This review is intended to summarize the status and the open issues in the studies of boiling in saturated superfluid helium under microgravity condition. Superfluid helium has been utilized even in microgravity for cooling detectors and mirrors onboard satellites. Superfluid helium is called a quantum fluid that has many characteristic features. The heat transfer mechanism in superfluid helium due to internal convection is much different from that in ordinal fluid even in microgravity. In this review paper, the fundamental properties of superfluid and the effect of gravity upon boiling in superfluid helium will be described, and several microgravity experiments results will be reviewed. To conclude, the several numerical studies and some open issues will be summarized.
In the future exploration for deep space, cryogenic fluid will be used as propellant and oxidizer for spacecraft. The increasing of tank pressure is caused by boil off gas (BOG) induced by heat leakage into the tank from the surrounding environment. Reducing of BOG is derived from destroy of thermal stratification of a bulk liquid in the tank. Therefore, development of Thermodynamic Vent System (TVS) for the purpose of prevent of loss of cryogenics propellant in future space system is needed. TVS combining jet mixing, spray, and heat spot removal by forced cooling using Electro-hydro-dynamics is under consideration by authors. Destroying thermal stratification without venting by using subcooling mixing jet will be developed for a key technology of TVS. In this paper, the behavior of the mixing jet by visualization method and description about the motion of the jet with a simple one-dimensional model without heat transfer is reported. In our simple dynamic model, a single sphere droplet as the tip of the jet is assumed and an equation of the motion is applied for the droplet. The results of analysis model and experimental data taken by shadowgraph system are compared. In addition, microgravity experiment is performed, and flow behavior in microgravity is described.
Fluid behavior in microgravity (µg) is different from in ground gravity since surface tension and wetting are dominant in µg conditions. In propellant tanks for artificial satellites and future on-orbit spacecraft, sloshing due to disturbance and settling behavior from changes in acceleration have to be understood for the design of the propellant supply system and attitude control system. In this paper, we observed sloshing behaviors in cylindrical containers in µg conditions created by a drop tower facility. In order to investigate the effects of the contact line velocity on dynamic contact angle, we measured dynamic contact angle using a capillary tube. CFD analysis introducing Cox’s equation in consideration of capillary experimental results were also conducted and these results were compared with µg experimental results. Regarding the experimental results, the diameter of the test tank, excitation acceleration, and kinematic viscosity were found to have a significant effect on sloshing behavior in a µg condition. Regarding the comparison between the CFD analysis results and the experimental results, there was a slight difference in the wave shape and the time required for the liquid to reach the top of the test tank. Conversely, there was a qualitative agreement between the fluctuation period and the approximate shape of the liquid surface over time.