Experimental and computational investigation into hydrodynamic and heat transfer characteristics of subcooled flow boiling on the International Space Station

Abstract

This study is part of a long-term initiative to investigate flow boiling of n-perfluorohexane (n-PFH) under microgravity on the International Space Station (ISS). Investigated are data received from the ISS during 2022 using the Flow Boiling and Condensation Experiment (FBCE) (actual name of experimental payload). FBCE is designed to accommodate one of two test modules, one for flow boiling and another for condensation. Data for the present study are acquired using FBCE's Flow Boiling Module (FBM), which features a rectangular channel of 5.0-mm height, 2.5-mm width, and 114.6-mm heated length. Examined are results for three different mass velocities of 199.9, 799.9, and 2399.9 kg/m2.s, and heat fluxes corresponding to approximately 20, 40, and 60% of critical heat flux (CHF). Detailed development of the interfacial behavior is captured by high-speed video through the channel's transparent sidewalls. In the Computational Fluid Dynamics (CFD) model, numerical solver is constructed in ANSYS-Fluent wherein the multiphase model is combined with appropriate models for turbulence, surface tension, and interfacial phase change. Also incorporated are momentum source terms governing bubble shear-lift, bubble drag, and bubble dispersion. Accuracy of the CFD predictions is assessed by comparison against both the heat transfer data and video-captured interfacial behavior. Very good agreement is achieved against measured axial profile of heated wall temperatures and further validated by accurately capturing such interfacial features as bubble formation, detachment, coalescence, and downstream wavy vapor layer development. Additionally, the CFD simulations enable prediction of other transport parameters vitally important to understanding evolution of the boiling flow but not possible from experiment, such as cross-sectional profiles of void fraction, fluid velocity, and mixture temperature.