Visualization of gas fl.ow in a thermal chemical vapor deposition (CVD) furnace under microgravity (µg) has been studied. The sample gas of the experiment is N2 or He and gas pressure is 500 Torr. For visualization, tracer particles (Ti02) are injected into the thermal CVD furnace with the sample gas. In order to explain the tracer pattern, numerical simulation is performed employing a finite volume method. The results showed that N2 gas flow under µg is the forced convection without the natural convection. This result agrees with the numerical simulation. The He gas flow under µg is quite diffrent from the numerical simulation. It is considered that notable thermophoretic transport of the tracer particles occurs, because the He gas has high thermal conductivity which realizes large thermal gradient in entire fluid path.
In this study, we discuss the reliability of surface tension which is determined by digital video image processing of a sessile drop with using computer. The image of a sessile drop of pure water formed on a teflon plate was recorded on a digital video tape and converted into digital data of profile by using the technique of digital image acquisition and processing. The segmented drop image is fitted with numerical solution of theoretical equations by performing a least-squares comparison to determine a surface tension. The measurements was repeated many times for various size (diameter of 3 mm-35 mm) of drops. At the drop range from 12 to 17 mm, most results were agreed well with the international standard value (IAPS) of surface tension of water. We found the water drop of 12-17 mm is suitable for surface tension measurement and this range corresponds to Bond number of 20- 150.
A fundamental study on spray combustion was carried out by using microgravity conditions produced by the fifth TR-IA rocket. Very lean methanol-air premixtures were ignited by a hot wire to investigate the behavior of the ignition process of fuel vapor-air mixture which exists in an ethanol spray. Shadowgraphy and shearing interferometry were employed to observe the ignition process. Experiments were performed three times in six minutes of microgravity conditions. Since the amount of fuel charged into a combustion chamber became unknown, quantitative analysis of the experimental data could not be made. However, it was observed that a flame kernel grew spherically up to about 14 mm in diameter in very lean premixtures. These detailed data on the ignition of lean premixtures have never been obtained under normal gravity conditions. From the results of simple numerical calculations, it was suggested that a flame kernel which does not transit to a self-supporting flame is sustained steadily by the mass diffusion and the heat from the heat source.
The experiment of capillary gap penetration of molten Ag-Cu-Li alloy into gaps of stainless steel sleeve joint under microgravity was carried out using the sounding rocket TR-IA#5. The purpose of this experiment was to understand capillary penetration phenomena under microgravity in order to establish a guideline for the decision of brazing process parameters in space environments. The experimental results showed that gap penetration of molten alloy is very sensitive to temperature distribution during heating and brazing under microgravity is not so easy as it was thought before.
The shear cell method is a diffusion coefficient measuring method which facilitates measuring diffusion coefficient accurately. The shear cell method was developed in this investigation. A preliminary investigation using fluid simulation was performed to determine the best shear cell cartridge design. Diffusion coefficient of a germanium semiconductor melt was measured in microgravity environment using this shear cell cartridge. The experiment temperature was 1200°C, the experiment time was 357 sec. These experiment conditions were selected to fully utilize the microgravity environment in a sounding rocket. The concentration distribution of the experiment sample was measured by SIMS after flight experiment. The diffusion coefficient was calculated to be 1.94 x 10- 4 cm2 / s from the results. Technological development of shear cell method was thus achieved in this experiment.
To obtain the temperature dependence of the diffusion coefficient for Pb0.75Sn0.25Te, diffusion experiments were conducted during space shuttle mission MSL-1, launched in April and July 1997. The diffusion coefficient were measured from 1223 K to 1573 K with a diffusion couple of Pb0.8Sn0.2Te and Pb0.7Sno.3Te under controlled cooling to avoid having segregation influence solidification. MSL-1 data was much smaller than ground data, particularly at high temperature, even though almost the same value was obtained near the melting point. Temperature dependence was determined from the MSL-1 experiment as (6.7 x 10- 9 m2/ s) x (Tl Tm) 2· 6 , Tm is the melting point.
Diamond thin-film was synthesized under microgravity using Japanese free-flyer (SFU, Space Flyer Unit) launched in March 1995. This program achieved the first space-based production of diamond by Chemical Vapor Deposition (CVD). The DC plasma excitation method was applied to hydrogen-methane mixed gas within the pressure range of 2.66~6.55 X 103 Pa. Remarkable differences of the electron temperature of hydrogen plasma were confirmed between the microgravity and the on-ground experiments. The intensity ratio of CH/Ha measured by emission spectroscopy was found as a sensitive indicator of gravity effects on gaseous chemistry and diamond quality.