INERTIAL RETRACTION OF LIQUID FILM ON MODERATELY WETTABLE PLATE
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摘要: 液滴撞击平板的动力学机理研究具有重要的理论与工程价值, 对该过程中液滴的形貌变化及主要影响因素的研究是科学技术界关注的重点之一. 液滴在高速撞击平板达到最大铺展半径以后发生毛细-惯性收缩, 收缩速率满足类Taylor-Culick公式. 结合实验与有限元方法, 对平板上铺展液滴的收缩过程进行了研究. 结果表明, 在中性润湿(接触角约为90°)平板上液滴/液膜的收缩在经历上述收缩过程以后, 会有一个慢匀速收缩过程, 速度约为第一阶段收缩速度的1/10. 对后一阶段的撞击参数影响测试显示, 该收缩过程主要与液体密度、液膜初始形状有关; 而与液体黏性、壁面润湿条件等无关——其仍然是一种毛细-惯性机制主导的液面演化行为, 类似于液体射流的Rayleigh-Plateau失稳. 尽管黏性效应对于液滴撞击的铺展行为有明显影响, 但上述结论在10倍黏性的液体测试中仍然成立. 本研究可以为液滴反弹机理研究和相关工艺控制提供参考.Abstract: Spreading and rebounding of drop on solid substrate are of great significance in industry and scientific research, where the evolution of morphology of a drop is investigated frequently. It is normally believed that a spread drop retracts in inertia-capillary regime with a speed deduced by a Taylor-Culick procedure. Experimental and finite element method studies were conducted, which show that a drop retracts on moderately wettable plate with a low speed after the aforementioned inertia-capillary retraction. The speed has a value as low as 1/10 of the first retracting stage. The mechanism is explored according to the experiments and additional numerical simulations. It is found that the low-speed retraction depends on the density and capillary of the liquid, rather than the viscosity and wall condition (including the wettability and slip characters). It is revealed that the process is still dominated by capillary-inertial effects. The findings are also validated on the liquid with viscosity as high as 10 times of the original one in simulations. The research is valuable for studying droplet dynamics and relative industrial processes.
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Key words:
- drop /
- retraction /
- capillary-inertial effect /
- wettability
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图 5 石蜡平板上液滴撞击过程的形状演化. 蓝、黑、红色分别对应
$ We=150, 120, 90 $ , “ + ”为$ \widetilde{R} $ , “ × ”为$ \widetilde{H} $ , “○”为$ S $ Figure 5. The evolution of geometry of drops impacting on parafilm plates. The blue, black and red symbols represent Weber numbers of
$ 150, 120, 90 $ , respectively. + :$ \widetilde{R} $ , × :$ \widetilde{H} $ , ○:$ S $ 表 1 固体平板润湿性
Table 1. The wettability of the substrates
Material $ {\theta }_{a} $/(°) $ {\theta }_{r} $/(°) glass 31 24 TEFLON 91 60 parafilm 120 89 coated 161 150 -
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