• EFFECT OF VARIABLE VISCOSITY ON THERMAL CONVECTIVE INSTABILITY IN A NANOFLUID SATURATED POROUS LAYER

Abstract

The effect of nanofluid viscosity varying with temperature on the onset of thermal convection in a layer of nanofluid saturated Darcy porous medium is studied. Both top and bottom-heavy basic nanoparticle distributions are considered and the resulting eigenvalue problem is solved numerically by the Galerkin method. In the case of top-heavy nanoparticle distribution, the onset is hastened with increasing basic volume fraction difference of nanoparticles and the instability sets in only as stationary convection. To the contrary, the onset is delayed and the instability occurs via oscillatory convection in the case of bottom-heavy nanoparticle distribution. Besides, oscillatory convection occurs when the volume fraction difference of nanoparticles exceeds a threshold value depending on the thermophysical properties of nanofluids. It is observed that the viscosity parameter enhances the stability of the system in both stationary and oscillatory modes. The effect of increasing Prandtl number is to hasten the onset of oscillatory convection.