Experimental Investigation of Thermal Stratification in Cryogenic Tank Subjected to Multi-Species Bubbling

Abstract

Liquid oxygen (LOX) and liquid hydrogen (LH2) are used as oxidizer and fuel respectively in Cryogenic engine based launch vehicles. These propellants are stored in large insulated tanks under pressurized condition and having low structural mass for gaining payload benefit. LOX and LH2 are stored at sub-cooled temperatures of 77K and 20K, respectively. One of the disadvantages of sub-cooling the cryogenic tank is the development of thermal stratification. It is the accumulation of high temperature liquid close to liquid vapor interface of the tank. Cryogenic propellant tanks used in launch vehicles are well insulated using low density foam. Despite the presence of insulation, significant heat in-leak seeps into the cryogenic propellant tank from ambient due to aerodynamic heating, leading to thermal stratification phenomenon to occur. Presence of high temperature liquid in the propellant bulk leads to cavitation in cryo pump of the engine system during engine operation. It will be the major contributing factor towards abrupt engine firing and possible mission failure. In the present study, experiments are carried out to compare the evolution of thermal stratification in the absence and presence of helium bubbling into a pressurized cryogenic tank filled with 77K LN2 as well as in demineralized water under ambient pressure. Effect of helium bubbling flow rate on thermal stratification is the major outcome from the study.