Droplet jumping: Effects of the droplet group mass dispersion and symmetry

Abstract

The self-propelled droplet jumping phenomenon during condensation on superhydrophobic surfaces has applications in various fields such as heat transfer enhancement, anti-icing/frosting and self-cleaning. The initial geometrical state of droplet group has great influence on the merging process, thereby affecting the jumping characteristics. In this paper, the initial geometrical state of droplet group is defined and the influences of several characteristics of the initial geometrical state, mainly including the mass dispersion and the degree of symmetry, are investigated based on numerical simulation results. The mass dispersion means the degree of mass being distributed away from the centroid of the droplet group; the degree of symmetry is quantified as two measures: order of rotational symmetry in eigenstate and amount of deviation from the eigenstate. During coalescence, a more dispersed mass distribution facilitates the impinging of liquid flow from different directions and the production of vertical momentum; a better symmetry makes the downward flow that pushes the droplet upward more perpendicular to the bottom surface; therefore, higher mass dispersion and better symmetry are both beneficial to jumping and will lead to higher energy conversion efficiency. This work reveals quantitative relation between the energy conversion efficiency and the initial geometrical state of droplet group, which shall contribute to the understanding of droplet jumping dynamics and bring insights into the droplet jumping enhancement and manipulation.