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

TL;DR

This study demonstrates that applying an external electric field enhances the evaporation rate of saline droplets by inducing internal electrohydrodynamics, which are not explained by classical diffusion models.

Contribution

It introduces a scaled analytical model that captures the combined electrothermal and electrosolutal effects on droplet evaporation, validated by experimental internal flow measurements.

Findings

Electric fields increase evaporation rates of saline droplets.

Internal advection is enhanced by electrohydrodynamics, improving evaporation.

The proposed model accurately predicts internal circulation based on key dimensionless numbers.

Abstract

The article experimentally reveals and theoretically establishes the influence of electric fields on the evaporation kinetics of pendant droplets. It is shown that the evaporation kinetics 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 insufficient for explaining the observed physics. Consequently, the internal hydrodynamics of the droplet is probed employing particle image velocimetry. It is revealed that the electric field induces enhanced internal advection, which improves the evaporation rates. A scaled analytical model is proposed to understand the role of internal electrohydrodynamics, electrothermal and the electrosolutal effects. Stability maps reveal that the advection is caused nearly equally by the electrosolutal and electrothermal 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 well predicted by the proposed model, which validates the proposed mechanism.