Oscillatory thermocapillary convection in a liquid bridge: Part 1—1 g Experiments

Abstract

An empirical study was conducted to investigate convection in a silicone oil liquid bridge of dimensionless volume V/ V o between hot and cool disks under both normal gravity (1 g) conditions and under microgravity (μg) conditions in free-fall. The study explored the influences on the critical temperature difference (Δ T c) at which thermocapillary convection changes from steady to oscillatory, and on the process of transition from periodic to chaotic thermocapillary convection. This paper is divided into two parts. Part 1 (this part) describes the experiments conducted under normal gravity conditions, and part 2 describes experiments under μg conditions in free-fall. The results of the study indicate that Δ T c is very sensitive to V/ V o. Very high critical temperature difference ranges (the gap or stable range) were examined over the V/ V o range. In cases where V/ V o is larger than the specific V/ V o range, it was found that Δ T c decreases with increasing V/ V o. Conversely, where V/ V o is smaller than the specific V/ V o range, Δ T c increases with increasing V/ V o. The study also clarified the effects of the kinematic viscosity of the working medium. These findings suggest that the striations of grown crystals can be controlled by varying the volume of the melt. Five types of temperature oscillatory phenomena (P, P2, QP, P2+QP, and C) were identified and shown on a Δ T– V/ V o plane diagram under 1 g and μg conditions. Moreover, the velocity pattern in a transverse cross-section of the liquid bridge, the critical condition for the onset of oscillation, and simultaneous measurements of three-dimensional flow pattern and temperature were obtained under normal gravity conditions. The findings of these experiments may be useful for establishing techniques for controlling thermocapillary convection when semiconductor or opto-electronic crystals are grown by the floating zone method under 1 g and μg conditions.