Dynamic Thermal Characteristics of the Liquid Hydrogen Tank Filling Process Under Different Gas Phase Space Configurations

Abstract

The gas phase space influences liquid redistribution and pressure evolution during liquid hydrogen (LH2) filling, but the effects of its geometry remain insufficiently understood. A 34 L onboard LH2 tank was investigated using a two-dimensional volume-of-fluid (VOF) model incorporating two-phase flow, conjugate heat transfer, and phase change. The effects of gas phase space volume ratio, connecting orifice diameter, and length-to-diameter ratio were evaluated under identical filling conditions. Increasing the volume ratio did not necessarily improve pressure buffering. The 20% case developed a larger liquid-occupied region and a markedly higher pressure than the 10% and 15% cases. The connecting orifice diameter produced a non-monotonic pressure response because both restricted liquid redistribution at a small diameter and rapid liquid occupation at larger diameters reduced vapor buffering. Among the examined cases, the 3 mm orifice produced the lowest pressure. Length-to-diameter ratios of 0.8 and 1.2 showed comparable pressure responses within the numerical resolution, whereas the short and wide 0.4 configuration produced a clearer pressure increase. All configurations approached similar average inner wall temperatures of approximately 22 K, indicating that pressure was more sensitive to phase distribution than to the overall wall thermal response. These findings provide guidance for gas phase space design in onboard LH2 tanks.