Abstract
A liquid bridge of molten tin was held between two stainless-steel rods to study thermocapillary convection in liquid metal. The experiment was conducted in a vacuum chamber in order to prevent oxidation. Molten tin was injected into the liquid bridge with a graphite syringe, which acted as a filter to keep oxide scum from entering the liquid bridge. The liquid bridge was 4 mm diameter by 4 mm height. The upper rod was kept at a higher temperature than the lower rod to induce thermocapillary convection in the liquid bridge. The dynamic Bond number Bo=0.26, suggesting predominance of thermocapillary convection over buoyancy convection. Temperature oscillation was detected by a thermocouple in contact with the free surface at its mid-height. Oscillation was observed when the temperature difference between the rods was increased to 18.8±1.5°C. The frequency of oscillation was 1.1±0.1 Hz and the amplitude of oscillation was about 0.1°C. This temperature difference corresponds to a critical Marangoni number Ma c=194±14 for the onset of flow oscillation. For low Prandtl number (Pr) materials such as metals and semiconductors, this appears to be the first Ma c measured in a liquid bridge with a clean free surface (without scum). The following Ma c vs. Pr relationship fits reasonably well the experimental data of low Pr materials such as Sn, Si, Bi, GaSb and GaAs, and higher Pr materials such as KCl, NaNO 3 and C 24H 50: Ma c =2000 Pr 0.6 with 10 − 2 < Pr<10 2 .
Published Version
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