Abstract Droplet spray cooling has wide applications in electronic cooling, steam generators, evaporators and condensers etc due to its high efficiency. The cooling effect depends on the droplet spreading dynamics greatly. In our study the transient two-dimensional axisymmetric model for droplet cooling is developed with a level set method, where the dynamics of the moving contact line is described with the Molecular Kinetic Theory (MKT). After validation with experimental data, the effect of impact velocity, surface tension, initial droplet radius, equilibrium contact angle and liquid viscosity on droplet spreading is investigated. It is found that the dynamics of the moving contact line can be described accurately with MKT, and the predicted droplet spreading radius agrees quite well with the experimental data, while the Constant Contact Angle (CCA) model overpredicts the droplet spreading rate. The maximum heat flux occurs at the point when the droplet spreading transits from capillary-inertial spreading to capillary-viscous spreading. The droplet spreading rate will increase with the increasing impact velocity, surface tension and initial radius, or decreasing equilibrium contact angle and liquid viscosity. Due to the effect of thermo-capillary force, the cold substrate can promote the droplet spreading, and the hot substrate can retard the droplet spreading. These findings may be of great significance for effective droplet spreading cooling.

中文翻译：

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热基板上液滴扩散和传热的数值研究

摘要 液滴喷雾冷却以其高效率而广泛应用于电子冷却、蒸汽发生器、蒸发器和冷凝器等领域。冷却效果很大程度上取决于液滴扩散动力学。在我们的研究中，液滴冷却的瞬态二维轴对称模型是用水平集方法开发的，其中移动接触线的动力学是用分子动力学理论 (MKT) 描述的。在用实验数据验证后，研究了冲击速度、表面张力、初始液滴半径、平衡接触角和液体粘度对液滴扩散的影响。发现用MKT可以准确地描述动接触线的动力学，并且预测的液滴扩散半径与实验数据非常吻合，而恒定接触角 (CCA) 模型高估了液滴扩散率。最大热通量出现在液滴扩散从毛细管惯性扩散转变为毛细管粘性扩散时。随着冲击速度、表面张力和初始半径的增加，或平衡接触角和液体粘度的降低，液滴扩散速率将增加。由于热毛细作用力的作用，冷基体可以促进液滴扩散，而热基体可以阻滞液滴扩散。这些发现可能对有效的液滴扩散冷却具有重要意义。随着冲击速度、表面张力和初始半径的增加，或平衡接触角和液体粘度的降低，液滴扩散速率将增加。由于热毛细作用力的作用，冷基体可以促进液滴扩散，而热基体可以阻滞液滴扩散。这些发现可能对有效的液滴扩散冷却具有重要意义。随着冲击速度、表面张力和初始半径的增加，或平衡接触角和液体粘度的降低，液滴扩散速率将增加。由于热毛细作用力的作用，冷基体可以促进液滴扩散，而热基体可以阻滞液滴扩散。这些发现可能对有效的液滴扩散冷却具有重要意义。