IMPACT OF MODULATED MAGNETIC FIELD ON THE ADVENT OF FERROCONVECTION IN A PERMEABLE MEDIUM

IMPACT OF MODULATED MAGNETIC FIELD ON THE ADVENT OF FERROCONVECTION IN A PERMEABLE MEDIUM

C. Balaji, C. Rudresha, V. V. Shree, S. Maruthamanikandan

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Abstract

The e ect of time-periodic magnetic  eld modulation on the onset of ferro- convection in a magnetic uid saturated densely packed porous medium is examined. In many systems, such as charges in electrostatic  eld and ferromagnetic resonance, mod- ulation of a suitable parameter can have marked e ects 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  eld modulation frequency. The inuence of various physical factors is perceived to be signi cant at moderate values of magnetic  eld modulation fre- quency. It is found that subcritical instability is possible for low frequency magnetic  eld modulation. The e ect of magnetic mechanism is shown to be attenuating the stabilizing inuence of magnetic  eld modulation for moderate and large values of the frequency of modulation. However, the stabilizing e ect of magnetic  eld modulation gets ampli ed due to an increase in the values of Vadasz number. Further, it is delineated that the normalized porosity and magnetic  eld modulation work in tandem in destabilizing the system for low frequency modulation. The study reveals that the e ect of magnetic  eld modulation could be exploited to control ferroconvective instability in a porous medium saturated with magnetic uids.

Keywords

Magnetic uid, Magnetic  eld modulation, Perturbation method, Stability, Porous medium.