Sessile droplet evaporation: The impact of surface charge convection

Abstract

The electric field plays a significant role in droplet evaporation, where electric stresses are usually calculated by leaky dielectric or charge conservative model. This assumption neglects the effect of surface charge convection (SCC), which may significantly enhance the internal flow within the droplet under high electric Reynolds number and potentially alter heat convection. This work develops a lattice Boltzmann method (LBM) model to solve the full electrohydrodynamic (EHD) equations, enabling investigation of SCC on sessile droplet evaporation. For non-radiative dielectric liquids, heat transfer within the droplet occurs through conduction and convection. Therefore, this work examines the role of substrate temperature, a critical factor governing conductive heat transfer, to comprehensively investigate evaporation characteristics. By introducing the Péclet ($Pe$) number, this study systematically analyzes the competition between conduction and convection in the presence of SCC. The electric field enhances the evaporation when $Pe>1$, and an increase in substrate temperature can accelerate evaporation by enhancing heat convection as $Pe$ reducing. The presence of SCC slightly enhances the prolate deformation and reduces heat conduction. However, $\mathrm{Pe}$ number is significantly increased by enhancing heat convection. Therefore, the droplet evaporation could be remarkedly enhanced in higher electric intensity.