Rapid melt growth of Ge was conducted by using NASDA (National Space Development Agency of Japan) TR-IA sounding rocket. To understand the growth, the computer simulation was carried out and it was found that the shape of the solid liquid interface will take at first a strong convex shape to the melt. However, the interface during the growth will be quickly recovered to have a nearly flat surface. A single crystal was grown with the velocity of 0.6cm/min which was measured in-situ by CCD camera. The longitudinal cross section of the space grown sample showed the melted and unmelted interface was strongly convex to the melt which agrees with the computer simulation. The dislocation density in the regrown crystal was 105 - 106 /cm2 and this was explained by assuming the presence of strong stress due to the sticking between the melt and the quartz wall.
The response of bubble ensembles to periodic accelerations was evaluated using BDH (Bubble Dynamics Handling) system designed for TR-IA #2 rocket launched in August 1992. Periodic accelerations with a low-level stationary acceleration were generated by the newly developed piezoelectric actuator. The time dependent function of g-jitter was formulated as:
g(t)=0.60 X 10―4g+(2.l X 10―3 g) X cos(Z 1r X 1.4 7Hz X t).
The generated g-jitter is a model of residual gravity in space station. Bubbles of 2-5mm in diameter were injected into silicone oil using a motor-driven syringe. The recorded behavior of bubbles showed sensitivity to periodic accelerations. Various kind of hydrodynamic interactions were confirmed.
1) Response to background residual gravity
2) Response to periodic accelerations generated by piezoelectric actuator
3) Increase of hydrodynamic drag due to the oscillatory motion of bubbles
4) Hydrodynamic interactions between bubble and wall
5) Hydrodynamic interactions between bubbles
The accelerations of the hydrodynamic forces were evaluated at an order of 10―5g. Thus the phenomena cannot be observed under normal gravity. The results indicate the valuable use of the microgravity environment for the study of bubble dynamics under controlled accelerations.
There has been an increasing interest in understanding the underlying mechanisms and obtaining accurate data on mass and heat transport in liquid. All terrestrial experiments are distored by gravity-driven flow, which makes it virtually impossible to carry out precise measurements. In the transparent organic crystal of succinonitrile-acetone binary alloy, transient behavior of unidirectional dissolution is directly observed in order to precisely determine diffusion-controlled mass transport properties in microgravity environment.
In order to study the microstructure of oscillatory Marangoni convection, and to clarify the relation between the temperature fluctuation in the interior of the liquid bridge and that inside a solid/liquid boundary layer, Marangoni convection in a liquid bridge of silicone oil was observed during 6 minutes microgravity condition by TR-IA sounding rocket. The experimental results were compared with the unsteady numerical simulations. At the first stage with small temperature difference. laminar Marangoni convect10n was observed. At the second stage with large temperature difference, oscillatory Marangoni convection was observed. The amplitude of both velocity and temperature fluctuation increased as time passed. The frequency of these fluctuation was about O.lHz. The amplitude of temperature fluctuation was decreased inside a solid/liquid boundary layer.
A binary Li2O-SiO2 glass containing CoO (1 mol%) was melted in an image furnace under microgravity aboard the rocket (TR-IA #2) and the super cooling phenomena and crystallization process were observed. The sample was fixed at the focus point with the supporting base and connected with thermocouple for measuring the supercooling and crystallization temperature (1201°C). Supercooling and exothermic phenomenon by crystallization were observed during the cooling process and supercooling temperature from melting temperature was 57°C. Crystallization occurred, with exothermic change and initial crystallization took place at the contact point of molten glass and supporting base and its crystal growth speed was 0.26cm/sec under microgravity. According to results of X-ray diffraction analysis, crystals was identified as Li2SiO3.
Behavior of a candle flame and gas jet diffusion flames under super gravitational fields was experimentally investigated. To realize super gravitational fields in a laboratory, a spin tester was employed. The influences of super gravity on flame length and width were measured by using a video recording system installed on the spin tester. It was found that the flame length and width of a candle or a jet flame decreased with an increase in gravity. It is explained by an increase of natural convection flow that causes a higher combustion rate of a laminar diffusion flame. Furthermore, the results showed that a decrease in length of the candle flame appeared more obviously than that of the gas diffusion flame. It suggests that a super gravitational field also influenced the fuel supplement through a candle wick.
A numerical simulation code of the unsteady convection-solidification combined process was developed to study solidification processes under microgravity. Boundary fixing method was applied for the method to get a solution. Time evolutions of solid-liquid interface, isotherms, and flow patterns of unidirectional solidification of succinonitrile were calculated for several gravity vectors and boundary conditions to obtain the informations about the following cases: (1) solidification when changing gravity vector, (2) solidification for endothermic boundary condition and (3) solidification when changing gravity level. It was demonstrated that the interfacial patterns varied with time, boundary condition, gravity direction and gravity levels. It was found that the numerical results well explained experimental ones for both interfacial patterns and average solidification rates.