Oscillatory Behaviors of PACE/OCI Loop Heat Pipe Engineering Test Units in Ground Testing

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2020 International Conference on Environmental Systems

Oscillatory behaviors of the Loop Heat Pipe (LHP) temperatures were first discovered in the late 1990s and early 2000s. So far, two types of temperature oscillations have been found in LHP operations: High Frequency Low Amplitude (HFLA) and Low Frequency High Amplitude (LFHA). Each type occurred in distinct regimes of system performance. The linear stability theory for LHPs originally developed in 2011 was able to reveal the mechanisms causing the aforementioned ""dynamical"" stability/instability. The theory has been verified against test data from several LHPs of different designs utilizing ammonia or propylene as the working fluid. The PACE/OCI LHP consists of a 5/8""OD x 4""L capillary pump, 1/8""OD x 220""L transport line. It underwent ground testing in both ambient and vacuum environments and the LHP exhibited both LFHA and HFLA temperature oscillations. Once again, the LHP linear stability theory was called upon to explain the oscillatory behaviors and to devise a method to mitigate their potential impacts on 0-g performance.

Triem Hoang, TTH Research Inc., US
Jentung Ku, National Aeronautics and Space Administration (NASA), US
Christopher Stull, National Aeronautics and Space Administration (NASA), US
Deepak Patel, National Aeronautics and Space Administration (NASA) Goddard Space Flight Center, US
ICES201: Two-Phase Thermal Control Technology
The proceedings for the 2020 International Conference on Environmental Systems were published from July 31, 2020. The technical papers were not presented in person due to the inability to hold the event as scheduled in Lisbon, Portugal because of the COVID-19 global pandemic.
Loop heat pipe, Capillary-pumped technology, Two-phase heat transport