THERMOCAPILLARY CONVECTION FEATURE FROM LAMINAR TO OSCILLATORY FLOW UNDER NORMAL GRAVITY AND MICROGRAVITY CONDITIONS (DROP SHAFT EXPERIMENTS)

摘要

We report experimental observations in a liquid bridge with cylindrical free surface heated from above. From normal gravity experiments, it is clarified that the critical temperature difference (ΔTc) (at which point laminar thermocapillary convection would change to oscillatory thermocapillary convection) is very sensitive to (V/Vo; liquid bridge volume/cylinder volume between upper and lower disk). In case of short liquid bridge, there was discontinuity of the boundary line because of very high critical temperature difference (the gap region) in the specific V/Vo range was observed. As liquid bridge length increase, discontinuity of the boundary line was not observed, however in the specific V/Vo range, high critical temperature difference region were still observed. We defined this region as stable region. The shorter the liquid bridge length is, the wider the gap or stable V/Vo range is observed under 1g condition. Drop shaft experiments were carried out using these results obtained under 1g condition. This gap region disappeared in the case of shorter liquid bridge (L = 1.6-2.5 mm of liquid bridge length) under the μg conditions. This means that the 1g critical temperature difference is larger than that of mg. While, in the case of longer liquid bridge (L = 3.3 mm), it is observed that there are specific ranges of V/Vo and ΔT where the convection is steady under mg condition but oscillatory under 1g condition. The various temperature oscillatory features can be defined with 5 oscillatory features; Periodic state (P), Quasi Periodic state (QP), Period Doubling state (P2), a mixture of the Period Doubling state and Quasi Periodic state (P2+QP), and Chaotic state (C ) on a ΔT-V/Vo plane diagram for 1g. After gravity was changed from 1g to mg conditions, various oscillatory state change to only periodic state. The oscillatory state was seemed to be disturbed by the gravity effect.