Abstract:
A refrigeration system includes a multiple stage compressor  10  having at least two stages  12,14  for sequentially compressing the refrigerant together with a gas cooler  21  connected to the compressor  10  for receiving compressed refrigerant from the last stage  14  of the compressor to cool the same. An evaporator  18  is connected to the gas cooler  21  via an expansion device to receive cool refrigerant therefrom and cool the fluid stream passing through the evaporator  18 . A return passage connects the evaporator  18  to the first stage  12  of the compressor and an intercooler  26  is connected between the first stage  12  and the last stage  14  of the compressor to cool refrigerant compressed by the first stage  12  and direct the refrigerant cooled thereby to the last stage  14  for further compression. The intercooler  26  and the gas cooler  21  are integrated into a single unit  22  and receive a single cooling heat exchange fluid and the gas cooler  21  has a larger heat transfer surface area than the intercooler  26.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to refrigeration systems and to an integrated heat exchanger for use in such systems.  
       BACKGROUND OF THE INVENTION  
       [0002]     Most refrigeration systems (which term, as used herein, is intended to include air conditioning systems) operate on the vapor compression cycle. In such a cycle, a refrigerant is compressed and then the compressed refrigerant cooled before being expanded in an evaporator to cool a heat exchange fluid. The heat exchange fluid may be used to cool various objects, such as the contents of a refrigerator or the occupants of a space. Until relatively recently, common refrigerants were chloro-fluoro carbons (CFC&#39;s) or hydro-chloro-fluoro carbons (HCFC&#39;s) because of their non combustibility and relatively easy cycling through the system. However, many such systems have been prone to refrigerant leakage, particularly those in vehicular applications. The escaping refrigerant, depending upon the type, is believed to damage the ozone layer surrounding the earth in varying degrees. Consequently, certain refrigerants such as CFC 12 are no longer manufactured and resort has been made to more environmentally friendly refrigerants such as HFC 134a. The search continues for even more environmentally friendly refrigerants.  
         [0003]     With the new refrigerants that are being utilized, changes are required in many of the refrigeration systems in which they are used to achieve optimum efficiency. And this is true whether one is employing some of the newer refrigerants which still actually physically condense from the gaseous phase to the liquid phase in the system condenser or whether one is employing a so-called transcritical refrigerant, such as CO 2  which does not truly condense during typical system operation but nonetheless requires cooling after compression in a so-called gas cooler.  
         [0004]     Some of these systems utilize a multiple-stage compressor for increased efficiency, usually a two stage compressor, to compress the expanded refrigerant after it is passed through the evaporator to an elevated pressure at which it enters the system condenser or gas cooler. For brevity, both condensers for true condensing refrigerants and gas coolers used in transcritical refrigerant systems will hereinafter be referred to as gas coolers.  
         [0005]     In any event, when multiple-stage compressors are utilized, some means of cooling the refrigerant between stages is often needed. This is typically accomplished using an air cooled intercooler.  
         [0006]     In common refrigeration systems, the gas cooler and intercooler are typically separate components in the system loop. Where there are few space constraints in the system, the use of separate components is not a major concern. However, in applications where space constraints are significant, it would be desirable to have an integrated gas cooler/intercooler component which functions with an efficiency that will match that of a system utilizing separate components.  
         [0007]     For example, in vehicular applications, available space for air conditioning units is at a premium. Large components limit the ability of the designer of the vehicle to achieve aerodynamic slipperiness which, of course, affects fuel economy as well as the ability to achieve a pleasing appearance. Further, a weight saving may be achieved in an integrated unit over a system utilizing separate components which similarly contributes to the fuel economy. Thus, there is a real need for a refrigeration system employing a multistage compressor that avoids the problems associated with separate gas coolers and intercoolers.  
         [0008]     The present invention is directed to fulfilling that need.  
       SUMMARY OF THE INVENTION  
       [0009]     It is the principal object of the invention to provide a new and improved refrigeration system of the multistage compressor type. It is also an object of the invention to provide a new and improved integrated heat exchanger which may find use in such a system as an integrated gas cooler and intercooler.  
         [0010]     According to one aspect of the invention, a refrigeration system having a multistage compressor with at least two stages for sequentially compressing a refrigerant is provided. A gas cooler is connected to the compressor for receiving compressed refrigerant from the last stage of the compressor to cool the same. After an expansion device, an evaporator is connected to the gas cooler to receive compressed, cooled refrigerant therefrom and expand the same to cool a fluid stream passing through the evaporator. A return passage is provided and connects the evaporator to a first stage of the compressor to return expanded refrigerant thereto to be compressed therein and an intercooler is connected between the first stage and the last stage of the compressor to cool refrigerant compressed by the first stage and direct the refrigerant cooled thereby to the last stage for further compression in the compressor. The intercooler and the gas cooler are integrated into a single unit to receive a single cooling heat exchange fluid. The gas cooler has a larger heat transfer area than that of the intercooler, the heat transfer area being the area of the respective coolers through which heat transfer between the refrigerant and the single cooling heat exchange fluid occurs.  
         [0011]     In a preferred embodiment, the gas cooler is a cross-counter flow heat exchanger having plural tube or passage rows through which the refrigerant serially passes from back to front in relation to the direction of flow of the single cooling heat exchange fluid through the gas cooler.  
         [0012]     According to one embodiment of the invention, the gas cooler and the intercooler are in side-by-side abutting relation to define a single, split face through which the single cooling heat exchange fluid enters the unit and includes common header assemblies extending between remote sides of the gas cooler and the intercooler. Baffles are located in the header assemblies to isolate the refrigerant flow paths in the intercooler from refrigerant flow paths in the gas cooler.  
         [0013]     In the embodiment described in the preceding paragraph, the intercooler has plural tubes or passage rows through which the refrigerant serially passes and the number of tubes or passage rows in the intercooler is less than the number of tubes or passage rows in the gas cooler.  
         [0014]     Preferably, the number of rows in the gas cooler is at least twice the number of rows in the intercooler.  
         [0015]     In a highly preferred embodiment, the rows in the gas cooler are defined by aligned runs of serpentine tubes and the rows in the intercooler are defined by U-shaped or serpentine tubes.  
         [0016]     In another embodiment of the invention, the gas cooler and intercooler are interleaved with the tubes or passages of the gas cooler being located between adjacent tubes or passages of the intercooler.  
         [0017]     In this embodiment as well, the gas cooler runs are defined by serpentine tubes and the intercooler runs are defined by U-shaped or serpentine tubes.  
         [0018]     In a preferred embodiment, there are more tubes or passages in each row of the gas cooler than in each row of the intercooler and the tubes or passages of the intercooler are substantially uniformly distributed between tubes or passages of the gas cooler.  
         [0019]     According to another facet of the invention, an integrated, interleaved heat exchanger is provided which includes a first plurality of tubes bent to define a plurality of parallel runs. A second plurality of tubes bent to define a plurality of parallel runs is also provided. First header assemblies are connected to the ends of the tubes in the first plurality and are in fluid communication with the interiors thereof while second header assemblies are connected to the ends of the tubes of the second plurality and are in fluid communication with the interiors of the second plurality. The tubes of the first plurality are located between the tubes of the second plurality in a substantially uniformed manner and in spaced relation to one another. The parallel runs of the tubes in each plurality defines rows, and fins extend between adjacent tubes in the rows.  
         [0020]     In one embodiment, the tubes of both of the pluralities have the same number of runs while in another embodiment, the number of runs defined by each tube in the first plurality is greater than the number of runs defined by each tube of the second plurality.  
         [0021]     In preferred embodiment, the first and second plurality of tubes and the fins define a generally rectangular heat exchanger core and the header assemblies are all on one side of the core.  
         [0022]     A preferred embodiment again contemplates that the tubes of the first plurality be serpentine tubes and that the tubes of the second plurality be U-shaped or serpentine tubes.  
         [0023]     In one embodiment of the heat exchanger, the second plurality of tubes have corresponding ends located inwardly of the ends of the first plurality and the second header assemblies are located between the first header assemblies. In another embodiment, the second plurality of tubes have corresponding ends located outwardly of the ends of the first plurality and the first header assemblies are located between the second header assemblies.  
         [0024]     Other objects and advantages will become apparent from the following specification taken in connection with the accompanying drawings. 
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1  is a schematic illustrating a system made according to the invention;  
         [0026]      FIG. 2  is a front elevation of an integrated gas cooler and intercooler made according to the invention;  
         [0027]      FIG. 3  is a view similar to  FIG. 2  but of another embodiment of an integrated gas cooler and intercooler;  
         [0028]      FIG. 4  is an exploded side elevation of the intercooler and gas cooler components utilized in the integrated gas cooler and intercooler of the embodiment of  FIG. 2 ;  
         [0029]      FIG. 5  is a somewhat schematic, enlarged, fragmentary view of the arrangement of tubes employed in the embodiment of  FIG. 3 ;  
         [0030]      FIG. 6  is a side elevation of one embodiment of a header and tube structure utilized in the embodiment of  FIG. 3 ; and  
         [0031]      FIG. 7  is a view similar to  FIG. 6  but showing a modified header and tube arrangement. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]     Before proceeding to the detailed description of the various embodiments, it is to be understood that the term “refrigeration system” as used herein is used in a broad sense to include any vapor compression based system utilized for cooling other objects. It is intended to include not only refrigeration systems in the narrow sense, such as refrigerators, refrigerated vehicles, etc. but also to include systems utilized for cooling spaces and/or occupants of such spaces, more narrowly understood to refer to air conditioning systems.  
         [0033]     It is also to be noted that the invention is applicable to systems employed with refrigerants that in fact substantially fully change from the vapor phase to the liquid phase in a heat exchanger typically termed a condenser as well as in the systems utilizing so called transcritical refrigerants, such as carbon dioxide, wherein true condensation does not fully occur but nonetheless require a gas cooler for cooling the refrigerant after it has been compressed. Thus, the term gas cooler, as used herein, and as alluded to previously, is intended to be generic to both gas coolers in transcritical systems as well as to condensers in subcritical systems.  
         [0034]     It is also to be noted that the integrated gas cooler and intercooler described herein is not restricted to use as an integrated intercooler and gas cooler. It may be utilized in systems wherein a single heat exchange fluid at two different stages in its processing, may be heated or cooled by a single stream of a heat transfer medium or where two different heat exchange fluids can be advantageously heated or cooled by a single stream of a heat transfer medium.  
         [0035]     Consequently, no restriction to particular types of refrigeration systems is intended except insofar as expressly stated in the appended claims. Similarly, no restriction to a specific use of the embodiments of heat exchanger described herein in refrigeration systems is intended except insofar as specified in the appended claims.  
         [0036]     With the foregoing in mind, the system in  FIG. 1  will now be described.  
         [0037]     The system is based on a multi-stage compressor, generally designated  10  which typically will be a two stage compressor. Thus, a first stage is shown at  12  and a second stage is shown at  14 . An inlet  16  to the compressor is connected to the outlet of an evaporator  18  through which a heat exchange fluid is driven by a fan  19  to be cooled, the heat exchange fluid typically being air but in some instances could be another gas or even a liquid.  
         [0038]     The compressor  10  includes an outlet  20  from the second stage  14  which is connected to the gas cooler part  21  of an integrated gas cooler, intercooler unit, generally designated  22 . The unit  22  is adapted to receive a heat exchange fluid, again typically air, but which could be another gas or even a liquid, driven by a fan  24  in a single stream through the gas cooler part  21  and through an intercooler part  26  of the unit  22 .  
         [0039]     The outlet  28  of the first compressor stage  12  is connected to the intercooler part  26  to provide refrigerant compressed by the first stage to the intercooler part  26 . From the intercooler part  26 , the refrigerant compressed by the first stage  12  is directed to an inlet  30  to the second stage  14  of the compressor unit  10 .  
         [0040]     Compressed refrigerant cooled in the gas cooler part  21  exits the unit  22  and is directed through an expansion device (EXP DEVICE) and then passed to the evaporator  18  where it cools the heat exchange fluid directed through the evaporator  18  by the fan  19 .  
         [0041]     Other components may optionally be included in the system of  FIG. 1 . Typically, such components would include an accumulator for the refrigerant and, in large non-transcritical systems or in transcritical systems, a so called suction line heat exchanger (SLHX) as well.  
         [0042]     Turning now to  FIG. 2 , one embodiment of an integrated heat exchanger that may be employed as the unit  22  is illustrated. The same includes the gas cooler part  21  located in side-by-side relation with the intercooler part  26  and which abut at a common boundary  31 . A remote side of the intercooler is shown at  32  while a remote side of the gas cooler is shown at  34 . Refrigerant flow passages  27 , and only a few are shown, make up the gas cooler. The flow passages  27  are conventionally tubes or tube runs in spaced relation as shown in  FIG. 2  and fins, typically serpentine fins  38 , are located between spaced ones of the flow passages  27 .  
         [0043]     The intercooler part  26  includes spaced flow passages  40  also typically tubes or tube runs separated by fins  38  in the usual case. As it will be explained in greater detail hereinafter, in a preferred embodiment, the flow passages  27  and  40  are made up of flattened tubes. However, other types of flow passages could be provided, including those of the so called “drawn-cup” type.  
         [0044]     Common headers  42  (only one of which is shown) are connected to and in fluid communication with the interior of the flow passages  27  and  40  and extend basically from the remote side  32  of the intercooler to the remote side  34  of the gas cooler. In the ususal case, the headers  42  will be tubes but they could consist of a header plate and attached tank if desired. A baffle  46  is located along the interface  30  in each of the headers  42  to isolate refrigerant flow within the gas cooler from refrigerant flow within the intercooler  26 . One of the headers  42  includes an inlet  48  for the gas cooler part  21  and, on the opposite side of the baffle  46 , an inlet  50  for the intercooler part  26 . Similarly, the other header  42 , specifically the header  42 , illustrated in  FIG. 2 , includes an outlet  52  for the gas cooler part  21  while, on the opposite side of the baffle  46 , the intercooler  26  includes an outlet  54 .  
         [0045]     In  FIG. 2 , the front of the unit  22  is illustrated which is to say that gas flow from the fan  24  ( FIG. 1 ) enters through the face side illustrated in  FIG. 2  and passes through the fins  38  between the passages  27 ,  40  and exits through the opposite or back side of the unit  22 . Thus, it will be appreciated that in the embodiment illustrated, the inlets  48  and  50  are at the back of the unit  22  while the outlets  52  and  54  are on the front of the unit. Consequently, as will become apparent from the explanation of the passages  27 , 40  and their structure, the refrigerant enters the rear of the heat exchanger and flows through the passages  27  across a common face forwardly in the unit  22  to exit through the outlets  52 ,  54  to define a cross-counter flow heat exchanger for maximum efficiency. However, if desired, flow regimes other than cross-counter flow could be used.  
         [0046]     It will also be appreciated that in the embodiment shown in  FIG. 2 , the frontal area of the intercooler  26  is less than the frontal area of the gas cooler  21 . Also, different fin densities could be used in the two sections to balance the air flow.  
         [0047]      FIG. 3  shows an alternate embodiment of the invention wherein the passages  27  and  40  are interleaved in a uniform matter across the entire face of the unit  22 . With reference to  FIGS. 3 and 5 , it will be seen that flow passages  40  for the intercooler are interleaved or interlaced with the flow passages  27  for the gas cooler  21 . The flow passages are again spaced and provided with fins  38  which extend between and are typically bonded as by brazing to adjacent ones of the tubes.  
         [0048]     The ends of the flow passages  27  and  40  end in first and second sets of headers which may be in the form of tubes or in the form of header plates and separate tanks. In the embodiment illustrated in  FIG. 3 , a first set of headers  56  is connected to the ends of the flow passages  40  while a second set of headers  58  is connected to the ends of the flow passages  27 . Only one of each of the headers  56  and  58  is illustrated in  FIG. 3 .  
         [0049]     The illustration in  FIG. 3  views the unit  22  from the front thereof and thus, the forward most header  56  includes an outlet  60  which serves as the outlet for the intercooler passages  40 . An inlet  64  to the rearmost one of the headers  56  (not shown in  FIG. 3 ) and the passages  40  are also disposed in such header.  
         [0050]     The forward most header  58  includes an outlet  66  for the flow paths  27  while an inlet  68  in the rearmost one of the headers  58  provides an inlet for the passages  27 .  
         [0051]     Scrutiny of  FIGS. 3 and 5  will illustrate that the passages  27  are located in groups of twos separated by a passage  40  across the entire face of the unit  22 . Thus, there are more of the passages  27  for the gas cooler than there are passages  40  for the intercooler  26 .  
         [0052]     Turning now to  FIG. 4 , the arrangements of the components for the embodiment illustrated in  FIG. 2 , specifically, the components including the headers  42 , the passages  27  and  40  the fins  38  are illustrated in exploded form. In a preferred embodiment, as mentioned previously, the passages  27  are formed of flattened tubes and as seen in  FIG. 4 , each flattened tube  27  in the gas cooler part  21  is a serpentine tube bent upon itself to define four straight, parallel runs  70 ,  72 ,  74 , and  76 . The corresponding runs  70 ,  72 ,  74 , and  76  for each of the passages  27  are aligned with one another in the assembly to provide four rows of the runs  70 ,  72 ,  74 , and  76 . The fins  38  extend from the face of the unit  22 , shown at  78  in  FIG. 4  and, to the rear  80  thereof.  
         [0053]     On the other hand, the passages  40  in a highly preferred embodiment, are formed of a flattened tube having a single bend to define a U-shaped tube having two straight, elongated, parallel runs  82  and  84 . The runs  82  and  84  are in two rows of runs with individual fins  38  extending just slightly more than the major dimension of the corresponding tube runs  82 ,  84 .  
         [0054]     Thus, in the embodiment of  FIG. 2 , the number of runs  70 ,  72 ,  74 ,  76  and the gas cooler part  21  is greater than the number of runs  82 ,  84  in the intercooler part  26 .  
         [0055]     If desired, the passages  40 , rather than being U-shaped as shown in  FIG. 4 , may be of serpentine form and in the same form as the passages  27 .  
         [0056]      FIGS. 6 and 7  show two alternate structures for use in constructing the embodiment of  FIG. 3 .  
         [0057]     In both of the embodiments shown in  FIGS. 6 and 7 , the same configuration of the passages  27  and  40  as described in connection with  FIG. 4  may be employed. Of course, if desired, again, the passages  40  could be other than U-shaped as shown in  FIG. 4 , specifically, they could be serpentine and have the same number of runs as the passages  27 .  
         [0058]     In the embodiments shown in both  FIGS. 6 and 7 , individual fins  38  as shown in  FIG. 4  for the passages  40  are dispensed with in favor of fins  38  that extends through the entire front to back dimension of the core defined by the passages  27  and  40  and the fins  38 .  
         [0059]     Referring specifically to  FIG. 6 , it will be seen that ends  90  of the passages  40  are bent somewhat inwardly at the location whereat they enter the headers  56  and thus, are disposed inwardly of the tube ends  92  which receive the headers  58  for the passages  27 .  
         [0060]     In both embodiments, the headers  56  and  58  are on the same side of the rectangular core defined by the passages  27 ,  40  and fins  38  and in the embodiment illustrated in  FIG. 6 , the core width at the headers is substantially the same as core width elsewhere on the unit  22 . In any event, the structure results in the headers  56  being nested between the headers  58 .  
         [0061]     In the embodiment illustrated in  FIG. 7 , the opposite is true, namely, the headers  58  are nested between the headers  56  which are displaced slightly outwardly of respective front and back side  78  and  80  by bends in the tubing ends  92  which flare outwardly.  
         [0062]     The principal difference between the embodiments of  FIG. 6  and  FIG. 7  is that the embodiment of  FIG. 6 , while having a narrow core width, has a slightly greater core height than the embodiment of  FIG. 7 .  
         [0063]     Either header arrangement may be employed, depending upon the spacial constraints of any particular system installation.  
         [0064]     On some instances, the fins  38 , where they extend between passages  27  on the one hand and passages  40  on the other may be so called split or slit fins wherein the slits minimize heat conduction through the fins between the passages  27  and the passages  40 . Various constructions for achieving this are well known and form no part of the present invention. Alternatively, conventional fins, including louver fins could be used throughout.  
         [0065]     In the most preferred and optimal embodiment of the invention, of which, is mentioned previously, is a cross-counter flow construction, there can be any number of rows for the gas cooler part  21  as desired. In general, the number of rows in the intercooler part  26  will be less than the number of rows in the gas cooler. This type of arrangement is preferred when the unit is used as a integral gas cooler and intercooler unit. In such a case, the ratio of the heat transfer area of the gas cooler to that of the intercooler is typically somewhat greater than 2:1. By heat transfer area, it is meant that area of each unit which transfers heat from a refrigerant stream, typically the exposed area of the passages  27 ,  40  and fins  38 , to the fluid stream passing through the unit as provided by, for example, the fan  24  shown in  FIG. 1 . Stated another way, if the total heat transfer area of the integrated unit  22  is one, the optimal ratio will be between 0.65:0.35 ranging to about 0.85: to 0.15.  
         [0066]     In a refrigeration system, it will be recognized that the mass flow rate through both the gas cooler part  21  and the intercooler part  26  will be the same. If the same size of tubes are used for the passages  27 ,  40 , while maintaining the above mentioned heat transfer surface ratio, the pressure drop of refrigerant could reach excessively high levels in the intercooler part  26 . The reason for this is that the number of passages in the intercooler part  26  is relatively small and pressure drop can become too high because of increasing fluid velocity. For gas cooler parts  21  that require four or more rows of runs than the passages  27 , the situation intensifies and the intercooler part  26  pressure drop becomes too high.  
         [0067]     Accordingly, It is desirable that the pressure drop in both parts be at similar levels. To achieve this desire, one embodiment of the invention contemplates the use of fewer of the rows of the flow paths  40  in the intercooler part  26  than the number of rows of the passages  27  and the gas cooler part  21 . In the described embodiments, because the length of the flow paths  40  for the intercooler part  26  is approximately half of that of the flow paths  27  for the gas cooler part  21 , the pressure drop in the intercooler section  26  will be less in spite of the fact that fewer of the flow paths  40  exists in the intercooler part  26  in comparison to the number of flow paths  27  in the gas cooler  21 . That is to say, the reduced intercooler part pressure drop will be directly linked to the reduction in length of the flow paths  40 .  
         [0068]     Another possibility is to increase the number of flow paths  40  in the intercooler part  26 . The use of a lesser fin height in the intercooler part  26  will allow the use of more tubes or flow paths  40  in the intercooler part  26 , although at the expense of frontal free flow air for the coolant.  
         [0069]     Alternatively, tubes with different internal cross sectional areas may be employed in making up the flow paths  27  and  40 . By using a larger cross sectional area in the tubes making up the flow paths  40 , a reduction in pressure drop within the intercooler part  26  will result.  
         [0070]     Most desirably, however, from the manufacturing standpoint, one would use the same tubes and rely on changes in the number of tubes or the number of runs or both to achieve the desired similarity in pressure drop in both section in the unit  22 .  
         [0071]     From the foregoing, it will be appreciated that the invention provides an improved refrigeration system by integrating an intercooler between the stages of a multi-stage compressor with the system gas cooler to achieve a significant spacial savings. Similarly, a heat exchanger made according to the invention is ideally suited for use in refrigeration systems but may be used with efficacy in other systems where spacial requirements are of concern.