Augmented Droplet Evaporation by Electric Field Stimulus*

The presence of ionic inclusions is known to trigger solutal advection, which enhances the evaporation rate of the pendant droplet. The present work experimentally investigates the effect of a transverse alternating electric field on the evaporation dynamics of the saline droplet. The changes in evaporation characteristics are probed as functions of field strength and frequency. The evaporation rate is observed to follow the D² law. However, enhancement in evaporation rate is observed under field stimulus. The classical diffusion driven evaporation model fails to predict the improved evaporation rate. The involvement of electrohydrodynamic circulation within a droplet in addition to solutal advection is proposed.  Flow visualization was performed to quantify the internal circulation and augmented electrohydrodynamic advection and its dominance is observed. The improved internal advection is responsible for the improved evaporation by interfacial shear driven replenishment of the diffusion layer shrouding the droplet. The present study improves the understanding of electric field modulated fluid flow, thermal and mass transfer within a droplet.