Analysis of Unsteady Heat Transfer in the Pre-Cooling Process of 300 m(3) Liquid Hydrogen Tank

A mathematical model for the pre-cooling process was established to solve the problems of the long pre-cooling time and uncertain parameters of cryogenic propellant tanks. The pre-cooling parameters of a 300 m(3) liquid hydrogen tank at several cooling rates were calculated and analyzed. The results show that the liquid hydrogen flow required to pre-cool the gas in the tank, tank wall, accessories, and interlayer thermal insulation materials increases first and then decreases and that the liquid hydrogen flow needed to offset the heat leakage gradually increases with the temperature reduction. When the average cooling rate rose from 0.1 K/min to 1 K/min, the pre-cooling time was shortened from 2730 min to 273 min, and the consumption of liquid hydrogen decreased from 2115 kg to 2091 kg. Among the various heat loads, the inner tank wall and accessories consumed the most significant proportion of liquid hydrogen, accounting for 87.84% to 88.61%. The cooling capacity was derived from the liquid hydrogen's evaporation and the cryogenic hydrogen gas's heating process, of which the liquid hydrogen accounted for 23.00%. Considering the principle of safe operation, it is recommended that stepped pre-cooling in two or three stages based on the maximum cooling rate is conducted.