Mixed convection of variable properties Al2O3-EG-water nanofluid in a two-dimensional lid-driven enclosure

In this paper, mixed convection of al2o3-eg-water nanofluid in a square lid-driven enclosure is investigatednumerically. the focus of this study is on the effects of variable thermophysical properties of the nanofluid onthe heat transfer characteristics. the top moving and the bottom stationary horizontal walls are insulated, whilethe vertical walls are kept at different constant temperatures. the study is carried out for richardson numbers of0.01–1000, the solid volume fractions of 0–0.05 and the grashof number of 104. the transport equations aresolved numerically with a finite volume approach using the simpler algorithm. the results show that thenusselt number is mainly affected by the viscosity, density and conductivity variations. for low richardsonnumbers, although viscosity increases by increasing the nanoparticles volume fraction, due to high intensityconvection of enhanced conductivity nanofluid, the average nusselt number increases for both constant andvariable cases. however, for high richardson numbers, as the volume fraction of nanoparticles increases heattransfer enhancement occurs for the constant properties cases but deterioration in heat transfer occurs for thevariable properties cases. the distinction is due to underestimation of viscosity of the nanofluid by the constantviscosity model in the constant properties cases and states important effects of temperature dependency ofthermophysical properties, in particular the viscosity distribution in the domain.