Recent Ground-based Test Results for the Closed Loop Two-Phase Flow Chilldown Test Module for Future Integration with the Flow Boiling and Condensation Experiment onboard International Space Station

Abstract

Effective cryogenic fluid management is important to the success of future manned and unmanned NASA missions, and the transfer line chilldown process is recognized as a key technological challenge. To address this challenge, the Two-phase Flow and Thermal Management Lab (TFTML) at Case Western Reserve University is collaborating with NASA Glenn Research Center to develop, test and deploy a closed loop two-phase flow chilldown test section onboard the International Space Station to be integrated with the current Flow Boiling and Condensation Experiment (FBCE) module. The final results of this project will create the first chilldown process database under pure and sustained microgravity conditions and will significantly advance the understanding of the chilldown process for cryogenic fluid management. In the present work, the ground-based test results of the closed loop SS-316 chilldown test section in a horizontal configuration at varying inlet mass flow rates (3-40 g/s) and inlet liquid subcooling (5-35 0C) are presented. The working fluid is PF-5060 and the chilldown curves captured the entire quenching curve involving the different boiling regimes and temperature transition points viz., film boiling, Leidenfrost/re-wetting point, transition boiling, critical heat flux (CHF), nucleate boiling, onset of nucleate boiling (ONB) and single-phase liquid flow regions, when the test section is pre-heated to around 250 0C. The major findings of the present study are, (i) the bottom part of the test section sees a lower re-wetting temperature due to the horizontal flow configuration, (ii) the re-wetting temperatures are relatively unaffected by inlet liquid mass flow rates though the increase in mass flow rates reduce the chilldown time, and (iii) the re-wetting temperatures decrease with decrease in inlet liquid subcooling. Further, preliminary flow visualization studies in a transparent pyrex test section will also be presented to understand the intricate flow boiling regime transitions during the chilldown process.