RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 61/160,775 filed Mar. 17, 2009, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to the field of solar energy collector systems, and more particularly, to parabolic trough solar collectors. 
       BACKGROUND OF THE INVENTION 
       [0003]    There are a variety of solar energy collector systems available for converting solar energy into other forms of energy that can be more readily used or stored. These systems typically employ solar collectors that collect solar radiation and convert it into a more useable form of energy, such as heat. 
         [0004]    Solar collectors of the flat plate type have been used in low energy applications such as heating water, generating low pressure steam, supplementing air conditioning and heating systems, and the like. Flat plate collectors do not focus the sun&#39;s radiation and have limited applicability. 
         [0005]    Another type of collector is generically called a concentrating collector. These collectors focus or concentrate the sun&#39;s radiation energy in a particular area. Concentrating collectors can be designed to operate at high temperatures with reasonable flow rates, thus substantially increasing the versatility of systems incorporating these collectors over systems employing flat plate collectors. 
         [0006]    One type of concentrating collector is the parabolic trough collector. This type of collector uses an elongated reflective trough having a parabolic cross-section to concentrate the sun&#39;s radiation along a longitudinal focal line extending through the focal points of the parabolic elements of the trough. A conduit can be positioned along this longitudinal focal line and a heat transfer liquid can be circulated through the conduit, where it will be heated by the sun&#39;s energy. Satisfactory flow rates at high temperatures can be obtained from these collectors. 
         [0007]    With the assistance of a tracking system, parabolic trough collectors can become very efficient as they follow the movement of the sun. U.S. Pat. No. 6,886,339 discloses a solar power collection system comprising parabolic trough collectors that operate with a positioning system that provides movement about a single axis of rotation. A controller drives a motor to pivot the parabolic trough collectors about the longitudinal focal line. However, because of the need for such a tracking system, parabolic trough collectors have typically relied on complicated and expensive rotating assemblies to position the parabolic trough collectors directly toward the sun as the sun travels from east to west during the day. Consequently, there is a need for a solar energy collector system that does not rely on complicated and expensive rotating assemblies to position the parabolic trough collectors directly toward the sun. 
         [0008]    Another problem associated with solar energy collector systems is with respect to the conduit positioned along the focal line. A small focal point is desired to maximize the efficiency of the collectors. However, this typically requires regular adjustments of the reflecting surfaces. A tradeoff is to use a larger focal point to collect more energy, but this reduces efficiency since a larger volume of liquid is to be heated. Consequently, there is also a need to improve the efficiency of the conduit for solar energy collector systems. 
       SUMMARY OF THE INVENTION 
       [0009]    In view of the foregoing background, it is therefore an object of the present invention to provide a straightforward solar energy collector system that is also efficient. 
         [0010]    This and other objects, advantages and features in accordance with the present invention are provided by a solar energy collector system comprising at least one base, and at least one parabolic trough collector carried by the at least one base for reflecting sunlight to a longitudinal focal line. The parabolic trough collector may comprise a center section horizontally positioned with respect to ground, and opposing end sections adjacent the center section. Each end section may be angled towards the ground. 
         [0011]    The parabolic trough collector and the base may remain stationary when reflecting sunlight to the longitudinal focal line. An advantage of a stationary solar energy collector system is that the parabolic trough collectors do not need to be rotated as the sun travels from east to west during the day since a section thereof is always pointed toward the sun. 
         [0012]    The solar energy collector system may further comprise at least one tilting device coupled to each base for adjusting a latitudinal angle of the parabolic trough collector with respect to the ground. This advantageously compensates for the seasonal rotation of the sun. 
         [0013]    The solar energy collector system may further comprise a conduit positioned along the longitudinal focal line to receive the reflected sunlight. The conduit is to circulate a heat transfer liquid therethrough to be heated by the reflected sunlight. 
         [0014]    The conduit may comprise a center section horizontally positioned with respect to the ground, and opposing end sections adjacent the center section. Each end section may be angled towards the ground. In other words, a profile of the conduit corresponds to a profile of the parabolic trough collector. 
         [0015]    The conduit may comprise an inner tube and a spaced apart outer tube, with the heat transfer liquid to be circulated between the inner and outer tubes. By circulating the heat transfer liquid between the inner and outer tubes, a larger focal point is advantageously obtained with a reduced volume of the heat transfer liquid. 
         [0016]    The inner and outer tubes may be U-shaped. The conduit may further comprise a conduit cover covering exposed upper portions of the U-shaped inner and outer tubes to seal off the heat transfer liquid. The conduit cover may also cover the inner tube between the exposed portions of the U-shaped inner tube. The conduit cover may comprise a clear material, and the inner and outer tubes may each comprise an opaque coating. 
         [0017]    The parabolic trough collector and the base may be formed as a monolithic unit. The parabolic trough collector and the base may comprise a thermoplastic material and/or a thermosetting material. This significantly reduces setup, shipping and maintenance costs typically associated with a parabolic trough solar collector panel that is rotated to track the sun. 
         [0018]    The solar energy collector system may comprise a plurality of bases adjacent one another. Likewise, there may be a plurality of parabolic trough collectors adjacent one another. Each base is carried by a respective parabolic trough collector having a conduit positioned along the longitudinal focal line. The conduit may further comprise a respective interconnecting section for connecting adjacent conduits together. In addition, the adjacent parabolic trough collectors may be coupled together. 
         [0019]    Another aspect is directed to a solar energy collector system comprising at least one base, at least one collector carried by the at least one base for reflecting sunlight to a longitudinal focal line, and a conduit positioned along the longitudinal focal line to receive the reflected sunlight. The conduit may comprise an inner tube, and an outer tube spaced apart from the inner tube. A heat transfer liquid is to be circulated between the inner and outer tubes. An advantage of the conduit associated with a basic collector is that a larger focal point is advantageously obtained with a reduced volume of the heat transfer liquid since the heat transfer liquid circulates between the inner and outer tubes. 
         [0020]    Yet another aspect is directed to a method for collecting solar energy using a solar energy collector system as described above. The method may comprise providing at least one base, and at least one parabolic trough collector carried by the at least one base. The at least one parabolic trough collector comprises a center section horizontally positioned with respect to ground, and opposing end sections adjacent the center section, with each end section angled towards the ground. The method may further comprise using the at least one parabolic trough collector for reflecting sunlight to a longitudinal focal line. A conduit is positioned along the longitudinal focal line to receive the reflected sunlight, and a heat transfer liquid is circulated through the conduit to be heated by the reflected sunlight. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a perspective view of a stationary parabolic solar power system in accordance with the present invention. 
           [0022]      FIG. 2  is a perspective side view of a single parabolic trough collector in accordance with the present invention. 
           [0023]      FIG. 3  is a side view of the parabolic trough collector illustrated in  FIG. 2 . 
           [0024]      FIG. 4  is an end view of the parabolic trough collector illustrated in  FIG. 2 . 
           [0025]      FIG. 5  is a perspective side view of a single parabolic trough collector with a tilting device associated therewith to compensate for the seasonal rotation of the sun in accordance with the present invention. 
           [0026]      FIG. 6  is a perspective view of another embodiment of the stationary parabolic solar power system illustrated in  FIG. 1 . 
           [0027]      FIG. 7  is a partial perspective side view of the parabolic trough collector and a conduit positioned thereabove in accordance with the present invention. 
           [0028]      FIG. 8  is a partial perspective side view of the conduit illustrated in  FIG. 7 . 
           [0029]      FIG. 9  is a flowchart illustrating a method for collecting solar energy using a solar energy collector system in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and prime notation is used to indicate similar elements in alternative embodiments. 
         [0031]    Referring initially to  FIG. 1 , a stationary parabolic solar power system  10  comprises a plurality of spaced apart side-by-side parabolic trough collectors  12 , and a conduit  14  associated therewith. Each parabolic trough collector  12  is shaped so that a section thereof is always pointed toward the sun. An advantage of the stationary parabolic solar power system  10  is that the parabolic trough collectors  12  do not need to be rotated as the sun travels from east to west during the day since a section thereof is always pointed toward the sun. 
         [0032]    Referring now to  FIGS. 2-6 , each parabolic trough collector  12  includes a center section  22  and a pair of angled end sections  24 ,  26 . One of the angled end sections  24  is pointed toward the sun in the morning as the sun rises, whereas the other end section  26  is pointed toward the sun in the afternoon as the sun sets. Each end section  24 ,  26  may be angled within a range of 25 to 65 degrees with respect to the ground. The illustrated end sections  24 ,  26  are shown at 45 degrees with a curved transition to the center section  22 . The center section  22  is flat so that it is pointed toward the sun when the sun is more directly overhead. 
         [0033]    The center section  22  and the pair of angled end sections  24 ,  26  are coupled to a base  30 . The base may also be referred to as a cradle. The base  30  is bolted to the ground and holds the parabolic trough collector  12  in place. Since there are no moving parts, each parabolic trough collector  12  may be formed as one piece with its base  30 . This advantageously increases manufacturing efficiency. 
         [0034]    Each parabolic trough collector  12  may be formed out of a molding material comprising a thermoplastic material or a thermosetting material, as readily appreciated by those skilled in the art. The molding material may be based on a polymer or elastomer. The polymers may also be fiber-reinforced. 
         [0035]    In forming each parabolic trough collector  12 , a STF Sheetless ThermoForming™ process may be used to deliver a dynamically controlled layer of material directly to a mold as it is extruded. This process is a fast and cost-effective way to mold large thermoformed products with a one-step operation directly from an extruder. 
         [0036]    Since each parabolic trough collector  12  is stationary, and may be formed as one piece with the base  30 , this significantly reduces setup, shipping and maintenance costs typically associated with a parabolic trough solar collector panel that is rotated to track the sun. 
         [0037]    The dimensions of a parabolic trough collector  12  may be 8 feet wide, 15 feet long, and 8 feet tall. Of course, the parabolic trough collector  12  may be formed in other dimension depending on the intended application. Even though the illustrated parabolic trough collectors  12  are spaced apart in  FIG. 1 , they may be positioned so that there is no space between, as illustrated in  FIG. 6 . Moreover, the sides of the parabolic trough collectors  12  may be configured so that they have interlocking sides. In lieu of interlocking sides, clips or clamps may be used to couple together an adjacent pair of parabolic trough collectors  12 . 
         [0038]    Each parabolic trough collector  12  has a reflective surface for reflecting sunlight to a longitudinal focal line. A reflective film or coating is on the reflective surface. The coating may be a reflective paint, for example. The use of mirrors is avoided, which would significantly add to the weight of the parabolic trough collector  12 . 
         [0039]    Tilting devices  33  may be carried by each base  30  to adjust a latitudinal angle of the parabolic trough collector  12  with respect to the ground. As illustrated, one side of the base  30  is tilted to increase the surface area of the parabolic trough collector  12  as the sun moves during its seasonal rotation. In other words, the parabolic trough collector  12  is rotated in a north-south direction. 
         [0040]    The tilting devices  33  may be jackscrews, for example. Rotation of the parabolic trough collector  12  throughout the year may be within plus/minus 10 degrees, for example. Although the illustrated base  30  has a pair of tilting devices  33  associated therewith, the actual number will vary depending on the configuration of the base. 
         [0041]    A controller  35  is connected to the tilting devices  33  for control thereof so that each base  30  is incrementally adjusted to provide the desired rotation, as readily appreciated by those skilled in the art. One controller  35  may control the tilting devices  33  for a plurality of bases  30  making up the stationary parabolic solar power system  10 . 
         [0042]    The conduit  14  will now be discussed in greater detail. Although the conduit  14  is discussed with respect to the parabolic trough collectors  12 , the conduit  14  can be applied other types of solar energy collector systems, as readily appreciated by those skilled in the art. In other words, the illustrated conduit  14  associated with parabolic trough collectors  12  is for illustration purposes, and this is not to be viewed as limiting. 
         [0043]    The conduit  14  comprises spaced apart parallel sections  16  positioned along the longitudinal focal line of a parabolic trough collector  12 . Interconnecting sections  18  are coupled to the parallel sections  16 . A heat transfer liquid (i.e., a fluid) is circulated through the conduit  14 , where it will be heated by the sun&#39;s energy. 
         [0044]    As best illustrated by the partial perspective views in  FIGS. 7 and 8 , the parallel sections  16  of the conduit  14  comprise an inner tube or pipe  40  and an outer tube or pipe  42 , wherein the heat transfer liquid is circulated between the inner and outer tubes. By limiting the heat transfer liquid to within the inner and outer tubes  40  and  42 , the volume of fluid to be heated is reduced. However, the outer tube  42  provides a larger focal point for collecting the sunlight. 
         [0045]    As readily appreciated by those skilled in the art, the volume of a tube is equal to πΓ 2 times the length L of the tube. A larger diameter tube has a larger focal point, which makes it easier to collect the solar energy for heating the heat transfer liquid. However, this requires a larger volume of heat transfer liquid to be heated which in turn reduces efficiency of the solar power system  10 . 
         [0046]    A smaller diameter tube has a smaller focal point, which means that a smaller volume of heat transfer liquid is to be heated. However, a smaller diameter tube typically requires periodic adjustments so that the tube is properly aligned with respect to the longitudinal focal lines of the parabolic trough collectors  12  for collecting the solar energy. 
         [0047]    By circulating the heat transfer liquid between the inner and outer tube  42  and  44 , a larger focal point is advantageously obtained with a reduced volume of heat transfer liquid. Both the inner and outer tube  42  and  44  may have an opaque coating. 
         [0048]    Another distinctive feature of the parallel sections  16  of the conduit  14  is that it has a U-shape or half-circle shape. In otherwords, the uppermost or top half of each parallel section  16  has been removed. This advantageously reduces the volume of the heat transfer liquid to be heated. A conduit cover  50  is attached to the exposed inner and outer tube  42  and  44  to seal off the heat transfer liquid as well as the inner surfaces of the inner tube  40 . The conduit cover  50  may be clear in order to create a green house effect by letting sunlight in but trapping the heat from escaping. 
         [0049]    The interconnecting sections  18  coupled to the parallel sections  16  do not need the inner/outer tube configuration as in the parallel sections. Instead, the interconnecting sections  18  comprise a single tube or pipe for circulating the heat transfer liquid to or from the parallel sections  16 . The interconnecting sections  18  may also be insulated. 
         [0050]    Another aspect is directed to a method for collecting solar energy using a solar energy collector system  10  as described above. Referring now to the flowchart  100  illustrated in  FIG. 9 , from the start (Block  102 ), the method comprises providing at least one base  30 , and at least one parabolic trough collector  12  carried by the at least one base at Block  104 . The at least one parabolic trough collector  12  comprises a center section  22  horizontally positioned with respect to ground, and opposing end sections  24 ,  26  adjacent the center section, with each end section angled towards the ground. The method further comprises at Block  106  using the at least one parabolic trough collector  12  for reflecting sunlight to a longitudinal focal line. A conduit  16  is positioned along the longitudinal focal line to receive the reflected sunlight at Block  108 . A heat transfer liquid is circulated through the conduit  16  to be heated by the reflected sunlight at Block  110 . The method ends at Block  112 . 
         [0051]    Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims.
An apparatus includes a sample chamber constructed according to a design certified by the Department of Transportation for transporting fluids at a first pressure P 1. A cylindrical sample compartment exists within the sample chamber. The sample compartment is designed to withstand the pressure P 1. The cylindrical sample compartment has a cylindrical inner surface with a radius r and a height h. A hollow cylindrical sleeve is secured to the cylindrical inner surface of the sample compartment and has a wall of thickness t. The sample chamber is capable of transporting fluids at a second pressure P 2. P 2 is higher than P 1.