Liquid Propulsion System Centre, Indian Space Research Organization, Trivandrum – 695547, INDIA
LPSC-ISRO, Valiamala, Thiruvananthapuram Kerala, India
Liquid Propulsion Systems Centre, ISRO, Valiamala, Thiruvananthapuram-695547
Liquid propellants in propellant tanks of launch vehicles are expelled with the help of pressurant gas stored in high pressure gas bottles. Accurate estimation of the change in temperature of the gas during pressurization or depressurization is required to arrive at quantity of stored gas as well as the usable volume. The estimation needs to be accurate as well as with essential margin to have a successful mission.
Development of a mathematical model for the depressurization is brought out in this study to assess the pressure and temperature changes in gas bottle subjected to high depressurization rate. A mathematical model is developed for estimating the pressure, considering all associated variables, namely temperature of gas inside the gas tank and temperature of wall of the gas tank, gas and bottle properties. Mass and energy conservation is applied along with the real gas equation to derive the governing equation for system variables. Free as well as forced convective heat transfer is possible inside the gas bottle and the suitability of various empirical relations for estimating the heat transfer co-efficient is studied. The model was validated with two sets of different stages ground test data. It was found that the results of mathematical model considering the natural convection inside the gas bottle are comparable with test/flight observations within 5 %. The residual mass of gas is estimated using this model and the sensitivity of residual mass to the expulsion flow rate is studied.