This invention relates to a heat exchanger that utilizes a high temperature aluminum subject to thermal fatigue due to heat cycles.
Aircraft air management systems utilize heat exchangers to provide cooling and/or heating for various components as well as cabin comfort. In an effort to reduce the weight of the systems, aluminum is used as the material of choice for some of the high operating temperature heat exchangers. Recent applications have exposed the aluminum heat exchangers to even higher temperatures. The result is a greater possibility for failures due to thermal fatigue.
To minimize structural failures and increase reliability, it has been shown that restricting cold side flow to certain areas of the cooling core within the heat exchanger reduces thermal stresses and thus thermal fatigue. A piece of sheet metal is typically used to serve as a blocking surface to divert flow around a portion of the heat exchanger that is typically subject to thermal fatigue. Welding the sheet metal to the core about its perimeter is not feasible because the welds cracked due to thermal stresses during the heat cycles.
To address this problem, the sheet metal has been secured to the core using a high temperature RTV to permit thermal expansion of the core. The sheet metal is also riveted to the heat exchanger since the RTV alone cannot reliably secure the sheet metal to the core over time.
The core must be cleaned so that the RTV can securely bond the sheet metal to the core. The additional time, preparation, and materials needed to secure the sheet metal to the core with this method adds cost to the heat exchanger. What is needed is an improved method and apparatus for providing the blocking surface on the heat exchanger.
The heat exchanger includes a core having first and second bars arranged transverse to one another to form a skeleton. The skeleton forms a box-like structure supporting hot and cold cooling fins. The bars are spaced from one another in a lattice to form gaps between the bars permitting airflow to pass through the skeleton and into the core. Blocking bars are arranged within the gaps, typically at the corners, between at least several of the bars to provide a blocking surface. The blocking surface diverts flow around a portion of the core that is typically subject to undesired thermal stresses due to a high temperature gradient in that area.
The core is typically constructed using a brazing material. The blocking bars are secured to the bars of the skeleton and/or other components within the heat exchanger using the same brazing material and preferably at the same time that the rest of the heat exchanger is assembled.
In this manner, bar material that is already used to provide the skeleton can also be used to provide the blocking surface. Furthermore, the same brazing material is used to construct the core and secure the blocking bars to the bars of the skeleton, and the blocking bars can be assembled at the same time. As a result, the cost and assembly time of the heat exchanger is reduced.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
The cold and hot fins 14 and 16 are separated from one another to provide enclosed air passages by securing parting sheets 18 to the cold and hot fins 14 and 16, which is best shown in
Typically the parting and end sheets 18 and 20 and the cold and hot fins 14 and 16 are secured together using a brazing material. One suitable example is a foil-type braze material that has a melt temperature of approximately between 1100-1175° F. The flow is directed through the cold and hot fins 14 and 16 by headers. The cold-in header is not shown in
Blocking bars 44 are arranged between the gaps 42 in desired locations typically subject to thermal fatigue, such as the corners of the skeleton. One such corner is shown in
The blocking bars 44 can be constructed from the same material as the first and second bars 36 and 38. The blocking bars 44 can be secured using the same brazing material used to secure the first and second bars 36 and 38 to one another and assembled the same assembly time. The same brazing material is used to secure the cold and hot fins 14 and 16 and the parting sheets and end sheets 18 and 20 so that an additional retention material is not necessary for providing the blocking surface.
Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
Number | Name | Date | Kind |
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3216732 | Foust | Nov 1965 | A |
3587731 | Hays | Jun 1971 | A |
3992168 | Toyama et al. | Nov 1976 | A |
4330308 | Grenier et al. | May 1982 | A |
4971137 | Thompson | Nov 1990 | A |
Number | Date | Country | |
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20070144717 A1 | Jun 2007 | US |