Numerical Simulation And Preliminarv Experimental Study On Unloading Process Of Crvogenic Propellants

The cryogenic propellant provides the main impetus for future rockets,especially high-thrust rockets.The unloading of cryogenic propellant is essential for its large-scale application.The purity of cryogenic propellant should be monitored during the unloading process,which is one of the necessary and standard requests.Generally,the lower boiling gas is used to pressurize the propellant,which inevitably leads to the heat and mass transfer on the gas-liquid surface,leading to the deterioration of the purity of the propellant in the surface layer.While in China,few study of gas-liquid interface mass transfer in the pressurizing and unloading process of cryogenic propellant has been performed so far.The author built an unsteady numerical model to simulate the pressurizing and unloading process of liquid oxygen by gaseous nitrogen,based on the VOF two-phase framework.The heat and mass transfer characteristic of unloading the liquid oxygen from the storage tank with normal temperature nitrogen as pressurizing gas was modeled.The changes of pressure,temperature,liquid level and liquid oxygen transfer rate in the tank during the unloading process were analyzed.The special attention are paid to determine when the gas phase appears at the liquid outlet of the tank and the volume fraction of nitrogen in the gas phase.The simulation results show that the inlet baffle plate can play a good role in shunting;in the initial stage of pressurization,the gas nitrogen was kept from the liquid oxygen interface due to the sharp vaporization of the liquid oxygen,therefore,limiting the diffusion of nitrogen into liquid oxygen;The volume fraction of nitrogen in two-phase mixture would reach more than 10%in the final stage.An experimental equipment for simulating the loading and unloading of the cryogenic propellant on the ground was built.It can monitor the temperature and pressure at different depth of liquid oxygen,and a multi-point multi-time sampling system was designed to realize the measurement of nitrogen mole fraction at different locations and times in the unloading process.Then we can get the purity of liquid oxygen in the unloading process.The experimental results show that the experimental equipment system can monitor the variety of the gas condition parameters and the flow of the cryogenic fluid in the pressurization process,and it is reliable to some extent,which laid the foundation for the experimental study on the oxygen discharge of pressurized nitrogen.