Numerical analysis on pre-cooling processes of liquefied hydrogen tank

When a high-temperature liquefied hydrogen tank is initially charged with liquefied hydrogen, the liquefied hydrogen evaporates by absorbing heat from the tank. A proper pre-cooling method must be developed to reduce the consumption of hydrogen and reduce cooling time. In this study, a numerical model was developed to simulate pre-cooling processes: the vented chill (VC) and hold-vent (HV) processes with various venting pressures. The model considers nucleate boiling, film boiling, and natural convection, and can calculate the temperatures of the tank and hydrogen, heat transfer area, internal pressure, and hydrogen evaporation loss at each time step. The developed model was validated through experiments and data from previous studies. Among the analyzed pre-cooling processes, the shortest cooling time was achieved using the VC process, which was 29 % faster than the slowest HV process with a venting pressure of 12 bar. The hydrogen loss was the lowest in the HV process with a venting pressure of 7 bar, and was 75 % lower than that in the VC process. Considering both cooling time and hydrogen loss, the HV process with a venting pressure of 4 bar exhibited the best performance among the various processes. This study provides critical information on the pre-cooling characteristics of liquefied hydrogen tanks. The developed model can be used to optimize pre-cooling methods according to different user requirements.