Study On Droplet Coalescence-jumping Behavior On Superhydrophobic Surface Under External Force

The removal of condensate is a very important step in the droplet condensation process.In recent years,with the rise of research on superhydrophobic surfaces,researchers have discovered the phenomenon of droplet jumping-condensation on superhydrophobic surfaces,and many scholars have begun to study methods for efficiently removing condensed droplets on superhydrophobic surfaces based on this phenomenon.Since there are many limiting factors for the spontaneous jumping movement of droplets on the superhydrophobic surface,researchers began to committed to the effects of external forces,including the effects of gravity and electric field forces.In this paper,the influencing factors of coalescence-jumping of superhydrophobic surface droplets are experimentally studied under the action of gravity.At the same time,based on the level set method,combining the flow field and the electric field,a model of droplet coalescence-jump behavior on the superhydrophobic surface under the action of a uniform electric field was established,and the influencing factors of droplet coalescence-jump behavior under the electric field were analyzed.Experimental studies on droplet coalescence-jumping of superhydrophobic surfaces under the action of gravity show that the contact angle has an important effect on droplet coalescence-jumping behavior under the action of gravity,which not only reduces the resistance of droplets to gravity,but also improves the frequency of droplet coalescence,while increasing the droplet jumping speed and benifiting the droplets leaving the superhydrophobic surface.The simulation results of electric field on coalescence and jumping of super-hydrophobic surface droplets show that there is an electric field threshold E_L for droplet coalescence-jumping behavior under various conditions.Only when the electric field strength exceeds the electric field threshold,the coalescence-jumping behavior of the droplet pair will occur under the action of the electric field.As the electric field strength continues to increase,the droplet coalescence-jumping can be effectively promoted within a certain range.And as the diameter of the droplet increases,the electric field threshold required for droplet coalescence decreases and droplets coalesce more easily.As the distance between droplets increases,the electric field threshold required for droplet coalescence increases,which is not conducive to droplet coalescence.For the pair of equal-diameter droplets,the optimal range of the electric field to promote droplet coalescence-jumping behavior should be less than 40%of the diameter.For the pair of unequal-diameter droplets,the optimal distance of the electric field to promote droplet coalescence-jumping behavior should be no more than 30%of the diameter of the large droplet.The electric field threshold of the coalescence-jumping behavior of the droplet pairs with equal diameter and unequal diameter decreases with the increase of the static contact angle and increases with the increase of the surface tension,but the surface tension and the static contact angle have a weaker effect on coalescence-jump behavior of unequal-diameter droplets.The electric field threshold for coalescence-jumping of equal-diameter droplets decreases as the relative dielectric constant increases.At the same time,the critical unequal diameter ratioω_L of unequal diameter droplet pairs jumping after coalescence is studied.For pairs of unequal-diameter droplets,when the contact angle is 180°and the surface tension coefficient is 0.0726N/m,the critical unequal-diameter ratio for droplets to jump after coalescence is 0.33,and the critical unequal-diameter ratioω_L increases with decreasing contact angle and surface tension.On this basis,this paper summarizes the regular of coalescence-jumping behavior of droplets on the superhydrophobic surface under the action of a uniform electric field,and obtained preliminary research results,which provides a theoretical basis for the application of electric field to remove condensate on the superhydrophobic surface.