This invention relates generally to heat exchangers and, more particularly, to microchannel heat exchangers for use in air conditioning and refrigeration vapor compression systems.
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.
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.
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.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
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:
An example of a basic vapor compression system 20 is illustrated in
Referring now to
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 (
Referring now to
As known, a plurality of heat transfer fins 50 may be disposed between and rigidly attached, usually 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.
In a conventional microchannel 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
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.
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.
This application claims the benefit of U.S. provisional patent application Ser. No. 61/985,888 filed Apr. 29, 2014, the entire contents of which are incorporated herein by reference.
Filing Document | Filing Date | Country | Kind |
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PCT/US2015/028196 | 4/29/2015 | WO | 00 |
Number | Date | Country | |
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61985888 | Apr 2014 | US |