The maximum allowable evaporator heat flux in a grooved pipe is relatively low, typically 10-15 W/cm2. As spacecraft electronics increase in power and packing density, this can present a thermal control problem. Sintered wicks have much higher evaporator heat flux limits, typically four times higher than grooved wicks. The main non-NASA application will be for CCHPs that remove waste heat from high power components on commercial spacecraft.
Hybrid wick CCHPs for high power electronics on spacecraft, and NASA landers and rovers is the immediate NASA application. Conventional grooved aluminum/ammonia CCHPs are heat flux limited and are only suitable for operation in space, or when they can be engineered to operate in a gravity aided mode. The hybrid wicks developed on this program will remove this design constraint, and expand the design space to include higher heat flux operation on future missions. In addition, some vertical, grooved CCHPs have had startup problems, requiring an electric heater to generate a vapor bubble. The large number of nucleation sites in the sintered wick will eliminate this problem. Wicks developed on this program will enable the use of 3-D CCHPs for some NASA applications. Conventional grooved aluminum/ammonia heat pipes can be ground-tested with the evaporator elevated 0.10 inch above the condenser. This is only possible if the heat pipe is all in a single plane, i.e., a 2-D heat pipe. In some cases, 3-D CCHPs, with bends in multiple planes, simplify spacecraft thermal design. However, grooved 3-D pipes cannot be tested on the ground, since there is no way to keep the maximum elevation to 0.10 inch with the bends in multiple planes. With a hybrid wick, 3-D pipes can be fabricated and ground tested.
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