Investigation On The Thermal Dynamic Characteristics Of The Liquid Oxygen In Storage And Transport

The cryogenic storage tank takes key roles in storing and supplying fuels for rockets,and thus research on the thermal dynamic characteristics of the cryogenic fluid in storage and transport are highly valuable.In this research,the thermal dynamic characteristics of the liquid oxygen in a storage tank are studied through 3D numerical simulation,and the main work is focused on the following,(1)In the cryogenic tank,temperature distribution of the stored liquid oxygen is closely related to the thermal state,such as the state of overheat,and in real working conditions of the tank,the working fluid is usually charged in the state of overheat.Therefore,thermal stratification of the overheated liquid oxygen is investigated through CFD simulations of a 2D axisymmetric model.The results indicate that temperature of the overheated liquid oxygen rise gradually from the liquid-gas interface to the bottom of the tank.(2)The thermal dynamic characteristics of the overheated liquid oxygen in the tank are studied through 3D numerical simulations under the normal pressure and pressurization stage.The results show that the lowest temperature occurs at gas-liquid interface because of the initial overheating.Moreover,the heat convection takes the main role for the heat transfer of the liquid oxygen and the thermal stratification is not obvious.When the exhaust valve is closed,pressure of the ullage area increases and the liquid oxygen becomes super-cooling.The temperature decrease gradually from liquid-gas interface to the tank bottom and the heat conduction takes the main role for the heat transfer of the liquid oxygen,leading to the obvious thermal stratification in the tank.At the end of the opening stage,the liquid oxygen evaporation rate is 0.022kg/s,0.025kg/s and 0.027kg/s under surrounding temperature of 253 K,273K and 313 K respectively,while the evaporation rate becomes 0.0014g/s,0.0019g/s and 0.002g/s after the valve is closed.(3)At the state of pre-pressurization of the liquid oxygen in the tank without discharge,the evaporation rate at the gas-liquid interface is fluctuating around 0.0126kg/sand the average boiling rate reaches 0.086kg/s.At the state of discharge,the high temperature pre-pressured gas is ejected to the ullage area through the diffuser,and the liquid level remains stable decrease.In the aviation period,the temperature decreases from the gas-liquid interface to the bottom,and the lowest temperature of the gas-liquid interface occurs at the beginning to be 89.50 K,the highest temperature occurs at the time of 185.6s to be 93.87 K.At the end of the aviation,the interface temperature is 90.44 K.(4)The phase-transition model of bubble growth was built to simulate bubble growth process in pool boiling.From the simulations,diameter of the oxygen departure bubble is closely related to the Ja number and the gravity(g-1/3),and the departure frequency is also related to the gravity(g-0.5).The results also indicate that the circular bubble moves upward inline after departure.(5)Base on the CFD simulations,a method to measure the contact angle of the cryogenic fluids is proposed.For the method,the maximum wetting diameter is directly measured and then the contact angle is deduced.The method is validated through a measurement of water,and a test instrument is further proposed and designed.