Abstract In this study, droplet impact dynamics on superheated cylindrical surfaces are investigated experimentally, through high-speed imaging. The outcome regimes of impacting droplets observed in the experiments are mapped and described. Four distinguishable regimes are identified, namely rebound-transition boiling, rebound-film boiling, breakup-transition boiling, and breakup-film boiling. In addition, the effects of Weber number, surface temperature and curvature diameter on boiling mode, film thickness, droplet spreading and contact time are examined. The scaling laws of maximum spreading ratio and liquid film thickness with the impact Weber number are established. The larger film thickness on the concave surface reduces the dynamic Ledifenfrost temperature, meanwhile improves the critical Weber number for droplet breakup. Under the effect of the tangential gravity component, the spreading of droplets in the circumferential direction is suppressed on the concave surface, while is promoted on the convex surface. Increasing the curvature diameter, the maximum spreading increases on the concave surface, but decreases on the convex surface. The maximum spreading on both surfaces decreases with the wall temperature in the transition boiling state. Noticeable reduction in the contact time of droplets in the rebound regimes are observed on both surfaces, especially on the concave surface. The contact time is shown to generally decrease with the wall temperature, but increase with the curvature diameter.

中文翻译：

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液滴撞击过热圆柱面的实验研究

摘要 在这项研究中，通过高速成像实验研究了过热圆柱表面上的液滴撞击动力学。绘制并描述了在实验中观察到的撞击液滴的结果机制。确定了四种可区分的状态，即回弹-过渡沸腾、回弹-膜沸腾、破碎-过渡沸腾和破碎-膜沸腾。此外，还研究了韦伯数、表面温度和曲率直径对沸腾模式、膜厚、液滴扩散和接触时间的影响。建立了最大铺展率和液膜厚度随影响韦伯数的标度规律。凹面上较大的薄膜厚度降低了动态 Ledifenfrost 温度，同时提高了液滴破裂的临界韦伯数。在切向重力分量的作用下，液滴沿圆周方向的扩散在凹面上受到抑制，而在凸面上得到促进。增大曲率直径，最大展宽在凹面上增大，但在凸面上减小。在过渡沸腾状态下，随着壁温的升高，两个表面上的最大扩散减小。在两个表面上都观察到液滴在回弹状态下的接触时间显着减少，特别是在凹面上。接触时间通常随着壁温的增加而减少，但随着曲率直径的增加而增加。增大曲率直径，最大展宽在凹面上增大，但在凸面上减小。在过渡沸腾状态下，随着壁温的升高，两个表面上的最大扩散减小。在两个表面上都观察到液滴在回弹状态下的接触时间显着减少，特别是在凹面上。接触时间通常随着壁温的增加而减少，但随着曲率直径的增加而增加。增大曲率直径，最大展宽在凹面上增大，但在凸面上减小。在过渡沸腾状态下，随着壁温的升高，两个表面上的最大扩散减小。在两个表面上都观察到液滴在回弹状态下的接触时间显着减少，特别是在凹面上。接触时间通常随着壁温的增加而减少，但随着曲率直径的增加而增加。尤其是在凹面上。接触时间通常随着壁温的增加而减少，但随着曲率直径的增加而增加。尤其是在凹面上。接触时间通常随着壁温的增加而减少，但随着曲率直径的增加而增加。