Mixed convection heat transfer of nanofluid over microscale vertical duct preceded with a double-step expansion using Lattice Boltzmann Method

Abstract

A numerical investigation of laminar mixed convection flow through a water-alumina nanofluid in a microscale vertical duct preceded with a double-step expansion has been executed. The governing equations are solved by using Lattice Boltzmann equation (LBE) with multiple-relaxation-time (MRT) collision model. The thermal conductivity and effective viscosity of nanofluid have been calculated by Brinkman and Maxwell models, respectively. To examine the effects of nanoparticles concentrations on the heat transfer and the flow behavior, the study has been carried out for the Reynolds number Re=10 to 40, Richardson number Ri=0 to 1.0 and the solid volume fraction 0 to 20%. The results obtained from Lattice Boltzmann modeling clearly show that the inclusion of nanoparticles into the base fluid produces a significant enhancement of the convective heat transfer, especially in the channel entry region. This enhancement increases as function of growing Reynolds number. In addition, the increase in Richardson number leads to decrease the solid concentration effect. Results also show that adding solid particles decreases significantly the fanning friction factor in mixed convection case.