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Natural convection and heat transfer of nanofluids considering the soret effect

Convection in a horizontal fluid layer of a binary mixture is studied numerically. The flow is driven by buoyancy force due to externally applied constant temperature difference on the vertical wall of the cavity while the horizontal surfaces are impermeable and adiabatic. A nanofluid is used and the effects of cross phenomena "Soret effect" were considered in the analysis. The flows are found to be dependent of the nanoparticle concentration φ , the Rayleigh number, T R , the Lewis number, Le , the particles to thermal buoyancy ratio, φ , and the thermal boundary conditions. Numerical results for finite amplitude convection, obtained by solving numerically the full governing equations, are found to be in good agreement with the analytical solution based on the scale analysis approach. We have proposed a modified formulation of the conservation equations governing the flow and heat transfer of nanofluids, taking into account important changes of nanofluid thermal conductivity and viscosity as well as the spatial change of particle concentration that is induced by Soret effect. Results have shown that such an effect increases nanofluids heat transfer. The optimal particle volume concentration, which maximizes heat transfer, is estimated to be 2%. The increase in natural convection is weak in comparison to what was found in forced convection.