Thermal transport characteristics of impinging ferrofluid droplets in the presence of a magnetic field

Abstract

Droplet interactions with solid surfaces are fundamental to natural phenomena and hold significant commercial relevance across diverse applications. While the impingement dynamics of conventional aqueous droplets on solid substrates are well-characterized, the behavior of non-aqueous droplets, particularly those influenced by external force fields like electric or magnetic fields, remains a less explored domain. This study addresses this gap by investigating the impact of a magnetic field on the impingement dynamics of ferrofluid droplets on a heated solid surface. Ferrofluids are unique colloidal suspensions of magnetic nanoparticles within a non-magnetic carrier fluid, enabling external manipulation of their dynamic properties through magnetic forces. The application of a magnetic field introduces an attractive force within the ferrofluid, fundamentally altering the droplet's spreading behavior and, consequently, its transport characteristics upon impact. Our findings reveal a substantial increase in both the maximum spreading diameter and the contact time between the droplet and the substrate, directly leading to enhanced thermal transport efficiency. Furthermore, the magnetic force effectively suppresses droplet bounce-off from hydrophobic surfaces. These critical parameters can be precisely controlled by adjusting the strength of the induced magnetic force. Such interactions can be used in the design of thermal switches and thermal management systems. The multi-physics interactions of magnetic fields, fluid flow, interface tracking, and heat transfer within the multiphase system are computationally modelled to examine the effect of Weber number and contact angle on maximum spreading and associated heat transfer characteristics.