Oscillatory thermocapillary convection in a liquid bridge: Part 2—Drop shaft experiments

Abstract

To study the effects of gravity on thermocapillary convective phenomena, observations were made of thermocapillary convection in different lengths of silicone oil liquid bridge that simulated a half floating zone under normal gravity (1 g) and microgravity (μ g) conditions in a free-falling capsule. Thermocapillary convection is dominant at the interface. However, in bulk, gravity has an effect on the velocity field. The experiments clarified the effects of gravity on the velocity distributions of laminar thermocapillary convection. The onset of temperature oscillation was observed in the transition from 1 g to μ g conditions in free-fall. In the case of a short liquid bridge, the temperature showed oscillation in the gap or stable region after the start of free-fall. The critical temperature difference under μ g conditions therefore appears to be smaller than that under 1 g conditions. In the case of a long liquid bridge, temperature oscillation disappeared during free-fall, and the critical temperature difference under μ g conditions appeared to be larger than that under 1 g conditions. Analysis of the temperature signals revealed six types of temperature state. Various temperature oscillatory states (S, P, P2, QP, P2+QP, C) were obtained on a Δ T− V/ V o plane under 1 g and μ g conditions. Under μ g conditions, all temperature oscillatory states exhibited only the Periodic state.