Cooling behaviors of liquid hydrogen by helium gas injection

Abstract

The cooling method of helium bubbling is of great importance in the acquisition system of densified liquid hydrogen because of its safety, reliability and easy operation. To obtain better cooling effect in the cooling system, in this paper, a mathematical model of instantaneous heat and mass transfer is developed by using two-film theory to describe the cooling behavior of a single helium bubble. The solubility and diffusion processes for the single helium bubble injected into liquid hydrogen are quantitatively analyzed. The dominant factors affecting the cooling capacity are obtained on the basis of discussion on several influencing factors. Taking these as important basis of the assumption, a thermodynamic model considering effects of static pressure and thermo-physical properties is established to accurately predict the temperature dropping process of liquid hydrogen by helium bubbling. Compared with the associated experimental data, it is found that the calculating results using the thermodynamic model proposed in the present paper are well consistent with the experimental data. The cooling effect becomes better with the decreases of ullage pressure, injected helium temperature and environmental heat flux. The helium gas consumption gradually reduces with the increase of helium injection rate and the decrease of environment heat flux. Meanwhile, the same method is also used for the cooling of liquid oxygen, liquid nitrogen and liquid methane. It shows that the cooling effect using the method of helium gas bubbling varies for different cryogenic liquids. The triple-point temperatures of LN2 and LCH4 can easily be reached by the helium injection, but it is hardly cooled down to their freezing points for the LH2 and LO2. Among the four cryogenic liquids, the LH2 cooling needs the largest consumption of GHe to meet the requirement of a certain subcooling degree.