Abstract:
Disclosed is a microchannel heat exchanger ( 10 ) including at least one manifold ( 14 ) for distributing fluid and a plurality of tubes ( 12 ) extending from the at least one manifold ( 14 ). At least one tube ( 12 ) of the plurality of tubes ( 12 ) has a substantially curvilinear cross-section and includes a plurality of ports ( 24 ) extending from a first end of each tube ( 12 ) to a second end of each tube ( 12 ), the ports ( 24 ) capable of carrying fluid therethrough. A plurality of fins ( 16 ) are located along a length of the plurality of tubes ( 24 ). Further disclosed is a method for extracting thermal energy from a flow via a microchannel heat exchanger ( 10 ).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein generally relates to microchannel heat exchangers. More specifically, this disclosure relates to tube configurations for microchannel heat exchangers. 
         [0002]    Microchannel heat exchangers find use in a wide variety of applications, including automotive, residential and aerospace. As shown in  FIG. 9 , a typical microchannel heat exchanger  100  includes a plurality of flat tubes  102  each having a plurality of ports  104  therethrough. The tubes  102  are typically arranged such that a flat surface  106  of each tube  102  is substantially horizontal. Air flows through an array of fins  108  which extend from the tubes  102 , while a liquid or two-phase refrigerant flows through the plurality of ports  104 . Due to the high density of fin  108  surface area and tube  102  surface area, during the heat exchange process, however, the microchannel heat exchanger is subject to moisture and condensate accumulation, and also frost accumulation. This problem is magnified in the exchangers where the tubes  102  are arranged so that the flat surface  106  is substantially horizontal as the moisture collects and remains on the flat surfaces  106 . The moisture and frost accumulation makes operation of the heat exchanger less efficient by increasing flow resistance and thermal resistance through the heat exchanger. Further, the moisture accumulation causes corrosion and pitting of the tube  102  surfaces, thus decreasing their useful life. The art would well receive a microchannel heat exchanger configuration which maintains the high surface density of a typical microchannel heat exchanger while reducing the efficiency-reducing moisture accumulation. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0003]    According to one aspect of the invention, a microchannel heat exchanger includes at least one manifold for distributing fluid and a plurality of tubes extending from the at least one manifold. At least one tube of the plurality of tubes has a substantially curvilinear cross-section and includes a plurality of ports extending from a first end of each tube to a second end of each tube, the ports capable of carrying fluid therethrough. A plurality of fins are located along a length of the plurality of tubes. 
         [0004]    According to another aspect of the invention, a method for extracting thermal energy from a flow includes urging a coolant from a manifold into a plurality of tubes in flow communication with the manifold. At least one tube of the plurality of tubes has a substantially curvilinear cross-section and includes a plurality of ports extending from a first end of each tube to a second end of each tube, the ports capable of carrying fluid therethrough. The coolant is urged along a length of the tubes via the plurality of ports. The flow is urged across a plurality of fins in thermal communication with the plurality of tubes and thermal energy is transferred to the coolant via the plurality of fins. 
         [0005]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0006]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0007]      FIG. 1  is a perspective view of an embodiment of a microchannel heat exchanger; 
           [0008]      FIG. 2  is another view of the microchannel heat exchanger of  FIG. 1 ; 
           [0009]      FIG. 3  is an alternative embodiment of the microchannel heat exchanger of  FIG. 1 ; 
           [0010]      FIG. 4  is a cross-sectional view of an embodiment of a tube of a microchannel heat exchanger; 
           [0011]      FIG. 5  is a cross-sectional view of another embodiment of a tube of a microchannel heat exchanger; 
           [0012]      FIG. 6  is a cross-sectional view of yet another embodiment of a tube of a microchannel heat exchanger; 
           [0013]      FIG. 7  is a cross-sectional view of another embodiment of a microchannel heat exchanger; 
           [0014]      FIG. 8  is a perspective view of a microchannel heat exchanger having u-connecters disposed at tube ends; and 
           [0015]      FIG. 9  is a perspective view of a typical microchannel heat exchanger. 
       
    
    
       [0016]    The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    Illustrated in  FIG. 1  is an embodiment of a microchannel heat exchanger  10 . The heat exchanger  10  includes a plurality of tubes  12  extending from at least one manifold  14 . Two manifolds  14  are illustrated in  FIG. 1 , but it is to be appreciated that other quantities of manifolds  14 , for example, one or three manifolds  14 , are contemplated within the present scope. Each tube  12  of the plurality of tubes  12  is connected to the at least one manifold  14  by, for example, brazing, or other suitable connection means. Disposed across the plurality of tubes  12  is an array of fins  16 . The fins  16  may be comprised of folded fins as shown in  FIG. 2  or individual fin plates  16  as shown in  FIG. 3 , and further may include louvers  18  or similar enhancements to increase heat transfer capability of the fins  16 . As shown in  FIG. 4 , the fins  16  have fin openings  20  which may be made by, for example, a punching operation. The fin openings  20  allow the passage of one tube  12  of the plurality of tubes  12  therethrough. Each fin  16  may have multiple fin openings  20  so that multiple tubes  12  may pass through each fin  16 . For example, as shown in  FIG. 4 , each fin  16  has two fin openings  20  which allows for the passage of two tubes  12  through each fin  16 . It is to be appreciated, however, that other quantities of fin openings  20  may be disposed in each fin  16 , for example three or four fin openings  20 . In some embodiments, the fin openings  20  have a collar  22  extending at least partially around a perimeter of the fin openings  20  to determine a spacing between adjacent fins  16 . In some embodiments, the fins  16  may be brazed to the tubes  12  at each fin opening  20  to secure the fins  16  in position relative to the tubes  12  and to improve thermal contact between the fins  16  and the tubes  12 . 
         [0018]    In some embodiments, as shown in  FIG. 4 , each tube  12  of the plurality of tubes  12  may have a substantially circular cross-section, with a plurality of ports  24  arranged around a central axis  26  of the tube  12  and in some embodiments extending from a first end to a second end of the tube  12 . The ports  24  are about 0.1 mm to about 5 mm in width. As shown in  FIG. 4 , the ports  24  may be circular in cross-section, or, in some embodiments, as shown in  FIG. 5 , the ports  24  may have cross sections which are circular sector. It is to be appreciated that the port  24  cross-sectional shapes shown in  FIGS. 4 and 5  are merely examples, and that other cross-sectional shapes of the tubes are contemplated within the present scope. Further, the shapes and sizes of ports  24  within a single tube  12  or throughout multiple tubes  12  of the microchannel heat exchanger  10  may be varied to enhance performance of the microchannel heat exchanger  10 . 
         [0019]    Referring again to  FIG. 4 , in some embodiments, the tube  12  may have a hollow portion  28  which extends through the tube  12  along its length. The hollow portion  28  may be circular in cross-section as shown in  FIG. 4 , or may be another shape if so desired. In the embodiment of  FIG. 4 , the hollow portion  28  is located at the central axis  26 , but it is to be appreciated that in some embodiments the hollow portion  28  may be offset from the central axis  26 . In such embodiments, the ports  24  are arrayed between the hollow portion  28  and an outer surface  30  of the tube  12 . The hollow portion  28  reduces the amount of material necessary to fabricate the tube  12 , which may be formed by extrusion or other suitable process. The hollow portion  28  is plugged at at least one end of the tube  12  before operation of the microchannel heat exchanger  10  to prevent refrigerant from bypassing the ports  24  and/or proceeding to flow through the hollow portion  28 . 
         [0020]    Referring now to  FIG. 6 , the tubes  12  may be have cross-sectional shapes other than circular. For example, the as shown in  FIG. 6 , the tubes  12  may have a teardrop or airfoil cross-sectional shape. In some embodiments, the airfoil shaped cross section may include the hollow portion  28  with the ports  24  arrayed between the hollow section  28  and the outer surface  30 . Tubes  12  having an airfoil or teardrop cross-section improve pressure drop across the tubes  12 , provide better heat transfer and improve moisture drainage from the tubes  12 . 
         [0021]    Referring to  FIG. 7 , in configurations of the microchannel heat exchanger  10  where multiple tubes  12  pass through each fin  16 , the tubes  12  are disposed closely to each other such that there are interactions of the flows passing between the tubes  12  in, for example, a first row  32  and a second row  34 . To take advantage of, and improve the interactions to enhance heat transfer, the shape and/or positioning of the tubes  12  may be tuned. For example, tubes  12  in the second row  34  may be positioned such that they are substantially between adjacent tubes  12  of the first row  32  so a flow  36  directed at the tubes  12  of the second row  34  is not shielded by the tubes  12  of the first row  32 . Further, a trailing edge  38  of tubes in the first row  32  may be turned toward an adjacent tube  12  of the second row  34  thereby turning the flow  36  toward the tubes  12  of the second row  34  to improve heat transfer. 
         [0022]    In some embodiments, the microchannel heat exchanger  10  is a multi-pass configuration, meaning that each tube  12  may pass through the plurality of fins  16  more than once. As shown in  FIG. 8 , this may be accomplished by providing at least one u-shaped connector  40  at at least one end of each tube  12 . The connector  40  may be brazed to the tube  12  and is configured to direct refrigerant flow from a first tube portion  42  through the connector  40  and redirects it into a second tube portion  44  to pass through plurality of fins  16  again. In some embodiments, the first tube portion  42  is disposed in the first row  32  and the second tube portion  44  is disposed in the second row  34 . 
         [0023]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.