Natural Convection Boundary Layer Flow over a Horizontal Plate Embedded in a Porous Medium Saturated with a Nanofluid: Case of Variable Thermophysical Properties

There is a rising interest in application of nanofluids in porous media. As such, this paper is aimed at numerically investigating convective boundary layer flow over a plate embedded in a porous medium filled with nanofluid. Influence of multifarious boundary layers’ applications namely concentration boundary layer of nanoparticles and thermal ones on thermal conductivity and dynamic viscosity of the nanofluid is studied. A new enhanced boundary condition, zero mass flux of nanoparticles through the surface, is adopted to calculate the volume fraction of nanoparticles on the surface. Furthermore, the effect of different practical non-dimensional parameters such as Brownian motion, thermophoresis, Lewis number, and buoyancy ratio on the hydrodynamic, thermal, and concentration boundary layers is investigated. It is revealed that an increase in buoyancy ratio culminates in temperature rise and velocity reduction. The results also show that as the dimensionless Lewis number increases, the fraction of nanoparticles at the sheet soars; on the other hand, the variation of Lewis number does not have considerable effect on the thermal and hydrodynamic boundary layers. Moreover, introducing an enhancement ratio as a criterion to examine the variation of thermal convective coefficient reveals that this value is a decreasing function of buoyancy ratio parameter. In some cases, the value of enhancement ratio becomes less than unity as the buoyancy ratio gets stronger.