Impact of modulated magnetic field on the advent of ferroconvection in a permeable medium

Abstract

The effect of time-periodic magnetic field modulation on the onset of ferroconvection in a magnetic fluid saturated densely packed porous medium is examined. In many systems, such as charges in electrostatic field and ferromagnetic resonance, modulation of a suitable parameter can have marked effects on the motion and can result in increased stability of the system. Making use of isothermal boundary conditions, the subsequent eigenvalue problem is attacked by means of the regular perturbation method with the assumption of small amplitude of modulation. The onset criteria are derived based on the assumption that the principle of exchange of stabilities holds good. The thermal Rayleigh number shift is determined as a function of magnetic force, porous parameters, and magnetic field modulation frequency. The influence of various physical factors is perceived to be significant at moderate values of magnetic field modulation frequency. It is found that subcritical instability is possible for low frequency magnetic field modulation. The effect of magnetic mechanism is shown to be attenuating the stabilizing influence of magnetic field modulation for moderate and large values of the frequency of modulation. However, the stabilizing effect of magnetic field modulation gets amplified due to an increase in the values of Vadasz number. Further, it is delineated that the normalized porosity and magnetic field modulation work in tandem in destabilizing the system for low frequency modulation. The study reveals that the effect of magnetic field modulation could be exploited to control ferroconvective instability in a porous medium saturated with magnetic fluids.