Electromagnetic field orientation and characteristics governed hydrodynamics within pendent droplets

Abstract

The article reports the domineering governing role played by the direction of electric and magnetic fields on the internal advection pattern and strength within salt solution pendant droplets. Literature shows that solutal advection drives circulation cells within salt based droplets. Flow visualization and velocimetry reveals that the direction of the applied field governs the enhancement/reduction in circulation velocity and the directionality of circulation inside the droplet. Further, it is noted that while magnetic fields augment the circulation velocity, the electric field leads to deterioration of the same. The concepts of electro and magnetohydrodynamics are appealed to and a Stokesian stream function based mathematical model to deduce the field mediated velocities has been proposed. The model is found to reveal the roles of and degree of dependence on the governing Hartmann, Stuart, Reynolds and Masuda numbers. The theoretical predictions are observed to be in good agreement with experimental average spatio-temporal velocities. The present findings may have strong implications in microscale electro and/or magnetohydrodynamics.

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

“…5 (b) and (c). This change in direction of advection of a conducting paramagnetic fluid is consistent with the description of Fleming's right hand rule [31,35]. Hence it is seen that the evaporation of the ferrofluid droplet in field environment is conjugated to increase in internal advection.…”

“…Some recent studies have explored the physics behind such advection in saline fluids [31,35,37] and the present observations can also be explained on similar grounds. The internal hydrodynamics shears the droplet-vapor interface, leading to entrainment of the ambient air, which replenishes the species boundary layer at the droplet-vapor interface.…”

“…The shape of the pendant drop is known to induce non-uniform evaporation rates along the droplet surface [23,[35][36][37], thereby leading to thermal gradients and thereby thermal Marangoni advection. Additionally, the evaporation induced cooling of the droplet leads to thermal gradients across the droplet, leading to internal thermal advection.…”

Advection kinetics induced self-assembly of colloidal nanoflakes into microscale floral structures

“…The experimental details are described briefly (details available elsewhere [18,25]). For the HRSEM (high resolution scanning electron microscopy) imaging, aluminum foil cut-outs (10 mm x 10 mm) are used as conducting substrates.…”

“…Noise suppression and contrast enhancement algorithms are used to obtain better peak matching and high SNR. Detailed description of the PIV methodology followed is reported by the author [25].…”