In the present study, the dynamics of sessile droplet coalescence driven by electro-capillary action (due to external electric field) is investigated numerically. An electro-hydrodynamic model based on finite volume method is used to account the transient electric forces in the two-phase Navier-Stokes equation. The flow field inside the droplet during the initial stages of merging is analyzed thoroughly. The dynamics of electrically driven coalescence is influenced by actuation voltage, droplet volume and the dissimilarity of the coalescing droplet. The internal circulation and kinetic energy produced by the electric stress assists the coalescence. The asymmetry in the velocity and size for dissimilar droplet coalescence produces directional preference in the velocity field. The interplay between surface tension, internal circulation and kinetic energy is analyzed by tracking the dimension of the liquid connection in both parallel and perpendicular direction of the solid surface during coalescence. The outcome of the present study could be utilized in the design of micro-mixers operated by electrostatic actuation.
Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .