NECESSARY CONDITION ON THE ONSET OF DOUBLE-DIFFUSIVE CONVECTION IN COUPLE-STRESS FLUID IN HYDROMAGNETICS SATURATED BY A POROUS MEDIUM

In this paper, the effect of magnetic field on double-diffusive convection in couple-stress fluid saturating a porous medium is considered. By applying linear stability theory and normal mode analysis method, a necessary condition is derived which states that the viscoelastic double-diffusive convection at marginal state, cannot manifest as stationary convection if the thermal Rayleigh number R, the medium permeability parameter P-l the couple-stress parameter F, the stable solute gradient S, medium porosity epsilon and the Chandrasekhar number Q, satisfy the inequality R <= 4 pi(2)/P-l[1 + 2 pi F-2 + P(l)Q/2 epsilon + P(l)Sa(2)/4 pi(4)] the result clearly established the stabilizing character of couple-stress parameter, stable solute gradient and magnetic field whereas destabilizing character of medium permeability and porosity.