Abstract:
An evaporator includes plates disposed in pairs in first and second groups, along spaced tanks. Dimples extend from the interior portions in the first group, and interior fins are disposed against the interior portions of the second group. The dimples enhance the distribution of liquid refrigerant in the passageways and the thermal energy exchange between ambient air and an upstream, low vapor quality flow of fluid passing between upstream and downstream side edges, of the first group of plates. The evaporator also eliminates the tonal noise or whistle under certain transient operating conditions.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to a heat exchanger for use in a vehicle climate control system. More specifically, the invention relates to an evaporator for transferring heat between a cross-flow of air through the evaporator and a refrigerant circulating within the evaporator.  
         [0003]     2. Description of the Related Art  
         [0004]     Various evaporator designs exist in the art that incorporate components for promoting heat exchange between a refrigerant fluid flowing within tubes and air flowing through fins that are disposed on the exterior surfaces of the tubes. The tubes typically incorporate features that force the refrigerant entering the evaporator to flow in a number of passes before it exits the evaporator. The evaporators often also include specific modifications to the interior surfaces of the tubes, which increase the surface area available for heat exchange between the ambient air and the fluid. For example, some evaporators are formed entirely of tubes having interior surfaces upon which interior fins are disposed. Other evaporators utilize tubes having interior surfaces from which “dimpled”, or “bumped”, protrusions extend into the interior (refrigerant side) of the evaporator.  
         [0005]     While interior fins and “bumped” or “dimpled” surfaces increase heat exchange within the evaporator, limiting use of one or the other of the fins or dimples throughout all of the tubes in an evaporator is not necessarily the optimum way to maximize heat exchange. This is especially the case in climate control systems utilizing thermostatic expansion valves (“TXVs”). In a TXV system, the evaporator outlet superheat is normally set at about 15° F.; however, when a TXV system is under transient operation, the superheat can increase to 30° F. or more. This reduces cooling capacity and causes the temperature distribution of the discharge air to become more non-uniform.  
         [0006]     Another problem with dimpled evaporators is that under certain transient vehicle operating conditions, vapor flowing over the dimples gives rise to a pure tone noise or “whistle” emanating from the evaporator. By providing fins inside the refrigerant tube plates in appropriate locations, as described in this invention, it is possible to eliminate this whistling transient noise.  
       BRIEF SUMMARY OF THE INVENTION AND ADVANTAGES  
       [0007]     The invention provides a laminate-type evaporator having first and second tanks and fabricated from a plurality of plates. Each plate has upstream and downstream side edges with an interior portion recessed relative thereto. The plates are disposed in pairs with the side edges of each pair in abutting engagement with one another and the interior portions defining a passageway between each pair. The pairs are spaced along the tanks in first and second groups, and the passageways are in fluid communication with the tanks for permitting a fluid to flow between the tanks through the passageways. A thermal energy exchange occurs between the fluid and a cross-flow of air through the first and second groups from the upstream to downstream side edges. Dimples extend from the interior portions into the passageways of the first group. Interior fins are disposed against the interior portions and extend to the upstream and downstream side edges, which enhances the thermal energy exchange between the fluid and the cross-flow of air between the upstream and downstream side edges of the second group of plates.  
         [0008]     Disposing dimples on the first group of plates enhances the thermal energy exchange between the air and a first flow of the fluid passing from the upstream to downstream side edges of the first group of plates. The fins on the second group of plates enhance thermal energy exchange between the air and a second flow of fluid passing from the upstream to downstream side edges of the second group of plates independently and separately from the first flow of fluid.  
         [0009]     The subject invention overcomes the limitations of the art by providing an evaporator which utilizes tubes having interior fins in combination with a separate, distinct group of tubes having interior surfaces upon which dimples are formed. The interior fins are utilized in those tubes which define the final refrigerant passes of the evaporator. Doing so reduces refrigerant side thermal resistance by providing increased refrigerant side surface area to compensate for the decrease in the refrigerant side heat transfer coefficient that often occurs in the last passes of evaporators, especially in those operating at high outlet superheats. Additionally, providing interior fins in the final refrigerant passes also improves the thermal contact between the air fins and the tubes, because the tubes in this region of the evaporator have no dimples. Thus, in the final evaporator passes, a higher overall heat transfer coefficient is achieved resulting from reduced thermal resistance on the refrigerant side and in the conduction path from the air fins to the tube. Tubes having dimples formed on the interior surfaces are utilized in the initial refrigerant passes on the upstream airside of the evaporator where high refrigerant side surface area is not critical to initiate heat exchange, because of the prevailing high refrigerant side heat transfer coefficients associated with low to medium vapor quality two-phase flow. Providing interior fins in the final refrigerant passes also eliminates the tonal noise or whistle originating in the evaporator under certain transient operating conditions. This is because high velocity refrigerant vapor flow over the dimples in the last passes is the cause of a phenomenon called acoustic resonance, which is perceptible as whistling. Combining different surface enhancements by providing them only where they are truly necessary reduces total evaporator mass, decreases manufacturing costs, eliminates transient whistling noise, and improves heat exchange efficiency and temperature uniformity and stability. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0010]     Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:  
         [0011]      FIG. 1  is an exploded perspective view of an evaporator according to one embodiment of the present invention;  
         [0012]      FIG. 2  is a cross-sectional view taken along line  2 - 2  of the second group of plates in the evaporator shown in  FIG. 1 ;  
         [0013]      FIG. 3  is a cross-sectional perspective view of a selected plurality of the second group of plates in the evaporator shown in  FIG. 1 ;  
         [0014]      FIG. 4  is an exploded perspective view of an evaporator according to an alternative embodiment of the invention;  
         [0015]      FIG. 5  is a fragmentary perspective view of the second group of plates in the evaporator shown in  FIG. 4 ;  
         [0016]      FIG. 6  is a cross-sectional view taken along line  6 - 6  of  FIG. 4  of plate pairs and exterior fins in the second group of the evaporator, and  
         [0017]      FIG. 7  is a cross sectional view across the bottom of the left most group shown in  FIG. 4 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     Referring now to the Figures, wherein like numerals indicate like or corresponding parts throughout the several views, a laminate-type evaporator is generally shown at  10  in  FIGS. 1 through 3 . The evaporator  10  includes upper and lower or first and second tanks  12 ,  14  and is fabricated from a plurality of plates  16 .  
         [0019]     Each of the plates  16  has upstream and downstream side edges  18 ,  20  with an interior portion  22  recessed relative thereto. As shown in  FIG. 2 , the plates  16  are disposed in pairs  24 , with the side edges  18  and  20  in overlapping and abutting engagement with one another such that the interior portions  22  define a passageway  26  between the plates  16  in each pair  24 .  
         [0020]     Referring now to  FIG. 1 , the pairs  24  are spaced along the tanks  12 ,  14  in first and second groups  28 ,  30  with the passageways  26  in fluid communication with the tanks  12 ,  14 . The manner in which the passageways  26  are interconnected permits a fluid, or fluid stream of refrigerant,  32  to flow through the passageways  26  for allowing a thermal energy exchange to occur between the fluid  32  which flows through the passageways  26  in a specific number of passes or circuits and a cross-flow of air across the first and second groups  28 ,  30  from the upstream side edges  18  to the downstream side edges  20 .  
         [0021]     The evaporator  10  also includes a plurality of dimples  34  which extend from the interior portions  22  of the first group  28  of plates  16  into the passageways  26  for enhancing the thermal energy exchange between the fluid  32  and the cross-flow of air between the upstream and downstream side edges  18 ,  20 . The thermal efficiency of the evaporator  10  is further improved by a plurality of interior fins  36 . The fins  36  are disposed against the interior portions  22  of the second group of plates  30 . As shown in  FIG. 3 , the fins  36  extend to the upstream and downstream side edges  18 ,  20  of the plates  16  in the second group  30 .  
         [0022]     Disposing the dimples  34  on the first group  28  of plates  16  enhances the thermal energy exchange of air with the flow of the fluid  32  passing between the upstream and downstream side edges  18 ,  20  of the first group  28  of plates  16 , while the fins  36  on the second group  30  of plates  16  enhance the thermal energy exchange of air with the flow of the fluid  32  passing through the second group of plates  30 .  
         [0023]     As is best shown in  FIG. 2 , which shows a representative example of the plates  16  used in the second group  30 , each plate  16  includes a pair of tubular projections  38  disposed within the periphery of the plates  16 . The interior portion  22  interconnects and is in fluid communication with the projections  38 . The tubular projections  38  on the plates  16  are in abutting engagement with one another, which in turn defines the upper and lower tanks  12 ,  14 .  
         [0024]     The plates  16  include upper and lower side edges  40 ,  42  that interconnect the upstream and downstream side edges  18 ,  20 . The upper tank  12  is disposed adjacent the upper edges  40 , and the lower tank  14  is disposed adjacent the lower side edges  42 . The tanks  12 ,  14  are in fluid communication with the passageways  26 , which permits the fluid  32  to flow between the first and second groups  28 ,  30  of plates  16 .  
         [0025]     The evaporator  10  also includes exterior fins  48  which are disposed against the exterior surfaces of the adjacent pairs  24  of plates  16 . The fins  48  extend from the upper tank  12  to the lower tank  14 . Each exterior fin  48  has a plurality of folds  50 . The folds  50  extend perpendicularly to the longitudinal axes  51  of the plates  16  between the upstream and downstream side edges  18 ,  20 . The orientation of the folds  50  relative to the longitudinal axis  51  of each plate  16  maximizes the total surface area available on the exterior fins  48  for transferring thermal energy between the cross-flow of air and the fluid  32  as the air passes across the exterior fins  48  from the upstream to downstream side edges  18 ,  20  of the plates  16 .  
         [0026]     The evaporator  10  also has upstream or right and downstream or left endplates  52 ,  54 . The upstream endplate  52  is disposed against that plate  16  which is located rightmost from the remaining plates  16  forming the first group  28 . The right endplate  52  includes an inlet aperture  56 . As is shown in  FIG. 1 , the endplate  52  is positioned in longitudinal alignment with the plates  16  in the first group  28 , with the inlet aperture  56  in axial alignment with the upper tank  12 .  
         [0027]     The left endplate  54  includes an outlet aperture  58 , and is positioned against that plate  16  which is located leftmost from the rest of the plates  16  in the second group  30 . Like the inlet aperture  56 , the outlet aperture  58  is in axial alignment with the upper tank  12  for permitting the fluid  32  to exit the evaporator  10  after flowing through the plates  16  in the second group  30 .  
         [0028]     The evaporator  10  is configured in a manner that directs the fluid  32  through a plurality of passes through the passageways  26  and across the path of the cross-flow of air through the exterior fins  48 . As is shown in  FIG. 1 , a downstream flow separator  60  directs the fluid  32  to flow from the first group  28  of plates  16  to the second group  30 . The downstream flow separator  60  may be positioned in either the upper or lower tank  12 ,  14  and fabricated from any components suitable for diverting the flow of fluid  32  from one tank  12 ,  14  to the other. However, as is shown in  FIG. 1 , the downstream flow separator  60  consists of a planar surface, or blind  62  which is disposed across one of the tubular projections  38  that form the upper tank  12  to block and divert flow.  
         [0029]     The blind  62  is disposed in the upper tank  12  within the tubular projection  38  of the first plate pair  24  positioned immediately downstream from the first group  28  of plates  16 . Positioning the blind  62  in this location prevents the fluid  32  from flowing further to the left in the upper tank  12  past the blind  62 , and instead diverts the fluid  32  to flow into the lower tank  14  through the plate pairs  24  of the third pass of the first group  28 . From the lower tank  14 , the fluid  32  then flows through the plate pairs  24  in the second group  30 .  
         [0030]     The evaporator  10  also utilizes upstream and intermediate flow separators  64 ,  66 , which consist of blinds  68 ,  70  identical in shape and structure to the blind  62  described above with reference to the first flow separator  60 . The blind  68  which forms the rightmost flow separator  64  is disposed within the upper tank  12  intermediate two of the plate pairs  24  that are located in the first group  28  a predetermined distance to the left of the inlet aperture  56 .  
         [0031]     The intermediate flow separator  66  is positioned within the first group  28  to the left of the rightmost flow separator  64 . However, in contrast to the blind  68 , the blind  70  forming the intermediate flow separator  66  is disposed within the lower tank  14  between a plate pair  24  located a predetermined distance to the right of the flow separator  60 , and a plate pair  24  located a predetermined distance to the left of the upstream flow separator  64 .  
         [0032]     Although any number of flow separators may be utilized in the evaporator  10  to define flow path configurations with any number of passes, the rightmost, leftmost and intermediate flow separators  64 ,  60 ,  66  are utilized in combination with the upstream and downstream endplates  52 ,  54  to define four passes through the evaporator  10  in the particular case shown in  FIG. 1 . Specifically, upon entering the evaporator  10  by passing through the inlet aperture  56 , the fluid  32  flows into the upper tank  12 , encounters the blind  68  of the rightmost flow separator  64 , and is diverted through the passageways  26  defined by the first group  28  of plates  16  into the lower tank  14  to complete a first pass through the evaporator  10 .  
         [0033]     The fluid  32  continues to flow to the left through the lower tank  14  and is diverted through the passageways  26  located immediately between the intermediate blind  70  and the rightmost blind  68 . The fluid  32  flows back into the upper tank  12 , thus completing a second pass through the evaporator  10 .  
         [0034]     The fluid  32  completes a third pass through the first group  28  by flowing to the left through the upper tank  12  to the flow separator  60 . The blind  62  defining the flow separator  60  causes the fluid  32  to flow through the passageways  26  of the selected group of the plate pairs  24  in the first group  28  positioned immediately upstream from the second group  30 . The fluid  32  is diverted back into the second tank  14  and into the second group  30  of plates  16 . The fluid  32  then makes a fourth, or final, pass from the second tank  14 , through the passageways  26  and across the interior fins  36  of the plates  16  in the second group  30  prior to re-entering the upper tank  12  and exiting the evaporator  10  through the outlet aperture  58  located in the left end plate  54 .  
         [0035]     Referring now to  FIGS. 4 through 7 , an evaporator according to an alternative embodiment of the invention is generally shown at  110 . The evaporator  110  includes many of the same components and is formed from the same materials as the evaporator  10 . Like elements are numbered the same as the first embodiment but differ by one hundred (100) The plates  116  of the evaporator  110  include upstream and downstream side edges  118 ,  120  that interconnect upper and lower edges  140 ,  142 . Each plate  116  also includes a pair of tubular projections  138  interconnected by an interior portion  122 . However, in contrast to each pair of tubular projections  38  of the evaporator  10 , each projection  138  in the evaporator  110  is disposed adjacent the upper edge  140  of a selected one of the plates  116 . The tubular projections  138  form first and second tanks  112 ,  114 . Unlike the tanks  12 ,  14  of the evaporator  10 , the first and second tanks  112 ,  114  in the evaporator  110  are disposed adjacent the upper edges  140  of the plates  116 .  
         [0036]     In contrast to the plates  16  utilized in the evaporator  10 , the interior portions  122  of the plates  116  in both the first group  128  and the second group, generally shown at  130  in  FIGS. 5, 6  and  7  each include a central rib defined by an elongate projection  172 . The rib  172  extends from the interior portion  122  to abut a like rib  172  in the opposite plate  116  to define a first recess  174  adjacent the upstream side edges  118  and a second recess  176  adjacent the downstream side edge  120 . A return recess interconnects the first and second recesses  174 ,  176 . As is best shown in  FIG. 5 , the ribs  172  in each of the adjacent pairs  124  of plates  116  in the second group  130  are in abutting engagement with one another such that the passageways  126  define a plurality of U-shaped channels  180  interconnecting the first and second tanks  112 ,  114 .  
         [0037]     As is shown in  FIG. 5 , each of the plates  116  also includes first and second flanges  182 ,  184  that extend from each of the lower edges  142 . The first flange  182  has a shape complementary to that of the second flange  184 . As is shown in  FIG. 4 , this permits the first and second flanges  182 ,  184  to be placed in interlocking engagement with respective second and first flanges  184 ,  182  on an adjacent plate  116  to define an evaporator base  186 .  
         [0038]     While the exterior fins  148  are disposed against the exterior surfaces of the adjacent pairs  124  of plates  116 , in contrast to the exterior fins  48  of the evaporator  10 , the fins  148  extend from the first and second tanks  112 ,  114  to the lower edges  142  of the plates  116  adjacent the base  186 .  
         [0039]     The U-shaped channels  180  affect both the rate of heat exchange within the evaporator  110  and the location of the interior fins  136  and dimples  134  disposed within the passageways  126 . As is shown in  FIGS. 5 and 6 , the interior fins  136  on each of the plates  116  in the second group  130  include a first fin group  188 . The first fin group  188  is disposed against the first recess  174  adjacent the upstream side edge  118 . A second fin group  190  is disposed against the second recess  176  adjacent the downstream side edge  120 .  
         [0040]     Referring again to  FIG. 4 , the dimples  134  on the interior portions  122  of the plates  116  in the first group  128  are randomly dispersed across the first recesses  174 , second recesses  176  and return recesses  178 . Although not required, the evaporator  110  also has a plurality of second dimples  192 , as shown in both  FIGS. 4 and 7 . As is shown in  FIGS. 5 and 7 , the second dimples  192  extend from the interior portion  122  and into the passageway  126  of each of the plates  116  in the second group  128 , which further enhances distribution of liquid refrigerant and the thermal energy exchange between the fluid  132  flowing therethrough and the cross-flow of air flowing through the evaporator  110  from the upstream to downstream side edges  118 ,  120 . The second dimples  192  extend from the interior portions  122  intermediate the first and second fin groups  188 ,  190 . Specifically, the second dimples  192  extend from one or more of the return recesses  178 .  
         [0041]     The evaporator  110  utilizes right or upstream and left or downstream endplates  152 ,  154  which have respective inlet and outlet apertures  156 ,  158 . The endplates  152 ,  154  are identically shaped. The right endplate  152  is disposed against that plate  116  which is located to the right of the remaining plates  116  that constitute the first plate group  128 . The endplate  152  is disposed in abutting engagement with the aforementioned plate  116  with the inlet aperture  156  in axial alignment with the first tank  112 . The left endplate  154  is similarly disposed against the plate  116  in the second group  130  which is located furthest to the left of the other plates  116  of the evaporator  110 . The left endplate  154  is oriented in axial alignment with the first tank  112  with the outlet aperture  158  adjacent the side edge  118 . As described in greater detail below, this allows the fluid  132  to exit the evaporator  110  after flowing through the passageways  126  in the second group  130 .  
         [0042]     The evaporator  110  utilizes right and left flow separators  164 ,  160  to direct the fluid  132  through a predetermined flow configuration within the evaporator  110 . In order to accommodate the U-shaped configuration of the plates  116 , the shape and components of the flow separators  160 ,  164  differ from those utilized in the evaporator  10 . In particular, the left flow separator  160  includes a planar surface, or blind  194 . The blind  194  covers a selected one of the tubular projections  138  in a single plate pair  124  positioned intermediate the first and second plate groups  128 ,  130 . As is shown in  FIG. 4 , the blind  194  covers the tubular projection  138  on the first plate  116  immediately to the right of the second group  130 , which in turn blocks the leftmost portion of the second tank  114 . The blind  194  effectively blocks the fluid  132  from flowing further to the left through the second tank  114  and from the second tank  114 , through the U-shaped channels  180  within the second group  130 . After the fluid  132  exits the first plate group  128 , it first flows through the leftmost portion of tank  112 , then through the U-shaped channels  180  within the second group  130 , and finally the fluid  132  flows through the leftmost portion of the second tank  114  prior to exiting the evaporator  110  through the outlet aperture  158 .  
         [0043]     The upstream flow separator  164  includes a single blind  198 , which covers a tubular projection  138  in a selected plate  116  in the first group  128 . In particular, the blind  198  covers the projection  138  located adjacent the downstream side edge  120 , which effectively blocks the portion of first tank  112  to the left of blind  198 . The blind  198  diverts the fluid  132  to flow in a first pass through the U-shaped channels  180 , over the dimples  134  and into the second tank  114 . The fluid  132  continues flowing through the second tank  114  and encounters the other blind  194  in the second tank  114  and is then diverted to flow in a second pass through the U-shaped channels  180  of a selected plurality of plates  116  in the first group  128 . These plates  116  are located immediately to the right of the second group  130 . The fluid  132  then flows back into the first tank  112  and flows in a third, or final, pass through the second plate group  130  in the manner described above.  
         [0044]     While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.