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An evaporative heat sink has been designed and built by AlliedSignal for NASA's Johnson Space Center. The unit is a demonstrator of a primary heat exchanger for NASA's prototype Crew Return Vehicle (CRV), designated the X-38. The primary heat exchanger is responsible for rejecting the heat produced by both the flight crew and the avionics. Spacecraft evaporative heat sinks utilize space vacuum as a resource to control the vapor pressure of a liquid. For the X-38, water has been chosen as the heat transport fluid. A portion of this coolant flow is bled off for use as the evaporant. At sufficiently low pressures, the water can be made to boil at temperatures approaching its freezing point. Heat transferred to liquid water in this state will cause the liquid to evaporate, thus creating a heat sink for the spacecraft's coolant loop. The CRV mission requires the heat exchanger to be compact and low in mass.

Thermal management requirements for aerospace applications continue to grow while weight and volume allotments remain constant or shrink. Compact, high performance and lightweight heat transfer equipment is needed to meet these high heat flux removal requirements. Several innovative heat transfer enhancement techniques are being considered for development of thermal management components that will meet these challenging demands. Honeywell, under an AFRL funded program, is developing two new heat exchanger technologies; microchannel and advanced heat transfer surfaces to improve thermal management systems for a fuel-to-air heat exchanger. Heat transfer systems in military aircraft are increasingly using fuel as a heat sink. Heat transport loops containing several fuel-to-liquid heat exchangers are used to cool electronics, engine oil, hydraulic oil, and elements of the thermal management system.