Oscillatory Marangoni convection in a silicone oil liquid bridge was observed under normal gravity conditions. The effect of physical properties and operational variables on the criti cal temperature difference at which point laminar Marangoni convection would change to the oscillatory Marangoni convection was discussed. The oscillatory features of Marangoni convection were also discussed. As the temperature difference increased, both the amplitude and the frequency of temperature fluctuation increased. Under the same temperature differences, as the distance between the disks increases, the amplitude also increases but frequency decreases. The amplitude of temperature oscillation decays in a boundary layer.
In order to study the effect of gravity on Marangoni convective phenomena, Marangoni convection in a silicone oil liquid bridge that was simulating a half floating zone was observed under 1 g and µg conditions. The effect of gravity on the velocity distributions of laminar Marangoni convection was clarified. Marangoni convection is dominant at the interface; however, in bulk, gravity has an effect on the velocity field. The onset of temperature oscillation was observed under µg while a capsule was freefalling. The fundamental frequency of temperature oscillation under µg conditions was smaller than that under 1 g conditions when the non-dimensional liquid bridge volume was V /Vo=73.8 vol%, Fundamental frequency of temperature oscillation under 1 g conditions, however, was smaller than that under µg conditions when the liquid bridge volume was V /Vo=88.1 vol%. From these results, we can see that the fundamental frequency of temperature oscillation between under 1 g and µg conditions depends on the liquid bridge volume. Temperature oscillation amplitude of under µg was smaller than that under 1 gin both of the V /Vo=73.8, 88.1 vol%.
This paper will clarify the effect of temperature difference between hot disk and cool disks (L1T), and non-dimensional liquid bridge volume (V /Vo) on the transition process from periodic temperature oscillation to chaotic temperature oscillation under 1 g and µg conditions. As temperature differences between the two disks that were suspending a liquid bridge increased, period doubling cascade was observed (D=5 mm, L=2 mm, V /Vo=90 vol %, v= 1 cSt). The regime of steady and oscillatory states was clarified on the L1T-V /Vo plane
under 1 gandµgconditions (D=5 mm, L= 1.6 mm, v=2 cSt). The discontinuity of the boundary line between the steady and oscillatory states was observed at approximately V /Vo=70- 80 vol% under 1 g conditions, while under µg conditions the onset of temperature oscillation was observed at approximately the same range: V /Vo=70-80 vol%. From these results, the critical temperature difference at which the steady state would change to the oscillatory state under µg conditions appeared to be smaller than that under 1 g around V /Vo=70-80 vol%; that is, gravity seemed to be one of the factors in temperature field stability for Marangoni convection. By comparing the regime of periodic and quasi-periodic states on the L1T-V /Vo plane with 1 g and µg conditions, gravity appeared to be one of the instability factors that is related to the transition process from a periodic state to a quasi-periodic state.
lnterfacial stability under microgravity is studied in drop shaft facility at MG LAB in Gifu-prefecture . Breake-down wave-lengths of planar interface and tip radii of curvature of the critical dendrite grown in microgravity are measured , and it is shown that the wave-lengths and the radii of dendrite become larger than those grown on the earth (1G). [Keyword] interfacial stability, wave-length of perturbation , tip radius of dendrite
We investigated thermal energy transfer near the critical point of xenon. We introduced thermofluid dynamic equations and carried out a linear analysis. It has been found that temperature propagates as acoustic waves rather than molecular diffusion near the critical point.
We analysed thermal energy transfer near the critical point of xenon by the molecular dynamics method. The heat transfer mode is investigated and compared with a macroscopic analysis. It has been found that temperature propagates as acoustic waves near the critical point, which agrees with the macroscopic analysis.
The classical nucleation theories by Volmer and Weber, by Becker and Doring, and by Turnbull and Fisher, and its extension to alloy systems by Thompson and Spaepen have been shortly summarized for the better understanding of nucleation phenomena in the containerless solidification of metals and alloys. Time-dependent nucleation rate is also discussed in terms of transient time necessary for cluster distribution to attain an equilibrium one. Some formulas and equations to be used in the calculation of the degree of undercooling in the experiments of metals and alloys are described in the text.
Difficulty in experimental study on high-pressure droplet combustion is due to soot formation and strong effect of natural convection. These prevent the researchers from detailed measurements. The authors, therefore, started the study on high-pressure droplet combustion in microgravity environment, by using non-sooting methanol fuel. To advance the activity in this research area, LCSR (Laboratoire de Combustion et Systems Reactifs; Research director, I. Gokalp.) of CNRS (Centre National de la Recherche Scientifique) and the laboratory of the authors started collaborating in 1996. Recent results of the parabolic flight experiments, which were done in France, are briefly introduced here. servations were made of the burning behavior of a methanol droplet under high pressure and microgravity conditions, during the parabolic flights of NASA KC135. The droplet diameter was measured from the backlighted droplet images recorded on high-speed video system. The burning rate constant of the droplet, which was derived from the time history of square of droplet diameter, increased continuously with increasing ambient pressure even at pressures higher than its critical pressure. This result is not in agreement with that reported previously by another researcher. The cause of this disagreement remains unexplained now. To make clear the above cause and to explicate the mechanism of high-pressure droplet combustion, the authors are carrying out experiments in cooperation with LCSR.