Dynamic Observation for Marangoni Flow in a Liquid Bridge of Low-Prandtl Number Liquids

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Temperature oscillation and surface oscillation were examined experimentally using thermocouples and phase-shift interferometry for Marangoni convection in the geometry of a half-zone structure. For instability at high Reynolds (Marangoni) number region, various mode wave numbers appeared time-dependently. The relationship between the aspect ratio of a liquid bridge and mode wave number was kept even for high Reynolds (Marangoni) number conditions, as long as frequency of appearance of mode wave numbers was observed. Trough the wavelet transformation analysis, band structures of oscillations with various frequencies were observed for the condition with the Marangoni number of 10^4. It was also confirmed that the mode wave numbers, which appeared when flow mode transition took place from stationary to oscillator one, were sustained.Under the low Reynolds (Marangoni) number conditions, numerical modeling was performed for the liquid bridge with partial confinement and flow structure and mechanism of instability were discussed as functions of the bridge height, the open area ratio and the position of a open window. We found for the first time that two mechanisms, i.e., elliptical and centrifugal instabilities contribute to flow mode transition from stationary one to oscillatory one. The shorter the liquid bridge is, the more spherical the main flow cell becomes. It is also the case, when the open window is located at the hot are. These suggest that under these conditions elliptical instability becomes weak and that centrifugal instability becomes comparably dominant. Direct transition was also found when the open window is located at the hot portion of the liquid bridge. Flow structure was similar to that of the normal half zone structure, when the open window is located at the cold side. This geometry is effective to reduce the Marangoni number experimentally.