel thickness, vapor channel thickness, channel length, number of water channels, porosity of the membrane structural support, and backpressure valve throat area. Preliminary designs of each configuration were developed to determine total mass and volume as well as to understand manufacturing issues. Review of configurations led to the selection of a concentric annulus configuration that meets the requirements of 800 watts (W) of heat rejection. Detailed design of the SWME development unit will be followed by fabrication of a prototype test unit, with thermal testing expected to start in 2008.
Vogel, Matt R.; Peterson, Keith; Zapata, Felipe, III; Dillon, Paul; Trevino, Luis A.
Analysis of condensation and evaporation of ammonia/water mixtures in matrix heat-exchangers
NASA Astrophysics Data System (ADS)
A theoretical analysis is carried out for the condensation and evaporation of water/ammonia mixtures in matrix heat-exchangers. A set of equations is formulated and a calculation algorithm is developed to predict the local rate of heat and mass transfer for binary-component systems. A thermodynamic property model is developed for ammonia/water mixtures on the basis of the Peng-Robinson equation of state. The two-phase flow heat-transfer coefficient for matrix heat-exchangers is calculated by using the analytical method developed in a previous study. The experimental data are analyzed to determine the effects of small amounts of water in ammonia on the rate of evaporation. The role of diffusion in simultaneous heat and mass transfer associated with condensation and evaporation processes are analyzed by comparing the results from three limiting cases, which include equilibrium conditions, and liquid-phase diffusion- resistance of finite and infinite values. The results show that the vapor-phase mass-transfer resistance is the controlling mechanism for condensation, and the liquid-phase mass-transfer resistance is the controlling mechanism for evaporation.
Panchal, C. B.; Arman, B.
Evaporation of tiny water aggregation on solid surfaces with different wetting properties.
The evaporation of a tiny amount of water on the solid surface with different wettabilities has been studied by molecular dynamics simulations. From nonequilibrium MD simulations, we found that, as the surface changed from hydrophobic to hydrophilic, the evaporation speed did not show a monotonic decrease as intuitively expected, but increased first, and then decreased after it reached a maximum value. The analysis of the simulation trajectory and calculation of the surface water interaction illustrate that the competition between the number of water molecules on the water-gas surface from where the water molecules can evaporate and the potential barrier to prevent those water molecules from evaporating results in the unexpected behavior of the evaporation. This finding is helpful in understanding the evaporation on biological surfaces, designing artificial surfaces of ultrafast water evaporating, or preserving water in soil. PMID:23051060
Wang, Shen; Tu, Yusong; Wan, Rongzheng; Fang, Haiping
Formation of Soil Water Repellency by Laboratory Burning and Its Effect on Soil Evaporation
NASA Astrophysics Data System (ADS)
Fire-induced soil water repellency can vary with burning conditions, and may lead to significant changes in soil hydraulic properties. However, isolation of the effects of soil water repellency from other factors is difficult, particularly under field conditions. This study was conducted to (i) investigate the effects of burning using different plant leaf materials and (ii) of different burning conditions on the formation of soil water repellency, and (iii) isolate the effects of the resulting soil water repellency on soil evaporation from other factors. Burning treatments were performed on the surface of homogeneous fully wettable sand soil contained in a steel frame (60 x 60 cm; 40 cm depth). As controls a sample without a heat treatment, and a heated sample without fuel, were also used. Ignition and heat treatments were carried out with a gas torch. For comparing the effects of different burning conditions, fuel types included oven-dried pine needles (fresh needles of Pinus densiflora), pine needle litter (litter on a coniferous forest floor, P. densiflora + P. rigida), and broad-leaf litter (Quercus mongolica + Q. aliena + Prunus serrulata var. spontanea + other species); fuel loads were 200 g, 300 g, and 500 g; and heating duration was 40 s, 90 s and 180 s. The heating duration was adjusted to control the temperature, based on previous experiments. The temperature was measured continuously at 3-second intervals and logged with two thermometers. After burning, undisturbed soil columns were sampled for subsequent experiments. Water Drop Penetration Time (WDPT) test was performed at every 1 mm depth of the soil columns to measure the severity of soil water repellency and its vertical extent. Soil water repellency was detected following all treatments. As the duration of heating increased, the thickness of the water repellent layer increased, whilst the severity of soil water repellency decreased. As regards fuel amount, the most severe soil water repellency was formed at a fuel load of 300 g. Pine needle litter formed the most severe soil water repellency and fresh pine needle formed the thickest water repellent layer, whilst broad-leaf litter did only cause water repellency on the surface of the sand. The soil evaporation rate was measured by a gravitational method at an isothermal condition. Undisturbed soil columns were sealed after adding 50 ml of tap water through the bottom. After twelve hours of stabilization, the columns were opened and covered with filter paper. The rate of soil evaporation through the soil surface was measured by the hourly weight change at 45¯ C. The initial 65 hours' evaporation rate was analyzed, while the slope of cumulative evaporation over time maintained its linearity. It was found that as the thickness of the water repellent layer increased, the evaporation rate tended to decrease. These two variables showed a good correlation (Pearson's correlation coefficient =-0.8916, p=0.0170) and a large coefficient of determination (R2=0.795) in the linear regression. This suggests that a layer of water repellent soil can affect water evaporation rate and that the rate is negatively correlated with the thickness of the repellent layer.
Ahn, Sujung; Im, Sangjun
Environmental and Groundwater Controls on Evaporation Rates of A Shallow Saline Lake in the Western Sandhills Nebraska, USA
NASA Astrophysics Data System (ADS)
The western Sand Hills of Nebraska exhibit many shallow saline lakes that actively mediate groundwater-lake-atmospheric exchanges. The region is home to the largest stabilized dune field in the western hemisphere. Most of the lakes in the western Sand Hills region are saline and support a wide range of ecosystems. However, they are also highly sensitive to variability in evaporative and groundwater fluxes, which makes them a good laboratory to examine the effects of climate on the water balance of interdunal lakes. Despite being semiarid, little is known about the importance of groundwater-surface water interactions on evaporative rates, or the effects of changes in meteorological and energy forcings on the diel, and seasonal dynamics of evaporative fluxes. Our study is the first to estimate evaporation rates from one of the hundreds of shallow saline lakes that occur in the western Sand Hills region. We applied the energy balance Bowen ratio method at Alkali Lake, a typical saline western Sand Hills lake, over a three-year period (2007-2009) to quantify summer evaporation rates. Daily evaporation rates averaged 5.5 mm/day from July through September and were largely controlled by solar radiation on a seasonal and diel scales. Furthermore, the range of annual variability of evaporation rates was low. Although less pronounced, groundwater level effects on evaporation rates were also observed, especially from August through October when solar radiation was lower. The lake exhibits significant fluctuation in lake levels and combined with a shallow lake bed, large changes in lake surface area are observed. Our findings also show that with the onset of summer conditions, lake surface area can change very rapidly (e.g. 24% of its surface area or ~16.6 hectares were lost in less than ~2 months). In every year summer evaporation exceeded annual rainfall by an average of 28.2% suggesting that groundwater is a significant component of the lake water balance, it is important for sustaining life of surrounding ecosystems, and during the growing season it is transiently stored in the lake before it is rapidly lost to the atmosphere.
Peake, C.; Riveros-Iregui, D.; Lenters, J. D.; Zlotnik, V. A.; Ong, J.
Electron Beam Evaporation Source with Integrated Rate Control.
National Technical Information Service (NTIS)
A certain portion of the vapour atoms produced in the electron beam evaporation source is ionized by the electron beam and, by means of the deflecting magnetic field around the beam source, projected to a measuring probe. Because of an ion current in the ...
G. Wulff
Al/Si Metallization by Rate Controlled Dual EB-Gun Evaporation.
National Technical Information Service (NTIS)
An industrial process for aluminium-silicon metallization using two rate controlled electron beam evaporators will be described. The two sources are operated simultaneously. The silicon source rate control is achieved by the direct measurement of the depo...
F. Hegner A. Feuerstein
Stable isotopes in pedogenic calcite: Can the positive linear covariant trends be used to quantify paleo-evaporation rates?
NASA Astrophysics Data System (ADS)
Paleoclimatological models suggest enhanced evaporation rates in subtropical regions during greenhouse- world conditions. Laboratory evaporation experiments show that calcites precipitated from variably saturated solutions yield a positive linear covariant trend (PLCT) in ?18O vs ?13C values. This investigation experimentally quantifies calcite PLCT so that ?13C of subtropical paleosol calcretes may be used as a regional proxy of paleo-evaporation rates. A series of powdered CaCO3 samples with ?18O and ?13C values of -19.6 and -37.2 VPDB respectively were dissolved in deionized water in a pressure sealed container; it also contained separate vials of calcite reacted with HCl to generate a range of pCO2 environments, thus simulating a soil atmosphere. The variable pCO2 conditions simulate expected soil atmosphere pCO2 conditions in a calcrete horizon during alternative phases of calcite dissolution and precipitation. After 24 hrs, the solutions were placed in an open beaker in an incubator at 36¯C and allowed to evaporate. Aliquots of 100 ?L were removed at 24 hr intervals and the time of calcite crystal nucleation was also noted. Water analyses yielded ?18O enrichments ranging from an initial value of -4.8 VSMOW to a range of +10.0 to +14.8 VSMOW after an evaporation period of 75 hrs. The most enriched water values were attained from the solutions formed under lower pCO2 conditions (more enriched calcite ?18O, ?13C). The array of calcite ?18O vs ?13C values fall upon a PLCT that projects from a theoretical meteoric calcite line (MCL) calculated from the incubation temperature and deionized water ?18O and ?13C values. The precipitated calcite ?18O values range from the MCL value of -8.8 VPDB to +0.5 VPDB. The higher pCO2 waters precipitated calcite very early during evaporation, and thus the ?18O and ?13C calcite values are slightly enriched relative to the theoretical MCL. The lower pCO2 conditions precipitated calcite late in the evaporation of the fluids, and thus yield more enriched calcite ?18O and ?13C values. Ongoing experiments under warmer and cooler evaporation temperatures will aid in the development of a quantitative model for paleo-evaporation rates from paleosol calcretes.
Gr—cke, D.; Ufnar, D.; Beddows, P. A.
Development of an evaporation-optimized and water-permeable pavement
NASA Astrophysics Data System (ADS)
During recent decades, urban areas have been threatened more frequently by flood events. Furthermore, the potential for damage from these events has increased on average. The construction of houses, streets and parking lots has caused this trend by sealing the ground surface, i.e. these water-impermeable areas reduce the natural infiltration and evaporation-rates, and in some cases it is even completely stopped. The consequence is the so called "urban water cycle". Water from precipitation cannot be stored anywhere and so there is an immediate and very high surface run-off effect. Especially after intense rain events, canalisations and sewage-treatment plants are overloaded and this leads to higher costs for water treatment and to environmental damage. A practical solution to this problem is the use of water-permeable pavements. Here higher infiltration rates lead to a groundwater recharge that is greater than that of natural soils. The consequences from using these surfaces are already noticeable in many places through increasing groundwater levels. These increases cause damage to buildings. A second difference from a natural-soil water-balance is a lower evapotranspiration rate. Up to now the evaporation rates for water-permeable pavements has not been established accurately. The aim of the applied research project at the University of Muenster, which is sponsored by the DBU (The German Federal Environmental Foundation), is to gain knowledge of urban evaporation rates and of water-permeable surfaces, especially water-permeable pavements. Water-permeable pavements consist of the paving stone surface and the two sub-base layers below. Pre-investigations show that evaporation can be influenced by the complete sub-base. Therefore, the first step was to investigate which materials are used for sub-base construction. All in all, 27 materials were collected from throughout Germany and these materials were then tested (in terms of physical and hydraulic attributes) in the soil-mechanics laboratory of the University of Muenster. For their street construction useability, and having regard to evaporation, a selection of appropriate materials were built into a test field. The test field consisted of seven hexagonal areas each about 10 m2 large, which are placed in a honeycomb manner. The evaporation measurements are carried out with a WERNER tunnel-evaporation gauge (TUV) which is able to detect the actual evaporation rate. Its functional principle also allows a direct comparison between the middle reference area and one outer area of the test field. Every measuring period lasts one week and after that the TUV is moved to between the next outer area and the reference area. So the TUV rotates over the whole test field and every measuring area is covered by a measurement. In addition, a Hellman rain-gauge near the test field enables the measurement of a direct precipitation-evaporation ratio. Since the start of the measurements in July 2008, the first results collected showed that measureable differences in evaporation rates could be detected after a few measuring periods, i.e. the differences are up to 32% between the reference area and one outer area. In July 2009, the six outer measuring areas of the test field will be replaced and, based on the actual results collected, the sub-base layers will be replaced by an evaporation-optimized sub-base. The new outer measuring areas will only differ in terms of a different paving-stone surface. These paving stones are actually under developement and under laboratory testing (i.e. permeability, porosity, capillary water and evaporationrates), and so they will be evaporation-opimized. The open-air test in the test field is to assure and compare the evaporation rates. As a final result, the evaporation-optimized and water-permeable pavement and the knowledge of its exact drainage ratio will allow city planners or architects to build water-permeable streets with due regard to the respective area-specific conditions. This new developed pavement is an approximation to the water balanc
Starke, P.; G—bel, P.; Coldewey, W. G.
A kinetic analysis of evaporative water loss barriers.
A simple kinetic analysis of evaporation solves a number of current theoretical conflicts and provides a much needed insight into waterproofing barriers. Although the saturation deficit law approximates the gradient across a free water surface, it is not necessarily applicable when a barrier is present. Any gaseous diffusion barrier reduces water loss by increasing condensation at the interface, whereas a hydrophobic barrier reduces both vaporization and condensation. Hydrophilic barriers may decrease vaporization without inhibiting condensation but are ineffective when fully hydrated. A general model is derived for steady state water loss across a biological barrier consisting of a mosaic of hydrophilic and hydrophobic bonds. These principles are applied to organisms inhabiting temporally heterogeneous environments. PMID:3796002
Damstra, K S
Absolute evaporation rates of non-rotating neutral polycyclic aromatic hydrocarbon clusters
NASA Astrophysics Data System (ADS)
Context. Clusters of polycyclic aromatic hydrocarbons (PAHs) have been proposed as candidates for evaporating very small grains, which are thought to be precursors of free-flying PAHs. Evaporation rates have been calculated so far only for species containing up to a few 100-C atoms, whereas interstellar PAH clusters could contain up to ~1000 C atoms. Aims: We present a method that generalises the calculation of the statistical evaporation rate of large PAH clusters and provides rates for species containing up to ~1000 C-atoms. Methods: The evaporation of non-rotating neutral homo-molecular PAH clusters containing up to 12 molecules from a family of highly symmetric compact PAHs is studied. Statistical calculations were performed and completed with molecular dynamics simulations at high internal energies to provide absolute values for the evaporation rate and distributions of kinetic energy released. The calculations used explicit atom-atom Lennard-Jones potentials in the rigid molecule approximation. A new method is proposed to take both inter- and intra-molecular vibrations into account. Results: Without any parameter adjustment, the calculated evaporation rates agree well with available experimental data. We find that the non-rotation assumption has a limited impact on the evaporation rates. The photostability of PAH clusters increases dramatically with the size of molecules in the clusters, and to a lesser extent with the number of molecules in the clusters. For values of the UV radiation field that are typical of the regions where evaporating very small grains are observed, the smallest clusters in this study (~50 C-atoms) are found to be quickly photo-evaporated, whereas the largest clusters (~1000 C-atoms) are photostable. Conclusions: Our results support the idea that large PAH clusters are good candidates for evaporating very small grains.
Montillaud, J.; Joblin, C.
Trade Study for 9 kW Water Membrane Evaporator
NASA Technical Reports Server (NTRS)
Sublimators have been proposed and used in spacecraft for heat rejection. Sublimators are desirable heat rejection devices for short duration use because they can transfer large amounts of heat using little mass and are self-regulating devices. Sublimators reject heat into space by freezing water inside a porous substrate, allowing it to sublimate into vapor, and finally venting it into space. The state of the art thermal control system in orbiting spacecraft is a two loop, two fluid system. The external coolant loop typically uses a toxic single phase fluid that acquires heat from the spacecraft and rejects most of it via a radiator. The sublimator functions as a transient topper for orbiting spacecraft during day pass periods when radiator efficiency decreases. The sublimator interfaces with the internal loop through a built in heat exchanger. The internal loop fluid is non-toxic and is typically a propylene glycol and water solution with inhibitors to prevent corrosion with aluminum fins of the heat exchangers. Feedwater is supplied from a separate line to the sublimator to maintain temperature control of the cabin and vehicle hardware. Water membrane evaporators have been developed for spacecraft and spacesuits. They function similar to a sublimator but require a backpressure valve which could be actuated for this application with a simple fully open or fully closed modes. This technology would be applied to orbital thermal control (lunar or planetary). This paper details a trade study showing that evaporators would greatly reduce the consumable that is used, effectively wasted, by sublimators during start up and shut down during the topping phases of each orbit. State of the art for 9 kW sublimators reject about 870 W per kilogram of mass and 1150 W per liter of volume. If water with corrosion inhibitors is used the evaporators would be about 80% of the mass and volume of the equivalent system. The size and mass increases to about 110% if the internal fluid is 50% propylene glycol/50% water. The true benefit comes from the backpressure valve, that prevents the cyclical shutdown/startup loss of the sublimator and amounts to as much as 0.85 kg per orbit.
Bue, Grant C.; Ungar, Gene; Stephan, Ryan
Evaporation Rate Study and NDMA Formation from UDMH/NO2 Reaction Products
NASA Technical Reports Server (NTRS)
Laboratory samples of uns-dimethylhydrazine (UDMH) fuel/oxidizer (nitrogen dioxide) non-combustion reaction products (UFORP) were prepared using a unique permeation tube technology. Also, a synthetic UFORP was prepared from UDMH, N-nitrosodimethylamine (NDMA), dimethylammonium nitrate, sodium nitrite and purified water. The evaporation rate of UFORP and synthetic UFORP was determined under space vacuum (approx 10(exp -3) Torr) at -40 ?C and 0 ?C. The material remaining was analyzed and showed that the UFORP weight and NDMA concentration decreased over time; however, NDMA had not completely evaporated. Over 85% of the weight was removed by subjecting the UFORP to 10(-3) Torr for 7 hours at -40 ?C and 4 hours at 0 ?C. A mixture of dimethylammonium nitrate and sodium nitrite formed NDMA at a rapid rate in a moist air environment. A sample of UFORP residue was analyzed for formation of NDMA under various conditions. It was found that NDMA was not formed unless nitrite was added.
Buchanan, Vanessa D.; Dee, Louis A.; Baker, David L.
The effect of additives on the treatment of oil-in-water emulsions by vacuum evaporation.
A simple batch vacuum evaporation process for the treatment of several oil-in-water (O/W) emulsions is reported. The experiments were carried out with waste emulsions from an industrial copper rolling process and with model emulsions prepared in the laboratory. No detailed information on the formulation of the industrial waste O/W emulsions was available. Several model emulsions were formulated using the same base oil (an 85-15% (w/w) mixture of a synthetic poly-alpha-olefin and a trimethylol propane trioleate ester, respectively) and one of the three following surfactants: Brij-76 (polyethylene glycol octadecyl ether, non-ionic), CTAB (hexadecyltrimethyl ammonium bromide, cationic), and Oleth-10 (glycolic acid ethoxylate oleyl ether, anionic). Experimental results show a strong influence of operating conditions, such as pressure or bath temperature, on the evaporation performance. As a general trend, the higher the values of these parameters, the higher the pollutant content in the obtained aqueous effluent. The presence of surfactants increase the evaporation rate, especially at low operating vacuum pressures, the solubility of oil molecules in water and the evaporation temperature of model O/W emulsions. Furthermore, COD reductions higher than 99.5% for the treated waste O/W emulsions were achieved. PMID:17321675
GutiÕrrez, Gemma; Cambiella, Angel; Benito, JosÕ M; Pazos, Carmen; Coca, JosÕ
Stability of evaporating water when heated through the vapor and the liquid phases.
The stability of a water layer of uniform thickness held in a two-dimensional container of finite or semi-infinite extent is examined using linear stability theory. The liquid-vapor interface can be heated both through the liquid and through the vapor, as previously experimentally reported. The need to introduce a heat transfer coefficient is eliminated by introducing statistical rate theory (SRT) to predict the evaporation flux. There are no fitting or undefined parameters in the expression for the evaporation flux. The energy transport is parametrized in terms of the evaporation number, Eev, that for a given experimental circumstance can be predicted. The critical Marangoni number for the finite, Macf, and for the semi-infinite system, Mac(infinity), can be quantitatively predicted. Experiments in which water evaporated from a stainless-steel funnel and from a polymethyl methacrylate (PMMA) funnel into its vapor have been previously reported. Marangoni convection was observed in the experiments that used the stainless-steel funnel but not with the PMMA funnel even though the Marangoni number for the PMMA funnel was more than 27,000. The SRT-based stability theory indicates that the critical value of the Marangoni number for the experiments with the PMMA funnel was greater than the experimental value of the Marangoni number in each case; thus, no Marangoni convection was predicted to result from an instability. The observed convection with the stainless-steel funnel resulted from a temperature gradient imposed along the interface. PMID:20365865
Das, Kausik S; MacDonald, Brendan D; Ward, C A
Salinity and Compaction Effects on Soil Water Evaporation and Water and Solute Distributions
and 0.06 m deep after 25 d of evapo- ration potentials of 0.0051, 0.0073, 0.0113, and 0.0192 m Water evaporation and solute transport were studied in open soil d2 1 , respectively. The evaporation zones under evapora- columns. The study included two different soil materials Clarinda clay (fine, montmorillonitic, mesic, sloping Typic Argiaquoll) and tion potential of 0.01 m
I. N. Nassar; Robert Horton
Comparing the mechanism of water condensation and evaporation in glassy aerosol.
Atmospheric models generally assume that aerosol particles are in equilibrium with the surrounding gas phase. However, recent observations that secondary organic aerosols can exist in a glassy state have highlighted the need to more fully understand the kinetic limitations that may control water partitioning in ambient particles. Here, we explore the influence of slow water diffusion in the condensed aerosol phase on the rates of both condensation and evaporation, demonstrating that significant inhibition in mass transfer occurs for ultraviscous aerosol, not just for glassy aerosol. Using coarse mode (3-4 um radius) ternary sucrose/sodium chloride/aqueous droplets as a proxy for multicomponent ambient aerosol, we demonstrate that the timescale for particle equilibration correlates with bulk viscosity and can be ?10(3) s. Extrapolation of these timescales to particle sizes in the accumulation mode (e.g., approximately 100 nm) by applying the Stokes-Einstein equation suggests that the kinetic limitations imposed on mass transfer of water by slow bulk phase diffusion must be more fully investigated for atmospheric aerosol. Measurements have been made on particles covering a range in dynamic viscosity from < 0.1 to > 10(13) Pa s. We also retrieve the radial inhomogeneities apparent in particle composition during condensation and evaporation and contrast the dynamics of slow dissolution of a viscous core into a labile shell during condensation with the slow percolation of water during evaporation through a more homogeneous viscous particle bulk. PMID:22753520
Bones, David L; Reid, Jonathan P; Lienhard, Daniel M; Krieger, Ulrich K
Combustion rates of coal-water slurry droplets.
National Technical Information Service (NTIS)
This paper reports on experimental findings and theoretical calculations on the combustion rates of coal-water fuels. Combustion of coal-water fuels (CWF) takes place upon evaporation of the water and heat-up of the remaining solid agglomerate. Combustion...
Y. A. Levendis A. Atal
Theoretical investigation of the injection and evaporation of water in a hydrogen/oxygen steam generator
NASA Astrophysics Data System (ADS)
Water is injected into the gas stream for the purpose of cooling the reaction products resulting from the stochiometric combustion of hydrogen with oxygen. The penetration of the jet decisively influences the temperature profile across the flow cross section in the water vapor. The penetration of the water jet into the stream is calculated using the jet shedding model and compared with the garden hose model. Models for the evaporation of water droplets in superheated steam are developed for calculating the evaporation paths. The parameters which influence the injection and evaporation process are subjected to variation and their effects in the evaporation paths are analyzed.
Beer, Stefan
Impact of Natural Conditioners on Water Retention, Infiltration and Evaporation Characteristics of Sandy Soil
NASA Astrophysics Data System (ADS)
Soil conditioners i.e., natural deposits and organic fertilizer are used for alleviate some of poor physical properties of sandy soils such as low water retention and inefficient water use, especially in arid and semi-arid regions such as in Saudi Arabia conditions. The present study aims to investigate the impact of clay deposits and organic fertilizer on water characteristics, cumulative infiltration and intermittent evaporation of loamy sand soil. Soil sample was collected from surface layer (0-30 cm depth) of the Agricultural Experiment and Research Station at Dierab, 40 km south west of Riyadh, Saudi Arabia. Two samples of clay deposits (CD#22 and CD#23) collected from Khyleis area, Jeddah-Madina road in addition of commercial Organic Fertilizer (OF) were used in the present study. The experiments were done during August to December 2005 in soil physics laboratory, the soil was mixed with clay deposits and organic fertilizer at rates of 0, 1, 2.5, 5.0 and 10.0% (w/w). The transparent PVC columns were packed with soil to depth of 30 cm every 5.0 cm intervals to insure a homogeneity of soil in columns. The clay deposits (CD#22 and CD#23) and Organic Fertilizer (OF) mixed with the soil were packed in the upper 0-5.0 cm of each soil column. The infiltration experiment was done using a flooding apparatus (Marriot device) with constant head of 3.0 cm over the soil surface. The cumulative infiltration and wetting front depth as a function of time were recorded. The evaporation experiment was conducted in 40 cm long transparent sectioned Lucite cylinders (5.0 cm ID). Fifty millimeters of tap water were applied weekly for three wetting/drying cycles. Cumulative evaporation against time was measured daily by weighing each soil column. The soil moisture distribution at the end of the experiment was determined gravimetrically for each 5.0 cm interval. The results indicated that the three conditioners significantly increased the water constants of mixed soil (i.e., SWC, FC, PWP and AW), but the CD#22 has a superior effect. The results clearly indicated that increasing the application rate of conditioners significantly decreased the cumulative infiltration (D). The decrease in D more pronounced at higher rates. The CD#22 was more effective in reducing the cumulative infiltration. The relationship between (D) as a function of Time (T) was done by fitting the data to the Kostiakov and Philip equations. Increasing the application rate of natural conditioners restricted the wetting front movement and need more time to reach 30 cm depth. The natural conditioners significantly reduced the cumulative evaporation throughout the 3 evaporation cycles. The reduction significantly increased with increasing the application rate, except for the higher rate (10%), which increases the cumulative evaporation under the present conditions. The improvement of soil hydro-physical properties and reduction in water infiltration and cumulative evaporation are good practices for plant growth in region limited in water such as most regions in Saudi Arabia.
Abdel-Nasser, G.; Al-Omran, A. M.; Falatah, A. M.; Sheta, A. S.; Al-Harbi, A. R.
Estimation of daily soil water evaporation using an artificial neural network
In field water balance studies, one of the major difficulties is the separation of evapo-transpiration into plant transpiration and soil evaporation. In this paper, the radial basis function (RBF) neural network was implemented using C language to estimate daily soil water evaporation from average relative air humidity, air temperature, wind speed and soil water content in a cactus field study.
Huien Han; Peter Felker
Role of transpiration suppression by evaporation of intercepted water in improving irrigation efficiency
Sprinkler irrigation efficiency declines when applied water intercepted by the crop foliage, or gross interception (Igross), as well as airborne droplets and ponded water at the soil surface evaporate before use by the crop. However, evaporation of applied water can also supply some of the atmospheric demands usually met by plant transpiration. Any suppression of crop transpiration from the irrigated
J. A. Tolk; T. A. Howell; J. L. Steiner; D. R. Krieg; A. D. Schneider
Evaporation From Lake Superior
NASA Astrophysics Data System (ADS)
Evaporation is a critical component of the water balance of each of the Laurentian Great Lakes, and understanding the magnitude and physical controls of evaporative water losses are important for several reasons. Recently, low water levels in Lakes Superior and Michigan/Huron have had socioeconomic, ecological, and even meteorological impacts (e.g. water quality and quantity, transportation, invasive species, recreation, etc.). The recent low water levels may be due to increased evaporation, but this is not known as operational evaporation estimates are currently calculated as the residual of water or heat budgets. Perhaps surprisingly, almost nothing is known about evaporation dynamics from Lake Superior and few direct measurements of evaporation have been made from any of the Laurentian Great Lakes. This research is the first to attempt to directly measure evaporation from Lake Superior by deploying eddy covariance instrumentation. Results of evaporation rates, their patterns and controlling mechanisms will be presented. The direct measurements of evaporation are used with concurrent satellite and climate model data to extrapolate evaporation measurements across the entire lake. This knowledge could improve predictions of how climate change may impact the lake's water budget and subsequently how the water in the lake is managed.
Spence, C.; Blanken, P.; Hedstrom, N.; Leshkevich, G.; Fortin, V.; Charpentier, D.; Haywood, H.
Inundation and groundwater dynamics for quantification of evaporative water loss in tropical wetlands
NASA Astrophysics Data System (ADS)
The remoteness, complexity and heterogeneity of tropical wetlands make the characterisation of their hydrological processes challenging. In particular estimates of evaporative water loss are inherently uncertain. In view of the large influence on the local and regional climate, the quantification of evaporation is essential for the determination of the water balance of permanent and intermittent water bodies. Data for tropical wetlands are scarce where their remoteness impedes direct evaporation measurements. Seasonal inundation dynamics affect evaporation processes in tropical wetlands, which can be analysed in two stages: the first stage during the wet season and the second stage during the dry season. As yet no adequate method exists for determining second stage evaporation without soil moisture data, which are usually unavailable for the remote tropical wetlands. Our study aimed at developing a process-based model to simulate first and second stage evaporation in tropical wetlands. We selected a set of empirical potential evaporation (PET) models of varying complexity, each based on different assumptions and available datasets, and evaluated the models with pan evaporation observations in the Pantanal of South America, one of the largest tropical wetlands in the world. We used high-resolution measurements of surface and groundwater levels at different locations to determine the water available for evaporation. Actual evaporation (AET) was derived by constraining simulated PET based on available water. The model of best fit was applied to different types of water bodies with varying inundation durations and captured first and second stage evaporation. With our new model we could quantify evaporative water loss in the dry and the wet season for different locations in the Pantanal. This new spatially-explicit approach represents an improvement in our understanding of the role of evaporation in the water balance of the Pantanal. We recommend the application of this model in other remote tropical wetlands, since only a minimum of input data is necessary.
Schwerdtfeger, J.; Johnson, M. S.; Couto, E. G.; Amorim, R. S. S.; Sanches, L.; Campelo Jºnior, J. H.; Weiler, M.
Deuterium in water vapor evaporated from a coastal salt marsh
NASA Astrophysics Data System (ADS)
Atmospheric water vapor was sampled simultaneously at two heights in the atmospheric surface layer above a coastal salt marsh near New Haven, Connecticut, during June 11-27, 1997. The water vapor samples were analyzed for their mixing ratio, Q, and deuterium isotope ratio, ?D. The observed ?D varied in the range of -145 to -89 per mil and was positively correlated with Q, reflecting the influence of in-cloud condensation and surface evapotranspiration processes at a regional scale. Both Q and ?D were, in general, lower at the upper level, indicating an upward transport of H216O and HD16O. The Craig-Gordon model reproduced reasonably well the combined effects of equilibrium and kinetic fractionations and atmospheric demand on the evaporation process. Transpiration of the marsh plants, Spartina patens (Ait.), was a minor component (11%) of the total evapotranspiration during the experimental period. We also suggest that the relationship between ?D and salinity, S, of the marsh surface water can be used to infer the isotope flux ratio. More data, however, are needed to verify this mass balance approach.
He, Hui; Lee, Xuhui; Smith, Ronald B.
Evaporation of J13 water: laboratory experiments and geochemical modeling
We report results from experiments on the evaporative chemical evolution of synthetic J13 water, representative of water from well J13, a common reference water in the Yucca Mountain Project. Data include anion and cation analysis and qualitative mineral identification for a series of open system experiments, with and without crushed tuff present, conducted at sub-boiling temperatures. Ca and Mg precipitated readily as carbonates and anions Cl, F, NO{sub 3} and SO{sub 4} remained in solution in nearly identical ratios. The pH stabilized at about 10. After {approx} 1000x concentration, the minerals formed were amorphous silica, aragonite and calcite. The presence of tuff appears to have very little effect on the relative distribution of the anions in solution, except for possibly F, which had a relatively lower concentration ratio. The Si was lower in the solutions with tuff present suggesting that the tuff enhances SiO{sub 2} precipitation. Even though the tools to model highly-concentrated salt solutions are limited, we compare our experimental results with the results of geochemical models, with (perhaps) surprising good results. In response to different assumed CO{sub 2} levels, pH varied, but anion concentrations were not greatly affected.
Dibley, M.J.; Knauss, K.G.; Rosenberg, N.D.
Water-evaporation reduction by duplex films: application to the human tear film.
Water-evaporation reduction by duplex-oil films is especially important to understand the physiology of the human tear film. Secreted lipids, called meibum, form a duplex film that coats the aqueous tear film and purportedly reduces tear evaporation. Lipid-layer deficiency is correlated with the occurrence of dry-eye disease; however, in-vitro experiments fail to show water-evaporation reduction by tear-lipid duplex films. We review the available literature on water-evaporation reduction by duplex-oil films and outline the theoretical underpinnings of spreading and evaporation kinetics that govern behavior of these systems. A dissolution-diffusion model unifies the data reported in the literature and identifies dewetting of duplex films into lenses as a key challenge to obtaining significant evaporation reduction. We develop an improved apparatus for measuring evaporation reduction by duplex-oil films including simultaneous assessment of film coverage, stability, and temperature, all under controlled external mass transfer. New data reported in this study fit into the larger body of work conducted on water-evaporation reduction by duplex-oil films. Duplex-oil films of oxidized mineral oil/mucin (MOx/BSM), human meibum (HM), and bovine meibum (BM) reduce water evaporation by a dissolution-diffusion mechanism, as confirmed by agreement between measurement and theory. The water permeability of oxidized-mineral-oil duplex films agrees with those reported in the literature, after correction for the presence of mucin. We find that duplex-oil films of bovine and human meibum at physiologic temperature reduce water evaporation only 6-8% for a 100-nm film thickness pertinent to the human tear film. Comparison to in-vivo human tear-evaporation measurements is inconclusive because evaporation from a clean-water surface is not measured and because the mass-transfer resistance is not characterized. PMID:23694847
Cerretani, Colin F; Ho, Nghia H; Radke, C J
Evaluation of the correlations for predicting evaporative loss from water body
Water evaporation (evaporation from here on) is a natural phenomenon that is important for system design and system safety in many engineering branches. Indeed, evaporative heat and mass loss are observed and calculated in very diverse situations, such as irrigation plants, water purification plants, cooling ponds, lakes, dams, swimming pools, health spas, management of liquid wastes as in evaporation pools, and spent fuel pools in nuclear power plants. There are a number of correlations obtained from experimental studies that predict the evaporative heat and mass loss from a water body. This study aims to summarize and to compare the existing evaporation correlations to determine the upper and lower bounding correlations for use in various thermal-hydraulic analyses of systems. Currently and widely used, six correlations found in the literature have been selected and tested using the major parameters of evaporation such as water temperature, air relative humidity, air velocity, and temperature. The comparison test cases show that ASHRAE (1991) and Ryan et al. (1974) equations result in the highest evaporative loss, while the Brady et al. (1969) equation provides the lowest evaporative loss in most conditions. Engineering designers may sometimes need the upper bound value of evaporative loss or sometimes the lower bound value for a conservative calculation. The authors conclude that using a single equation does not provide the conservative calculation for every situation and show which correlation gives the lower or upper bound for different conditions.
Yilmaz, T.P.; Aybar, H.S.
The Effect of Water Evaporation on Photoacoustic Signals in Transition and Molecular Flow
Evaporation of water changes the response of photoacoustic instruments to light-absorbing particles. Previous calculations of this effect are valid for particles much larger than the mean free path of air. These calculations are extended here to include transition and molecular flow as well as various mass accommodation coefficients for water. For commonly encountered conditions, evaporation can significantly reduce the photoacoustic
D. M. Murphy
The influence of droplet evaporation on fuel-air mixing rate in a burner
NASA Technical Reports Server (NTRS)
Experiments involving combustion of a variety of hydrocarbon fuels in a simple atmospheric pressure burner were used to evaluate the role of droplet evaporation in the fuel/air mixing process in liquid fuel spray flames. Both air-assist atomization and pressure atomization processes were studied; fuel/air mixing rates were determined on the basis of cross-section average oxygen concentrations for stoichiometric overall operation. In general, it is concluded that droplets act as point sources of fuel vapor until evaporation, when the fuel jet length scale may become important in determining nonuniformities of the fuel vapor concentration. In addition, air-assist atomizers are found to have short droplet evaporation times with respect to the duration of the fuel/air mixing process, while for the pressure jet atomizer the characteristic evaporation and mixing times are similar.
Komiyama, K.; Flagan, R. C.; Heywood, J. B.
Treatment of a waste oil-in-water emulsion from a copper-rolling process by ultrafiltration and vacuum evaporation.
A process is proposed for the treatment of a waste oil-in-water (O/W) emulsion generated in an industrial copper-rolling operation. The use of demulsifier agents improves the subsequent treatment by techniques such as ultrafiltration (UF) or evaporation. The effluent COD is reduced up to 50% when the O/W emulsion is treated by UF using a flat 30 nm TiO(2) ceramic membrane (?P = 0.1 MPa) and up to 70% when it is treated by vacuum evaporation, after an emulsion destabilization pretreatment in both cases. Increases in the UF permeate flux and in the evaporation rate are observed when a chemical demulsifier is used in the pretreatment step. A combined process consisting of destabilization/settling, UF, and vacuum evaporation can yield a very high-quality aqueous effluent that could be used for process cooling or emulsion reformulation. PMID:21112152
GutiÕrrez, Gemma; Lobo, Alberto; Benito, JosÕ M; Coca, JosÕ; Pazos, Carmen
The evaporative requirement for heat balance determines whole-body sweat rate during exercise under conditions permitting full evaporation
Although the requirements for heat dissipation during exercise are determined by the necessity for heat balance, few studies have considered them when examining sweat production and its potential modulators. Rather, the majority of studies have used an experimental protocol based on a fixed percentage of maximum oxygen uptake (%). Using multiple regression analysis, we examined the independent contribution of the evaporative requirement for heat balance (Ereq) and % to whole-body sweat rate (WBSR) during exercise. We hypothesised that WBSR would be determined by Ereq and not by %. A total of 23 males performed two separate experiments during which they exercised for 90 min at different rates of metabolic heat production (200, 350, 500 W) at a fixed air temperature (30¯C, n= 8), or at a fixed rate of metabolic heat production (290 W) at different air temperatures (30, 35, 40¯C, n= 15 and 45¯C, n= 7). Whole-body evaporative heat loss was measured by direct calorimetry and used to calculate absolute WBSR in grams per minute. The conditions employed resulted in a wide range of Ereq (131487 W) and % (1555%). The individual variation in non-steady-state (030 min) and steady-state (3090 min) WBSR correlated significantly with Ereq (P < 0.001). In contrast, % correlated negatively with the residual variation in WBSR not explained by Ereq, and marginally increased (?2%) the amount of total variability in WBSR described by Ereq alone (non-steady state: R2= 0.885; steady state: R2= 0.930). These data provide clear evidence that absolute WBSR during exercise is determined by Ereq, not by %. Future studies should therefore use an experimental protocol which ensures a fixed Ereq when examining absolute WBSR between individuals, irrespective of potential differences in relative exercise intensity.
Gagnon, Daniel; Jay, Ollie; Kenny, Glen P
Evaporation rates of freely falling liquid nitrogen droplets in air
The rates of heat transfer to individual droplets of liquid nitrogen falling freely in air were measured under different air temperatures similar to the conditions in a cryogenic freezing system. High-speed cinephotography was used to measure drop size and velocity. Experimental results of heat transfer rates to individual droplets were analyzed and the data were compared to those obtainable using other types of dimensionless correlations. Droplets of initial size range investigated (2.5-0.72 mm diameter) attained terminal velocities at distances of 4-6 cm freefall away from the drop generator tip. The velocity values used in the correlation of heat transfer data were averaged over the time traveled by individual droplet.
Awonorin, S.O.
Evaporation of ethanol/water droplets: examining the temporal evolution of droplet size, composition and temperature.
The evolving size, composition, and temperature of evaporating ethanol/water aerosol droplets 25-57 microm in radius are probed by cavity enhanced Raman scattering (CERS) and laser induced fluorescence. This represents the first study in which the evolving composition of volatile droplets has been probed with spatial selectivity on the millisecond time scale, providing a new strategy for exploring mass and heat transfer in aerosols. The Raman scattering intensity is shown to depend exponentially on species concentration due to the stimulated nature of the CERS technique, providing a sensitive measure of the concentration of the volatile ethanol component. The accuracy with which we can determine droplet size, composition, and temperature is discussed. We demonstrate that the CERS measurements of evolving size and composition of droplets falling in a train can be used to characterize, and thus avoid, droplet coagulation. By varying the surrounding gas pressure (7-77 kPa), we investigate the dependence of the rate of evaporation on the rate of gas diffusion, and behavior consistent with gas diffusion-limited evaporation is observed. We suggest that such measurements can allow the determination of the vapor pressures of components within the droplet and can allow the determination of activity coefficients of volatile species. PMID:16834174
Hopkins, Rebecca J; Reid, Jonathan P
Enhancement of Photodegradation of Pesticides in Soil by Transport Upward in Evaporating Water.
National Technical Information Service (NTIS)
The research examined the extent of photolysis of three pesticides in soils of differing texture and organic matter content under the influence of evaporating soil water, to evaluate the impact of transport of water soluble compounds on photodegradation a...
G. C. Miller S. G. Donaldson
Spacesuit Water Membrane Evaporator Integration with the ISS Extravehicular Mobility
NASA Technical Reports Server (NTRS)
NASA has developed a Solid Water Membrane Evaporation (SWME) to provide cooling for the next generation spacesuit. One approach to increasing the TRL of the system is to incorporate this hardware with the existing EMU. Several integration issues were addressed to support a potential demonstration of the SWME with the existing EMU. Systems analysis was performed to assess the capability of the SWME to maintain crewmember cooling and comfort as a replacement for sublimation. The materials of the SWME were reviewed to address compatibility with the EMU. Conceptual system placement and integration with the EMU via an EVA umbilical system to ensure crew mobility and Airlock egress were performed. A concept of operation for EVA use was identified that is compatible with the existing system. This concept is extensible as a means to provide cooling for the existing EMU. The cooling system of one of the EMUs on orbit has degraded, with the root cause undetermined. Should there be a common cause resident on ISS, this integration could provide a means to recover cooling capability for EMUs on orbit.
Margiott, Victoria; Boyle, Robert
Partitioning of evaporative water loss into respiratory and cutaneous pathways in Wahlberg's epauletted fruit bats (Epomophorus wahlbergi).
The relative contributions of respiratory and cutaneous evaporation to total evaporative water loss (TEWL) and how the partitioning of these two avenues varies with environmental temperature has received little attention in bats. We trained Wahlberg's epauletted fruit bats (Epomophorus wahlbergi) captured in Pretoria, South Africa, to wear latex masks while hanging in respirometry chambers, and we measured respiratory evaporative water loss (REWL) and cutaneous evaporative water loss (CEWL) over air temperatures (Ta) from 10¯ to 40¯C. The bats' normothermic body temperature (Tb) was approximately 36¯C, which increased at higher Ta to 40.5¯ Ý 1.0¯C at Ta ? 40¯C. Both TEWL and resting metabolic rate (RMR) increased sharply at Ta >35¯C, with a mean TEWL at 40¯C equivalent to 411% of that at 30¯C. The increase in TEWL was driven by large increases in both CEWL and REWL. CEWL comprised more than 50% of TEWL over the entire Ta range, with the exception of Ta ? 40¯C, where REWL accounted for 58% of evaporative water loss. Surface area-specific CEWL increased approximately sixfold with increasing Ta. Thermoregulation at Ta approaching or exceeding Tb involved a considerable energetic cost, with RMR at Ta ? 40¯C exceeding by 24% that measured at Ta ? 10¯C. Our data do not support recent arguments that respiratory gas exchange across the wing membranes represents 5%-10% of the total in E. wahlbergi. PMID:24769711
Minnaar, Ingrid A; Bennett, Nigel C; Chimimba, Christian T; McKechnie, Andrew E
Instability and dewetting of evaporating thin water films on partially and completely wettable substrates
NASA Astrophysics Data System (ADS)
Stability, dynamics and dewetting of thin (<100 nm) evaporating water films on partially and completely wettable substrates are studied based on numerical solutions of the nonlinear thin film equation, as well as by simplified semianalytical approaches. The instability and rupture of aqueous films are engendered by the hydrophobic attraction, whereas the net van der Waals force is repulsive for aqueous films on most substrates. An evaporating aqueous film on a partially wettable surface thins uniformly to a critical thickness, and then spontaneously dewets the substrate by the formation of growing holes. Complete nonlinear simulations as well as the linear analyses are used to predict the most important, experimentally accessible characteristics of the instability such as the length scale and time scale of the instability and the mean film thickness at the instant of rupture. Curiously, in contrast to nonthinning films, the number density of holes decreases slightly with increased strength and range of hydrophobic attraction, and also with decreased strength of LW repulsion, even though both of these factors promote the macroscopic nonwettability. The rate of evaporation has the most significant influence on the length scale, ?~Eq, where the exponent, q lies in a narrow range from -0.17 to about -0.26, depending on the rate of evaporation and the critical thickness. Thin aqueous films on completely wettable (free energy per unit area is positive) surfaces are also unstable when the free energy does not decrease monotonically with the film thickness. Simulations show that instability in such cases leads to the formation of quasiequilibrium microscopic ``islands'' or ``pancakes'' made up of largely flat thin and thick films.
Padmakar, A. S.; Kargupta, Kajari; Sharma, Ashutosh
Estimation of soil water evaporative loss after tillage operation using the stable isotope technique
NASA Astrophysics Data System (ADS)
Application of stable isotopes in soil studies has improved quantitative evaluation of evaporation and other hydrological processes in soil. This study was carried out to determine the effect of tillage on evaporative loss of water from the soil. Zero tillage and conventional tillage were compared. Suction tubes were installed for soil water collection at the depths 0.15, 0.50, and 1.0 m by pumping soil water with a peristaltic pump. Soil water evaporation was estimated using stable isotopes of water. The mean isotopic composition of the soil water at 0.15 m soil depth were -1.15 (?18O) and -0.75 (?D) and were highly enriched compared with the isotopic compositions of the site precipitation. Soil water stable isotopes (?18O and ?D) were more enriched near the surface under zero tillage while they were less negative down the profile under zero tillage. This suggests an occurrence of more evaporation and infiltration under conventional then zero tillage, respectively, because evaporative fractionation contributes to escape of lighter isotopes from liquid into the vapour phase leading to enrichment in heavy isotopes in the liquid phase. The annual evaporation estimated using the vapour diffusion equation ranges from 46-70 and 54-84 mm year-1 under zero and conventional tillage, respectively, indicating more evaporation under conventional tillage compared with zero tillage. Therefore, to reduce soil water loss, adoption of conservation tillage practices such as zero tillage is encouraged.
Busari, M. A.; Salako, F. K.; Tuniz, C.; Zuppi, G. M.; Stenni, B.; Adetunji, M. T.; Arowolo, T. A.
Influence of forced air volume on water evaporation during sewage sludge bio-drying.
Mechanical aeration is critical to sewage sludge bio-drying, and the actual water loss caused by aeration can be better understood from investigations of the relationship between aeration and water evaporation from the sewage sludge bio-drying pile based on in situ measurements. This study was conducted to investigate the effects of forced air volume on the evaporation of water from a sewage sludge bio-drying pile. Dewatered sewage sludge was bio-dried using control technology for bio-drying, during which time the temperature, superficial air velocity and water evaporation were measured and calculated. The results indicated that the peak air velocity and water evaporation occurred in the thermophilic phase and second temperature-increasing phase, with the highest values of 0.063 Ý 0.027 m s(-1) and 28.9 kg ton(-1) matrix d(-1), respectively, being observed on day 4. Air velocity above the pile during aeration was 43-100% higher than when there was no aeration, and there was a significantly positive correlation between air volume and water evaporation from day 1 to 15. The order of daily means of water evaporation was thermophilic phase > second temperature-increasing phase > temperature-increasing phase > cooling phase. Forced aeration controlled the pile temperature and improved evaporation, making it the key factor influencing water loss during the process of sewage sludge bio-drying. PMID:23648285
Cai, Lu; Chen, Tong-Bin; Gao, Ding; Zheng, Guo-Di; Liu, Hong-Tao; Pan, Tian-Hao
The Response of Phreatic Water Evaporation of Huaibei Plain to Climate Change
NASA Astrophysics Data System (ADS)
Phreatic water evaporation intensity of bare soil is mainly controlled by climate condition, under the condition of the same soil and unchanged water level depth. According to the long series measured data of Wudaogou hydrological experiment station located in Huaibei plain of China, the variation trend of phreatic water evaporation of bare soil is tested with Mann-Kendall method and the linear regression method. Then, the response of phreatic water evaporation of bare soil to climate change is given detailed analysis. These results obviously indicate that the phreatic water evaporation shows different increasing trend in different month and season in recent twenty years, with a significance level of 0.05. There is significant increase trend in March, June and July. The other month mostly also shows increasing trend, but not significant. In addition, the seasonal scale phreatic water evaporation of bare soil shows relative significantly increase trend in spring and summer. And the annual phreatic water evaporation of bare soil also demonstrates significant increase trend. It would increase 7.24%~14.21% if air temperature rises 1 centigrade, while it would increase 1.52%~7.38% if the average saturation deficit rise 1mb. The research can provide some useful information for thorough understanding the response of regional evaporation to climate change.
Shang, M.; Zhang, J.; Liu, J.; Wang, G.; Wang, X.
Thermal and Hydrologic Signatures of Soil Controls on Evaporation: A Combined Energy and Water Balance Approach with Implications for Remote Sensing of Evaporation
NASA Technical Reports Server (NTRS)
The overall goal of this research is to examine the feasibility of applying a newly developed diagnostic model of soil water evaporation to large land areas using remotely sensed input parameters. The model estimates the rate of soil evaporation during periods when it is limited by the net transport resulting from competing effects of capillary rise and drainage. The critical soil hydraulic properties are implicitly estimated via the intensity and duration of the first stage (energy limited) evaporation, removing a major obstacle in the remote estimation of evaporation over large areas. This duration, or 'time to drying' (t(sub d)) is revealed through three signatures detectable in time series of remote sensing variables. The first is a break in soil albedo that occurs as a small vapor transmission zone develops near the surface. The second is a break in either surface to air temperature differences or in the diurnal surface temperature range, both of which indicate increased sensible heat flux (and/or storage) required to balance the decrease in latent heat flux. The third is a break in the temporal pattern of near surface soil moisture. Soil moisture tends to decrease rapidly during stage I drying (as water is removed from storage), and then become more or less constant during soil limited, or 'stage II' drying (as water is merely transmitted from deeper soil storage). The research tasks address: (1) improvements in model structure, including extensions to transpiration and aggregation over spatially variable soil and topographic landscape attributes; and (2) applications of the model using remotely sensed input parameters.
Salvucci, Guido D.
Thermal and Hydrologic Signatures of Soil Controls on Evaporation: A Combined Energy and Water Balance Approach with Implications for Remote Sensing of Evaporation
NASA Technical Reports Server (NTRS)
The overall goal of this research is to examine the feasibility of applying a newly developed diagnostic model of soil water evaporation to large land areas using remotely sensed input parameters. The model estimates the rate of soil evaporation during periods when it is limited by the net transport resulting from competing effects of capillary rise and drainage. The critical soil hydraulic properties are implicitly estimated via the intensity and duration of the first stage (energy limited) evaporation, removing a major obstacle in the remote estimation of evaporation over large areas. This duration, or "time to drying" (t(sub d)), is revealed through three signatures detectable in time series of remote sensing variables. The first is a break in soil albedo that occurs as a small vapor transmission zone develops near the surface. The second is a break in either surface to air temperature differences or in the diurnal surface temperature range, both of which indicate increased sensible heat flux (and/or storage) required to balance the decrease in latent heat flux. The third is a break in the temporal pattern of near surface soil moisture. Soil moisture tends to decrease rapidly during stage 1 drying (as water is removed from storage), and then become more or less constant during soil limited, or "stage 2" drying (as water is merely transmitted from deeper soil storage). The research tasks address: (1) improvements in model structure, including extensions to transpiration and aggregation over spatially variable soil and topographic landscape attributes; and (2) applications of the model using remotely sensed input parameters.
Salvucci, Guido D.
Determination of soil water evaporation and transpiration from energy balance and stem flow measurements
Ham, J.M., Heiiman, J.L. and Lascano, R.J., i 990. Determination of soil water evaporation and tran- spiration from energy balance and stem flow measurements. Agric. For. Meteorol., 52: 287-301. Frequent measurements of soil water evaporation (E) and transpiration (T) are needed to quan- tify energy and water balances of sparse crops. Field experiments were conducted in Lubbock, TX to examine
Jay M. Ham; J. L. Heilman; R. J. Lascano
Influence of municipal waste compost amendment on soil water and evaporation
Municipal Waste Compost was added to soils in the glasshouse and field to assess its impact upon soil physical properties. Application was by mulch and incorporation, and the amelioration of temperature, soil water content, unsaturated hydraulic conductivity, and evaporation were investigated. Incorporation in the glasshouse pot experiments increased early season evaporation, while compost applied by either means raised soil temperature.
S. A. R. Movahedi Naeini; H. F. Cook
RESEARCH NOTES: Rate of evaporation of thorium from carburized thoriated tungsten cathodes measured by activation analysis
The rate of evaporation of thorium from carburized thoriated tungsten cathodes has been measured by means of activation analysis at different temperatures. Values found are about ten times higher than those from previous measurements based on the saturated emission of a receptor wire.
H. Schmied; M. DeÃk
NRMRL-CIN-0988 Smith*, R.L. Predicting Evaporation Rates and Times for Spills of Chemical Mixtures. The Annals of Occupational Hygiene (Ogden, T. (Ed.), Elsevier) 45 (6):437-445 (2001). EPA/600/J-00/125. 03/16/2000 Spreadsheet and short-cut methods have been developed for p...
Radial water infiltration advance evaporation processes during irrigation using point source emitters in rigid and swelling soils
NASA Astrophysics Data System (ADS)
SummaryIn this paper we investigate the dynamic water balance of radial flows during irrigation using point source emitters. The components of radial flows of this kind include infiltration simultaneously coupled to the storage and advance on the soil surface, and evaporation into the air while the source continuously supplies water. The soils we consider here can be rigid or swelling. Because the infiltration equations reported for both rigid and swelling soils have an identical mathematical structure, the analysis for rigid soils using Philip's two-term infiltration equation applies to both swelling and rigid soils. As such, we emphasise that our analysis is applicable to both rigid and swelling soils. We first extend the radial Lewis-Milne equation (RLME) given by Rasmussen to analyse the radial flow mechanics by incorporating evaporation as a key component in the radial dynamic water balance. Then we present a set of four solutions of the RLME using Philip's two-parameter infiltration equation and two-term and three-term equations for cumulative evaporation. With the two-term cumulative evaporation equation, we show that the three solutions yield a simple identical asymptotic formulae at large times, which can be used to design the area to be irrigated, or to derive the final infiltration rate, A, and the final evaporation rate, E2. Analyses show that evaporation plays an important role in the radial dynamic water balance at large times, and as expected it plays a minor role during the early stage of irrigation (small time solutions).
Su, Ninghu
Oxygen consumption and evaporative water loss in infants with congenital heart disease.
The relation between environmental temperature, heat production, oxygen consumption, and evaporative water loss was studied in 67 infants with congenital heart disease. The majority of the cyanosed infants had a low minimum oxygen consumption, a low evaporative water loss, and a diminished metabolic response to cold stress. Minimum oxygen consumption and evaporative water loss rose in 6 of these infants after the construction of a surgical shunt. Many of the ill acyanotic infants had an abnormally high minimum oxygen consumption, and those in cardiac failure often continued to sweat in an environment below the thermoneutral temperature zone.
Kennaird, D L
Interactions among evaporation, ice cover, and water temperature on the world's largest lake: Seasonal feedbacks and long-term change
NASA Astrophysics Data System (ADS)
Lake Superior, the largest freshwater lake in the world by surface area, has enormous impacts on the regional weather and climate. The lake also comprises over half of the total water volume in the Great Lakes system and is an important resource for commercial shipping, water supplies, hydropower, recreation, and aquatic ecosystems. Analysis of historical summer water temperature data and modeled evaporation rates for Lake Superior show significant increases in both parameters in recent decades, while ice cover has been decreasing at a rapid pace. A careful analysis of the long-term trends, however, shows that these changes have not been linear through time. Rather, a pronounced regime shift occurred in 1997/98 that resulted in a drop in ice duration of nearly 40 days, a 3¯C increase in summer water temperature, and a near doubling of July-August evaporation rates. Linear regression analysis of data on either side of this step change shows trends which are largely insignificant and even opposite in sign from those of the step change. Using time-lagged correlation and composite analyses, interactions among ice cover, water temperature, and evaporation are explored across seasonal and interannual timescales. Contrary to what is often expected for inland water bodies, evaporation and ice cover do not show a simple, inverse relationship. Rather, seasonal feedbacks and temporal lags lead to complex interactions among multiple variables. For example, high evaporation rates in the autumn are found to be associated with more extensive ice cover during the subsequent winter months, presumably as a result of strong latent heat flux and correspondingly rapid ice onset and growth. In turn, high ice cover leads to cooler summer water temperatures and reduced evaporation rates in late summer and early fall. Thus, the overall relationship between ice cover and annual evaporation totals is often muted and complex. Quantifying these seasonal feedbacks and interactions is important for assessing the potential impacts of future climate change on large-lake systems. Direct measurements of lake surface processes such as evaporation and sensible heat flux are greatly needed to help further this understanding. As such, this study includes an analysis of the first direct observations of evaporation rates on the Great Lakes, using eddy covariance data collected from monitoring stations on Granite Island and Stannard Rock (north of Marquette, Michigan). The data are analyzed over multi-year periods to explore seasonal and interannual variations in latent and sensible heat fluxes over Lake Superior, as well as some of the primary climatic factors driving this variability. Despite the short observational record, the direct measurements of evaporation show seasonal variability during high- and low-ice years that largely mimics those seen in the historical ice cover records and modeled evaporation rates.
Lenters, J. D.; Van Cleave, K.; Blanken, P.; Hanes, J.; Hedstrom, N.; Spence, C.; Suyker, A. E.; Wang, J.
The daily evaporation characteristics of deeply buried phreatic water in an extremely arid region
NASA Astrophysics Data System (ADS)
Measurements of the daily evaporation characteristics of deeply buried phreatic water in an extremely arid area are reported. The results are used to analyze the mechanism responsible for water movement in the groundwater-soil-plant-atmosphere continuum. A closed PVC greenhouse was set up on Gobi land at the top of the Mogao Grottoes where phreatic water is more than 200 m deep. An air-conditioning unit and an automatic weighing scale were placed inside the greenhouse to condense and monitor phreatic evaporation and soil water changes in this extremely arid region. Soil temperature and humidity at various depths (0-40 cm) and other meteorological factors were also recorded on a sub-hourly basis. The relationship between evaporated water and soil water movement was analyzed by observing changes in soil weight, the condensate from the air-conditioning unit, and air moisture. The results show that phreatic water evaporation occurs from this deeply buried source in this extremely arid zone. The daily characteristics are consistent with the variation in the Suns radiation intensity (i.e. both show a sinusoidal behavior). In the daytime, most of the soil water does not evaporate but moves to cooler sub-layers. In the afternoon, the shallow soil layer absorbs moisture as the temperature decreases. At night, an abundance of water vapor moves upwards from the sub-layers and supplements the evaporated and downward-moving moisture of the superstratum in the daytime, but there is no evaporation. The stable, upwardly migrating vapor and film water is supported by geothermy and comes from phreatic water, the daily evaporation characteristics of which changes according to soil temperature when it reaches the ground.
Li, Hongshou; Wang, Wanfu; Liu, Benli
Control of Leaf Expansion Rate of Droughted Maize Plants under Fluctuating Evaporative Demand (A Superposition of Hydraulic and Chemical Messages?).
We have analyzed the possibility that chemical signaling does not entirely account for the effect of water deficit on the maize (Zea mays L.) leaf elongation rate (LER) under high evaporative demand. We followed time courses of LER (0.2-h interval) and spatial distribution of elongation rate in leaves of either water-deficient or abscisic acid (ABA)-fed plants subjected to varying transpiration rates in the field, in the greenhouse, and in the growth chamber. At low transpiration rates the effect of the soil water status on LER was related to the concentration of ABA in the xylem sap and could be mimicked by feeding artificial ABA. Transpiring plants experienced a further reduction in LER, directly linked to the transpiration rate or leaf water status. Leaf zones located at more than 20 mm from the ligule stopped expanding during the day and renewed expansion during the night. Neither ABA concentration in the xylem sap, which did not appreciably vary during the day, nor ABA flux into shoots could account for the effect of evaporative demand. In particular, maximum LER was observed simultaneously with a minimum ABA flux in the droughted plants, but with a maximum ABA flux in ABA-fed plants. All data were interpreted as the superposition of two additive effects: the first involved ABA signaling and was observed during the night and in ABA-fed plants, and the second involved the transpiration rate and was observed even in well-watered plants. We suggest that a hydraulic signal is the most likely candidate for this second effect.
Salah, HBH.; Tardieu, F.
Impacts of Evaporation from Saline Soils on Soil Hydraulic Properties and Water Fluxes
NASA Astrophysics Data System (ADS)
Saline soils are common in arid zones, where evaporation from shallow groundwater is generally the major component of the water balance. Thus, accurate quantification of soil water evaporation is crucial to improve water resource management in these regions. Evaporation from saline soils is a complex process that couples the movement of salts, heat, liquid water and water vapor. Precipitation/dissolution reactions can alter the soil structure and modify flow paths. The impact of evaporation from shallow groundwater on soil properties and water fluxes poses a major hydrologic challenge that remains to be answered. As a preliminary approach to consider these effects, we used the SiSPAT model (Simple Soil Plant Atmospheric Transfer) to represent the movement of liquid water and water vapor in a saline soil column subjected to two groundwater levels under nonisothermal conditions. To parameterize the model, we determined the hydraulic properties of the soil before performing the soil column experiments. When the SiSPAT model was run using uniform and constant hydraulic properties, it was unable to predict the moisture and thermal profiles, or the cumulative evaporation. This inability to reproduce the observed data is most likely due to alterations of the soil structure as a result of precipitation/dissolution reactions. When the soil hydraulic properties were allowed to vary in space, the model reproduced the experimental data successfully, suggesting that the structure of the initially homogeneous soil column was modified. It is thus necessary to incorporate salt precipitation to correctly simulate evaporation in saline soils.
Fierro, V.; Hernandez, M. F.; Braud, I.; Cristi Matte, F.; Hausner, M. B.; Suarez, F. I.; Munoz, J.
Effects of water vapor density on cutaneous resistance to evaporative water loss and body temperature in green tree frogs (Hyla cinerea).
Increased cutaneous resistance to evaporative water loss (Rc) in tree frogs results in decreased water loss rate and increased body temperature. We examined sensitivity of Rc to water vapor density (WVD) in Hyla cinerea by exposing individual frogs and agar models to four different WVD environments and measuring cutaneous evaporative water loss rate and body temperature simultaneously using a gravimetric wind tunnel measuring system. We found that water loss rate varied inversely and body temperature directly with WVD but that models were affected to a greater extent than were animals. Mean Rc was significantly different between the highest WVD environment and each of the three drier environments but did not differ among the drier environments, indicating that Rc initially increases and then reaches a plateau in response to decreasing WVD. Rc was equivalent when calculated using either WVD difference or WVD deficit as the driving force for evaporation. We also directly observed secretions from cutaneous glands while measuring body temperature and tested secretions and skin samples for the presence of lipids. We found that irregular transient body temperature depressions observed during wind tunnel trials occur due to evaporative cooling from intermittent skin secretions containing lipids, although we were unable to identify lipid-secreting glands. PMID:23995486
Wygoda, Mark L; Kersten, Constance A
Probing the evaporation of ternary ethanol-methanol-water droplets by cavity enhanced Raman scattering.
Cavity enhanced Raman scattering is used to characterise the evolving composition of ternary aerosol droplets containing methanol, ethanol and water during evaporation into a dry nitrogen atmosphere. Measurements made using non-linear stimulated Raman scattering from these ternary alcohol-water droplets allow the in situ determination of the concentration of the two alcohol components with high accuracy. The overlapping spontaneous Raman bands of the two alcohol components, arising from C-H stretching vibrational modes, are spectrally-resolved in stimulated Raman scattering measurements. We also demonstrate that the evaporation measurements are consistent with a quasi-steady state evaporation model, which can be used to interpret the evaporation dynamics occurring at a range of pressures at a particular evaporation time. PMID:17914471
Howle, Chris R; Homer, Chris J; Hopkins, Rebecca J; Reid, Jonathan P
Evaporation from Seven Reservoirs in the Denver Water-Supply System, Central Colorado.
National Technical Information Service (NTIS)
Seven reservoirs in central Colorado, operated by the Denver Board of Water Commissioners, were studied during 1967-73 to determine evaporation losses. These reservoirs, Elevenmile Canyon, Dillon, Gross, Antero, Cheesman, Williams Fork, and Ralston, are l...
J. F. Ficke D. B. Adams T. W. Danielson
Low temperature evaporation and reverse osmosis systems were each evaluated (on a pilot scale) on their respective ability to process rinse water collected from a nickel electroplating operation. ach system offered advantages under specific operating conditions. he low temperatur...
Low temperature evaporation and reverse osmosis systems were each evaluated (on a pilot scale) on their respective ability to process rinse water collected from a nickel electroplating operation. Each system offered advantages under specific operating conditions. The low temperat...
Potable water recovery for spacecraft application by electrolytic pretreatment/air evaporation
NASA Technical Reports Server (NTRS)
A process for the recovery of potable water from urine using electrolytic pretreatment followed by distillation in a closed-cycle air evaporator has been developed and tested. Both the electrolytic pretreatment unit and the air evaporation unit are six-person, flight-concept prototype, automated units. Significantly extended wick lifetimes have been achieved in the air evaporation unit using electrolytically pretreated, as opposed to chemically pretreated, urine feed. Parametric test data are presented on product water quality, wick life, process power, maintenance requirements, and expendable requirements.
Wells, G. W.
Evaporative assembly of MEH-PPV rings using mixed solvents at the air/water interface.
Controlling the morphology of conjugated polymers has recently attracted considerable attention because of their applications in photovoltaic (PV) devices and organic light-emitting diodes (OLEDs). Here, we describe the self-assembly of a common conjugated polymer, poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), into ringlike structures via solvent evaporation on an air/water interface. The films are monitored using Brewster angle microscopy (BAM) and transferred onto a solid substrate by either the Langmuir-Blodgett (LB) or the Langmuir-Schaefer (LS) method and further characterized by atomic force microscopy (AFM). The morphology of the MEH-PPV thin film at the air/water interface can be controlled by the spreading solvent. By mixing solvents of varying spreading coefficients and evaporation rates, such as chloroform and chlorobenzene, MEH-PPV can be assembled into micrometer-sized ring structures. The optical properties of these MEH-PPV ring structures are also characterized. Lastly, MEH-PPV can be used as a soft template to organize microscale structures of nanoparticles. PMID:24684587
Chao, Kung-Po; Biswal, Sibani L
Evaporation Rates of Chemical Warfare Agents Measured Using 5 CM Wind Tunnels. 2. Munitions Grade Sulfur Mustard From Sand.
National Technical Information Service (NTIS)
The evaporation of sulfur mustard from sand was studied as a function of temperature, drop size and air flow rate, using the same instrumentation as prior studies on glass. The evaporation rate increased with higher temperature, drop size, and wind speed;...
C. A. Brevett C. V. Giannaras E. L. Maloney J. P. Myers R. G. Nickol
Effects of Surface Dipole Lengths on Evaporation of Tiny Water Aggregation
NASA Astrophysics Data System (ADS)
Using molecular dynamics simulation, we compared evaporation behavior of a tiny amount of water molecules adsorbed on solid surfaces with different dipole lengths, including surface dipole lengths of 1 fold, 2 folds, 4 folds, 6 folds and 8 folds of 0.14 nm and different charges from 0.1e to 0.9e. Surfaces with short dipole lengths (1-fold system) can always maintain hydrophobic character and the evaporation speeds are not influenced, whether the surface charges are enhanced or weakened; but when surface dipole lengths get to 8 folds, surfaces become more hydrophilic as the surface charge increases, and the evaporation speeds increase gradually and monotonically. By tuning dipole lengths from 1-fold to 8-fold systems, we confirmed non-monotonic variation of the evaporation flux (first increases, then decreases) in 4 fold system with charges (0.1e-0.7e), reported in our previous paper [S. Wang, et al., J. Phys. Chem. B 116 (2012) 13863], and also show the process from the enhancement of this unexpected non-monotonic variation to its vanishment with surface dipole lengths increasing. Herein, we demonstrated two key factors to influence the evaporation flux of a tiny amount of water molecules adsorbed on solid surfaces: the exposed surficial area of water aggregation from where the water molecules can evaporate directly and the attraction potential from the substrate hindering the evaporation. In addition, more interestingly, we showed extra steric effect of surface dipoles on further increase of evaporation flux for 2-folds, 4-folds, 6-folds and 8-folds systems with charges around larger than 0.7e. (The steric effect is first reported by parts of our authors [C. Wang, et al., Sci. Rep. 2 (2012) 358]). This study presents a complete physical picture of the influence of surface dipole lengths on the evaporation behavior of the adsorbed tiny amount of water.
Wang, Shen; Tu, Yu-Song; Wan, Rong-Zheng; Fang, Hai-Ping
NSDL National Science Digital Library
This is a hands-on lab activity about evaporation. Learners will conduct experiments to observe the process of evaporation. They will then describe the process of evaporation, and the general water cycle, through discussion and pictures. Background information, common preconceptions, a glossary and more is included. This activity is part of the Aquarius Hands-on Laboratory Activities.
Measurement of water by oven evaporation using a novel oven design. 2. Water in motor oils and motor oil additives
The measurement of water in lubricating oils is important because water accelerates the corrosion of metal parts and bearings in motors. Some of the additives added to lubricating oils to improve their performance react with the Karl Fischer reagent (KFR) causing a positive bias in the water measurement. A new oven evaporation technique for measuring water in oils has been
Sam A. Margolis; Kevin Vaishnav; John R. Sieber
Measured and estimated evaporation and soil moisture deficit for growers and the water industry
NASA Astrophysics Data System (ADS)
Measurements and estimates of evaporation have been routinely carried out for over a century. In the United Kingdom the most well-known method of estimating evaporation and its derivatives such as soil moisture deficit (SMD) is the Meteorological Office Rainfall and Evaporation Calculation System (MORECS) which is based on the Penman-Monteith equation. Direct measurements of evaporation have become less common in recent years. A comparison of measurements and estimates of evaporation and SMD at a single site and over two catchment areas is presented in this paper. Measurements of actual evaporation from a grassed lysimeter have been achieved for the period 1995-98 and they agree well with catchment losses over the same time period in two natural catchments, the Upper Brue and Upper Cary. In contrast to this, MORECS estimates of actual evaporation are different by an average of +20% for the Upper Brue catchment and +27% for the Upper Cary catchment. The largest difference is nearly +40% for the Upper Cary catchment. Similarly, there are substantial differences in the estimates of SMD, often up to 50 mm. When local rainfall is used together with MORECS estimates of potential evaporation the discrepancy is reduced but significant differences remain during much of the growing season, although improvements do occur. The results from this paper will be of great importance to growers, water resource planners, engineers who give flood warnings, and to river flow modellers.
Clark, C.
Variation of Phreatic Evaporation of Bare Soil and Integration Application in Water Allocation in Shule Basin
NASA Astrophysics Data System (ADS)
Phreatic evaporation is a key element in regional water balance, but it is hardly measured directly. Recently the development of some new technologies brings new dawn to phreatic evaporation measurement, such as eddy covariance, remote sensing ET and so on. But the new technologies have no ability to connect to groundwater yet. Conventional groundwater balance equipment was set up in Shule basin in northwestern China, with located E97¯01', N45¯13' , altitude 1520m, annual average precipitation 61.8mm and annual evaporation 2600mm (pan 20cm). The experiment field contains 45 lysimeters (65cm diameter). 11 different water table depths are set in the lysimeters, which are 0.5m, 0.75m, 1.0m, 1.25m, 1.5m, 2.0m, 2.5m, 3.0m, 4.0m, 5.0m and 6.0m. The water table in the lysimeter is controlled by Marriott Bottle System. The evaporation and percolation is measured for three different soil types (silt sandy soil, loam soil and clay soil) in the 11 different water table depths. Based on the data from 2006 to 2010, the influences of atmosphere evaporation capacity, phreatic water depth and soil textures are analyzed. Empirical formulae for estimating phreatic evaporation are regressed. The fitting precision of the different formulae are evaluated. The results show that, fitting effect of common empirical formulae is good in Shule river basin. For the different soil types, fitting effect of silt soil is the best, while that of clay soil is relatively low. At last, formulae fitted in other areas and phreatic evaporation tests are summarized. The reasons of difference of fitted coefficients lie in three aspects: the range of depth of groundwater, choice of the value of water evaporation, method to optimize coefficients. Physical meaning of the coefficients in empirical formulae is analyzed. The features, fitting effect and notes in application of formulae are evaluated. The results are applied in water requirement calculation of ecological conservation Dunhuang Xihu Nature Reserve. Water sources, plant transpiration, and phreatic evaporation are simulated by the groundwater numerical model and the total ET of nature reserve is calculated. The supplementary water requirement is advanced. Key words: phreatic evaporation; empirical formulae; fitting precision; Shule river basin
Wang, Z.; Huang, P.; Gong, G.
Evaporative Evolution of Carbonate-Rich Brines from Synthetic Topopah Spring Tuff Pore Water, Yucca Mountain
The evaporation of a range of synthetic pore water solutions representative of the potential high-level-nuclear-waste repository at Yucca Mountain, NV is being investigated. The motivation of this work is to understand and predict the range of brine compositions that may contact the waste containers from evaporation of pore waters, because these brines could form corrosive thin films on the containers and impact their long-term integrity. A relatively complex synthetic Topopah Spring Tuff pore water was progressively concentrated by evaporation in a closed vessel, heated to 95 C in a series of sequential experiments. Periodic samples of the evaporating solution were taken to determine the evolving water chemistry. According to chemical divide theory at 25 C and 95 C our starting solution should evolve towards a high pH carbonate brine. Results at 95 C show that this solution evolves towards a complex brine that contains about 99 mol% Na{sup +} for the cations, and 71 mol% Cl{sup -}, 18 mol% {Sigma}CO{sub 2}(aq), 9 mol%SO{sub 4}{sup 2-} for the anions. Initial modeling of the evaporating solution indicates precipitation of aragonite, halite, silica, sulfate and fluoride phases. The experiments have been used to benchmark the use of the EQ3/6 geochemical code in predicting the evolution of carbonate-rich brines during evaporation.
Sutton, M; Alai, M; Carroll, S A
Charge separation by ice and water drops during growth and evaporation
NASA Astrophysics Data System (ADS)
Experiments reveal complicated charging behavior during evaporation and vapor growth of ice and water in air. In the laboratory environment, the ice specimen acquires a positive charge during growth and a negative charge during evaporation, except in the temperature region between -4¯C and 0¯C, where ice behaves like water, acquiring a negative charge during condensation growth. The current is in excess of 10-16 amps cm-2 s-1. The ion concentration in the air has a strong effect on the charging direction. The analysis shows that the charging direction is not simply the result of evaporation or growth as suggested in earlier work but is determined by the properties of the charge carriers in ice (or water) and in the air. The new hypothesis can explain the charging behavior of both the growth of ice and water from the vapor and also evaporation observed in the present experiments. This new hypothesis also gives interpretation of some discrepancies in the earlier studies. The mechanism does not require absolute growth or evaporation to operate, and it is possibly an important contributory factor in charge separation both in thunderstorms and weakly electrified clouds when long growth or evaporation times are available.
Dong, Yayi; Hallett, John
Effects of the water retention curve on evaporation from arid soils
NASA Astrophysics Data System (ADS)
Water retention curves approaching infinitely negative matric potentials at residual water content are widely employed to model soil moisture dynamics. When used in numerical simulations, these retention curves fail to satisfactorily describe evaporation from arid soil (moisture-limited regime) because they do not allow the soil to dry below residual water content. We show that simple modifications can be introduced to prevent unrealistic water retention at residual water content and predict more physically sound moisture dynamics. Modified retention models that allow drying below residual predict a moisture-limited regime characterized by a thin subsurface evaporation zone and produce vapor fluxes up to 3 times larger than classical retention models. This might reduce the need to introduce empirical enhancement factors and improve the capability of modeling evaporation into the atmosphere and runoff in arid regions.
Ciocca, Francesco; Lunati, Ivan; Parlange, Marc B.
Air Evaporation closed cycle water recovery technology - Advanced energy saving designs
NASA Technical Reports Server (NTRS)
The Air Evaporation water recovery system is a visible candidate for Space Station application. A four-man Air Evaporation open cycle system has been successfully demonstrated for waste water recovery in manned chamber tests. The design improvements described in this paper greatly enhance the system operation and energy efficiency of the air evaporation process. A state-of-the-art wick feed design which results in reduced logistics requirements is presented. In addition, several design concepts that incorporate regenerative features to minimize the energy input to the system are discussed. These include a recuperative heat exchanger, a heat pump for energy transfer to the air heater, and solar collectors for evaporative heat. The addition of the energy recovery devices will result in an energy reduction of more than 80 percent over the systems used in earlier manned chamber tests.
Morasko, Gwyndolyn; Putnam, David F.; Bagdigian, Robert
Evaporation of single atoms from an adsorbate island or a step to a terrace: Evaporation rate and the underlying atomic-level mechanism
NASA Astrophysics Data System (ADS)
We examine the kinetics of atom ``evaporation'' from an adsorbate island onto the surrounding single-crystal surface. In our model the atoms forming the island move on a square lattice with rate constants qualitatively consistent with the values found for metal-on-metal systems. At the temperatures of interest here the rates are such that only atoms having no neighbors along the island's edge can evaporate. The rate constant of this elementary evaporation step is denoted by ke. Our simulations show that an atom leaves an N-particle island at a time t with a probability proportional to exp[-kNt]. The rate constant kN is determined by simulations and has several very interesting properties. (1) It depends on temperature according to the Arrhenius formula, but with an activation energy that is substantially higher than that of ke. (2) The rate constants kN and ke are connected through kN/ke=
Shao, Hongxiao; Weakliem, Paul C.; Metiu, Horia
Recycling nickel electroplating rinse waters by low temperature evaporation and reverse osmosis
Low temperature evaporation and reverse osmosis systems were each evaluated (on a pilot scale) on their respective ability to process rinse water collected from a nickel electroplating operation. Each system offered advantages under specific operating conditions. The low temperature evaporation system was best suited to processing solutions with relatively high (greater than 4,000 to 5,000 mg\\/L) nickel concentrations. The reverse
T. C. Lindsey; P. M. Randall
Epiphyte Water Retention and Evaporation in Native and Invaded Tropical Montane Cloud Forests in Hawaii
NASA Astrophysics Data System (ADS)
Epiphyte water retention was quantified at two montane cloud forest sites in Hawai'i Volcanoes National Park, one native and the other invaded by an alien tree species. Water storage elements measured included all epiphytic mosses, leafy liverworts, and filmy ferns. Tree surface area was estimated and a careful survey was taken to account for all epiphytes in the sample area of the forest. Samples were collected and analyzed in the lab for epiphyte water retention capacity (WRC). Based on the volume of the different kinds of epiphytes and their corresponding WRC, forest stand water retention capacity for each survey area was estimated. Evaporation from the epiphyte mass was quantified using artificial reference samples attached to trees that were weighed at intervals to determine changes in stored water on days without significant rain or fog. In addition, a soil moisture sensor was wrapped in an epiphyte sample and left in the forest for a 6-day period. Epiphyte biomass at the Native Site and Invaded Site were estimated to be 2.89 t ha-1 and 1.05 t ha-1, respectively. Average WRC at the Native Site and Invaded Site were estimated at 1.45 mm and 0.68 mm, respectively. The difference is likely due to the presence of the invasive Psidium cattleianum at the Invaded Site because its smooth stem surface is unable to support a significant epiphytic layer. The evaporation rate from the epiphyte mass near WSC for the forest stand at the Native Site was measured at 0.38 mm day-1, which represented 10.6 % of the total ET from the forest canopy at the Native Site during the period. The above research has been recently complemented by a thorough investigation of the WSC of all water storage elements (tree stems, tree leaves, shrubs, grasses, litter, fallen branches, and epiphytes) at six forested sites at different elevations within, above, and below the zone of frequent cloud-cover. The goal of this study was to create an inexpensive and efficient methodology for acquiring estimates of above-ground water retention in different types of forests by means of minimally-destructive sampling and surveying. The results of this work serve as baseline data providing a range of possible values of the water retention of specific forest elements and the entire above-ground total where no values have been previously recorded.
Mudd, R. G.; Giambelluca, T. W.
Evaporation of J13 and UZ pore waters at Yucca Mountain
This work is motivated by a need to characterize the chemistry of aqueous films that might form at elevated temperatures on engineered components at the potential high-level, nuclear-waste repository at Yucca Mountain, Nevada. Such aqueous films might form through evaporation of water that seeps into the drifts, or by water vapor absorption by hydroscopic salts directly deposited on these components (possibly from previous evaporation events or possibly from air-blown particles drawn into the drifts through a drift ventilation system). There is no consensus at this time on the chemical composition of water that might come in contact with engineered components at Yucca Mountain. Two possibilities have received the most attention: well J13 water and pore waters from the unsaturated zone (UZ) above the repository horizon. These waters represent the two major types of natural waters at Yucca Mountain. Well J13 water is a dilute Na-HCO{sub 3}-CO{sub 3} water, representative of regional perched water and groundwater. The UZ pore waters are Ca-Cl-SO{sub 4}-rich waters with a higher dissolved ion content. These waters are less well-characterized. We have studied the evaporative evolution of these two major types of waters through a series of open system laboratory experiments, with and without crushed repository-horizon tuff present, conducted at sub-boiling temperatures (75 C-85 C).
Rosenberg, N D; Gdowski, G E; Knauss, K G
Rates of Water Loss and Estimates of Survival Time under Varying Humidity in Juvenile Snapping Turtles ( Chelydra serpentina )
Juvenile snapping turtles may be highly susceptible to dehydration during over- land movement because of their aquatic nature and large surface area to volume ratio. The present study examined the influence of body size and relative humidity on rates of evaporative water loss and estimates of survival time. Larger hatchlings had higher rates of evaporative water loss but longer survival
Michael S. Finkler
Importance of Rain Evaporation and Continental Convection in the Tropical Water Cycle
NASA Technical Reports Server (NTRS)
Atmospheric moisture cycling is an important aspect of the Earth's climate system, yet the processes determining atmospheric humidity are poorly understood. For example, direct evaporation of rain contributes significantly to the heat and moisture budgets of clouds, but few observations of these processes are available. Similarly, the relative contributions to atmospheric moisture over land from local evaporation and humidity from oceanic sources are uncertain. Lighter isotopes of water vapour preferentially evaporate whereas heavier isotopes preferentially condense and the isotopic composition of ocean water is known. Here we use this information combined with global measurements of the isotopic composition of tropospheric water vapour from the Tropospheric Emission Spectrometer (TES) aboard the Aura spacecraft, to investigate aspects of the atmospheric hydrological cycle that are not well constrained by observations of precipitation or atmospheric vapour content. Our measurements of the isotopic composition of water vapour near tropical clouds suggest that rainfall evaporation contributes significantly to lower troposphere humidity, with typically 20% and up to 50% of rainfall evaporating near convective clouds. Over the tropical continents the isotopic signature of tropospheric water vapour differs significantly from that of precipitation, suggesting that convection of vapour from both oceanic sources and evapotranspiration are the dominant moisture sources. Our measurements allow an assessment of the intensity of the present hydrological cycle and will help identify any future changes as they occur.
Worden, John; Noone, David; Bowman, Kevin; Beer, R.; Eldering, A.; Fisher, B.; Gunson, M.; Goldman, Aaron; Kulawik, S. S.; Lampel, Michael; Osterman, Gregory; Rinsland, Curtis P.; Rogders, Clive; Sander, Stanley; Shepard, Mark; Webster, Christopher R.; Worden, H. M.
Using water stable isotopes to assess evaporation and water residence time of lakes in EPAs National Lakes Assessment.
Stable isotopes of water (?18O and ?2H) can be very useful in large-scale monitoring programs because water samples are easy to collect and water isotopes integrate information about basic hydrological processes such as evaporation as a percentage of inflow (E/I), w...
Dynamics of Water Absorption and Evaporation During Methanol Droplet Combustion in Microgravity.
National Technical Information Service (NTIS)
The combustion of methanol droplets is profoundly influenced by the absorption and evaporation of water, generated in the gas phase as a part of the combustion products. Initially there is a water-absorption period of combustion during which the latent he...
D. L. Dietrich F. A. Williams M. C. Hicks V. Nayagam
Evaporation of J13 and UZ pore waters at Yucca Mountain
This work is motivated by a need to characterize the chemistry of aqueous films that might form at elevated temperatures on engineered components at the potential high-level, nuclear-waste repository at Yucca Mountain, Nevada. Such aqueous films might form through evaporation of water that seeps into the drifts, or by water vapor absorption by hydroscopic salts directly deposited on these components
N D Rosenberg; G E Gdowski; K G Knauss
Contribution of evaporating water to precipitation and atmospheric residence times distribution: An evaporation tagging study for the Poyang Lake Region in Southeast China
NASA Astrophysics Data System (ADS)
Land - atmosphere interaction analysis still lacks adequate methods for explicitly answering the central question of "where and when precipitated water has originally evaporated", and likewise, where, when, and to which extent evaporating water of one region returns as precipitation in the same or another region, and what are water residence times across the atmosphere. Here, a process based evaporation tagging (ET-Tagging) approach combined with residence time information has been implemented into a regional climate model. It allows to tag the moisture evaporating from a certain region into the atmosphere, and to track it till returning to the land surface as tagged precipitation. The model also calculates the spatial distribution of the residence times, defined as lifetime between original evaporation till returning to the surface as precipitation. Our case study investigates, where, when, and to which extent the evapotranspirating water of the Poyang Lake region (about 28,000 km2), i.e. the largest freshwater lake in China, returns back to the land surface as precipitation. The simulation reveals that the location and magnitude of tagged precipitation show large spatial and temporal variations controlled by synoptic weather conditions. On monthly scale, maximum precipitation recycling ratio is in August and in an amount of up to 6% near the Poyang Lake Region. To investigate the impact of different land use types on total tagged precipitation, Evapotranspiration was splitted into evaporation and transpiration. The results show that in 2005, 68% of total tagged precipitation is contributed by evaporated water, and 32% by transpirated water. In January, evaporation contributes to a maximum of 95% of total tagged precipitation. With temperature increasing and vegetation growing, transpiration increases and accounts for around 50% in June and August.
Wei, Jianhui; Knoche, Hans Richard; Kunstmann, Harald
Evaporation from porous media in the presence of a water table
NASA Astrophysics Data System (ADS)
Improved understanding of soil evaporation in presence of a water table is important in many hydrological processes such as analysis of water and energy balance at land surface, and soil salinization. During evaporation, liquid water is transported from water table toward the surface by capillary forces opposed by the downward gravity and viscous forces. In presence of a shallow water table, the capillary forces may be strong enough to maintain liquid continuity extending from water table to the surface where the liquid vaporization occurs. However, when the water table depth is deep, capillary forces may not be able to overcome the resistive forces resulting in interruption of the liquid continuity. In such cases, using hydraulic conductivity and Richards equation across the entire soil profile to estimate the evaporative flux causes overlooking the physical mechanisms governing the process, though good agreements might be obtained by applying some fitting parameters in unsaturated hydraulic conductivity to match the prediction with the experimental data. The main objective of the present study is to enhance the awareness of limitation of rather automatic assumption of hydraulic continuity through unsaturated zone across large distances above the water table. We used the concept of evaporation characteristic lengths to predict the maximum height of liquid continuity above the water table. When the depth of water table exceeds this characteristic length deduced from the pore size distribution, the hydraulic connection with surface is interrupted resulting in considerable suppression of evaporation due to the evolution of vaporization plane from the surface to a level below the surface defined by the maximum height of the liquid continuity above the water table. To test this model, laboratory evaporation experiments were conducted using Plexiglas columns (600 mm in height and 70 mm in diameter) packed with sand initially saturated with water exposed to evaporation from top boundary. For water supply, Mariotte bottles mounted on digital balances were connected to the bottom of the columns. We used three types of sand differing in particle size distribution. To maintain constant levels of water table, Mariotte bottles were fixed at different depths below the sand surface. The mass loss from the columns and relative humidity and temperature above the columns were recorded digitally each five minutes for nearly 500 hours. Our results confirmed the critical role of liquid continuity above the water table on the evaporative water losses from porous media. The predicted maximum water table depths marking the transition from atmospheric-limited fluxes to the much lower fluxes limited by the transport properties of the porous medium were in good agreement with the experimental results. In addition to the detailed analysis of the relation between water table depths and evaporative water losses, our results provide new insights regarding solute transports and deposition patterns affected by the depth of water table during evaporation.
Shokri, N.; Salvucci, G.
Partitioning of evaporative water loss in white-winged doves: plasticity in response to short-term thermal acclimation
We investigated changes in the relative contributions of respiratory evaporative water loss (REWL) and cutaneous evaporative water loss (CEWL) to total evaporative water loss (TEWL) in response to short-term thermal acclimation in western white-winged doves Zenaida asiatica mearnsii. We measured REWL, CEWL, oxygen consumption and carbon dioxide production in a partitioned chamber using flow-through respirometry. In doves housed for 2-4
Andrew E. McKechnie; Blair O. Wolf
Tracing Water Sources and Quantifying Evaporation in the Brazos River, Central Texas
NASA Astrophysics Data System (ADS)
Situated in the subtropical dry zone, Central Texas is sensitive to the effects of climate change, notably drought; furthermore, developments over the last century in agriculture, urban infrastructure, and river engineering have altered the landscape extensively. This study models water source mixing and seasonal variation in evaporation in Brazos River waters in Central Texas. The Brazos River from Waco to College Station, Texas is generally characterized as having dissolved salt load derived mostly from Lake Whitney (a flood-control and hydroelectric storage reservoir) and groundwater baseflow from the adjacent shallow alluvial aquifer. Brazos River water ?18O, ?D, and conductivity were measured bi-weekly in Brazos County, Texas from January 2012 through August 2013. Conductivity, ?18O, and ?D vary seasonally and are positively correlated. The Brazos River ?18O-?D data from Brazos County fall along a local evaporation line (?D = 5.66 * ?18O - 2.47, r2 = 0.95) that intersects and surpasses values for Lake Whitney. In contrast, the ?18O-conductivity trend for the Brazos River does not intersect data for Lake Whitney. These observations suggest mixing with an evaporated water source of lower conductivity. The relative contribution of other Brazos River water sources is uncertain. Percent evaporation of original rain sampled as Brazos River water was estimated using a Rayleigh distillation model and the method of Gonfiantini (1986) while assuming 1) a closed system with an atmospheric exchange component, and 2) ?18O and ?D values of local rain are -5.33 and -32.6, respectively. Modeled percent evaporation of original rain varies from winter (JFM; 1%-20%) to spring (AMJ; 9-25%) to summer (JAS; 16-33%), to fall (OND; 15-24%). Rayleigh distillation modeling estimates are consistently higher (~5%) than those estimated by Gonfiantini's method. A simple mass-balance model predicts that Brazos River water percent evaporation and ?18O enrichment are 2.8% and 0.40 respectively for low flow in Brazos County (200 cubic feet per second or cfs) and 0.9% and 0.12 respectively for high flow (1000 cfs). This implies that a small percentage of evaporation of original rain in the Brazos River could be attributed to the alluvial aquifer. Thus, we believe that the alluvial aquifer is not dominating the Brazos River water supply as much as previously thought, even in times of low flow. Other surface waters more evaporatively enriched in 18O, specifically those derived from the network of local reservoirs and tributaries, likely influence the Brazos River more than previously thought.
VanPlantinga, A.; Hunt, L. E.; Winning, D.; Robertson, J.; Stockert, E.; Roark, E.; Grossman, E. L.
Reduced Volume Prototype Spacesuit Water Membrane Evaporator; A Next-Generation Evaporative Cooling System for the Advanced Extravehicular Mobility Unit Portable Life Support System
NASA Technical Reports Server (NTRS)
Development of the Advanced Extravehicular Mobility Unit (AEMU) portable life support subsystem (PLSS) is currently under way at NASA Johnson Space Center. The AEMU PLSS features a new evaporative cooling system, the reduced volume prototype (RVP) spacesuit water membrane evaporator (SWME). The RVP SWME is the third generation of hollow fiber SWME hardware. Like its predecessors, RVP SWME provides nominal crew member and electronics cooling by flowing water through porous hollow fibers. Water vapor escapes through the hollow fiber pores, thereby cooling the liquid water that remains inside of the fibers. This cooled water is then recirculated to remove heat from the crew member and PLSS electronics. Major design improvements, including a 36% reduction in volume, reduced weight, and a more flight-like backpressure valve, facilitate the packaging of RVP SWME in the AEMU PLSS envelope. The development of these evaporative cooling systems will contribute to a more robust and comprehensive AEMU PLSS.
Makinen, Janice V.; Anchondo, Ian; Bue, Grant C.; Campbell, Colin; Colunga, Aaron
Experimental study of evaporation of sessile water droplet on PDMS surfaces
NASA Astrophysics Data System (ADS)
Evaporation of sessile water droplet on polydimethylsiloxane (PDMS) surfaces with three different curing ratios (5: 1, 10: 1, and 20: 1) was experimentally investigated in this paper. We show that the constant contact radius (CCR) evaporation on surface with high curing ratio lasts longer than that with low curing ratio. We also measured Young's moduli of PDMS films by using atomic force microscopy (AFM) and simulated surface deformation of PDMS films induced by sessile water droplet. With increasing curing ratio of PDMS film, Young's modulus of PDMS film is getting lower, and then there will be larger surface deformation and more elastic stored energy. Since such energy acts as a barrier to keep the three-phase contact line pinned, thus it will result in longer CCR evaporation on PDMS surface with higher curing ratio.
Yu, Ying-Song; Wang, Zi-Qian; Zhao, Ya-Pu
``Boiling'' in the water evaporating meniscus induced by Marangoni flow
NASA Astrophysics Data System (ADS)
A counterintuitive phenomenon, ``boiling,'' was directly observed near the contact line of the pure water meniscus formed in a ball and disk configuration, when the ball temperature was far lower than the saturation temperature of water. The number of the emerging bubbles due to ``boiling'' increased with ball temperature rising; each bubble would expanse initially and then collapse. When two surfaces were heated to the same temperature, ``boiling'' disappeared. It was proposed that the temperature gradient between the two surfaces initiated Marangoni flow, which hindered flow toward the film, resulting in the negative pressure and cavitation in the liquid film.
Liu, Xiang; Guo, Dan; Xie, Guoxin; Liu, Shuhai; Luo, Jianbin
Urban Signatures: Evaporation (WMS)
NSDL National Science Digital Library
Big cities influence the environment around them. For example, urban areas are typically warmer than their surroundings. Cities are strikingly visible in computer models that simulate the Earths land surface. This visualization shows evaporation rates predicted by the Land Information System (LIS) for a day in June 2001. Evaporation is lower in the cities because water tends to run off pavement and into drains, rather than being absorbed by soil and plants from which it later evaporates. Only part of the global computation is shown, focusing on the highly urbanized northeast corridor in the United States, including the cities of Boston, New York, Philadelphia, Baltimore, and Washington.
Delabeaujardiere, Jeff
Evaporation of a Water Droplet Deposited on a Hot High Thermal Conductivity Solid Surface.
National Technical Information Service (NTIS)
A model is presented that predicts major features of the evaporation of water droplets deposited on a hot non-porous solid surface. In the temperature range of interest, nucleate boiling heat transfer is fully suppressed, hence the model is only concerned...
M. di Marzo D. D. Evans
Effects of ozone on evaporative water loss and thermoregulatory behavior of marine toads (Bufo marinus).
Ozone (O(3)) is a strong pulmonary irritant and causes a suite of respiratory tract inflammatory responses in humans and other mammals. In addition to lung injury, rodents exposed to O(3) exhibit a pronounced decrease in core body temperature at rest, which may offer a protective effect against O(3) damage. The effects of O(3) on other vertebrates have not been studied. Compared to individuals exposed to air (N=34), Bufo marinus toads exposed to O(3) (N=32) for 4 h lost 3.78 g body mass (adjusted mean from analysis of covariance, body mass mean+/-SD, 90.1+/-21.90 g). We tested the thermoregulatory responses of 22 toads in a thermal gradient 1, 24, and 48 h after 4-h exposure to air (N=11) or 0.8 ppm O(3) (N=11). Individual toad thermal preferences were also significantly repeatable across all trials (intraclass correlation=0.66, P <0.001). We did not observe a direct effect of O(3) exposure on the preferred body temperatures (PBT) of toads. However, O(3) exposure did have an indirect effect on selected temperatures. Ozone-exposed toads with higher evaporative water loss rates, in turn, also selected lower PBT, voluntary minimum, and voluntary maximum temperatures 24 h post-exposure. Ozone exposure may thus alter both water balance and thermal preferences in anuran amphibians. PMID:11453678
Dohm, M R; Mautz, W J; Looby, P G; Gellert, K S; Andrade, J A
Measuring forest evaporation and transpiration rates with fibre optic temperature sensing
NASA Astrophysics Data System (ADS)
Evaporation is one of the most important fluxes of the water balance as it accounts for 55-80% of the precipitation. However, measuring evaporation remains difficult and requires sophisticated and expensive equipment. In this paper we propose a new measuring technique based on the existing Bowen ratio method. With a fibre optic cable a temperature and a vapour pressure profile can be measured by the principle of a psychrometer and combined with the net radiation (and ground heat flux) the latent heat can be calculated. Compared to the conventional Bowen ratio method the advantages of this method is that the profiles are measured with a single sensor (resulting in a smaller error), and contain more measuring points in the vertical and therefore give more insight into the developed profiles. The method also allows to measure through a forest canopy. Applying the Bowen ratio above and below the canopy an estimation of the transpiration flux can be obtained. As a first test, we compared in a pine forest in The Netherlands (Loobos) the transpiration estimates of the fibre optic cable with sapflow measurements, and eddy covariance measurements above and below the canopy. The experiment was carried out on three days in September 2013 and the preliminary results show reasonable correlation with the eddy covariance estimates, but not with the sapflow observations. To explain the differences further investigation is needed and a longer measuring period is required.
Coenders-Gerrits, Miriam; Luxemburg, Wim; Hessels, Tim; de Kloe, Arjan; Elbers, Jan
Some Experiments on Evaporation of High-TDS Phreatic Water in an Arid Area
NASA Astrophysics Data System (ADS)
Most experiments that had been done on evaporation of phreatic water were limited to waters with fresh or low total dissolved solids (TDS, no more than 10g/L). The TDS of phreatic water is always dozens or even hundreds of grams per liter in extremely arid areas. Thus, experiments on phreatic water evaporation of different TDS (3g/L, 30g/L, 100g/L, 250g/L) were carried out in an arid plain of south Xinjiang, China. The results showed that there was significant linear positive correlation between TDS of phreatic water and cumulative salinity in soil profile. The variation of phreatic water evaporation was lag behind the change of surface water measured by E20 equipment, but both of them were more drastic at nighttime than the daytime. The research shows that the daytime evaporation capacity has significant effect on nighttime evaporation, and the soil water vapor condense at profile also is an important driving factor for the nighttime evaporation. Capillary rise is a significant contributor of soil salinity in extremely arid areas. Experiments about effects of different grains of sand soil and TDS of phreatic water (1, 30, 100, 250 g/L) on capillary rise showed that TDS had significant effects on capillary rise in later stage of experiments. For coarse sand, the higher TDS made the lower height of capillary rise. But for fine sand, the height of capillary rise of 1g/L was obviously larger than others. The sequence of height from larger to lower of capillary rise in silt was 30, 100, 250 and 1g/L. At the beginning of experiments on coarse sand, the higher TDS made the lower velocity of capillary rise, but other soil groups were not. Compared to high-TDS, the grain of sand soil was a more primary controlling factor of capillary rise. The research indicates that high-TDS not only changes the gravity of capillary water but also the pore size of soil during the processes of capillary rise in fine sand.
Li, X.; Jin, M.; Zhou, J.; Liu, Y.; Zhao, Y.
Insight into the molecular mechanism of water evaporation via the finite temperature string method
NASA Astrophysics Data System (ADS)
The process of water's evaporation at its liquid/air interface has proven challenging to study experimentally and, because it constitutes a rare event on molecular time scales, presents a challenge for computer simulations as well. In this work, we simulated water's evaporation using the classical extended simple point charge model water model, and identified a minimum free energy path for this process in terms of 10 descriptive order parameters. The measured free energy change was 7.4 kcal/mol at 298 K, in reasonable agreement with the experimental value of 6.3 kcal/mol, and the mean first-passage time was 1375 ns for a single molecule, corresponding to an evaporation coefficient of 0.25. In the observed minimum free energy process, the water molecule diffuses to the surface, and tends to rotate so that its dipole and one O-H bond are oriented outward as it crosses the Gibbs dividing surface. As the water molecule moves further outward through the interfacial region, its local density is higher than the time-averaged density, indicating a local solvation shell that protrudes from the interface. The water molecule loses donor and acceptor hydrogen bonds, and then, with its dipole nearly normal to the interface, stops donating its remaining hydrogen bond. At that point, when the final, accepted hydrogen bond is broken, the water molecule is free. We also analyzed which order parameters are most important in the process and in reactive trajectories, and found that the relative orientation of water molecules near the evaporating molecule, and the number of accepted hydrogen bonds, were important variables in reactive trajectories and in kinetic descriptions of the process.
Musolino, Nicholas; Trout, Bernhardt L.
Isotope effects in the evaporation of water: a status report of the CraigGordon model
The CraigGordon model (CG model) [H. Craig, L.I. Gordon. Deuterium and oxygen 18 variations in the ocean and the marine atmosphere. In Stable Isotopes in Oceanographic Studies and Paleotemperatures, E. Tongiorgi (Ed.), pp. 9130, Laboratorio di Geologia Nucleare, Pisa (1965).] has been synonymous with the isotope effects associated with the evaporation of water from surface waters, soils, and vegetations, which
Juske Horita; Kazimierz Rozanski; Shabtai Cohen
Insight into the molecular mechanism of water evaporation via the finite temperature string method
The process of water's evaporation at its liquid/air interface has proven challenging to study experimentally and, because it constitutes a rare event on molecular time scales, presents a challenge for computer simulations as well. In this work, we simulated water's evaporation using the classical extended simple point charge model water model, and identified a minimum free energy path for this process in terms of 10 descriptive order parameters. The measured free energy change was 7.4 kcal/mol at 298 K, in reasonable agreement with the experimental value of 6.3 kcal/mol, and the mean first-passage time was 1375 ns for a single molecule, corresponding to an evaporation coefficient of 0.25. In the observed minimum free energy process, the water molecule diffuses to the surface, and tends to rotate so that its dipole and one OH bond are oriented outward as it crosses the Gibbs dividing surface. As the water molecule moves further outward through the interfacial region, its local density is higher than the time-averaged density, indicating a local solvation shell that protrudes from the interface. The water molecule loses donor and acceptor hydrogen bonds, and then, with its dipole nearly normal to the interface, stops donating its remaining hydrogen bond. At that point, when the final, accepted hydrogen bond is broken, the water molecule is free. We also analyzed which order parameters are most important in the process and in reactive trajectories, and found that the relative orientation of water molecules near the evaporating molecule, and the number of accepted hydrogen bonds, were important variables in reactive trajectories and in kinetic descriptions of the process.
Musolino, Nicholas; Trout, Bernhardt L.
The hydrogen and oxygen isotopic composition of precipitation, evaporated mine water, and river water in Montana, USA
NASA Astrophysics Data System (ADS)
SummaryThe isotopic composition of 42 samples of rain and snow collected in 2004 were used to construct a local meteoric water line (LMWL) for Butte, Montana. The derived equation (?D = 7.31? 18O - 7.5, r2 = 0.987), represents one of the first published LMWLs based on direct precipitation for any location in the northern Rocky Mountains. Samples of underground and surface mine waters in Butte, including the Berkeley pit-lake and a nearby tailings pond, define a linear trend with a much lower slope and intercept than the LMWL (?D = 5.00? 18O - 49.5, r2 = 0.991), consistent with non-equilibrium evaporation at an average relative humidity of roughly 65%. Detailed evaporation calculations are presented which indicate that the shallow Berkeley pit-lake was approximately 25% evaporated in October, 2003, whereas the surface of the tailings pond was at least 50% evaporated. The intersection of the LMWL and mine water evaporation trend was used to calculate the average composition of recharge water to the flooded mine complex (?D = -139, ? 18O = -18.0). These values are considerably lighter than the weighted total of precipitation for the 2004 calendar year (?D = -118, ? 18O = -15.3), which is partly explained by the unusually low snowfall that Montana experienced in 2004. Based on this study, the LMWL recently proposed by Kendall and Coplen (2001) [Kendall, C., Coplen, T.B., 2001. Distribution of oxygen-18 and deuterium in river waters across the United States, Hydrological Processes 15, 1363-1393] from regression of isotopic data from a number of Montana rivers is more accurately interpreted as an evaporation line. Isotopic trends based on river data should be treated with caution, particularly in a semi-arid region such as Montana where rivers are often influenced by dams and irrigation withdrawals.
Gammons, Christopher H.; Poulson, Simon R.; Pellicori, Damon A.; Reed, Pamela J.; Roesler, Amber J.; Petrescu, Eugene M.
Evaporation and wetting dynamics of sessile water droplets on submicron-scale patterned silicon hydrophobic surfaces
The evaporation characteristics of 1 l sessile water droplets on hydrophobic surfaces are experimentally examined. The proposed hydrophobic surfaces are composed of submicron diameter and 4.2- m-height silicon post arrays. A digital image analysis algorithm was developed to obtain time-dependent contact angles, contact diameters, and center heights for both non-patterned polydimethylsiloxane (PDMS) surfaces and patterned post array surfaces, which have the same hydrophobic contact angles. While the contact angles exhibit three distinct stages during evaporation in the non-patterned surface case, those in the patterned silicon post array surface case decrease linearly. In the case of post array hydrophobic surfaces, the initial contact diameter remains unchanged until the portion of the droplet above the posts completely dries out. The edge shrinking velocity of the droplet shows nonlinear characteristics, and the velocity magnitude increases rapidly near the last stage of evaporation.
Choi, Chang Kyoung [Michigan Technological University; Shin, Dong Hwan [Chung-Ang University; Lee, Seong Hyuk [Chung-Ang University; Retterer, Scott T [ORNL
Water droplet evaporation in air during compression in a gas turbine engine. Technical memo
A water fog concept is being considered for evaporative cooling of the air as it is compressed in a ship gas turbine engine. The following analysis is presented to clarify the physics associated with liquid droplet evaporation in this situation, to understand the conditions affecting the cooling, and to identify any further information required to achieve such a concept. The vaporization of small liquid drops in a warm ideal gas is controlled by the outward motion of the vapor and the inward flow of heat to cause evaporation. Following the standard analysis of Spalding, as given in `Principles of Combustion` by Kuo, it is assumed that the process is `quasi steady.` This means that the conditions far removed from the drop are constant, and that there are no time varying terms in the Eulerian description of the mass and energy flows.
Quandt, E.
A phylogenetic analysis of basal metabolism, total evaporative water loss, and life-history among foxes from desert and mesic regions
We measured basal metabolic rate (BMR) and total evaporative water loss (TEWL) of species of foxes that exist on the Arabian Peninsula, Blanfords fox ( Vulpes cana) and two subspecies of Red fox ( Vulpes vulpes). Combining these data with that on other canids from the literature, we searched for specialization of physiological traits among desert foxes using both conventional
J. B. Williams; A. Muþoz-Garcia; S. Ostrowski; B. I. Tieleman
Effects of ambient water vapor pressure and temperature on evaporative water loss in Peromyscus maniculatus and Mus musculus
Summary The effects of ambient water vapor pressure (VP) and temperature on evaporative water loss (EWL) from the head and trunk ofPeromyscus maniculatus andMus musculus were measured with dew point hygrometry. At a given ambient temperature both head and trunk EWL were directly proportional to the water vapor pressure deficit. Cutaneous EWL in both species was directly related to the difference
Richard M. Edwards; Howard Haines
Floating brine crusts, reduction of evaporation and possible replacement of fresh water to control dust from Owens Lake bed, California
NASA Astrophysics Data System (ADS)
SummaryOwens Lake, California, a saline terminal lake desiccated after diversion of its water source, was formerly the single largest anthropogenic source of fugitive dust in North America. Over 100 billion m -3 yr -1 of fresh water are projected to be used for mandated dust control in over 100 km 2 of constructed basins required to be wetted to curtail emissions. An extensive evaporite deposit is located at the lake's topographic low and adjacent to the dust control basins. Because this deposit is non-dust-emissive, it was investigated as a potential replacement for the fresh water used in dust control. The deposit consists of precipitated layers of sodium carbonate and sulfate bathed by, and covered with brine dominated by sodium chloride perennially covered with floating salt crust. Evaporation ( E) rates through this crust were measured using a static chamber during the period of highest evaporative demand, late June and early July, 2009. Annualized total E from these measurements was significantly below average annual precipitation, thus ensuring that such salt deposits naturally remain wet throughout the year, despite the arid climate. Because it remains wetted, the evaporite deposit may therefore have the potential to replace fresh water to achieve dust control at near zero water use.
Groeneveld, D. P.; Huntington, J. L.; Barz, D. D.
Effects of crop residue on soil and plant water evaporation in a dryland cotton system
NASA Astrophysics Data System (ADS)
Dryland agricultural cropping systems emphasize sustaining crop yields with limited use of fertilizer while conserving both rain water and the soil. Conservation of these resources may be achieved with management systems that retain residues at the soil surface simultaneously modifying both its energy and water balance. A conservation practice used with cotton grown on erodible soils of the Texas High Plains is to plant cotton into chemically terminated wheat residues. In this study, the partitioning of daily and seasonal evapotranspiration ( E t) into soil and plant water evaporation was compared for a conventional and a terminated-wheat cotton crop using the numerical model ENWATBAL. The model was configured to account for the effects of residue on the radiative fluxes and by introducing an additional resistance to latent and sensible heat fluxes derived from measurements of wind speed and vapor conductance from a soil covered with wheat-stubble. Our results showed that seasonal E t was similar in both systems and that cumulative soil water evaporation was 50% of E t in conventional cotton and 31% of E t in the wheat-stubble cotton. Calculated values of E t were in agreement with measured values. The main benefit of the wheat residues was to suppress soil water evaporation by intercepting irradiance early in the growing season when the crop leaf area index (LAI) was low. In semiarid regions LAI of dryland cotton seldom exceeds 2 and residues can improve water conservation. Measured soil temperatures showed that early in the season residues reduced temperature at 0.1 m depth by as much as 5¯C and that differences between systems diminished with depth and over time. Residues increased lint yield per unit of E t while not modifying seasonal E t and reducing cumulative soil water evaporation.
Lascano, R. J.; Baumhardt, R. L.
Temperature dependence of the evaporation coefficient of water in air and nitrogen under atmospheric pressure: study in water droplets.
The evaporation coefficients of water in air and nitrogen were found as a function of temperature by studying the evaporation of a pure water droplet. The droplet was levitated in an electrodynamic trap placed in a climatic chamber maintaining atmospheric pressure. Droplet radius evolution and evaporation dynamics were studied with high precision by analyzing the angle-resolved light scattering Mie interference patterns. A model of quasi-stationary droplet evolution accounting for the kinetic effects near the droplet surface was applied. In particular, the effect of thermal effusion (a short-range analogue of thermal diffusion) was discussed and accounted for. The evaporation coefficient alpha in air and in nitrogen were found to be equal. The alpha was found to decrease from approximately 0.18 to approximately 0.13 for the temperature range from 273.1 to 293.1 K and follow the trend given by the Arrhenius formula. The agreement with condensation coefficient values obtained with an essentially different method by Li et al. [Li, Y.; Davidovits, P.; Shi, Q.; Jayne, J.; Kolb, C.; Worsnop, D. J. Phys. Chem. A. 2001, 105, 10627] was found to be excellent. The comparison of experimental conditions used in both methods revealed no dependence of the evaporation/condensation coefficient on the droplet charge nor the ambient gas pressure within the experimental parameters range. The average value of the thermal accommodation coefficient over the same temperature range was found to be 1 +/- 0.05. PMID:18491849
Zientara, M; Jakubczyk, D; Kolwas, K; Kolwas, M
Adaptation of metabolism and evaporative water loss along an aridity gradient.
Broad-scale comparisons of birds indicate the possibility of adaptive modification of basal metabolic rate (BMR) and total evaporative water loss (TEWL) in species from desert environments, but these might be confounded by phylogeny or phenotypic plasticity. This study relates variation in avian BMR and TEWL to a continuously varying measure of environment, aridity. We test the hypotheses that BMR and TEWL are reduced along an aridity gradient within the lark family (Alaudidae), and investigate the role of phylogenetic inertia. For 12 species of lark, BMR and TEWL decreased along a gradient of increasing aridity, a finding consistent with our proposals. We constructed a phylogeny for 22 species of lark based on sequences of two mitochondrial genes, and investigated whether phylogenetic affinity played a part in the correlation of phenotype and environment. A test for serial independence of the data for mass-corrected TEWL and aridity showed no influence of phylogeny on our findings. However, we did discover a significant phylogenetic effect in mass-corrected data for BMR, a result attributable to common phylogenetic history or to common ecological factors. A test of the relationship between BMR and aridity using phylogenetic independent constrasts was consistent with our previous analysis: BMR decreased with increasing aridity.
Tieleman, B Irene; Williams, Joseph B; Bloomer, Paulette
Characterization of the LGFSTF wind tunnel in preparation for the DOE/EPA hazardous chemical evaporation rate experiments
The Environmental Protection Agency and the Department of Energy are conducting chemical evaporation rate experiments in the DOE`s Liquefied Gaseous Fuels Spill Test Facility (LGFSTF) wind tunnel to determine the effect on evaporation rate of pool temperature and wind speed. Evaporation rates measured in these tests will be used to verify mathematical models used to define the source (gas) rate inputs to dispersion models. In preparation for the experiments the LGFSTF tunnel has been modified to provide for the simulation of an atmospheric boundary layer flow on the tunnel floor. This report describes work performed by the DOE Modeling Support Center at the University of Arkansas to define (characterize) the turbulence properties in the boundary layer of the (modified) wind tunnel test section. Hot wire anemometry measurements were made to characterize the boundary layer flow over the evaporation test pan. Mean velocity and turbulence statistics were measured along a verticle line (extending from 0.5 cm to 60 cm above the tunnel floor) located on the tunnel centerline immediately upwind of the evaporation pan. The x-direction mean velocity data were analyzed to estimate the applicable values of the surface roughness and friction velocity for four tunnel (variable frequency controller) speed settings: 15 Hz, 30 Hz, 45 Hz, and 60 Hz.
Havens, J.; Walker, H.; Spicer, T.
Sensitivity of Hollow Fiber Spacesuit Water Membrane Evaporator Systems to Potable Water Constituents, Contaminants and Air Bubbles
NASA Technical Reports Server (NTRS)
The Spacesuit Water Membrane Evaporator (SWME) is the baseline heat rejection technology selected for development for the Constellation lunar suit. The first SWME prototype, designed, built, and tested at Johnson Space Center in 1999 used a Teflon hydrophobic porous membrane sheet shaped into an annulus to provide cooling to the coolant loop through water evaporation to the vacuum of space. This present study describes the test methodology and planning and compares the test performance of three commercially available hollow fiber materials as alternatives to the sheet membrane prototype for SWME, in particular, a porous hydrophobic polypropylene, and two variants that employ ion exchange through non-porous hydrophilic modified Nafion. Contamination tests will be performed to probe for sensitivities of the candidate SWME elements to ordinary constituents that are expected to be found in the potable water provided by the vehicle, the target feedwater source. Some of the impurities in potable water are volatile, such as the organics, while others, such as the metals and inorganic ions are nonvolatile. The non-volatile constituents will concentrate in the SWME as evaporated water from the loop is replaced by the feedwater. At some point in the SWME mission lifecycle as the concentrations of the non-volatiles increase, the solubility limits of one or more of the constituents may be reached. The resulting presence of precipitate in the coolant water may begin to plug pores and tube channels and affect the SWME performance. Sensitivity to macroparticles, lunar dust simulant, and air bubbles will also be investigated.
Bue, Grant C.; Trevino, Luis A.; Fritts, Sharon; Tsioulos, Gus
A Hydraulic Model Is Compatible with Rapid Changes in Leaf Elongation under Fluctuating Evaporative Demand and Soil Water Status.
Plants are constantly facing rapid changes in evaporative demand and soil water content, which affect their water status and growth. In apparent contradiction to a hydraulic hypothesis, leaf elongation rate (LER) declined in the morning and recovered upon soil rehydration considerably quicker than transpiration rate and leaf water potential (typical half-times of 30 min versus 1-2 h). The morning decline of LER began at very low light and transpiration and closely followed the stomatal opening of leaves receiving direct light, which represent a small fraction of leaf area. A simulation model in maize (Zea mays) suggests that these findings are still compatible with a hydraulic hypothesis. The small water flux linked to stomatal aperture would be sufficient to decrease water potentials of the xylem and growing tissues, thereby causing a rapid decline of simulated LER, while the simulated water potential of mature tissues declines more slowly due to a high hydraulic capacitance. The model also captured growth patterns in the evening or upon soil rehydration. Changes in plant hydraulic conductance partly counteracted those of transpiration. Root hydraulic conductivity increased continuously in the morning, consistent with the transcript abundance of Zea maize Plasma Membrane Intrinsic Protein aquaporins. Transgenic lines underproducing abscisic acid, with lower hydraulic conductivity and higher stomatal conductance, had a LER declining more rapidly than wild-type plants. Whole-genome transcriptome and phosphoproteome analyses suggested that the hydraulic processes proposed here might be associated with other rapidly occurring mechanisms. Overall, the mechanisms and model presented here may be an essential component of drought tolerance in naturally fluctuating evaporative demand and soil moisture. PMID:24420931
Caldeira, Cecilio F; Bosio, Mickael; Parent, Boris; Jeanguenin, Linda; Chaumont, FranÓois; Tardieu, FranÓois
Burned and unburned peat water repellency: Implications for peatland evaporation following wildfire
NASA Astrophysics Data System (ADS)
Water repellency alters soil hydrology after periods of wildfire, potentially modifying the ecosystem recovery to such disturbance. Despite this potential importance, the extent and severity of water repellency within burned peatlands and its importance in regulating peatland recovery to wildfire disturbance remains poorly understood. We characterised the water repellency of peat in a burned (one year post-fire) and unburned peatland in the Western Boreal Plain utilising the water drop penetration time and ethanol droplet molarity tests. Burned Sphagnum moss and feather moss sites had a more severe degree of water repellency than unburned sites, with differences being more pronounced between burned and unburned feather moss sites. Burned feather moss exhibited the most extreme water repellency, followed by unburned feather moss, and burned Sphagnum. The severity of water repellency varied with depth through the near surface of the moss/peat profile. This was most evident within the burned feathermoss where more extreme water repellency was observed at the near-surface compared to the surface, with the most extreme water repellency found at 1 and 5 cm depths. Unburned Sphagnum was completely hydrophilic at all depths. We suggest that the extreme water repellency in near-surface feather moss peat acts as a barrier that impedes the supply of water to the surface that replaces that lost via evaporation. This leads to drying of the near-surface vadose zone within feather moss areas and a concomitantly large decrease in peatland evaporation within feather moss dominated peatlands. This negative feedback mechanism likely enhances the resilience of such peatland to wildfire disturbance, maintaining a high water table position, thereby limiting peat decomposition. In comparison, such a feedback is not observed strongly within Sphagnum, leaving Sphagnum dominated peatlands potentially vulnerable to low water table positions post disturbance.
Kettridge, N.; Humphrey, R. E.; Smith, J. E.; Lukenbach, M. C.; Devito, K. J.; Petrone, R. M.; Waddington, J. M.
Improvement to Air2Air Technology to Reduce Fresh-Water Evaporative Cooling Loss at Coal-Based Thermoelectric Power Plants
This program was undertaken to enhance the manufacturability, constructability, and cost of the Air2Air{TM} Water Conservation and Plume Abatement Cooling Tower, giving a validated cost basis and capability. Air2Air{TM} water conservation technology recovers a portion of the traditional cooling tower evaporate. The Condensing Module provides an air-to-air heat exchanger above the wet fill media, extracting the heat from the hot saturated moist air leaving in the cooling tower and condensing water. The rate of evaporate water recovery is typically 10% - 25% annually, depending on the cooling tower location (climate). This program improved the efficiency and cost of the Air2Air{TM} Water Conservation Cooling Tower capability, and led to the first commercial sale of the product, as described.
Ken Mortensen
Physiological regulation of evaporative water loss in endotherms: is the little red kaluta (Dasykaluta rosamondae) an exception or the rule?
It is a central paradigm of comparative physiology that the effect of humidity on evaporative water loss (EWL) is determined for most mammals and birds, in and below thermoneutrality, essentially by physics and is not under physiological regulation. Fick's law predicts that EWL should be inversely proportional to ambient relative humidity (RH) and linearly proportional to the water vapour pressure deficit (?wvp) between animal and air. However, we show here for a small dasyurid marsupial, the little kaluta (Dasykaluta rosamondae), that EWL is essentially independent of RH (and ?wvp) at low RH (as are metabolic rate and thermal conductance). These results suggest regulation of a constant EWL independent of RH, a hitherto unappreciated capacity of endothermic vertebrates. Independence of EWL from RH conserves water and heat at low RH, and avoids physiological adjustments to changes in evaporative heat loss such as thermoregulation. Re-evaluation of previously published data for mammals and birds suggests that a lesser dependence of EWL on RH is observed more commonly than previously thought, suggesting that physiological independence of EWL of RH is not just an unusual capacity of a few species, such as the little kaluta, but a more general capability of many mammals and birds. PMID:24741015
Withers, Philip C; Cooper, Christine E
Evaporation Rates of Chemical Warfare Agents using 5 CM Wind Tunnels. 5. VX From Sand and Concrete.
National Technical Information Service (NTIS)
The evaporation of VX from sand and concrete was studied as a function of temperature, drop size and air flow rate. One sand substrate and five carefully controlled concrete compositions were used in this study. For VX on sand and concrete, an equation wa...
C. A. Brevett C. V. Giannaras J. J. Pence J. P. Myers R. G. Nickol
Climate Processes of Lake Evaporation and Snowmelt Runoff: Part I. Evaporation Rates from Temperature-Stratified Saline - Lake as a Case Study. Part II. Snowmelt Runoff and Climate - Lake Basin as a Case Study
In part I, a methodology for determining the evaporation rates from temperature-stratified saline lakes has been developed. The initial motivation was to develop a technique which would be more accurate than the widely used evaporation pan method, and which would use meteorological data inputs that are normally available at weather stations, or are otherwise easy and inexpensive to gather. Four
Ben Jei Tsuang
A direct, evaporatively cooled, three-ton lithium bromide-water absorption chiller for solar application
Lithium bromide absorption machines first appeared commercially circa 1940. In all designs marketed, absorber/condenser heat has been rejected from the cycle through shell-and-tube exchangers to circulating water that is then processed in contact with the ambient air through a cooling tower. In mechanical refrigeration technology, evaporative condensing products have been an available alternative to water-cooled condensers with separate cooling towers. Lithium bromide machines have not been available with this alternative, mainly because of the difficulty of managing internal and external heat transfer processes through a common surface configuration that would meet all the needs satisfactorily. The main focus of this paper is the development of a direct, evaporatively cooled absorber/condenser. Other features of the chiller already displayed in the past or presently available hardware on the market will not be a part of this discussion. A second objective is to establish the significance of evaporative cooling for active solar-cooling devices and, in particular, as an alternative to dry-air cooling as the means of heat rejection for solarcooling equipment.
Merrick, R.H.
Analysis of rate-limiting processes in soil evaporation with implications for soil resistance models
Numerical integrations of coupled equations of moisture, vapor and heat diffusion in soil are analyzed to explore the relative roles of vapor and liquid fluxes in rate-limiting the transfer of water to the soilatmosphere interface. Approximate analytical integrations of a simpler isothermal system are then introduced to explore the interactions of vapor and liquid transport. Although vapor diffusion dominates total
Thambirajah Saravanapavan; Guido D. Salvucci
Peculiarities of evaporation of a thin water layer in the presence of a solvable surfactant
NASA Astrophysics Data System (ADS)
Evaporation of a thin layer of a polar liquid (water) having a free surface and located on a solid substrate is investigated. A solvable surfactant is placed on the free liquid-vapor interface. The surface tension is a linear function of the surface concentration of the surfactant. The surface energy of the solid-liquid contact line is a nonmonotonic function of the layer thickness and is the sum of the Van der Waals interaction and the specific interaction of the double electric layer on the interface. The effect of the solvable surfactant on the dynamics and stability of the propagation of the evaporation front in the thin liquid film is analyzed in the long-wave approximation in the system of Navier-Stokes equations.
Gordeeva, V. Yu.; Lyushnin, A. V.
Effects of viscosity, surface tension, and evaporation rate of solvent on dry colloidal structures: A lattice Boltzmann study
NASA Astrophysics Data System (ADS)
Understanding the mechanisms of how colloidal solution properties and drying processes result in dry colloidal structures is essential for industrial applications such as paint, ceramics, and electrodes. In this study, we develop a computational method to simulate the drying process of colloidal suspensions containing solid particles and polymers. The method consists of a solvent evaporation model, a fluid particle dynamics method, and a two-phase lattice Boltzmann method. We determine that a high-viscosity solvent, small surface tension, and a high evaporation rate of the solvent lead to a structure with dispersed particles and interconnected pores. When these conditions are not present, the particles agglomerate and the pores are disconnected.
Munekata, Toshihisa; Suzuki, Takahisa; Yamakawa, Shunsuke; Asahi, Ryoji
Minihalo photoevaporation during cosmic reionization: evaporation times and photon consumption rates
NASA Astrophysics Data System (ADS)
The weak, R-type ionization fronts (I-fronts) which swept across the intergalactic medium during the reionization of the Universe often found their paths blocked by cosmological minihaloes (haloes with virial temperatures Tvir<= 104 K). When this happened, the neutral gas which filled each minihalo was photoevaporated. In a cold dark matter universe, minihaloes formed in abundance before and during reionization and, thus, their photoevaporation is an important, possibly dominant, feature of reionization, which slowed it down and cost it many ionizing photons. In a previous paper, we described this process and presented our results of the first simulations of it by numerical gas dynamics with radiation transport in detail. In view of the importance of minihalo photoevaporation, both as a feedback mechanism on the minihaloes and as an effect on cosmic reionization, we have now performed a larger set of high-resolution simulations to determine and quantify the dependence of minihalo photoevaporation times and photon consumption rates on halo mass, redshift, ionizing flux level and spectrum. We use these results to derive simple expressions for the dependence of the evaporation time and photon consumption rate on these halo and external flux parameters. These can be conveniently applied to estimate the effects of minihaloes on the global reionization process in both semi-analytical calculations and larger-scale, lower-resolution numerical simulations, which cannot adequately resolve the minihaloes and their photoevaporation. We find that the average number of ionizing photons each minihalo atom absorbs during its photoevaporation is typically in the range 2-10. For the collapsed fraction in minihaloes expected during reionization, this can add about one photon per total atom to the requirements for completing reionization, potentially doubling the minimum number of photons required to reionize the Universe.
Iliev, Ilian T.; Shapiro, Paul R.; Raga, Alejandro C.
Regional water balance trends and evaporation-transpiration partitioning from a stable isotope survey of lakes in northern Canada
Regional variations in evaporation losses and water budget are interpreted from systematic isotopic patterns in surface waters across a 275,000 km2 region of northern Canada. Differential heavy isotope enrichment in a set of >255 nonheadwater lakes sampled by floatplane during 1993 and 1994 is strongly correlated to varying hydroclimatic conditions across the region. Calculated catchment-weighted evaporation losses typically range from
J. J. Gibson; T. W. D. Edwards
Variability in cold front activities modulating cool-season evaporation from a southern inland water in the USA
Understanding seasonal variations in the evaporation of inland waters (e.g., lakes and reservoirs) is important for water resource management as well as the prediction of the hydrological cycles in response to climate change. We analyzed eddy covariance-based evaporation measurements from the Ross Barnett Reservoir (32¯26'N, 90¯02'W which is always ice-free) in central Mississippi during the cool months (i.e., September-March) of
Heping Liu; Peter D. Blanken; Tamas Weidinger; Annika Nordbo; Timo Vesala
Hollow Fiber Space Suit Water Membrane Evaporator Development for Lunar Missions
NASA Technical Reports Server (NTRS)
The Space Suit Water Membrane Evaporator (SWME) is the baseline heat rejection technology selected for development for the Constellation lunar suit. The Hollow Fiber (HoFi) SWME is being considered for service in the Constellation Space Suit Element (CSSE) Portable Life Support Subsystem (PLSS) to provide cooling to the thermal loop through water evaporation to the vacuum of space. Previous work described the test methodology and planning to compare the test performance of three commercially available hollow fiber materials as alternatives to the sheet membrane prototype for SWME: 1) porous hydrophobic polypropylene, 2) porous hydrophobic polysulfone, and 3) ion exchange through nonporous hydrophilic modified Nafion. Contamination tests were performed to probe for sensitivities of the candidate SWME elements to organics and non-volative inorganics expected to be found in the target feedwater source, i.e., potable water provided by the vehicle. The resulting presence of precipitate in the coolant water could plug pores and tube channels and affect the SWME performance. From this prior work, a commercial porous hydrophobic hollow fiber was selected to satisfy both the sensitivity question and the need to provide 800 W of heat rejection. This paper describes the trade studies, the design methodology, and the hollow fiber test data used to design a full
Bue, Grant C.; Trevino, Luis A.; Hanford, Anthony J.; Mitchell, Keith
Coupled water and heat flow in laboratory evaporation experiments and its effects on soil hydraulic properties estimated by the simplified evaporation method
NASA Astrophysics Data System (ADS)
The prediction of water fluxes in the field requires an accurate determination of soil hydraulic parameters which define the soil water retention and hydraulic conductivity function. The evaporation method has become a standard tool to quickly and reliably determine soil hydraulic properties in the wet to medium pressure head range. Recently, the method has profited from a significant improvement of soil sensors and data evaluation methods. In most cases, the data obtained from a transient evaporation experiment are evaluated using simplifying assumptions, like the ones implicit to Schindler's or Wind's methods. In the past, the effect of these simplifications on the identification of hydraulic properties has been investigated and found to be relatively minor. These studies were based on the evaluation of computer-generated data which were created by numerical modeling of the evaporation process with the Richards equation, i.e. by assuming isothermal liquid flow. Since evaporation from bare soil will always lead to loss of energy, the assumption of constant temperature is questionable. In addition, the effects of thermal and vapor fluxes on simplified evaluation methods have so far hardly been investigated. In this contribution we analyze the effects of (1) coupled heat and water flow and (2) temperature effects on physical parameters. We firstly generated data by a numerical model which solves the coupled heat and water flow problem first derived by Philip and de Vries, and then used these data as source for the estimation of hydraulic properties with the evaluation methods of Schindler and Wind. The virtual realities covered different atmospheric forcings like changing wind speed and varying incoming shortwave radiation. The objective of this study was to identify under which atmospheric conditions, for which soil textures, and in which pressure head range the simplified evaluation methods lead to unbiased estimates of the soil hydraulic properties.
Iden, Sascha C.; Bl—cher, Johanna; Diamantopoulos, Efstathios; Durner, Wolfgang
Characteristic size for onset of coffee-ring effect in evaporating lysozyme-water solution droplets.
Liquid droplets containing suspended particles deposited on a solid surface often form a ring-like structure due to the redistribution of solute during evaporation, a phenomenon known as the "coffee ring effect". The complex patterns left on the substrate after evaporation are characteristic of the nature of the solute and the particle transport mechanisms. In this study, the morphological evolution and conditions for coffee ring formation for simplified model biological solutions of DI water and lysozyme are examined by AFM and optical microscopy. Lysozyme is a globular protein found in high concentration, for example, in human tears and saliva. The drop diameters studied are very small, ranging from 1 to 50 ?m. In this size range, protein motion and the resulting dried residue morphology are highly influenced by the decreased evaporation time of the drop. In this work, we consider the effect of droplet size and concentration on the morphology of the deposited drop as well as the minimal conditions for coffee ring formation in this system. Two distinct deposit types are observed: a simple cap-shaped deposit for drops with small diameters and a ring-like deposit at larger diameters. Ring formation occurs at a critical diameter, which depends systematically on initial lysozyme concentration. PMID:22998072
Gorr, Heather Meloy; Zueger, Joshua M; Barnard, John A
Testing of Commercial Hollow Fiber Membranes for Space Suit Water Membrane Evaporator
NASA Technical Reports Server (NTRS)
Three commercial-off-the-shelf (COTS) hollow fiber (HoFi) membrane evaporators, modified for low pressure, were tested in a vacuum chamber at pressures below 33 pascals as potential space suit water membrane evaporator (SWME) heat rejection technologies. Water quality was controlled in a series of 25 tests, first simulating potable water reclaimed from waste water and then changing periodically to simulate the ever concentrating make-up of the circulating coolant over that is predicted over the course of 100 EVAs. Two of the systems, comprised of non-porous tubes with hydrophilic molecular channels as the water vapor transport mechanism, were severely impacted by the increasing concentrations of cations in the water. One of the systems, based on hydrophobic porous polypropylene tubes was not affected by the degrading water quality, or the presence of microbes. The polypropylene system, called SWME 1, was selected for further testing. An inverse flow configuration was also tested with SWME 1, with vacuum exposure on the inside of the tubes, provided only 20% of the performance of the standard configuration. SWME 1 was also modified to block 50% and 90% of the central tube layers, and tested to investigate performance efficiency. Performance curves were also developed in back-pressure regulation tests, and revealed important design considerations arising from the fully closed valve. SWME 1 was shown to be insensitive to air bubbles injected into the coolant loop. Development and testing of a full-scale prototype based on this technology and these test results is in progress.
Bue, Grant C.; Trevino, Luis; Tsioulos, Gus; Hanford, Anthony
Partitioning of Evapotranspiration Into Soil Evaporation and Plant Transpiration Using Isotopes of Water in Controlled Conditions
NASA Astrophysics Data System (ADS)
Rainfall recycling by evapotranspiration from continental surfaces is certainly the most unknown component of the global water cycle. This is due to the large variability of rainfall as well as the heterogeneity of these continental surfaces, both in time and space. Traditional measuring methods such as sap flow, micro lysimeter, water and energy balance estimation (Bowen ratio, eddy correlation) have been used since the 70s for a monitoring of real evapotranspiration fluxes over crops and others plant covers. A complementary method consists in using isotopic biogeochemistry. When making specific hypothesis, it is possible to identify and quantify the different sources of the atmospheric water vapour (vegetation and soil at different scales). Analysis of the heavy stable isotopic ratios of water in both liquid and vapour phases: 18O and 2H can allow determining the history of the water in the soil since the last rainfall event (infiltration, re-evaporation) or the root extraction depths. Field campaigns measurements (plants and soils), interpreted using the Keeling Plot method allowed some progress in the partition between evaporation and transpiration understanding. But the experimental design is not sufficient to mechanistically describe the water processes involved. The study of all the interactions is difficult due to the large number of controlling variables describing climate, vegetation and soil characteristics. A monolith experiment (including soil and growing plant) was carried out in a reactor called RUBIC (Reactor Used for Continental Isotopic Biogeochemistry, Bariac et al., Geochim. Cosmochim. Acta., 1991). Controlled conditions allowed a monitoring and regulation of climatic parameters (net radiation, air temperature, vapour pressure deficit, CO2 partial pressure, and wind speed). It was also necessary to fix soil (structure, texture, and water content) and vegetation (specie and seeding density) parameters. The collected data allow us to improve our understanding of the partition of evapotranspiration into soil evaporation and plant transpiration and to assess the hypothesis (often made in isotopic biochemistry) of a stationary state reached in the two reservoirs (soil and plant). These data also allow the evaluation of the hypothesis included in a transfer module of heavy stable isotopes of water within the bare soil and the plant (Braud et al., Journ. of Hydrol., 2005). The latter is coupled to a SVAT model (Soil-Plant-Atmosphere Transfer) called SiSPAT (Simple Soil Plant Atmosphere Transfer model, Braud et al., Journ. of Hydrol., 1995) and was extended to take into account isotopes transfer within the vegetation (root extraction and transpiration). The experimental design of RUBIC as well as the first modelling results will be presented.
Rothfuss, Y.; Bariac, T.; Braud, I.; Biron, P.; Richard, P.; Canale, L.; Durand, J.; Gaudet, J.
The Defense Waste Processing Facility (DPWF) presently is in the process to determine means to reduce water utilization in the Slurry Mix Evaporator (SME) process, thus reducing effluent and processing times. The frit slurry addition system mixes the dry frit with water, yielding approximately a 50 weight percent slurry containing frit and the other fraction water. This slurry is discharged
Comparative analysis of cutaneous evaporative water loss in frogs demonstrates correlation with ecological habits.
Most frog species show little resistance to evaporative water loss (EWL), but some arboreal species are known to have very high resistances. We measured EWL and cutaneous resistance to evaporation (Rc) in 25 species of frogs from northern Australia, including 17 species in the family Hylidae, six species in the Myobatrachidae, and one each in the Bufonidae and the Microhylidae. These species display a variety of ecological habits, including aquatic, terrestrial, and arboreal specialisations, with the complete range of habits displayed within just the one hylid genus, Litoria. The 25 species measured in this study have resistances that range from Rc=0 to 63.1. These include low values indistinguishable from a free water surface to high values typical of "waterproof" anuran species. There was a strong correlation between ecological habit and Rc, even taking phylogenetic relationships into account; arboreal species had the highest resistance, aquatic species tended to have little or no resistance, and terrestrial species tended to have resistance between those of arboreal and aquatic frogs. For one species, Litoria rubella, we found no significant changes in EWL along a 1,500-km aridity gradient. This study represents the strongest evidence to date of a link between ecological habits and cutaneous resistance to water loss among species of frogs. PMID:16052451
Young, Jeanne E; Christian, Keith A; Donnellan, Stephen; Tracy, Christopher R; Parry, David
Development of a preprototype thermoelectric integrated membrane evaporation subsystem for water recovery
NASA Technical Reports Server (NTRS)
A three-man urine water recovery preprototype subsystem using a new concept to provide efficient potable water recovery from waste fluids on extended duration space flights has been designed, fabricated, and tested. Low power, compactness, and gravity insensitive operation are featured in this vacuum distillation subsystem that combines a hollow fiber polysulfone membrane evaporator with a thermoelectric heat pump. Application and integration of these key elements have solved problems inherent in previous reclamation subsystem designs. The hollow fiber elements provide positive liquid/gas phase control with no moving parts other than a waste liquid recirculation pump and a product water withdrawal pump. Tubular membranes provide structural integrity, improving on previous flat sheet membrane designs. A thermoelectric heat pump provides latent energy recovery.
Winkler, H. E.; Roebelen, G. J., Jr.
A New Approach to Measure Contact Angle and Evaporation Rate with Flow Visualization in a Sessile Drop
NASA Technical Reports Server (NTRS)
The contact angle and the spreading process of sessile droplet are very crucial in many technological processes, such as painting and coating, material processing, film-cooling applications, lubrication, and boiling. Additionally, as it is well known that the surface free energy of polymers cannot be directly, measured for their elastic and viscous restraints. The measurements of liquid contact angle on the polymer surfaces become extremely important to evaluate the surface free energy of polymers through indirect methods linked with the contact angle data. Due to the occurrence of liquid evaporation is inevitable, the effects of evaporation on the contact angle and the spreading become very important for more complete understanding of these processes. It is of interest to note that evaporation can induce Marangoni-Benard convection in sessile drops. However, the impacts of the inside convection on the wetting and spreading processes are not clear. The experimental methods used by previous investigators cannot simultaneously measure the spreading process and visualize the convection inside. Based on the laser shadowgraphic system used by the present author, a very simple optical procedure has been developed to measure the contact angle, the spreading speed, the evaporation rate, and to visualize inside convection of a sessile drop simultaneously. Two CCD cameras were used to synchronously record the real-time diameter of the sessile drop, which is essential for determination of both spreading speed and evaporation rate, and the shadowgraphic image magnified by the sessile drop acting as a thin plano-convex lens. From the shadowgraph, the inside convection of the drop can be observed if any and the image outer diameter, which linked to the drop profile, can be measured. Simple equations have been derived to calculate the drop profile, including the instantaneous contact angle, height, and volume of the sessile drop, as well as the evaporation rate. The influence of the inside convection on the wetting and spreading processes can be figured out through comparison of the drop profiles with and without inside convection when the sessile drop is placed at different evaporation conditions.
Zhang, Nengli; Chao, David F.
A New Approach to Quantify Evaporative Water Loss in Tropical Wetlands
NASA Astrophysics Data System (ADS)
Tropical wetlands are challenging research environments. Their high complexity and heterogeneity make the characterization of hydrological processes very difficult. In particular, large uncertainties complicate estimations of water loss by evapotranspiration (ET). ET influences the local and regional climate systems, and the quantification of ET is fundamental for the water balance of the continuous and intermittent water bodies. One of the largest freshwater wetlands in the world is the Pantanal located in central South America. Data availability is scarce and its remoteness makes direct measurements of ET even more challenging. Due to the variability and the complexity of this unique ecosystem, no adequate method for determining ET exists. In our study, we developed a process-based model to simulate ET that accounts for inundation dynamics, the type of water body, as well as vegetation cover for the dry and rainy seasons. A set of simple and complex empirical models were selected to calculate ensembles of potential evapotranspiration (PET) based on different assumptions and available datasets. We use high-resolution measurements of surface and groundwater levels of different types of water bodies to define the water availability. Stable water isotopes collected from these water bodies serve as qualitative information to describe the evaporation dynamics. Actual evapotranspiration (AET) was derived using the modeled PET with correction factors and the models were validated using local class A pan observations. Defining different types of water bodies on the basis of their differences in inundation time and dynamics, we apply the best-fitting model of our ensemble to each of the water body types. This finally allows us to quantify ET losses on a large spatial scale for dry and wet years. With this new spatially explicit approach we achieve an improvement in our understanding of the role of ET in the Pantanal wetland's water balance and quantify the actual water loss by ET.
Schwerdtfeger, J.; Weiler, M.; Johnson, M. S.; Couto, E. G.
Water Requirements and Application Rates for Lawns.
National Technical Information Service (NTIS)
Lawn water application rates were measured for 55 homes in Laramie and Wheatland, Wyoming, during 1975 and 1976. In addition, evapotranspiration rates were measured at both cities during 1976. Lawn water application rates in 1976 were 122 percent of the a...
L. O. Pochop J. Borrelli J. R. Barnes P. K. O'Neill
Georgia utilities use many different rate struc- tures and practices under an economic regulatory frame- work that has few rate setting standards. These different structures have financial impacts on utility revenue stabili- ty, customer expenditures, and water consumption. This paper describes the results of a survey of residential water and sewer utility rates in Georgia. This survey is far more
Andrew Westbrook; Jeffrey Hughes
Global distribution of moisture, evaporation-precipitation, and diabatic heating rates
NASA Technical Reports Server (NTRS)
Global archives were established for ECMWF 12-hour, multilevel analysis beginning 1 January 1985; day and night IR temperatures, and solar incoming and solar absorbed. Routines were written to access these data conveniently from NASA/MSFC MASSTOR facility for diagnostic analysis. Calculations of diabatic heating rates were performed from the ECMWF data using 4-day intervals. Calculations of precipitable water (W) from 1 May 1985 were carried out using the ECMWF data. Because a major operational change on 1 May 1985 had a significant impact on the moisture field, values prior to that date are incompatible with subsequent analyses.
Christy, John R.
Water Accounting and Vulnerability Evaluation (WAVE): Considering Atmospheric Evaporation Recycling and the Risk of Freshwater Depletion in Water Footprinting.
Aiming to enhance the analysis of water consumption and resulting consequences along the supply chain of products, the water accounting and vulnerability evaluation (WAVE) model is introduced. On the accounting level, atmospheric evaporation recycling within drainage basins is considered for the first time, which can reduce water consumption volumes by up to 32%. Rather than predicting impacts, WAVE analyzes the vulnerability of basins to freshwater depletion. Based on local blue water scarcity, the water depletion index (WDI) denotes the risk that water consumption can lead to depletion of freshwater resources. Water scarcity is determined by relating annual water consumption to availability in more than 11?000 basins. Additionally, WDI accounts for the presence of lakes and aquifers which have been neglected in water scarcity assessments so far. By setting WDI to the highest value in (semi)arid basins, absolute freshwater shortage is taken into account in addition to relative scarcity. This avoids mathematical artifacts of previous indicators which turn zero in deserts if consumption is zero. As illustrated in a case study of biofuels, WAVE can help to interpret volumetric water footprint figures and, thus, promotes a sustainable use of global freshwater resources. PMID:24660893
Berger, Markus; van der Ent, Ruud; Eisner, Stephanie; Bach, Vanessa; Finkbeiner, Matthias
Experimental and theoretical investigations of evaporation of sessile water droplet on hydrophobic surfaces.
Experiments of sessile water droplet evaporation on both polydimethylsiloxane (PDMS) and Teflon surfaces were conducted. All experiments begin with constant contact area mode (the initial contact angle is greater than 90¯), switch to constant contact angle mode and end with mixed mode. Based on the assumptions of spherical droplet and uniform concentration gradient, theoretical analyses for both constant contact area and constant contact angle modes are made and theoretical solutions are derived accordingly, especially a theoretical solution of contact angle is presented first for CCR stage with any value of the initial contact angle. Moreover, comparisons between the theoretical solutions and experimental data of contact angle in CCR stage demonstrate the validity of the theoretical solution and it would help for a better understanding and application of water droplet on solid surfaces, which is quite often encountered in lab-on-a-chip, polymerase chain reaction (PCR) and other micro-fluidics devices. PMID:21962433
Yu, Ying-Song; Wang, Ziqian; Zhao, Ya-Pu
Hollow Fiber Flight Prototype Spacesuit Water Membrane Evaporator Design and Testing
NASA Technical Reports Server (NTRS)
The spacesuit water membrane evaporator (SWME) is being developed to perform thermal control for advanced spacesuits and to take advantage of recent advances in micropore membrane technology. This results in a robust heat-rejection device that is potentially less sensitive to contamination than is the sublimator. The Membrana Celgard X50-215 microporous hollow-fiber (HoFi) membrane was selected after recent extensive testing as the most suitable candidate among commercial alternatives for continued SWME prototype development. The current design was based on a previous design that grouped the fiber layers into stacks, which were separated by small spaces and packaged into a cylindrical shape. This was developed into a full-scale prototype consisting of 14,300 tube bundled into 30 stacks, each of which is formed into a chevron shape and separated by spacers and organized into three sectors of 10 nested stacks. The new design replaced metal components with plastic ones, and has a custom built flight like backpressure valve mounted on the side of the SWME housing to reduce backpressure when fully open. The spacers that provided separation of the chevron fiber stacks were eliminated. Vacuum chamber testing showed improved heat rejection as a function of inlet water temperature and water vapor backpressure compared with the previous design. Other tests pushed the limits of tolerance to freezing and showed suitability to reject heat in a Mars pressure environment with and without a sweep gas. Tolerance to contamination by constituents expected to be found in potable water produced by distillation processes was tested in a conventional way by allowing constituents to accumulate in the coolant as evaporation occurs. For this purpose, the SWME cartridge has endured an equivalent of 30 EVAs exposure and demonstrated minimal performance decline.
Bue, Grant; Vogel, Matt; Makinen, Janice; Tsioulos, Gus
Hollow Fiber Space Water Membrane Evaporator Flight Prototype Design and Testing
NASA Technical Reports Server (NTRS)
The spacesuit water membrane evaporator (SWME) is being developed to perform thermal control for advanced spacesuits and to take advantage of recent advances in micropore membrane technology. This results in a robust heat-rejection device that is potentially less sensitive to contamination than is the sublimator. The current design was based on a previous design that grouped the fiber layers into stacks, which were separated by small spaces and packaged into a cylindrical shape. This was developed into a full-scale prototype consisting of 14,300 tube bundled into 30 stacks, each of which is formed into a chevron shape and separated by spacers and organized into three sectors of 10 nested stacks. The new design replaced metal components with plastic ones, eliminated the spacers, and has a custom built flight like backpressure valve mounted on the side of the SWME housing to reduce backpressure when fully open. A number of tests were performed in order to improve the strength of the polyurethane header that holds the fibers in place while the system is pressurized. Vacuum chamber testing showed similar heat rejection as a function of inlet water temperature and water vapor backpressure was similar to the previous design. Other tests pushed the limits of tolerance to freezing and showed suitability to reject heat in a Mars pressure environment with and without a sweep gas. Tolerance to contamination by constituents expected to be found in potable water produced by distillation processes was tested in a conventional way by allowing constituents to accumulate in the coolant as evaporation occurs. For this purpose, the SWME cartridge has endured an equivalent of 30 EVAs exposure and demonstrated acceptable performance decline.
Bue, Grant C.; Makinen, Janice; Vogel, Mtthew; Honas, Matt; Dillon, Paul; Colunga, Aaron; Truong, Lily; Porwitz, Darwin; Tsioulos, Gus
Evaluation of the return periods of water crises and evaporation in Monte Cotugno reservoir (Southern Italy)
NASA Astrophysics Data System (ADS)
In the past water resources management has been dealt and solved increasing water availabilities; today such opportunities have been considerably reduced and the technical-scientific perspectives are addressed above all to improve water system effectiveness and to promote an use of water resources that holds account of the droughts frequency and based on a correct estimate of the hydrologic balance. In this work a study on the water stored in Monte Cotugno reservoir in Sinni river - Basilicata (Southern Italy) - is proposed, estimating water crises return periods and reservoir evaporation. For such purpose the runs method was applied, based on the comparison between the temporal series of the "water volume" hydrological variable and a threshold representative of the "normal" conditions regarding which the availability in excess or defect was estimated. This allowed to individualize the beginning and the end of a water crisis event and to characterize the droughts in terms of duration, sum deficit and intensity. Therefore the return period was evaluated by means of the methodology proposed by Shiau and Shen in 2001, turned out equal approximately to 6 years. Such value was then verified with a frequency analysis of the "water volume" random variable, using the Weibull's distribution. Subsequently, the Fourier's analysis in the last twenty years was carried out, obtaining the same result of the previous methods. Moreover, in proximity of the Monte Cotugno reservoir the weather station of Senise is located, managed by ALSIA (Agenzia Lucana di Sviluppo e Innovazione in Agricultura), that provides in continuous measurements of air temperature and humidity, wind speed and direction, and global solar radiation since 2000. Such parameters allowed to apply five methods for reservoir evaporation estimate selected from those proposed in the literature, of which the first three, the Jensen-Haise's method, Makkink's method and Stephens-Stewart's one are based on solar radiation and temperature, while the Blaney-Criddle's method is based on temperature and duration of the day, and the Thornthwaite's method is based only on air temperature measurement.
Copertino, Vito; Lo Vecchio, Giuseppina; Marotta, Lucia; Pastore, Vittoria; Ponzio, Giuseppe; Scavone, Giuseppina; Telesca, Vito; Vita, Michele
Global prediction of ?A and ?2H-?18O evaporation slopes for lakes and soil water accounting for seasonality
NASA Astrophysics Data System (ADS)
Global trends in the ?2H-?18O enrichment slope of continental lakes and shallow soil water undergoing natural evaporation are predicted on the basis of a steady state isotope balance model using basic monthly climate data (i.e., temperature and humidity), isotopes in precipitation data, and a simple equilibrium liquid-vapor model to estimate isotopes in atmospheric moisture. The approach, which demonstrates the extension of well-known conceptual models in stable isotope hydrology to the global scale, is intended to serve as a baseline reference for evaluating field-based isotope measurements of vapor, surface water, and soil water and as a diagnostic tool for more complex ecosystem models, including isotope-equipped climate models. Our simulations reproduce the observed local evaporation line slopes (4-5 range for lakes and 2-3 range for soil water) for South America, Africa, Australia, and Europe. A systematic increase in slopes (5-8 range for lakes) toward the high latitudes is also predicted for lakes and soil water in northern North America, Asia, and Antarctica illustrating a latitudinal (mainly seasonality-related) control on the evaporation signals that has not been widely reported. The over-riding control on the poleward steepening of the local evaporation lines is found to be the isotopic separation between evaporation-flux-weighted atmospheric moisture and annual precipitation, and to lesser extents temperature and humidity, all of which are influenced by enhanced seasonality in cold regions.
Gibson, J. J.; Birks, S. J.; Edwards, T. W. D.
Modeling Equity for Alternative Water Rate Structures
NASA Astrophysics Data System (ADS)
The rising popularity of increasing block rates for urban water runs counter to mainstream economic recommendations, yet decision makers in rate design forums are attracted to the notion of higher prices for larger users. Among economists, it is widely appreciated that uniform rates have stronger efficiency properties than increasing block rates, especially when volumetric prices incorporate intrinsic water value. Yet, except for regions where water market purchases have forced urban authorities to include water value in water rates, economic arguments have weakly penetrated policy. In this presentation, recent evidence will be reviewed regarding long term trends in urban rate structures while observing economic principles pertaining to these choices. The main objective is to investigate the equity of increasing block rates as contrasted to uniform rates for a representative city. Using data from four Texas cities, household water demand is established as a function of marginal price, income, weather, number of residents, and property characteristics. Two alternative rate proposals are designed on the basis of recent experiences for both water and wastewater rates. After specifying a reasonable number (~200) of diverse households populating the city and parameterizing each household's characteristics, every household's consumption selections are simulated for twelve months. This procedure is repeated for both rate systems. Monthly water and wastewater bills are also computed for each household. Most importantly, while balancing the budget of the city utility we compute the effect of switching rate structures on the welfares of households of differing types. Some of the empirical findings are as follows. Under conditions of absent water scarcity, households of opposing characters such as low versus high income do not have strong preferences regarding rate structure selection. This changes as water scarcity rises and as water's opportunity costs are allowed to influence uniform rates. The welfare results of these exercises indicate that popular conceptions about increasing block rates may be incorrect insofar as the scarcity-endogenous uniform rate favors low-income households. That is, under scarcity conditions a switch from increasing block rates to full price uniform rates redistributes welfare so as to place more of the welfare burden of conservation on high-income households. Similarly, any household characteristic that tends to accompany low water use (e.g. low property value) generates a the same rate structure preference. These results are an intriguing addition to existing knowledge pertaining to the properties of increasing block rates and uniform rates with respect to criteria such as efficiency, simplicity, effectiveness, and (now) equity.
Griffin, R.; Mjelde, J.
Wide Range Equation of State of Water Taking into Account Evaporation, Dissociation and Ionization
NASA Astrophysics Data System (ADS)
Here we present new wide range equation of state for water. It has been constructed by sewing together a number of local models describing the matter in different regions of the phase diagram. At the temperatures under dissociation and moderate densities semiempirical equations of state describing water with high accuracy and taking evaporation into account have been used. To construct thermodynamic model describing properties of water in the region covered by shock data Variational Perturbation Theory has been applied. Dissociation reactions have also been introduced in the model. In this region water is considered as a mixture of molecular fluids. Some peculiarities of intermolecular potential for water and their effect upon parameters of shock compression have been investigated. Results of calculation have been compared with experimental data on shock compression of porous ice and snow. At high densities the matter is considered as homogeneous mixture of atoms and Thomas-Fermi model with quantum corrections and nuclei treatment by Kopyshev is applied. At low densities and high temperatures the model of weakly non-perfect dissociating gas and Saha model of ionized gas have been used. The EOS has been converted into tabular form to make it efficient when using in hydrodynamic codes.
Dremov, V. V.; Sapozhnikov, A. T.; Smirnova, M. A.
Effects of viscosity, surface tension, and evaporation rate of solvent on dry colloidal structures: a lattice Boltzmann study.
Understanding the mechanisms of how colloidal solution properties and drying processes result in dry colloidal structures is essential for industrial applications such as paint, ceramics, and electrodes. In this study, we develop a computational method to simulate the drying process of colloidal suspensions containing solid particles and polymers. The method consists of a solvent evaporation model, a fluid particle dynamics method, and a two-phase lattice Boltzmann method. We determine that a high-viscosity solvent, small surface tension, and a high evaporation rate of the solvent lead to a structure with dispersed particles and interconnected pores. When these conditions are not present, the particles agglomerate and the pores are disconnected. PMID:24329271
Munekata, Toshihisa; Suzuki, Takahisa; Yamakawa, Shunsuke; Asahi, Ryoji
Performance of a Water Recirculation Loop Maintenance Device and Process for the Advanced Spacesuit Water Membrane Evaporator
NASA Technical Reports Server (NTRS)
A water loop maintenance device and process to maintain the water quality of the Advanced Spacesuit Water Membrane Evaporation (SWME) water recirculation loop has been undergoing a performance evaluation. The SWME is a heat rejection device under development at the NASA Johnson Space Center to perform thermal control for advanced spacesuits. One advantage to this technology is the potential for a significantly greater degree of tolerance to contamination when compared to the existing Sublimator technology. The driver for the water recirculation maintenance device and process is to further enhance this advantage through the leveraging of fluid loop management lessons-learned from the International Space Station (ISS). A bed design that was developed for a Hamilton Sundstrand military application, and considered for a potential ISS application with the Urine Processor Assembly, provides a low pressure drop means for water maintenance in a recirculation loop. The bed design is coupled with high capacity ion exchange resins, organic adsorbents, and a cyclic methodology developed for the Extravehicular Mobility Unit (EMU) Transport Water loop. The maintenance process further leverages a sorbent developed for ISS that introduces a biocide in a microgravity-compatible manner for the Internal Active Thermal Control System (IATCS). The leveraging of these water maintenance technologies to the SWME recirculation loop is a unique demonstration of applying the valuable lessons learned on the ISS to the next generation of manned spaceflight Environmental Control and Life Support System (ECLSS) hardware. This
Rector, Tony; Steele, John W.; Bue, Grant C.; Campbell, Colin; Makinen, Janice
Full-Scale Hollow Fiber Spacesuit Water Membrane Evaporator Prototype Development and Testing for Advanced Spacesuits
NASA Technical Reports Server (NTRS)
The spacesuit water membrane evaporator (SWME) is being developed to perform the thermal control function for advanced spacesuits to take advantage of recent advances in micropore membrane technology in providing a robust heat-rejection device that is potentially less sensitive to contamination than is the sublimator. Principles of a sheet membrane SWME design were demonstrated using a prototypic test article that was tested in a vacuum chamber at JSC in July 1999. The Membrana Celgard X50-215 microporous hollow fiber (HoFi) membrane was selected after recent contamination tests as the superior candidate among commercial alternatives for HoFi SWME prototype development. Although a number of design variants were considered, one that grouped the fiber layers into stacks, which were separated by small spaces and packaged into a cylindrical shape, was deemed best for further development. An analysis of test data showed that eight layer stacks of the HoFi sheets that had good exposure on each side of the stack would evaporate water with high efficiency. A design that has 15,000 tubes, with 18 cm of exposed tubes between headers has been built and tested that meets the size, weight, and performance requirements of the SWME. This full-scale prototype consists of 30 stacks, each of which are formed into a chevron shape and separated by spacers and organized into three sectors of ten nested stacks. Testing has been performed to show contamination resistance to the constituents expected to be found in potable water produced by the distillation processes. Other tests showed the sensitivity to surfactants.
Bue, Grant; Trevino, Luis; Tsioulos, Gus; Mitchell, Keith; Dillon, Paul; Weaver, Gregg
Evaporative Concentration of 100x J13 Ground Water at 60% Relative Humidity and 90C
In these experiments we studied the behavior of a synthetic concentrated J13 solution as it comes in contact with a Ni-Cr-Mo-alloy selected for waste canisters in the designated high-level nuclear-waste repository at Yucca Mountain, Nevada. Concentrated synthetic J13 solution was allowed to drip slowly onto heated test specimens (90 C, 60% relative humidity) where the water moved down the surface of the specimens, evaporated and minerals precipitated. Mineral separation or zoning along the evaporation path was not observed. We infer from solid analyses and geochemical modeling, that the most corrosive components (Ca, Mg, and F) are limited by mineral precipitation. Minerals identified by x-ray diffraction include thermonatrite, natrite, and trona, all sodium carbonate minerals, as well as kogarkoite (Na{sub 3}SO{sub 4}F), halite (NaCl), and niter (KNO{sub 3}). Calcite and a magnesium silicate precipitation are based on chemical analyses of the solids and geochemical modeling. The most significant finding of this study is that sulfate and fluoride concentrations are controlled by the solubility of kogarkoite. Kogarkoite thermodynamic data are needed in the Yucca Mountain Project database to predict the corrosiveness of carbonate brines and to establish the extent to which fluoride is removed from the brines as a solid.
Staggs, K; Maureen Alai,; Hailey, P; Carroll, S A; Sutton, M; Nguyen, Q A
Magnetic resonance imaging of slow water flow during infiltration and evaporation by tracer motion
NASA Astrophysics Data System (ADS)
Water fluxes in soils control many processes in the environment like plant nutrition, solute and pollutant transport. In the last two decades non-invasive visualization methods have been adapted to monitor flux processes on the small scale. Magnetic resonance imaging (MRI), also well known from medical diagnostics, is one of the most versatile ones. It mostly probes directly the substance of interest: water, and it offers many opportunities to manipulate the observed signals for creating different contrasts and thus probing different properties of the porous medium and the embedded fluids. For example, one can make the signal sensitive to the total proton density, i. e. water content, to spatial distributions of relaxation times which reflect pore sizes, to spatial distributions of transport coefficients, and to concentration of contrast agents by using strongly T1 weighted MRI pulse sequences. In this presentation we use GdDTPA2- for monitoring flux processes in soil columns in an ultra-wide bore MRI scanner. It offers the opportunity for monitoring slow water fluxes mainly occurring in soil systems which are not monitorable with direct MRI flow imaging. This contrast agent is most convenient since it behaves conservatively, i.e. it does not sorb at different soil materials and it is chemically stable. Firstly, we show that its mode of action in natural porous media is identical to that known from medical applications as proved by the identical relaxivity parameters [1]. Secondly, the tracer is applied for the visualization of flux processes during evaporation-driven flow. Theoretical considerations by forward simulation predicted a lateral redistribution of solutes during evaporative upward fluxes from highly conductive fine material to neighbouring domains with low water content and conductivity. Here we could prove that such near-surface redistribution really takes place [2]. Thirdly, this tracer is applied for the investigation of water uptake by root systems. Depending on the transpiration conditions slow uptake in the dark is present, where the tracer moves directly into the xylem. When fully illuminated, the tracer uptake is limited by the Caspari band, and it is enriched strongly in the roots cortex. The results so far show that this tracer offers a new window for monitoring slow water fluxes in bare and grown soil columns. [1] Haber-Pohlmeier S, Bechtold M, Stapf, S, Pohlmeier, A. (2010) Vadose Zone Journal 9, 835-845 [2] Bechtold M, Haber-Pohlmeier S, Vanderborght J, Pohlmeier A, FerrÕ T, Vereecken H. (2011) Geophysical Research Letters 38, L17404
Pohlmeier, A.; Haber-Pohlmeier, S.; Bechtold, M.; Vanderborght, J.; Vereecken, H.
Evaporation from open microchannel grooves.
The evaporation of water from open u-shaped microchannel grooves was investigated with particular emphasis on the roles of channel width and air flow conditions. Given the small dimensions of the microchannels, all measurements were conducted in a range where convection and diffusion are of equal importance and known correlations for the calculation of mass transfer coefficients cannot be applied. The evaporation rates were measured using a new optical method and a gravimetric method. Both measurement methods yielded mass transfer coefficients that are in agreement with each other. The observed relation between mass transfer coefficient, air velocity and channel width vastly differs from the predictions obtained from macroscopic structures. With respect to diagnostic devices we conclude that analyte concentration in an open microchannel groove strongly increases even within short times due to the evaporation process and we show that wider channels are more favourable in terms of minimizing the relative evaporation rate. PMID:24345870
Kachel, Sibylle; Zhou, Ying; Scharfer, Philip; Vran?i?, Christian; Petrich, Wolfgang; Schabel, Wilhelm
Performance of a Water Recirculation Loop Maintenance Device and Process for the Advanced Spacesuit Water Membrane Evaporator
NASA Technical Reports Server (NTRS)
A dual-bed device to maintain the water quality of the Advanced Spacesuit Water Membrane Evaporation (SWME) water recirculation loop has been designed and is undergoing testing. The SWME is a heat rejection device under development at the NASA Johnson Space Center to perform thermal control for advanced spacesuits. One advantage to this technology is the potential for a significantly greater degree of tolerance to contamination when compared to the existing Sublimator technology. The driver for the development of a water recirculation maintenance device is to further enhance this advantage through the leveraging of fluid loop management lessons-learned from the International Space Station (ISS). A bed design that was developed for a Hamilton Sundstrand military application, and considered for a potential ISS application with the Urine Processor Assembly, provides a low pressure drop means for water maintenance in a recirculation loop. The bed design is coupled with high capacity ion exchange resins, organic adsorbents, and a cyclic methodology developed for the Extravehicular Mobility Unit (EMU) Transport Water loop. The bed design further leverages a sorbent developed for ISS that introduces a biocide in a microgravity-compatible manner for the Internal Active Thermal Control System (IATCS). The leveraging of these water maintenance technologies to the SWME recirculation loop is a unique demonstration of applying the valuable lessons learned on the ISS to the next generation of manned spaceflight Environmental Control and Life Support System (ECLSS) hardware.
Steele, John W.; Rector, Tony; Bue, Grant C.; Campbell, Colin; Makinen, Janice
Design and Evaluation of a Water Recirculation Loop Maintenance Device for the Advanced Spacesuit Water Membrane Evaporator
NASA Technical Reports Server (NTRS)
A dual-bed device to maintain the water quality of the Advanced Spacesuit Water Membrane Evaporation (SWME) water recirculation loop has been designed and is undergoing testing. The SWME is a heat rejection device under development at the NASA Johnson Space Center to perform thermal control for advanced spacesuits. One advantage to this technology is the potential for a significantly greater degree of tolerance to contamination when compared to the existing sublimator technology. The driver for the development of a water recirculation maintenance device is to further enhance this advantage through the leveraging of fluid loop management lessons learned from the International Space Station (ISS). A bed design that was developed for a Hamilton Sundstrand military application, and considered for a potential ISS application with the Urine Processor Assembly, provides a low pressure drop means for water maintenance in a recirculation loop. The bed design is coupled with high-capacity ion exchange resins, organic adsorbents, and a cyclic methodology developed for the Extravehicular Mobility Unit Transport Water Loop. The bed design further leverages a sorbent developed for the ISS that introduces a biocide in a microgravity-compatible manner for the Internal Active Thermal Control System. The leveraging of these water maintenance technologies to the SWME recirculation loop is a unique demonstration of applying the valuable lessons learned on the ISS to the next generation of crewed spaceflight Environmental Control and Life Support System hardware.
Steele, John W.; Rector, Tony; Bue, Grant C.; Campbell, Colin; Makinen, Janice
Design and Evaluation of a Water Recirculation Loop Maintenance Device for the Advanced Spacesuit Water Membrane Evaporator
NASA Technical Reports Server (NTRS)
A dual-bed device to maintain the water quality of the Advanced Spacesuit Water Membrane Evaporation (SWME) water recirculation loop has been designed and is undergoing testing. The SWME is a heat rejection device under development at the NASA Johnson Space Center to perform thermal control for advanced spacesuits. One advantage to this technology is the potential for a significantly greater degree of tolerance to contamination when compared to the existing Sublimator technology. The driver for the development of a water recirculation maintenance device is to further enhance this advantage through the leveraging of fluid loop management lessons-learned from the International Space Station (ISS). A bed design that was developed for a Hamilton Sundstrand military application, and considered for a potential ISS application with the Urine Processor Assembly, provides a low pressure drop means for water maintenance in a recirculation loop. The bed design is coupled with high capacity ion exchange resins, organic adsorbents, and a cyclic methodology developed for the Extravehicular Mobility Unit (EMU) Transport Water loop. The bed design further leverages a sorbent developed for ISS that introduces a biocide in a microgravity-compatible manner for the Internal Active Thermal Control System (IATCS). The leveraging of these water maintenance technologies to the SWME recirculation loop is a clear demonstration of applying the valuable lessons learned on the ISS to the next generation of manned spaceflight Environmental Control and Life Support System (ECLSS) hardware.
Steele, John W.; Rector, Tony; Bue, Grant C.; Campbell, Colin; Makinen, Janice
Hollow Fiber Spacesuit Water Membrane Evaporator Development and Testing for Advanced Spacesuits
NASA Technical Reports Server (NTRS)
The spacesuit water membrane evaporator (SWME) is being developed to perform the thermal control function for advanced spacesuits to take advantage of recent advances in micropore membrane technology in providing a robust heat-rejection device that is potentially less sensitive to contamination than is the sublimator. Principles of a sheet membrane SWME design were demonstrated using a prototypic test article that was tested in a vacuum chamber at JSC in July 1999. The Membrana Celgard X50-215 microporous hollow fiber (HoFi) membrane was selected after recent contamination tests as the most suitable candidate among commercial alternatives for HoFi SWME prototype development. A design that grouped the fiber layers into stacks, which were separated by small spaces and packaged into a cylindrical shape, was developed into a full-scale prototype consisting 14,300 tube bundled into 30 stacks, each of which are formed into a chevron shape and separated by spacers and organized into three sectors of ten nested stacks. Vacuum chamber testing has been performed characterize heat rejection as a function of inlet water temperature and water vapor backpressure and to show contamination resistance to the constituents expected to be found in potable water produced by the distillation processes. Other tests showed the tolerance to freezing and suitability to reject heat in a Mars pressure environment.
Bue, Grant C.; Trevino, Luis A.; Tsioulos, Gus; Settles, Joseph; Colunga, Aaron; Vogel, Matthew; Vonau, Walt
Determination of evaporation from a catchment water balance at a monthly time scale
NASA Astrophysics Data System (ADS)
A method is presented to determine total evaporation from the earth's surface at a spatial scale that is adequate for linkage with climate models. The method is based on the water balance of catchments, combined with a calibrated autoregressive rainfall-runoff model. The time scale used is in the order of decades (10 days) to months. The rainfall-runoff model makes a distinction between immediate processes (interception and short term storage) and the remaining longer-term processes. Besides the calibrated rainfall-runoff model and the time series of observed rainfall and runoff, the method requires a relation between transpiration and soil moisture storage. The method is applied to data of the Bani catchment in Mali, a sub-catchment of the Niger river basin.
Savenije, H. H. G.
Evaluation of a Remotely Sensed Evaporative Stress Index for Monitoring Patterns of Anomalous Water Use
NASA Astrophysics Data System (ADS)
Drought assessment is a complex endeavor, requiring monitoring of deficiencies in multiple components of the hydrologic budget. Precipitation anomalies reflect variability in water supply to the land surface, while soil moisture (SM), ground and surface water anomalies reflect deficiencies in moisture storage. In contrast, evapotranspiration (ET) anomalies provide unique yet complementary information, reflecting variations in actual water use by crops and direct evaporation from the soil. For example, precipitation- and ET-based anomalies may differ significantly in regions of intensive irrigation, shallow water table, or deep rooting depth - areas where plants may be more resilient to soil moisture deficiencies inferred from rainfall patterns. In addition, an ET-based index can better capture impacts of hot, windy conditions leading to "flash droughts", where anomalously high water use precipitates rapid decay in soil moisture and crop condition. Here we describe a remotely sensed Evaporative Stress Index (ESI) based on anomalies in actual-to-reference ET ratio, and compare with patterns in precipitation-based drought indicators. Actual ET is derived from thermal remote sensing, using the morning land-surface temperature (LST) rise observed with geostationary satellites. In comparison with vegetation indices, LST is a fast-response variable, with the potential for providing early warning of crop stress reflected in increasing canopy temperatures. Spatiotemporal patterns in ESI reasonably match those in precipitation-based indices (such as SPI and modeled SM) and patterns in the U.S. Drought Monitor. However, because ESI does not use precipitation as an input, it provides an independent assessment of evolving drought conditions, and is more portable to data-sparse parts of the world lacking dense rain-gauge and Doppler radar networks. Integrating LST information from polar orbiting systems, the ESI has unique potential for sensing moisture stress at field scale, benefiting yield estimation and loss compensation efforts. Techniques for identifying flash drought events will be demonstrated, as well as ESI performance over the heat-induced drought events of 2012. The ESI is routinely produced over the continental U.S. using data from GOES, with expansion to North and South America underway. In addition drought monitoring applications are being developed over Africa and Europe using Meteosat land-surface products.
Anderson, M. C.; Hain, C.; Otkin, J.; Zhan, X.
On the evaporation of ammonium sulfate solution
Aqueous evaporation and condensation kinetics are poorly understood, and uncertainties in their rates affect predictions of cloud behavior and therefore climate. We measured the cooling rate of 3 M ammonium sulfate droplets undergoing free evaporation via Raman thermometry. Analysis of the measurements yields a value of 0.58 {+-} 0.05 for the evaporation coefficient, identical to that previously determined for pure water. These results imply that subsaturated aqueous ammonium sulfate, which is the most abundant inorganic component of atmospheric aerosol, does not affect the vapor-liquid exchange mechanism for cloud droplets, despite reducing the saturation vapor pressure of water significantly.
Drisdell, Walter S.; Saykally, Richard J.; Cohen, Ronald C.
On the evaporation of ammonium sulfate solution.
Aqueous evaporation and condensation kinetics are poorly understood, and uncertainties in their rates affect predictions of cloud behavior and therefore climate. We measured the cooling rate of 3 M ammonium sulfate droplets undergoing free evaporation via Raman thermometry. Analysis of the measurements yields a value of 0.58 +/- 0.05 for the evaporation coefficient, identical to that previously determined for pure water. These results imply that subsaturated aqueous ammonium sulfate, which is the most abundant inorganic component of atmospheric aerosol, does not affect the vapor-liquid exchange mechanism for cloud droplets, despite reducing the saturation vapor pressure of water significantly. PMID:19861551
Drisdell, Walter S; Saykally, Richard J; Cohen, Ronald C
Evaporative control on soil water isotope ratios: implications for atmosphere-land surface water fluxes and interpretation of terrestrial proxy records
NASA Astrophysics Data System (ADS)
The moisture balance of the continental boundary layer plays an important role in regulating the exchange of water and energy between the land surface and atmosphere. In particular, the near-surface moisture balance is controlled by a number of factors including precipitation, infiltration and evapotranspiration. Measurements of stable isotope ratios in water can be exploited to better understand the mechanisms controlling atmosphere-land surface water fluxes. In addition, understanding the processes that set sub-surface water isotope ratios can prove useful for refining paleoclimate interpretations of stable oxygen and hydrogen isotope-based proxies. We present in situ tower-based measurements of stable isotope ratios in water vapor (?D and ?18O) from the Boulder Atmospheric Observatory, a semi-arid tall-tower site in Erie, Colorado, during July-September 2012. Near surface profiles from 0 to 10 meters were measured approximately every ninety minutes. Long-term measurements of soil water content show that most of the variation in soil water occurs in the top 30 cm on weekly to monthly time scales. Therefore, soil profiles from 0 to 30 cm were sampled on a weekly basis. Water from soil samples was cryogenically extracted for stable water isotope measurement. Intra-storm precipitation samples were collected using a fully automated evaporation-proof rain collector. Results show that there is perpetual disequilibrium between the surface vapor and soil water isotopes. The top 10 cm of soil water approaches equilibrium with the surface vapor right after a rain event because of high infiltration and saturation at the surface. At this semi-arid site with little vegetation, evaporative exchange is the main driver for soil water fluxes as the soil dries. This is corroborated by soil Dexcess profiles showing progressive enrichment through evaporation. Soil water isotope ratios at >15cm in July and >10 cm in September reflect either: (a) rain from 1-2 days prior, if a rain event occurred, or (b) typical day-time seasonal surface water vapor. The former suggests that infiltration controls the soil water isotope value, while the latter suggests that evaporation at the surface and diffusion within the soil are more dominant controls. We use these observations to constrain a Craig-Gordon evaporation model to weight the contributions of rainfall and surface water vapor exchange to soil water isotope values. These findings show that in arid or semi-arid sites, the soil water isotope ratios are likely dominated by evaporative exchange rather than precipitation. Therefore proxies like cave deposits that rely on soil water could be considered reliable in estimating past evaporative conditions.
Kaushik, A.; Noone, D. C.; Berkelhammer, M. B.; O'Neill, M.
Measurements of Evaporation Kinetics of Aqueous Aerosols
NASA Astrophysics Data System (ADS)
The rates of water evaporation and condensation govern the growth, size distribution, and number concentration of cloud droplets, yet the details of these fundamental processes remain poorly understood. In this work, the effect of acetic acid on the evaporation rate of water is studied using a liquid microjet technique. A collimated train of micron-sized droplets containing 1M acetic acid is injected into a vacuum chamber, and their temperature is measured at various distances from the jet nozzle using Raman thermometry. The data are compared to an evaporative cooling model to determine the evaporation coefficient, ?. In previous studies, ? was determined for pure water, D2O, 3M ammonium sulfate, and 4M sodium perchlorate to be 0.62 Ý0.09, 0.57 Ý0.06, 0.58 Ý0.05, and 0.47 Ý0.02, respectively. It is hypothesized that more surface-active species have a greater effect on evaporation rates. Acetic acid has been shown to be surface-active and is therefore representative of the small, surfactant-like molecules often found in aerosols. Preliminary results show a slight reduction in the evaporation coefficient for acetic acid compared to pure water. These experimental findings are being compared with calculations from the Chandler group at UC Berkeley in order to better understand the molecular mechanism of water evaporation.
Duffey, K.; Shih, O.; Liu, F.; Saykally, R.; Cohen, R. C.
Flow Visualization in Evaporating Liquid Drops and Measurement of Dynamic Contact Angles and Spreading Rate
NASA Technical Reports Server (NTRS)
A new hybrid optical system, consisting of reflection-refracted shadowgraphy and top-view photography, is used to visualize flow phenomena and simultaneously measure the spreading and instant dynamic contact angle in a volatile-liquid drop on a nontransparent substrate. Thermocapillary convection in the drop, induced by evaporation, and the drop real-time profile data are synchronously recorded by video recording systems. Experimental results obtained from this unique technique clearly reveal that thermocapillary convection strongly affects the spreading process and the characteristics of dynamic contact angle of the drop. Comprehensive information of a sessile drop, including the local contact angle along the periphery, the instability of the three-phase contact line, and the deformation of the drop shape is obtained and analyzed.
Zhang, Neng-Li; Chao, David F.
Tried and True: Evaporating is cool
NSDL National Science Digital Library
Many students hold misconceptions about evaporation. In this short exercise, students will apply the kinetic molecular theory to explain how cold water can evaporate and to observe the cooling effect of evaporation, and develop their own evaporation experiments.
Hand, Richard
Concentrating solar collector system for the evaporation of low-level radioactive waste water
The Los Alamos National Laboratory has recently been awarded a grant under the Solar Federal Buildings Program to design, construct, and operate a high-temperature solar energy system for the processing of low-level radioactive waste water. Conceptual design studies have been completed, and detailed design work is under way for a solar system to produce process heat to evaporate 38,000 gal (143,830 L) of waste water per month. The system will use approximately 11,000 ft/sup 2/ (1022 m/sup 2/) of concentrating parabolic trough collectors operating at about 500/sup 0/F (262/sup 0/C). Construction of the system is anticipated to begin in 1981. Performance optimization of collector array size and configuration, storage medium and capacity, system operation, and control schemes are done using the active solar system simulator in the DOE-2 building energy analysis computer program. Results of this optimization are reported. This project represents a unique application of solar energy to an increasingly significant problem area in the energy field.
Diamond, S.C.; Cappiello, C.C.
Separating soil evaporation and crop transpiration to improve crop water use efficiency
NASA Astrophysics Data System (ADS)
A network of a FAO/IAEA Coordinated Research Project (CRP) on "Managing Irrigation Water to Enhance Crop Productivity under Water-Limiting Conditions: A Role for Isotopic Techniques", involving seven countries was implemented from 2007 to 2012, to identify approaches to improve crop water productivity (production per unit of water input) under water-limiting conditions using isotopic and related techniques. This paper presents findings from the two of the studied sites, one in China and another in Morocco, in using both isotopic and conventional techniques to separate soil evaporation (E) and crop transpiration (T) from total water losses in evapotranspiration (ET) for winter wheat grown under different climatic conditions and methods of irrigation management practices. In the North China Plain (NCP), the estimated E/ET of winter wheat by the isotopic method (Keeling plot using delta oxygen-18 (?18O)) was in agreement with that obtained by conventional methods (eddy covariance and micro-lysimeter). The high correlation between these methods (R2=0.85, n=27) showed that the E from wheat-growing field contributes an average of 30% of water losses for the whole growing season (Nov-June), with higher E percentage (68%) can be expected before elongation stage due to incomplete canopy cover. The results also showed that through deficit irrigation and improved irrigation scheduling, soil E losses could be reduced by 10-30% of the total water loss compared with full irrigation. In Morocco, field Keeling plot isotopic E and T separation study was carried out for two days in spring of 2012 at Sidi Rahal. The percentage contribution of T to total ET was approximately 73%. The experimental results obtained from both China and Moroccan sites were used to validate FAO's AquaCrop model for E and T, and for improving irrigation scheduling and agronomic practices. Good correlation (R2=0.83) was obtained between measured (isotopic) and AquaCrop simulated ET from NCP. The measured and simulated E and T results from Morocco also compared well; the difference in E between the two approaches was only 5-12% over the two-day study.
Heng, Lee; Nguyen, Long; Gong, Daozhi; Mei, Xurong; Amenzou, Noureddine
Water retention curves of loamy-sandy soils: Transient evaporation method versus steady-state tension and pressure techniques
NASA Astrophysics Data System (ADS)
Water retention curves of loamy-sandy soils at the agricultural test site Wagna (Austria) were measured using both the simplified evaporation method according to Schindler (Arch. Acker- u. Pflanzenbau u. Bodenkd. Berlin 24, 1-7, 1980) and steady-state tension and pressure techniques. The soil was sampled with 250-ccm and 100-ccm steel pipes for the evaporation method and the steady-state technique, respectively. In the transient evaporation method two tensiometers with a measurement range between 0 and 850 hPa are installed at a depth of 1.25 cm and 3.75 cm in a sample of 5 cm in height; the mean values of the two tensiometers and the water contents measured by weighing are used to obtain the water retention curve. The steady-state method employs a tension table (sand box) at tensions below 100 hPa and a pressure extractor at tensions between 300 hPa and 15,000 hPa; the water content is measured by weighing after the sample has equilibrated at the tension value set on the table or plate. First results of both methods suggest that the soil samples release water over the entire tension range measured. In particular, the release of water at very low tension values may suggest the presence of macropores. Despite the generally good agreement between the two methods, the values appear to deviate systematically close to saturation. This is potentially caused by the large relative error of the tension measurement close to saturation. Alternatively, the different size of the samples used for the evaporation experiment (250 ccm) and the steady-state method (100 ccm) might play a role. Because of the limited measurement range of the tensiometers used for the evaporation method, the measured curve must be extrapolated between 850 hPa and 15,000 hPa to allow comparison with the steady-state method. To this end, it was attempted to match the Brooks-Corey, the Van-Genuchten, and a bimodal Van-Genuchten retention function to the data from the evaporation experiments. This involves a simultaneous fit of both water-retention and hydraulic-conductivity function. Only the bimodal Van-Genuchten model was found to be able to produce satisfactory fits to the data. The extrapolated water retention curves, however, do not match the data from the steady-state method. This suggests that alternative soil hydraulic functions are needed to provide an adequate representation of the water retention characteristics of the loamy-sandy soils considered in this investigation.
Winkler, G.; Eberhard, E.; Fank, J.; Birk, S.
Estimation of evaporation from open water - A review of selected studies, summary of U.S. Army Corps of Engineers data collection and methods, and evaluation of two methods for estimation of evaporation from five reservoirs in Texas
Organizations responsible for the management of water resources, such as the U.S. Army Corps of Engineers (USACE), are tasked with estimation of evaporation for water-budgeting and planning purposes. The USACE has historically used Class A pan evaporation data (pan data) to estimate evaporation from reservoirs but many USACE Districts have been experimenting with other techniques for an alternative to collecting pan data. The energy-budget method generally is considered the preferred method for accurate estimation of open-water evaporation from lakes and reservoirs. Complex equations to estimate evaporation, such as the Penman, DeBruin-Keijman, and Priestley-Taylor, perform well when compared with energy-budget method estimates when all of the important energy terms are included in the equations and ideal data are collected. However, sometimes nonideal data are collected and energy terms, such as the change in the amount of stored energy and advected energy, are not included in the equations. When this is done, the corresponding errors in evaporation estimates are not quantifiable. Much simpler methods, such as the Hamon method and a method developed by the U.S. Weather Bureau (USWB) (renamed the National Weather Service in 1970), have been shown to provide reasonable estimates of evaporation when compared to energy-budget method estimates. Data requirements for the Hamon and USWB methods are minimal and sometimes perform well with remotely collected data. The Hamon method requires average daily air temperature, and the USWB method requires daily averages of air temperature, relative humidity, wind speed, and solar radiation. Estimates of annual lake evaporation from pan data are frequently within 20 percent of energy-budget method estimates. Results of evaporation estimates from the Hamon method and the USWB method were compared against historical pan data at five selected reservoirs in Texas (Benbrook Lake, Canyon Lake, Granger Lake, Hords Creek Lake, and Sam Rayburn Lake) to evaluate their performance and to develop coefficients to minimize bias for the purpose of estimating reservoir evaporation with accuracies similar to estimates of evaporation obtained from pan data. The modified Hamon method estimates of reservoir evaporation were similar to estimates of reservoir evaporation from pan data for daily, monthly, and annual time periods. The modified Hamon method estimates of annual reservoir evaporation were always within 20 percent of annual reservoir evaporation from pan data. Unmodified and modified USWB method estimates of annual reservoir evaporation were within 20 percent of annual reservoir evaporation from pan data for about 91 percent of the years compared. Average daily differences between modified USWB method estimates and estimates from pan data as a percentage of the average amount of daily evaporation from pan data were within 20 percent for 98 percent of the months. Without any modification to the USWB method, average daily differences as a percentage of the average amount of daily evaporation from pan data were within 20 percent for 73 percent of the months. Use of the unmodified USWB method is appealing because it means estimates of average daily reservoir evaporation can be made from air temperature, relative humidity, wind speed, and solar radiation data collected from remote weather stations without the need to develop site-specific coefficients from historical pan data. Site-specific coefficients would need to be developed for the modified version of the Hamon method.
Harwell, Glenn R.
TDR water content inverse profiling in layered soils during infiltration and evaporation
NASA Astrophysics Data System (ADS)
During the last three decades, time domain reflectometry (TDR) has become one of the most commonly used tools for soil water content measurements either in laboratory or in the field. Indeed, TDR provides easy and cheap water content estimations with relatively small disturbance to the investigated soil. TDR measurements of soil water content are based on the strong correlation between relative dielectric permittivity of wet soil and its volumetric water content. Several expressions of the relationship between relative dielectric permittivity and volumetric water content have been proposed, empirically stated (Topp et al., 1980) as well as based on semi-analytical approach to dielectric mixing models (Roth et al., 1990; Whalley, 1993). So far, TDR field applications suffered the limitation due to the capability of the technique of estimating only the mean water content in the volume investigated by the probe. Whereas the knowledge of non homogeneous vertical water content profiles was needed, it was necessary to install either several vertical probes of different length or several horizontal probes placed in the soil at different depths, in both cases strongly increasing soil disturbance as well as the complexity of the measurements. Several studies have been recently dedicated to the development of inversion methods aimed to extract more information from TDR waveforms, in order to estimate non homogeneous moisture profiles along the axis of the metallic probe used for TDR measurements. A common feature of all these methods is that electromagnetic transient through the wet soil along the probe is mathematically modelled, assuming that the unknown soil water content distribution corresponds to the best agreement between simulated and measured waveforms. In some cases the soil is modelled as a series of small layers with different dielectric properties, and the waveform is obtained as the result of the superposition of multiple reflections arising from impedance discontinuities between the layers (Nguyen et al., 1997; Todoroff et al., 1998; Heimovaara, 2001; Moret et al., 2006). Other methods consider the dielectric properties of the soil as smoothly variable along probe axis (Greco, 1999; Oswald et al., 2003; Greco, 2006). Aim of the study is testing the applicability to layered soils of the inverse method for the estimation of water content profiles along vertical TDR waveguides, originally applied in laboratory to homogeneous soil samples with monotonic moisture distributions (Greco, 2006), and recently extended to field measurements with more general water content profiles (Greco and Guida, 2008). Influence of soil electrical conductivity, uniqueness of solution, choices of parametrization, parameters identifiabilty, sensitivity of the method to chosen parameters variations are discussed. Finally, the results of the application of the inverse method to a series of infiltration and evaporation experiments carried out in a flume filled with three soil layers of different physical characteristics are presented. ACKNOWLEDGEMENTS The research was co-financed by the Italian Ministry of University, by means of the PRIN 2006 PRIN program, within the research project entitled Definition of critical rainfall thresholds for destructive landslides for civil protection purposes'. REFERENCES Greco, R., 1999. Measurement of water content profiles by single TDR experiments. In: Feyen, J., Wiyo, K. (Eds.), Modelling of Transport Processes in Soils. Wageningen Pers, Wageningen, the Netherlands, pp. 276-283. Greco, R., 2006. Soil water content inverse profiling from single TDR waveforms. J. Hydrol. 317, 325-339. Greco R., Guida A., 2008. Field measurements of topsoil moisture profiles by vertical TDR probes. J. Hydrol. 348, 442- 451. Heimovaara, T.J., 2001. Frequency domain modelling of TDR waveforms in order to obtain frequency dependent dielectric properties of soil samples: a theoretical approach. In: TDR 2001 - Second International Symposium on Time Domain Reflectometry for Innovative Geotechnical Applications. Northwestern Univer
Greco, R.; Guida, A.
Spacesuit Water Membrane Evaporator Integration with the ISS Extravehicular Mobility Unit
NASA Technical Reports Server (NTRS)
NASA has developed a Solid Water Membrane Evaporation (SWME) to provide cooling for the next generation spacesuit. The current spacesuit team has looked at this technology from the standpoint of using the ISS EMU to demonstrate the SWME technology while EVA, and from the standpoint of augmenting EMU cooling in the case of a fouled EMU cooling system. One approach to increasing the TRL of the system is to incorporate this hardware with the existing EMU. Several integration issues were addressed to support a potential demonstration of the SWME with the existing EMU. Systems analysis was performed to assess the capability of the SWME to maintain crewmember cooling and comfort as a replacement for sublimation. The materials of the SWME were reviewed to address compatibility with the EMU. Conceptual system placement and integration with the EMU via an EVA umbilical system to ensure crew mobility and Airlock egress were performed. A concept of operation for EVA use was identified that is compatible with the existing system. This concept is extensible as a means to provide cooling for the existing EMU. The cooling system of one of the EMUs on orbit has degraded, with the root cause undetermined. Should there be a common cause resident on ISS, this integration could provide a means to recover cooling capability for EMUs on orbit.
Margiott, Victoria; Boyle, Robert
Body temperature and resistance to evaporative water loss in tropical Australian frogs.
Although the skin of most amphibians measured to date offers no resistance to evaporative water loss (EWL), some species, primarily arboreal frogs, produce skin secretions that increase resistance to EWL. At high air temperatures, it may be advantageous for amphibians to increase EWL as a means to decrease body temperature. In Australian hylid frogs, most species do not decrease their resistance at high air temperature, but some species with moderate resistance (at moderate air temperatures) gradually decrease resistance with increasing air temperature, and some species with high resistance (at moderate air temperatures) abruptly decrease resistance at high air temperatures. Lower skin resistance at high air temperatures decreases the time to desiccation, but the lower body temperatures allow the species to avoid their critical thermal maximum (CT(Max)) body temperatures. The body temperatures of species with low to moderate resistances to EWL that do not adjust resistance at high air temperatures do not warm to their CT(Max), although for some species, this is because they have high CT(Max) values. As has been reported previously for resistance to EWL generally, the response pattern of change of EWL at high air temperatures has apparently evolved independently among Australian hylids. The mechanisms involved in causing resistance and changes in resistance are unknown. PMID:16829148
Tracy, Christopher R; Christian, Keith A; Betts, Gregory; Tracy, C Richard
Field evaporation of doubly charged ions from a polar liquid
NASA Astrophysics Data System (ADS)
The effect of charge on field evaporation of ions from polar liquids is considered. Using the electromembrane ion source, we performed mass-spectral analysis of field evaporation of ions from the solution of sodium sulfate in a water-glycerol mixture. The composition of doubly charged cluster ions in the field evaporation from glycerol is determined. The rates of the field evaporation of doubly charged ions and singly charged ions are compared. It is shown that the ion charge as well as its localization considerably influences the efficiency of field evaporation of ions from polar liquids.
Balakin, A. A.; Novikova, L. I.
Soil Water Accumulation under Different Precipitation, Potential Evaporation, and Straw Mulch Conditions
TX, in the southern U.S. Great Plains, an analysis ofrates, three water application levels, and three PE rates. The 60 yr of records showed that precipitation for 69% of soils, both from Bushland, were Pullman clay loam (fine, the storms was ,6.4 mm, and those storms accounted mixed, superactive, thermic Torrertic Paleustoll), which con- for only ?18% of total precipitation.
Shangning Ji; Paul W. Unger
Evaporation determined by the energy-budget method for Mirror Lake, New Hampshire
Evaporation was determined by the energy-budget method for Mirror Lake during the open water periods of 1982-1987. For all years, evaporation rates were low in spring and fall and highest during the summer. However, the times of highest evaporation rates varied during the 6 yr. Evaporation reached maximum rates in July for three of the years, in June for two of the years, and in August for one of the years. The highest evaporation rate during the 6-yr study was 0.46 cm d-1 during 27 May-4 June 1986 and 15-21 July 1987. Solar radiation and atmospheric radiation input to the lake and long-wave radiation emitted from the lake were by far the largest energy fluxes to and from the lake and had the greatest effect on evaporation rates. Energy advected to and from the lake by precipitation, surface water, and ground water had little effect on evaporation rates. In the energy-budget method, average evaporation rates are determined for energy-budget periods, which are bounded by the dates of thermal surveys of the lake. Our study compared evaporation rates calculated for short periods, usually ???1 week, with evaporation rates calculated for longer periods, usually ???2 weeks. The results indicated that the shorter periods showed more variability in evaporation rates, but seasonal patterns, with few exceptions, were similar.
Winter, T. C.; Buso, D. C.; Rosenberry, D. O.; Likens, G. E.; Sturrock, Jr. , A. M.; Mau, D. P.
[Photosynthetic rate, transpiration rate, and water use efficiency of cotton canopy in oasis edge of Linze].
The measurement system of Li-8100 carbon flux and the modified assimilation chamber were used to study the photosynthetic characteristics of cotton (Gossypium hirsutum L.) canopy in the oasis edge region in middle reach of Heihe River Basin, mid Hexi Corridor of Gansu. At the experimental site, soil respiration and evaporation rates were significantly higher in late June than in early August, and the diurnal variation of canopy photosynthetic rate showed single-peak type. The photosynthetic rate was significantly higher (P < 0.01) in late June than in early August, with the daily average value being (43.11 +/- 1.26) micromol CO2 x m(-2) x s(-1) and (24.53 +/- 0.60) micromol CO2 x m(-2) x s(-1), respectively. The diurnal variation of canopy transpiration rate also presented single-peak type, with the daily average value in late June and early August being (3.10 +/- 0.34) mmol H2O x m(-2) x s(-1) and (1.60 +/- 0.26) mmol H2O x m(-2) x s(-1), respectively, and differed significantly (P < 0.01). The daily average value of canopy water use efficiency in late June and early August was (15.67 +/- 1.77) mmol CO2 x mol(-1) H2O and (23.08 +/- 5.54) mmol CO2 x mol(-1) H2O, respectively, but the difference was not significant (P > 0.05). Both in late June and in early August, the canopy photosynthetic rate was positively correlated with air temperature, PAR, and soil moisture content, suggesting that there was no midday depression of photosynthesis in the two periods. In August, the canopy photosynthetic rate and transpiration rate decreased significantly, because of the lower soil moisture content and leaf senescence, but the canopy water use efficiency had no significant decrease. PMID:20873616
Xie, Ting-Ting; Su, Pei-Xi; Gao, Song
A Comparison of Methods for Estimating Open-Water Evaporation in Small Wetlands
We compared evaporation measurements from a floating pan, land pan, chamber, and the Priestley-Taylor (PT) equation. Floating\\u000a pan, land pan, and meteorological data were collected from June 6 to July 21, 2005, at a small wetland in the Canadian River\\u000a alluvium in central Oklahoma, USA. Evaporation measured with the floating pan compared favorably to 12 h chamber measurements.\\u000a Differences between chamber
Jason R. Masoner; David I. Stannard
A Hydraulic Model Is Compatible with Rapid Changes in Leaf Elongation under Fluctuating Evaporative Demand and Soil Water Status1[C][W][OPEN
Plants are constantly facing rapid changes in evaporative demand and soil water content, which affect their water status and growth. In apparent contradiction to a hydraulic hypothesis, leaf elongation rate (LER) declined in the morning and recovered upon soil rehydration considerably quicker than transpiration rate and leaf water potential (typical half-times of 30 min versus 12 h). The morning decline of LER began at very low light and transpiration and closely followed the stomatal opening of leaves receiving direct light, which represent a small fraction of leaf area. A simulation model in maize (Zea mays) suggests that these findings are still compatible with a hydraulic hypothesis. The small water flux linked to stomatal aperture would be sufficient to decrease water potentials of the xylem and growing tissues, thereby causing a rapid decline of simulated LER, while the simulated water potential of mature tissues declines more slowly due to a high hydraulic capacitance. The model also captured growth patterns in the evening or upon soil rehydration. Changes in plant hydraulic conductance partly counteracted those of transpiration. Root hydraulic conductivity increased continuously in the morning, consistent with the transcript abundance of Zea maize Plasma Membrane Intrinsic Protein aquaporins. Transgenic lines underproducing abscisic acid, with lower hydraulic conductivity and higher stomatal conductance, had a LER declining more rapidly than wild-type plants. Whole-genome transcriptome and phosphoproteome analyses suggested that the hydraulic processes proposed here might be associated with other rapidly occurring mechanisms. Overall, the mechanisms and model presented here may be an essential component of drought tolerance in naturally fluctuating evaporative demand and soil moisture.
Caldeira, Cecilio F.; Bosio, Mickael; Parent, Boris; Jeanguenin, Linda; Chaumont, Francois; Tardieu, Francois
Short-term evaporation and water budget comparisons in shallow Arctic lakes using non-steady isotope mass balance
Shallow lakes in a continental, low Arctic setting are found to undergo substantial fluctuations in heavy-isotope content during the annual cycle due to extreme seasonality in water balance processes. Progressive isotope enrichment during the ice-free period occurs as a consequence of isotope exchange during evaporation under seasonally arid conditions, while enhanced input and flushing by heavy-isotope depleted precipitation and snowmelt
J. J. Gibson
Effects of alternative control strategies of water-evaporative cooling systems on energy efficiency and plume control: A case study
This paper reports the evaluations of energy efficiency, plume potential as well as plume control of a huge chiller plant using water-evaporative cooling towers for heat rejection for a super high-rising commercial office building in a subtropical region of Hong Kong. The evaluations were carried out in a dynamic Transient Simulation Program (TRNSYS)-based simulation platform using alternative control strategies including
Shengwei Wang; Xinhua Xu
Electrocatalytic reduction of oxygen to water at Au nanoclusters vacuum-evaporated on boron-doped diamond in acidic solution
Electrocatalytic reduction of oxygen at a boron (B)-doped diamond (BDD) electrode on which Au nanoclusters (GNCs) were deposited by vacuum-evaporation was investigated in 50 mM H2SO4 solution. Oxygen reduction current started to flow at a more positive potential at the GNCs\\/BDD electrode than at a polycrystalline gold electrode. Formation of water through a 4-electron reduction pathway at the GNCs\\/BDD electrode
Ichizo Yagi; Tomotaka Ishida; Kohei Uosaki
[Optimal irrigation index for cotton drip irrigation under film mulching based on the evaporation from pan with constant water level].
A field experiment with two irrigation cycles and two irrigating water quotas at squaring stage and blossoming-boll forming stage was conducted in Urumqi of Xinjiang Autonomous Region, Northwest China in 2008-2009, aimed to explore the high-efficient irrigation index of cotton drip irrigation under film mulching. The effects of different water treatments on the seed yield, water consumption, and water use efficiency (WUE) of cotton were analyzed. In all treatments, there was a high correlation between the cotton water use and the evaporation from pan installed above the plant canopy. In high-yield cotton field (including the treatment T4 which had 10 days and 7 days of irrigation cycle with 30.0 mm and 37.5 mm of irrigating water quota at squaring stage and blossoming-boll forming stage, respectively in 2008, and the treatment T1 having 7 days of irrigation cycle with 22.5 mm and 37.5 mm of irrigating water quota at squaring stage and blossoming-boll forming stage, respectively in 2009), the pan-crop coefficient (Kp) at seedling stage, squaring stage, blossoming-boll forming stage, and boll opening stage was 0.29-0.30, 0.52-0.53, 0.74-0.88, and 0.19-0.20, respectively. As compared with the other treatments, T4 had the highest seed cotton yield (5060 kg x hm(-2)) and the highest WUE (1.00 kg x m(-3)) in 2008, whereas T1 had the highest seed cotton yield (4467 kg x hm(-2)) and the highest WUE (0.99 kg x m(-3)) in 2009. The averaged cumulative pan evaporation in 7 days and 10 days at squaring stage was 40-50 mm and 60-70 mm, respectively, and that in 7 days at blossoming-boll forming stage was 40-50 mm. It was suggested that in Xinjiang cotton area, irrigating 45 mm water for seedling emergence, no irrigation both at seedling stage and at boll opening stage, and irrigation was started when the pan evaporation reached 45-65 mm and 45 mm at squaring stage and blossoming-boll stage, respectively, the irrigating water quota could be determined by multiplying cumulative pan evaporation with Kp (the Ko was taken as 0.5, 0.75, 0.85, and 0.75 at squaring stage, early blossoming, full-blossoming, and late blossoming stage, respectively), which could be the high efficient irrigation index to obtain high yield and WUE in drip irrigation cotton field and to save irrigation water resources. PMID:24564144
Shen, Xiao-Jun; Zhang, Ji-Yang; Sun, Jing-Sheng; Gao, Yang; Li, Ming-Si; Liu, Hao; Yang, Gui-Sen
A Method for Direct Assessment of the "Non Rainfall" Atmospheric Water Cycle: Input and Evaporation From the Soil
NASA Astrophysics Data System (ADS)
"Non rainfall" atmospheric water (dew, fog, vapour adsorption) supplies a small amount of water to the soil surface that may be important for arid soil micro-hydrology and ecology. Research into the direct effects of this water on soil is, however, lacking due to instrument and technical constraints. We report on the design, development, construction and findings of an automated microlysimeter instrument to directly measure this soil water cycle in Stellenbosch, South Africa during winter. Performance of the microlysimeter was satisfactory and results obtained were compared to literature and fell within the expected range. "Non rainfall" atmospheric water input into bare soil (river sand) was between 0.88 and 1.10 mm per night while evaporation was between 1.39 and 2.71 mm per day. The study also attempted to differentiate the composition of "non rainfall" atmospheric water and results showed that vapour adsorption contributed the bulk of this input.
Kaseke, Kudzai Farai; Mills, Anthony J.; Brown, Roger; Esler, Karen J.; Henschel, Johannes. R.; Seely, Mary K.
Effects of evaporator frosting and defrosting on the performance of air-to-water heat pumps
The performance of an 8 kW air-to-water heat pump operating under frosting conditions was investigated over a wide range of ambient temperatures and humidities. The results showed that the rate of frost formation and degradation in the heat pump performance is dependent upon both temperature and humidity, the effects of which should be taken into consideration in the design of
S. A. Tassou; C. J. Marquand
Characteristic lengths for evaporation suppression from patchy porous surfaces
NASA Astrophysics Data System (ADS)
For non-uniformly wet porous surfaces, evaporation rates vary nonlinearly with mean surface water content and with the areal fraction of wet patches. The nonlinearity stems from the complex vapor field forming over individual pores and patches that could enhance vapor fluxes from pores surrounded by dry area (relative to fluxes from the same area of free water surface). The resulting evaporation rates from such a surface are similar to free water surface evaporation despite considerably lower evaporating area (low surface water content). Theoretically, such flux compensation could be suppressed by lumping isolated pores into clusters with equal mean water content. The resulting arrangement in wet patches ensures nearly 1D conditions within the patch and some flux enhancement at the periphery. The interplay between patch water content, patch size, and mean surface water content within a prescribed air flow boundary layer was modeled analytically using single pore diffusion as a building block. Results show existence of a characteristic cluster size that yields the largest evaporation suppression for a given boundary layer thickness and spacing between patches. For patches larger than this size, the relative evaporation rate from patchy surface (relative to free water surface evaporation) reaches a predictable rate equal to the fractional area of clusters. Model predictions for the relation between pore cluster size and evaporation suppression were evaluated numerically and in a series of wind tunnel experiments using porous surfaces with different pore clusters. The findings could be used for the design of optimal porous covers for suppressing evaporation losses from water reservoirs, or for controlling evaporative drying from engineered porous surfaces.
Lehmann, Peter; Or, Dani
OPA oxidation rates in supercritical water.
Supercritical water oxidation can effectively destroy a large variety of high-risk wastes resulting from munitions demilitarization and complex industrial chemical. An important design consideration in the development of supercritical water oxidation is the information on the oxidation rate. In this paper, the oxidation rate of isopropyl amine (OPA), one of high-risk wastes resulting from munitions demilitarization, was investigated under supercritical water oxidation (SCWO) conditions in an isothermal tubular reactor. H2O2 was used as the oxidant. The reaction temperatures were ranged from 684 to 891 K and the residence times varied from 9 to 18s at a fixed pressure of 25 MPa. The conversion of OPA was monitored by analyzing total organic carbon (TOC) on the liquid effluent samples. The initial TOC concentrations of OPA varied from 7.21 to 143.78 mmol/l at the conversion efficiencies from 88.94 to 99.98%. By taking into account the dependence of reaction rate on oxidant and TOC concentration, a global power-law rate expression was regressed from 38 OPA experimental data. The resulting pre-exponential factor was 2.46(+/-0.65)x10(3)l(1.37)mmol(-0.37)s(-1); the activation energy was 64.12+/-1.94 kJ/mol; and the reaction orders for OPA (based on TOC) and oxidant were 1.13+/-0.02 and 0.24+/-0.01, respectively. PMID:15941618
Veriansyah, Bambang; Kim, Jae-Duck; Lee, Jong-Chol; Lee, Youn-Woo
Evaporation of a water droplet deposited on a hot high thermal conductivity surface
Many studies have been performed to quantify the vaporization process for both single droplets and multiple-droplet arrays impacting on hot surfaces. For the studies found in the published literature, the full span of the droplet vaporization processes is usually reported. These would include evaporation, nucleate boiling, film boiling, and Leidenfrost transition. The present investigation is concerned with the evaporation of a droplet on a hot surface The study reports detailed results for spital and temporal variation of the heat flux at the exposed surface of the droplet, and for temporal variation of the droplet volume. Limiting the study to evaporation implies that conditions are maintained under which nucleate boiling is fully suppressed.
diMarzo, M. (Mechanical Engineering Dept., Univ. of Maryland, College Park, MD (US)); Evans, D.D. (Center for Fire Research, National Bureau of Standards, Gaithersburg, MD (US))
Combined Evaporation and Salt Precipitation in Porous Media
NASA Astrophysics Data System (ADS)
The vadose zone pore water contains dissolved salts and minerals; therefore, evaporation results in high rates of salt accumulation that may change the physical and chemical properties of the porous media. Here, a series of experiments, together with a mathematical model, are presented to shed new light on these processes. Experiments included: (1) long-term column evaporation experiments to quantify changes in evaporation rates due to salt precipitation; (2) CT scans of evaporated porous media samples saturated with salt solutions, to observe salt precipitation from micro to macro scales; and (3) Infrared thermography analysis to quantify evaporation rates from porous media surfaces for homogeneous and heterogeneous conditions and constant water table, in the presence of salt precipitation. As expected, the majority of salt crystallization occurs in the upper parts of the matrix, near the evaporation front. For heterogeneous porous matrices, salt precipitation will occur mainly in the fine pore regions as preferential evaporation takes place in these locations. In addition, it was found that the precipitated NaCl salt crust diffusion coefficient for water vapor is one to two orders of magnitude lower than the vapor diffusion coefficient in free air, depending on environmental conditions and salt crystallization rates. Three new stages of evaporation were defined for saline solutions: SS1, SS2 and SS3. SS1 exhibits a low and gradual decrease in the evaporation rate due to osmotic pressure. During SS2, the evaporation rate falls progressively due to salt precipitation; SS3 is characterized by a constant low evaporation rate and determined by the diffusion rate of water vapor through the precipitated salt layer. Even though phenomenologically similar to the classical evaporation stages of pure water, these stages correspond to different mechanisms and the transition between stages can occur regardless the hydraulic conditions. As well, it was shown that matrix heterogeneity lessens the salt effect on evaporation as coarse pore regions are relatively free of salt crystals, facilitating vapor transport towards the atmosphere. This was verified by the thermography analysis that enabled independent quantification of evaporation rates from coarse and fine sections of the media during salt precipitation. This is in contrast to homogeneous conditions, where the salt is distributed homogeneously in the matrix's upper parts, resulting in an increase in matrix resistivity to vapor flow. This research sheds new light on the dynamics of the evaporation process of a saline solution and the importance of considering that natural pore solutions typically include electrolytes.
Weisbrod, N.; Dragila, M. I.; Nachshon, U.; Or, D.; Shaharani, E.; Grader, A.
Formation of Nitrogen- and Sulfur-Containing Light-Absorbing Compounds Accelerated by Evaporation of Water from Secondary Organic Aerosols
Aqueous extracts of secondary organic aerosols (SOA) generated from the ozonolysis of dlimonene were subjected to dissolution, evaporation, and re-dissolution in the presence and absence of ammonium sulfate (AS). Evaporation with AS at pH 4-9 produced chromophores that were stable with respect to hydrolysis and had a distinctive absorption band at 500 nm. Evaporation accelerated the rate of chromophore formation by at least three orders of magnitude compared to the reaction in aqueous solution, which produced similar compounds. Absorption spectroscopy and high-resolution nanospray desorption electrospray ionization (nano-DESI) mass spectrometry experiments suggested that the molar fraction of the chromophores was small (< 2%), and that they contained nitrogen atoms. Although the colored products represented only a small fraction of SOA, their large extinction coefficients (>10{sup 5} L mol{sup -1} cm{sup -1} at 500 nm) increased the effective mass absorption coefficient of the residual organics in excess of 10{sup 3} cm{sup 2} g{sup -1} - a dramatic effect on the optical properties from minor constituents. Evaporation of SOA extracts in the absence of AS resulted in the production of colored compounds only when the SOA extract was acidified to pH {approx} 2 with sulfuric acid. These chromophores were produced by acid-catalyzed aldol condensation, followed by a conversion into organosulfates. The presence of organosulfates was confirmed by high resolution mass spectrometry experiments. Results of this study suggest that evaporation of cloud or fog droplets containing dissolved organics leads to significant modification of the molecular composition and serves as a potentially important source of light-absorbing compounds.
Nguyen, Tran B.; Lee, Paula B.; Updyke, Katelyn M.; Bones, David L.; Laskin, Julia; Laskin, Alexander; Nizkorodov, Sergey
The Case of the Disappearing Water
NSDL National Science Digital Library
In this experiment, students investigate the evaporation of water as part of a solution to a simulated mystery. They will compare rates of evaporation under different conditions, demonstrate knowledge of the concepts of evaporation, and be able to explain evaporation in the context of the water cycle.
Soil water content and evaporation determined by thermal parameters obtained from ground-based and remote measurements
NASA Technical Reports Server (NTRS)
Soil water contents from both smooth and rough bare soil were estimated from remotely sensed surface soil and air temperatures. An inverse relationship between two thermal parameters and gravimetric soil water content was found for Avondale loam when its water content was between air-dry and field capacity. These parameters, daily maximum minus minimum surface soil temperature and daily maximum soil minus air temperature, appear to describe the relationship reasonably well. These two parameters also describe relative soil water evaporation (actual/potential). Surface soil temperatures showed good agreement among three measurement techniques: in situ thermocouples, a ground-based infrared radiation thermometer, and the thermal infrared band of an airborne multispectral scanner.
Reginato, R. J.; Idso, S. B.; Jackson, R. D.; Vedder, J. F.; Blanchard, M. B.; Goettelman, R.
Evaporative Cooling Membrane Device
NASA Technical Reports Server (NTRS)
An evaporative cooling membrane device is disclosed having a flat or pleated plate housing with an enclosed bottom and an exposed top that is covered with at least one sheet of hydrophobic porous material having a thin thickness so as to serve as a membrane. The hydrophobic porous material has pores with predetermined dimensions so as to resist any fluid in its liquid state from passing therethrough but to allow passage of the fluid in its vapor state, thereby, causing the evaporation of the fluid and the cooling of the remaining fluid. The fluid has a predetermined flow rate. The evaporative cooling membrane device has a channel which is sized in cooperation with the predetermined flow rate of the fluid so as to produce laminar flow therein. The evaporative cooling membrane device provides for the convenient control of the evaporation rates of the circulating fluid by adjusting the flow rates of the laminar flowing fluid.
Lomax, Curtis (Inventor); Moskito, John (Inventor)
In the preparation of the gaseous reactant feed to undergo a chemical reaction requiring the presence of steam, the efficiency of overall power utilization is improved by premixing the gaseous reactant feed with water and then heating to evaporate the water in the presence of the gaseous reactant feed, the heating fluid utilized being at a temperature below the boiling point of water at the pressure in the volume where the evaporation occurs.
Vakil, Himanshu B. (Schenectady, NY) [Schenectady, NY; Kosky, Philip G. (Ballston Lake, NY) [Ballston Lake, NY
Thermal signatures help deduce evaporative fluxes into turbulent airflows
NASA Astrophysics Data System (ADS)
Evaporative fluxes and energy balance of terrestrial surfaces are affected by interplay between water availability, energy input, and exchange across the air boundary layer. Commonly occurring turbulent airflows impose complex and highly dynamic boundary conditions that challenge prediction of surface evaporation rates. During stage-I evaporation where the vaporization plane is at the surface, intermittent turbulent interactions with the surface give rise to distinct thermal signatures that could be recorded using infrared thermography (IRT). The study links measured thermal signatures with spatio-temporal distribution of eddy-induced localized evaporation rates towards characterization of turbulent momentum field and estimation of overall evaporative fluxes. Results highlight potential of the approach for remote quantification of interactions between turbulent eddies and evaporating surfaces. Surface thermal inertia present a challenge to high resolution implementation, and strategies for overcoming these are presented including applications to plant canopies (low thermal inertia surfaces). Applications for larger scales will be discussed.
Haghighi, E.; Or, D.
New explicit equations for the accurate calculation of the growth and evaporation of hydrometeors by the diffusion of water vapor
NASA Technical Reports Server (NTRS)
The traditional explicit growth equation has been widely used to calculate the growth and evaporation of hydrometeors by the diffusion of water vapor. This paper reexamines the assumptions underlying the traditional equation and shows that large errors (10-30 percent in some cases) result if it is used carelessly. More accurate explicit equations are derived by approximating the saturation vapor-density difference as a quadratic rather than a linear function of the temperature difference between the particle and ambient air. These new equations, which reduce the error to less than a few percent, merit inclusion in a broad range of atmospheric models.
Srivastava, R. C.; Coen, J. L.
Evaporation from the shallow Lake Massaciuccoli (Tuscany, Italy) studied using stable isotopes and evaporation pan data
NASA Astrophysics Data System (ADS)
Oxygen and hydrogen isotope variations monitored in Lake Massaciuccoli (7 km2, 2 m deep, seasonally variable water level) during summer 2008, were compared with those observed in a Class A evaporation pan (diameter 120.6 cm, depth 25.4 cm) placed on the lake eastern shore. Air temperature, pressure, relative humidity, wind speed and direction, solar radiation, water temperature in the lake and the pan were also measured. The pluviometer indicated that no precipitation occurred during the study period. The pan was initially filled with groundwater up to the level of 19.2 cm (219 L), depleted in heavy isotopes with respect to tha lake water. Sodium chloride was added up to the concentration of 1 gæL-1, which is assumed do not affect significantly the evaporation rate till the water volume is reduced to less than 10 %. The Cl- concentration was used to provide an estimation of the evaporated water fraction, in addition to the micrometer measuring the water level variations. The pan water was sampled every 2-3 days and Cl- and stable isotopes determined. The set of stable isotope and evaporation data enabled us to compute the parameters governing the evaporation process and the isotopic exchanges with the atmospheric moisture, according to the procedure proposed by Gonfiantini (1986). The values were applied to test three working hypotheses of water balance of Lake Massaciuccoli: (i) surface inflow and outflow of liquid water are negligible and only evaporation is important; (ii) the inflow is negligible and outflow and evaporation are both significant; (iii) the three terms of balance are all important but the losses by evaporation and outflow exceed inflow (as the lake water level was decreasing). Water exchanges with groundwater are considered negligible. The best agreement between lake and pan data was obtained with the second hypothesis, for which the fraction of water removed by evaporation was estimated to be about 40 % ot he total water losses. This residual 60 % of losses consists essentially of water pumped from the lake for irrigation, in rough agreement with independent estimations. In the final stages of pan water evaporation, the well known hook trend of heavy isotope delta values versus residual water fraction was observed. The data elaboration is being continued and refined. Correction factors for the so called pan effect will also be applied. Collection of atmospheric vapour samples has been started. R. Gonfiantini, 1986. Isotopes in lake studies, in Handbook of Environmental Isotope Geochemistry (P. Fritz and J-Ch. Fontes, Eds.), Vol. 2, pp.113-168.
Baneschi, I.; Gonfiantini, R.; Guidi, M.
Simulation of temporal and spatial distribution of required irrigation water by crop models and the pan evaporation coefficient method
NASA Astrophysics Data System (ADS)
Hebei Plain is the most important agricultural belt in North China. Intensive irrigation, low and uneven precipitation have led to severe water shortage on the plain. This study is an attempt to resolve this crucial issue of water shortage for sustainable agricultural production and water resources management. The paper models distributed regional irrigation requirement for a range of cultivated crops on the plain. Classic crop models like DSSAT- wheat/maize and COTTON2K are used in combination with pan-evaporation coefficient method to estimate water requirements for wheat, corn, cotton, fruit-trees and vegetables. The approach is more accurate than the static approach adopted in previous studies. This is because the combination use of crop models and pan-evaporation coefficient method dynamically accounts for irrigation requirement at different growth stages of crops, agronomic practices, and field and climatic conditions. The simulation results show increasing Required Irrigation Amount (RIA) with time. RIA ranges from 5.08æ109 m3 to 14.42æ109 m3 for the period 1986~2006, with an annual average of 10.6æ109 m3. Percent average water use by wheat, fruit trees, vegetable, corn and cotton is 41%, 12%, 12%, 11%, 7% and 17% respectively. RIA for April and May (the period with the highest irrigation water use) is 1.78æ109 m3 and 2.41æ109 m3 respectively. The counties in the piedmont regions of Mount Taihang have high RIA while the central and eastern regions/counties have low irrigation requirement.
Yang, Yan-Min; Yang, Yonghui; Han, Shu-Min; Hu, Yu-Kun
Evaluation of the freeze-thaw/evaporation process for the treatment of produced waters. Final report, August 1992--August 1996
The use of freeze-crystallization is becoming increasingly acknowledged as a low-cost, energy-efficient method for purifying contaminated water. The natural freezing process can be coupled with natural evaporative processes to treat oil and gas produced waters year round in regions where subfreezing temperatures seasonally occur. The climates typical of Colorado`s San Juan Basin and eastern slope, as well as the oil and gas producing regions of Wyoming, are well suited for application of these processes in combination. Specifically, the objectives of this research are related to the development of a commercially-economic FTE (freeze-thaw/evaporation) process for the treatment and purification of water produced in conjunction with oil and natural gas. The research required for development of this process consists of three tasks: (1) a literature survey and process modeling and economic analysis; (2) laboratory-scale process evaluation; and (3) field demonstration of the process. Results of research conducted for the completion of these three tasks indicate that produced water treatment and disposal costs for commercial application of the process, would be in the range of $0.20 to $0.30/bbl in the Rocky Mountain region. FTE field demonstration results from northwestern New Mexico during the winter of 1995--96 indicate significant and simultaneous removal of salts, metals, and organics from produced water. Despite the unusually warm winter, process yields demonstrate disposal volume reductions on the order of 80% and confirm the potential for economic production of water suitable for various beneficial uses. The total dissolved solids concentrations of the FTE demonstration streams were 11,600 mg/L (feed), 56,900 mg/L (brine), and 940 mg/L (ice melt).
Boysen, J.E.; Walker, K.L.; Mefford, J.L.; Kirsch, J.R. [Resource Technology Corp., Laramie, WY (United States); Harju, J.A. [North Dakota Univ., Grand Forks, ND (United States). Energy and Environmental Research Center
Infrared thermography of evaporative fluxes and dynamics of salt deposition on heterogeneous porous surfaces
NASA Astrophysics Data System (ADS)
Evaporation of saline solutions from porous media, common in arid areas, involves complex interactions between mass transport, energy exchange and phase transitions. We quantified evaporation of saline solutions from heterogeneous sand columns under constant hydraulic boundary conditions to focus on effects of salt precipitation on evaporation dynamics. Mass loss measurements and infrared thermography were used to quantify evaporation rates. The latter method enables quantification of spatial and temporal variability of salt precipitation to identify its dynamic effects on evaporation. Evaporation from columns filled with texturally-contrasting sand using different salt solutions revealed preferential salt precipitation within the fine textured domains. Salt precipitation reduced evaporation rates from the fine textured regions by nearly an order of magnitude. In contrast, low evaporation rates from coarse-textured regions (due to low capillary drive) exhibited less salt precipitation and consequently less evaporation rate suppression. Experiments provided insights into two new phenomena: (1) a distinct increase in evaporation rate at the onset of evaporation; and (2) a vapor pumping mechanism related to the presence of a salt crust over semidry media. Both phenomena are related to local vapor pressure gradients established between pore water and the surface salt crust. Comparison of two salts: NaCl and NaI, which tend to precipitate above the matrix surface and within matrix pores, respectively, shows a much stronger influence of NaCl on evaporation rate suppression. This disparity reflects the limited effect of NaI precipitation on matrix resistivity for solution and vapor flows.
Nachshon, Uri; Shahraeeni, Ebrahim; Or, Dani; Dragila, Maria; Weisbrod, Noam
Impact of plant water uptake strategy on soil moisture and evaporation dynamics during drydown
Experiments have shown that plants can compensate for water stress in the upper, more densely rooted, soil layers by increasing the water uptake from deeper layers. By adapting root water uptake to water availability, plants are able to extend the period of unstressed transpiration. This strategy conflicts with the approach in many land surface schemes, where plant water uptake is
Adriaan J. Teuling; Remko Uijlenhoet; FranÓois Hupet; Peter A. Troch
Determination of Summertime VOC Emission Rates from Produced Water Ponds in the Uintah Basin
NASA Astrophysics Data System (ADS)
The observance of excess ozone concentrations in Utah's Uintah Basin over past several years has prompted several investigations into the extent and causes of the elevated ozone. Among these is the assessment of potential emissions of reactive VOCs. Evaporation ponds, used a remediation technique for treatment of contaminated production and other waters, are one potential source of significant VOC emissions and is estimated that there are around 160 such ponds within the Uintah Basin's oil and gas production areas. In June 2012 VOC emission rates for several reactive VOCs were derived for an evaporation facility consisting of a small inlet pond (?0.03 acres) and two larger, serial ponds (?4.3 acres each). The emission rates were determined over three sampling periods using an inverse modeling approach. Under this methodology, ambient VOC concentrations are determined at several downwind locations through whole-air collection into SUMMA canisters, followed by GC/MS quantification and compared with predicted concentrations using an EPA-approved dispersion model, AERMOD. The presumed emission rates used within the model were then adjusted until the modeled concentrations approach the observed concentrations. The derived emission rates for the individual VOCs were on the order of 10-3 g/s/m2 from the inlet pond and 10-6 g/s/m2 from the larger ponds. The emissions from the 1st pond in series after the inlet pond were about 3-4x the emissions from the 2nd pond. These combined emission rates are about an order of magnitude those reported for a single study in Colorado (Thoma, 2009). It should be noted, however, that the variability about each of the VOC emission rates was significant (often æ100% at the 95% confidence interval). Extrapolating these emission rates to the estimated total areas of all the evaporation ponds within Basin resulted in calculated Basin-wide VOC emissions 292,835 tons/yr. However, Bar-Ilan et al. (2009) estimated 2012 VOC oil and gas related emissions within the Uintah Basin to be 119,974 tons/yr. Given the large observed variabilities and the uncertainties with extrapolating the derived emission rates across varying pond types and differing climatic conditions, the comparisons are not unreasonable. If the lower, literature emission rates of Thoma (2009) are used the estimated Basin-wide evaporation emissions, the pond emissions would still be approximately 30% of the total emissions compiled by Bar-Ilan et al. (2009). Although the study described herein only represents a single facility and a single set of seasonal conditions, extrapolating these rates can give potential insight into the significance of VOC emissions into the Basin atmosphere from evaporation ponds.
Martin, R. S.; Woods, C.; Lyman, S.
Development of Statistical Typhoon Intensity Prediction: Application to Satellite-Observed Surface Evaporation and Rain Rate (STIPER)
NASA Astrophysics Data System (ADS)
A statistical-dynamical model has been used for operational guidance for tropical cyclone (TC) intensity prediction. In this study, several multiple linear regression models and neural network (NN) models are developed for the intensity prediction of western North Pacific TCs at 24-, 48-, and 72-h intervals. The multiple linear regression models include a model of climatology and persistence (CLIPER), a model based on the Statistical Typhoon Intensity Prediction System (STIPS), which serves as the base regression model (BASE), and a model of STIPS with additional satellite estimates of surface evaporation (SLHF) and innercore rain rate (IRR, STIPER model). A revised equation for the TC maximum potential intensity is derived using Tropical Rainfall Measuring Mission Microwave Imager optimally interpolated sea surface temperature data, which have higher temporal and spatial resolutions. Analyses of the resulting models show the marginal improvement of STIPER over BASE. However, IRR and SLHF are found to be significant predictors in the predictor pool. Neural network models using the same predictors as STIPER show reductions of the mean absolute errors of 7%, 11%, and 16% relative to STIPER for 24-, 48-, and 72-h forecasts, respectively. The largest improvement is found for the intensity forecasts of the rapidly intensifying and rapidly decaying TCs. (top) The 24-h BASE, STIPER, and NN24 model mean absolute errors (MAEs) stratified by best-track initial intensity (MWS0) in 5-kt bins and (bottom) 24-h intensity change (DELV) in 5-kt bins for all nine verification years. Lower values of MAEs represent better forecasts. Dashed dotted lines represent the numbers of valid observations within a particular bin.
Gao, S.; Chiu, L.
Pentachlorophenol oxidation rates in supercritical water.
The oxidation rate of pentachlorophenol, [C(6)HCl(5)O] which is used to control termites and as a general herbicide and also as the probable human's carcinogen, was investigated in an isothermal continuous tubular reactor under supercritical water oxidation (SCWO) conditions. The experiments were conducted at a temperature of 400-550 degrees C and a fixed pressure of 25 MPa, with a residence time that ranged from 6 s to 26 s. The conversion of PCP was monitored by analyzing total organic carbon (TOC) on the liquid effluent samples. The initial TOC concentrations of PCP were varied from 0.74 mmol/L to 2.91 mmol/L and the oxygen concentrations were varied from 0.46 mmol/L to 3.52 mmol/L. By taking into account the dependence of the oxidant and TOC concentration on the reaction rate, a global PCP oxidation rate was regressed from the data of 48 experiments, to a 95% confidence level. The resulting activation energy was determined to be 43.56 +/- 1.47 kJ/mol, and the pre-exponential factor was (1.92 +/- 0.46) x 10(2) L(1.16) mmol(-0.16) s(-1). The reaction orders for the PCP (based on TOC) and the oxidant were 0.74 +/- 0.02 and 0.42 +/- 0.05, respectively. PMID:18074281
Han, Seung Ho; Veriansyah, Bambang; Kim, Jae-Duck; Lee, Jong-Chol
Seasonal and intraseasonal variations in evaporation and surface energy budget from eddy covariance measurements over an open water surface in Mississippi, U.S.A
Understanding seasonal and intraseasonal variations in evaporation over lake\\/reservoir is important for water resource management as well as predicting variations in hydrology as a result of climate change. Since August of 2007, we have conducted a long-term eddy covariance measurement of evaporation and the surface energy budget over Ross Barnett Reservoir (32o26'N, 90o02'W) in Mississippi, USA. The fetch for eddy
H. Liu; Y. Zhang; Q. L. Williams; H. Jiang; L. Sheng
Evaporation has been an established technology in the metal finishing industry for many years. In this process, wastewaters containing reusable materials, such as copper, nickel, or chromium compounds are heated, producing a water vapor that is continuously removed and condensed....
Interannual variability in the surface energy budget and evaporation over a large southern inland water in the United States
NASA Astrophysics Data System (ADS)
Understanding how the surface energy budget and evaporation over inland waters respond to climate change and variability remains limited. Here we report 2 year measurements of the surface energy budget using the eddy covariance method over Ross Barnett Reservoir, Mississippi, USA, for 2008 and 2009. Annual mean sensible (H) and latent (LE) heat fluxes in 2008 were 9.5%, and 10.0% greater than in 2009, respectively. Most of the interannual variations in the surface energy fluxes and meteorological variables primarily occurred in the cool seasons from October to March, which was enhanced by frequent large wind events associated with cold front passages. These large wind events greatly promoted H and LE exchange and produced H and LE pulses that increased variations in H and LE between these two cool seasons. In the warm seasons from April to September, H and LE pulses were also present, which largely increased variations in LE and dampened those in H between the two warm seasons. The H and LE pulses contributed to approximately 50% of the annual H and 28% of the annual LE, although they only covered about 16% of the entire year. The interannual variations in H and LE pulses contributed to about 78% of the interannual variations in H and 40% of those in LE. Our results imply that the increased interannual variability in cold front activities as a result of climate change would amplify interannual variations in the evaporation and the surface energy exchange over inland waters in this region.
Zhang, Qianyu; Liu, Heping
Effects of Lily Pads on Evaporation
NASA Astrophysics Data System (ADS)
Measurements of evaporation from open water and water partially covered by lily pads have indicated that for the portion of the surface area covered by lily pads, evaporation is reduced to about 84% of that occurring from open water.
Cooley, Keith R.; Idso, Sherwood B.
Experimental investigations of water fluxes within the soil-vegetation-atmosphere system: Stable isotope mass-balance approach to partition evaporation and transpiration
NASA Astrophysics Data System (ADS)
Irrigated agriculture is the largest user of freshwater worldwide and the scale of irrigated agriculture can be so large that it can have dramatic effects on the water cycle and even alter regional climates. Therefore, it is vital to improve the water use efficiency of irrigated lands in order to address the sustainable use of water resources, the growing need for agricultural products, and the health of ecosystems. Environmental isotopes have unique attributes that make them particularly suitable for tracing hydrological pathways and quantifying hydrological fluxes within the soil-vegetation-atmosphere system. The stable isotopic composition of soil water is mainly controlled by precipitation or irrigation inputs and evaporative losses. Because transpiration does not fractionate soil water isotopes, it is possible to estimate the relative proportions of evaporation and transpiration using isotopic mass balance calculations. In this study experimental investigations, combining classical hydrometric measurements, tracer hydrological methods and a soil water model were applied to laboratory lysimeters to study the transpiration processes of Teff ( Eragrostis tea (Zucc.) Trotter). Teff is an annual bunch cereal and an important aliment in Ethiopia and Eritrea and it is also gaining popularity in other countries. To determine the soil water contents, sensors using a capacitance/frequency domain technology were installed at different depths and soil water samples for the isotope analysis were taken using pore water samplers. Water contents in different depths and water fluxes, such as percolation and evaporation were modeled using the HYDRUS-1D software package. By using an isotope mass balance model the total evaporation and the fractions between soil evaporation and transpiration could be determined. The water losses which were estimated using the isotope mass-balance approach are in good agreement with the measured values using classical hydrometric measurements. The proportion of water lost by transpiration (T/ET) during the study period was about 0.7 for the Teff covered laboratory set-up.
Wenninger, Jochen; Beza, Desta Tadesse; Uhlenbrook, Stefan
The role of pore clusters (wet patches) on evaporation dynamics from drying porous surfaces
NASA Astrophysics Data System (ADS)
Theoretical and experimental evidence suggests that the relationship between evaporative flux and porous surface water content is nonlinear (i.e., the reduction in flux is not proportional to reduction in water content). These nonlinearities are attributed to flux compensation due to interactions between evaporation from discrete pores whose spacing increases with surface drying and air boundary layer. Motivated by recent insights on the interplay between boundary layer thickness, pore size and spacing on surface fluxes, we examine effects of pore clustering on evaporation rates, addressing the question do pore clusters behave like large pores? Evaporation rate from clustered surfaces was determined theoretically using analytical and numerical methods, and results were compared to experiments. We exposed porous surfaces with different pore clusters arranged in different patterns to prescribed evaporative conditions in a wind tunnel with air velocities between 1 and 4 m/s (to vary the thickness of viscous boundary layer). The water saturated porous plates were covered by impervious plates with fixed evaporating area distributed between 1 to 169 clusters. The evaporation rate (relative to free water evaporation) decreased with increasing cluster size ("big pores") and decreasing boundary layer thickness. Experimental findings suggest that clustering reduces evaporation rates relative to distributed pores, however this effect is limited to cluster sizes of about 10 mm (of the order of maximum boundary layer thickness studied). The results were in agreement with model predictions that yield a universal scaling function for estimation of evaporation reduction by pore clustering for different boundary conditions.
Or, Dani; Breitenstein, Daniel; Lehmann, Peter
Time-Resolved Evaporation Rate of Attoliter Glycerine Drops Using On-Chip CMOS Mass Sensors Based on Resonant Silicon Micro Cantilevers
The time-resolved evaporation rate of small glycerine drops (in the attoliter range) is determined by means of a mass sensor based on a resonant cantilever integrated in a CMOS chip. The cantilever is fabricated on crystalline silicon, using silicon-on-insulator (SOI) substrates for the integration of the CMOS-MEMS. Glycerine drops are deposited at the free end of the cantilever. The high
Maria Villarroya GaudÆ; Gabriel Abadal; Jaume Verd; Jordi Teva; Francesc PÕrez-Murano; Eduardo Figueras Costa; Josep Montserrat; Arantxa Uranga; Jaume Esteve; Nºria Barniol
Quantitative Microbiological Analysis of Bacterial Community Shifts in a High-Rate Anaerobic Bioreactor Treating Sulfite Evaporator Condensate
The bacterial population of a high-rate, anaerobic, fixed-bed loop reactor treating sulfite evaporator condensate from the pulp industry was studied over a 14-month period. This period was divided into seven cycles that included a startup at the beginning of each cycle. Some 82% of the total biomass was immobilized on and between the porous glass rings filling the reactor. The range of the total number of microorganisms in these biofilms was 2 æ 109 to 7 æ 109 cells per ml. Enumeration and characterization by microbiological methods and by phase-contrast, epifluorescence, and electron microscopy showed that the samples consisted mainly of the following methanogens: a Methanobacterium sp., a Methanosarcina sp., a Methanobrevibacter sp., and a Methanothrix sp., as well as furfural-degrading sulfate-reducing bacteria resembling Desulfovibrio furfuralis. Viable counts of hydrogenotrophic methanogens were relatively stable (mostly within the range of 3.2 æ 108 to 7.5 æ 108 cells per ml), but Methanobrevibacter cells increased from <5 to 30% of the total hydrogenotrophic count after transfer of the fixed bed into a second reactor vessel. Acetotrophic methanogens reached their highest numbers of 1.3 æ 108 to 2.6 æ 108 cells per ml in the last fermentation cycles. They showed a morphological shift from sarcinalike packets in early samples to single coccoid forms in later phases of the fermentation. Furfural-degrading sulfate reducers reached counts of 1 æ 107 to 5.8 æ 107 cells per ml. The distribution of the chief metabolic groups between free fluid and biofilms was analyzed in the fifth fermentation cycle: 4.5 times more furfural degraders were found in the free fluid than in the biofilms. In contrast, 5.8 times more acetotrophic and 16.6 times more hydrogenotrophic methanogens were found in the biofilms than in the free liquid. The data concerning time shifts of morphotypes among the trophic groups of methanogens corroborated the trends observed by using immunological assays on the same samples. Images
Ney, U.; Macario, A. J. L.; de Macario, E. Conway; Aivasidis, A.; Schoberth, S. M.; Sahm, H.
Quantitative microbiological analysis of bacterial community shifts in a high-rate anaerobic bioreactor treating sulfite evaporator condensate.
The bacterial population of a high-rate, anaerobic, fixed-bed loop reactor treating sulfite evaporator condensate from the pulp industry was studied over a 14-month period. This period was divided into seven cycles that included a startup at the beginning of each cycle. Some 82% of the total biomass was immobilized on and between the porous glass rings filling the reactor. The range of the total number of microorganisms in these biofilms was 2 x 10 to 7 x 10 cells per ml. Enumeration and characterization by microbiological methods and by phase-contrast, epifluorescence, and electron microscopy showed that the samples consisted mainly of the following methanogens: a Methanobacterium sp., a Methanosarcina sp., a Methanobrevibacter sp., and a Methanothrix sp., as well as furfural-degrading sulfate-reducing bacteria resembling Desulfovibrio furfuralis. Viable counts of hydrogenotrophic methanogens were relatively stable (mostly within the range of 3.2 x 10 to 7.5 x 10 cells per ml), but Methanobrevibacter cells increased from <5 to 30% of the total hydrogenotrophic count after transfer of the fixed bed into a second reactor vessel. Acetotrophic methanogens reached their highest numbers of 1.3 x 10 to 2.6 x 10 cells per ml in the last fermentation cycles. They showed a morphological shift from sarcinalike packets in early samples to single coccoid forms in later phases of the fermentation. Furfural-degrading sulfate reducers reached counts of 1 x 10 to 5.8 x 10 cells per ml. The distribution of the chief metabolic groups between free fluid and biofilms was analyzed in the fifth fermentation cycle: 4.5 times more furfural degraders were found in the free fluid than in the biofilms. In contrast, 5.8 times more acetotrophic and 16.6 times more hydrogenotrophic methanogens were found in the biofilms than in the free liquid. The data concerning time shifts of morphotypes among the trophic groups of methanogens corroborated the trends observed by using immunological assays on the same samples. PMID:16348253
Ney, U; Macario, A J; Conway de Macario, E; Aivasidis, A; Schoberth, S M; Sahm, H
Water-quality and sediment-chemistry data of drain water and evaporation ponds from Tulare Lake Drainage District, Kings County, California, March 1985 to March 1986
Trace element and major ion concentrations were measured in water samples collected monthly between March 1985 and March 1986 at the MD-1 pumping station at the Tulare Lake Drainage District evaporation ponds, Kings County, California. Samples were analyzed for selected pesticides several times during the year. Salinity, as measured by specific conductance, ranged from 11,500 to 37,600 microsiemens/centimeter; total recoverable boron ranged from 4,000 to 16,000 micrg/L; and total recoverable molybdenum ranged from 630 to 2,600 microg/L. Median concentrations of total arsenic and total selenium were 97 and 2 microg/L. Atrazine, prometone, propazine, and simazine were the only pesticides detected in water samples collected at the MD-1 pumping station. Major ions, trace elements, and selected pesticides also were analyzed in water and bottom-sediment samples from five of the southern evaporation ponds at Tulare Lake Drainage District. The water samples increased in specific conductance and concentrations of total arsenic, total recoverable boron and total recoverable molybdenum going from pond 1 to pond 10, respectively. Median concentrations of total arsenic and total selenium in the bottom sediments were 4.0 and 0.9 microg/g, respectively. 6 refs., 2 figs., 12 tabs.
Fujii, R.
Evaporative roof cooling system
An evaporative roof cooling system is described for placement upon a roof surface exposed to relatively high levels of solar radiation causing high under roof temperatures and comprising: (a) water distribution mist\\/spray nozzles positioned on the roof surface for supplying substantially uniform mist\\/sprays of water to lay down a substantially uniform thin film of water on the roof surface; (b)
Evaporation and canopy characteristics of coniferous forests and grasslands
Canopy-scale evaporation rate (E) and derived surface and aerodynamic conductances for the transfer of water vapour (gs and ga, respectively) are reviewed for coniferous forests and grasslands. Despite the extremes of canopy structure, the two vegetation types have similar maximum hourly evaporation rates (Emax) and maximum surface conductances (gsmax) (medians = 0.46 mm h-1 and 22 mm s-1). However, on
F. M. Kelliher; R. Leuning; E. D. Schulze
Spacesuit Evaporator-Absorber-Radiator (SEAR)
NASA Technical Reports Server (NTRS)
For decades advanced spacesuit developers have pursued a regenerable, robust non-venting system for heat rejection. Toward this end, this paper investigates linking together two previously developed technologies, namely NASA's Spacesuit Water Membrane Evaporator (SWME), and Creare's lithium chloride Heat Pump Radiator (HPR). Heat from a liquid cooled garment is transported to SWME that provides cooling through evaporation. The SEAR is evacuated at the onset of operations and thereafter, the water vapor absorption rate of the HPR maintains a low pressure environment for the SWME to evaporate effectively. This water vapor captured by solid LiCl in the HPR with a high enthalpy of absorption, results in sufficient temperature lift to reject most of the heat to space by radiation. After the sortie, the HPR would be heated up in a regenerator to drive off and recover the absorbed evaporant. A one-fourth scale prototype was built and tested in vacuum conditions at a sink temperature of 250 K. The HPR was able to stably reject 60 W over a 7-hour period. A conceptual design of a full-scale radiator is proposed. Excess heat rejection above 240 W would be accomplished through venting of the evaporant. Loop closure rates were predicted for various exploration environment scenarios.
Bue, Grant C.; Hodgson, Ed; Izenso, Mike; Chan, Weibo; Cupples, Scott
NASA Technical Reports Server (NTRS)
Evaporation is the consequence of slow plasma heating near the tops of streamers where the plasma is only weakly contained by the magnetic field. The form it takes is the slow opening of field lines at the top of the streamer and transient formation of new solar wind. It was discovered in polytropic model calculations, where due to the absence of other energy loss mechanisms in magnetostatic streamers, its ultimate endpoint is the complete evaporation of the streamer. This takes, for plausible heating rates, weeks to months in these models. Of course streamers do not behave this way, for more than one reason. One is that there are losses due to thermal conduction to the base of the streamer and radiation from the transition region. Another is that streamer heating must have a characteristic time constant and depend on the ambient physical conditions. We use our global Magnetohydrodynamics (MHD) model with thermal conduction to examine a few examples of the effect of changing the heating scale height and of making ad hoc choices for how the heating depends on ambient conditions. At the same time, we apply and extend the analytic model of streamers, which showed that streamers will be unable to contain plasma for temperatures near the cusp greater than about 2xl0(exp 6) K. Slow solar wind is observed to come from streamers through transient releases. A scenario for this that is consistent with the above physical process is that heating increases the near-cusp temperature until field lines there are forced open. The subsequent evacuation of the flux tubes by the newly forming slow wind decreases the temperature and heating until the flux tubes are able to reclose. Then, over a longer time scale, heating begins to again refill the flux tubes with plasma and increase the temperature until the cycle repeats itself. The calculations we report here are first steps towards quantitative evaluation of this scenario.
Suess, Steven T.; Wang, A. H.; Wu, Shi T.; Nerney, S.
Temperature field beneath evaporating surface resolved by infrared thermography
NASA Astrophysics Data System (ADS)
Land-atmosphere mass exchange is intimately linked with radiation and energy balance of terrestrial surfaces. Surface evaporation is a key hydrologic flux affected by interplay between water supply from below, surface energy input, and exchange across air boundary layer. The thermal signature depression of an evaporating surface is proportional to the magnitude of the flux which makes remote monitoring of fluxes from heterogeneous surface feasible using advanced Infrared thermography (IRT). Inversion of IRT data to evaporation fluxes relies on knowledge of thickness of thermal depression beneath evaporation zone. We develop a mathematical model for 3D temperature field induced by evaporation from a patchy evaporative surface and compare the results with direct IRT measurements of cross section beneath an evaporating surface. Results yield a universal description of evaporative temperature depression that could serve for predicting spatial and temporal evaporation rates distributions based on IRT data. The thickness of thermo-evaporative zone is typically in the range of 10-40 mm for a wide range of soil properties and fluxes.
Shahraeeni, Ebrahim; Or, Dani
Precipitate formation in a porous rock through evaporation of saline water
NASA Astrophysics Data System (ADS)
We examine the motion of a high-pressure aqueous solution, through a low-permeability fracture, towards a low-pressure well. As the liquid decompresses in the fractures it expands, and for sufficiently high initial temperature the liquid reaches the boiling point. A vaporization front then develops, so that vapour issues from the well. As the fluid evaporates near the well, the salt concentration of the residual fluid increases. If the salt concentration increases beyond the saturation limit, then the evaporation leads to precipitation of salt in the fracture. We find a new family of self-similar solutions to describe the boiling and precipitation in a single idealized fracture, which at long times remains approximately isothermal owing to the cross-fracture heat transfer. The solutions describe the mass of salt that precipitates as a function of the initial salt concentration, the reservoir temperature and pressure, and the well pressure. In fact, this family of self-similar solutions is multi-valued: we identify a liquid-advection-dominated regime, in which the boiling front advances slowly and the fracture porosity decreases significantly, and a boiling-dominated regime, in which the boiling front advances more rapidly, and less precipitate forms at each point in the fracture. As the pressure difference between the well and the far field reservoir increases, these solutions converge, and eventually coincide. Beyond this critical point, there is no similarity solution, since the advective flux of salt from the far-field would produce more precipitate than can be taken up in the fracture adjacent to the boiling front. Instead, the rock will become fully sealed through precipitation, thereby suppressing flow into the well. We extend the model to show that an analogous result also occurs within an extensive porous layer. However in that case, the system is not isothermal; instead, the heat flux is supplied in the direction of flow, while the cross-flow heat flux is small. We discuss the relevance of the work to the natural venting of steam in high-temperature geothermal systems.
Tsypkin, George G.; Woods, Andrew W.
Formation of Soil Water Repellency by Laboratory Burning and Its Effect on Soil Evaporation
Fire-induced soil water repellency can vary with burning conditions, and may lead to significant changes in soil hydraulic properties. However, isolation of the effects of soil water repellency from other factors is difficult, particularly under field conditions. This study was conducted to (i) investigate the effects of burning using different plant leaf materials and (ii) of different burning conditions on
Sujung Ahn; Sangjun Im
Absorptionevaporation kinetics of water vapour on highly hygroscopic powder: Case of ammonium nitrate
The conditioning of industrial powders or granulates is strongly dependent on their behaviour with respect to the atmospheric humidity. Adsorption and capillary condensation of water vapour at the points of contact between particles change the rheology of the powder and may result in the formation of aggregates with high mechanical resistance. In some cases water vapour causes partial dissolution of
L. Komunjer; C. Affolter
NASA Technical Reports Server (NTRS)
A flash evaporator heat rejection system representative of that proposed for the space shuttle orbiter underwent extensive system testing at the NASA Johnson Space Center (JSC) to determine its operational suitability and to establish system performance/operational characteristics for use in the shuttle system. During the tests the evaporator system demonstrated its suitability to meet the shuttle requirements by: (1) efficient operation with 90 to 95% water evaporation efficiency, (2) control of outlet temperature to 40 + or - 2 F for partial heat load operation, (3) stability of control system for rapid changes in Freon inlet temperature, and (4) repeated dormant-to-active device operation without any startup procedures.
Dietz, J. B.
Experiments on Effect of Water Injection Rate on Imbibition Rate in Fractured Reservoirs
A relationship has been established in the laboratory between rate of water injection into a simulated fracture- matrix type reservoir model and rate of imbibition. In a series of experiments involving linear countercurrent flow, it was discovered that the higher the water injection rate, the higher the imbibition rate and the greater the indicated ultimate oil recovery. Repeated runs, made
Robert Mannon; George Chilingar
Vacuum Evaporation of Pure Metals
NASA Astrophysics Data System (ADS)
Theories on the evaporation of pure substances are reviewed and applied to study vacuum evaporation of pure metals. It is shown that there is good agreement between different theories for weak evaporation, whereas there are differences under intensive evaporation conditions. For weak evaporation, the evaporation coefficient in Hertz-Knudsen equation is 1.66. Vapor velocity as a function of the pressure is calculated applying several theories. If a condensing surface is less than one collision length from the evaporating surface, the Hertz-Knudsen equation applies. For a case where the condensing surface is not close to the evaporating surface, a pressure criterion for intensive evaporation is introduced, called the effective vacuum pressure, p eff. It is a fraction of the vapor pressure of the pure metal. The vacuum evaporation rate should not be affected by pressure changes below p eff, so that in lower pressures below p eff, the evaporation flux is constant and equal to a fraction of the maximum evaporation flux given by Hertz-Knudsen equation as 0.844 dot{n}_{Max } . Experimental data on the evaporation of liquid and solid metals are included.
Safarian, Jafar; Engh, Thorvald A.
NASA Astrophysics Data System (ADS)
During the 1974 growing season, a micrometeorological measurement program was conducted at Simcoe, Ontario, Canada to study atmospheric and surface control on hourly and daytime evaporation from soybeans. For days when leaf area index exceeded unity, daytime evaporation varied linearly with volumetric soil moisture content when the latter was less than 0.12. At larger volumetric soil moisture contents, evaporation proceeded at a potential rate. The data confirm the usefulness of the Priestley and Taylor model with a proportionality constant of 1.26.
Bailey, W. G.; Davies, J. A.
Encapsulation of water-soluble drugs by a modified solvent evaporation method. I. Effect of process and formulation variables on drug entrapment.
Pseudoephedrine HCl, a highly water-soluble drug, was entrapped within poly (methyl methacrylate) microspheres by a water/oil/water emulsification-solvent evaporation method. An aqueous drug solution was emulsified into a solution of the polymer in methylene chloride, followed by emulsification of this primary emulsion into an external aqueous phase to form a water/oil/water emulsion. The middle organic phase separated the internal drug-containing aqueous phase from the continuous phase. Microspheres were formed after solvent evaporation and polymer precipitation. The drug content of the microspheres increased with increasing theoretical drug loading, increasing amounts of organic solvent, polymer and polymeric stabilizer, and decreased with increasing stirring time, increasing pH of the continuous phase and increased volume of the internal and external aqueous phase. PMID:2384837
Alex, R; Bodmeier, R
Differences in evaporation between a floating pan and class a pan on land
Research was conducted to develop a method for obtaining floating pan evaporation rates in a small (less than 10,000 m2) wetland, lagoon, or pond. Floating pan and land pan evaporation data were collected from March 1 to August 31, 2005, at a small natural wetland located in the alluvium of the Canadian River near Norman, Oklahoma, at the U.S. Geological Survey Norman Landfill Toxic Substances Hydrology Research Site. Floating pan evaporation rates were compared with evaporation rates from a nearby standard Class A evaporation pan on land. Floating pan evaporation rates were significantly less than land pan evaporation rates for the entire period and on a monthly basis. Results indicated that the use of a floating evaporation pan in a small free-water surface better simulates actual physical conditions on the water surface that control evaporation. Floating pan to land pan ratios were 0.82 for March, 0.87 for April, 0.85 for May, 0.85 for June, 0.79 for July, and 0.69 for August. ?? 2008 American Water Resources Association.
Masoner, J. R.; Stannard, D. I.; Christenson, S. C.
ENSO and multi-decadal 'trends' in continental evaporation
NASA Astrophysics Data System (ADS)
While the hydrological cycle is expected to intensify in response to global warming, little unequivocal evidence of such an acceleration has yet been found on a global scale. This holds in particular for terrestrial evaporation, the crucial return flow of water from continents to atmosphere. Counterintuitively, the few studies that have applied satellite and in situ observations to evaluate multi-decadal trends have uncovered prolonged declines in global average continental evaporation. A priori, these reductions contradict the expectations of an intensifying water cycle. Up to date, the question of whether these declines in evaporation reflect a more permanent feature of global warming or they result from internal climate variability, has been left unanswered. Here, we attempt to answer that question by analyzing global satellite-based datasets of evaporative fluxes, soil moisture and NDVI. Our findings reveal that the reported recent declines in global continental evaporation are not a consequence of a persistent reorganization of the water cycle, but a consequence of internal climate variability. During El Niþo, limitations in the supply of moisture in central Australia, southern Africa and eastern South America cause vegetation water-stress and reduced terrestrial evaporation. These regional terrestrial evaporation declines are so pronounced that that determine the total annual volumes of water vapour from continental land surfaces into the atmosphere. Meanwhile, in northern latitudes (where the effects of ENSO are weaker) continental evaporation has raised since the '80s at rates that are consistent with the expectations calculated from air temperature trends. Future changes in continental evaporation will be determined by the response of ENSO to changes in global radiative forcing, which still remains highly uncertain. Opportunely, the increasing timespan of satellite observation records will enable a more significant assessment of the trends in global evaporation in coming years.
Miralles, Diego; Teuling, Ryan; van den Berg, Martinus; Gash, John; Parinussa, Robert; De Jeu, Richard; Beck, Hylke; Holmes, Thomas; JimÕnez, Carlos; Verhoest, Niko; Dorigo, Wouter; Dolman, Han
Nationwide Study of High Municipal Water Rates.
National Technical Information Service (NTIS)
The study identifies the largest possible number of public water supplies (population greater than 1,000) that price delivered water at $7.50 per first 10,000 gallons or greater. This price was assumed to be a threshold value where desalination can be con...
W. Q. Sorsby E. F. Spitzer
An evaporation system for aqueous radioactive waste uses standard 30 and 55 gallon drums. Waste solutions form cascading water sprays as they pass over a number of trays arranged in a vertical stack within a drum. Hot dry air is circulated radially of the drum through the water sprays thereby removing water vapor. The system is encased in concrete to prevent exposure to radioactivity. The use of standard 30 and 55 gallon drums permits an inexpensive compact modular design that is readily disposable, thus eliminating maintenance and radiation build-up problems encountered with conventional evaporation systems.
Black, Roger L. (Idaho Falls, ID)
Determining the virtual surface in the thermal evaporation process of magnesium fluoride from a tungsten boat for different deposition rates, to be used in precision optical components
NASA Astrophysics Data System (ADS)
Vacuum thermal evaporation has, for some time now, been the principal method for the deposition of thin films, given, among other aspects, its simplicity, flexibility, and relatively low cost. Therefore, the development of models attempting to predict the deposition patterns of given thin film materials in different locations of a vacuum evaporation chamber are arguably important. With this in mind, we have designed one of such models for the thermal evaporation process of magnesium fluoride (MgF2), a common material used in optical thin films, originating from a tungsten boat source. For this we took several deposition samples in glass slide substrates at different locations in the vacuum chamber, considering as independent variables the mean deposition rate, and the axial and vertical distances of the source to the substrate. After a careful analysis by matrix method from the spectral transmittance data of the samples, while providing as output data the spectral transmittance, as well as the physical thickness of the films, both as functions of the aforementioned variables, the virtual surface of the source was determined.
Tejada Esteves, A.; GÃlvez de la Puente, G.
Water vapour transmission rates in burns and chronic leg ulcers: influence of wound dressings and comparison with in vitro evaluation.
One of the main functions of wound dressings is to control water vapour transmission rate (WVTR) from wounded skin. In this paper, the influence of hydrocolloid, knitted viscose and gauze dressings was evaluated through in vivo measurement of WVTR in burns and chronic leg ulcers utilizing an evaporimeter. The results suggest that the evaporative water vapour loss from exposed skin wounds depends mainly on the wound depth, and that chronic leg ulcers have the same level of the WVTR as full thickness burns. Compared with the knitted viscose and gauze dressings, hydrocolloid dressing has a greater effect on reducing evaporative water loss, with WVTR being 20-30% of that of exposed wounds under the conditions used in this study. This result is in agreement with that obtained in an in vitro evaluation. PMID:8830962
Wu, P; Nelson, E A; Reid, W H; Ruckley, C V; Gaylor, J D
Evaporation of water and uptake of HCl and HBr through hexanol films at the surface of supercooled sulfuric acid.
Vacuum evaporation and molecular beam scattering experiments have been used to monitor the loss of water and dissolution of HCl and HBr in deuterated sulfuric acid at 213 K containing 0 to 100 mM hexanol. The addition of 1-hexanol to the acid creates a surface film of hexyl species. This film becomes more compact with decreasing acidity, ranging from approximately 62% to approximately 68% of maximum packing on 68 to 56 wt % D(2)SO(4), respectively. D(2)O evaporation from 68 wt % acid remains unaltered by the hexyl film, where it is most porous, but is impeded by approximately 20% from 56 and 60 wt % acid. H --> D exchange experiments further indicate that the hexyl film on 68 wt % acid enhances conversion of HCl and HBr into DCl and DBr, which is interpreted as an increase in HCl and HBr entry into the bulk acid. For this permeable hexyl film, the hydroxyl groups of surface hexanol molecules may assist uptake by providing extra sites for HCl and HBr hydrogen bonding and dissociation. In contrast, HCl --> DCl exchange in 60 wt % D(2)SO(4) at first rises with hexyl surface coverage but then drops back to the bare acid value as the hexyl species pack more tightly. HCl entry is actually diminished by the hexyl film on 56 wt % acid, where the film is most compact. These experiments reveal a transition from a porous hexanol film on 68 wt % sulfuric acid that enhances HCl and HBr uptake to one on 56 wt % acid that slightly impedes HCl and D(2)O transport. PMID:16774202
Glass, Samuel V; Park, Seong-Chan; Nathanson, Gilbert M
NEG (non evaporable getter) pumps for organic compounds and water removal in EUVL tools
One of present EUVL challenges is to reduce as much as possible the organic compounds and water partial pressures during the lithographic process. These gases can in fact interact with sensitive surfaces and, in the presence of EUV radiation, decompose to generate carbon-based films and oxides, which are detrimental to the optics, reducing its performance, lifetime and significantly increasing the
A. Conte; P. Manini; S. Raimondi
Evaporative Cooling by Mist and Sprinkle Irrigation and Conserving Water in Vegetable Irrigation in Arizona.
National Technical Information Service (NTIS)
Temperature, yield response and water-use efficiency are given for eight cultivars of peppers, two of tomatoes and one of potatoes irrigated by dead-level furrow, regular and intermittent rotating sprinkling and micromist with bare soil, with black plasti...
A. J. Pratt F. C. Harper
Preferred temperature correlates with evaporative water loss in hylid frogs from northern Australia.
We measured temperature preferences of 12 species of hylid frogs (Litoria and Cyclorana) from northern Australia in a laboratory thermal gradient. These species represented a range of ecological habitat use (aquatic, terrestrial, arboreal), adult body size (0.5-60 g), and cutaneous resistance to water loss (Rc=0.6-63.1 s cm-1). We found significant differences among species in selected skin temperature and gradient temperature but not in the variances of these measures (an index of precision of temperature selection). The species' differences correlated significantly with cutaneous resistance to water loss, with more-resistant frogs selecting higher skin and substrate temperatures in the thermal gradient, even after phylogenetic relationships are taken into account. Because cutaneous resistance to water loss also correlates with ecological habit (arboreal>terrestrial>aquatic), we suggest that their higher resistance to water loss allows arboreal and terrestrial species better ability to tolerate high temperatures, where growth or locomotory speed may be higher, without the associated risk of desiccation. PMID:16082612
Tracy, Christopher R; Christian, Keith A
Incorporated evaporative condenser
The incorporated evaporative condenser developed in this work comprises of a system of fins, basin of water condensates, circuit pump and system of drop cloud via spraying. In the whole provision a system of drop collector is also included for the minimisation of water escapes now essential for the operation of system. Actually, the present work aims on the development
Michalis Gr. Vrachopoulos; Andronikos E. Filios; Georgios T. Kotsiovelos; Eleftherios D. Kravvaritis
Experimental evaluation of a breadboard heat and product-water removal system for a space-power fuel cell designed with static water removal and evaporative cooling
NASA Technical Reports Server (NTRS)
A test program was conducted to evaluate the design of a heat and product-water removal system to be used with fuel cell having static water removal and evaporative cooling. The program, which was conducted on a breadboard version of the system, provided a general assessment of the design in terms of operational integrity and transient stability. This assessment showed that, on the whole, the concept appears to be inherently sound but that in refining this design, several facets will require additional study. These involve interactions between pressure regulators in the pumping loop that occur when they are not correctly matched and the question of whether an ejector is necessary in the system.
Hagedorn, N. H.; Prokipius, P. R.
Evaporation-induced cavitation in nanofluidic channels.
Cavitation, known as the formation of vapor bubbles when liquids are under tension, is of great interest both in condensed matter science as well as in diverse applications such as botany, hydraulic engineering, and medicine. Although widely studied in bulk and microscale-confined liquids, cavitation in the nanoscale is generally believed to be energetically unfavorable and has never been experimentally demonstrated. Here we report evaporation-induced cavitation in water-filled hydrophilic nanochannels under enormous negative pressures up to -7 MPa. As opposed to receding menisci observed in microchannel evaporation, the menisci in nanochannels are pinned at the entrance while vapor bubbles form and expand inside. Evaporation in the channels is found to be aided by advective liquid transport, which leads to an evaporation rate that is an order of magnitude higher than that governed by Fickian vapor diffusion in macro- and microscale evaporation. The vapor bubbles also exhibit unusual motion as well as translational stability and symmetry, which occur because of a balance between two competing mass fluxes driven by thermocapillarity and evaporation. Our studies expand our understanding of cavitation and provide new insights for phase-change phenomena at the nanoscale. PMID:22343530
Duan, Chuanhua; Karnik, Rohit; Lu, Ming-Chang; Majumdar, Arun
Evaporative Concentration of 100x J13 Ground Water at 60% Relative Humidity and 90C
In these experiments we studied the behavior of a synthetic concentrated J13 solution as it comes in contact with a Ni-Cr-Mo-alloy selected for waste canisters in the designated high-level nuclear-waste repository at Yucca Mountain, Nevada. Concentrated synthetic J13 solution was allowed to drip slowly onto heated test specimens (90 C, 60% relative humidity) where the water moved down the surface
K Staggs; Maureen Alai; P Hailey; S A Carroll; M Sutton; Q A Nguyen
Analysis of the Effect Exerted by the Initial Temperature of Atomized Water on the Integral Characteristics of Its Evaporation During Motion Through the Zone of "Hot" Gases
NASA Astrophysics Data System (ADS)
We have carried out an experimental investigation of the integral characteristics of atomized water evaporation during its motion through high-temperature combustion products using a flame of fixed height as an example and a high-response measurement system of two-phase vapor-liquid flow diagnostics. The scales of the influence of the initial liquid temperature on the intensity of phase transition in the region of the combustion zone at different atomization parameters have been established. Approximate relations for the dependences of the evaporated fraction of atomized liquid on its initial temperature and droplet size have been formulated.
Volkov, R. S.; Kuznetsov, G. V.; Strizhak, P. A.
Effect of argon gas flow rate on properties of film electrodes prepared by thermal vacuum evaporation from synthesized Cu2SnSe3 source
NASA Astrophysics Data System (ADS)
This work describes a new technique to enhance photoresponse of metal chalcogenide-based semiconductor film electrodes deposited by thermal vacuum evaporation under argon gas flow from synthesized Cu2SnSe3 sources. SnSe formation with Cu-doped was obtained under higher argon gas flow rate (VA = 25 cm3/min). Higher value of photoresponse was observed for films deposited under VA = 25 cm3/min which was 9.1%. This finding indicates that Cu atoms inside the SnSe film were important to increase carrier concentrations that promote higher photoresponse.
Sabli, Nordin; Talib, Zainal Abidin; Yunus, Wan Mahmood Mat; Zainal, Zulkarnain; Hilal, Hikmat S.; Fujii, Masatoshi
A Scanning Electron and Atomic Force Microscopy Study of the Surface Morphology and Composition of CsI Films as Affected by Evaporation Rate and Humid-Air Exposure
Evaporation rate and subsequent exposure to humid air affect the surface morphology and composition of cesium iodide (CsI) films and, in turn, their photoemissive efficiency when used as photocathodes. The surface morphology and elemental composition of 300-nm-thick CsI films grown at two different rates (1 nm\\/s and 0.04 nm\\/s), both freshly evaporated and after 24-h exposure to humid air were
Giorgio S. Senesi; Mariangela A. Nitti; Antonio Valentini
Nanoparticle-mediated evaporation at liquid-vapor interface
NASA Astrophysics Data System (ADS)
Solution-processed electronic materials for printed electronics frequently take the form of nano-colloidal dispersions of inorganic materials. In standard printing processes, evaporation of the solvent plays a critical role in the deposition of the dispersed nanoparticles. To date, there is no quantitative study of the effects of particles on the interface on the evaporative flux. We provide experimental evidence that nanoparticles present at the interface attenuate evaporation relative to the pure solvent case. To avoid the effects of the complex interfacial shapes attending patterned deposition by printing, we regularize the interface by conducting evaporation experiments in circular-bore cylindrical glass crucibles. The crucible was initially charged with water, and the silica particles were placed on the interface using a modified Langmuir-Blodgett technique. Evaporation rates were measured as a function of surface coverage, contact angle, and surface properties of the nanoparticles.
Fan, Wenxiong
Seasonal performance rating of heat pump water heaters
Seasonal performance evaluation methods for water heaters are reviewed and an experimental method for rating air-source heat pump water heaters is presented. The rating method is based on measured heat pump performance during heat-up operation of particular products rather than a generic simulation model of heat pump performance. The measured performance is used in a correlation model of the heat
G. L. Morrison; T. Anderson; M. Behnia
Evaporative water loss and oxygen uptake in two casque-headed tree frogs, Aparasphenodon brunoi and Corythomantis greeningi (Anura, Hylidae).
Evaporative water loss (EWL) and oxygen uptake (Vo2) was measured in two species of tree frogs with cranial co-ossification, Aparasphenodon brunoi and Corythomantis greeningi. Both species use their head to seal the entrance of bromeliads, tree holes or rocky crevices used as shelters. EWL was significantly reduced in sheltered individuals of both species as compared with those exposed nude to desiccation. EWL per unit area through the head surface was significantly lower than the body skin for A. brunoi but not for C. greeningi, EWL per unit surface area through C. greeningi body skin was about 50% that of A. brunoi, indicating a less permeable skin in the former species. The relationship between cranial coossification and EWL is discussed. Vo2 in A. brunoi was comparable with other anurans of similar size, whereas in C. greeningi, it was lower than predicted from body mass. Moreover, Vo2 in C. greeningi showed less sensitivity to temperature increase than in A. brunoi. C. greeningi occurs in a drier environment than A. brunoi, and this appears to be reflected in their EWL and Vo2 characteristics. PMID:9406443
de Andrade, D V; Abe, A S
Evaporation from groundwater discharge playas, Estancia Basin, central New Mexico
Bowen ratio meteorological stations have been deployed to measure rates of evaporation from groundwater discharge playas and from an adjacent vegetated bench in the Estancia Basin, in central New Mexico. The playas are remnants of late Pleistocene pluvial Lake Estancia and are discharge areas for groundwater originating as precipitation in the adjacent Manzano Mts. They also accumulate water during local precipitation events. Evaporation is calculated from measured values of net radiation, soil heat flux, atmospheric temperature, and relative humidity. Evaporation rates are strongly dependent on the presence or absence of standing water in the playas, with rates increasing more than 600% after individual rainstorms. Evaporation at site E-12, in the southeastern part of the playa Complex, measured 74 cm over a yearlong period from mid-1997 through mid-1998. This value compares favorably to earlier estimates from northern Estancia playas, but is nearly three times greater than evaporation at a similar playa in western Utah. Differences in geographical position, salt crust composition, and physical properties may explain some of the difference in evaporation rates in these two geographic regions.
Menking, Kirsten M.; Anderson, Roger Y.; Brunsell, Nathaniel A.; Allen, Bruce D.; Ellwein, Amy L.; Loveland, Thomas A.; Hostetler, Steven W.
Evaporation for Lithium Bromide Aqueous Solution in a Falling Film Heater under Reduced Pressures
NASA Astrophysics Data System (ADS)
Experiments on evaporation for water and lithium bromide (LiBr) aqueous solution were made in a externally heated wetted-wall column under reduced pressures. For water, evaporation rate increased slightly as feed rate decreased. The heat transfer coefficients of falling film agreed with those for filmwise condensation. For LiBr solution, evaporation rate decreased and outlet temperature of LiBr solution increased as feed rate decreased. The equations of continuity, diffusion and energy which assume that only water moves to the surface and LiBr doesn't move through falling film of LiBr solution were solved numerically. Calculated values of evaporation rate and outlet temperature of solution agreed with experimental results. The results of this work were compared with pool boiling data reported previously, and it was shown that falling film heater is superior to pool boiling heater concerning heat transfer.
Matsuda, Akira; Ide, Tetsuo; Yukino, Keiji
Parameterizations for sulfuric acid\\/water nucleation rates
We present parametrized equations for calculation of sulfuric acid\\/water critical nucleus compositions and homogeneous nucleation rates. The parameterizations are in agreement with the thermodynamically consistent version of classical binary homogeneous nucleation theory [Wilemski, 1984] incorporating the hydration effect. The new parameterizations produce nucleation rates that differ by several orders of magnitude from the rates predicted by other parameterizations available in
Markku Kulmala; Ari Laaksonen; Liisa Pirjola
The hydrogen and oxygen isotopic composition of precipitation, evaporated mine water, and river water in Montana, USA
The isotopic composition of 42 samples of rain and snow collected in 2004 were used to construct a local meteoric water line (LMWL) for Butte, Montana. The derived equation (deltaD = 7.31delta18O - 7.5, r2 = 0.987), represents one of the first published LMWLs based on direct precipitation for any location in the northern Rocky Mountains. Samples of underground and
Christopher H. Gammons; Simon R. Poulson; Damon A. Pellicori; Pamela J. Reed; Amber J. Roesler; Eugene M. Petrescu
NSDL National Science Digital Library
Explore the concept of evaporative cooling through a hands-on experiment. Use a wet cloth and fan to model an air-conditioner and use temperature and relative humidity sensors to collect data. Then digitally plot the data using graphs in the activity. In an optional extension, make your own modifications to improve the cooler's efficiency.
Consortium, The C.
Droplet evaporation on heated hydrophobic and superhydrophobic surfaces.
The evaporation characteristics of sessile water droplets on smooth hydrophobic and structured superhydrophobic heated surfaces are experimentally investigated. Droplets placed on the hierarchical superhydrophobic surface subtend a very high contact angle (?160¯) and demonstrate low roll-off angle (?1¯), while the hydrophobic substrate supports corresponding values of 120¯ and ?10¯. The substrates are heated to different constant temperatures in the range of 40-60?¯C, which causes the droplet to evaporate much faster than in the case of natural evaporation without heating. The geometric parameters of the droplet, such as contact angle, contact radius, and volume evolution over time, are experimentally tracked. The droplets are observed to evaporate primarily in a constant-contact-angle mode where the contact line slides along the surface. The measurements are compared with predictions from a model based on diffusion of vapor into the ambient that assumes isothermal conditions. This vapor-diffusion-only model captures the qualitative evaporation characteristics on both test substrates, but reasonable quantitative agreement is achieved only for the hydrophobic surface. The superhydrophobic surface demonstrates significant deviation between the measured evaporation rate and that obtained using the vapor-diffusion-only model, with the difference being amplified as the substrate temperature is increased. A simple model considering thermal diffusion through the droplet is used to highlight the important role of evaporative cooling at the droplet interface in determining the droplet evaporation characteristics on superhydrophobic surfaces. PMID:24827255
Dash, Susmita; Garimella, Suresh V
Kinetic multi-layer model of gas-particle interactions in aerosols and clouds (KM-GAP): linking condensation, evaporation and chemical reactions of organics, oxidants and water
NASA Astrophysics Data System (ADS)
We present a novel kinetic multi-layer model for gas-particle interactions in aerosols and clouds (KM-GAP) that treats explicitly all steps of mass transport and chemical reaction of semi-volatile species partitioning between gas phase, particle surface and particle bulk. KM-GAP is based on the PRA model framework (P—schl-Rudich-Ammann, 2007), and it includes gas phase diffusion, reversible adsorption, surface reactions, bulk diffusion and reaction, as well as condensation, evaporation and heat transfer. The size change of atmospheric particles and the temporal evolution and spatial profile of the concentration of individual chemical species can be modeled along with gas uptake and accommodation coefficients. Depending on the complexity of the investigated system and the computational constraints, unlimited numbers of semi-volatile species, chemical reactions, and physical processes can be treated, and the model shall help to bridge gaps in the understanding and quantification of multiphase chemistry and microphysics in atmospheric aerosols and clouds. In this study we demonstrate how KM-GAP can be used to analyze, interpret and design experimental investigations of changes in particle size and chemical composition in response to condensation, evaporation, and chemical reaction. For the condensational growth of water droplets, our kinetic model results provide a direct link between laboratory observations and molecular dynamic simulations, confirming that the accommodation coefficient of water at ~270 K is close to unity (Winkler et al., 2006). Literature data on the evaporation of dioctyl phthalate as a function of particle size and time can be reproduced, and the model results suggest that changes in the experimental conditions like aerosol particle concentration and chamber geometry may influence the evaporation kinetics and can be optimized for efficient probing of specific physical effects and parameters. With regard to oxidative aging of organic aerosol particles, we illustrate how the formation and evaporation of volatile reaction products like nonanal can cause a decrease in the size of oleic acid particles exposed to ozone.
Shiraiwa, M.; Pfrang, C.; Koop, T.; P—schl, U.
Variations in Soil Evaporation and its Contribution to the Water Balance of a Semi-arid Forest
NASA Astrophysics Data System (ADS)
Variability of components and processes is present in all forests but is enhanced at dry ones due to the contrasting differences between shaded and exposed areas and the large amplitudes of diurnal, seasonal and inter-annual weather conditions. In such ecosystems, soil evaporation (E) is expected to have large variability and account for a significant part of the total evapotranspiration flux (ET), therefore important for the understanding of processes such as water use, respiration and ecosystem productivity. We report on a four years study (2003-2007) in the Yatir semi-arid pine forest in Southern Israel (40 years old P. halepensis; LAI=1.5; mean precipitation 280 mm/yr). E was directly measured using a modified soil respiration chamber (LI-COR) on 14 permanent soil collars in sites covering the forest spatial variability, carried out on a weekly basis during the research period. Field-averaged E was compared to eddy flux measurements of ET, heat-pulse measurements of tree transpiration (T) and environmental measurements (precipitation, P; soil water content, SWC; radiation, measured as PAR). Our results showed large spatial variability in E (daily SD between sites ~47%), with fluxes measured at exposed areas doubled that of shaded areas, on average. Variability was found to be correlated with PAR (up to 92% higher in exposed compared to shaded sites) and SWC (which was higher in exposed areas during the wetting seasons but higher in shaded areas during the drying seasons). The proportion of forest floor shaded fraction was shown to be a function of tree height, canopy width and tree density. Differential seasonal patterns in E and T were observed: E peaked twice - during early and late winter (up to 0.80 mm/day) and T peaked in spring (up to 1.20 mm/d; coinciding with maximum SWC in the root zone). Low E (0.10 mm/day) was measured during mid winter (max daily temp below 15¯) and low E and T in summer (SWC below 10%). The E/ET ratio varied seasonally and on an annual basis E accounted for 44% of ET (102Ý8 mm). The results indicated that E was a significant part of the hydrological budget in this forest. Simulations based on quantitative relations between E and canopy structure developed here could provide a simple predictive/management tool to optimize tree water use and efficiency.
Yakir, D.; Raz Yaseef, N.
Evaporation of pure liquid sessile and spherical suspended drops: a review.
A sessile drop is an isolated drop which has been deposited on a solid substrate where the wetted area is limited by a contact line and characterized by contact angle, contact radius and drop height. Diffusion-controlled evaporation of a sessile drop in an ambient gas is an important topic of interest because it plays a crucial role in many scientific applications such as controlling the deposition of particles on solid surfaces, in ink-jet printing, spraying of pesticides, micro/nano material fabrication, thin film coatings, biochemical assays, drop wise cooling, deposition of DNA/RNA micro-arrays, and manufacture of novel optical and electronic materials in the last decades. This paper presents a review of the published articles for a period of approximately 120 years related to the evaporation of both sessile drops and nearly spherical droplets suspended from thin fibers. After presenting a brief history of the subject, we discuss the basic theory comprising evaporation of micrometer and millimeter sized spherical drops, self cooling on the drop surface and evaporation rate of sessile drops on solids. The effects of drop cooling, resultant lateral evaporative flux and Marangoni flows on evaporation rate are also discussed. This review also has some special topics such as drop evaporation on superhydrophobic surfaces, determination of the receding contact angle from drop evaporation, substrate thermal conductivity effect on drop evaporation and the rate evaporation of water in liquid marbles. PMID:22277832
Erbil, H Yildirim
Changes in wintertime evaporation and surface energy budget in 2007 and 2008 over an open water surface in Mississippi, U.S.A
Using data measured from an eddy covariance system during two winters in 2007 and 2008, we examined how synoptic weather events affect wintertime evaporation and surface energy budget over an open water surface. The measurements were conducted in the Ross Barnett reservoir (32o26'N, 90o02'W), Mississippi, U.S.A. The fetch for the eddy covariance system exceeded 2 km in all directions and
H. Liu; Y. Zhang
The Impact of Mass Distribution of Water Conservation Devices and a Water Conservation Rate Structure on Residential Water Use.
National Technical Information Service (NTIS)
A study of 545 residential customers of the Washington Suburban Sanitary Commission in the suburban Washington, DC area was undertaken to determine the impacts of mass water conservation device distribution and a water conservation water rate on their lon...
W. E. Sharpe C. E. Young K. R. Kinsley
An indirect evaporative chiller
A novel indirect evaporative chiller driven by outdoor dry air to produce cold water as the cooling source for air conditioning\\u000a systems is introduced, and the principle and the structure of the chiller is presented. The cold water can be produced almost\\u000a reversibly under ideal working conditions, with its temperature infinitely close to the dew point temperature of the inlet
Xiaoyun Xie; Yi Jiang
Thermal evaporation-induced anhydrous synthesis of Fe3O4-graphene composite with enhanced rate performance and cyclic stability for lithium ion batteries.
We present a high-yield and low cost thermal evaporation-induced anhydrous strategy to prepare hybrid materials of Fe3O4 nanoparticles and graphene as an advanced anode for high-performance lithium ion batteries. The ~10-20 nm Fe3O4 nanoparticles are densely anchored on conducting graphene sheets and act as spacers to keep the adjacent sheets separated. The Fe3O4-graphene composite displays a superior battery performance with high retained capacity of 868 mA h g(-1) up to 100 cycles at a current density of 200 mA g(-1), and 539 mA h g(-1) up to 200 cycles when cycling at 1000 mA g(-1), high Coulombic efficiency (above 99% after 200 cycles), good rate capability, and excellent cyclic stability. The simple approach offers a promising route to prepare anode materials for practical fabrication of lithium ion batteries. PMID:23558566
Dong, Yucheng; Ma, Ruguang; Hu, Mingjun; Cheng, Hua; Yang, Qingdan; Li, Yang Yang; Zapien, Juan Antonio
Analysis of energy use in tomato evaporation
Field performance data for four tomato product evaporators are presented and analyzed. Steam and feed flow rates along with steam economies were measured and are compared to steady state theoretical evaporator models.
Rumsey, T.; Conant, T.
NASA Technical Reports Server (NTRS)
Evaporation is the consequence of heating near the top of streamers in ideal Magnetohydrodynamics (MHD) models, where the plasma is weakly contained by the magnetic field. Heating causes slow opening of field lines and release of new solar wind. It was discovered in simulations and, due to the absence of loss mechanisms, the ultimate end point is the complete evaporation of the streamer. Of course streamers do not behave in this way because there are losses by thermal conduction and radiation. Physically, heating is also expected to depend on ambient conditions. We use our global MHD model with thermal conduction to examine the effect of changing the heating scale height. We also apply and extend an analytic model of streamers developed by Pneuman (1968) to show that steady streamers are unable to contain plasma for temperatures near the cusp greater than approximately 2 x 10(exp 6) K.
Suess, S. T.; Wang, A.-H.; Wu, S. T.; Nerney, S. F.
Evaporation-driven instability of the precorneal tear film.
Tear-film instability is widely believed to be a signature of eye health. When an interblink is prolonged, randomly distributed ruptures occur in the tear film. "Black spots" and/or "black streaks" appear in 15 to 40 s for normal individuals. For people who suffer from dry eye, tear-film breakup time (BUT) is typically less than a few seconds. To date, however, there is no satisfactory quantitative explanation for the origin of tear rupture. Recently, it was proposed that tear-film breakup is related to locally high evaporative thinning. A spatial variation in the thickness of the tear-film lipid layer (TFLL) may lead to locally elevated evaporation and subsequent tear-film breakup. We examine the local-evaporation-driven tear-film-rupture hypothesis in a one-dimensional (1-D) model for the evolution of a thin aqueous tear film overriding the cornea subject to locally elevated evaporation at its anterior surface and osmotic water influx at its posterior surface. Evaporation rate depends on mass transfer both through the coating lipid layer and through ambient air. We establish that evaporation-driven tear-film breakup can occur under normal conditions but only for higher aqueous evaporation rates. Predicted roles of environmental conditions, such as wind speed and relative humidity, on tear-film stability agree with clinical observations. More importantly, locally elevated evaporation leads to hyperosmolar spots in the tear film and, hence, vulnerability to epithelial irritation. In addition to evaporation rate, tear-film instability depends on the strength of healing flow from the neighboring region outside the breakup region, which is determined by the surface tension at the tear-film surface and by the repulsive thin-film disjoining pressure. This study provides a physically consistent and quantitative explanation for the formation of black streaks and spots in the human tear film during an interblink. PMID:23842140
Peng, Cheng-Chun; Cerretani, Colin; Braun, Richard J; Radke, C J
Realistic Hot Water Draw Specification for Rating Solar Water Heaters: Preprint
In the United States, annual performance ratings for solar water heaters are simulated, using TMY weather and specified water draw. A more-realistic ratings draw is proposed that eliminates most bias by improving mains inlet temperature and by specifying realistic hot water use. This paper outlines the current and the proposed draws and estimates typical ratings changes from draw specification changes for typical systems in four cities.
Burch, J.
Monitoring water stress using time series of observed to unstressed surface temperature difference
Remote sensing data in the thermal infra red (TIR) part of the spectrum provides indirect estimates of water stress defined as a function of the ratio between actual and potential evaporation rates at the earth surface. During the first stage of evaporation (energy limited evaporation), this ratio is close to one. During the second stage of evaporation (soil
G. Boulet; A. Chehbouni; P. Gentine; B. Duchemin; J. Ezzahar; R. Hadria
Improving the conceptualization of the evaporation flux in conceptual rainfall-runoff models by using remotely sensed catchment scale evaporation estimates.
NASA Astrophysics Data System (ADS)
If we look at how evaporation is modelled in commonly used lumped conceptual rainfall-runoff models, the static nature of the conceptualization is striking. In this conceptualization the evaporation flux usually is linearly related to the relative soil moisture content until a certain threshold is reached, after which evaporation takes place at the potential rate. The potential evaporation is a function of meteorological parameters, sometimes it includes a surface resistance term or a scaling factor to account for different land use types in the catchment. Vegetation specific variables and the dynamics associated with the seasons (e.g. phenology, effects of soil temperature) are generally not explicitly taken into account. This means that the dynamic character of evaporation in these lumped rainfall-runoff models is only expressed by the dynamics in water availability - i.e. a function of precipitation (model input) and the partitioning of water - and a form of available energy for vaporization. Moreover, the modeled evaporation flux is the aggregated flux over the entire catchment. How can spatial variability in the temporal dynamics be expressed in these models? In other words, to what extent does the modeled evaporation flux represent the 'real' evaporation integrated over the entire catchment? Since temporally continuous evaporation observations are not available at the scale of the catchment this cannot be tested straightforwardly. What is available is a range of remote sensing techniques for upscaling point measurements of evaporation to the catchment scale or to estimate evaporation from thermal images. In this research catchment scale evaporation estimates from the SEBS algorithm combined with optical remote sensing data are explored. This provides snapshots of the spatial variability of evaporation throughout the year, which can be used to determine homogeneous functional areas within the catchment with comparable temporal dynamics in evaporation. With that information the switch to a semi-distributed model can be made, providing the possibility to capture more of the spatial and temporal character of evaporation by adjusting the conceptualization and/or parameterization of the evaporation flux per 'functional area'. We analyze the value of the ancillary remote sensing evaporation data and whether we can use this data to actually improve the conceptualization of the evaporation flux and therewith model performance.
Aalbers, Emma; Coenders-Gerrits, Miriam; Savenije, Hubert
Stable isotopes of water vapor during the Strasse cruise in the sub-tropical North Atlantic; atmospheric boundary layer composition in relation to local evaporation.
NASA Astrophysics Data System (ADS)
During the Strasse cruise, a PICARRO L2130-i equipment was installed on the top deck of RV Thalassa with air pumped at an altitude of 20m above the sea surface. With this installation, the isotopic composition of water vapor was continuously measured from mid-August 2012 to mid-Septembre 2012 in the North Atlantic subtropical gyre, mostly around 26¯N/36¯W. The sea surface water was also regularly collected as well as rain water during a few showers during the cruise. The isotopic composition of these water samples was measured after the cruise at LOCEAN. Two weather packages were continuously measuring relative humidity, air temperature, strength and direction of wind, which provide data close to where the air was pumped, and allow to estimate net evaporation. Radiosondes were also launched during part of the survey in the morning and evening to get information on the lower atmosphere vertical structure. These measurements allow a better understanding of the budget of the atmospheric mixed layer during the cruise in this region of high excess evaporation. In particular, we will comment a two-day event of large deviation in water vapor isotopic composition. We will also discuss to which extent the atmospheric boundary layer acquires its isotopic composition during exchanges with the surface ocean.
Marion, Benetti; Gilles, Reverdin; Catherine, Pierre; Jerome, Demange; Camille, Risi
Evaporation of ice in planetary atmospheres - Ice-covered rivers on Mars
NASA Technical Reports Server (NTRS)
The existence of ice covered rivers on Mars is considered. It is noted that the evaporation rate of water ice on the surface of a planet with an atmosphere involves an equilibrium between solar heating and radiative and evaporative cooling of the ice layer. It is determined that even with a mean Martian insolation rate above the ice of approximately 10 to the -8th g per sq cm/sec, a flowing channel of liquid water will be covered by ice which evaporates sufficiently slowly that the water below can flow for hundreds of kilometers even with modest discharges. Evaporation rates are calculated for a range of frictional velocities, atmospheric pressures, and insolations and it is suggested that some subset of observed Martian channels may have formed as ice-choked rivers. Finally, the exobiological implications of ice covered channels or lakes on Mars are discussed.
Wallace, D.; Sagan, C.
Effects of water flow rate, salt concentration and water temperature on efficiency of an electrolyzed oxidizing water generator
A three-factor central composite design was adopted to investigate the effects of water flow rate, water temperature and salt concentration on electrolysis efficiency and separation efficiency of an electrolyzed oxidizing water generator. Results indicated that electric potential (7.915.7 V) and power consumption (16120 W) of the electrolysis cell were not affected by water flow rate, water temperature or salt concentration
S. Y. Hsu
Soil water content and evaporation determined by thermal parameters obtained from ground-based and remote measurements
NASA Technical Reports Server (NTRS)
A procedure is presented for calculating 24-hour totals of evaporation from wet and drying soils. Its application requires a knowledge of the daily solar radiation, the maximum and minimum, air temperatures, moist surface albedo, and maximum and minimum surface temperatures. Tests of the technique on a bare field of Avondale loam at Phoenix, Arizona showed it to be independent of season.
Reginato, R.; Idso, S.; Vedder, J.; Jackson, R.; Blanchard, M.; Goettelman, R.
Evaporation and the mass and energy balances of the Dead Sea (Invited)
NASA Astrophysics Data System (ADS)
The Dead Sea is a hypersaline terminal lake experiencing a water level drop of about 1 m/yr over the last decade. The existing estimations for the water balance of the lake are widely variable, reflecting the unknown subsurface water inflow, the rate of evaporation, and the rate of salt accumulation at the lake bottom. To estimate these we calculate the energy and mass balances for the Dead Sea utilizing measured meteorological and hydrographical data from 1996 to 2009. The data is measured from a buoy located in the Dead Sea 5, km from the nearest shore. The data includes solar radiation (incoming), long wave radiation (downward and upward looking), wind velocity, relative humidity, air temperature, air pressure and water temperature profile. Using energy balance we calculate the evaporation rate, taking into account the impact of lowered surface water activity. From mass balance considerations we calculate the salt precipitation rate, which was about 0.1 m/yr during this period. Using an overall mass balance we get the relation between water inflows, which are the least constrained quantity, and the evaporation rate. The average annual inflow is 265-325 mcm/yr, corresponding to an evaporation rate of 1.1-1.2 m/yr. Higher inflows, suggested in previous studies, call for increased evaporation rate and are therefore not in line with the energy balance. We also take into account the spatial variations and discuss how well the data measured in the buoy represent the Dead Sea surface conditions.
Lensky, N.; Gavrieli, I.; Gertman, I.; Nehorai, R.; Lensky, I. M.; Lyakhovsky, V.; Dvorkin, Y.
An evaporation model of colloidal suspension droplets
NASA Astrophysics Data System (ADS)
Colloidal suspensions of polymers in water or other solvents are widely used in the pharmaceutical industry to coat tablets with different agents. These allow controlling the rate at which the drug is delivered, taste or physical appearance. The coating is performed by simultaneously spraying and drying the tablets with the colloidal suspension at moderately high temperatures. The spreading of the coating on the pills surface depends on the droplet Webber and Reynolds numbers, angle of impact, but more importantly on the rheological properties of the drop. We present a model for the evaporation of a colloidal suspension droplet in a hot air environment with temperatures substantially lower than the boiling temperature of the carrier fluid. As the liquid vaporizes from the surface, a compacting front advances into the droplet faster than the liquid surface regresses, forming a shell of a porous medium where the particles reach their maximum packing density. While the surface regresses, the evaporation rate is determined by both the rate at which heat is transported to the droplet surface and the rate at which liquid vapor is diffused away from it. This regime continues until the compacting front reaches the center of the droplet, at which point the evaporation rate is drastically reduced.
Sartori, Silvana; Li\\ NÃn, Amable; Lasheras, Juan C.
A Scanning Electron and Atomic Force Microscopy Study of the Surface Morphology and Composition of CsI Films as Affected by Evaporation Rate and Humid-Air Exposure
NASA Astrophysics Data System (ADS)
Evaporation rate and subsequent exposure to humid air affect the surface morphology and composition of cesium iodide (CsI) films and, in turn, their photoemissive efficiency when used as photocathodes. The surface morphology and elemental composition of 300-nm-thick CsI films grown at two different rates (1 nm/s and 0.04 nm/s), both freshly evaporated and after 24-h exposure to humid air were investigated by means of atomic force microscopy and scanning electron microscopy/electron diffraction spectroscopy. The CsI film freshly evaporated at a slow rate exhibited a granular surface presenting circular holes or craters where the CsI material was moved from the center to the boundaries. After 24-h exposure to humid air, this film coalesced in large grain showing a marked increase of surface roughness. Conversely, the CsI film grown at a fast rate mostly retained its original surface uniformity and homogeneity with no presence of holes and craters after 24-h exposure to humid air. Further, surface roughness and average peak height decreased, but the surface coalesced in large grains spaced by small fractures where the CsI coverage was almost lost. In conclusion, the films grown at a fast evaporation rate were affected by 24-h exposure to humid air less than those grown at a slow rate, and are thus expected to possess a greater long-term stability.
Senesi, Giorgio S.; Nitti, Mariangela A.; Valentini, Antonio
A scanning electron and atomic force microscopy study of the surface morphology and composition of CsI films as affected by evaporation rate and humid-air exposure.
Evaporation rate and subsequent exposure to humid air affect the surface morphology and composition of cesium iodide (CsI) films and, in turn, their photoemissive efficiency when used as photocathodes. The surface morphology and elemental composition of 300-nm-thick CsI films grown at two different rates (1 nm/s and 0.04 nm/s), both freshly evaporated and after 24-h exposure to humid air were investigated by means of atomic force microscopy and scanning electron microscopy/electron diffraction spectroscopy. The CsI film freshly evaporated at a slow rate exhibited a granular surface presenting circular holes or craters where the CsI material was moved from the center to the boundaries. After 24-h exposure to humid air, this film coalesced in large grain showing a marked increase of surface roughness. Conversely, the CsI film grown at a fast rate mostly retained its original surface uniformity and homogeneity with no presence of holes and craters after 24-h exposure to humid air. Further, surface roughness and average peak height decreased, but the surface coalesced in large grains spaced by small fractures where the CsI coverage was almost lost. In conclusion, the films grown at a fast evaporation rate were affected by 24-h exposure to humid air less than those grown at a slow rate, and are thus expected to possess a greater long-term stability. PMID:15817141
Senesi, Giorgio S; Nitti, Mariangela A; Valentini, Antonio
The Preparation and Characterization of Poly(lactide-co-glycolide) Microparticles. II. The Entrapment of a Model Protein Using a (Water-in-Oil)inWater Emulsion Solvent Evaporation Technique
Poly(lactide-co-glycolide) (PLG) microparticles with entrapped antigens have recently been investigated as controlled-release vaccines. This paper describes the preparation of PLG microparticles with an entrapped model antigen, ovalbumin (OVA), using a (water-in-oil)-in-water emulsion solvent evaporation technique. In a series of experiments, the effects of process parameters on particle size and OVA entrapment were investigated. It was found that smooth, spherical microparticles
Hayley Jeffery; Stanley S. Davis; Derek T. O'Hagan
Photoluminescence and anti-deliquesce of cesium iodide and its sodium-doped films deposited by thermal evaporation at high deposition rates
NASA Astrophysics Data System (ADS)
Cesium iodide (CsI) and sodium iodide (NaI) are good scintillators due to their high luminescence efficiency. These alkali halides can be excited by ultra-violet or by ionizing radiation. In this study, CsI and its Na-doped films about 8 ?m thick were deposited by thermal evaporation boat without heating substrates at high deposition rates of 30, 50, 70, 90, and 110 nm/sec, respectively. The as-deposited films were sequentially deposited a silicon dioxide film to protect from deliquesce. And, the films were also post-annealed in vacuum at 150, 200, 250, and 300 ¯C, respectively. We calculated the packing densities of the samples according to the measurements of Fourier transform infrared spectroscopy (FTIR) and observed the luminescence properties by photoluminescence (PL) system. The surfaces and cross sections of the films were investigated by scanning electron microscope (SEM). From the above measurements we can find the optimal deposition rate of 90 nm/sec and post-annealing temperature of 250 ¯C in vacuum for the asdeposited cesium iodide and its sodium-doped films.
Hsu, Jin-Cherng; Chiang, Yueh-Sheng; Ma, Yu-Sheng
The stable isotope composition of transpired water and the rate of change in leaf water enrichment in response to variable environments
NASA Astrophysics Data System (ADS)
Previous research has shown that during daylight hours the isotope composition of leaf water is generally well approximated by steady-state leaf water isotope enrichment models. However, there is little direct confirmation of isotopic steady state (ISS) transpiration. Here we use a novel method to evaluate the frequency (or infrequency) of ISS transpiration and the rate of change in leaf water enrichment when leaves are exposed to a variable environment. Specifically, our study had three goals. First, we wanted to develop a new method to measure the isotope fluxes of transpiration that relies on isotope ratio infrared spectroscopy (IRIS) and highlight how an IRIS instrument can be coupled to plant gas exchange systems. In doing so, we also developed a method for controlling the absolute humidity entering the gas exchange cuvettes across a wide range of concentrations (approximately 4000 ppmv to 22000 ppmv) without changing the isotope composition of water vapour entering the cuvette. Second, we quantified variation in the isotope composition of transpired water vapor and the rate of change in leaf water enrichment that can occur as a result of changes in relative humidity, leaf surface conductance to water vapour, leaf temperature and the isotope composition of atmospheric water vapor. Third, we examine the differences between steady state and non-steady state model predictions of leaf water enrichment at the site of evaporation. In our measurements the isotopic compositions of transpired water were neither stable nor equal to source water until leaves had been maintained at physiological steady state for at least 40 minutes. Additionally when transpiration was not at ISS, the steady state model predictions of leaf water enrichment at the site of evaporation exceeded non steady-state model predictions by up to 8 per mil. Further, the rate of change in leaf water enrichment was highly sensitive to variation in leaf water content. Our results suggest that a variable environment is likely to preclude isotopic steady-state transpiration and that this effect would be exacerbated by lengthy leaf water turnover times.
Simonin, K. A.; Roddy, A. B.; Link, P.; Apodaca, R. L.; Tu, K. P.; Hu, J.; Dawson, T. E.; Barbour, M.
Experimental Investigation of Microstructured Evaporators
NASA Astrophysics Data System (ADS)
Microfluidic devices have become more and more popular over the last decades [1]. Cooling is a topic where microstructures offer significant advantages compared to conventional techniques due the much higher possible surface to volume ratios and short heat transfer lengths. By evaporating of a fluid in microchannels, compact, fast and powerful cooling devices become possible [2]. Experimental results for different designs of microstructured evaporators are presented here. They have been obtained either using water as evaporating coolant or the refrigerant R134a (Tetrafluoroethane). A new microstructured evaporator design consisting of bended microchannels instead of straight channels for a better performance is shown and compared to previous results [2] for the evaporation of R134a in straight microchannels.
Wibel, W.; Westermann, S.; Maikowske, S.; Brandner, J. J.
Application of Taguchi method for the optimization of system parameters of centrifugal evaporative air cooler
NASA Astrophysics Data System (ADS)
A new evaporative cooling system based on the action of centrifugal forces is proposed. Such systems are suitable for cooling large air volumes in tropical climates. Effects of geometrical and operational parameters on system performance are optimized using Taguchi method. It is observed that disc speed, air flow rate and water flow rate are found to have major influence on system performance and other parameter, viz., disc diameter, pin geometry, evaporation chamber length and orientation of pin have less influence.
Senthilkumar, K.; Srinivasan, Pss.
High framing rate PIV studies of an impinging water drop
The flow field formed by the impact of a water drop in the vortex ring region was studied using high framing rate particle image velocimetry (HFRPIV). A survey of the current hardware available for HFRPIV is given followed by the results for a HFRPIV study at 1 kHz (double frames). The HFRPIV results are matched against observations from a dyed
J.-L. Liow; D. E. Cole
Forecasting corn nitrogen fertilizer rate based on soil water fluctuation
The objective of this paper has been to develop a model for nitrogen(N) fertilizer rate forecasting for corn crop (Zea mays L.) based on plant available soil water (PAW) and precipitation. Crop N requirements, soil organic matter, N supplying capability of soil, or initial soil nitrate were used as the basis for N fertilizer recommendations. Often a standard average N
D. Isfan
Rain Erosion-Does the Rate of Water Effect Erosion?
NSDL National Science Digital Library
This activity is a guided inquiry investigation where students gather data on rate of water falling on erosion. Student will interpret their data, and develop a conclusion from the data. The data will lead to further questions, which can be developed by the students.
Johnson, Kyle
Recent studies are reviewed to provide a comprehensive volume on state-of-the-art formulations used in surface water quality modeling along with accepted values for rate constants and coefficients. Topics covered include system geometric representation (spatial and temporal), phy...
Development of Elastomers Having Low Water-Vapor Transmission Rate.
National Technical Information Service (NTIS)
The effect of various types of fillers on the water-vapor transmission rate (WVTR) of vulcanizates of ethylene propylene terpolymer rubber was determined. Carbon-black and most nonblack fillers produced only a small reduction in the WVTR, whereas platelik...
J. A. Williams
High-rate and low-temperature growth of ZnO:Ga thin films by steered cathodic arc plasma evaporation
NASA Astrophysics Data System (ADS)
Ga-doped ZnO (GZO) thin films with various thicknesses (120-520 nm) are deposited on the glass substrate at a high growth rate of 220 nm/min and a low temperature of 120 ¯C by a steered cathodic arc plasma evaporation (steered CAPE). The growth mechanism, microstructure, residual stress, surface morphology, electrical and optical properties, chemical states, electron transport behaviors and thickness effect of the GZO films are investigated. The film stress is gradually relaxed from -0.516 GPa to -0.090 GPa with thickness increasing. Transmission electron microscopy (TEM) images show that the GZO microstructure consists of c-axis textured columnar grains accompanied by some embedded nanodroplets. The droplet size is significantly reduced when a high-melting-point (1975 ¯C) GZO ceramic target is adopted. High-resolution TEM image shows the GZO crystallites nucleated directly onto the amorphous substrate. The electrical properties improve with increasing thickness. The lowest resistivity (4.72 æ 10-4 ? cm) is achieved at the thickness of 520 nm, with a corresponding transmittance of 89% in the visible region. Temperature-dependent resistivity measurements show that metal-semiconductor transition temperature increases from 136 K to 225 K when decreasing the thickness, which is due to the increasing the localized states caused by the defects and chemisorbed oxygen in thinner film.
Liang, Chih-Hao; Wang, Wei-Lin; Hwang, Weng-Sing
Evaluation of the freeze-thaw/evaporation process for the treatment of produced waters. Quarterly technical progress report, January 1--March 31, 1994
The use of freeze-crystallization is being increasingly acknowledged as a low-cost, energy-efficient method for purifying contaminated water. Freeze-crystallization has been shown to be effective in removing a wide variety of contaminants from water. Water purification by using natural conditions to promote freezing appears to be an extremely attractive process for the treatment of contaminated water in many areas where natural climatic conditions will seasonally promote freezing. The natural freezing process can be coupled with natural evaporative processes to treat oil and gas produced waters year round in regions where subfreezing temperatures seasonally occur. The objectives of this research are related to development of a commercially-economic natural freeze-thaw/evaporation (FTE) process for the treatment and purification of water produced in conjunction with oil and gas. During the reporting period of 1/1/94 to 3/31/94, project research concentrated on Subtasks 2.0 (Task 2 Project Reporting) and 2.1 (Laboratory-scale FTE Simulations) . The objectives of Task 2 are to conduct laboratory- and bench-scale simulations for optimizing the design of the FTE process. Task 2 requires completion of six subtasks: Subtask 2.0 - Task 2 Project Reporting (initiated 3/1/93), Subtask 2.1 - Laboratory-scale FTE Simulations, Subtask 2.2 Re-evaluation of Process Economics Based on Laboratory-scale Process Simulation Results, Subtask 2.3 - Bench-scale FTE Simulations, Subtask 2.4 - Economic Assessment of Bench-scale Simulations, and Subtask 2.5 - Technical Report of Task 2. The construction, shakedown, and operation of the laboratory-scale process simulations planned were planned for this quarter (Subtask 2.1).
Boysen, J.; Morotti, J.
Effect of pressure on aragonite dissolution rates in sea water
Aragonite dissolution in sea water at variable pressure is well described by the equation Rate = kappa'((CO/sub 3//sup 2 -/)s - (CO/sub 3//sup 2 -/))/sup n/ where (CO/sub 3//sup 2 -/)s is the carbonate ion concentration at saturation, (CO/sub 3//sup 2 -/) is the observed carbonate ion concentration, and kappa' and n are empirical constants. Application of the equation Rate = kappa(1-Omega)/sup n/ to descriptions of aragonite dissolution rates is appropriate at constant pressure, temperature and salinity. The authors measurements in sea water at 5/sup 0/C are consistent with the estimate - ..delta.. V = 36.5 cm/sup 3/mole for the volume change accompanying aragonite dissolution. This result is somewhat higher than laboratory estimates, but lower than estimates based on calcite and the difference between calcite and aragonite molar volumes.
Acker, J.G.; Byrne, R.H.; Yaakov, S.B.; Feely, R.A.; Betzer, P.R.
Evaporation of forsterite in H 2 gas
Kinetics of evaporation of forsterite in hydrogen gas was investigated by high temperature vacuum experiments in the pressure range plausible for the solar nebula. The evaporation rate at total pressure (Ptot) below 10?6 bar is nearly constant and is similar to that in vacuum, whereas the rate at 10?6 to 10?3 bar is dependent on Ptot. The evaporation rate, JexpFo,
Hiroko Nagahara; Kazuhito Ozawa
Fabrication of Micropatterns using Salt Crystals from Solvent Evaporation
NASA Astrophysics Data System (ADS)
Herein, we investigated the crystallization behaviors of sodium carbonate (Na2CO3) from highly diluted aqueous solutions. Aqueous Na2CO3 solutions which were applied on substrate surfaces by either dropping or draining exhibited a variety of well-defined crystal structures over large areas during water evaporation. It was also found that both sizes and shapes of salt crystals could be effectively controlled by the experimental conditions such as their concentration, evaporation rate, temperature and humidity. Furthermore, it was observed that the salt crystals could be oriented to specific direction as the evaporation of water occurred on the tilted substrates. The crystals of Na2CO3were then employed as the master pattern to fabricate the soft mold of poly(dimethyl siloxane) (PDMS). Then silver (Ag) inks were filled into the pores of PDMS molds and transferred to various substrates by imprinting techniques to produce electrically conductive electrodes for potential electric devices.
Lee, Dong-Eun; Go, Seung Jae; Lee, Dong Hyun
Evaporation in the Atacama Desert: An empirical study of spatio-temporal variations and their causes
NASA Astrophysics Data System (ADS)
SummaryThe Atacama Desert is hyper-arid, and areas where adequate moisture exists for evaporation are spatially highly restricted. Nevertheless, water resources exist and their evaluation requires knowledge of this elusive but important component of the hydrological cycle. Evaporation may occur in four typical areas: rivers and associated riparian zones, localized springs, large playas and extensive areas of bare soil after infrequent precipitation events. Transpiration is locally possible where moisture is sufficiently close to the surface to allow phreatophytes or scarce grass cover to grow, but virtually no information is available for quantification. Pan evaporation data from 11 stations for the period 1977-1991 is analyzed and complemented by analysis of an evaporation study conducted in the Salar de Atacama during 1987/1988. The results show that pan evaporation, and hence maximum potential evaporation may be considered largely a function of maximum temperature and elevation as well as density of the evaporating fluid. Actual evaporation is limited by available moisture and diminishes rapidly as the level of soil moisture saturation drops below the soil surface, extinguishing at ca. 2 m depth. Evaporation is greatest during the summer, but at higher elevations convective cloudiness develops during January and February reducing evaporating rates at a time when significant precipitation may occur. Inter-annual variations in pan evaporation are considerable and weakly correlated with ENSO, but variations in actual evaporation are damped by comparison. Regression equations are developed which have widespread applicability and may be used to estimate evaporation in areas where no site-specific data exists.
Houston, John
Development of novel zein-sodium caseinate nanoparticle (ZP)-stabilized emulsion films for improved water barrier properties via emulsion/solvent evaporation.
This work attempted to develop novel high barrier zein/SC nanoparticle (ZP)-stabilized emulsion films through microfluidic emulsification (ZPE films) or in combination with solvent (ethyl acetate) evaporation techniques (ZPE-EA films). Some physical properties, including tensile and optical properties, water vapor permeability (WVP), and surface hydrophobicity, as well as the microstructure of ZP-stabilized emulsion films were evaluated and compared with SC emulsion (SCE) films. The emulsion/solvent evaporation approach reduced lipid droplets of ZP-stabilized emulsions, and lipid droplets of ZP-stabilized emulsions were similar to or slightly lower than that of SC emulsions. However, ZP- and SC-stabilized emulsion films exhibited a completely different microstructure, nanoscalar lipid droplets were homogeneously distributed in the ZPE film matrix and interpenetrating protein-oil complex networks occurred within ZPE-EA films, whereas SCE films presented a heterogeneous microstructure. The different stabilization mechanisms against creaming or coalescence during film formation accounted for the preceding discrepancy of the microstructures between ZP-and SC-stabilized emulsion films. Interestingly, ZP-stabilized emulsion films exhibited a better water barrier efficiency, and the WVP values were only 40-50% of SCE films. A schematic representation for the formation of ZP-stabilized emulsion films was proposed to relate the physical performance of the films with their microstructure and to elucidate the possible forming mechanism of the films. PMID:24175664
Wang, Li-Juan; Yin, Ye-Chong; Yin, Shou-Wei; Yang, Xiao-Quan; Shi, Wei-Jian; Tang, Chuan-He; Wang, Jin-Mei
Material and method to dissociate water at controlled rates
A material and method for the decomposition/dissociation of water into hydrogen and oxygen is disclosed. The material comprises an amalgam of an alkali metal, mercury, and aluminum combined with a catalytically effective amount of an alloy comprising platinum and at least one metal selected from the group consisting of germanium, antimony, gallium, thallium, indium, cadmium, bismuth, lead, zinc and tin, and with an extender metal to control the rate of dissociation of the water while being non-reactive with the amalgam during dissociation.
Anderson, E.R.
Evaporation of extrasolar planets
NASA Astrophysics Data System (ADS)
This article presents a review on the observations and theoretical modeling of the evaporation of extrasolar planets. The observations and the resulting constraints on the upper atmosphere (thermosphere and exosphere) of the ``hot-Jupiters'' are described. The early observations of the first discovered transiting extrasolar planet, HD209458b, allowed the discovery that this planet has an extended atmosphere of escaping hydrogen. Subsequent observations showed the presence of oxygen and carbon at very high altitude. These observations give unique constraints on the escape rate and mechanism in the atmosphere of hot-Jupiters. The most recent Lyman-alpha HST observations of HD189733b and MgII observations of Wasp-12b allow for the first time a comparison of the evaporation from different planets in different environments. Models to quantify the escape rate from the measured occultation depths, and an energy diagram to describe the evaporation state of hot-Jupiters are presented. Using this diagram, it is shown that few already known planets like GJ876d or CoRot-7b could be remnants of formerly giant planets.
Lecavelier Des Etangs, A.
Rate of oxygen isotope exchange between selenate and water.
The rate of oxygen isotope exchange between selenate and water was investigated at conditions of 10 to 80 ¯C and pH -0.6 to 4.4. Oxygen isotope exchange proceeds as a first-order reaction, and the exchange rate is strongly affected by reaction temperature and pH, with increased rates of isotope exchange at higher temperature and lower pH. Selenate speciation (HSeO(4)(-) vs SeO(4)(2-)) also has a significant effect on the rate of isotope exchange. The half-life for isotope exchange at example natural conditions (25 ¯C and pH 7) is estimated to be significantly in excess of 10(6) years. The very slow rate of oxygen isotope exchange between selenate and water under most environmental conditions demonstrates that selenate-?(18)O signatures produced by biogeochemical processes will be preserved and hence that it will be possible to use the value of selenate-?(18)O to investigate the biogeochemical behavior of selenate, in an analogous fashion to the use of sulfate-?(18)O to study the biogeochemical behavior of sulfate. PMID:22428618
Kaneko, Masanori; Poulson, Simon R
A phylogenetic analysis of basal metabolism, total evaporative water loss, and life-history among foxes from desert and mesic regions.
We measured basal metabolic rate (BMR) and total evaporative water loss (TEWL) of species of foxes that exist on the Arabian Peninsula, Blanford's fox (Vulpes cana) and two subspecies of Red fox (Vulpes vulpes). Combining these data with that on other canids from the literature, we searched for specialization of physiological traits among desert foxes using both conventional least squares regression and regressions based on phylogenetic independent contrasts. Further, we explored the consequences of reduced body size of foxes on life history parameters such as litter size and neonate mass. For Blanford's foxes, Red foxes from the central desert of Arabia, and Red foxes from the more mesic Asir mountains, body mass averaged 1,285 +/- 52 g, 1,967 +/- 289 g, and 3,060 +/- 482 g, respectively, whereas mean BMR, during summer, was 304.5 +/- 32.3 kJ/day, 418.0 +/- 32.4 kJ/day, and 724.1 +/- 120.2 kJ/day (+/- SD). An analysis of covariance with body mass as a covariate showed no statistical differences in BMR among foxes. Analysis of covariance indicated that Red fox from the Asir mountains had a higher TEWL than Red foxes from central Arabia or than Blanford's foxes also from the mountains. Comparisons of all species of desert and mesic foxes showed no significant differences in BMR, nor did desert foxes have a significantly lower BMR than other carnivores. TEWL of desert foxes was lower than other more mesic carnivores; deviations in TEWL ranged from -17.7% for the Fennec fox (Fennecus zerda) to -57.4% for the Kit fox (Vulpes velox). Although desert foxes have a BMR comparable to other more mesic species, it appears that desert foxes do have a smaller body mass, lowering overall energy requirements. We attribute this reduction in body size to the "resource limitation hypothesis" whereby natural selection favors smaller individuals in a resource-limited environment, especially during periods of severe food shortage. However, until common garden experiments are performed, developmental plasticity and acclimation cannot be ruled out as contributors to this pattern. PMID:14564467
Williams, J B; Muþoz-Garcia, A; Ostrowski, S; Tieleman, B I
Performance rating method of thermosyphon solar water heaters
A rating method for the thermal performance of thermosyphon solar water heaters was developed. Except that the outdoor test procedure still follows the Taiwan Standard CNS B7277, a system characteristic efficiency [eta][sub s]* which is defined as the [alpha][sub o], value corrected at M\\/A[sub c]= 75 kg\\/m[sup 2], was derived so that [eta][sub s]* is independent of the M\\/A, ratio.
Dynamics of transition from stage-1 to stage-2 evaporation from porous media
NASA Astrophysics Data System (ADS)
The early stages of evaporation from porous media are marked by a relatively high and constant evaporation rate (the so-called stage-1 evaporation) sustained by capillary liquid flow from the porous medium interior. Following interruption of hydraulic connections at a certain drying front depth, the vaporization plane migrates below the surface leading to transition to stage-2 evaporation limited by vapour diffusion through the porous medium. The nature of the transition and the wide range of transition dynamics from stage-1 to stage-2 were studied using evaporation experiments from sand-filled Hele-Shaw cells (172x81x4 mm) with three mean particle sizes of 0.27, 0.46, and 0.84 mm. The initially water saturated cells were placed on digital balances (cell top exposed to air) to record evaporation rates. Experiments were conducted in an environmental chamber where the relative humidity and temperature could be varied and controlled accurately. The effects of grains size, ambient temperature and relative humidity (both affecting potential evaporation rates) on transition dynamics were systematically evaluated. The results illustrate the role of potential evaporation rate on transition duration and shape transcending the expected scaling with cumulative mass loss that defines the evaporative characteristic length. The transition becomes more abrupt at higher atmospheric demand perhaps due to enhanced role of viscous effects that accelerate pore disconnection. Pore size did not affect the shape of transition much except for the medium sand with prolonged transition (the exact pore size distribution needs to be examined). Interestingly the evaporation rate at the onset of stage 2 was not affected by atmospheric conditions (Shokri and Or, 2011).
Shokri, Nima; Shahraeeni, Ebrahim; Shahabdeen, Rumeena; Or, Dani
The rate of oxygen isotope exchange between nitrate and water
NASA Astrophysics Data System (ADS)
The oxygen isotope exchange rate between nitrate and water was measured at a temperature of 50-80 ¯C and pH -0.6 to 1.1. Oxygen isotope exchange is a first-order reaction, with the exchange rate being strongly affected by both reaction temperature and pH, with increased rates of isotope exchange at higher temperatures and lower pH values. The rate of oxygen isotope exchange under natural conditions is extremely slow, with an estimated half-life for isotope exchange of 5.5 æ 109 years at 25 ¯C and pH 7. The extremely slow rate of oxygen isotope exchange between nitrate and water under typical environmental conditions illustrates that nitrate-?18O signatures (and also nitrate ?17O and ?17O signatures) associated with various nitrate sources, as well as isotope compositions produced by biogeochemical processes, will be preserved. Hence, it is valid to use the value of nitrate-?18O to investigate the sources and biogeochemical behavior of nitrate, in a similar manner to the use of sulfate-?18O signatures to study the sources and biogeochemical behavior of sulfate. Equilibrium oxygen isotope fractionation factors have been determined, although quantification of the nitrate-water equilibrium fractionation factor is not possible due to the presence of nitrate as both protonated (i.e. HNO3) and unprotonated forms (i.e. NO3-) under the experimental conditions, and the difficulty in accurately calculating nitrate speciation in low pH, high ionic strength solutions.
Kaneko, Masanori; Poulson, Simon R.
Influence of algae on photolysis rates of chemicals in water
Sunlight-induced algal transformations of 22 nonionic organic chemicals were studied in order to provide kinetic results and equations concerning the influence of algae on the behavior of pollutants in freshwater environments. Screening studies indicated that green and blue-green algae, at concentrations of 1-10 mg of chlorophyll a/L, accelerate photoreaction of certain polycylic aromatic hydrocarbons, organophosphorus compounds, and anilines in water. The rate of change in aniline concentration, (P), in the aniline-Chlamydomonas photoreaction can be described by the following expression: rate = A(1 + B/(P))-1. At low substrate concentrations, the reaction rate is first order with respect to both algae and substrate concentration. Methyl parathion and parathion photoreacted 390 times more rapidly when sorbed by algae than in distilled water, and aniline and m-toluidine reacted over 12000 times faster, indicating that light-induced algal transformations of certain pollutants may be significant. Other results indicated that reaction rates are unaffected by heat-killing the algae. 27 references
Zepp, R.G.; Schlotzhauer, P.F.
Evaporative losses from soils covered by physical and different types of biological soil crusts
Evaporation of soil moisture is one of the most important processes affecting water availability in semiarid ecosystems. Biological soil crusts, which are widely distributed ground cover in these ecosystems, play a recognized role on water processes. Where they roughen surfaces, water residence time and thus infiltration can be greatly enhanced, whereas their ability to clog soil pores or cap the soil surface when wetted can greatly decrease infiltration rate, thus affecting evaporative losses. In this work, we compared evaporation in soils covered by physical crusts, biological crusts in different developmental stages and in the soils underlying the different biological crust types. Our results show that during the time of the highest evaporation (Day 1), there was no difference among any of the crust types or the soils underlying them. On Day 2, when soil moisture was moderately low (11%), evaporation was slightly higher in well-developed biological soil crusts than in physical or poorly developed biological soil crusts. However, crust removal did not cause significant changes in evaporation compared with the respective soil crust type. These results suggest that the small differences we observed in evaporation among crust types could be caused by differences in the properties of the soil underneath the biological crusts. At low soil moisture (<6%), there was no difference in evaporation among crust types or the underlying soils. Water loss for the complete evaporative cycle (from saturation to dry soil) was similar in both crusted and scraped soils. Therefore, we conclude that for the specific crust and soil types tested, the presence or the type of biological soil crust did not greatly modify evaporation with respect to physical crusts or scraped soils.
Chamizo, S.; Cantµn, Y.; Domingo, F.; Belnap, J.
Evaluation of evaporation estimation methods for a covered reservoir in a semi-arid climate (south-eastern Spain)
NASA Astrophysics Data System (ADS)
SummaryThe main purpose of this study was to evaluate different methods of evaporation estimation for covered water reservoirs. A reservoir equipped with a suspended cover was fully monitored to register the evaporation rate and microclimate below the cover. The datasets were used to evaluate the performance of commonly used evaporation methods, namely energy budget, mass-transfer, combination (Penman and FAO-56 Penman-Monteith) and floating class-A pan. The mass-transfer formula based on the Sherwood number proposed for free convection conditions, which were observed to prevail below the cover, supplied reasonably good estimates of covered reservoir evaporation and it is a good option from a practical point of view, with low input data requirements. Detailed input data and modifications in the calculation of energy fluxes are required to get good evaporation estimations of covered surfaces with the energy budget and FAO-56 Penman-Monteith methods. Besides, some of the standard meteorological input data (such as wind speed at 2 m height) cannot be registered below the cover. Penman equation presented a poor performance related to the overestimation of the advective component for free convection conditions. The pan evaporation was found to be substantially higher than the reservoir evaporation, due to the particular characteristics of the tank, that increased surface temperature and hence evaporation rate. A simplified empirical mass-transfer formula was also proposed to estimate evaporation of covered water bodies from the only knowledge of the surface-to-air mixing ratio gradient.
Gallego-Elvira, B.; Baille, A.; MartÚn-Gorriz, B.; Maestre-Valero, J. F.; MartÚnez-Alvarez, V.
Transpiration and evaporation from heather Moorland
NASA Astrophysics Data System (ADS)
The energy balance of an upland heath dominated by heather ( Calluna vulgaris) was measured in dry and wet weather. Median values of both transpiration and evaporation rates were ca. 2 mm hr-1. The median Bowen ratio for the dry canopy was 2.0 and for the wet canopy 0.6. On dry days the median value of the saturation deficit was only 3.8 mb and that of the climatological resistance was 30 s m-1. The bulk stomatal resistance increased from ca. 50 s m -2 in the morning to over 290 s m-1 in the afternoon with an overall median value of 110 s m-1. Transpiration from the dry canopy was controlled by a combination of small saturation deficits and large stomatal resistances. The median value of the boundary-layer resistance of the canopy was 22 s m-1 and was low partly because of a large low-level drag coefficient. Saturation deficits on wet days were close to zero and evaporation of intercepted water proceeded at close to the equilibrium rate, being largely limited by the low fluxes of available energy. The water loss from heather was compared with simulated losses from coniferous forest, herbaceous crops and grassland in the same conditions to evaluate the effects of vegetation on water loss from catchments.
Miranda, A. C.; Jarvis, P. G.; Grace, J.
Permeability of cellulose polymers: water vapour transmission rates.
The water vapour transmission rates (WVTR) through solvent cast polymer films prepared from cellulose acetate, cellulose acetate propionate, and cellulose acetate butyrate have been determined. They were influenced by the relative humidity, the substituent type and the extent of substitution. Increasing the relative humidity from 32 to 90% increased the WVTR 3 to 5 times depending on the polymer used. The WVTR increased in the order of butyrate less than propionate less than acetate. An increase in the extent of substitution with acetyl and/or butyryl groups resulted in an exponential decline in the WVTR. PMID:1974608
Sprockel, O L; Prapaitrakul, W; Shivanand, P
Evaporation control research, 1959-60
Two hundred and forty-five dispersions of long-chain alkanols were formulated by using various emulsifiers and alkanols. The dispensing and spreading ability of each of these formulations was tested. The most promising emulsifier that could be used with any of the alkanols was glyceryl monostearate (self-emulsifying). However, the concentration of the alkanol in the dispersion form varied somewhat: with the length of the carbon chain. A maximum concentration of 16 percent was obtained using the longer chain alkanols in the dispersion form without losing any of the properties of a fluid. Nine field tests were undertaken on small stock tanks. The retardant materials used in these tests were dodecanol, hexadecanol, and octadecanol. These materials were applied in either liquid or dispersion form. Four types of dispensing equipment were tested. The first type used a pressure system which sprayed a liquid onto the surface of the water. An anemometer and wind-controlled vane, operated by an electrical system, determined the length End frequency of application. The second type was similar to the first except that gravity was utilized to force the liquid onto the surface. The third type. used a drip system with rates of about 10 drops per minute. The fourth type used a gravity feed and a wind-controlled valve which allowed the dispersion material to flow onto the surface of the water when the wind was in the proper direction. In the field tests, the best reduction in evaporation was obtained using octadecanol in dispersion form and dispensed with the wind-controlled valve and gravity feed system. The maximum reduction in evaporation for a 2-week period was 27 percent. However, the economics of suppressing evaporation from stock tanks is questionable because of the short travel time across the tank by the film. There are still many problems unsolved. Some of these can be resolved in the laboratory whereas others can be resolved only in the field. Some of the more serious problems are the effect of impurities in the alkanols; the rate of cooling of the alkanol from a liquid to a solid state ; the effect of the film on the exchange of water molecules between the air and water; whether the film remains effective in suppressing evaporation for any rate of movement downwind; and the possible use of dodecanol and eicosanol as suppressants.
Geological Survey (U.S.)
Use of the Priestley-Taylor evaporation equation for soil water limited conditions in a small forest clearcut
The Priestley-Taylor equation, a simplification of the Penman equation, was used to allow calculations of evapotranspiration under conditions where soil water supply limits evapotranspiration. The Priestley-Taylor coefficient, ??, was calculated to incorporate an exponential decrease in evapotranspiration as soil water content decreases. The method is appropriate for use when detailed meteorological measurements are not available. The data required to determine the parameter for the ?? coefficient are net radiation, soil heat flux, average air temperature, and soil water content. These values can be obtained from measurements or models. The dataset used in this report pertains to a partially vegetated clearcut forest site in southwest Oregon with soil depths ranging from 0.48 to 0.70 m and weathered bedrock below that. Evapotranspiration was estimated using the Bowen ratio method, and the calculated Priestley-Taylor coefficient was fitted to these estimates by nonlinear regression. The calculated Priestley-Taylor coefficient (?????) was found to be approximately 0.9 when the soil was near field capacity (0.225 cm3 cm-3). It was not until soil water content was less than 0.14 cm3 cm-3 that soil water supply limited evapotranspiration. The soil reached a final residual water content near 0.05 cm3 cm-3 at the end of the growing season. ?? 1991.
Flint, A. L.; Childs, S. W.