Experimental study on pressure control of liquid nitrogen tank by thermodynamic vent system

Long-term storage of cryogenic propellants on orbit as the replenishing fuel for spacecraft and energy supply source for space station is a crucial part of future space exploration. Thermodynamic vent system (TVS) was proposed as an effective technology to maintain the propellant tank pressure and reduce the mass loss of liquid propellant. This study presents an experimental investigation on the pressure control effect of a TVS installed in a 1.36 m3 liquid nitrogen (LN2) tank of the testing facility named Efficient Cryogenic Fluid Storage Test Platform (ECFSTP). Two operation modes, namely the mixing-only mode and the mixing-venting mode of TVS were compared and analyzed. The degree of superheat of the ullage dropped more rapidly and significantly under the mixing-venting mode, which produces the cooling effect by the venting stream from the throttling valve in addition to venting itself. The effects of different pressure control bands on the performance of the TVS have also been comparatively investigated. The results confirmed the feasibility and effectiveness of the TVS to control the tank pressure within the range of 220-260 kPa for long time running, with 50% fill level and 9.31 W m−2 leaking heat flux.