Thermocapillary instabilities in half zone liquid bridges of low Prandtl fluid with non-equal disks under microgravity

Abstract

Thermocapillary convection and its stability are of particular importance during the floating zone crystal growth process. In this paper, three-dimensional (3D) transient numerical simulations are conducted to study the onset and general features of thermocapillary instabilities in half zone liquid bridges of low Prandtl fluid (Pr = 0.01) with non-equal disks under microgravity. The effect of disk radius ratio on the critical conditions is investigated. The results reveal that both the first critical Reynolds number Rec1 and the second critical Reynolds number Rec2 are sensitive to the disk radius ratio. However, for a liquid bridge with fixed length and volume, varying the disk radius ratio does not change the critical azimuthal wave number of the first bifurcation, as well as the critical oscillation mode of the second bifurcation. Characteristics of the 3D steady thermocapillary convection and the 3D oscillatory thermocapillary convection are presented. For the supercritical state at Re = 1.2Rec1 after the first bifurcation, the flow is 3D steady. The deviations between the amplitudes of azimuthal flow in liquid bridges with different disk radius ratios are insignificant. For the supercritical state at Re = 1.2Rec2 after the second bifurcation, the flow is 3D oscillatory. The oscillating frequency decreases with disk radius ratio. The oscillating frequency in a liquid bridge with a convex free surface is higher than that in one with a concave free surface.