Abstract:
A parallel flow thermal transfer unit is disclosed having high efficiency and a constant gradient along the length of the flow. The thermal transfer unit includes flow control elements within the path of the flow to produce desired flow characteristics.

Description:
PRIORITY CLAIM TO RELATED U.S. APPLICATIONS 
       [0001]    To the full extent permitted by law, the present non-provisional patent application claims priority to and the benefit of U.S. Provisional patent application Ser. No. 60/864,046, entitled “REVERSE FLOW PARALLEL THERMAL TRANSFER UNIT,” filed on Nov. 2, 2006, which is hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field 
         [0003]    The present invention relates generally to heat exchangers, and more specifically, to a method and apparatus for exchanging heat using countercurrent fluid flow. 
         [0004]    2. Description of Related Art 
         [0005]    In various processes, it is desirable to increase the efficiency of the process by transferring thermal energy from one process where the thermal energy is not needed to another process that needs to be heated. Such transfers of thermal energy often occur across an exchange medium or barrier, and utilize one or more gases or fluids (generally, “fluid” or “fluids”) as the transfer agents. 
         [0006]    One system which has been used to achieve such a result is a concurrent heat exchanger. In a concurrent heat exchanger, two or more process fluids are thermally joined in a parallel flow, such that the temperature differential between the two fluids decreases as the time in which the two fluids are transferring heat increases. In that manner, at the outlet of the heat exchanger, if the two fluids transfer heat for a sufficient period of time, the resulting temperature will be a mean or average of the two incoming inlet fluid temperatures and the heat exchange at or near the outlet will be negligible. 
         [0007]    An alternative system is a countercurrent heat exchanger. Countercurrent heat exchangers are used to simultaneously cool an incoming high energy working fluid, i.e. an initially warm fluid, and to warm a lower energy fluid, i.e. an initially cool fluid. The warm fluid and cold fluid flow in opposite directions while in thermal contact with a heat transfer barrier, normally a high thermal conductivity metal, which facilitates the transfer of heat or energy from the warm fluid to the cold fluid while maintaining the physical separation of the two fluids. 
         [0008]    Countercurrent heat exchangers are typically the most efficient means by which energy may be transferred from a high energy fluid to a lower energy fluid, because the temperature difference between the two fluids is maintained; thus, maintaining the rate at which heat is exchanged. Additionally, because of the manner in which the two fluids exchange heat, the incoming high energy fluid can be brought to a temperature that approaches the incoming low energy fluid, and vise versa. Thus, heat exchange in a countercurrent heat exchanger occurs throughout the length of the fluid flow in the heat exchanger, provided that there exists a difference in temperature between the high energy and low energy fluid. 
         [0009]    Countercurrent heat exchangers of the current art, nonetheless, have several disadvantages. First, the efficiency of the heat exchanger suffers due to energy movement within the structure of the heat exchanger by conduction. This causes a breakdown in the maintenance of the temperature difference between the two fluids, and, thus, causes a reduced efficiency due to fluctuation in the temperature differential. Second, the efficiency of the heat exchanger suffers due to energy loss to the environment. Third, the size and configuration of the flow channels within the heat exchanger contribute to uneven temperature gradients within the fluids and to uneven flow rates within the flow channels due to turbulence. 
         [0010]    It is desirable, therefore, to provide a heat exchanger system which improves the efficiency of the heat exchange between process fluids, particularly by controlling energy losses, and both fluid and thermal flow characteristics. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    Briefly described, in a preferred embodiment, the present invention overcomes the above-mentioned disadvantages and meets the recognized need for such a device by providing a thermal transfer unit comprising at least one first flow channel having a first interior space, at least one second flow channel having a second interior space, at least one thermal barrier thermally connecting the at least one first flow channel with the at least one second flow channel, a first flow medium disposed within the first interior space, a second flow medium disposed within the second interior space, and a plurality of flow control elements disposed within at least one of the first flow channel and the second flow channel, the plurality of flow control elements creating a predetermined flow pattern. 
         [0012]    According to one aspect of the preferred embodiment, the flow control elements create a vortex flow pattern. 
         [0013]    According to another aspect of the preferred embodiment, the flow channels comprise a low heat conducting material. 
         [0014]    According to another aspect of the preferred embodiment, the thermal transfer unit comprises a thermal insulation material to reduce thermal energy loss to the environment. 
         [0015]    According to another aspect of the preferred embodiment, the thermal barrier includes thermally insulating portions which prevent the transfer of thermal energy along the length of the thermal barrier. 
         [0016]    According to another aspect, the present invention overcomes the above-mentioned disadvantages and meets the recognized need for such a device by providing a thermal transfer system comprising a first modular thermal transfer unit comprising a first flow channel, a second flow channel, a first thermal barrier thermally connecting said first flow channel to said second flow channel, a first connector connected to an input of said first flow channel, a second connector connected to an output of said first flow channel, a third connector connected to an input of said second flow channel, and a fourth connector connected to an output of said second flow channel, and a second modular thermal transfer unit comprising a third flow channel, a fourth flow channel, a second thermal barrier thermally connecting said third flow channel to said fourth flow channel, a fifth connector connected to an input of said third flow channel, a sixth connector connected to an output of said third flow channel, a seventh connector connected to an input of said fourth flow channel, and an eighth connector connected to an output of said fourth flow channel, wherein said second connector is removably connected to said fifth connector, and said eighth connector is removably connected to said third connector. 
         [0017]    These and other objects, features, and advantages of the invention will become more apparent to those ordinarily skilled in the art after reading the following Detailed Description and Claims in light of the accompanying drawing Figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    Accordingly, the present invention will be understood best through consideration of, and reference to, the following Figures, viewed in conjunction with the Detailed Description of the Preferred Embodiment referring thereto, in which like reference numbers throughout the various Figures designate like structure and in which: 
           [0019]      FIG. 1  is a longitudinal cross-section view of a preferred embodiment of the thermal transfer unit of the present invention; 
           [0020]      FIG. 2  is a longitudinal cross-section view of an alternative embodiment of the thermal transfer unit of the present invention; 
           [0021]      FIG. 3  is a side view of the thermal transfer unit of the present invention; 
           [0022]      FIG. 4  is a transverse cross-section view of the thermal transfer unit of the present invention; 
           [0023]      FIG. 5  is an exploded perspective view of the thermal transfer unit of the present invention; 
           [0024]      FIG. 6  is a perspective view of modular sections comprising the thermal transfer unit according to a preferred embodiment of the present invention; 
           [0025]      FIG. 7  is an end view of the thermal transfer unit according to the embodiment of  FIG. 6 ; 
           [0026]      FIG. 8  is a transverse cross-section view of the thermal transfer unit according to a preferred embodiment illustrating vortexes in a working fluid; 
           [0027]      FIG. 9  is a perspective view of an alternative flow pattern of a working fluid in the thermal transfer unit; 
           [0028]      FIG. 10  is a perspective view of flow control elements on thermal barriers of the thermal transfer unit; 
           [0029]      FIG. 11  is a longitudinal cross-section view of the thermal transfer unit according to an alternative embodiment; 
           [0030]      FIG. 12  is an exploded view of a connector for use with the thermal transfer unit according to the embodiment of  FIG. 11 ; and, 
           [0031]      FIG. 13  is a transverse cross-section view of the thermal transfer unit according to the embodiment of  FIG. 11 , illustrating vortexes in a working fluid. 
       
    
    
       [0032]    It is to be noted that the drawings presented are intended solely for the purpose of illustration and that they are, therefore, neither desired nor intended to limit the invention to any or all of the exact details of construction shown, except insofar as they may be deemed essential to the claimed invention. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0033]    In describing preferred embodiments of the present invention illustrated in the Figures, specific terminology is employed for the sake of clarity. The invention, however, is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that operate in a similar manner to accomplish a similar purpose. 
         [0034]    It will also be understood that the present invention is intended for function, use, and application to heat transfers within and between gases, liquids, gaseous media, fluids, fluidized media, combined gaseous and/or fluid media, and combinations thereof. Accordingly, any reference herein to a fluid should be understood to include reference to gases, liquids, gaseous media, fluids, fluidized media, combined gaseous and/or fluid media, and combinations thereof. 
         [0035]    In that form of the preferred embodiment of the present invention chosen for purposes of illustration,  FIG. 1  shows a cross-sectional view of thermal transfer unit  100  according to the present invention. Thermal transfer unit  100  is shown in a serpentine configuration in order to reduce the overall size of the unit. Thermal transfer unit  100  comprises a plurality of layers  101 ,  102 ,  103 ,  104 ,  105 ,  106 , and  107 . Thermal transfer unit  100  has a length dimension that follows the serpentine configuration from first end  100   a  to second end  100   b,  a thickness dimension in the direction from layer  101  to layer  107 , and a width dimension orthogonal to both the length dimension and the thickness dimension. 
         [0036]    Layers  101  and  107  are the bottom and top layer, respectively, of the main body of thermal transfer unit  100 , and are preferably made of thermally insulating material. Layers  102 ,  104 , and  106  comprise flow channels that carry a low thermal energy flow medium from first end  100   a  to second end  100   b  along the length of each layer. The low thermal energy flow medium can be a process fluid that requires heating, or can be a waste fluid that can absorb thermal energy. Layers  103  and  105  comprise flow channels that carry a high thermal energy flow medium from second end  100   b  to first end  100   a.  The high thermal energy flow medium can be a process fluid that requires cooling, or can be a waste fluid from which thermal energy can be extracted. 
         [0037]    Between each of layers  102  through  106  is a thermal barrier  110 . Each thermal barrier  110  preferably comprises a high thermal conductivity material that thermally connects the flow media in adjacent flow channels, and is preferably no thicker than is necessary for structural integrity given desired configuration and an intended application, including process pressures thereof and longevity requirements. In a preferred embodiment, each thermal barrier  110  comprises thermally insulating portions disposed along the length of thermal transfer unit  100  from first end  100   a  to second end  100   b.  The thermally insulating portions prevent the transfer of thermal energy within the thermal barrier  110  along the length of the thermal barrier  110 . 
         [0038]    Also shown in  FIG. 1  are thermal insulating layers  111 , disposed between layers  101  and  107  of the interior layers of the thermal transfer unit  100 . The thermal insulating layers  111  prevent unwanted transfer of thermal energy between the adjacent flow medium and layers  101  and  107  of the main body of thermal transfer unit  100 . Additionally, exterior insulation and/or heat reflective films may be added to exterior portions of thermal transfer unit  100  to further reduce transfer of thermal energy to an outside environment. Additionally, thermal transfer unit  100  may optionally be stored in a vacuum to reduce thermal transfer to the outside environment. Additionally, the configuration, serpentine or other, of thermal transfer unit  100  is preferably selected such that potions of thermal transfer unit  100  carrying flow media of similar temperatures are disposed near one another so as to reduce the temperature differential between adjacent or proximate portions of thermal transfer unit  100 . 
         [0039]    Referring again to layers  102  and  106 , as is best shown in the inset drawings, outer layers  102  and  106  have a depth in the thickness direction that is less than the depth in the thickness direction of inner layers  103 ,  104 , and  105 . Preferably the depth of outer layers  102  and  106  is half of the depth of inner layers  103 ,  104 , and  105 . The smaller depth dimension of layers  102  and  106  serves to equalize the volume of fluid in thermal contact with each thermal barrier so that the transfer of thermal energy from the high thermal energy fluid medium to the low thermal energy fluid medium is consistent between all the layers at a given length along thermal transfer unit  100 . Additionally, if the fluid medium in one flow channel has a thermal capacity different than the thermal capacity of the fluid medium in an adjacent flow channel, the depth in the thickness direction of the respective flow channels is preferably configured such that the thermal capacities of the respective flow channels are equal, or nearly equal. 
         [0040]      FIG. 2  shows an alternative embodiment of thermal transfer unit  100 , which is in most respects identical to the embodiment of  FIG. 1 . The main difference is illustrated in the inset drawing. As shown in  FIG. 2 , the alternative embodiment has layers  103  and  105  open to the back side and closed to the front side at first end  100   a  of thermal transfer unit  100  by two flow diverters  120 , and has layers  102 ,  104 , and  106  open to the front side and closed to the back side at first end  100   a  of thermal transfer unit  100  by three additional flow diverters (not shown). By contrast, the embodiment of  FIG. 1  has an opposite configuration with layers  103  and  105  open to the front side and closed to the back side at first end  100   a  of thermal transfer unit  100  by two flow diverters (not shown), and with layers  103 ,  104 , and  106  open to the back side and closed to the front side at first end  100   a  of thermal transfer unit  100  by three flow diverters  120 . 
         [0041]      FIG. 3  shows the embodiment of  FIG. 1  from the front side. From this view, port  130  can be seen at each of first end  100   a  and second end  100   b.  Each port  130  comprises an opening in the front side layer  108  of the main body of the thermal transfer unit  100 . Ports  130  work in conjunction with flow diverters  120  to make each of layers  102  through  106  selectively open or closed to the port. 
         [0042]    Referring now to  FIG. 4 , a transverse cross-sectional view of thermal transfer unit  100  is shown. Main body bottom layer  101 , main body top layer  107 , main body front side layer  108 , and main body back side  109  are shown as comprising two unitary halves of the main body of thermal transfer unit  100 : upper half  100   c  and lower half  100   d.  Also shown are thermal insulating layers  111  disposed on front side layer  108  and back side layer  109 . 
         [0043]    Flow control elements  140  can be seen projecting from both the upper and lower surface of each thermal barrier  110 . Without flow control elements  140 , the fluid medium flowing through the flow channels defined by layers  102  through  106  would be characterized by turbulence due to the shape and the size of the layer and by the interaction of the fluid medium with the interior surfaces of the flow channel. Such turbulence can cause uneven flow speeds and an uneven distribution of thermal energy within the flow medium along the length of the flow channel. Flow control elements  140  are designed to reduce the effects of turbulence on the efficiency of the thermal transfer unit by reducing turbulence and creating a predetermined flow pattern, such as a vortex. The vortex flow pattern is particularly beneficial because in addition to creating even flow within the flow channel, the vortex flow pattern effectively increases the length of the flow channel for a given set or exterior dimensions. The result is that the fluid medium spends more time within the flow channel and comes into contact with more surface area of thermal barrier  110 , increasing the amount of thermal energy transferred to or from the other fluid medium through thermal barrier  110 . 
         [0044]    In use, a vortex flow pattern causes movement of the fluid medium from a region proximate to the surface of the thermal barrier to a central region of the flow channel. This causes removal of fluid medium that has a temperature close to the average temperature of the thermal barrier from regions nearby the thermal barrier, and causes fluid medium that has a temperature closer to the average temperature of the fluid medium in areas at the same length along the thermal transfer unit to move into the regions nearby the thermal barrier. 
         [0045]      FIG. 5  shows an exploded view of the first end  100   a  of thermal transfer unit  100  according to the embodiment of  FIG. 1 . The main body of thermal transfer unit  100  is shown including two pieces comprised of layers  101 ,  107 ,  108 , and  109 . When combined, openings in each of the two pieces form front side port  130  and back side port  130 . Also shown is thermal insulator  111 , also formed in two pieces, which lines the interior surfaces of each piece of the main body. First flow diverter  120  is disposed adjacent the bottom of thermal insulator  111  and is shaped such that a side surface extends completely over front port  130 ; thereby, closing off the front port  130  from layer  102 . The other side of flow diverter  120  is tapered along its length to allow fluid medium flowing in the flow channel of layer  102  to flow into or out of the flow channel through back port  130 . Thermal barrier  110  is disposed on top of flow diverter  120  and encloses the flow channel of layer  102 . 
         [0046]    Another flow diverter  120  is disposed on top of thermal barrier  110  enclosing layer  102  and has a tapered front side, opening the flow channel of layer  103  to front port  130 , and an elongated back side closing the flow channel of layer  103  from back port  130 . Another thermal barrier  110  is disposed on top of this flow diverter  120  and encloses the flow channel of layer  103 . In this way, each subsequent layer of thermal transfer unit  100  includes a flow diverter  120  of alternating configuration. 
         [0047]    Also shown in  FIG. 5  are portions  111   a  of thermal insulator  111  that protrude from the openings in the main body that comprise front and back ports  130 . Portions  111   a  can optionally serve as connectors to which fluid conduits can be attached to distribute the fluid media as required by the application process. 
         [0048]    Now referring to  FIG. 6 , thermal transfer system  600  is shown comprising a plurality of modular sections  600   a,    600   b,    600   c,    600   d,  and  600   e.  Each of the plurality of modular sections comprises an individual thermal transfer unit  100 . As shown in  FIG. 6 , each thermal transfer unit  100  is U-shaped, although alternative configurations, such as the serpentine configuration of  FIG. 1  are contemplated. Connectors  610  are connected to each of the front and back side ports of ends  100   a  and  100   b  of each thermal transfer unit  100  making up the thermal transfer system  600 . Connectors  610  can also be interconnected as shown in  FIG. 6  such that flow channels in each of the modular sections are connected to form a single flow channel from a first end of a first modular section to a second end of the last modular section. 
         [0049]      FIG. 7  shows the thermal transfer system  600  from an end view, and further shows how the front side ports of the first and second end are connected to respective front side ports of adjacent modular sections. For example, front side port of the second end of modular section  600   b,  designated O 1  is connected to front side port of the first end of modular section  600   c,  designated I 1 , and the back side port of the first end of modular section  600   c,  designated O 2  is connected to the back side port of the second end of modular section  600   b,  designated I 2 . 
         [0050]    Now referring to  FIG. 8 , a transverse cross-sectional view of thermal transfer unit  800  of  FIG. 4  is shown.  FIG. 8  includes arrows that indicate the direction of flow of the fluid medium created by flow control elements  840 . As shown, the flow pattern created by flow control elements  840  is a plurality of vortexes. Flow control elements  840  can be discrete projections or fins, or can be continuous along the length of the thermal transfer unit  800 . Preferably, flow control elements  840  comprise fins that are thermally connected to the thermal barriers  810  and comprise a similar thermally conductive material; thereby, effectively increasing the surface area of thermal barrier  810  over which thermal energy can be gathered or dissipated. 
         [0051]      FIG. 9  shows a perspective view of an alternative flow pattern of the fluid medium caused by flow control elements  840 . In this alternative flow pattern, adjacent vortexes have opposing rotation, such that turbulence at the edges of adjacent vortexes is reduced by eliminating opposing directions of flow at adjacent portions. 
         [0052]      FIG. 10  shows a perspective view of flow control elements  840  on thermal barriers  810  that produce the flow pattern of  FIG. 9 . 
         [0053]    Now referring to  FIG. 11 , an alternative configuration of thermal transfer unit  1100  is shown. According to the alternative embodiment, thermal transfer unit  1100  comprises a plurality of tubes arranged in a serpentine configuration. Outer tube  1101  serves as the body for thermal transfer unit  1101 , and comprises a thermally insulating material. First flow tube  1102  is disposed proximate an interior surface of outer tube  1101 . Second flow tube  1103  is disposed centrally within first flow tube  1102  and spaced from an interior surface thereof; thereby, defining first flow channel  1104 . Second flow tube  1103  is hollow and defines second flow channel  1105 . Additionally, solid displacement tube  1106  may optionally be disposed centrally within second flow tube  1103  and can be held in place at the center of the second flow tube  1103  by spacers. The inclusion of solid displacement tube  1106  serves to reduce the volume of second flow tube  1103  while maintaining the larger surface area of second flow tube  1103 . 
         [0054]    In the embodiment of  FIG. 11 , second flow tube  1103  serves as the thermal barrier and is made of a high thermal conductivity material in order to facilitate the transfer of thermal energy to or from a first fluid medium disposed in first flow channel  1104 , to or from a second fluid medium disposed in second flow channel  1105 . 
         [0055]    First flow tube  1102  has an input and an output connection that comprises an extension of first flow tube  1102  that projects from each end of thermal transfer unit  1100  and is offset from the center of the plurality of tubes. Second flow tube  1103  likewise has an input and an output at each end of thermal transfer unit  1100 . 
         [0056]    As shown in  FIG. 12 , connector  1200  can be used to facilitate connection of first flow channel  1104  and second flow channel  1105  to process flow conduits. Connector  1200  comprises a molded adapter that includes offset connection portion  1201  for connecting to first flow channel  1104  and central connection portion  1202  for connecting to second flow channel  1105 . Inner sleeve  1203  attaches to an interior of connection portion  1202  at a first end, and attaches to second flow tube  1103  at a second end, forming a sealed flow channel from connection portion  1202  to second flow channel  1105 . Outer sleeve  1204  attaches to connection portion  1201  at a first end, and attaches to first flow tube  1102  at a second end, forming a sealed flow channel from connection portion  1201  to first flow channel  1104 . 
         [0057]    Now referring to  FIG. 13 , a cross-sectional view of thermal transfer unit  1200  is shown. Flow control elements  1240  are disposed on the interior surface of first flow tube  1102 , interior and exterior surfaces of second flow tube  1103 , and the exterior surface of solid displacement tube  1106 . The flow control elements create vortexes represented by arrows indicating the motion of the fluid medium flowing through first flow channel  1104  and second flow channel  1105 . Also shown are spacers  1160  that maintain second flow tube  1103  and solid displacement tube  1106  at the desired spacing. Optionally, spacers  1160  may be arranged such that they do not interfere with the creation of a desired flow control pattern, and may optionally be configured to aid in such creation. 
         [0058]    The use of flow control devices to regulate a rate of flow through one or more flow channels is contemplated in order to ensure a desired flow rate prevails in the flow channel such that equalized thermal capacity between adjacent flow control channels is maintained. 
         [0059]    Having, thus, described exemplary embodiments of the present invention, it should be noted by those skilled in the art that the within disclosures are exemplary only and that various other alternatives, adaptations, and modifications may be made within the scope and spirit of the present invention. Accordingly, the present invention is not limited to the specific embodiments as illustrated herein, but is only limited by the following claims.