BACKGROUND OF THE INVENTION
The subject matter disclosed herein generally relates to microchannel heat exchangers. More specifically, this disclosure relates to tube configurations for microchannel heat exchangers.
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
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.
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.
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
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:
FIG. 1 is a perspective view of an embodiment of a microchannel heat exchanger;
FIG. 2 is another view of the microchannel heat exchanger of FIG. 1;
FIG. 3 is an alternative embodiment of the microchannel heat exchanger of FIG. 1;
FIG. 4 is a cross-sectional view of an embodiment of a tube of a microchannel heat exchanger;
FIG. 5 is a cross-sectional view of another embodiment of a tube of a microchannel heat exchanger;
FIG. 6 is a cross-sectional view of yet another embodiment of a tube of a microchannel heat exchanger;
FIG. 7 is a cross-sectional view of another embodiment of a microchannel heat exchanger;
FIG. 8 is a perspective view of a microchannel heat exchanger having u-connecters disposed at tube ends; and
FIG. 9 is a perspective view of a typical microchannel heat exchanger.
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
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.
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.
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.
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.
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.
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.
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.
Patent Application
20100263847
