Speaker
Description
As mankind expands its sphere of activity into outer space, such as the moon and Mars, it is expected that cryogenic fluids management technology in the environment that its gravity acceleration differs from that on the earth will be increasingly required. In general, when developing equipment that uses cryogenic fluids, especially for use in space, it is extremely difficult to conduct experiments in the actual operating environment. Therefore, it is essential to use CFD or numerical models to numerically predict the fluid flow in the equipment. In this situation, this research mainly focusses on cryogenic fluid filling into tank. To predict the condition of cryogenic fluid tanks over a long period of time, a low-dimensional model that models the phenomena inside the tank is necessary. On the other hand, the simplest method that assumes that thermal equilibrium is established inside the tank is not suitable for predicting the pressure in the tank at the time of filling. Generally, in a tank that storing cryogenic fluids, there is liquid with a temperature lower than the saturation temperature, called subcooled liquid, at the bottom of the tank, gas and liquid with a saturation temperature near the gas-liquid interface, and gas with a temperature higher than the saturation temperature, called superheated gas, at the top of the tank, if the fluid in the tank is not mixed. This temperature distribution has a significant effect on the pressure inside the tank, and therefore, the temperature distribution inside the tank must be considered within the prediction model for more accurate prediction. This study aims to develop a tank filling model that can consider thermal non-equilibrium condition, and to enable numerical prediction of phenomena in environments where experiments cannot be easily conducted.
The tank model divides the interior of the tank into several layers, and layers are tracked in a Lagrangian manner, that allows to track easily the gas-liquid interface. Each layer exchanges heat with the tank wall and other layers and the temperature distribution inside the tank can be considered. The solver that calculates the layer properties is the same for single-phase and gas-liquid two-phase, which has the advantage that there are less “if” branches during the calculation. Since this model is a one-dimensional model, the computational cost is very small compared to CFD. It can analyze long-time phenomena that are difficult to predict with using CFD, in a sufficiently realistic time.
To verify the accuracy of the model, the results of the model calculations were compared with the results of ground tests. Numerical experiments were also conducted during the process of model validation to understand the phenomena inside the tank during filling. The results of the model validation showed that the pressure time history calculated by the model and that the test results were well matched, by using the amount heat absorption of the fluid to be filled, which has a significant influence on the tank pressure, from the test results. And more, it was revealed that the factors that have a large influence on the tank pressure are the heat absorption, the initial conditions, and the temperature distribution in the tank from the discussion about the experiment results and some numerical experiment using the model. In detail, the dominant factor is the initial temperature of the tank wall, which has a large heat capacity, for the initial stage, and is the temperature distribution in the tank after some time has passed. It is also revealed that the temperature distribution in the tank is greatly affected by the effect of the tank wall surface acting as a heat path to diffuse the temperature. Some of the effects of different gravity accelerations were also discussed.
