Two-phase mixture numerical simulation of natural convection of nanofluid flow in a cavity partially filled with porous media to enhance heat transfer

Natural convection of Cu-water nanofluid inside a square cavity partially filled with porous media is investigated numerically using two-phase mixture model. The mixture density and viscosity are defined by Corcione's model and Darcy-Brinkman-Forchheimer relation is employed for fluid flow simulation in porous media. Horizontal walls of the enclosure are adiabatic and its vertical walls are exposed to constant hot and cold temperature. A porous layer is placed on the walls and effects of nanoparticle concentration, Rayleigh and Darcy numbers, and the porous layer thickness ratio on heat transfer rate are investigated. Results are presented and compared in terms of the average Nusselt number, streamlines and isotherms. The single effect of nanoparticles and also simultaneous impact of the nanofluid and the porous layer on heat transfer characteristics are discussed. Use of the nanofluid and porous media have both positive and negative influences on heat transfer, since they can weaken the convection and also strengthen the conduction. Consequently, optimal volume fraction and porous layer thickness exist for different conditions of Ra and Da in order to maximize Nu.