Hybrid Manufacturing Process of Loop Heat Pipe Evaporator

Currently, to ensure the effective heat transfer of Loop Heat Pipes (LHPs), the Knife Edge Seal (KES) in the LHP evaporator is a key component that seals the primary wick and prevents high-pressure vapor from entering the lower-pressure interior of the evaporator and compensation chamber (CC). However, the KES may be susceptible to failure after long-time exposure to thermal cycles and vibration. Additionally, the KES insertion process is labor intensive and has an intrinsic risk that may increase the lead time and cost. To address the challenge, Advanced Cooling Technologies, Inc. (ACT), in collaboration with FormAlloy, Inc., utilized Direct Energy Deposition (DED), an Additive Manufacturing (AM) technique, to eliminate the KES, improve the LHP reliability and performance, streamline the LHP manufacturing process, and further enable innovative LHP designs. In the Phase I Program, we have successfully demonstrated using DED technology to deposit dense sealing layers on a testing specimen and thus eliminate the KES. The DED seal improves the overall LHP reliability and performance while lowering the cost and the lead time. Further, we have successfully demonstrated the operation of a complete LHP with a DED-sealed evaporator. The Phase II Program will optimize the DED process and further leverage the DED to the LHP fabrication process. Specifically, we will optimize the DED conditions including laser power, scanning paths, etc. In addition, we will conduct reliability and lifetime tests for the DED-sealed parts. ACT will also compare the performance of KES-sealed LHP with that of DED-sealed LHP. Further, we will develop Functional Gradient Material (FGM) that transits from aluminum alloy to nickel to further streamline the LHP manufacturing process. Finally, we will leverage the AM nature of the DED process to enable different CC and the evaporator body shape designs. By the end of Phase II, a complete hybrid manufactured LHP is one major deliverable to NASA. To ensure the effective heat transfer of LHPs, the Knife Edge Seal (KES) in the LHP evaporator is a key component that seals the porous primary wick and prevents high-pressure vapor in the vapor line from entering the lower-pressure interior of the evaporator and compensation chamber.  However, the KES susceptible to failure after long-time exposure to thermal cycles and vibration.  In addition, the KES insertion process is labor intensive and has an intrinsic risk that leads to extended lead time and higher costs.   In the Phase I Program, Advanced Cooling Technologies, Inc. (ACT), in collaboration with FormAlloy, Inc., has developed a hybrid LHP evaporator manufacturing process that utilizes Direct Energy Deposition (DED), an Additive Manufacturing (AM) technique, to deposit dense sealing layers directly on the porous primary wick and thus eliminate the KES.  The DED seal improves the overall LHP reliability and performance while lower the cost and the lead time. In Phase I, we successfully demonstrated the DED seal on testing specimens and operational LHP with the DED seal. The overall objective of this SBIR Program is to utilize DED process to improve the reliability and performance of the LHPs, reduce the LHP manufacturing cost and lead time, and enable innovative LHP designs that cannot be manufactured in a conventional approach.  The goal of the Phase II program is to continue optimizing the DED process through extensive testing and further adopt the DED technique to the LHP fabrication process.   Specifically, ACT and FormAlloy will optimize the DED condition in terms of heat treatment, laser power, scanning paths, etc.  In addition, we will conduct the manufacturing reliability test (Thermal cycle, shock, and vibration) and lifetime tests for the DED-sealed parts.  ACT will also conduct performance comparisons between conventional LHP with the KES and DED-sealed LHP.  Further, ACT and FormAlloy will develop Functional Gradient Material (FGM) that transits from aluminum alloy to nickel, with the aim to further eliminate bi-metallic parts and streamline the LHP manufacturing process.  Finally, we will explore using DED to build the compensation chamber and the evaporator body to enable innovative LHP designs that cannot be achieved by the conventional LHP manufacturing approach.   As one major deliverable, ACT will build one hybrid-manufactured LHP and deliver it to NASA.

Ammonia and propylene LHPs are currently used in most NASA and commercial satellites.  In comparison with Constant Conductance Heat Pipes (CCHPs), they carry much higher powers (1 kW vs. 100 W) over longer distances (10 m vs. 2-3 m).  They also are better suited for ground testability.  An LHP can operate with the evaporator 2 meters above the condenser, versus 2.5 mm for a CCHP.  With the DED-sealed, hybrid-manufactured LHP, improved performance, shorter lead time, and lower cost are well expected. For Universities and other Research institutes with a limited budget to perform space research, the reduced cost of the LHP via the hybrid manufacturing process will enable their adoption of the high-performance LHP to conduct high-heat-generation research activities such as space computing.

This is early/mid-stage (TRL 4) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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