Effect of Regulated Draining With Non-Condensable Gas on Liquid Temperature Evolution In a Cryogenic Tank

Cryogenic fuels are generally stored in large insulated tanks. These tanks are subjected to external thermal loads which raise the temperature of the stored fluids thereby leading to convection currents of warmer layers of liquid moving from the boundary to the liquid-vapour interface. The continuous heat in-leak into the tank leads to an increase in the mass of the high temperature fluid termed as stratified propellant mass. Stratified propellant mass is considered a penalty for the launch vehicle. Hence, the accurate prediction of formation of stratified mass is crucial and understanding the evolution of stratified mass and methods to nullify it in a cryogenic tank is essential for increasing payload mass. Objective of the paper is to study the effect of ullage gas properties on interface temperature and thereby stratified mass of LN2 in the tank during draining in the presence of multi-species ullage. Results indicate lower temperature for liquid layers when a non-condensable gas is used for pressurization and draining. Some variations in the temperature of top liquid layers with respect to pressurant gases are also observed. This can be inferred probably due to rate of evaporation and condensation at liquid vapour interface with multispecies ullage.