Interplay of electro-thermo-solutal advection and internal electrohydrodynamics governed enhanced evaporation of droplets.

Abstract

The article experimentally examines and theoretically establishes the influence of electric field on the evaporation kinetics of pendant droplets. It is observed that the evaporation of saline-pendant droplets can be augmented by the application of an external alternating electric field. The evaporation behaviour is modulated by an increase in the field strength and frequency. The classical diffusion driven evaporation model is found insufficient in predicting the improved evaporation rates. The change in surface tension due to field constraint is also unable to explain the observed physics. Consequently, the internal hydrodynamics of the droplet is investigated through particle image velocimetry. The electric field is found to induce enhanced internal advection, which improves the evaporation rates. A scaled analytical model is proposed to quantify the role of internal electrohydrodynamics, electro-thermal and electro-solutal effects. Stability maps reveal that the advection is caused nearly equally by the electro-solutal and electro-thermal effects within the droplet. The model is able to illustrate the influence played by the governing thermal and solutal Marangoni number, the electro-Prandtl and electro-Schmidt number, and the associated electrohydrodynamic number. The magnitude of the internal circulation can be predicted by the proposed model, which validates the proposed mechanism.