电场下液滴合并自弹跳行为的分子动力学研究

Molecular Dynamics Simulation of Water Droplet Coalescence-induced Jumping in an Electric Field

在工程上通常利用滴状冷凝提高冷凝换热效率、进而强化传热。而当冷凝液滴发生合并自弹跳时,冷凝换热系数是传统滴状冷凝的1.3至1.5倍,因此液滴合并自弹跳现象对冷凝传热强化的贡献是非常大的。一些宏观实验和理论研究表明,加入外电场能进一步促进冷凝液滴合并自弹跳的频率和高度,但在纳米尺度下是否仍遵守这一规律还未可知,因此本文使用分子动力学模拟方法,探究了在超疏水表面上电场的方向和强度对纳米纯水液滴合并自弹跳行为的影响,模拟结果表明垂直向上方向电场会抑制液滴合并自弹跳,垂直向下方向存在一个电场促进弹跳的区间,在此区间内电场强度越大,弹跳速度越大.

Dropwise condensation is significantly more efficient at heat transfer than filmwise condensation in energy and industrial application.Recently,coalescence-induced droplet self-jumping on superhydrophobic surface has attracted more attention due to enhancing heat transfer(1.3 to 1.5 times normal) compared with state-of-the-art dropwise condensation,which has great contributions to further efficiency increase on condensation heat transfer.Previous studies showed that the electric field had the potential applications to coalescence-induced droplet self-jumping for the efficiency and height enhancement experimentally and theoretically,however,most of mechanisms focused on the macroscale droplets which are limited and inconclusive on nano/microscale droplets.Therefore,we employ the molecular dynamic(MD) simulations to investigate coalescence-induced nanodroplet self-jumping under constant voltage field at the molecular level,the simulation results show that the coalescence-induced jumping is significantly affected by the direction and strength of perpendicular electric field:suppressed in an upward but augmented in an downward electric field at a particular field strength range by improving the jumping velocity of coalesced droplet,which is called the electric-field-enhanced jumping interval.