Effect of pressurant flow rate and ullage conditions on mass transfer and thermal stratification in a partially filled LN2 tank

Abstract

Experimental and numerical computations have been carried out to investigate the evolution of pressure and temperature in the liquid nitrogen (LN2) tank pressurized with gaseous nitrogen (GN2). A parametric study has been carried out to study the effect of ullage volume and pressurant gas (GN2) flow rate (0.25–2 g/s) and temperature (250–350 K) on the pressure evolution and thermal stratification in the tank during active pressurization from 1 bar to 3 bar. Experiments are conducted in a small range of mass flow rates at a given pressurant gas temperature (302 K). The numerical simulations are validated with the experiments and a parametric study has been performed. It has been observed that pressurization time varies linearly with the liquid depth. Thermally stratified mass in LN2 increases with the decrease in pressurant mass flow rate for a given pressure rise. Numerical simulations revealed that mass condensed during the pressurization is a weak function of ullage depth and temperature but a strong function of the mass flow rate. The pressurant gas requirement follows the correlation of Ludwig and Dreyer (2014) for relatively higher mass flow rates. The pressurant gas temperature has a strong influence on the flow pattern in the ullage. The pressurant gas flows along the wall and reaches the interface without disturbing the bulk vapor. Heat transfer at the interface is dominated by the heat carried by the pressurant than by transfer from the bulk vapor