Ferro-advection aided evaporation kinetics of ferrofluid droplets in magnetic field ambience

Abstract

The present article discusses the physics and mechanics of evaporation of pendent, aqueous ferrofluid droplets and modulation of the same by external magnetic field. We show experimentally and by mathematical analysis that the presence of magnetic field improves the evaporation rates of ferrofluid droplets. First we tackle the question of improved evaporation of the colloidal droplets compared to water, and propose physical mechanisms to explain the same.Experiments show that the changes in evaporation rates aided by the magnetic field cannot be explained on the basis of changes in surface tension, or based on classical diffusion driven evaporation models. Probing using particle image velocimetry shows that the internal advection kinetics of such droplets plays a direct role towards the augmented evaporation rates by modulating the associated Stefan flow. Infrared thermography reveal changes in the thermal gradients within the droplet and evaluating the dynamic surface tension reveals presence of solutal gradients within the droplet, both brought about by the external field. Based on the premise, a scaling analysis of the internal magneto-thermal and magneto-solutal ferroadvection behavior is presented. The model incorporates the role of the governing Hartmann number, the magneto-thermal Prandtl number and the magneto-solutal Schmidt number. The analysis and stability maps reveal that the magneto-solutal ferroadvection is the more dominant mechanism, and the model is able to predict the internal advection velocities with accuracy. Further, another scaling model to predict the modified Stefan flow is proposed, and is found to accurately predict the improved evaporation rates.

Evaporation and drying characteristics of the sessile ferrofluid droplet under a horizontal magnetic field

“…Chattopadhyay et al. investigated the modulation effect of a horizontal magnetic field on the evaporation of suspended ferrofluid droplets, explaining why magnetic fields can accelerate droplet evaporation [41] . Lama et al.…”

Vapor mediation as a tool to control micro-nano scale dendritic crystallization and preferential bacterial distribution in drying respiratory droplets

“…Since the flow inside the droplet is primarily responsible for the final deposit formed, the final deposit can be controlled by controlling the flow as a corollary. However, most techniques used to control the flow inside droplets, such as acoustic excitation [17], heating [18], magnetic stirring [19], the addition of surfactant [20], are highly intrusive and can lead to denaturing of the biological sample. Hence we propose the non-intrusive vapor mediated interaction [21,22] to control the flow and subsequent patterns formed on drying of the bio-fluid droplet.…”

An Experimental Validation Study of Ferrofluid Evaporation

“…Bolotov et al derived equations of evaporation rate to estimate the life of a tribounit with ferro uid in the ambience of a vacuum [20] and a gas [21] . Jaiswal et al [22] and Chattopadhyay et al [23] studied the evaporation kinetics of a magnetic salt solution pendent droplet under a horizontal magnetic eld. Experimental observations revealed that the evaporation rate enhanced with a magnetic eld and magneto-solutal advection was thought to be the domineering factor in augmented evaporation rate.…”