Abstract:
A refrigeration system includes a compressor for driving a refrigerant along a flow path in at least a first mode of system operation; a first heat exchanger along the flow path downstream of the compressor in the first mode; a second heat exchanger along the flow path upstream of the compressor in the first mode; and an expansion device in the flow path downstream of the first heat exchanger and upstream of the second heat exchanger in the first mode, wherein the second heat exchanger includes a combined header and accumulator for collecting liquid and vapor refrigerant.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of the filing date of earlier filed Provisional Application Ser. No. 60/663,911 filed Mar. 18, 2005. Further, copending application docket 05-258-WO, entitled HIGH SIDE PRESSURE REGULATION FOR TRANSCRITICAL VAPOR COMPRESSION SYSTEM and filed on even date herewith, and the aforesaid Provisional Application Ser. No. 60/663,911 disclose prior art and inventive cooler systems. The disclosure of said application is incorporated by reference herein as if set forth at length. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    In many refrigeration applications space is a limited resource. Any reduction in space requirements for the refrigeration system application can improve the overall design of the system—either by reducing the overall size or by utilizing the space that becomes available for other purposes, such as increased heat exchanger area. Thus, a consolidated component design can reduce system cost and increase system performance. 
         [0003]      FIG. 1  shows a prior art vapor compression system having a compressor  1 , a gas cooler  2 , an expansion device  3 , and an evaporator  4 . In evaporator  4 , refrigerant passes through a series of heat exchanger tubes  5  in a heat exchange relationship with air being cooled as desired. Refrigerants typically enters tubes  5  through a header  6  and exits tubes  5  into a header  7 . Refrigerant collected in header  7  then flows to an accumulator  8  where liquid phase refrigerant and oil separate from vapor phase refrigerant, and vapor is drawn back to compressor  1 . 
         [0004]    While the system illustrated in  FIG. 1  is functional, as set forth above, a functional system which occupies less space is desirable. 
         [0005]    It is therefore the primary object of the present invention to provide such a system. 
         [0006]    Other objects and advantages will appear herein. 
       SUMMARY OF THE INVENTION 
       [0007]    A refrigeration system is provided which includes a compressor for driving a refrigerant along a flow path in at least a first mode of system operation; a first heat exchanger along the flow path downstream of the compressor in the first mode; a second heat exchanger along the flow path upstream of the compressor in the first mode; and an expansion device in the flow path downstream of the first heat exchanger and upstream of the second heat exchanger in the first mode, wherein the second heat exchanger includes a combined header and accumulator for collecting liquid and vapor refrigerant. The combined header and accumulator serves to conserve space which is particularly advantageous, for example in transcritical vapor compression systems. 
         [0008]    A method is also provided for operating a refrigeration system in accordance with the present invention, which method comprises operating a compressor to drive a refrigerant along a flow path, sequentially, to a first heat exchanger, an expansion device, a second heat exchanger, a combined header and accumulator, and back to the compressor, wherein flow is directly from the second heat exchanger to the combined header and accumulator, and wherein flow is directly from the combined header and accumulator to the compressor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0009]    A detailed description of preferred embodiments of the present invention follows, with reference to the attached drawings, wherein: 
           [0010]      FIG. 1  is an illustration of a prior art vapor compression system; 
           [0011]      FIG. 2  is a schematic illustration of a system having a combined accumulator and header according to the invention; 
           [0012]      FIG. 3  is a schematic illustration of an alternative embodiment of the combined accumulator and header according to the invention; and 
           [0013]      FIG. 4  is a schematic illustration of a further alternative embodiment of the combined accumulator and header in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    The invention relates to a heat exchanger configuration for a vapor compression system and, more particularly, to a space-saving combination of the refrigerant accumulator and the heat exchanger header in a transcritical vapor compression cycle. In transcritical vapor compression systems, heat rejection occurs at a pressure above the critical pressure of the refrigerant. During the heat rejection the refrigerant does not condense. The charge management in a transcritical system is usually accomplished by adding an accumulator to the evaporator outlet, following an outlet header (See  FIG. 1 ). 
         [0015]      FIG. 2  shows the vapor compression system  10  in accordance with the present invention which includes a compressor  12 , a first heat exchanger or gas cooler  14 , an expansion device  16  and a second heat exchanger or evaporator  18 . As compared to  FIG. 1 , it should be readily appreciated that evaporator  18  includes an inlet header  20  as in conventional devices, but that evaporator  18  also includes a combined header and accumulator  22  which combines the functions of separate outlet header  7  and accumulator  8  as illustrated in  FIG. 1 . This advantageously allows for conservation of space while providing the desired functions of both the header and the accumulator of this device. 
         [0016]    As shown in  FIG. 2 , combined header and accumulator  22  in accordance with the present invention is a single chamber which defines a lower liquid refrigerant zone  24  and an upper vapor refrigerant zone  26 . Flow enters the combined header and accumulator  22  directly from tubes  28  of second heat exchanger  18 . In this regard, it is noted that  FIG. 2  shows lower liquid refrigerant zone  24  defined at a location which is lower than the inlet from the lower most tube  30 . This advantageously prevents masking and/or back-flow of liquid refrigerant with respect to lower most tube  30 . As shown in  FIG. 2 , this chamber is defined by side, front, back, top and bottom walls around the end of the heat exchanger tubes. 
         [0017]    Also as shown in  FIG. 2 , combined header and accumulator  22  advantageously has an inner conduit  32  which extends from a bottom surface of combined accumulator and header  22  upwardly above the expected liquid level of liquid within lower liquid refrigerant zone  24 . Compressor  12  draws vapor phase refrigerant out of vapor refrigerant zone  26  and through conduit  32  to the compressor suction line. 
         [0018]    A lower portion  34  of conduit  32  is preferably provided with a pin hole  36  which advantageously allows oil within the lower liquid refrigerant zone  24  to be drawn back to compressor  12  as desired. 
         [0019]    The heat exchangers  14 ,  18  of the present invention can be provided as any known type of heat exchanger, preferably as refrigerant-air heat exchangers. Specific examples of suitable heat exchangers include but are not limited to wire on tube heat exchangers, fin heat exchangers, and the like. 
         [0020]    The system of the present invention is particularly well suited to a transcritical vapor compression system, for example, a system which uses CO 2  as working fluid. Of course, other refrigerants, particularly those with similar properties to CO 2  under expected operating conditions, can be used and are considered to be well within the broad scope of the present invention. 
         [0021]    Expansion device  16  can be any suitable expansion device known to a person of skill in the art. A pressure regulator, for example a pressure regulator such as that disclosed in commonly owned and simultaneously filed PCT Application bearing attorney docket number 05-258-WO and entitled HIGH SIDE PRESSURE REGULATION FOR TRANSCRITICAL VAPOR COMPRESSION SYSTEM, is also well within the scope of the present invention and is considered to be an expansion device as used herein. 
         [0022]    Header and accumulator  22  can advantageously be incorporated into heat exchanger  18  as shown in  FIG. 2 . Alternatively, header and accumulator  22  can be a separate structure defining a chamber and communicated with heat exchanger  18 , preferably through direct flow from tubes of the heat exchanger into the chamber. 
         [0023]      FIG. 3  shows a further alternative embodiment of the present invention, having the same basic components as the embodiment of  FIG. 2 . In the embodiment of  FIG. 3 , evaporator  18  is divided into two components  38 ,  40 , and combined header and accumulator  22  is connected to each component  38 ,  40  through a short flow conduit  42 . In this embodiment, it should be noted that by positioning lower most tube  30  sufficiently high on second heat exchanger  18 , the lower liquid refrigerant zone  24  can be defined within combined accumulator and header  22  so that a bottom surface  44  of combined accumulator and header  22  does not extend substantially beyond a bottom surface  46  of second heat exchanger  18 . Conduit  42  is preferably very short, most preferably having a length of less than about 5 inches. 
         [0024]      FIG. 4  shows a further embodiment of the present invention, wherein system  10  includes the same components as those described in connection with  FIGS. 2 and 3 . With the embodiment of  FIG. 4 , refrigerant fed from expansion device  16  to evaporator  18  flows through a single conduit  48  to combined header and accumulator  22  in accordance with the present invention. From this point, vapor phase refrigerant is drawn back to compressor  12  as desired. 
         [0025]    Embodiments of the invention as indicated in  FIGS. 2-4  of the present invention integrate the accumulator and the evaporator outlet header into a single chamber. This single chamber performs the function of both the header and accumulator of the conventional system of  FIG. 1 . Advantageously, the functions normally performed in the separate header and accumulator are now performed in the same space. This design reduces the space requirements for the accumulator as well as the overall tubing length and the number of tube connections. 
         [0026]    Two-phase flow leaving the evaporator is separated in the header. The liquid refrigerant is collected by gravity at the bottom of the accumulator-header. The vapor leaves the accumulator header through the tube inserted into the header. The tube has a pin-hole in the accumulator section of the header to allow oil return to the compressor. 
         [0027]    One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, when implemented as a remanufacturing of an existing system or reengineering of an existing system configuration, details of the existing configuration may influence details of the implementation. Accordingly, other embodiments are within the scope of the following claims.