This paper reports the overview of Dynamic Surf project conducted in the Japanese Experiment Module Kibo on board the International Space Station (ISS), especially focusing on the experimental conditions, the measurement systems, and the g-jitter effects. Oscillatory Marangoni convection in the liquid bridge is associated with oscillatory motion of the liquid-gas interface due to velocity oscillation inside the liquid bridge, where such a motion is called dynamic surface deformation (DSD). The present project aims at understanding the DSD effect in the transition mechanisms of temperature gradient-driven Marangoni convection in large-scale liquid bridges of high-Prandtl-number fluids through the long-term microgravity experiments on board the ISS. A series of microgravity experiments have been conducted in the period from September 2013 to November 2016 to understand the instability mechanisms and the role of DSD in Marangoni convection.
In order to use hydrogen as a fuel for spacecraft propulsion system, utilization of aluminum and water reaction system is considered. Liquid-gas separation is necessary for water tank in this propulsion system. The purpose of this study is to confirm the applicability of water to the surface tension liquid acquisition mechanism in tank by improving wettability using a silica coating. It was demonstrated that silica coating could improve the wettability of water against metallic material applied to practical tanks. By the microgravity experiment using drop tower facility, it was confirmed that water in tank could be acquired on the liquid outlet by vane device with silica coating.
This study investigated the flammability of the fire-resistant material ethylene-tetrafluoroethylene (ETFE) as insulation for copper wires under different flow velocity and gravity conditions. The limiting oxygen concentration (LOC) of flame spreading horizontally over the sample was investigated at external opposed flow velocities ranging from 0 to 200 mm/s under normal gravity (1g0) and microgravity (μg0). The LOC under μg0 showed a U-shape, which has been reported in previous studies. A minimum LOC of approximately 26% was found at external flow velocities ranging 50–100 mm/s. An expanded heat balance model and radiation number for wire combustion (𝑅𝑟𝑎𝑑,𝑤𝑖𝑟𝑒) were proposed considering the heat conduction through the copper core, which is a notable feature of wire combustion. The U-shaped LOC curve was qualitatively explained in the low flow velocity region by this model and in the high flow velocity region by the Damköhler number. We also compared the LOC trend of ETFE with that of polyethylene (PE)-insulated wires reported in a previous study and demonstrated that the drop of LOC in ETFE was much larger than that of PE when the gravitational condition was changed from 1g0 to μg0 (∆LOC). This large difference was explained by two factors. First, the rate of change of flame temperature with an increasing oxygen concentration is small at high oxygen concentrations. Second, the increase in heat input through the copper core owing to gravity change was larger for ETFE than for PE because of the difference in the rate of change in flame length along the copper core.
To understand behavior of molten core materials is an urgent issue to investigate the progression of a core meltdown accident in nuclear power plants. Zirconium (Zr) based alloys have been widely used as nuclear fuel claddings and structural materials in the nuclear power plants. Since the typical atmosphere during most accident scenarios is steam, Zr liquid containing significant amount of O (Zr-O liquid alloys) will be generated in the case of the core meltdown accident. In this study we aim to provide thermophysical properties of Zr-O liquid alloys. To avoid a difficulty in measurement due to high melting point and high reactivity of Zr liquid, electrostatic levitation technique was employed for the measurement. Zr-O alloys with nominal compositions of Zr0.9O0.1 and Zr0.8O0.2 were prepared from powder Zr and ZrO2 by solid-state reaction. The oxygen composition was evaluated by thermogravimetric analysis. The measured viscosities of Zr-O liquids are higher than those of Zr liquid (experimental) and ZrO2 liquid (calculated), which indicates that the composition-dependent viscosity may have maxima in Zr-O liquids.