Heatline visualization of natural convection in a porous cavity occupied by a fluid with temperature-dependent viscosity

Temperature dependent viscosity effect in buoyancy driven flow, of a gas or a liquid, in an enclosure filled with a porous medium is studied numerically, based on the general model of momentum transfer in a porous medium. The Arrhenius model, which proposes an exponential form of viscosity-temperature relation, is applied to examine three cases of viscosity-temperature relation: constant, decreasing and increasing. Application of arithmetic and harmonic mean values of the viscosity is also investigated for their ability to represent the Nusselt number versus the effective Rayleigh number. Heatlines are illustrated for a more comprehensive investigation of the problem