Peng Xiaoyun, Wang Tianyou, Jia Feifei, Sun Kai, Li Zhe, Che Zhizhao
State Key Laboratory of Engines, Tianjin University, Tianjin, 300350, China.
State Key Laboratory of Engines, Tianjin University, Tianjin, 300350, China; National Industry-Education Platform of Energy Storage, Tianjin University, Tianjin, 300350, China.
J Colloid Interface Sci. 2023 Dec;651:870-882. doi: 10.1016/j.jcis.2023.07.186. Epub 2023 Aug 3.
The impact of droplets is prevalent in numerous applications, and jetting during droplet impact is a critical process controlling the dispersal and transport of liquid. New jetting dynamics are expected in different conditions of droplet impact on super-hydrophobic surfaces, such as new jetting phenomena, mechanisms, and regimes.
In this experimental study of droplet impact on super-hydrophobic surfaces, the Weber number and the Ohnesorge number are varied in a wide range, and the impact process is analyzed theoretically.
We identify a new type of singular jets, i.e., singular jets induced by horizontal inertia (HI singular jets), besides the previously studied singular jets induced by capillary deformation (CD singular jets). For CD singular jets, the formation of the cavity is due to the propagation of capillary waves on the droplet surface; while for HI singular jets, the cavity formation is due to the large horizontal inertia of the toroidal edge during the retraction of the droplet after the maximum spreading. Key steps of the impact process are analyzed quantitatively, including the spreading of the droplet, the formation and the collapse of the spire, the formation and retraction of the cavity, and finally the formation of singular jets. A regime map for the formation of singular jets is obtained, and scaling relationships for the transition conditions between different regimes are analyzed.
液滴的撞击在众多应用中普遍存在，并且液滴撞击过程中的喷射是控制液体分散和传输的关键过程。在液滴撞击超疏水表面的不同条件下，预计会出现新的喷射动力学，例如新的喷射现象、机制和状态。
在这项关于液滴撞击超疏水表面的实验研究中，韦伯数和奥内佐格数在很大范围内变化，并对撞击过程进行了理论分析。
除了先前研究的由毛细管变形诱导的奇异射流（CD奇异射流）之外，我们还识别出一种新型的奇异射流，即由水平惯性诱导的奇异射流（HI奇异射流）。对于CD奇异射流，空穴的形成是由于液滴表面上毛细管波的传播；而对于HI奇异射流，空穴的形成是由于液滴在最大铺展后回缩期间环形边缘的大水平惯性。对撞击过程的关键步骤进行了定量分析，包括液滴的铺展、尖顶的形成和坍塌、空穴的形成和回缩，以及最终奇异射流的形成。获得了奇异射流形成的状态图，并分析了不同状态之间转变条件的标度关系。
