Modeling liquid-vapor phase change experiments: Cryogenic hydrogen and methane

Mass accommodation coefficients are essential inputs to kinetic models of liquid-vapor phase change, yet after nearly 100 years there remains significant discrepancy in reported values. These discrepancies have been attributed to a wall material or geometric dependency resulting in the need for an empirical correction factors. The lack of experimental results for cryogenic fluids poses a serious impediment to modeling/predicting propellant behavior for long term space missions. Using a combination of neutron imaging experiments and multi-scale modeling, mass accommodation coefficients for liquid hydrogen and methane are determined. When the local variation in thermophysical properties are accounted for, the experimentally derived accommodation coefficients for hydrogen are invariant to container size, material and evaporation rate. The discrepancy in prior measurements of the accommodation coefficient for other fluids can be alleviated by a multi scale analysis that incorporates local variation in thermophysical properties. The values of accommodation coefficients for hydrogen and methane are consistent with generalized transition state theory. This suggests that a mass accommodation coefficient is a solely a function of the liquid-vapor density ratio, making it a fluid-independent property easily determined without the need for empirical correction factors as reported in previous investigations.