Investigation on pressurization behaviors of two-side-insulated cryogenic tank during discharge

Reducing pressurant gas requirement is of importance to the design of pressurization systems. In the present paper, a two-side-insulated tank, in which both of interior and outside surfaces of the tank wall are covered by insulation layers, is proposed, and a computational fluid dynamic (CFD) approach is introduced to investigate its thermal behaviors and pressurization performance. The pressurant gas requirement, temperature distributions, and energy distributions within the tank system are obtained and analyzed. The results show that the inner insulation layer can remarkably reduce the gas requirement during the liquid discharge period. For the event of pressuring a liquid oxygen (LO2) tank with 300 K helium gas, a decrease in gas requirement of 16% could be reached by using a 3-mm-thickness foam layer at the tank interior surface. For the event of pressuring a liquid hydrogen (LH2) tank with 300 K hydrogen gas, the same thickness foam layer produces a decrease of 14.2% in gas requirement. Moreover, the effect of inner insulation layer in reducing gas requirement is more significant with the increase of inlet gas temperature. When 600 K helium gas is used to pressure the LO2 tank, a decrease of 23.2% in gas requirement is reached by only a 1-mm-thickness foam layer in comparison with the tank without inner layer. The effect of inner insulation layer in reducing gas requirement is mainly because the energy distribution, occupied by ullage, wall, inner insulation layer and liquid propellant, is changed. Since the character of low thermal conductivity for the insulation material, there is a significant temperature drop within the insulation layer by which the heat transfer from ullage to insulation layer is reduced apparently, resulting in more energy left in ullage to provide pressurization effect. However, the gas-to-liquid heat transfer is also enhanced due to the warmer ullage caused by the introduction of inner insulation layer, which suppresses the energy proportion rise in the ullage region. In general, the introduction of inner insulation layer can distinctly reduce the pressurant gas requirement in the pressurized discharge process of cryogenic tanks, and the two-side-insulated tank technique may be an alternative technique in the design of pressurization system.