Patent Publication Number: US-6991025-B2

Title: Cross-over rib pair for heat exchanger

Description:
BACKGROUND OF THE INVENTION 
   This invention relates to heat exchangers that are formed from plate pairs in which an internal flow path through the plate pair is defined by cross-over ribs. 
   Heat exchangers are often formed from multiple plate pairs that are stacked and brazed, soldered, or mechanically or otherwise joined and sealed. In some applications, for example in refrigerant evaporator systems, heat exchangers are formed from stacked plate pairs that each define an internal U-shaped flow path for the refrigerant. In some plate pair heat exchangers outwardly projecting ribs provided on each of the plates of a plate pair cooperate to form the internal U-shaped flow path. In such a ribbed plate construction, the ribs on each plate are angled in a common direction, such that when two plates are arranged facing each other to form a plate pair, the internal groove provided by each rib on one plate crosses-over a number of the internal grooves provided by ribs on the facing plate, thereby forming the internal flow path. Typically, at the U-turn portion of the flow path, the angled ribs are longer in order to pass the fluid around the U-turn. Examples of cross-over rib heat exchangers can be seen in U.S. Pat. No. 3,258,832 issued Jul. 5, 1966 and U.S. Pat. No. 4,249,597 issued Feb. 10, 1981. 
   In conventional designs for U-shaped flow path cross-over rib heat exchangers, the internal fluid is subjected to a relatively large pressure drop at the turn-around portion of a plate pair flow path, relative to the total drop across the rest of the plate pair. Additionally, in conventional designs, the internal fluid is not always directed around the turn-around portion in the most efficient manner for promoting heat exchange. For example, fluid entering the turn-around zone may have different phase characteristics based on a relative location of the fluid within the internal flow path. In conventional cross-rib plate designs, fluid passing around the turn-around portion is indiscriminately mixed without regard for such differing characteristics. Thus, there is a need for a cross-rib type plate pair heat exchanger in which the pressure drop in transferring fluid around the turn-around portion is minimized and fluid is routed around the turn-around portion in a pattern that increases heat exchanger efficiency. 
   SUMMARY 
   According to one example of the invention, there is provided a multipass plate pair for conducting a fluid in a heat exchanger. The plate pair includes first and second plates, each plate having at least two longitudinal columns of externally protruding obliquely angled ribs formed therein and separated by a longitudinal flat section extending from substantially a first end of the plate to a terminus spaced apart from a second end of the plate. Each plate includes, between the terminus and the second end, a turn portion joining the two longitudinal columns. The first and second plates are joined together about peripheral edge sections thereof with the longitudinal flat sections abutting each other and the columns of angled ribs cooperating to form undulating first and second internal flow channels separated by the abutting longitudinal flat sections. The first and second internal flow channels each have an upstream area and a downstream area relative to a flow direction of an external fluid flowing over the plate pair. The turn portions of the plates cooperate to define at least a first internal flow path for directing fluid from the upstream area of the first internal flow channel to the downstream area of the second internal flow channel and a second internal flow path for directing fluid from the downstream area of the first internal flow channel to the upstream area of the second internal flow channel. 
   According to another example of the invention, there is provided a heat exchanger including an aligned stack of U-flow tube-like flat plate pairs for conducting an internal heat exchanger fluid between an inlet manifold and an outlet manifold. Each of the plate pairs has an inlet opening and an outlet opening for the internal fluid and an upstream edge and a downstream edge relative to a flow direction of an external fluid over the plate pairs. Each plate pair includes first and second interfacing plates each having a longitudinal axis and an end, each of the plates having a longitudinal upstream column of outwardly protruding ribs that are angled relative to the longitudinal axis, and a longitudinal downstream column of outwardly protruding ribs that are angled relative to the longitudinal axis, the upstream column starting at one of the inlet and outlet openings and terminating at a turn portion located adjacent the end and the downstream column starting at the other of the inlet and outlet openings and terminating at the turn portion, the upstream column being upstream of the downstream column relative to the flow direction of the external fluid. The turn portion includes first and second outwardly extending ribs. The first and second plates are joined together with the angled ribs in the upstream columns of each plate communicating in a cross-over arrangement to define an upstream internal flow channel for the internal fluid and the angled ribs in the downstream columns of each plate communicating in a cross-over arrangement to define a downstream internal flow channel for the internal fluid. The first outwardly extending ribs cooperate to provide a first internal flow path for the internal fluid between an upstream side of the upstream internal flow channel to a downstream side of the downstream internal flow channel, and the second outwardly extending ribs cooperate to provide a second internal flow path for the internal fluid between a downstream side of the upstream internal flow channel and an upstream side of the downstream internal flow channel. 
   According to another example of the invention, there is provided a U-flow plate pair for conducting an internal fluid therethrough for use in a multi-plate pair heat exchanger having an upstream side and a downstream side relative to flow of an external fluid between adjacent plate pairs of the heat exchanger. The plate pair includes first and second interfacing plates joined about peripheral edge sections and along elongated central sections thereof, the plate pair including an elongated upstream side located between an upstream edge of the plate pair and the joined central plate sections and a downstream side located between the joined central plate sections and a downstream edge of the plate pair. The upstream and downstream sides of the plate pair include a first internal flow channel and a second internal flow channel, respectively, defined by obliquely angled outwardly projecting interfacing ribs formed on the plates, the interfacing ribs on the first plate being oriented in an opposite direction than the interfacing ribs on the second plate. The plate pair includes a turn-around end defining a U-shaped first internal flow path connecting an upstream area of the first internal flow channel to a downstream area of the second internal flow channel, and a second internal flow path connecting a downstream area of the first internal flow channel to an upstream area of the second internal flow channel. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS: 
     Example embodiments of the invention will now be described, with reference to the accompanying drawings, in which: 
       FIG. 1  is a side view of an example embodiment of a heat exchanger; 
       FIG. 2  is a first side edge view of a plate of the heat exchanger of  FIG. 1 ; 
       FIG. 3  is an end view of the outside of a plate of the heat exchanger; 
       FIG. 4  is an end view of the inside of a plate of the heat exchanger; 
       FIG. 5  shows the opposite side edge, relative to  FIG. 2 , of a plate of the heat exchanger; 
       FIG. 6  is a partial perspective view showing the outside of a plate of the heat exchanger; 
       FIG. 7  is a partial end view of a plate pair of the heat exchanger; and 
       FIG. 8  is a partial end view of a further example of a plate for use in the heat exchanger. 
   

   Like reference numerals are used throughout the Figures to denote similar elements and features. 
   DESCRIPTION OF EXAMPLE EMBODIMENTS 
   Referring to  FIG. 1 , an example embodiment of a heat exchanger, indicated generally by reference  10 , is made up of a plurality of plate pairs  20  formed of back-to-back plates  14  of the type shown in  FIGS. 2 to 5 . Plate pairs  20  are stacked, tube-like members, formed from plates  14  having enlarged distal end portions or bosses  22 ,  26  having inlet  24  and outlet  28  openings, so that fluid flow travels in a generally U-shaped path through the plate pairs  20 . In an example embodiment, air-side fins  12  are located between adjacent plate pairs  20 . The bosses  22  on one side of the plates are joined together to form an inlet manifold and the bosses  26  on the other side of the plates are joined together to form an outlet manifold. The heat exchanger  10  may include a longitudinal inlet tube  15  that passes into the manifold openings  24  in the plates to deliver an incoming fluid, such as a two-phase, gas/liquid mixture of refrigerant, to one side of the heat exchanger  10 . The heat exchanger  10  can be divided into multiple parallel plate pair sections, with fluid routed serially through the various sections to ultimately exit from an outlet fitting  17  located at the same end of the heat exchanger  10  as an inlet fitting. Alternatively, the outlet and inlet fittings may be located at different ends or in different locations of the heat exchanger. The actual circuiting used between plate pairs  20  is not critical and the plate pair configuration described herein can be used with many different configurations of U-flow stacked plate type heat exchangers. Although the heat exchanger  10  is shown in the Figures with the inlet and outlet manifolds upwards oriented, the heat exchanger  10  may often be oriented with the inlet and outlet manifolds downwards. 
   With reference to  FIGS. 2 to 7 , each plate pair  20  is formed from a joined pair of elongated plates  14 . In an example embodiment, the two plates  14  in a plate pair  20  are identical, with one plate being rotated 180 degrees about its longitudinal axis relative to the other. In this respect,  FIG. 3  shows the outside of a plate  14 , and  FIG. 4  shows the inside of an identical plate  14  rotated 180 degrees relative to the plate shown in  FIG. 3 . The plates  14  of  FIGS. 3 and 4  are joined together to form a plate pair  20 . Each plate  14  is substantially planar, with a flat outer edge portion  16  extending about its periphery. Each plate  14  includes two longitudinal columns  30  of outwardly protruding obliquely angled ribs  32  that are separated by a longitudinal central flat section  34  that extends from a first or manifold end  42  of the plate to a terminus  40  that is spaced apart from a second end  38  of the plate. The central flat section  34  and the flat outer edge portion  16  are located in a substantially common plane, with ribs  32  protruding outward from such plane to define inwardly opening grooves  18 . In an example embodiment, all of the ribs  32  on the plate  14  are oriented in a common direction, at an oblique angle relative to the elongate side edges of the plate. In some example embodiments, however, each column could include multiple sections of parallel ribs, with adjacent sections of ribs being oriented at different angles. The ribs  32  in each column  30  extend from the central flat section  34  out to a respective peripheral edge portion  16 . Within each column, the ribs  32  are each separated by external valleys or grooves  92  that are in the same plane as flat outer peripheral section  16  and flat central section  34 . The columns  30  of angled ribs  32  terminate prior to the second plate end  38 , and each plate  14  includes a turn portion  36  between the central flat section terminus  40  and the second plate end  38 . 
   The plates  14  of a plate pair  20  are sealably joined together with their respective peripheral edge portions  16  and central flat sections  34  aligned and abutting each other, and with the angled ribs  32  cooperating in a cross-over arrangement to form undulating first and second internal flow channels  44 ,  46  through the plate pair  20  on opposite sides of the central flat sections  34 . The turn portions  36  in the plates  14  cooperate to provide a first or outer internal fluid flow path  62  and a second or inner internal fluid flow path  64  between the internal flow channels  44 ,  46 . 
     FIG. 7  illustrates the cooperation of ribs  32  and turn portions  36  in a plate pair  20 , with the ribs  32  of a hidden plate  14  of the plate pair being shown in phantom lines. When installed in a vehicle, the heat exchanger  10  will typically be oriented so that air will flow through the air side fins  12  between the plate pairs  20 . Thus, with reference to  FIG. 1 , the direction of air flow will be substantially perpendicular to the surface of the paper. Turning again to  FIG. 7 , the direction of air flow over the outside of plate pair  20  is represented by arrows  56 . Accordingly, relative to the direction of air flow travel, the plate pair  20  has a leading or upstream edge  58  and a trailing or downstream edge  60 , first flow channel  44  being upstream of the second flow channel  46 . As used herein, the terms “leading” or “upstream” and “trailing” or “downstream” are relative to direction of air flow through the plate pair  20 , unless the context requires a different interpretation. In the illustrated embodiment, the ribs  32  of one of the plates  14  (the visible plate in  FIG. 7 ) are all obliquely angled with their downstream rib ends closer to the turn-around end  38  of the plate than their upstream rib ends are. The ribs  32  of the other plate  14  (the hidden plate in  FIG. 7 ) are all obliquely angled in an opposite direction with their upstream rib ends closer to the turnaround end  38  of the plate than their downstream rib ends are. In the illustrated embodiment, each rib  32  (except those ribs near the manifold end  42  and those near the turnaround end  38 ) crosses over or interacts with four ribs  32  on the other plate  14  of the plate pair  20 . In other example embodiments, there may be more or less than four cross-over points between opposing ribs. As best seen in  FIGS. 3 and 4 , in the illustrated embodiment, three of the ribs  32  near the manifold end  42  are joined by joining ribs to  72  to the inlet and outlet openings  24 ,  28 , thus providing a path for fluid to enter and exit the flow channels  44 ,  46 . 
   The turn-around portions  36  of plates  14  of a plate pair  20 , each include first and second outwardly protruding ribs  66 ,  68  that cooperate to provide the first and second internal flow paths  62  and  64 , respectively, that connect the internal flow channels  44 ,  46 . The first turn-around rib  66  is located closer to the outer edges of the plate  14  than the second turn-around rib  68 . The first and second ribs  66 ,  68  each include central horizontal rib portions  74 ,  76 , respectively, that are substantially parallel to each other and to the end  38  of the plate  14  and which are located between the terminus  40  of the central flat section  34  and the plate end  38 . The central rib portions  74 ,  72  are interspaced by a flat diving section  70  that is in the same plane as peripheral edge section  16  and the central flat section  34  such that the flat dividing sections  70  of the plates  14  in a plate pair  20  abut together and separate central portions of the first and second internal flow paths  62  and  64  from each other. In the illustrated embodiment, the flat dividing sections  70  do not completely separate the flow paths  62  and  64 , and short connecting paths  86  and  88  are provided between the flow paths  62  and  64 . 
   As best seen in  FIG. 7 , a first vertical rib portion  78  extends substantially parallel to one longitudinal edge of the plate  14 , orthogonally from one end of horizontal central rib portion  74 , and a second vertical rib portion  80  extends substantially parallel to the opposite longitudinal edge of the plate  14  orthogonally from the other end of horizontal central rib portion  74 . Vertical rib portions  78  and  80  are separated from the central rib portion  76  by vertical flat plate sections  94  and  96 , which are in the same plane as edge section  16  and elongate central section  34 . Angled rib portions  82  and  84 , which are parallel to angled ribs  32 , extend from rib portions  80  and  76 , respectively, into respective rib columns  30 . Rib portions  74 ,  78  and  80  of facing plates  14  of a plate pair  20  define the first flow path  62 . The first flow path  62  is, in an example embodiment, U-shaped and closely follows the outer edges around the turn-around end of the plate pair  20 , thereby ensuring that the internal fluid gets to the corner areas of the plate pair  14 . Additionally, the outer first flow path  62  directs internal fluid from an upstream area  48  of the first flow channel  44  to a downstream area  54  of the second flow channel  46 . The inner second flow path  64 , which is also U-shaped in the presently described embodiment, directs internal fluid from a downstream area  50  of the first flow channel  44  to an upstream area  52  of the second flow channel  46 , as indicated by the flow arrows  90  shown in  FIG. 7 . 
   When heat exchanger  10  is in use, for example as an evaporator, the temperature difference between the external air and an internal refrigerant fluid at the upstream side of the first flow channel  44  will typically be much greater than the temperature difference at the downstream side of the first flow channel  44 , with the result that by the time the internal fluid reaches turn-around portion  36  the liquid phase component of the two phase internal fluid is concentrated more in the downstream area  50  of the first flow channel  44  than the upstream area  48 . 
   In order to improve the evaporation rate, it is desirable to transfer as much of the liquid phase component of the internal fluid from the first flow channel  44  to the leading edge of the second flow channel  46 , as the temperature differential between the external air and the internal fluid will typically be greater at the upstream edge of the second flow channel than the downstream edge thereof. The plate pair configuration described herein addresses this desirable feature by directing, through the inner flow channel  64 , fluid from the downstream area  50  of the first flow channel  44  to the upstream area  52  of the second flow channel  46 , and by directing through the outer flow channel  62 , fluid from the upstream area  48  of the first flow channel  44  to the downstream area  54  of the second flow channel  46 . This reduces mixing of the refrigerant fluid from the upstream and downstream areas of the first flow channel  44 . In other words, in evaporator applications, the multiple turn-around flow paths of the presently described example embodiment directs the upstream portion of the first pass to the downstream portion of the second pass and the downstream portion of the first pass to the upstream portion of the second pass. As the upstream portion of the first pass is depleted of liquid refrigerant relative to the downstream portion because of the greater air-to-refrigerant temperature difference at upstream edge of a pass as compared to the downstream edge, it is beneficial to direct the relatively liquid rich downstream portion of the first pass to the upstream portion of the second pass to take advantage of the larger air-to-refrigerant temperature difference at the upstream edge of the second pass as compared to the downstream edge. 
   As indicated above, in some example embodiments short connecting paths  86  and  88  are provided between the flow paths  62  and  64 . The connecting paths  86  and  88  are formed from externally protruding rib portions  87  and  89 . As noted above and as shown in  FIG. 1 , in an example embodiment air side fins  12  are located between adjacent plate pairs. The fins are secured to and supported by the outer surfaces of ribs  32 ,  66  and  68 . One function of rib portions  87  and  89  is to provide support for the external air fin  12  that would otherwise have a long unsupported distance if flat section  70  were extended all the way from plate area  94  to plate area  96 . Generally, the mixing of fluid between first and second flow paths  62  and  64  through connecting paths  86  and  88  will be quite low as the paths  86  and  88  connect areas of substantially equal refrigerant pressure and the connecting paths  86  and  88  are generally perpendicular to flow paths  62  and  64 . Thus, the refrigerant fluid flowing through the flow paths  62  and  64  substantially by-passes the connecting paths  86  and  88  such that flow paths  62  and  64  are effectively separate from each other in the turn-around end  36 . In some embodiments, paths  86  and  88  are omitted. 
   In an example embodiment, turn-around ribs  66 ,  68  and the angled ribs  32  that feed into the turn-around ribs  66 ,  68  have cross-sectional dimensions that are selected to reduce pressure drop in the internal fluid flowing around the turn portion of the plate pair. 
   With reference to  FIG. 6 , as noted above, the ribs  32  are each separated by external valleys or grooves  92  that are in the same plane as flat outer peripheral section  16  and flat central section  34 . An inner end of each groove  92  intersects with central section  34 , and an outer end intersects with the outer peripheral section  16 . This provides a continuous drainage surface such that condensate forming on the outer surface of the plate  12  can drain off through the grooves  92  (which will typically be spaced from the fin  12 ) to the downstream edge of the plate. In one example embodiment, ribs  32  have a larger external surface area than grooves  92 , thereby increasing the surface area contact between the internal fluid carrying ribs  32  and the air-side fin  12 . 
   In some embodiments, the heat exchanger  10  may have stacked plate pair sections in which the internal fluid flows in the opposite direction of that shown in  FIG. 7 , with the internal fluid first passing through the downstream or second flow channel  46 , then through flow paths  62  and  64 , and then into the upstream or first flow channel  44 . 
   The plates  14  may be formed in a variety of ways—for example they could be made from roll formed or stamped sheet metal or from non-metallic materials, and could be brazed or soldered or secured together using an adhesive, among other things. Although the plates have been shown as having only two flow paths  62 ,  64  between the first and second flow channels  44 ,  46 , more than two flow paths could be provided between the flow channels. The plates  14  have been shown as having two passes; however the turn portion configuration described herein could also be applied to plate pairs having more than one pass. 
   In some example embodiments, more than two turn-around flow paths are provided between the first and second flow channels  44 ,  46 . By way of example,  FIG. 8  shows a further plate pair  100  that can be used in heat exchanger  10 . The plate pair  100  is substantially identical to plate pair  20 , except that the plates  14  are configured to provide three parallel flow paths  102 ,  104  and  106  connecting the first and second flow channels  44 ,  46 . In the embodiment of  FIG. 8 , outwardly protruding ribs  108  formed on the interfacing plates  14  of the pair  100  cooperate to provide first U-shaped flow path  102  for directing fluid from the upstream side of first flow channel  44  to the downstream side of the second flow channel  46 . Similarly, ribs  110  on interfacing plates  14  cooperate to provide second U-shaped flow path  104  for directing fluid from a middle area of the first flow channel  44  to a middle area of the second flow channel  46 . Ribs  112  cooperate to provide third flow path  106  for directing fluid from a downstream side of the first flow channel  44  to an upstream side of the second flow channel  46 . The use of additional flow paths allows for greater control over the transfer of fluid from specific exit areas of the first channel  44  to specific entry areas of the second channel  46 . Generally, the choice between two, three, or more parallel flow paths will be related to the overall width of the plates and to the refrigerant mass flow rate (in an evaporator application). Depending on the application, relatively wide plates having high refrigerant flow rates may benefit from more parallel paths, whereas for narrower plates two paths may be sufficient. 
   As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. The foregoing description is of the preferred embodiments and is by way of example only, and is not to limit the scope of the invention.