FREE CONVECTION FLOW IN A DUCT FILLED WITH NANOFLUID AND SATURATED WITH POROUS MEDIUM: VARIABLE PROPERTIES

The present study addresses the non-Darcian effects on laminar natural convection flow in a vertical rectangular duct filled with nanofluids and saturated with porous medium for variable properties (viscosity and thermal conductivity). These fluid properties are taken to be dependent on temperature. The fluid is modeled using Brinkman-Forchheimer-extended Darcy equations. The transport equations which are coupled, nonlinear partial differential equations are solved numerically using the finite difference method of second-order accuracy. The fluid viscosity is assumed to vary exponentially with temperature, whereas the thermal conductivity is assumed to vary linearly with temperature. The results for the fluid velocity and temperature are presented pictorially and the influence of pertinent parameters on the volumetric flow rate, skin friction, and rate of heat transfer is tabulated. It is found that the negative values of viscosity and thermal conductivity parameters enhance the flow in the lower half of the duct, and the positive values will enhance the flow in the upper half of the duct. The Darcy number, Grashof number, Brinkman number, and aspect ratio support the motion, whereas inertial parameter and solid volume fraction demote the flow. The optimum rate of heat transfer is attained using diamond nanoparticles and the minimum is obtained using titanium oxide nanoparticles.