Osamu Kawanami

Flow and heat transfer on cryogenic flow boiling during tube quenching under upward and downward flow

The gravity effects on quenching of tube by cryogenic fluids for the development of cryogenic fluid management on orbit are studied. In this paper, the effects of the tube diameter, the flow directions, and the mass velocity on the tube quenching using liquid nitrogen are investigated systematically in the terrestrial conditions. The experiments are performed by the mass velocity between 100–600 kg/m2s in downward and upward flow directions by using three difference inner diameters of the transparent heated tube (7, 10, 13.6 mm) for measuring fluid behavior observations and heat transfer measurements simultaneously. The results indicate that the difference between the minimum heat fluxes under downward and upward flow conditions increased as the mass velocity increased. These characteristics of heat transfer were caused by filamentary flow pattern that was found in only downward flow and high mass velocity conditions.

Experiment on nucleate pool boiling in microgravity by using transparent heating surface ? Analysis of surface heat transfer coefficients

Investigation of mechanisms in nucleate boiling under microgravity conditions is essential for the development of the cooling systems handling a large amount of waste heat. A transparent heating surface with multiple arrays of 88 thin film temperature sensors and mini-heaters was developed for the clarification of boiling heat transfer mechanisms in microgravity. To investigate gravity effects on the microlayer behaviors and corresponding local heat transfer coefficients, images of liquid-vapor behaviors underneath attached bubbles and local heat transfer data were simultaneously obtained in microgravity pool boiling. The present paper reports the analysis of the data measured during the ESA parabolic flight campaign. It was found that the liquid-vapor behaviors were strongly affected by the direction and the level of residual gravity. Various patterns of liquid-vapor behaviours and corresponding enhancement or deterioration of the heat transfer are observed.

Gravitational Effects on Carbon Nano‐Materials Synthesized by Arc in Water

The “arc‐in‐liquid” method is a simple and inexpensive technique for the synthesis of carbon nanotubes and related nano‐materials. In this paper, we report on the synthesis of carbon nanotubes by means of the arc‐in‐water method under microgravity and normal gravity conditions. The heat of convection and two‐phase flow caused by the arc plasma are suppressed under microgravity, so the heat and fluid flow are stabilized under such conditions and a single huge bubble is generated around the electrodes. From the images captured during the experiment of the arc‐in‐liquid method, it can be observed that the bubble contained a layer of water vapor at the gas–liquid interface under microgravity conditions, and this layer blocked the carbon vapor reaching the liquid phase. Owing to this unique phenomenon, it was determined that the synthesis of carbon nanotubes by the arc‐in‐water method is strongly affected by gravity.

Flow boiling in transparent heated microtube

In the present study, a detailed investigation of flow boiling in a transparent heated microtube was performed. The transparent heated tube was made by electroless gold plating method. The enclosed gas-liquid interface could be clearly recognized through the tube wall, and the inner wall temperature measurement and direct heating of the film were simultaneously conducted by using the tube. The experimental conditions were: tube diameter 1 mm, mass velocity 100 kg/m2 s, inlet liquid sub-cooling 20 K and heat flux up to 384 kW/m2 in the open system. Flow fluctuation was minimized by employing a twin plunger pump. Among our experimental results, we observed a high-frequency fluctuation of the inner wall temperature and a sharp peak for the heat transfer coefficient with high heat flux conditions, which have not been reported in previous experiments. This abrupt increase in the heat transfer coefficient coincided with a slight rapid axial growth of an elongated bubble found in the observation of the flow behavior. Hence, in low heat flux conditions, the fluctuations of temperature and heat transfer coefficient are strongly suppressed except for the instances when there is no bubble in the tube.Copyright

Simulation on Solar Hydrogen Generation With PEM Cells and Solar Modules

A simulation of solar hydrogen generation with solar modules and PEM cells in consideration of the solar module temperature for one year was carried out using our measured weather data. The optimal combination of the number of PEM sheets and solar modules was determined and hydrogen conversion efficiency was estimated. Solar module temperature was predicted from the measured data of global solar radiation, ambient temperature, and wind velocity. The current-voltage (I-V) curves of a solar module in arbitrary states were calculated from the (I-V) curves in the reference states using conversion equations (JIS C8913).Copyright

A microgravity experiment of the on-orbit fluid transfer technique using swirl flow.

Abstract:  The cryogenic fluid transfer technique will prove useful for flexible and low‐cost space activities by prolonging the life cycle of satellites, orbital transfer vehicles, and orbital telescopes that employ cryogenic fluids, such as reactants, coolants, and propellants. Although NASA has conducted extensive research on this technique to date, a complicated mechanism is required to control the pressure in the receiver tank and avoid a large liquid loss by vaporization. We have proposed a novel fluid transfer method by using swirl flow combined with vapor condensation facilitated by spray cooling. This technique enables gas–liquid separation in microgravity and effectively facilitates vapor condensation without any special device like a mixer. In addition, since the incoming liquid flows along the tank wall, the tank wall would be cooled effectively, thereby minimizing the liquid loss due to vaporization. In this paper, the influence of the number of inlet points, fluid velocity at the inlet, fluid type, and boiling condition on swirl flow under microgravity conditions is investigated experimentally. The results indicated that the new fluid transfer technique using the swirl flow proposed by us is effective for cryogenic fluids that generally exhibit low surface tension and good wettability. In addition, it is possible to apply this technique to the real system because the swirl flow conditions are determined by the Froude number, which is dimensionless. Thus, the fundamental technique of fluid transfer by using the swirl flow under microgravity conditions was established.