CROSS-REFERENCE TO RELATED APPLICATION

[001] This application claims the benefit of U.S. provisional patent application serial number 61/985,888 filed April 29, 2014, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[002] This invention relates generally to heat exchangers and, more particularly, to microchannel heat exchangers for use in air conditioning and refrigeration vapor compression systems.

[003] Heating, ventilation, air conditioning and refrigeration (HVAC&R) systems include heat exchangers to reject or accept heat between the refrigerant circulating within the system and surroundings. One type of heat exchanger that has become increasingly popular due to its compactness, structural rigidity, and superior performance, is a microchannel or minichannel heat exchanger. A microchannel heat exchanger includes two or more containment forms, such as tubes, through which a cooling or heating fluid (i.e. refrigerant or a glycol solution) is circulated. The tubes typically have a flattened cross-section and multiple parallel flow channels. Fins are typically arranged to extend between the tubes to air in the transfer of thermal energy between the heating/cooling fluid and the surrounding environment. The fins have a corrugated pattern, incorporate louvers to boost heat transfer, and are typically secured to the tubes via brazing.

[004] A thermal stress acts on the region of the heat exchanger at the joints between the heat exchanger tubes and adjacent headers. This is because a header of the heat exchanger thermally expands by exposure to a high temperature, while the fins coupled to the heat exchanger tubes remain at a lower temperature. Therefore, each of the joints between the high temperature manifold and the low temperature tubes is subject to a high stress alternating between tensile and compressive stress due to simultaneous occurrence of expansion and contraction at each of the joints. As a result, cracking of a portion of the heat exchanger may occur, resulting in a decreased heat exchanger fatigue life.

BRIEF DESCRIPTION OF THE INVENTION

[005] According to an aspect of the invention, a heat exchanger is provided including a first manifold and a second manifold. The first manifold and the second manifold are separated from one another. A plurality of heat exchanger tubes is arranged in a spaced parallel relationship. The heat exchanger tubes fluidly couple the first manifold and the second manifold. A plurality of fins is attached to the plurality of heat exchanger tubes such that a first end of each fin is spaced apart from the first manifold by a first distance.

[006] These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[007] 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:

[008] FIG. 1 is a schematic diagram of an example of a refrigeration system;

[009] FIG. 2 is a perspective view of a microchannel heat exchanger according to an embodiment of the invention;

[0010] FIG. 3 is a cross-sectional view of a microchannel heat exchanger according to an embodiment of the invention; and

[0011] FIG. 4 is a cross-sectional view of a microchannel heat exchanger according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0012] An example of a basic vapor compression system 20 is illustrated in FIG. 1, including a compressor 22, configured to compress a refrigerant and deliver it downstream to a condenser 24. From the condenser 24, the cooled liquid refrigerant passes through an expansion device 26 to an evaporator 28. From the evaporator 28, the refrigerant is returned to the compressor 22 to complete the closed-loop refrigerant circuit.

[0013] Referring now to FIG. 2-4, a heat exchanger 30 configured for use in the vapor compression system 20 is illustrated in more detail. In the illustrated non-limiting

embodiment, the heat exchanger 30 is a single tube bank microchannel heat exchanger 30; however, microchannel heat exchangers having mulitple tube banks, as well as other types of heat exchangers, such as tube and fin heat exchangers for example, are within the scope of the invention. The heat exchanger 30 includes a first manifold or header 32, a second manifold or header 34 spaced apart from the first manifold 32, and a plurality of heat exchange tubes 36 extending in a spaced parallel relationship between and connecting the first manifold 32 and the second manifold 34. Depending on the configuration of the heat exchanger 30, the heat exchanger 30 may be used as either a condenser 24 or an evaporator 28 in the vapor compression system 20. For example, in embodiments where the heat exchanger 30 is a condenser 24, the manifolds 32, 34 are oriented generally horizontally and tubes 36 extend vertically between the two headers 32, 34, as shown in FIG. 2. When the heat exchanger 30 is configured as an evaporator 28, the headers 32, 34 are typically vertically oriented such that the tubes 36 extend generally horizontally through the heat exchanger 30, as shown in FIG. 3.

[0014] The heat exchanger 30 may be configured in a single pass arrangement, such that refrigerant flows from the first header 32 to the second header 34 through the plurality of heat exchanger tubes 36 in the flow direction indicated by arrow B (FIG. 2). In another embodiment, the heat exchanger 30 is configured in a multi-pass flow arrangement. For example, with the addition of a divider or baffle 38 in the first header 32 (FIG. 3), fluid is configured to flow from the first manifold 32 to the second manifold 34, in the direction indicated by arrow B, through a first portion of the heat exchanger tubes 36, and back to the first manifold 32, in the direction indicated by arrow C, through a second portion of the heat exchanger tubes 36. The heat exchanger 30 may additionally include guard or "dummy" tubes (not shown) extending between its first and second manifolds 32, 34 at the sides of the tube bank. These "dummy" tubes do not convey refrigerant flow, but add structural support to the tube bank.

[0015] Referring now to FIG. 4, each heat exchange tube 36 comprises a flattened heat exchange tube having a leading edge 40, a trailing edge 42, a first surface 44, and a second surface 46. The leading edge 40 of each heat exchanger tube 36 is upstream of its respective trailing edge 42 with respect to an airflow A through the heat exchanger 36. The interior flow passage of each heat exchange tube 36 may be divided by interior walls into a plurality of discrete flow channels 48 that extend over the length of the tubes 36 from an inlet end to an outlet end and establish fluid communication between the respective first and second manifolds 32, 34. The flow channels 48 may have a circular cross-section, a rectangular cross-section, a trapezoidal cross-section, a triangular cross-section, or another non-circular cross-section. The heat exchange tubes 36 including the discrete flow channels 48 may be formed using known techniques and materials, including, but not limited to, extruded or folded. [0016] As known, a plurality of heat transfer fins 50 may be disposed between and rigidly attached, usual ly by a furnace braze process, to the heat exchange tubes 36, in order to enhance external heat transfer and provide structural rigidity to the heat exchanger 30, Each folded fin 50 is formed from a plurality of connected strips or a single continuous strip of fin material tightly folded in a ribbon-like serpentine fashion thereby providing a plurality of closely spaced fins 52 that extend generally orthogonal to the flattened heat exchange tubes 36. Heat exchange between the fluid within the heat exchanger tubes 36 and air flow A, occurs through the outside surfaces 44, 46 of the heat exchange tubes 36 collectively forming the primary heat exchange surface, and also through the heat exchange surface of the fins 52 of the folded fin 50, which form the secondary heat exchange surface.

[0017] In a conventional microcharmel heat exchanger, the fins mounted to each of the plurality of heat exchanger tubes extend over the full length of the tubes, from the first header to the second header. The fins 50 of the heat exchanger 30 illustrated and described herein, however, are shorter than the tubes 36. The fins 50 are mounted near the center of each tube 36 such that at least one end 54 of each fin 50 is spaced away from the adjacent header 32, 34. As illustrated in FIG. 3, the first and second end 54a, 54b of each fin 50 may be spaced away the first and second header 32, 34, respectively. The distance between a first end 54a of the fins 50 and the first manifold 32 may, but need not be substantially identical to the distance between a second end 54b of the fins 50 and the second header 34. The distance between the ends 54 and the headers 32, 34 may be selected based on a variety of factors, including, but not limited to the type of refrigerant configured for use with the heat exchanger 30, the length of the manifolds 32, 34, and the temperature gradient between the headers 32, 34 and the fins 50, and the size and geometry of the plurality of heat exchanger tubes 36. The distance between the ends 54 and an adjacent manifold 32, 34 is generally between about five millimeters and about twenty five millimeters, and more specifically, about nineteen millimeters.

[0018] By separating at least one end of the fins 50 from an adjacent header of the heat exchanger, the stress and strain created by the expansion and contraction of the microchannel heat exchanger tubes 36 is much reduced and more distributed. As a result, the fatigue life and reliability of the heat exchanger 30 is significantly improved.

[0019] 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.