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Publication Date: 2014-Oct-23
Document File: 8 page(s) / 317K

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The invention relates to a two stage heat exchanger for use in aircraft thermal management.

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This is the abbreviated version, containing approximately 29% of the total text.

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    The invention relates to a two stage heat exchanger for use in aircraft thermal management.


    Thermal management systems are important on aircraft to keep passengers comfortable and to protect the vehicles equipment. Modern turbofan/turbojet engines have an ever-increasing demand of cooling, including gearbox oil, cooling air and electronics, while at the same time their efficiency has to be pushed ever higher. Heat exchangers are often used to transfer heat as necessary, based on the operating conditions. These can be bulky and heavy which are energy inefficient with respect to weight and drag that require extra engine power to overcome.

    One method of using a heat exchanger is for providing a temperature controlled air stream for the thermal management system by using the hot, high pressure air from the outlet of the engines compressor and cooling it using a cooler air stream such as the air from the bypass stream. The air taken from the compressor outlet is the highest pressure gas found in the engine just before it enters the combustor. This pressure can be used advantageously to push the air through any number of heat exchangers required and also through the system. It eliminates the use for any further pumps, fans, or compressors.

    This method of using an engine air stream for the thermal management system and cooling it with another internal stream has advantages over other cooling methods commonly used. Some other methods take ram air as a cooling source which requires some external device

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to channel the air into the aircraft, which will increase drag while moving or require a fan while not moving. The pressure is also not nearly as high when using ram air as it is when using compressed engine air.

    One challenge in using the compressed air stream to flow through a heat exchanger is the high temperatures that are generated during compression. These temperatures are often too high to use with lightweight, highly conductive materials such as aluminum. Other heavier materials like stainless or nickel alloys are often used to make heat exchangers that operate in such high temperatures.

    Aircraft heat exchangers should also be compact and have a high cooling effectiveness (ETA). For the application where air is the heat transfer fluid, there needs to be a high surface area to volume ratio in order to achieve the cooling required.

    Other attempts have been made and research has been done regarding producing a lightweight, compact heat exchanger that holds up in high temperatures. A titanium heat exchanger has been proposed, but these are difficult to manufacture, especially in high quantities. They are also inferior to aluminum with respect to their heat transfer characteristics. A current development is a metal foam heat exchanger, which is lightweight and operable in high temperatures with great heat conductivity, but it is expensive to make and in trials so far...