由马兰戈尼流与重力流竞争导致的振荡液滴溶解
Oscillatory droplet dissolution from competing Marangoni and gravitational flows
AI总结：
本研究针对垂直排列的双液滴在水中的溶解过程，通过实验与模拟发现两液滴液体不同时会因溶质马兰戈尼流与密度驱动对流的竞争产生振荡溶解现象，并揭示了其机制与标度规律。
摘要：
液滴在主体液体中的溶解或生长是化学萃取、色谱法或乳化等工艺的重要环节。本工作通过实验与数值模拟两种方式，研究了浸没在水中的一对垂直排列液滴的溶解过程。构成液滴的液体为长链醇，其在水中溶解度较低但有限，且密度显著低于主体液体的密度。因此，底部液滴上方会形成溶质羽流，自然对流主导了溶解过程。我们随时间监测液滴的体积及其周围的速度场。当两个液滴的液体相同时，我们此前发现的舍伍德数与雷诺数作为瑞利数函数的标度律（Dietrich等人，2016年，《Journal of Fluid Mechanics》）可适用于下方液滴。然而值得注意的是，当顶部液滴的液体与底部液滴不同时，体积随时间的变化呈非单调性，且在顶部液滴处观测到振荡的马兰戈尼流。我们确定溶质马兰戈尼流与密度驱动对流之间的竞争是该振荡现象的成因，并对该过程进行了数值建模。
英文摘要：
The dissolution or growth of a droplet in a host liquid is an important part for processes like chemical extraction, chromatography or emulsification. In this work we look at the dissolution of a pair of vertically aligned droplets immersed in water, both experimentally and with numerical simulations. The liquids used for the droplets are long chain alcohols with a low but finite solubility in water and a significantly lower density than that of the host liquid. Therefore, a solutal plume is formed above of the bottom droplet and natural convection dominates the dissolution process. We monitor the volume of the droplets and the velocity field around them over time. When the liquids of the two droplets are the same, our previously found scaling laws for the Sherwood and Reynolds numbers as functions of the Rayleigh number (Dietrich et al., 2016, J. Fluid Mech.) can be applied to the lower droplet. However, remarkably, when the liquid of the top droplet is different than that of the bottom droplet the volume as function of time becomes non-monotonic, and an oscillatory Marangoni flow at the top droplet is observed. We identify the competition between solutal Marangoni flow and density driven convection as the origin of the oscillation, and numerically model the process.
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