Influence of competitive electro- and ferro-hydrodynamics on droplet vaporization phenomenology

Abstract

Modification and control of the vaporization kinetics of microfluidic droplets can find utilitarian implications in several scientific and technological applications. The article reports the control over the vaporization kinetics of pendant droplets under the influence of competing internal electrohydrodynamic and ferrohydrodynamic advection. Experimental and theoretical studies are performed and the morphing of vaporization kinetics of electrically conducting, paramagnetic fluid droplets using orthogonal electric and magnetic stimuli is explored. Analysis reveals that the electric field has a domineering influence compared to the magnetic field. While the magnetic field is observed to augment the vaporization rates, the electric field is observed to decelerate the same. Neither the vapour diffusion dominated model, nor the field induced modified surface tension characteristics can explain the observed behaviours. Velocimetry studies within the droplet show extensively modified internal ferro and electrohydrodynamic advection, which is noted to be the crux of the mechanism towards modified vaporization rates. A mathematical analysis is proposed, which takes into account the roles played by the concomitant governing Hartmann, Electrohydrodynamic, Interaction, thermal and solutal Marangoni, and the electro and magneto Prandtl and Schmidt numbers. It is observed that the morphing of the thermal and solutal Marangoni numbers by the electromagnetic Interaction number plays the dominant role towards morphing the advection dynamics. The model is able to predict the internal advection velocities accurately. The findings may hold importance towards smart control and tuning of vaporization kinetics in macro and microfluidic systems.