Abstract:
A microchannel heat exchanger includes a plurality of microchannel tubes including a first set of microchannel tubes and a second set of microchannel tubes. A first circuit of the microchannel heat exchanger includes the first set of microchannel tubes, and a portion of a first fluid flows through the first set of microchannel tubes and exchanges heat with a second fluid. A second circuit of the microchannel heat exchanger includes the second set of microchannel tubes, and a reminder of the first fluid flows through the second set of microchannel tubes and exchanges heat with the second fluid. The first fluid from the first circuit and the first fluid from the second circuit combine into a common flow.

Description:
RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 61/050,387, which was filed May 5, 2008. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention relates generally to a microchannel heat exchanger including multiple fluid circuits. 
         [0003]    A microchannel heat exchanger (MCHX) exchanges heat between a refrigerant and a fluid, such as air. The microchannel heat exchanger includes a plurality of microchannel tubes. The refrigerant flows through the plurality of microchannel tubes, and the air flows over the plurality of microchannel tubes. 
         [0004]    The microchannel heat exchanger utilizes a single refrigerant circuit. The refrigerant enters the circuit through an inlet and can make multiple passes through the microchannel heat exchanger. The refrigerant then exits the circuit through an outlet. This results in a high refrigerant side pressure drop for a given amount of refrigerant side heat transfer. This adverse relationship affects the overall system performance, particularly at high outdoor ambient conditions, which causes the discharge pressure to be higher than a comparable round tube plate fin (RTPF) heat exchanger. 
       SUMMARY OF THE INVENTION 
       [0005]    A microchannel heat exchanger includes a plurality of microchannel tubes including a first set of microchannel tubes and a second set of microchannel tubes. A first circuit of the microchannel heat exchanger includes the first set of microchannel tubes, and a portion of a first fluid flows through the first set of microchannel tubes and exchanges heat with a second fluid. A second circuit of the microchannel heat exchanger includes the second set of microchannel tubes, and a reminder of the first fluid flows through the second set of microchannel tubes and exchanges heat with the second fluid. The first fluid from the first circuit and the first fluid from the second circuit combine into a common flow. 
         [0006]    In another example, a refrigeration system includes a compressor for compressing a refrigerant, a condenser for cooling the refrigerant, an expansion device for expanding the refrigerant, and an evaporator for heating the refrigerant. One of the condenser and the evaporator is a microchannel heat exchanger. The microchannel heat exchanger includes a plurality of microchannel tubes including a first set of microchannel tubes and a second set of microchannel tubes. A first circuit of the microchannel heat exchanger includes the first set of microchannel tubes, and a portion of the refrigerant flows through the first set of microchannel tubes and exchanges heat with air. A second circuit of the microchannel heat exchanger includes the second set of microchannel tubes, and a reminder of the refrigerant flows through the second set of microchannel tubes and exchanges heat with the air. The refrigerant from the first circuit and the refrigerant from the second circuit combine into a common flow. 
         [0007]    These and other features of the present invention will be best understood from the following specification and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The various features and advantages of the invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows: 
           [0009]      FIG. 1  illustrates a prior art refrigeration system; 
           [0010]      FIG. 2  illustrates a multiple circuit microchannel heat exchanger; and 
           [0011]      FIG. 3  illustrates a multiple circuit microchannel heat exchanger including a subcooler. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0012]      FIG. 1  illustrates a refrigeration system  20  including a compressor  22 , a first heat exchanger  24 , an expansion device  26 , and a second heat exchanger  28 . Refrigerant circulates through the closed circuit refrigeration system  20 . 
         [0013]    When the refrigeration system  20  is operating in a cooling mode, the refrigerant exits the compressor  22  at a high pressure and a high enthalpy and flows through the first heat exchanger  24 , which acts as a condenser. In the first heat exchanger  24 , the refrigerant rejects heat to air and is condensed into a liquid that exits the first heat exchanger  24  at a low enthalpy and a high pressure. A fan  30  directs the air through the first heat exchanger  24 . The cooled refrigerant then passes through the expansion device  26 , expanding the refrigerant to a low pressure. After expansion, the refrigerant flows through the second heat exchanger  28 , which acts as an evaporator. In the second heat exchanger  28 , the refrigerant accepts heat from air, exiting the second heat exchanger  28  at a high enthalpy and a low pressure. A fan  32  blows air through the second heat exchanger  28 . The refrigerant then flows to the compressor  22 , completing the cycle. 
         [0014]    When the refrigeration system  20  is operating in a heating mode, the flow of the refrigerant is reversed with a four-way valve  34 . The first heat exchanger  24  accepts heat from the air and functions as an evaporator, and the second heat exchanger  28  rejects heat to the air and functions as a condenser. For ease of reference, the microchannel heat exchanger can be referred to as a microchannel heat exchanger  38  and is shown in further detail in  FIG. 2 . 
         [0015]    Either or both of the heat exchangers  24  and  28  can be the microchannel heat exchanger  38 . The microchannel heat exchanger  38  can be part of a refrigeration system  20  used with a microdevice, an automobile air conditioner or a residential system. 
         [0016]      FIG. 2  illustrates a first example microchannel heat exchanger  38 . The microchannel heat exchanger  38  includes an entry/exit header  40 , a return header  42 , and microchannel tubes  44  that extend between the headers  40  and  42 . The microchannel tubes  44  are substantially parallel. Each microchannel tube  44  is a flat multi-port tube, and each port has a hydraulic diameter of less than 1 mm. 
         [0017]    The microchannel heat exchanger  38  includes multiple independent and separate refrigerant sections or circuits. In one example, the microchannel heat exchanger  38  includes a first circuit  46  and a second circuit  48  that are separate from each other. In the below described example, the refrigerant makes two passes through each refrigerant circuit  46  and  48 . However, the refrigerant can make any number of passes through each refrigerant circuit  46  and  48 . For example, the refrigerant can make only one pass or can make more than two passes through the microchannel heat exchanger  38 . A pass is defined as one trip through the microchannel tubes  44  between the headers  40  and  42 . Therefore, the refrigerant makes two passes through the microchannel tubes  44  to complete a circuit. 
         [0018]    In one example, the microchannel heat exchanger  38  is a condenser, and a distributor  112  splits the refrigerant from the compressor  22  into two paths. One path of the refrigerant flows through a coil of the first circuit  46 , and one path of refrigerant flows through a coil of the second circuit  48 . In one example, the refrigerant is split equally between the two circuits  46  and  48 . 
         [0019]    A divider wall  56  splits the entry/exit header  40  into a first entry/exit section  52  and a second entry/exit section  54 , preventing refrigerant flow between the sections  52  and  54 . A divider wall  100  separates the first entry/exit section  52  into a first entry section  104  and a first exit section  102 . A divider wall  106  separates the second entry/exit section  54  into a second entry section  108  and a second exit section  110 . A divider wall  62  splits the return header  42  into a first return section  58  and a second return section  60 , preventing refrigerant flow between the sections  58  and  60 . 
         [0020]    The refrigerant enters the first circuit  46  through an inlet  64 . In one example, the refrigerant in the first entry section  104  of the first entry/exit section  52  of the entry/exit header  40  flows through a group  114  of microchannel tubes  44  in a direction A, rejecting heat to the air flowing over the microchannel tubes  44 . The refrigerant then flows into the first return section  58  of the return header  42 . The refrigerant flow then turns 180° in the first return section  58  and flows back into another group  116  of microchannel tubes  44  in an opposing second direction B, rejecting additional heat to the air flowing over the microchannel tubes  44 . This pattern is repeated for additional passes. The refrigerant then enters the first exit section  102  of the first entry/exit section  52  of the entry/exit header  40  and exits the first circuit  46  through an outlet  68 . The groups  114  and  116  of microchannel tubes  44  are exclusive to the first circuit  46 . 
         [0021]    In another example, the refrigerant enters the first circuit  46  through the first exit section  102  and exits the first circuit  46  through the first entry section  104 . 
         [0022]    The refrigerant enters the second circuit  48  through an inlet  70 . The refrigerant in the second entry section  108  of the second entry/exit section  54  of the entry/exit header  40  flows through a group  118  of microchannel tubes  44  in a direction A, rejecting heat to the air flowing over the microchannel tubes  44 . The refrigerant then flows into the second return section  60  of the return header  42 . The refrigerant flow then turns 180° in the second return section  60  and flows back into another group  120  of microchannel tubes  44  in an opposing second direction B, rejecting additional heat to the air flowing over the microchannel tubes  44 . This pattern is repeated for additional passes. The refrigerant then enters the second exit section  110  of the second entry/exit section  54  of the entry/exit header  40  and exits the second circuit  48  through an outlet  74 . The groups  118  and  120  of microchannel tubes  44  are exclusive to the second circuit  48 . 
         [0023]    In another example, the refrigerant enters the second circuit  48  through the second exit section  110  and exits the second circuit  48  through the second entry section  108 . 
         [0024]    The refrigerant from the outlets  68  and  74  are combined into a single flow path and then directed to the expansion device  26 . 
         [0025]    Although two refrigerant circuits  46  and  48  each including two passes through the microchannel tubes  44  are illustrated and described, it is to be understood that the microchannel heat exchanger  38  can include any number of circuits, and the refrigerant in each circuit can make any number of passes through the microchannel heat exchanger  38 . 
         [0026]    Additionally, the microchannel heat exchanger  38  can be an evaporator, and the refrigerant from the expansion device  26  is split into multiple circuits and accepts heat from the air passing over the microchannel tubes  44  before flowing to the compressor  22   
         [0027]    By employing multiple refrigerant circuits in the microchannel heat exchanger  38 , the mass flow of the refrigerant is divided equally between the multiple circuits, decreasing the refrigerant side pressure drop of the refrigerant and improving refrigerant side heat transfer. The refrigerant side heat transfer can be further raised by optimally selecting the number of passes and the number of microchannel tubes  44  for each pass within each circuit. This helps to reduce the refrigerant side pressure drop, as well as reduce the charge sensitivity of the microchannel heat exchanger  38 . 
         [0028]      FIG. 3  illustrates a second example microchannel heat exchanger  76 . The microchannel heat exchanger  76  includes the features of the microchannel heat exchanger  38  of  FIG. 2  and a subcooler  78  (a third circuit). In the example illustrated and described, the microchannel heat exchanger  76  is a condenser. However, the microchannel heat exchanger  76  can be an evaporator. 
         [0029]    The subcooler  78  is formed by a subcooler entry/exit section  80  of the entry/exit header  40 , a return subcooler section  82  of the return header  42 , and groups  122  and  124  of microchannel tubes  44 . A divider wall  86  separates the subcooler entry/exit section  80  from the sections  52  and  54  of the entry/exit header  40  to prevent refrigerant flow between the sections  52 ,  54  and  80 , and a divider wall  88  separates the return subcooler section  82  from the sections  58  and  60  of the return header  42  to prevent refrigerant flow between the sections  58 ,  60  and  82 . The subcooler entry/exit section  80  is further divided by a divider wall  126  that separates the subcooler entry/exit section  80  into a subcooler entry section  128  and a subcooler exit section  130  to enable the flow to enter and leave on the same side of the microchannel heat exchanger  76 . 
         [0030]    The refrigerant exchanges heat with the air as described above with reference to  FIG. 2 . Refrigerant from the outlets  68  and  74  merges into a single path, and the refrigerant enters an inlet  90  of a subcooler circuit  96 . Refrigerant in the subcooler entry section  128  of the subcooler entry/exit section  80  of the entry/exit header  40  flows through the group  122  of microchannel tubes  44  in a direction A, rejecting heat to the air flowing over the microchannel tubes  44 . The refrigerant then enters the return subcooler section  82  of the return header  42 . The refrigerant flow then turns 180° in the return subcooler section  82  and flows back into another group  124  of microchannel tubes  44  in the opposing second direction B, rejecting additional heat to the air flowing over the microchannel tubes  44 . The refrigerant then enters the subcooler exit section  130  of the subcooler entry/exit section  80  of the entry/exit header  40  and exits the subcooler circuit  96  through an outlet  94 . The refrigerant is then directed to the expansion device  26 . The subcooler groups  122  and  124  of microchannel tubes  44  are exclusive the subcooler circuit  96 . 
         [0031]    Although the subcooler circuit  96  includes two passes in the example illustrated and described, any number of passes can be employed. For example, the refrigerant can make a single pass through the subcooler  78  or make more than two passes through the subcooler  78 . By employing a subcooler  78 , the heat transfer and refrigerant side pressure drop can be further optimized. 
         [0032]    The foregoing description is only exemplary of the principles of the invention. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, so that one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.