Moradi Mostafa, Rahimian Mohammad Hassan, Chini Seyed Farshid
School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran.
Phys Rev E. 2019 Jun;99(6-1):063102. doi: 10.1103/PhysRevE.99.063102.
Coalescing water droplets on superhydrophobic surfaces can detach from the surface without the aid of any external forces. This self-propelled droplet detachment mechanism is useful in many applications, such as phase change heat transfer enhancement, self-cleaning surfaces, and anti-icing and antidew coatings. In this article, the coalescence-induced droplet jumping in a three-phase system is numerically investigated. The gaps between the surface structures are filled with a liquid that is immiscible with water, e.g., lubricant. A mass-conserving lattice Boltzmann method is implemented to study the effects of several parameters, such as interfacial tensions, droplet size, and surface wettability on the jumping process. The numerical results show that for relatively high values of lubricant-water interfacial tensions and large surface-water contact angles (>150^{∘}) the water droplets are capable of detaching. The critical droplet size for jumping is also highly dependent on the lubricant-water interfacial properties. The results of this study provide insights into the fluid-fluid and fluid-solid interactions and shed light on the underlying mechanisms involved in the droplet coalescence process on such surfaces.
超疏水表面上合并的水滴无需任何外力帮助就能从表面脱离。这种自驱动的液滴脱离机制在许多应用中都很有用，比如强化相变传热、自清洁表面以及防冰和防露涂层。在本文中，对三相系统中合并诱导的液滴跳跃进行了数值研究。表面结构之间的间隙填充有一种与水不混溶的液体，例如润滑剂。采用质量守恒的格子玻尔兹曼方法来研究几个参数，如界面张力、液滴尺寸和表面润湿性对跳跃过程的影响。数值结果表明，对于相对较高的润滑剂 - 水界面张力值和较大的表面 - 水接触角（>150°），水滴能够脱离。跳跃的临界液滴尺寸也高度依赖于润滑剂 - 水的界面性质。本研究结果为流体 - 流体和流体 - 固体相互作用提供了见解，并揭示了此类表面上液滴合并过程所涉及的潜在机制。
