Mohammadi Morteza, Tembely Moussa, Dolatabadi Ali
Islamic Azad University-Nour Branch , Nour, Mazandaran, Iran.
Department of Mechanical and Industrial Engineering, Concordia University , Montreal, Quebec, Canada.
Langmuir. 2017 Feb 28;33(8):1816-1825. doi: 10.1021/acs.langmuir.6b04394. Epub 2017 Feb 17.
Dynamical analysis of an impacting liquid drop on superhydrophobic surfaces is mostly carried out by evaluating the droplet contact time and maximum spreading diameter. In this study, we present a general transient model of the droplet spreading diameter developed from the previously defined mass-spring model for bouncing drops. The effect of viscosity was also considered in the model by definition of a dash-pot term extracted from experiments on various viscous liquid droplets on a superhydrophobic surface. Furthermore, the resultant shear force of the stagnation air flow was also considered with the help of the classical Homann flow approach. It was clearly shown that the proposed model predicts the maximum spreading diameter and droplet contact time very well. On the other hand, where stagnation air flow is present in contradiction to the theoretical model, the droplet contact time was reduced as a function of both droplet Weber numbers and incoming air velocities. Indeed, the reduction in the droplet contact time (e.g., 35% at a droplet Weber number of up to 140) was justified by the presence of a formed thin air layer underneath the impacting drop on the superhydrophobic surface (i.e., full slip condition). Finally, the droplet wetting model was also further developed to account for low temperature through the incorporation of classical nucleation theory. Homogeneous ice nucleation was integrated into the model through the concept of the reduction of the supercooled water drop surface tension as a function of the gas-liquid interface temperature, which was directly correlated with the Nusselt number of incoming air flow. It was shown that the experimental results was qualitatively predicted by the proposed model under all supercooling conditions (i.e., from -10 to -30 °C).
对超疏水表面上撞击液滴的动力学分析大多是通过评估液滴接触时间和最大铺展直径来进行的。在本研究中，我们提出了一个液滴铺展直径的通用瞬态模型，该模型是在先前定义的弹跳液滴质量 - 弹簧模型的基础上发展而来的。通过从超疏水表面上各种粘性液滴的实验中提取的阻尼项定义，模型中还考虑了粘度的影响。此外，借助经典的霍曼流方法，还考虑了滞止气流的合成剪切力。结果表明，所提出的模型能够很好地预测最大铺展直径和液滴接触时间。另一方面，在与理论模型相悖的存在滞止气流的情况下，液滴接触时间作为液滴韦伯数和入射空气速度的函数而减小。实际上，液滴接触时间的减少（例如，在液滴韦伯数高达140时减少35%）是由于在超疏水表面上撞击液滴下方形成了薄空气层（即完全滑移条件）。最后，通过纳入经典成核理论，液滴润湿模型也进一步得到发展以考虑低温情况。通过将过冷水滴表面张力随气 - 液界面温度降低的概念纳入模型，实现了均匀冰核化，该温度与入射气流的努塞尔数直接相关。结果表明，所提出的模型在所有过冷条件下（即从 - 10到 - 30°C）都能定性地预测实验结果。
