High Temperature Heat Pipes and Passive Two-Phase Cooling Systems

The objective of the proposed Phase I effort is to identify a technical development path that will yield a heat pipe with the following characteristics: • be passive, requiring no power input other than the heat to be transported; • provide equal or superior heat transport performance in the temperature range from 80°C to 200°C relative to aluminum/ammonia heat pipes operating in the temperature range between 0°C and 80°C; • achieve this performance with equal or lesser mass; and • survive exposure to temperatures as low as -60°C. Two paths will be considered in parallel. The first path pursues optimization of established constant conductance heat pipe designs, using water as the working fluid. The second path will investigate an innovative hybrid heat pipe design. In addition to offering a potential solution to the problem identified in this topic, development of the hybrid heat pipe may also lead to a low-cost loop heat pipe. At the conclusion of Phase I, one of these paths will be chosen for further development in Phase II. BENEFIT: High temperature heat pipes are a key enabler for advanced high temperature electronics space applications, such as the GaN phased array antenna, which is being developed to support future AF communications requirements. The development of high temperature heat pipes to replace aluminum/ammonia heat pipes will allow the evolution of GaN payloads to be used at significantly higher temperatures than today''s GaAs payloads or early implementations of GaN. By running GaN phased arrays hotter one will be able to save significant thermal radiator mass with slight drop off in GaN efficiency with increased temperature. The overall system trades show than not only will the radiators get smaller and less massive but the overall mass will also be reduced.