Mathematical modeling of cryogenic propellant tank pressurisation system provided with heat exchanger

Pressurisation of propellant tank during flight is required to maintain specified NPSP (Net Positive Suction Pressure) at pump inlet and also to ensure structural stability against buckling under flight loads. Selection of propellant tank pressurisation system plays a vital role in configuring a high performance propulsion stage. Heat exchanger is used to heat the pressurant gas so that overall mass of pressurization system is reduced considerably. When heated gas is used for pressurisation, it is imperative to quantify the mass of liquid attaining temperature higher than the acceptable value for cavitation free pump operation. Heat exchanger design is a trade-off between optimum pressurant gas temperature, the stratified propellant mass and pressurization system mass. The objective of this paper is to mathematically model the pressurization system for Liquid Oxygen (LOX) tank employed in a cryogenic propulsion stage.