Heat and mass transfer and hydrodynamics in cryogenic hydrogen fuel systems

Abstract

The paper presents the results of experimental and theoretical studies and the development of methods to calculate the parameters of heat and mass transfer as well as hydrodynamic processes occurring during the following operations: filling of reservoirs and tanks with LH2; drain-free storage of LH2; saturation of LH2 with non-condensable gas (helium) during tank pressurization; drainage of hydrogen vapors and displacement of LH2 from the storage tank. It is noted that the main design parameters characterizing the process of filling cryogenic reservoirs and tanks are the following: the time of filling to the required level; LH2 evaporation losses during cooling; thermal stresses in the walls of reservoirs and tanks. The time of LH2 drain-free storage in real reservoirs and tanks is reduced due to thermal stratification in the liquid and gas–vapor phases compared to the time of LH2 drain-free storage under conditions of its complete mixing. The drainage of LH2 vapors is characterized by the following main design parameters: the rate of pressure change in the cryogenic tank; the flow rate of the drained mass; the degree of non-equilibrium during LH2 boiling; drop entrainment; an increase in the LH2 volume during boiling (“swelling”); the degree of pressure increase in case of a sudden termination of drainage. When LH2 is displaced, the following parameters of the feed system have a decisive influence on the heat and mass transfer characteristics: displacement pressure; LH2 thermal stratification; the degree of LH2 saturation with non-condensable gas; the maximum temperature of the tank wall; the mass of pressurizing gas. Liquid hydrogen (LH2) can be saturated during pressurization and displacement with helium and during other operations involving the use of non-condensable gas. The process of LH2 saturation with pressurizing gas (helium) is characterized by the following parameters: absorption coefficient that determines the efficiency of gas saturation and is equal to the ratio of the dissolved amount of helium to the entire mass of non-condensable gas that has passed through the solution; change in the LH2 temperature during gas saturation; helium concentration in the solution and its homogeneity. Based on the obtained experimental data and mathematical modeling, we determined relationships that make it possible to calculate the listed main parameters of heat and mass transfer as well as hydrodynamic processes at the main stages of the design and operation of cryogenic hydrogen tanks, systems of LH2 storage and feeding. The presented relationships can be used as reference data in the design and optimization of LH2 fuel systems.