Abstract:

The phenomenon of droplet coalescence-induced self-propelled jumping is of great significance in enhancing heat transfer, preventing frosting and defrosting in heat pump air conditioning systems. The processes of droplet coalescence and self-propelled jumping are modeled independently in consideration with the released surface energy, gravity potential energy, the viscous dissipation and surface tension energy dissipation caused by contact angle hysteresis. The simulation values are in accordance with existing experimental data in the literature. It was found that the number of droplets, the uniformity of the radius and the surface characteristics do affect the process of coalescence and self-propelled jumping. With the increasing of droplet numbers, the critical contact angle in process of coalescence decreases from 120° to 105°. The critical contact angle in process of self-propelled jumping decreases from 140° to 130° with the increasing of uniformity of droplet radius. The results indicate that larger droplet number and higher uniformity of droplet radius are beneficial for coalescence and self-propelled jumping. In addition, the influence of solid-liquid contact fraction on the process coalescence and self-propelled jumping decreases with the increase of contact angle.

摘要：

液滴合并弹跳对强化热泵空调系统中的凝结传热及防结霜、除霜等方面均有良好的应用前景。在综合考虑固-液、气-固和气-液表面自由能，重力势能，液滴内部黏性耗散功及表面黏附功的基础上建立了液滴合并及弹跳的分阶段能量模型，并进行了超疏水表面不同半径液滴合并弹跳时的模型模拟与实验验证，得到较好的吻合。基于该模型研究了液滴数量、半径均匀性及不同表面状态对液滴合并弹跳过程的影响规律。结果表明，液滴数量增加时，合并阶段临界接触角由120°减小至105°，半径尺寸均匀性增加时，弹跳阶段临界接触角从140°减小至130°。当表面接触角大于140°时，固液接触系数影响微乎其微。可见，液滴数量的增多及液滴尺寸均匀性的提升有利于合并弹跳过程的发生，固液接触系数对合并弹跳过程的影响程度随表面接触角的增大而减小。