Large Diameter Pulsating Heat Pipe for Future Experiments on the International Space Station: Ground and Microgravity Thermal Response

This work describes the thermal characterization on ground and under a varying gravity field (parabolic flights) of a large diameter Pulsating Heat Pipe (PHP) especially designed for its future implementation on the heat transfer host module of the International Space Station (ISS) for long term microgravity experiments. A multi-turn compact closed loop PHP is made of aluminum and partially filled with FC-72 (50% vol.). The 3mm tube internal diameter is larger than the static capillary limit evaluated on ground conditions for the above working fluid, with the objective of dissipating larger heat power inputs compared to smaller diameter channels, under microgravity conditions, allowing the typical slug flow pattern of PHPs to occur. To provide a detailed insight on the thermo-hydraulics phenomena during the device start-up under the occurrence of microgravity, the PHP is equipped with a transparent sapphire tube insert, two miniature pressure transducers and two microthermocouples. The flow pattern and the liquid bulk temperature distribution are detected by a fast VIS camera and a medium wave IR camera respectively. The data recorded on the 67th ESA-NOVESPACE parabolic flight campaign are analyzed in the light of a future implementation on the ISS in 2020 and for the validation of actual numerical models. The device is continuously active during the whole microgravity periods without any stopover. The start-up tests (the heat power is provided after the 0-g occurrence) proved that the PHP operation is not primed by inertial effects. Finally, the thermal energy due to the sensible heat of the liquid phase is estimated showing a lower level than existing theoretical values.