Abstract:

Spontaneous coalescence of droplets is widespread in nature and industry. How to efficiently remove coalesced droplets is an important part of strengthening droplet condensation heat transfer and preventing icing. In this paper, the coalescence-induced droplet jumping with different radius ratios on superhydrophobic horizontal wall and superhydrophobic wavy wall is studied by numerical simulation. The horizontal and vertical velocities of the droplets coalescing on the flat wall surface differ by 1—2 orders of magnitude, the horizontal displacement of the droplets is small, so it's difficult to remove them effectively after coalescing. However, on the wavy wall surface, because the liquid bridge impinges on the inclined surface, the droplet is subjected to a large horizontal component force, and the horizontal velocity of the droplet remains at the same order of magnitude as the vertical velocity after coalescence, and the horizontal displacement increases significantly. Moreover, the wave structure has a significant effect. With the increase of the wave aspect ratio, the horizontal displacement of the droplet increases and the bounce height decreases, which can effectively promote the horizontal movement of the droplet. When the aspect ratio is 0.21, the promotion effect is close to the peak value. The findings provide a new reference for the efficient removal of coalesced droplets.

Key words: droplets jumping, two-phase flow, interfacial tension, superhydrophobic surface, numerical simulation, horizontal motion

摘要：

液滴自发聚并在自然和工业中广泛存在，如何高效去除聚并液滴是强化滴状冷凝换热、防结冰等的重要环节。采用数值模拟方法研究了不同半径比液滴在超疏水平壁面和超疏水波浪形壁面上的聚并起跳行为。研究发现，在平壁面上聚并的液滴水平速度与竖直速度差1～2个数量级，液滴的水平方向位移小，聚并后难以有效去除；在波浪形壁面上，由于液桥撞击在斜面上，产生较大的水平分力，聚并后其水平速度保持与竖直速度在同一数量级，水平位移显著增大；并且波浪结构对液滴弹跳过程影响显著，随波浪高宽比的增大液滴水平位移增大且弹跳高度减小，有效促进了液滴的水平运动，且当高宽比为0.21时，促进作用接近峰值。研究结果为聚并液滴的有效去除提供了新参考。

关键词: 液滴弹跳, 两相流, 界面张力, 超疏水表面, 数值模拟, 水平运动