Thermocapillary convection is studied in two immiscible liquid layers with one free surface, one liquid/liquid interface, and differential heating applied parallel to the interfaces. An analytical solution is introduced for infinite horizontal layers. The defining parameter for the flow pattern is λ, the ratio of the temperature coefficient of the interfacial tension to that of the surface tension. Four different flow patterns exist under zero gravity conditions. ‘‘Halt’’ conditions which halt the fluid motion in the lower encapsulated liquid layer have been found. A numerical experiment is carried out to study effects of vertical end walls on the double layer convection in a two-dimensional cavity. The halt condition obtained from the analytical study is found to be valid in the limit of small Reynolds numbers. The flow in the encapsulated liquid layer can be suppressed substantially.
Eutectic gallium-indium is studied in a horizontal Bridgman furnace geometry. Differential temperature gradients are applied to solidify and melt the alloy while observing in-situ the interface morphology and the chemical segregation in the melt and in the solid as well. Upon cooling, a wedge-type indiumrich mushy zone develops at the cold wall. The melt is initially stirred by convective flow. After solidification starts the roll cell recedes to be replaced by a chemically layered conductive melt that eventually solidifies with rather uniform eutectic structure. Upon re-melting, the morphology of the interface adopts a profile that is predetermined by the original solid structure. Those patterns, as well as the flow, are different from single element solid melting experiments and have yet to be modeled. Under high thermal gradient the convective flow mixes the binary melt and the visualized density pattern eventually becomes that of a homogeneous melt.
Free convective;flow was investigated experimentally in a variety of slender vertical gaps of large horizontal extent. Temperature fields were visualized by holographic real-time interferometry, and local temperatures measured by thermocouples at the lower and upper boundaries of the gap as well as in the fluid. The critical Rayleigh number at the onset of convection was determined for different gap geometries (aspect ratios) and different thermal properties of the sidewalls and the fluid. For supercritical Rayleigh numbers, bounds of stability of steady-state two-dimensional convection were determined for transient and oscillatory states of the flow. The oscillatory flow is caused by an instability of the thermal boundary layers at the lower and upper boundaries, as evidenced by direct interferometric observation and by the measured period of oscillation depending on the Rayleigh number. The oscillations of the flow exhibit a periodic behaviour at the threshold from steady to unsteady flow. However, the periodic character of the oscillations is superseded by stochastic features im- mediately beyond the threshold Rayleigh number.
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