Loop Heat Pipe Manufacturing via DMLS for CubeSAT Applications

Advanced Cooling Technologies, Inc. (ACT) proposes to develop a low-cost Loop Heat Pipe (LHP) evaporator using a technique known as Direct Metal Laser Sintering (DMLS), otherwise known as 3D printing, to produce low-cost LHPs to be used in CubeSat and SmallSat applications. The wick structure in an LHP assumes the role of a pump in a standard loop, pumping liquid from the lower pressure condenser to the higher pressure evaporator by capillary forces. The overall thermal performance of the system is therefore highly dependent on the in-situ characteristics of the wick structure. Current LHP wick manufacturing and installation processes are cumbersome, labor intensive, and suffer from a low yield rate. It is estimated that the cost to produce an LHP evaporator, including the attachment of the bayonet, secondary wick and compensation chamber, accounts for approximately 75% of the total system?s manufacturing cost. By 3D printing an evaporator envelope with an integral porous primary wick structure, the overall complexity and cost of the design can be significantly reduced. The Phase I program was fully successful. In Phase I, an LHP with a DMLS evaporator was built using ammonia as the fluid, and carried the predicted 45 W. The overall technical objective of the Phase II program will be to design, build, and test a complete LHP thermal management system for a CubeSat. Phase II work will include further optimization of the LHP manufacturing parameters, and the development of advanced wick structures such as a graded wick design. The deliverables at the end of the Phase II will include an LHP that has been thermal vacuum tested, and a second LHP flight unit with ethanol working fluid, that can be tested at NASA?s option on the ISS.