Abstract:
A double-wall heat exchanger includes a plurality of heat exchange plate pairs. Each heat exchange plate pair forms a double-wall structure including two heat exchange plates that are at least partially separated by a leak space. At least one weep hole is disposed through the plurality of heat exchange plate pairs and intersects the leak spaces of the plurality of plate pairs to channel leaking fluid from the leak spaces to a location outside of the heat exchanger. The at least one weep hole is positioned on a surface of the heat exchanger at a location that is spaced from a side boundary of the heat exchanger thereby enabling an operator of the heat exchanger to observe a leakage on the surface of the heat exchanger.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a double-wall, vented heat exchanger. 
       BACKGROUND OF THE INVENTION 
       [0002]    Heat exchangers are traditionally used to heat or cool potable or process critical fluids using non-potable fluids while providing a physical, mechanical boundary to prevent contact between the respective fluid streams. 
         [0003]    Heat exchangers, as with all mechanical devices, have finite operating timeframes at the end of which the devices fail for one or more reasons. One typical failure mode for heat exchangers is an external leak in which one or both fluids escape to the outside environment or atmosphere. Another typical failure mode for heat exchangers is an internal leak in which one or both fluids mix with one another without escaping to the outside environment. Internal leaks are not observable from the exterior of the heat exchanger, whereas external leaks may be visually evident. 
         [0004]    To avoid an internal leak, which may not be readily observed by an operator of a single-wall heat exchanger, it is desirable to provide a vented, double-wall boundary that exhausts the leaking fluid to the outside environment or atmosphere in lieu of having the respective fluids mix inside the heat exchanger while the heat exchanger continues to operate. A double-wall heat exchanger is one in which the boundary separating the two fluids is comprised of two separate surface layers, rather than one. Thus, if the first surface layer fails to provide a fluid tight barrier, the second layer should remain intact, causing the leaking fluid to flow between the surface layers to a location where the leaking fluid can be detected externally of the heat exchanger. The double-wall construction is intended to be a safety feature to prevent cross-contamination of the fluids. A double-wall heat exchanger is disclosed for example, in U.S. Patent Application Publication No. 2007/0169916 to Wand, which is incorporated by reference herein in its entirety. 
         [0005]    The double-wall heat exchanger disclosed in Pub. &#39;916 to Wand is vented, i.e., it includes an aperture that channels internal leaks to an exterior surface of the heat exchanger. The aperture is defined on the boundary edge of the heat exchanger. Any leakage that forms on the boundary edge of the heat exchanger may be difficult to observe. In view of the foregoing, it is preferable to direct the leaking fluid to a location on the heat exchanger where the leaking fluid can be readily detected so that the faulty heat exchanger can be removed from service. 
       SUMMARY OF THE INVENTION 
       [0006]    According to one aspect of the invention, a double-wall heat exchanger includes a plurality of heat exchange plate pairs. Each heat exchange plate pair forms a double-wall structure including two heat exchange plates that are at least partially separated by a leak space. At least one weep hole is disposed through the plurality of heat exchange plate pairs and intersects the leak spaces of the plurality of plate pairs to channel leaking fluid from the leak spaces to a location outside of the heat exchanger. The at least one weep hole is positioned on a surface of the heat exchanger at a location that is spaced from a side boundary of the heat exchanger thereby enabling an operator of the heat exchanger to observe a leakage on the surface of the heat exchanger. 
         [0007]    According to another aspect of the invention, a double-wall heat exchanger includes a plurality of heat exchange plate pairs. Each heat exchange plate pair forms a double-wall structure comprising two heat exchange plates that are at least partially separated by a leak space. At least one fluid port is defined on each plate pair through which a heat exchange fluid is distributed either into or out of a fluid channel that is defined between two adjacent plate pairs. Two adjacent plate pairs are mated together at a boundary of the at least one fluid port. A port vent groove is defined between the two adjacent plate pairs at a location surrounding the at least one fluid port. The port vent groove intersects and is in fluid communication with a leak space of one of the two adjacent plate pairs. At least one weep hole is disposed through the plurality of heat exchange plate pairs and intersects the leak spaces of the plurality of plate pairs to channel leaking fluid within one of the leak spaces or the port vent groove to a location outside of the heat exchanger. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0008]    The invention is best understood from the following detailed description when read in connection with the accompanying drawing. Included in the drawing are the following figures: 
           [0009]      FIG. 1  depicts an exploded perspective view of a double-wall, vented heat exchanger, according to an exemplary embodiment of the invention. 
           [0010]      FIG. 2  depicts an exploded perspective view of one plate pair of the heat exchanger of  FIG. 1 . 
           [0011]      FIG. 3  depicts a front elevation view of the heat exchanger of  FIG. 1 . 
           [0012]      FIG. 4  depicts a truncated cross-sectional side elevation view of the heat exchanger of  FIG. 3  taken along the lines  4 - 4 . 
           [0013]      FIGS. 4A and 4B  depict detailed views of the heat exchanger of  FIG. 4 . 
           [0014]      FIG. 5  depicts a cross-sectional side elevation view of the heat exchanger of  FIG. 3  taken along the lines  5 - 5  and rotated 90 degrees counterclockwise. 
           [0015]      FIG. 5A  depicts a detailed view of the heat exchanger of  FIG. 5 . 
           [0016]      FIG. 6  depicts a cross-sectional side elevation view of the heat exchanger of  FIG. 3  taken along the lines  6 - 6  and rotated 90 degrees counterclockwise. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention. In the figures, like item numbers are used to refer to like elements. 
         [0018]      FIG. 1  depicts an exploded perspective view of a double-wall, vented heat exchanger, according to an exemplary embodiment of the invention, which is denoted by numeral ‘ 10 .’ The heat exchanger  10  comprises a series of stacked double-walled heat transfer plate pairs  12 ( 1 ),  14 ( 1 ),  12 ( 2 ),  14 ( 2 ) and  12 ( 3 ). Heat transfer plate pairs  12 ( 1 ),  12 ( 2 ),  12 ( 3 ), which are structurally equivalent, are referred to collectively as plate pairs  12 . Heat transfer plate pairs  14 ( 1 ) and  14 ( 2 ), which are also structurally equivalent, are referred to collectively as plate pairs  14 . Heat transfer plate pairs  12  and  14  are structurally equivalent, however, plate pairs  14  are rotated by approximately 180 degrees with respect to plate pairs  12  (note the orientation of ports A-D) in  FIG. 1 . 
         [0019]    Each heat transfer plate pair  14  is sandwiched between two heat transfer plate pairs  12 , and each plate pair  12  is positioned against at least one plate pair  14 . The stack of plate pairs  12  and  14  are sandwiched between a rear plate  15  and a faceplate assembly  18 . The faceplate assembly  18  includes a seal plate  16 , a faceplate  19  and a series of fluid connectors  20 ,  22 ,  24  and  26 , which are fixedly mounted through ports defined on the interior plate  16  and the faceplate  19 . The seal plate  16  is an optional component of the faceplate assembly  18 . The fluid connectors  20 ,  22 ,  24  and  26  are configured to distribute fluid either into or out of the internal flow channels of the heat exchanger  10 , as described hereinafter. 
         [0020]    The plate pairs  12  and  14  are stacked and brazed together to create two discrete and isolated fluid flow passageways ‘E’ and ‘F’. The fluid flow passageway ‘E’ is defined by the fluid connector  20 , the flow channel  28  that is defined between plate pairs  12 ( 1 ) and  14 ( 1 ), the flow channel  30  that is defined between plate pairs  12 ( 2 ) and  14 ( 2 ), and the fluid connector  22 . The fluid flow passageway ‘F’ is defined by the fluid connector  24 , the flow channel  32  that is defined between plate pairs  14 ( 1 ) and  12 ( 2 ), the flow channel  34  that is defined between plate pairs  14 ( 2 ) and  12 ( 3 ), and the fluid connector  26 . 
         [0021]    Referring now to  FIGS. 1 and 5 , in operation, separate fluid streams are distributed through the discrete fluid flow passageways ‘E’ and ‘F’ of the heat exchanger  10  to exchange thermal energy with each other. One fluid stream is delivered through the connector  20  of the flow passageway ‘E’, directed through the two fluid flow channels  28  and  30  of the flow passageway ‘E’, and expelled out of the heat exchanger  10  through the fluid connector  22  of the flow passageway ‘E’. Another fluid stream is delivered through the fluid connector  24  of the flow passageway ‘F’, directed through the two fluid flow channels  32  and  34  of the flow passageway ‘F’, and expelled out of the heat exchanger  10  through the fluid connector  26  of the flow passageway ‘F’. 
         [0022]    Those skilled in the art will recognize that the position of the fluid connectors  20 ,  22 ,  24  and  26  may vary from that shown and described without altering the operation of the heat exchanger  10 . As one alternative, the fluid connectors  20 ,  22 ,  24  and  26  may be positioned on the rear plate  15 . As another alternative, some of the fluid connectors  20 ,  22 ,  24  and  26  may be positioned on the faceplate  19  while the remaining fluid connectors  20 ,  22 ,  24  and  26  are positioned on the rear plate  15 . For example, the fluid connectors  20 ,  24  and  26  can be positioned on the faceplate  19  (as shown) while the fluid connector  22  is positioned on the rear plate  15  at either port ‘B’ or port ‘C’ of the plate pair  12 ( 3 ) without significantly altering the operation of the heat exchanger  10 . In that example, a fluid stream is delivered through the connector  20  on the faceplate  19 , directed through the two fluid flow channels  28  and  30  of the flow passageway ‘E’, and expelled out of the heat exchanger  10  through the fluid connector  22  on the rear plate  15 . 
         [0023]    Referring back to  FIGS. 1 and 5 , the brazings between the plates of the plate pairs  12  and  14  prevent the fluid streams within adjacent fluid flow passageways E and F from combining together (see  FIG. 5 ). In other words, by virtue of the brazings, the flow channel  28  is maintained in fluid communication with flow channel  30 , but the flow channel  28  is fluidly isolated from the flow channels  32  or  34  to prevent the fluid within passageway ‘F’ from entering passageway ‘E’. Furthermore, the flow channel  32  is maintained in fluid communication with fluid channel  34 , but the flow channel  32  is fluidly isolated from the flow channels  28  or  30  to prevent the fluid within passageway ‘E’ from entering passageway ‘F’. 
         [0024]    To prevent fluid within passageway ‘F’ from entering passageway ‘E’, the ports ‘A’ and ‘D’ of plate pair  12 ( 1 ) are brazed to ports ‘C’ and ‘B’ of plate pair  14 ( 1 ), respectively, and ports ‘A’ and ‘D’ of plate pair  12 ( 2 ) are brazed to ports ‘C’ and ‘B’ of plate pair  14 ( 2 ). To prevent fluid within passageway ‘E’ from entering passageway ‘F’, the ports ‘D’ and ‘A’ of plate pair  14 ( 1 ) are brazed to ports and ‘B’ of plate pair  12 ( 2 ), respectively, and ports ‘D’ and ‘A’ of plate pair  14 ( 2 ) are brazed to ports ‘C’ and ‘B’ of plate pair  12 ( 3 ), respectively. Additionally, the entire side boundary  46  of the plate pairs  12  and  14  (see  FIG. 3 ) is sealed by brazings to prevent the escapement of fluid at the boundary of the heat exchanger  10 . 
         [0025]      FIG. 2  depicts an exploded perspective view of a heat transfer plate pair  12  of the heat exchanger  10 . The details of the plate pair  12  that are described hereinafter also apply to the plate pair  14 . As stated previously, the plate pairs  12  and  14  are the same, with the exception that the plate pairs  14  are rotated 180 degrees with respect to the plate pairs  12  in an assembled form of the heat exchanger  10 . 
         [0026]    Each plate pair  12  includes two plates  36  and  38  that are brazed together to form a double-wall structure. The benefits of a double-wall structure are described in the Background Section. The plates  36  and  38  may be formed from stainless steel, for example, or other metallic or polymeric materials. Each plate  36  and  38  is substantially rectangular and includes a centrally-located chevron area  44 . The term ‘chevron area’ will be understood by those of ordinary skill in the art. The chevron area  44  is an undulating surface that promotes heat transfer. The geometry, size, shape and orientation of the chevron area  44  may differ from that shown without departing from the scope or the spirit of the invention. 
         [0027]    Copper braze material  40 , which is positioned between the plates  36  and  38 , is utilized to braze the plates  36  and  38  together. Copper braze material  42 , which is positioned on the outer face of the plate  38 , is utilized to braze the plate  38  to the plate  36  of an adjacent plate pair (not shown). As best shown in  FIGS. 2 ,  5 ,  5 A and  6 , the areas of the plate pairs  12  and  14  which are not brazed by the braze materials  40  and  42  are the chevron area  44 , the ports A-D, the weep holes  50  and  52  and the leak passageways which will be described in greater detail hereinafter. Before brazing, a substance is applied to the chevron area  44  of the plate  38  to prevent wetting of the braze material  40  in that area. 
         [0028]    Four ports, which are labeled ‘A’ through ‘D’, are openings that are defined on the outer corners of the plates  36  and  38 . The ports ‘A’ through ‘D’ of plate  36  are positioned in alignment with the ports ‘A’ through ‘D’ of plate  38  upon assembling and brazing the plate pair  12 . 
         [0029]    Each plate  36  and  38  includes two weep holes  50  and  52 . Weep hole  50  is positioned at the top end of each plate, whereas weep hole  52  is positioned at the bottom end of each plate  36  and  38 . The weep holes  50  of the plates  36  and  38  are positioned in alignment upon assembling and brazing the plate pair  12 . The weep holes  52  of the plates  36  and  38  are also positioned in alignment upon assembling and brazing the plate pair  12 . 
         [0030]    Referring now to  FIGS. 1 and 3 , upper weep holes  50  and lower weep holes  52  are defined through every plate of the heat exchanger  10 . As will be described in greater detail later, the weep holes  50  and  52  are fluidly connected with leak passageways that are defined throughout the interior of the heat exchanger  10  such that any leaking fluid within the leak passage ways is expelled through the weep holes. The weep holes  50  and  52  are optimally defined on the surfaces of the rear plate  15  and the faceplate  19  at locations that are spaced from the side boundary  46  (see  FIG. 3 ) of the heat exchanger  10 . Such locations are better suited for visualizing a leaking fluid than a weep hole that is positioned on the boundary edge of a heat exchanger such as that disclosed in Pub. &#39;916, for example. 
         [0031]    The heat exchanger  10  includes leak passageways which channel internal leaks that occur within the heat exchanger  10  to the weep holes  50  and  52  of the heat exchanger  10 . The leak passageways are fluidly isolated from the fluid passageways ‘E’ and ‘F’. The leak passageways of the heat exchanger  10  comprise an network of channels, pockets and grooves that are interconnected to the weep holes  50  and  52  to channel internal leakages out of the heat exchanger. Further details of the leak passageways are described hereinafter. 
         [0032]    Referring now to  FIGS. 4 and 6 , an upper weep hole  50  and a lower weep hole  52  are defined through every plate of the heat exchanger  10 . The weep holes  50  and  52  are passages through which leaking fluid within the interior of the heat exchanger  10  is expelled. The upper weep hole  50  intersects an upper central vent pocket  66  that is defined between the plates  36  and  38  of every plate pair  12  and  14 . The lower weep hole  52  intersects a lower central vent pocket  66 ′ that is defined between the plates  36  and  38  of every plate pair  12  and  14 . 
         [0033]    Referring now to  FIGS. 2 ,  4 ,  5 ,  5 A and  6 , two central vent pockets  66  and  66 ′ are formed between the plates  36  and  38  of every plate pair  12  and  14 . Specifically, as shown in  FIGS. 2 ,  5  and  5 A, an upper central vent pocket  66  is a narrow channel that is formed between a wall  67  of plate  36  and a wall  68  of plate  38 . As shown in  FIG. 4 , each upper central vent pocket  66  extends between the chevron area  44  of the plates and the upper weep hole  50  of every plate pair  12  and  14 . Each upper central vent pocket  66  intersects a leak space  60  that is defined between chevron areas  44  of the plates  36  and  38  (see  FIG. 4 ) of a plate pair. Each upper central vent pocket  66  also intersects an upper port leak groove  64  that is defined between the plates  36  and  38  of a plate pair, as shown in  FIG. 6  (also note the intersection of groove  64  and wall  68  of plate  38  in  FIG. 2 ). 
         [0034]    As shown in  FIGS. 5 and 5A , the lower central vent pocket  66 ′ is a narrow channel that is formed between a lower wall  67 ′ of plate  36  and a lower wall  68 ′ of plate  38  of each plate pair. As shown in  FIG. 4 , the lower central vent pocket  66 ′ extends between the chevron area  44  of the plates and the lower weep hole  52 . The lower central vent pocket  66 ′ intersects a leak space  60  that is defined between the chevron areas  44  of the plates  36  and  38  (see  FIG. 4 ) of a plate pair. The lower central vent pocket  66 ′ also intersects a lower port leak groove  64 ′ of a plate pair (note the intersection of groove  64 ′ and wall  68 ′ of plate  38  in  FIG. 2 ). 
         [0035]    Referring now to  FIGS. 4A and 4B , a leak space  60  is defined between chevron areas  40  of the plates  36  and  38  of each plate pair. The leak spaces  60  may be non-continuous, as shown in  FIG. 4B , along the chevron areas  44  of the plates  36  and  38 . The leak spaces  60  intersect two central vent pockets  66  and  66 ′ that are formed between the plates  36  and  38  of each plate pair  12  and  14 . 
         [0036]    Referring now to  FIGS. 2 and 6 , two port leak grooves  64  and  64 ′ are formed between the plates  36  and  38  of each plate pair. The upper port leak groove  64  of each plate pair is a substantially straight and narrow channel that extends between an upper central vent pocket  66  and a port vent groove  62  that surrounds port ‘B’. The lower port leak groove  64 ′ of each plate pair is a substantially straight and narrow channel that extends between a lower central vent pocket  66 ′ and a port vent groove  62  that surrounds port ‘C’. 
         [0037]    Referring now to  FIGS. 5 and 5A , each port vent groove  62  is an annular channel that is defined at a location surrounding the brazed ports of adjacent plate pairs  12  and  14 . More particularly, each port vent groove  62  surrounds an annular brazing there the ports of adjacent plate pairs  12  and  14  are sandwiched together. In operation, upon failure of a brazed joint at one of the ports, leaking fluid collects in the port vent groove  62  that extends from that failed brazed joint. A port vent groove  62  surrounds the following port brazings: the brazing between port ‘A’ of plate pair  12 ( 1 ) and port ‘C’ of plate pair  14 ( 1 ); the brazing between port ‘D’ of plate pair  12 ( 1 ) and port ‘B’ of plate pair  14 ( 1 ); the brazing between port ‘D’ of plate pair  14 ( 1 ) and port ‘B’ of plate pair  12 ( 2 ); the brazing between port ‘A’ of plate pair  14 ( 1 ) and port ‘C’ of plate pair  12 ( 2 ); the brazing between port ‘A’ of plate pair  12 ( 2 ) and port ‘C’ of plate pair  14 ( 2 ); the brazing between port ‘D’ of plate pair  12 ( 2 ) and port ‘B’ of plate pair  14 ( 2 ); the brazing between port ‘D’ of plate pair  14 ( 2 ) and port ‘B’ of plate pair  12 ( 3 ); and the brazing between port ‘A’ of plate pair  14 ( 2 ) and port ‘C’ of plate pair  12 ( 3 ). 
         [0038]    As noted previously, the leak spaces  60 , port vent grooves  62 , port leak grooves  64 / 64 ′ central vent pockets  66 / 66 ′, and weep holes  50 / 52  of the leak passageway are all interconnected together to channel a leaking fluid out of the interior of the heat exchanger through the weep holes  50  and/or  52 . In summary, the weep holes  50  and  52  intersect central vent pockets  66  and  66 ′, respectively, that are defined directly between the plates of every plate pair  12  and  14 . The central vent pockets  66  and  66 ′ intersect leak spaces  60  that are defined directly between the chevron areas  44  of the plates of every plate pair. The central vent pockets  66  and  66 ′ also intersect port leak grooves  64  and  64 ′, respectively, that are defined directly between the plates of every plate pair. The port leak grooves  64  and  64 ′ intersect port vent grooves  62  that are defined directly between adjacent plate pairs  12  and  14  at a location surrounding where the brazed ports of adjacent plate pairs  12  and  14 . Leaking fluid can travel from a port vent groove  62  to port leak grooves  64 / 64 ′, then to central vent pockets  66 / 66 ′, and then to the weep holes  50 / 52 . Leaking fluid can also travel from a leak space  60  to central vent pockets  66 / 66 ′, and then to the weep holes  50 / 52   
         [0039]    For example, if the brazing  42  at location ‘Y’ (see  FIG. 6 ) fails, then the fluid in passageway ‘F’ will migrate through the failed brazing  42  and into the port vent groove  62  at the intersection of plate pairs  12 ( 1 ) and  14 ( 1 ). The leaking fluid will fill the annular channel defined by port vent groove  62  and travel into the port leak groove  64  of plate pair  14 ( 1 ) that intersects the port vent groove  62 . The leaking fluid will then travel into the central vent pocket  66  of the plate pair  14 ( 1 ) that intersects the port leak groove  64 . The leaking fluid will then travel into the weep hole  50  that intersects the central vent pocket  66  of the plate pair  14 ( 1 ). The leaking fluid will ultimately exit out of the weep hole  50  at the front and rear surfaces of the heat exchanger  10  at a location that is spaced from the side boundary  46  of the heat exchanger  10 . 
         [0040]    As another example, if a hole or crack were to form at location ‘Z’ (see  FIG. 4B ) of the chevron area  44  of the plate  36  of plate pair  12 ( 3 ), then the fluid within fluid passageway ‘F’ will leak through the crack and enter the leak space  60  that is defined between plates  36  and  38  of plate pair  12 ( 3 ). The double-wall construction of the heat exchanger  10  will prevent the leaking fluid of the fluid passageway ‘F’ from mixing with the fluid within the fluid passageway ‘E’. The leaking fluid will then migrate by capillary action through the leak space  60  of the plate pair  12 ( 3 ) and enter the central vent pockets  66  and  66 ′ (see  FIG. 4A ) of plate pair  12 ( 3 ). The leaking fluid will then travel into the weep hole  50  that intersects the central vent pocket  66  of the plate pair  14 ( 1 ), and/or travel into the weep hole  52  that intersects the central vent pocket  66 ′ of the plate pair  14 ( 1 ). The leaking fluid will ultimately exit out of the weep holes  50  and/or  52  at the front and rear surfaces of the heat exchanger  10  at a location that is spaced from the side boundary  46  of the heat exchanger  10 . 
         [0041]    Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention. For example, the number of flow channels and plate pairs may vary from that shown and described.