Existing studies of Marangoni convection are all concerned with the temperature gradient either parallel or vertical to the free surface. In the actual material processing, however, the temperature gradient may be inclined to the free surface. Thus, the Marangoni convection in a thin liquid layer with an inclined temperature gradient was investigated experimentally in the present study. The cellular motion which is well known in the Marangoni-Benard convection was observed over the whole surface at the early stage of the experiment. With elapse of time, the cellular pattern disappeared and a streak structure emerged. Four different flow patterns were observed depending on the magnitude of the vertical and parallel temperature gradients. Critical conditions for the occurrence of these flow patterns were obtained. Numerical simulation was performed and the cells and the streak structures were reproduced through the numerical analysis.
The study of -Double-layered Liquid Mass- under microgravity is undertaken in Tokai University. The DLM, in which the first spherical liquid mass is covered with the second liquid layer or shell, may be one of the promising material refining and processing schemes, where reaction occurs at all over the interface between the two liquid phases. This can be well applied to the container-free processes under microgravity. Experiments demonstrated that it is possible to produce the DLM in a plateau tank facility . The stability of DLM produced with silicone oil and water was carefully investigated. The fundamental factors to control the procedure were discussed with the change in the total interfacial energy for the agglomeration and rupture of DLM and the viscosity of constituent phases. The effect of applying ultrasonic waves on the separation of the two liquid phases was also discussed.
Temperature oscillation measurement and X-ray flow visualization in a half-zone molten silicon bridge were carried out under microgravity condition using the parabolic flight of a jet aircraft at a variety of oxygen partial pressures and under 1 G condition. A transition from non-periodic fluctuations to periodic oscillation was observed when oxygen partial pressure of the inlet was increased at the p nl••= 1.8 X 10- 5 MPa. It was found that the flow velocity decreased with increasing the oxygen partial pressure. The temperature oscillation mode transition and the Po-i dependence of the flow velocity clearly show that the temperature coefficient of surface tension decreased with increasing the oxygen partial pressure.
Under the microgravity environment , it is considered that thermal convection is suppressed. Therefore, diffusion becomes the main factor of material trans port . Thus it is expected that one can synthesize materials with fewer defects or unique structures and get new information about the growth mechanism of materials .
Diamond possesses superior properties, for example, high hardness, high thermal conductivity, high transparency, high electron and hole mobilities, and a wide bandgap . These unique properties suggest many potential applications. The conventional techniques for depositing diamond at low pressure utilize a flow of a hydrocarbon-hydrogen gas mixture with complicated gas tubing for introducing the reaction gas into a reaction chamber and evacuating reactant gas from it. For few years, one of us (YT) had been concentrated on developing completely closed diamond synthesizing system aimed for microgravity conditions. With our experiments, we successfully confirmed that diamond was synthesized with this completely closed system, and that this system was very suitable for mounting on large centrifuges and in spacecraft .
Preparation of micrometer-sized spherical particles containing Rhodamine 6G (R6G) has been investigated for the spherical cavity micro-laser . Using phenyl triethoxy silane (PTES) as a starting material, R6G-doped monodisperse spherical particles were prepared by the vibrating orifice technique . Processing is consist of two major processes: (1) Hydrolysis and polymerization of PTES and (2) Droplet formation from PTES oligomers by vibrating orifice technique. A cylindrical liquid jet (PT ES oligomer and R6G diluted with alcohol) passing through the orifice breaks up into equal-sized droplets by mechani cal vibration. Alcohol solvent of these droplets was evaporated during flying with carrier gas and subsequently solidified in ammonium water trap . For making smooth surface and good shaped particles, control of molecular weight of PTES oligomer was essential. R6G-doped hybrid spherical particles of 4~ 10 µm size of cavity structure were successfully obtained . The spherical particles were pumped by a second harmonic pulse of Q-switched Nd:YAG laser (532 nm wavelength) and laser emission peaks were observed at wavelengths which correspond to the resonance modes.
Experimental investigations are carried out about the combustion of new form of hybrid rocket propellants, in which oxidizer gas flows gap space in a fibrous fuel bed, under normal and micro gravity conditions. The new form of propellant has a potential to improve combustion efficiency and thrust level of hybrid rocket motors. Regression rates of fibrous strand fuels are measured with lower oxygen gas flow rates of near the combustion limit. Main results are in the followings: Gravity effects decrease with decreasing the oxygen gas flow rate until the effect almost diminishes near the combustion limit. In a certain range of oxygen gas flow rates near the combustion limit, the equivalence ratio keeps a constant value. The range of oxygen gas flow rates, in which equivalence ratio is constant, does not depend on the ambient pressure.
Opportunities to collect test pieces from various kind of bodies in space is increasing. In this study we obtained data required for design of a device which collects samples by shooting a small projectile onto the targeted bodies and concentrating ejected fragments through a funnel-shaped horn. We made a series of studies including experiments to investigate production of fragments at impact and motion of fragments reflecting inside the horn, capturing tests both in 1 G environment on the ground and under reduced gravity using an airplane. These investigations show that more than 40% of the ejecta from brick-like bodies can be caputured by this device.
The handling techniques of liquid (storage and transfer etc.) under micro-gravity condition are a key technology to construct an infrastructure of space transportation system. Especially, it is very important to make a measurement for the amount of liquid under micro-gravity condition and, for example, to know how much a fuel or cryogen is left in a tank . However, it is very difficult to measure the liquid amount in space because a liquid-gas system is not easily separated, rather mixed up under micro-gravity condition . In order to make an effective and low cost measurement system; the Helmholtz resonance is applied in this study . Water is used as test liquid and two different types of experiment are done in this study . One is without a liquid stabilization technique and the other is with a liquid stabilization technique that cylindrical sheets of metal mesh are set in the experimental cell. It is confirmed that the application of the Helmholtz resonance with the liquid stabilization technique is effective means to measure the amount of liquid under micro gravity condition.
A horizontally oriented glass pipe containing partially filled silicone oil or ethanol was dropped using the drop shaft facility of Japan Microgravity Center (JAMIC). The behavior of the liquid in the transient period from normal gravity to microgravity was observed with a CCD camera, and the velocity of the silicone oil flow was measured with a particle imaging velocimetry (PIV) based on the cross-correlation method . Just after the glass pipe was set in microgravity, the horizontal gas-liquid interface was deformed strongly and the liquid was transformed into liquid plugs. According to the velocity measurements and eye inspection of video images, the flow establishment time required to form the liquid plugs completely in the glass pipe was determined, and an empirical equation was derived for the flow establishment time.
Ignition characteristics of a fuel single droplet and a fuel droplet array which are exposed to very slow high
temperature airflow were studied for n-decane in microgravity field. In the droplet array experiment, five droplets with the same size were arranged horizontally at an equal spacing. Experimental results showed that ignition time has a minimum value at a certain airflow velocity and spacing. This result is explained by the competition between evaporation rate and chemical reaction rate . Also, according to OH emission image, it is observed that ignition occurs at wake region throughout all experimental conditions .
Any diamagnetic material has repulsive force against a gradient magnetic field. When this force is vertical and sufficiently strong to balance with the gravity, the material levitates at the stable position where the potential is minimum. Magnetic levitation is almost equivalent to microgravity condition and it is applied to containerless melt of glass materials. The advantages of this method are, 1) avoiding contamination from the container wall, 2) no thermal convection in the material, 3) formation of complete globe shape, 4) melt of material with melting point higher than that of crucible. The melt of glass is performed by using high magnetic field provided by a Hybrid Magnet and CO2 laser irradiation.