Abstract:
A condensate drainage enhancing device is provided for an evaporator. An integrally molded plastic part snap fits around the conventional lower manifold, with rails maintained in tight engagement with the front and rear edges of the refrigerant flow tubes. These interrupt the meniscus films of columns of retained water that would otherwise form and, which instead drains down ribs that depend from the rails.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates to cross-flow heat exchangers in general, and specifically to an air conditioning evaporator core in which entrained, condensed water from the ambient air blown over said evaporator is likely to become entrained in the core and partially block air flow 
       BACKGROUND OF THE INVENTION 
       [0002]    Cross flow evaporators typically are mounted vertically or nearly so with parallel pairs of refrigerant flow tubes extending between substantially horizontal, upper and lower manifolds. Especially in evaporators of compact design and high capacity, the refrigerant flow tubes are closely spaced, and the lower manifold is significantly wider than the edge to edge width of the flow tubes. Ambient air with substantial relative humidity is blown across the refrigerant flow tubes, condensing thereon and draining down toward the lower manifold. Because of the close spacing of the tubes and width of the lower manifold, condensed water tends to build up in columns between the lower ends of the tubes, blocked by the lower manifold These columns rise to and dynamically maintaining a characteristic height dependent on the dimensions of the particular core in question and the humidity, forming a slightly concave meniscus film that bulges out minutely past the front and back edges of the closely spaced pairs of tube ends. These retained columns of water can block air flow sufficiently to affect the efficiency of the core. 
         [0003]    One known and straightforward response has been to purposely stamp individual drain troughs or grooves directly into the surface of the lower manifold, between the pairs of tube ends. A typical example may be seen in U.S. Pat. No. 7,635, 019, and there are numerous variations of the same basic theme. This requires dedicated dies and tools for the lower manifold, of course, and can disrupt the flow of refrigerant in the lower manifold. 
       SUMMARY OF THE INVENTION 
       [0004]    The subject invention provides a separate drainage device that can be added and retrofitted to an existing evaporator of the type described, enhancing drainage and improving efficiency with no change to the basic core design. 
         [0005]    In the preferred embodiment disclosed, a plastic molded part consisting of a pair of horizontal rails, integrally and flexibly molded by generally C shaped depending ribs to a central keel, has a free state separation slightly less than the edge to edge width of the refrigerant tubes. This allows the rails to be spread apart far enough to snap over the wider lower manifold and into tight, resilient engagement with both the front and rear edges of the tubes, at a point near the surface of the lower manifold and well below the characteristic height of the retained columns of water that would otherwise form. 
         [0006]    In operation, as condensed water begins to form the characteristic retained columns, the meniscus film is interrupted by the tightly engaged rails and the condensed water runs down the surface of the ribs, dripping finally into a sump or simply off of the core. The edges of the ribs may be formed as semi-cylinders to enhance the drainage effect. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a perspective view of a preferred embodiment of the drainage device of the invention installed on an evaporator; 
           [0008]      FIG. 2  is an exploded view of the evaporator and the drainage device of the invention; 
           [0009]      FIG. 3  is a cross section of a portion of the drainage device; 
           [0010]      FIG. 4  is a cross section of a portion of the evaporator showing the presence of condensed and retained water pockets; 
           [0011]      FIG. 5  is similar to  FIG. 4 , but showing the drainage device installed; 
           [0012]      FIG. 6  is an end view of the drainage device in operation, with the manifold end cap removed; 
           [0013]      FIG. 7  is an end view of the drainage device installed. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0014]    Referring first to  FIGS. 1 and 2 , an evaporator indicated generally at  10  is a typical brazed aluminum design with a lower manifold  12 , parallel upper manifolds  14 , and, since it is a U flow construction, coplanar pairs of parallel, closely spaced refrigerant flow tubes  16 . A single pass construction would have single flow tubes with a similar spacing, but likely greater width. Front and rear tube edges  18  and  20  define parallel front and rear core faces. The lower manifold  12  is typically significantly wider than the tubes  16 , leaving a significant upper surface extending out from both the front and rear tube edges  18  and  20 . Corrugated fins  22  are brazed between the tubes  16  to enhance heat transfer, but do not extend all the way down to the upper surface of lower manifold  12 . The orientation shown is the orientation that evaporator  10  has in operation, substantially vertical, so that when humid ambient air is blown over the tubes in a so called cross-flow fashion, condensed water forms on the tube surfaces and drains and runs down, toward the upper surface of lower manifold  12 . 
         [0015]    Referring next to  FIGS. 1 and 4 , the result of the water condensed during operation, in the absence of the subject invention, is illustrated. The combined effect of the close spacing of tubes  16 , typical for a compact, high efficiency evaporator, the natural surface tension of water, and the extent of the manifold surface beyond the tube edges  18  and  20  is that condensed water forms retained columns  24  at and between the lower ends of the tubes  16 , where they enter the lower manifold  12 . While the upper surface of the lower manifold  12  is smooth and even downwardly curved, it presents enough resistance to drainage along its surface that the columns  24  will rise to a characteristic height h before creating enough pressure to drain down and off the edge of lower manifold  12 . Water is continually condensing, so the height h is dynamically maintained, though it will rise and fall somewhat with humidity, temperature and other conditions. Another effect of the downward pressure of the columns  24  and the surface tension of the water is that outwardly bulging meniscus films  26  are formed, extending out slightly from both the front and back tube edges  18  and  20 , as shown in  FIG. 4 . 
         [0016]    Referring next to  FIGS. 2 and 3 , a preferred embodiment of the drainage device of the invention is indicated generally at  28 . It is an integral, molded plastic part, with a pair of parallel, straight rails  30  joined to a stiff central keel  32  by an evenly spaced plurality of curved ribs  34 . As seen in  FIG. 2 , the free state separation of the rails  30  is just slightly less than the width measured between tube front and rear edges  18  and  20  and, substantially less that the width of lower manifold  12 . As best seen in  FIG. 3 , the inner edges of ribs  34  are concave, specifically semi-cylindrical troughs  36 , rather than sharp for a purpose described below. 
         [0017]    Referring next to  FIGS. 5 and 6 , the flexibility of ribs  34  allows the rails  30  to be pulled apart and snapped over the width of lower manifold  12 , thereby bringing the rails  30  into tight engagement with the tube front and rear edges  18  and  20 , and at a location near the upper surface of lower manifold  12 , well below the characteristic column height h described above. The inner surface of the ribs  34  also conforms closely to the outer surface of the lower manifold  12 . As a consequence, the water column meniscus films  26  are interrupted by the rails  30  as they attempt to form and run down the ribs  34 , through the channels formed by the outer surface of lower manifold  12  and the rib troughs  36 , ultimately dripping off of the ribs  34  at the keel  32 . This is best illustrated in  FIG. 6 . As a consequence, the retained water columns  24  described above are prevented from forming, and the problems of air blockage, pressure drop, and potential water “spitting” avoided. 
         [0018]    Referring again to  FIGS. 1 and 2 , additional structure can be provided to work in cooperation with the drainage device  28 , which fairly closely matches the profile of lower manifold  12 . A sump or drip pan  38  and a foam seal  40  can cradle the drainage device  28  and lower manifold  12 , preventing the blow-by of forced air. A strip seal  42  can be installed between the keel  32  and the underside of lower manifold  12  to also prevent air blow-by. The drip pan  38  can be open on the upstream air side, and closed on the downstream side, as shown, to allow forced air to blow water off of the drainage device  28  without loss from the drip pan  38 . One or more end clips  44  can be added to the ends of the lower manifold  12  to confine the drainage device  28  axially, if desired. 
         [0019]    Variations in the preferred embodiment  28  could be made. A single rail  30 , best situated on the air downstream side and in contact with just the tube rear edges  20 , could, in cooperation with the depending ribs  34 , provide for condensate drainage, but some other means of installation would have to be provided to maintain the device  28  in position. “Rail” as used here could encompass an aligned series of separate pieces, each of which touched and intruded into the entrained water columns enough to enhance the drainage as described. The two rails  30  provide more drainage paths and also allow for the self-retention after installation. Differently shaped ribs  34 , so long as they depended, could provide drainage paths, but the curved shaped matches well to the shape of manifold  12 , as noted, providing effective drainage paths. Localized, inwardly protruding features on rails  30  could be provided between the pairs of adjacent tubes  16 , to aid breaking the meniscus films  26 . It will be understood that the invention could be used with any heat exchanger in which a cold fluid flow tube has humid air passing over it to cause sufficient retained condensation to necessitate enhanced drainage.