Behavior of drops in contact with pool surfaces of different liquids

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Abstract
The behavior of small liquid drops, hanging from a circular disk and approaching a pool surface of the same liquid at different temperatures, is studied experimentally and numerically. The experiments show that if isothermal conditions prevail the drop is immediately engulfed by the liquid. On the contrary, if the temperature of the drop is sufficiently larger or sufficiently smaller than the temperature of the liquid surface, this engulfment is prevented even if the drop is pressed on the liquid surface and “enters” the liquid pool. A number of experiments have been carried out on silicone oils (with different viscosities). At the same time the problem was studied numerically with the assumption that a thin air film is formed between the drop and the liquid bath surface, due to the entrainment of the surrounding air caused by the Marangoni flow; the pressure in the air film balances the pressure necessary to keep the drop submerged in the liquid bath. The critical temperature differences for the drop engulfment are determined experimentally. A parametric numerical analysis is performed to determine the influence of the viscosities of the liquids. The experimental findings are correlated by computed critical temperature differences. A sufficient agreement is found between numerical and experimental results.