物性参数对液滴的聚并自弹跳的影响及其关联分析

Effect and relational analysis of physical parameters on coalescence-induced self-propelled jumping of droplets

超疏水表面上液滴因聚并诱导而引起的自弹跳行为具有巨大的潜在应用价值,因此有关问题引起了广泛关注.目前液滴的物性参数对其自弹跳特性的影响却鲜有报道.本文数值模拟了不同的液体物性参数下液滴的聚并自弹跳行为,并利用灰色关联法研究了物性参数变化分别与液滴跳起时的真实弹跳速度及液滴和表面的真实接触时间的关联程度.在无量纲的时间条件下,液滴的聚并自弹跳的动力学特性仅受Oh数的影响.在真实的时间条件下,黏度变化与液滴聚并所需的真实时间无关,而减小密度比会同时减少聚并过程和跳起过程中所需的真实时间.无量纲的弹跳速度随着Oh数的增大而减小,而减小黏度和密度都会增加液滴跳起时的真实弹跳速度.根据灰色关联度的计算结果可知,黏度的变化与真实弹跳速度的关联性更高,密度的变化与真实接触时间关联性更高.

Coalescence-induced self-propelled jumping of droplets on superhydrophobic surfaces has been widely concerned because of a great number of potential applications such as in the enhancement of condensation heat transfer,self-cleaning and anti-icing.The droplet jumping phenomenon exists in a gas-liquid two-phase system,and the physical parameters of fluid cannot be ignored.However,there are few reports on the influence of physical parameters on droplet jumping dynamics at present.In this paper,the three-dimensional volume-offluid method is used to simulate the coalescence-induced self-propelled jumping behaviors of droplets,then the energy terms are studied,and finally the grey relational analysis method is used to calculate the relation degree of the change of physical parameters(the viscosity and the density)to the real jumping velocity and the real solid-liquid contact time at the droplet departure time,respectively.Based on the changing trend of jumping velocity,the process of coalescence-induced self-propelled jumping can be divided into four stages,namely,the expansion of liquid bridge,the impact between the liquid bridge and the surface,the droplet departure from the surface,and the deceleration and oscillation in the air.Under the condition of dimensionless time,the dynamic characteristics of coalescence and jumping of droplets are affected only by Oh number,which is independent of the viscosity and the density.In addition,the change of Oh number only affects the above third stage of droplet departure from the surface.Under the condition of real time,the varied viscosity has no connection with the real time of droplet coalescence,and it only changes the real time of the third stage before droplet jumping.Meanwhile,the dimensionless jumping velocity decreases with Oh number increasing,while the real jumping velocity increases when the viscosity and the density both descend.According to the calculated results of grey relational degree,the relation between the change of viscosity and the real jumping velocity is greater,while the relation between the change of density and the real contact time is greater.This work not only is favorable for a better understanding of droplet jumping,but also provides more ideas and theoretical bases for follow-up relevant studies.