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A method of mixing two or more dissimilar fluids such a gas and a liquid is provided. The method includes the steps of introducing one fluid into the other to form a mixture, inducing cavitation in the mixture to reduce at least one of the fluids to a large number of relatively small units, and distributing the small units uniformly throughout the mixture. In a preferred embodiment, the step of inducing cavitation comprises introducing the mixture into a chamber having a rotating disk formed with a plurality of irregularities such as bores. The irregularities on the rotating disk induce cavitation in the mixture. The cavitation also breaks down van der Waals attractions within the mixture to enhance mixing.
1. An apparatus for mixing two or more fluids by inducing cavitation, said apparatus comprising:
a housing defining a substantially cylindrical interior chamber bounded by spaced substantially planar side walls joined by a cylindrical peripheral wall;
a substantially cylindrical rotor rotatably mounted within said interior chamber, said rotor having an axis, spaced substantially planar sides, and a cylindrical peripheral surface joining said planar sides;
said cylindrical peripheral surface of said rotor and said cylindrical peripheral wall of said chamber defining therebetween an annular space having a substantially uniform dimension in the axial direction of said rotor;
a first array of spaced bores formed in said peripheral surface of said rotor, each bore of said first array extending radially into said rotor a predetermined distance and opening into said annular space;
said bores of said first array being arranged in a first row that extends around said cylindrical peripheral surface of said rotor;
a second array of spaced bores formed in said peripheral surface of said rotor, each bore of said second array extending radially into said rotor a predetermined distance and opening into said annular space;
said bores of said second array being arranged in a second row that extends around said cylindrical peripheral surface of said rotor;
said first row of bores and said second row of bores being spaced apart in the axial direction of said rotor and defining therebetween a void zone wherein no bores are formed in said peripheral surface of said rotor;
a first fluid inlet in said housing positioned to introduce fluid into said chamber at a first predetermined location adjacent one of said substantially planar sides of said rotor;
a second fluid inlet in said housing positioned to introduce fluid into said chamber at a second predetermined location adjacent the other one of said substantially planar sides of said rotor;
said second fluid inlet being substantially axially aligned with said first fluid inlet to equalize pressure on said rotor as fluid is introduced into said chamber through said fluid inlets;
a fluid outlet in said housing positioned for withdrawal of fluid from said chamber at a third predetermined location adjacent said cylindrical peripheral surface of said rotor;
said third predetermined location being aligned within said void zone defined between said first row of bores and second row of bores for withdrawal of fluid after it has passed a row of bores and to minimize cavitation damage at the location of said fluid outlet.
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This application is a continuation application of co-pending U.S. patent application Ser. No. 10/618,119, filed on Jul. 11, 2003, which is a continuation application of U.S. patent application Ser. No. 09/747,469, filed on Dec. 20, 2000, now U.S. Pat. No. 6,627,784, which claims the benefit of U.S. Provisional Patent Application No. 60/204,838, filed on May 17, 2000, each of which are incorporated herein by reference in their entirety.
This invention relates generally to mixing and more specifically to methods and devices for mixing dissimilar fluids such as a gas and a liquid or two dissimilar liquids for industrial applications.
The mixing together of dissimilar fluids such as a gas and a liquid or two dissimilar liquids has many industrial applications. For example, the mixing of oxygen and a liquid has applications such as the oxygenation of water for biological purposes and the oxygenation of fuel prior to burning to enhance combustion efficiency. The mixing of air and a liquid may be used in the pulp and paper, textile, and other industries in a process known as dissolved air floatation to separate suspended particulate materials from the liquid. Mixing industrial stack gasses with a liquid such as water is useful for removing environmental contaminants from the stack gasses prior to its release to the atmosphere. The mixing of dissimilar fluids such as, for example, oil and water, has industrial application in the creation of emulsions. Further, an existing emulsion may be separated into its constituent components by mixing it with another gas or fluid such as, for example, methane, which acts as an inhibitor to prevent recombination of the constituent components once they are broken apart.
One particular industrial application of gas/liquid mixing occurs in the pulp and paper industry where black liquor, which is a byproduct of cooking wood chips, often is recycled by being burned as a fuel in boilers. Even though such recycling is economically efficient, an emissions problem arises from the fact that untreated black liquor contains concentrations of Sodium Sulfide (Na2S) that can be as high as 40 grams per liter or more. As a result, when untreated black liquor is burned, the Sodium Sulfide contained therein is converted to Sodium Dioxide (SO2) and Hydrogen Sulfide (H2S), which are known as totally reduced sulfur (TRS) compounds. TRS compounds are extremely harmful to the environment and therefore are highly regulated and may not be released to the atmosphere as a component of boiler stack gasses. Accordingly, black liquor often is treated before being burned in order to reduce or eliminate TRS emissions.
One method of treating black liquor prior to burning has been to mix or agitate it with air in a gas/liquid mixing process. When so mixed, Sodium Sulfide within the black liquor is oxidized in a chemical oxidation/reduction or �redux� reaction with oxygen molecules in the air and thereby converted to Sodium Thiosulfate (Na2S2O3). Unlike Sodium Sulfide, Sodium Thiosulfate exists in a stable chemical state and thus does not participate in chemical reactions when the treated black liquor is burned in a boiler. Instead, the Sodium Thiosulfate simply precipitates to the bottom of the boiler, where it is ejected as a smelt.
Prior art industrial methods of mixing gases and liquids in general, and air and black liquor in particular, have involved introducing air in the form of bubbles into black liquor and agitating the mixture to break up the air bubbles and distribute them throughout the liquor. The goal, of course, is that oxygen molecules in the air will react chemically with or �oxidize� sodium sulfide molecules in the black liquor, rendering them inert during combustion of the black liquor. In one prior art process, such mixing is accomplished with rotating mechanical beaters having blades that impact and cut up the air bubbles while agitating the liquid. The problem with such a system, however, is that there is a natural lower limit to the size of the resulting air bubbles because larger bubbles cannot be cut or chopped to a size smaller than the size of the beater blades. Thus, the total composite surface area of the air bubbles in contact with the black liquor is severely limited. As a result, the probability that an oxygen molecule within an air bubble will come into contact with and oxidize a Sodium Sulfide molecule within the black liquor is reduced.
A further exacerbating problem and limitation of prior art gas/liquid mixing methods in general, and black liquor oxidation processes in particular, arises from the fact that the bubbles that are created by the mechanical beater blades of the mixing apparatus tend not to be distributed evenly throughout the black liquor. Instead, the bubbles, partially because of their relatively large size and partially because of the mechanical nature of the process, tend to agglomerate or concentrate into pockets of bubbles separated by relative voids in the liquor. This further reduces the probability that an oxygen molecule within an air bubble with come into contact with or �find� a Sodium Sulfide molecule and thus reduces the efficiency of the oxidation process. To address this inefficiency, it may be necessary to inject many times the amount of air necessary to oxidize the Sodium Sulfide into the mixer and to increase mixing times substantially to increase the probability of oxidation. However, such a brute force method of increasing oxidation efficiency substantially increases the time, energy, and resources required in the mixing process and thus introduces its own inefficiencies.
A final limitation of prior art gas/liquid mixing methods as applied to the oxidation of black liquor is imposed by the fact that the molecules within the liquor are attracted to each other by weak molecular forces known as van der Waals attraction. This results in the molecules clumping together in mutually attracted groups. In many cases, a Sodium Sulfide molecule that needs to come into contact with an oxygen molecule within a bubble in order to be oxidized may be surrounded within such a group by other molecules within the liquid and thus shielded from contact with a bubble and an oxygen molecule. In these cases, oxidation of the Sodium Sulfide molecule can not occur regardless of the volume of gas introduced or the length of the mixing process. This is due, in part at least, to the fact that the energy imparted to the liquor by mechanical beater blades is far less than that required to break the van der Waals attractions and free trapped molecules. In effect, then, the molecular Van der Waals attraction within the liquor imposes a physical limit to the percentage of Sodium Sulfide molecules within black liquor that can be oxidized with traditional gas/liquid mixing techniques.
Thus, a specific need exists for a gas/liquid mixing method and apparatus applicable to the oxidation of black liquor in the pulp and paper industry that overcomes the problems, shortcomings, and limitation of prior art processes. More generally, a need exists for a new and unique method of mixing dissimilar fluids, be they gasses and liquids, dissimilar liquids, or otherwise, that is highly efficient, that results in virtually complete mixing in a short time and with a minimum of required energy and resources, and, in the case of oxidation applications, overcomes the physical limits on oxidation efficiency imposed by molecular van der Waals attraction. It is to the provision of such a method and an apparatus for carrying out the method that the present invention is primarily directed.
For clarity of disclosure and discussion, the present invention will be discussed herein primarily in the context of its application to the oxidation of environmental contaminants such as Sodium Sulfide in black liquor within the pulp and paper industry. Such an application is considered by the inventors to be a best mode of carrying out the invention. It will be understood and appreciated, however, that the method and apparatus of the invention is applicable to virtually any situation where dissimilar fluids are to mixed together for industrial or commercial purposes. For example, the invention is applicable in the pulp and paper industry alone to a variety of processes including micro-mixing prior to gasification, mixing stack gases with black liquor in direct contact evaporators, mixing salt cake and black liquor, pulp drying, sludge dewatering, oxygen de-lignification, pulp bleaching by mixing pulp with ozone or other appropriate gases, and atomization of black liquor prior to its use in a recovery boiler. In the petroleum industry, the invention is applicable among other things to the separation of tight emulsions using micro-mixing and to heavy oil upgrading. Within the food processing industry, the mixing methodology of the invention has application in homogenization, oxygenation, and spice mixing processes. Applications within the environmental industry include oxidation/reduction of liquids or components of liquids, concentration and evaporation, BOD and COD reduction, dissolved air floatation, and fuel aeration. Thus, the discussion of the invention herein within the context of black liquor oxidation should not be interpreted as a limitation of the invention but only as representing a preferred embodiment or application and a best mode of carrying out the invention.
Briefly described, the present invention in a preferred embodiment thereof, comprises a unique and highly efficient method of mixing dissimilar fluids together by mechanically inducing cavitation within the fluids in a controlled manner. The result and goal is to obtain mixing on a microscopic level, uniform distribution of one fluid throughout another, and a breaking of van der Waals attractions between molecules within the fluids. In the preferred embodiment and best mode, the invention comprises a method of oxidizing environmentally hazardous compounds such as Sodium Sulfide within black liquor in the pulp and paper industry by mixing air with black liquor using controlled mechanically induced cavitation. The result is a virtually complete oxidation of the hazardous compounds and thus assurance that environmental toxins are not created when the black liquor is burned.
The methodology of the invention, in the context of oxidizing black liquor, comprises the steps of introducing and entraining air in the form of bubbles into a stream of black liquor to form a mixture of black liquor and air bubbles. The liquor/air bubble mixture is then directed into a hydrosonic mixer, which generally comprises a rapidly spinning rotor disposed within a cylindrical chamber within a housing. The rotor is provided with one or more arrays of relatively shallow holes or bores formed around its periphery. A space, referred to herein as a cavitation zone, is formed between the periphery of the rotor and the cylindrical wall of the housing chamber.
As the mixture of gas bubbles and black liquor passes through the cavitation zone, microscopic cavitation bubbles are continuously generated and collapse within the mixture by the action of the bores on the periphery of the spinning rotor.1 The collapse of these cavitation bubbles creates violent and continuous cavitation within the gas/fluid mixture in the cavitation zone, and the energy of this cavitation acts to break up the air bubbles within the mixture into ever smaller bubbles or units. Since the minimum size of the air bubbles is not limited as in prior art mixers, the air bubbles are reduced by the cavitation into millions of substantially microscopic bubbles. Thus, the total surface area of air bubbles in contact with black liquor is significantly greater than in prior art mixers. The increased surface area increases the probability that an oxygen molecule within an air bubble will come into contact with and oxidize a Sodium Sulfide molecule within the black liquor. Further, because of the relatively violent agitation within the cavitation zone caused by rotor motion and cavitation effects, these microscopic air bubbles are mixed completely and uniformly throughout the black liquor, which further enhances the probability of contact between an oxygen molecule and a Sodium Sulfide molecule. Finally, the energy imparted to the mixture by the cavitation within the cavitation zone is more than sufficient to overcome the van der Waals attraction between molecules within the black liquor. This breaks apart the molecule clumps and frees Sodium Sulfide molecules that may be jacketed or shielded by other molecules within the black liquor. These freed molecules, then, are available to be contacted and oxidized by an oxygen molecule within one of the microscopic air bubbles. 1 The term �cavitation zone� is used herein to refer to the region between the outer periphery of the rotor wherein the bores are formed and the cylindrical wall of the housing chamber. This is where the most intense cavitation activity occurs. It should be understood, however, that cavitation may occur, albeit with less intensity, in regions other than this space such as, for example, in the reservoir or region between the sides or faces of the rotor and the housing. Thus �cavitation zone� is used herein to refer to the region of most intense cavitation, but should not be interpreted as an implication that cavitation cannot occur at some level in other regions of the hydrosonic mixer.
As a result of the creation and uniform distribution of microbubbles and the breaking of the van der Waals attractions, virtually complete oxidation of the Sodium Sulfide component of the black liquor is accomplished within the hydrosonic mixer. (Of course, a small amount of oxidation also may occur outside the mixer such as, for example, in the supply and outlet conduits of the system.) Further, the process can be accurately controlled by selecting rotation rate of the rotor and the amount of air initially introduced into the black liquor such that the complete oxidation is accomplished within a minimum time and with a minimum of energy and required introduction of air. The overall result is a gas/liquid mixing process that is far more efficient, faster, and more effective than is possible with prior art mechanical mixers. Once the Sodium Sulfide in the black liquor has been oxidized, the treated black liquor can be burned in a boiler with minimum of environmental toxins being produced and released to the atmosphere in stack gasses.
Thus, a method of mixing dissimilar fluids such as air and black liquor is now provided that addresses and overcomes the problems and shortcomings of the prior art. The method is highly efficient and effective and results in virtually complete oxidation of target components within black liquor or other liquids. These and other features, objects, and advantages of the methodology of this invention will become more apparent upon review of the detailed description set forth below when taken in conjunction with the accompanying drawing figures, which are briefly described as follows.
As mentioned above, the methodology of the present invention will be described within the context of its application to the oxidation of environmentally harmful compounds within black liquor in the pulp and paper industry. While this represents a preferred application and a best mode of carrying out the invention, it will be understood that the invention has numerous other applications wherever mixing of dissimilar fluids is required. In this regard, numerous examples of the application of the present invention in other mixing environments will be described following the detailed description of its application to black liquor oxidation.
Referring now in more detail to the drawings, in which like numerals refer to like parts throughout the several views,
A cylindrical rotor 17 is disposed within the cylindrical chamber 15 of the housing and is mounted on an axially extending shaft 18. The shaft 18 is journaled on either side of the rotor within bearing assemblies 19 that, in turn, are mounted within bearing assembly housings 21. The bearing assembly housings 21 are secured to the housing 12 by means of appropriate fasteners such as bolts 22. The shaft 18 projects from one of the bearing housings 21 for being coupled to a motive means such as an electric motor 46 (
The rotor 17 has a peripheral surface that is formed with one or more circumferentially extending arrays of irregularities in the form of relatively shallow holes or bores 24. In the illustrated embodiment, the rotor 17 is provided with two arrays of bores 24 separated by a void 26, the purpose of which is described in more detail below. It should be understood, however, that fewer or more than two arrays of bores may be provided in the peripheral surface of the rotor as desired depending upon the intended application of the hydrosonic mixer 11. Further, irregularities other than holes or bores also may be provided. The rotor 17 is sized relative to the cylindrical chamber 15 in which it is housed to define a space, referred to herein as a cavitation zone 32, between the peripheral surface of the rotor and the cylindrical wall of the chamber 15.
Inlet ports 25 are provided in the housing 12 for supplying fluids to be mixed to the interior chamber 15 within the housing. Supply conduits 30 are coupled to the inlet ports 25. A liquid supply conduit 27 is coupled to the supply conduits 30 for supplying liquid such as black liquor to the hydrosonic mixer 11. A gas supply conduit 28 communicates with the liquid supply conduit 27 for introducing and entraining gas in the form of bubbles within the stream of liquid flowing through the liquid supply conduit 27.
In the case of black liquor oxidation, within the context of which the present invention is described, black liquor is pumped through the liquid supply conduit 27 and air, which contains oxygen, is supplied through the gas supply conduit 28. At the junction of the liquid supply conduit 27 and the gas supply conduit 28, the black liquor and air form a gas/liquid mixture in the form of relatively large air bubbles 31 entrained within the flow of black liquor 29. This mixture of black liquor and air bubbles is directed into the cylindrical chamber 15 of the housing 12 through the supply conduits 30 and inlet ports 25 as shown. In the illustrated embodiment, an inlet port 25 is provided on either side of the housing 12 in order to equalize the hydraulic pressure on the rotor 17 to prevent undue stress on the bearing assemblies 19. However, this particular configuration is not a limitation of the invention and other configurations of inlet ports may be provided if desired.
An outlet port 35 is provided in the housing 12 and, in the illustrated embodiment, is located in the cylindrical wall of the housing to communicate with the cavitation zone 32 in a region of the rotor intermediate or between the arrays of bores 24. Location of the outlet port 35 in this way ensures that the entire volume of the gas/liquid mixture traverses at least one of the arrays of bores 24 and thus moves through a cavitation zone prior to exiting the hydrosonic mixer 11. Further, location of the outlet port 35 within the region of the inner chamber 15 aligned with the void 26 of the rotor prevents cavitation damage that otherwise might occur if the outlet port 35 were aligned with an array of bores 24. An outlet conduit 33 is coupled to the outlet port 35 for receiving treated black liquor and excess air from the hydrosonic mixer 11 and delivering it to a remote location for separation of the excess air from the treated black liquor and subsequent use of the treated black liquor.
In operation, the hydrosonic mixer 11 of
From the supply ports 25, the mixture moves toward the periphery of the rapidly rotating rotor 17 and enters the cavitation zones 32 in the region of the bores 24. As described in substantial detail in our previously issued U.S. Pat. No. 5,188,090, the disclosure of which is hereby incorporated by reference, within the cavitation zones 32, millions of microscopic cavitation bubbles are formed in the mixture within and around the rapidly moving bores 24 on the rotor. Since these cavitation bubbles are unstable, they collapse rapidly after their formation. As a result, the millions of microscopic cavitation bubbles continuously form and collapse within and around the bores 24 of the rotor, creating cavitation induced shock waves that propagate through the mixture in a violent albeit localized process.
As the mixture of black liquor and relatively large air bubbles moves into and through the cavitation zones 32, the air bubbles in the mixture are bombarded by the microscopic cavitation bubbles as they form and further are impacted by the cavitation shock waves created as the cavitation bubbles collapse. This results in a �chopping up� of the relatively large air bubbles into smaller air bubbles, which themselves are chopped up into even smaller air bubbles and so on in a process that occurs very quickly. Since the cavitation bubbles that cause the reduction of air bubbles into ever smaller air bubbles are microscopic in size, the practical lower limit to the size of the resulting air bubbles inherent in prior art mechanical mixing methods do not exist. Thus, the original air bubbles are continuously chopped up and reduced to millions of tiny microscopic air bubbles within the cavitation zone. The result is a total composite air bubble surface area in contact with the black liquor that is far greater than that possible in prior art mixing methods. Consequently, the probability that an oxygen molecule in an air bubble will �find� and come into contact with a sodium sulfide molecule within the black liquor is greatly increased.
In addition to creating a much larger surface area of air contacting the black liquor, the rapid rotary motion of the rotor within the housing in conjunction with the turbulent cavitation activity in the cavitation zones causes the very small air bubbles that are created to be distributed through the black liquor in an extremely uniform manner. This further increases the probability that oxygen molecules within the air bubbles will come into contact with sodium sulfide molecules within the black liquor. Such uniform distribution of air bubbles throughout the liquid has been confirmed by observing the electric current drawn by an electric motor driving the rotor. When air bubbles are introduced into the flow of black liquor, this current quickly reaches an equilibrium point, where it remains extremely constant for a given flow of air into the black liquor. If the air bubbles were not uniformly distributed the current drawn by the motor would fluctuate as the motor encountered pockets of more and less uniformly distributed bubbles within the black liquor. Thus, uniform current draw confirms the uniform distribution of bubbles throughout the black liquor.
Finally, the violent cavitation activity within the cavitation zone imparts sufficient energy to the mixture to break or loosen the molecular van der Waals attractions between the molecules within the black liquor. This results in a breaking up of molecule clusters within the black liquor thereby freeing sodium sulfide molecules that may be surrounded and shielded by other molecules within the liquor. These freed molecules are then available to come into contact with an oxygen molecule within an air bubble and thereby be oxidized. Therefore, the methodology of this invention also affects the black liquor on a molecular level to enhance and increase the percentage of sodium sulfide molecules within the black liquor that are oxidized.
After the black liquor has been treated and its environmentally hazardous compounds oxidized as described, it flows out of the chamber 15 along with residual air bubbles through the outlet port 35. At this point, the excess air within the black liquor quickly begins to agglomerate into larger and larger air bubbles, which naturally separate from the black liquor due to their buoyancy. The oxidized black liquor, which contains substantially smaller quantities of sodium sulfide than with prior art mixing processes, may be used as a fuel in the usual way without producing unacceptable levels of environmental toxins as described above.
As mentioned above, the methodology of the present invention has been described within the context of oxidizing environmentally harmful compounds within black liquor in the pulp and paper industry. However, the method is equally applicable to a wide variety of industrial processes, some of which are discussed briefly as follows.
1. Oxidation: The term �oxidation� is used throughout this specification to refer to an interaction between two compounds wherein a chemical reaction occurs between the compounds. Oxidation may, as in the case of the oxidation of black liquor discussed above, involve a chemical reaction with oxygen; however, the term �oxidation� as used herein is not intended to be limited to such reactions but rather to include chemical reactions between any elements and/or compounds. Such reactions may include classic oxidation/reduction reactions as well as other types of chemical reactions. The oxidation of environmentally harmful compounds within black liquor in the pulp and paper industry as described above is one example of the application of the present invention for oxidation. Other examples include, but are not limited to, satisfying biological oxygen demand (BOD) and chemical oxygen demand (COD) requirements in the wastewater treatment industry prior to discharging treated wastewater into rivers. In addition to the oxidation of black liquor in the pulp and paper industry, white liquor also may be oxidized for use in bleaching operations. Broadly, the methodology of the present invention is applicable to any situation where one substance is to be mixed with another in such a way that a chemical reaction occurs between the substances or a compound that is an integral part of one or more of the substances.
2. Oxygenation: The mixing of oxygen (or another gas) with a liquid in such a way that the oxygen molecules are trapped and held by van der Waals attractions between the liquid molecules is known as oxygenation. Oxygenation differs from oxidation in that a chemical reaction between the gas and liquid molecules does not occur but, instead, the gas molecules are dissolved in the liquid and loosely held between the liquid molecules. Oxygenation of liquids has applications, for example, in the oxygenation of fuels and fuel oils to enhance burning efficiency in boilers and in the oxygenation of water in aquariums and other aquatic tanks to provide essential oxygen to aquatic animals. Oxygenated drinking water also is becoming popular among many people.
Efficient and effective oxygenation of liquids may be obtained with the method of the present invention in much the same way as oxidation. Air in the form of bubbles is introduced into the liquid to be oxygenated and the mixture is introduced into the hydrosonic mixer, where the air bubbles are transformed into millions of microscopic bubbles by cavitation effects. The microscopic air bubbles are then distributed uniformly through the liquid and, at the same time, the van der Waals attractions between the liquid molecules are weakened or broken by the cavitation effects. Subsequently, when the molecules again begin to cluster as a result of van der Waals attractions, air or oxygen molecules become trapped and held within clusters of liquid molecules and the liquid is oxygenated. Because of the exceedingly small air bubbles, uniform distribution, and van der Waals effects, the methodology of the present invention results in substantially enhanced oxygenation efficiency over prior art techniques.
3. Heat Extraction From Stack Gases: In some applications, it is desirable to extract the heat from stack gases emanating from furnaces and boilers and to use the extracted heat in a constructive way such as to heat a liquid. Mixing of the hot stack gases with a liquid is one method of transferring the heat of the stack gases into the liquid. Other methods such as passing the gases through a heat exchanger immersed in the liquid also have been used to accomplish this goal. The methodology of the present invention is particularly efficient at transferring heat from hot stack gases to a liquid. In such an application, the hot stack gases are introduced into a stream of liquid and the mixture is directed into the hydrosonic mixer. Here, as in oxidation and oxygenation, the stack gases are distributed uniformly throughout the liquid. Because of the large composite area of contact between the hot stack gas bubbles and the liquid, the heat of the gases is transferred efficiently and effectively to the liquid. Thus, heat energy otherwise lost to the atmosphere or transferred inefficiently with prior art techniques is transferred to and heats the liquid. The stack gases (now cooled) and the liquid (now heated) can then be separated and the stack gases released to the atmosphere. Accordingly, the method of the invention may be applied in a highly efficient and effective process for recapturing and using the heat of stack gases.
4. Dissolved Air Flotation: Dissolved air flotation is a process whereby air (or another gas) is introduced into and mixed in a liquid having suspended particles that need to be separated from the liquid. Generally, the air molecules and small bubbles of air, once mixed in the liquid, attach themselves to the suspended particles within the liquid causing them to float to the surface of the liquid where they can be removed. Dissolved air flotation may be used, for example, in the pulp and paper industry to remove suspended fibers from a liquid. The method of the present invention is well suited for dissolved air flotation. In practicing the method for this application, air is introduced into the liquid and the mixture is directed to the hydrosonic mixer. There, the air bubbles are reduced to microscopic size and distributed uniformly through the liquid, resulting in a higher probability that the air bubbles will attach themselves to the suspended particles to be separated from the liquid. Upon leaving the hydrosonic mixture, the liquid may be directed to a separation tank, where the particles float to the surface under the buoyant influence of the attached air bubbles and can be skimmed or otherwise removed.
5. Mixing Of Dissimilar Fluids: In many industrial applications, it is desirable to mix two dissimilar fluids such as, for example, water and oil, to form an emulsion. The making of caulking compounds and the formation of oil and water emulsions are examples of such applications. The method of the present invention may be applied efficiently to form emulsions from dissimilar fluids. More specifically, one of the fluids, water for example, is introduced into a stream of the other fluid, oil for example, and the mixture is fed to the hydrosonic mixer. In the mixer, the cavitation bubbles and shock waves created mechanically by the rotating rotor impact the liquids breaking them down into extremely small units or droplets. The droplets are then distributed uniformly together by the violent agitation within the mixer. This, in conjunction with the weakening or breaking of the van der Waals attractions between fluid molecules, results in the small droplets of the fluids being attracted to and �holding onto� one another to form a tight and uniform emulsion.
6. Separation Of Emulsified Liquids: In some cases, it is desirable to separate a tight emulsion into its component liquids. For example, in the oil industry, oil from a well may take the form of an oil/water emulsion and it is necessary to separate the water from the oil prior to further processing. One way to accomplish this is to mix a gas, such as methane, with the oil/water emulsion to interfere with the van der Waals attraction between the oil and water molecules. The method of the present invention has been found to accomplish this task in a very reliable and efficient way. More specifically, the gas, methane for example, is introduced into a stream of the emulsion and the mixture is directed to the hydrosonic mixer according to the invention. In the mixer, the van der Waals attractions between the molecules of the two fluids in the emulsion are broken down and the methane gas is reduced to microscopic bubbles and distributed uniformly throughout the emulsion. Under these conditions, the methane gas molecules may attach themselves to one of the liquids preventing it from recombining with the other liquid and thereby separating the emulsion into its constituent components. The separated liquids may then be drawn off separately by conventional methods.
7. Atomization of Fuels to Enhance Burning
Atomizing a fuel before it is burned enhances the combustion efficiency of the fuel by exposing a significantly larger surface area of the fuel to heat and oxidizer. The mixing methodology of the present invention is well suited to the atomization of fuels. In an atomization application, a gas, which may be an oxygen containing gas to enhance burning further or may be an inert gas, is mixed with the fuel in the hydrosonic mixer according to the invention. The gas is broken down in to microscopic bubbles and dispersed uniformly throughout the fluid. This mixture may then be delivered to a boiler or other device in which the fuel is to be burned, where it is ejected as an atomized spray comprising very tiny droplets. The burning efficiency of the fuel is therefore enhanced.
The invention has been described and disclosed herein in terms of preferred specific examples, embodiments, and methodologies that represent the best mode known to the inventors of carrying out the invention. However, the invention is not limited to these illustrative embodiments and many other applications and variations may be made within the scope of the invention. Further, devices with configurations other than that illustrated herein for mechanically inducing cavitation effects used in the method of the invention are possible, the illustrated devices being only exemplary illustrations. In general, any mechanical apparatus capable of producing the cavitation effects described herein for purposes of mixing two dissimilar fluids is considered to be within the scope of the invention. These and many other additions, deletions, and modifications to the disclosed embodiments and methodologies may well be made by those of skill in the art without departing from the spirit and scope of the invention as set forth in the claims.
Patent Citations
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subset: commoncrawl


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» College News
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Christ Church's Tom Lees - Sportsman of the Year
Second year Christ Church student Tom Lees has been announced as Oxford University Sport Walter's Sportsman of the Year...
Updated: Sunday 16th February 2014 19:25
Students and Staff run Half Marathon
Students and Staff from Christ Church ran the Oxford Half Marathon on Sunday October 13th....
Updated: Tuesday 15th October 2013 8:47
New World Electric Land Speed Record
New World Electric Land Speed Record of 204mph set with YASA engine...
Updated: Friday 11th October 2013 14:08
Flautist Chloe Bradshaw wins Bryn Terfel prize
Christ Church music student Chloe-Angharad Bradshaw, wins the Bryn Terfel Scholarship at the Urdd Gobaith Cymru youth competition in Aberystwyth.
Updated: Sunday 16th February 2014 19:26
Belinda Jack appointed to London's Oldest Professorship
Four Century Old Tradition continued through The Mysteries of Reading and Writing:
Gresham College, London's oldest Higher Education Institution, is delighted to announce the appointment of Christ Church's Dr Belinda Jack as the new Professor of Rhetoric. Her free public lectures on The Mysteries of Reading and Writing will continue the College's tradition of offering free education for all, which began with the College's founding in 1597.
Updated: Friday 18th October 2013 16:37
Dr Edward Olleson RIP
We are sad to learn of the death of Dr Edward Olleson...
Updated: Saturday 28th September 2013 7:44
College Choir in Dublin
The Christ Church College Choir were on tour in July 2013, singing at Evensong and the Sunday Eucharist over four days at St Patrick' and Christ Church Cathedrals over days in Dublin.
Updated: Saturday 28th September 2013 7:44
Professor Sir John Gurdon Lecture - 24 May 2013
Sir John Gurdon is Christ Church's only living Nobel laureate, receiving the 2012 prize for Physiology or Medicine, shared with Professor Shinya Yakamata. The award recognised the profound consequences for human knowledge of his demonstration that mature animal cells can be reprogrammed to become stem cells, which can then develop into the various sorts of cells which form different types of animal tissue. In May 2013, Sir John inspired and entertained a packed Blue Boar lecture theatre with a lecture which both looked back to his time at Christ Church and explained the essential features of his work. A video of the lecture and the accompanying powerpoint presentation are available below.
Updated: Tuesday 9th July 2013 8:44
Michael Moritz, KBE
Michael Moritz, who studied Modern History at Christ Church in the 1970's has been made a Knight Commander of the British Empire (KBE) in the Queen's Birthday Honours list.
Updated: Saturday 28th September 2013 7:45
Professor Harry Anderson elected FRS
Professor Harry Anderson has been elected to the Fellowship of The Royal Society. Harry studied chemistry at Christ Church, Oxford, graduating in 1987.
Updated: Saturday 25th May 2013 11:38


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Redefining Girly: How Parents Can Fight the Stereotyping and Sexualizing of Girlhood, from Birth to TweenPaperback
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- Publisher: Chicago Review Press
- Format: Paperback | 256 pages
- Dimensions: 152mm x 228mm x 20mm | 160g
- Publication date: 1 January 2014
- Publication City/Country: Chicago
- Edition statement: New.
- Sales rank: 55,332
Product description
Containing practical, specific parenting advice; strategies for effecting change with educators, store managers, corporations, and more; and tips for challenging and changing the media, this essential guide gives parents the tools they need to fight back against the modern stereotyping and sexualization of young girls. Activist Melissa Wardy shares tangible advice for getting young girls to start thinking critically about sexed-up toys and clothes while also talking to girls about body image issues. She provides tips for creating a home full of diverse, inspiring toys and media free of gender stereotypes, using consumer power to fight companies that make such major missteps, and taking the reins to limit, challenge, and change the harmful media and products bombarding girls. Redefining Girly provides specific parenting strategies, templates, and sample conversations and includes letters from some of the leading experts in education, psychology, child development, and girls' advocacy.
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Melissa Atkins Wardy is the founder of Pigtail Pals & Ballcap Buddies, a company that sells empowering and inspirational children's apparel and products, and runs a blog of the same name focused on gender stereotypes and sexualization in childhood. Wardy discusses these issues facing families with thousands of parents using social media and workshops. She is also the cofounder of The Brave Girls Alliance, a gender equality think tank and advocacy group dedicated to communicating with and influencing media, corporations, and retailers. She has appeared on CNN and FOX News and in the "Boston Globe," "New York Daily News," "Huffington Post," and the "Ms. Magazine" blog, which have featured her work and her campaigns against national brands and retailers that resulted in the removal of sexist ads and products.
Review quote
"Melissa Wardy's book reads like a conversation with a smart, wise, funny friend; one who dispenses fabulous advice on raising a strong, healthy, full-of-awesome girl." --Peggy Orenstein, author, Cinderella Ate My Daughter "This eye-opening tome is an absolute must-read." --Starred review, Publishers Weekly "Melissa Atkins Wardy writes with incredible insight, respect and honesty." -- The Tribune (Greeley, CO) "Redefining Girly is as interesting as it is educational, and Wardy provides parents with an easy, at times step by step guide on how best to respond to various scenarios relating to girlhood." --Metapsychology.net "Taking on the media's widespread stereotyping and sexualization of childrenparticularly girlsadvocate Wardy offers a thoughtful, comprehensive guide to raising healthy, happy, confident children. She includes a savvy take on the consequences of "princess culture," along with suggestions for gender-neutral toys, clothing, and parenting." Publishers Weekl , Best Books of 2014 "Grounded in her own experiences as a mother and activist, Melissa Atkins Wardy offers honest and clear strategies to help girls define and decide what being a girl means to them. This is a vital guide for supporting girls as they navigate the rising tide of gender stereotyping." Deborah L. Tolman, professor of social welfare and psychology, Hunter College School of Social Work and the Graduate Center, CUNY, and cofounder, SPARK


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Alexander Mikulin
From Wikipedia, the free encyclopedia
|This article does not cite any references or sources. (November 2009)
Alexander Alexandrovich Mikulin (Russian: Алекса́ндр Алекса́ндрович Мику́лин) (February 14 (O.S. February 2), 1895, Vladimir – May 13, 1985, Moscow) was a Soviet aircraft engine designer and chief designer in the Mikulin OKB. His achievements include the first Soviet liquid-cooled piston aircraft engine Mikulin AM-34 and the Mikulin AM-3 turbojet engine for Soviet Union's first jet airliner Tupolev Tu-104. Mikulin also took part in the Tsar Tank project.
|This biographical article related to aviation is a stub. You can help Wikipedia by expanding it.


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Search results for breezy
Baby Breezy? Chris Brown Couples Up With Karrueche For Movie Night As She Sparks More Pregnancy Rumors [Photos]
Poor Thang: Haters Tell Karrueche To Be Breezy's "Main Chick" After She Asks For Halloween Costume Ideas
Karrueche as a main chick? That's a scary sight!
Badgal Diaries: Rihanna Secretly Rejoins Instagram & Says She's "Open" To Doing A Song Featuring Drake And Breezy?!
Peep pics from Rihanna's "new" IG page & see what the word is on her hitting the studio for a Drake-Breezy collabo…
Practicing For Parenthood? Breezy Kicks It With Karrueche And This Cute Kiddo At The Grove
We haven't seen them having this much fun in a minute.
Watch Ya Back Karrueche… Kendall Jenner Is "Obsessed" With Bad Boy Breezy!
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Bicken Back Being Breezy? LAPD Looks To Get Gang-Bangin' Chris And Crew Blacklisted From Nightclubs And Venues
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The BET Hip-Hop Awards and iHeartRadio festival weren't the only big events going on this weekend.
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Poor guy just had a little case of incarceration itis…
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It sounds like the future. Whirring electric skateboards, the joyous chatter of children in a distant playground and an unusual absence of petrol-powered machinery. It looks like the future, too. Glistening lakes dotting the background, lawns so lush they're mistaken for artwork and an unmistakabl
1 year ago 0 Comments


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Weber said feedback from wearers of these new Toasty Feet insoles include remarks such as:
"The Foot Warmers work! I recently moved to Alaska from North Carolina, now my feet are warm!"
"Excellent product. I am amazed how good these are, am going to buy more!"
"Got the foot warmers…they work!"
(2) Wrist & Ankle Wraps: are designed to help keep hands, fingers, feet and toes warm and comfortable in all kinds of weather. These non-electric Wraps are made to be used by people in physical therapy as well as all of those involved in a wide variety of outdoor activities. In addition, they have been found to be very beneficial to people who suffer with Raynaud's Syndrome. The Wraps use the same NASA insulation material as in the foot warmers. These wraps effectively maintain the temperature of the blood at approximately 72-degrees as it circulates naturally from the wrists to hands and fingers, and from ankles to feet and toes. It is suggested these wraps be worn 24/7 as much as possible, as a way to gradually, over time, improve blood circulation to those extremities as much as possible. When asked what kind of feedback he gets from users, Weber gave these examples of customer's comments:
"I have worn the heck out of the ankle and wrist wraps! They have helped with my circulation in both my hands and my feet."
"Wraps are as described, fast shipping, highly recommend these wrist wraps."
"Thrilled with the purchase of the wrist and ankle wraps."
"Fast shipping. Printed description is accurate. I'll recommend these wrist wraps."
"Wraps are as described. Fast shipping. Highly recommend."
(3) Cold Weather Breath Warming Face Mask: This non-electric mask is designed to eliminate the many dangers that can be the result of inhaling very cold winter a
|Source: PRWeb
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Wealth and Poverty of Nations
I think both arms of the Christian faith helped lay the foundation which allowed for the boom in economic prosperity and sowed the seeds of the Industrial revolution.
David Landes' book "Wealth and Poverty of Nations" was an interesting read pointing to the Protestant promotion of valuing hard work, savings, timeliness, enterprise and free-thinking in a way that hadn't been seen before which promoted economic prosperity.
Again, I think they both contributed and am looking forward to reading Wood's books on Church and Market and Church Built Wester Civ to see the arguments he makes for the Catholic contributions etc.
I don't think either one has a complete monopoly on the claim to being foundational, but perhaps one contributed more than the other.
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Roraima Adventures
Roraima Adventures offers professional multiday camping tours all over Roraima, including Serra do Tepequém and Mt Roraima in Venezuela,...
Porto do Babazinho
Porto do Babazinho is home-base for longtime local guide Sebastião de Souza e Silva (aka 'Babazinho'), who leads and arranges a variety...
Praia Grande
A tawny sandbar beach emerges on the far bank of the Rio Branco, opposite Boa Vista, during low water, roughly December to April. Known...
La Gondola
Facing the plaza across a busy intersection, this small per-kilo place offers outdoor, fan-cooled or air-con dining areas, in addition...
cnr Rua Araújo Filho & Av NS da Consolata · interesting places nearby
S69 information
Boa Vista's most prominent gay club makes the most of its once-weekly schedule, with dancing and drinking until dawn. This is actually a GLS spot – gay, lesbiana, e simpatizante (gay, lesbian, and down straight people) – and foreigners are welcome.


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Jerry Brown Declares His Candidacy For Governorship Of California Again
By Nicole Belle March 2, 2010 1:00 pm -
Don't look now, my fellow Californians, but it's official: Governor Moonbeam is back. Attorney General Jerry Brown will declare his Democratic cand
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Sen. Kyl: Unemployment Benefits A 'Job Disencentive'
Glenn Beck Claims Progressivism Leads To Nazism. Oh Really?


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The films of Morgan Freeman
Published: Jun 26 2012 06:13:29 PM EDT Updated On: Sep 12 2014 10:37:39 AM EDT
Oscar-winning actor Morgan Freeman has built up an impressive resume as one of Hollywood's most distinctive talents. Take a look back at the film star's career over the years as he appears in "Dolphin Tale 2."
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I am using Unity as my IoC framework and I am creating a type based on the value in the header of each request in a handler:
var container = new UnityContainer();
container.RegisterType<IFoo,Foo>(new InjectionConstructor(valuefromHeader));
GlobalConfiguration.Configuration.DependencyResolver =
new Unity.WebApi.UnityDependencyResolver(container);
The problem is that the handler's
SendAsync means that the global container is getting overwritten by different requests and the controllers that use IFoo in their constructor are getting the wrong values.
1) Can I make the SendAsync sync? 2) If not, how do I create different instances for each request and have the IoC container resolve safely?
I have looked at the following articles without success:
http://www.asp.net/web-api/overview/extensibility/using-the-web-api-dependency-resolver http://www.strathweb.com/2012/11/asp-net-web-api-and-dependencies-in-request-scope/ http://benfoster.io/blog/per-request-dependencies-in-aspnet-web-api-using-structuremap
Thanks in advance.


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Effortlessly Cool Anorak Jackets
Effortlessly cool and perfect for layering, the anorak jacket has been become a modern staple in our everyday lives. This season, the latest cuts from brands like 3.1 Phillip Lim, Madewell, and Burberry are offering up a bevy to choose from, featuring refreshing details and a wide range of silhouettes. Pair it with jeans and flats for an easy weekend getup, or style it with a moody floral dress ankle boots for a bohemian Fall ensemble.
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The quintessential cool-girl jacket (aka every girl needs one). In water-resistant waxed cotton with military-inspired pockets and snaps, this is our idea of standard issue. Boxy fit. Body length: 25". Sleeve length: 33 1/8". Hits at hip. Cotton. Standing collar. Snap front with hidden zip closure. Adjustable waist tabs. Chest pockets, hip pockets. Machine wash. Import.
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This military-inspired field jacket features authentic details—like epaulets and pockets that button—and a softly worn-in finish. It's just the layering piece for ever-changing weather (and makes everything underneath it look cooler too). True to size. Cotton with a hint of stretch. Machine wash. Import.
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The anorak-style hooded jacket that packs down small for travel and gives you water-resistant DWR protection wherever you end up. Adventure Travel Hike/Explore Semi-fitted Two-way front zip for extra ventilation, adjustable hood with hidden easy-pull cinches for extra rain coverage, internal waist cinch lends a more contoured fit Sleeves roll up and snap at two adjustable points, hidden side zip pockets secure your stuff Classic anorak-inspired style lines Body length in size medium: 29'' Polyester Water-resistant DWR finish wards off the elements to keep you fully covered Lightweight, sleek fabric packs down small to tote wherever you go Imported Machine wash and dry. Imported.
Athleta Yaletown Jacket $128 $79.99
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The presidential joint with the Ronald Reg sheets
from Fabolous (Ft. Freck Billionaire, Paul Cain & Red Cafe) – Taking Pictures Lyrics on Genius
This a play on former US President Ronald Reagan and a luxurious presidential suite in Las Vegas.
As a famous rapper, Fab only stays at the best, just like a president would and so even has presidential bed sheets.
To help improve the quality of the lyrics, visit "Taking Pictures" by Fabolous (Ft. Freck Billionaire, Paul Cain & Red Cafe) Lyrics and leave a suggestion at the bottom of the page


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White Sands 2013 Collection At Mercedes Benz Fashion Week Swim, Miami Beach (PHOTOS, VIDEO)
It was all feminine, all the time at White Sands' Swim Week runway show.
From ruffles to ruching to florals to sequins, taking in the Australian labels' 2013 collection was like a trip to a (considerably glamorous) pastel boudoir, except with a lot more sunscreen.
Do you love it? Hate it? Can't wait to wear it? Let us know!


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Updated 04/02/2013
In the 1920s, the swanky Palais de la Méditerranée drew performers like Charlie Chaplin and Edith Piaf; however, the establishment lost its glory and was demolished in 1990, save for the facade we see today. Reopened with hotel service in 2004, the contemporary version has 200 slot machines, plus roulette, blackjack, and Texas hold 'em poker tables. Theme-night Thursdays include a buffet and live entertainment (€25–€40). The casino is open weekdays from 10 am to
3 am and until 4 on the weekends.
15 Promenade des Anglais, Nice, 06300, France
/04–92–14–68–00-show reservations
Website: www.casinomediterranee.com
Updated 04/02/2013


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The Diablo 7-1/4 in. x 60 Tooth Carbide Circular Saw Blade contains Perma-Shield coating to protect against heat, gumming and corrosion. The TiCo high density carbide construction is durable and strong for fast, accurate wood and plywood cuts.
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|0.625 In.
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If for some reason you are not completely satisfied with your purchase this holiday season, choose our FREE pre-paid shipping label and we'll cover your return! This offer is only good on eligible orders placed between November 1, 2014 and December 24, 2014. We've extended our normal return period to January 15, 2015 or 30 days after your order is received - whichever comes later. Learn more about our return policy.
Enjoy free shipping this holiday season! Shop now and get Free Value Shipping on most orders over $29.95 to contiguous 48 states, DC and to all U.S. Military APO/FPO/DPO addresses.
Our Allen Mens and Womens Apparel page allows you to narrow down our incredibly extensive selection. As part of our continuing mission to be your one-stop retailer for Allen Mens and Womens Apparel and our other great product types, we've expanded OpticsPlanet to incorporate many hundreds of thousands of products. From our extensive selection of accurate riflescopes, reflex sights and leather holsters for hunters, shooters and law enforcement professionals to our many scientific microscopes, magnifiers and lab supplies for lab techs, we do whatever possible to give you the widest selection on the web! And we're always trying to go beyond what's necessary, giving you much more than a huge number of choices. Our customer service group is very well trained to aid you in your mission to find what you need, and when a question is outside of their level of expertise, one of our product specialists steps in to guide you to an answer on the most challenging queries. In addition, we have expanded our list of How-To Guide Articles and our blogs, which are regularly updated to give you the latest industry information and reviews of today's top tech so you can get the most out of your new Allen Mens and Womens Apparel! We will continue doing our best to add to our selection of Allen Mens and Womens Apparel so that OpticsPlanet can always be your favorite source for all things Mens and Womens Apparel!
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Safari Awards - Past Results
This section lists the winners and finalists from 2008 - 2014.
To view the 2014 Africa Results, click here.
To view the 2014 Country Results, click here.
Or click on the links below to view the winners from previous year's awards:
(Note that due to a change in our calendar, there were no 2012 Awards.)


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"Somewhat Interesting, But..."
To put it succinctly, the narrator ruined this book for me. Maybe Mr. Sklar would be great reading Shakespeare but this book is a work of non-fiction. I was constantly distracted by his attempts at reading life into the words, laughing at times, most times very animated, and always inappropriate in my perspective. There are very few books for which I am bothered by the narrator, but this is certainly one.
Now, as for the book itself... I like the history of science and great scientists. The Clockwork Universe did contain quite a bit of information about Newton, et al., that I didn't know and found intriguing. However it seemed a bit disjointed to me, even for non-fiction, bouncing around from one time period to another without context.
Other Ratings:
Probability of Listening to it Again: 1
Would Purchase Again Knowing What I Know Now: 1
"Hugo and Nebula???"
I have this completion problem. When I start a book I must finish it. Thankfully Blackout came to an end before I slit my wrists. This was painful so when the abrupt end came 1) I wasn't happy that I'd gone through 18 hours only to not have an ending, and 2) I had no interest at all in going through more pain to get to the ending.
I suppose condensing Blackout into five or six hours and giving it an ending could redeem it, but I'm no editor, just a reader (or listener as the case may be). And speaking of reading... if this book won a Hugo and Nebula, I certainly don't want to read the #2 books from 2011.
"Will not listen twice"
There are some books that I can listen to (or read when not driving) over and over again. This definitely is not one of them. It seems in search of a real plot and a real meaning.
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free shippingon most orders over $49*
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Safavieh Martha Stewart Reptilian Creme Area Rug
The exotic look of reptile skins inspires the textural geometric patterning of Reptilian. Viscose fibers create the lustrous colors and soft, silken feel of this beautifully crafted Belgian-made area rug. A chenille-weave background sets off the fine line detail of the contrasting cut-pile design.
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A discrete position sensor elimination technique for a sinusoidally wound synchronous reluctance motor drive uses induced voltage, phase currents, and excitation frequency to estimate rotor position at all speeds, including zero speed.
1. A method of detecting rotor position in a rotating sinusoidally excited synchronous reluctance electric machine having multiple stator phases which are energized by sinusoidal currents at an excitation frequency in all phases comprising the steps of:
interrupting the excitation to a first phase at a zero crossing for that phase current for a predetermined period of time to create a zero crossing window thereby enabling the reading of the induced voltage in the disconnected phase;
simultaneously coupling the other phases to sinusoidal excitation for the same period of time;
reading the induced voltage in the first phase;
detecting the phase currents in the other phases; and
calculating the rotor position from the read induced voltage, detected phase current, and the excitation frequency.
2. A method of determining rotor position in a sinusoidally excited, multi-phase synchronous reluctance machine at stand-still, comprising the steps of:
energizing a phase pair with a diagnostic signal to develop a diagnostic current;
detecting the diagnostic current;
determining the rate of change of the diagnostic current to determine the slope of the diagnostic current;
reading the induced voltage off another phase; and
using the read induced voltage and the slope of the diagnostic current to determine the rotor position at stand-still.
3. A device for determining the position of a rotor in a rotating, sinusoidally excited synchronous reluctance machine comprising:
a. a plurality of switches for selectively coupling the stator windings to a source of sinuosidal electrical excitation;
b. a driver to selectively de-couple one phase of the stator windings from the source of excitation and to couple the remaining phases of the stator windings to the source of excitation;
c. a voltage sensor to sense the voltage induced in the stator windings de-coupled from the source of excitation and to output a sensed voltage;
d. a current sensor to sense the current in the coupled windings and to output a sensed current;
e. means for determining the rate of change of the current sensed by the current sensor and to output a current slope;
f. means for determining the frequency of rotation of the rotor; and
g. means for determining the rotor position from the sensed voltage, the sensed current, the current slope, and the frequency of rotation.
4. The device of claim 3 wherein the means for determining rotor position comprises a controller including a look-up table with a plurality of rotor position determinations stored therein.
5. Apparatus for determining rotor position in a multi-phase sinusoidally excited synchronous reluctance machine at stand-still, comprising:
a source of excitation for energizing a phase pair with a diagnostic signal to develop a diagnostic current;
a current sensor for detecting the diagnostic current;
means for determining the rate of change of the diagnostic current to determine the slope of the diagnostic current;
a voltage sensor for detecting the induced voltage off another phase; and
a processor for determining the rotor position at stand-still using the read induced voltage and the slope of the diagnostic current.
6. The apparatus of claim 5 wherein the processor includes a controller including a look-up table with a plurality of rotor position determinations stored therein.
7. A device for determining the position of a rotor in a rotating, sinusoidally excited, multi-phase, synchronous reluctance machine comprising:
a. means for interrupting the excitation in a first phase of the stator windings to develop a zero-crossing window;
b. a voltage sensor to sense the voltage induced in the stator windings in the first phase;
c. a current sensor to sense the current in another phase;
d. means for determining the rate of change of the current sensed by the current sensor and to output a current slope;
e. means for determining the frequency of rotation of the rotor; and
f. means for determining the rotor position from the sensed voltage, the sensed current, the current slope, and the frequency of rotation.
The present invention relates generally to the field of shaft or rotor position sensors in synchronous motors, and more particularly, to a method and apparatus for the determination of rotor position in a sinusoidal synchronous reluctance motor from the voltage induced in a stator phase.
The present invention is directed to a specific reluctance motor referred to herein as a sinusoidal synchronous reluctance motor (SynRM). A sinusoidal synchronous reluctance motor is a synchronous machine with a well-defined salient pole rotor and a multi-pole stator excited by phased, sinusoidal currents. While such machines have been known for decades, recent advances in the manufacturing techniques for salient pole rotors and advanced current control techniques have only now made the power factor and efficiency of the machine competitive and consequently more attractive for a variety of applications.
Recent renewed interest in synchronous reluctance motors is mainly due to modern field oriented control strategies recently applied to these motors. In particular, it has been shown that a properly designed and field oriented SynRM can perform as well as an induction motor drive when the field weakening range is not too wide. On the other hand, the inherent characteristics of the SynRM make it preferable for some applications. For example, the stator of the SynRM is constructed from a cylindrical structure identical to an induction motor. Hence, the stator of both machines can be constructed from the same assembly line. Further, no starting cage is necessary with an inverter supply. The rotor can therefore be designed purely for synchronous performance.
The electronic control makes a SynRM auto-synchronous and can assure an optimum torque angle at all loads and torques, consequently giving the motor a very high pull-out torque. Also, no damping winding is necessary. This makes it possible to design the motor for the highest reluctance difference Xd -Xq, thereby increasing the power density of the machine. Finally, torque pulsations and acoustic problems are not as severe as those for variable reluctance machines and vector control techniques can be applied in order to achieve high performance.
However, like other ac machines, field orientation control of SynRM requires rotor position information. Particularly, high performance machines calling for torque control need such rotor position information.
A discrete rotor position sensor reduces the reliability and ruggedness of the drive and increases its cost. But, the SynRM possesses unique features which make position sensing much simpler and reliable than either conventional squirrel case induction machines or variable reluctance machines. In contrast to induction machines, the SynRM possesses saliency which permits the rotor position to be sensed since the inductance per phase is a function of rotor position. This allows sensing position at zero speed which is impossible for an induction machine. Secondly, in contrast to the variable reluctance motor, the stator windings of the SynRM are magnetically coupled. Hence, voltages are induced in the stator winding upon open circuit of a phase, which allows for sensing of the coupled voltage. These two features in combination make the task of sensing position easier than for either an induction or variable reluctance motor.
Thus, there remains a need for an indirect rotor position sensing technique and apparatus for a SynRM, utilizing only the input variables (voltages and phase currents) and the rotor saliency information. Further, there remains a need for a simple yet robust rotor position sensing technique that provides for sensing the rest position of the rotor (i.e., at no rotation) during startup operation. Such a rotor position sensing technique and apparatus should require no discreet, specially dedicated components, but rather should use available parameters, such as voltage and phase currents.
The present invention provides such a method and apparatus for determining rotor position using the mutual inductance of a synchronous machine. Power electronics techniques, involving pulse width modulation (PWM), are used to successfully produce adequate coupling voltages, even at zero speed, despite the fact that prior art study has made or assumed the mutual inductance between phases to be negligible or that the voltages caused by mutual couplings are too weak to be read accurately, especially at low motor speeds.
A variable speed :motor drive has a power electronic converter connected to it anyway and thus the present invention can be implemented at no additional cost. Furthermore, prior art devices have suffered from the fact that coupled or other airgap voltages cannot be read off the motors whose phases are in continuous conduction (such as a synchronous reluctance motor). However, the power converter switching technique of the present invention provides a sampling window at the instant of the zero crossing of the current in a particular phase; the coupled voltage induced in the disconnected phase of interest can be read with any degree of accuracy required.
The coupled voltage, which is read from the motor, will have predictable rotor position angle information embedded in it. By knowing the relationship between this voltage and the rotor angle, it is possible to estimate the rotor position, which is required in all high performance adjustable speed motor drives. The sensing device of the present invention is particularly useful in motors used with slowly changing loads, such as pumps, compressors, fans, etc. For a slowly changing load, the rotor position information need not be continuous and thus, such drives can be implemented by measuring rotor position periodically. Rotor position can be measured at the zero crossings of the phase currents, which provides six samples every electrical cycle for a three phase motor.
The method and apparatus of the present invention is also useful as an indirect startup technique for a synchronous reluctance motor drive. For most ac machines, it is either impossible or at least very complicated to determine rotor position during startup operation. Thus, these motors operate in open loop until the motor induced voltage is large enough to be sensed. Also, the sensed voltage is often noisy and very difficult to sense. The synchronous reluctance motor, however, possesses unique features which make position sensing much simpler and more reliable, even at standstill. In contrast to induction machines, the SynRM has saliency which permits the rotor position to be sensed since the inductance per phase is a function of rotor position. This allows sensing position at standstill which is impossible for an induction motor. The present invention also provides an indirect startup rotor position sensing technique for a synchronous reluctance motor drive which involves use of electrical quantities at the motor terminals.
These and other objects and features of the present invention will be apparent to those of skill in the art from reading the following detailed description.
FIG. 1 is a schematic diagram of the stator and rotor configurations of the sinusoidal synchronous reluctance machine to which the present invention is applicable.
FIG. 2 is a schematic diagram of the motor drive and coupled power converter that includes the sensing technique of the present invention.
FIG. 2(a) is a detail of the schematic diagram of FIG. 2.
FIGS. 3(a) and 3(b) depict circuit configurations during the extension of a zero crossing period of one phase current.
FIG. 4 is a plot of the current in phase A showing the extension of the zero crossing during a sampling period.
FIG. 5 is a plot of the currents in phases B and C during the same period as in FIG. 4 to show constant PWM during the extended zero crossing period of phase A.
FIG. 6 depicts phase induced voltage during the constant PWM of FIG. 5 of phases B and C.
FIG. 7 depicts line-to-line induced voltage in phases A and C for the period of FIG. 6.
FIG. 8 depicts the current through phases B and C when the induced voltage is measured across phase A at zero speed.
FIG. 9 and 10 depict induced voltages at zero speed for different rotor angles, FIG. 9 and 25 degrees, and FIG. 10 at 205 degrees.
FIGS. 11-16 depict waveforms of experimental results derived from tests of a machine built in accordance with the present invention. FIG. 11 depicts phase A current with an extended zero crossing period. FIG. 12 depicts phase B current during the period shown in FIG. 11. FIG. 13 depicts induced voltage in phase A. FIG. 14 depicts phase A current during acceleration from rest. FIG. 15 depicts induced voltage in phase A during start up. FIG. 16 depicts diagnostic current through phases B and C during startup.
FIG. 1 schematically depicts a 2-pole, 3-phase, wye connected SynRM 10. The three phases, as, bs, and cs, with associated currents and voltages, are shown conventionally. The three phases of stator windings are shown schematically as as-as', bs-bs', and cs-cs' in the conventional manner.
A rotor 12 comprises an axially laminated rotor of the type described in Lipo, "Synchronous Reluctance Machine--A Viable Alternative for AC Drives?", Electric Machines and Power Systems, vol. 19, pp. 659-671, 1991, incorporated herein by reference.
The performance of this machine can be described by: ##EQU1## where Vas, Vbs, and Vcs are the applied terminal voltages, as shown in FIG. 1, rs is the stator winding resistance, and λas, λbs, and λcs are the flux linkages of the individual phases. The flux linkages can be expressed as:
λas =Laa ias +Lab ibs +Lac ics(4)
λbs =Lab Ias +Lbb Ibs +Lbc Ics(5)
λcs =Lca ias +Lbc ibs +Lcc ics (6)
where the self and the mutual inductances of the machine can be written as: ##EQU2## where Lmq =3/2(LA -LB) and Lmd =3/2(LA +LB). Equations 4-6 show the coupling between different phases and equations 7-12 show the dependence of the mutual and self inductances on the rotor position, θr. The technique of the present invention utilizes these facts to determine the rotor position as described below.
FIG. 2 depicts the complete drive system of the present invention. The drive system includes a voltage source V and a coupled parallel capacitor C. The power source is connected to a set of switches S1-S6, as shown. The wye-connected windings tap off the center-points between switches S1 and S2, S3 and S4, and S5 and S6.
Between the switches and the windings are two sets of sensors, currents sensors 20 and induced voltage sensors 22. The induced voltage sensors 22 are coupled to a controller 24 via an isolation circuit 26. The current sensors 20 are coupled to the controller 24 via a zero crossing detector 28 and constant PWM generator 30.
IGBT's are used as the power semiconductor devices and are driven by high voltage integrated circuit gate drivers, preferably FUJI EXB841. The controller is configured to take the induced voltage and the phase currents and generate the gate switching signals for the three phases. The remainder of the drive system consists of the induced voltage sensing circuit which is interfaced with the phase coils. Isolation of the sensing circuit from the power circuit is accomplished by using a high frequency isolation transformer. The control algorithm routinely measures the rotor angular positions and makes the drive self-synchronized by advancing or retarding the phase currents.
FIG. 2(a) depicts further details of the schematic of FIG. 2. Elements in common with those of FIG. 2 are similarly numbered. The controller 24 has stored therein the sinusoidal waveform that ultimately excites the windings of the stator, as described. In the present invention, the zero crossing detector recognizes when the current in phase A, for example, crosses zero amps. At that instant, the controller issues control instructions that open switches S1 and S2 to de-couple phase A from the excitation for a short period of time, referred to herein as a "window" or extended zero crossing. In this way, the current in phase A is zero and the voltage in phase A comes only from mutual inductance from phases B and C. Similarly, the controller 24 issues control instructions that open switches S4 and S5 to provide the current path shown in FIG. 3(a). Significantly, the phase current in phase B (and phase C) goes into constant PWM during the period of extended zero crossing. This provides the state during which the measurements can be made from which rotor position can be calculated, as described below.
In a preferred embodiment, the controller 24 includes on-board memory, a portion of which includes a look-up table 40. The look-up table 40 includes rotor-position calculation results to any accuracy desired, depending upon the memory space available. (A similar memory space stores the sinusoidal waveform for excitation of the motor.) The calculation results provide an output θr over an output line for such applications as torque/speed control.
The rotor position information embedded in the SynRM equations above is obtained using the drive circuit of FIG. 2. This technique uses a switching technique for the current-regulated pulsewidth modulated (CR-PWM) converter. In a known CR-PWM converter, the phase switches are normally turned on and off in order to make the individual phase currents follow the desired reference within a desired band.
FIGS. 3(a) and 3(b) show the switching technique of the present invention. In this new switching technique, both switches of that phase are turned off when the current of a particular phase (e.g., phase A) crosses zero. The remaining two phases (in this case phases B and C) are excited in series by turning on alternate pairs of switches (the lower switch of phase B and the upper switch of phase C; FIG. 3(a)) or the lower switch of phase C and the upper switch of phase B (FIG. 3(b)).
This switching pattern will extend the zero crossing interval of phase A for a short interval. The currents in phases B and C can be controlled to follow a constant reference during this period. The description of this constant reference PWM of the phases B and C is explained below.
Although current of phase A during this extended zero crossing period will be zero, a voltage is induced in phase A due to the currents in the other two phases, which can be obtained by setting ias =0 in Equation 1, above. Thus, ##EQU3## Since phase B and phase C are now effectively in series, ibs =-ics and d/dt (ibs)=-d/dt (ics) and Equation 13 becomes ##EQU4## Using Equations 10 and 11, the induced voltage becomes: ##EQU5## In Equation 17, ωr is the rotor speed in hertz, which is equal to the frequency applied to the stator divided by the number of pole pairs. Thus, by knowing the induced voltage Vind, the slope and the instantaneous value of the current ibs and using ωr, yields by computation the instantaneous value of the rotor position.
FIG. 4 depicts the waveform of the phase A current of a SynRM drive wherein the zero crossing period of the phase A current is extended by applying the device of the present invention. During the extended zero crossing period of phase A current, phases B and C of the converter are switched in a special diagnostic manner for a short interval. This diagnostic switching interval consists of following a constant reference current, in each phase, by means of hysteresis control. The level of the constant reference currents in phases B and C are exactly the instantaneous values of these currents, respectively, at the instant of phase A current zero crossing, as shown in FIG. 5.
During this diagnostic PWM interval, the instantaneous slopes and the magnitudes of phases B and C currents become equal and opposite. The voltage induced in phase A due to the currents flowing through phases B and C is shown in FIG. 6. The sequence of coupled voltage pulses, shown in FIG. 6, has the instantaneous rotor angle encoded in their amplitudes, according to Equation 15. Each individual pulse amplitude sample can deliver one rotor angle sample by use of a look-up table. The table contains the inverse function of Equation 15, solved for θr, in discrete form. Thus, several samples of the rotor angle are obtained during each diagnostic PWM interval.
These samples can be used for two purposes. The multiple samples can be used in an error reduction and noise elimination algorithm. The change of θr, from sample to sample can also be used to enhance speed and rotor angle extrapolation algorithms between two zero crossings when the change of speed is very high, such as during start-up. Also, the mathematical analysis (Equations 4-12) is only used to show the background of the present invention. In practice, the actual measurements of voltages, currents, rotor angles, etc., from the motor are used to create the look-up table. Thus, the non-ideal variations, of the actual machine parameters, from the theory will be accounted for in the look-up table.
Although the proposed technique has been described only for phase A, the same technique can clearly be applied for phases B and C. Thus, for the six zero crossings within one electrical cycle of a three phase machine this technique gives six rotor position measurements. Therefore, extrapolation technique has to be applied in order to estimate rotor positions between two zero crossings. A linear extrapolation will be sufficient to estimate rotor positions during the constant speed operation of the drive. But, during the acceleration period of the drive, linear extrapolation will introduce errors in rotor position estimation. Thus, acceleration of the drive has to be limited so that the rotor estimation error between two zero crossings does not exceed a predefined error margin. If the individual sample error Δθsample at each zero crossing, is taken as the acceptable margin of error for extrapolation between two zero crossings, then the acceleration, a, of the drive is limited by,
α≦72�Δθsample ��e 2
where fe is the electrical frequency of the drive.
The zero crossing window of phase A current, FIG. 4, has been made longer than necessary in order to illustrate the concept of the new switching technique. This extension of the zero crossing period of one phase and constant PWM of the remaining two phases will introduce lower order harmonics in the stator currents. However, in a practical implementation of a SynRM drive this zero crossing window will be much smaller than shown here because a very high frequency PWM will provide the required number of voltage pulses as shown in FIG. 6 within a very short interval and consequently the zero crossing windows can be made very small. A small zero crossing window will ensure less torque pulsations as well as insignificant lower order harmonics introduced in the stator currents. Lower order harmonics introduced because of a 200 μsec window (which is enough to record the required voltage pulses using the microcontroller INTEL 196KR) are insignificant compared to the fundamental component of the stator current which can be seen from the following tables giving the ratio between fundamental and harmonic currents.
TABLE 1______________________________________Harmonics in phase A currentHarmonic No. Fund./Harm (%)______________________________________ 2 2.5 3 2.4 4 1.6>5 <1,5______________________________________
TABLE 2______________________________________Harmonic in phases B & C CurrentHarmonic No. Fund./Harm (%)______________________________________3 1.75 1.67 1.5>9 <1.3______________________________________
In one aspect, the present invention calls for access to the center point of the stator of the machine. This requirement can be avoided with a simple modification of the switching technique. When the center point is not available, the controller will read the induced voltage between phase A and either of the remaining two conducting phases. It is possible to formulate the induced voltage expression similar to Equation 14 for this modified form of switching. In the example shown in FIG. 6, the induced voltage is measured between the phases A and C. Pulses of the coupled voltages shown in FIG. 6 contain the rotor position information.
The method of the present invention can determine the rotor position even at zero speed. At zero speed all phase currents are zero. In this state, diagnostic PWM signals may be induced on any pair of phases while the current in the other phase is controlled at zero current. The additional advantage is that the zero crossing can be made to persist for as long as one wishes the diagnostic interval to be. Furthermore, the speed term ##EQU6## in Equation 14 is eliminated in the look-up table for θr, which can now be derived from: FIG. 8 depicts the diagnostic current of phases B and C during the induced voltage measurement of phase A at zero speed.
Viewed in another way, the induced voltage can be expressed as: ##EQU7## Thus, the induced voltage is dependent only upon θr, the rotor position, the slope of the impressed diagnostic current, and physical characteristics of the motor. Similar equations can be developed for the other two stator phase pairs.
The coupled voltage induced in phase A has the rotor angle encoded in its amplitude (See FIGS. 9 and 10). This induced voltage amplitude can be used to estimate the startup rotor position, b using a look-up table. The table contains the inverse function of equation 20, solved for θr, in discrete form.
To determine the rotor position uniquely, the induced voltages from all three phases have to be read. Induced voltage for phase A should be read by diagnostically energizing phases B and C. Similarly the induced voltages of phases B and C should be read by diagnostically energizing the remaining two phases. The induced voltages for three phases (with the rotor at 25 mechanical degrees) are shown in FIG. 9.
The phase inductance of a SynRM is a function of twice the rotor angle θr, i.e., 2θr. Hence, for every electrical cycle the phase inductance goes through two cycles. For this reason, the induced voltages at 205 mechanical degrees (FIG. 10) are the same as those shown in FIG. 9.
This apparent problem is insignificant since the rotor of a SynRM has no preferred polarity due to the absence of any winding on the rotor. During startup operation, the controller can be set to pick the lower or the higher angle.
To prove the efficacy of the foregoing, a synchronous reluctance machine employing the present invention was built and tested. As previously mentioned, the machine used an axially laminated rotor and the stator was a standard configuration for a 7.5 hp three phase induction machine.
Throughout these tests, the SynRM operated at 1000 RPM under a lightly loaded condition. FIG. 11 shows a measured trace of the phase A current with the extended zero crossing period corresponding to FIG. 4. The zero current interval is shown, in this case only one per cycle. FIG. 12 shows the constant current PWM interval of the phase B current during that extended zero crossing period of phase A. FIG. 13 shows the induced voltage measured in phase A. FIG. 14 shows the phase A current during acceleration of the motor from rest. Only one zero crossing window was created at every electrical cycle of the phase current. During the tests, the experimental drive was made self synchronized by advancing or retarding the phase currents depending on the rotor position. In order to calculate the starting rotor position, two phases were diagnostically energized and the induced voltage was read across the third phase. FIG. 16 shows the diagnostic constant current regulation flowing through the phases B and C of the experimental drive. FIG. 15 shows the voltage induced across phase A during this diagnostic interval. A strong, easily measurable signal is clearly evident. The accuracy of the individual rotor samples at the zero crossings of the phase currents can be obtained from the following expression, ##EQU8## where Δθr is the error in rotor position estimation, Vmax is the maximum measured induced voltage, Imax is the maximum phase current, Fs is the PWM switching frequency during the extended zero crossing period of the phase current and n is the number of output bits of the A/D converter. The maximum ∂θr /∂Vind, ∂θr /∂K1 and ∂θr /∂K2 was found analytically maximizing them in the possible range of the three dimensions, i, io and Vind. The worst case position error was found by substituting system parameters LB, n, Vmax, Imax in Equation 21 and the error was found to be equal to or less than 0.80 mechanical degrees. The acceleration of the drive must be,
K≦72�Δθsample �∫e 2(22)
in order to keep the estimation error between two zero crossings within Δθsample (here, Δθsample =0.80 mechanical degrees). The above mentioned analysis technique can be applied at zero speed to obtain the accuracy of the startup rotor position estimation. At zero speed the rotor position estimation error, Δθro, can be written as, ##EQU9## where, io .tbd.di/dt and fso is the diagnostic frequency of two stator phases when the induced voltage is measured across the remaining third phase. At zero speed, the error was found to be equal to or less than 0.50 mechanical degrees.
The principles, preferred embodiment, and mode of operation of the present invention have been described in the foregoing specification. This invention is not to be construed as limited to the particular forms disclosed, since these are regarded as illustrative rather than restrictive. Moreover, variations and changes may be made by those skilled in the art without departing from the spirit of the invention.
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