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Droplet mobilization at the walls of a microfluidic channel

机译：在微流体通道的墙壁上动员动员

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The mechanism of dynamic wetting and the fluid dynamics during the onset of droplet mobilization driven by a microchannel flow are not clearly understood. In this work, we use microparticle tracking velocimetry to visualize the velocity distribution inside the droplet both prior to and during mobilization. Time-averaged and instantaneous velocity vectors are determined using fluorescent microscopy for various capillary numbers. A circulating flow exists inside the droplet at a subcritical capillary number, in which case the droplet is pinned to the channel walls. When the capillary number exceeds a critical value, droplet mobilization occurs, and this process can be divided into two stages. In the first stage, the location of the internal circulation vortex center moves to the rear of the droplet and the droplet deforms, but the contact lines at the top walls remain fixed. In the second stage, the droplet rolls along the solid wall, with fixed contact angles keeping the vortex center in the rear part of the droplet. The critical capillary number for the droplet mobilization is larger for the droplet fluid with a larger viscosity. A force-balance model of the droplet, considering the effect of fluid properties, is formulated to explain the experimental trends of advancing and receding contact angles with the capillary number. Numerical simulations on internal circulations for the pinned droplet indicate that the reversed flow rate, when normalized by the inlet flow rate and the kinematic viscosity ratio of the wetting and nonwetting phases, is independent of the capillary number and the droplet composition.
机译：没有清楚地理解动态润湿和通过微通道流动驱动的液滴动员的发作过程中的动态润湿机制。在这项工作中，我们使用微粒跟踪速度测速程序在动员之前和期间可视化液滴内的速度分布。使用荧光显微镜针对各种毛细管数测定时间平均和瞬时速度载体。在亚临界毛细管数处的液滴内部存在循环流动，在这种情况下，液滴固定到通道壁上。当毛细数量超过临界值时，发生液滴动员，并且该过程可以分为两个阶段。在第一阶段中，内循环涡流中心的位置移动到液滴的后部，液滴变形，但顶壁处的接触线保持固定。在第二阶段，液滴沿着实心壁滚动，固定接触角保持涡流中心在液滴后部的涡流中心。对于具有较大粘度的液滴流体，液滴动员的关键毛细管数更大。考虑流体性质的效果的液滴的力平衡模型被配制成用于解释与毛细数量的推进和后退接触角的实验趋势。用于固定液滴的内部循环的数值模拟表明，当润湿和非擦除相的入口流速和运动粘度比标准化时，逆流流速与毛细管数和液滴组成无关。

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    《Physics of fluids》 |2020年第1期|共10页
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  • 正文语种 eng
  • 中图分类 流体力学;
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