Lattice Boltzmann simulation for mixed convection of nanofluids in a square enclosure

Abstract In this paper, the lattice Boltzmann method is applied to investigate the natural and mixed convection of Al 2 O 3 /water nanofluids in a square enclosure. The Rayleigh number is considered from 10 3 to 10 6 to present the buoyancy effects. In mixed convection problems, the Richardson number representing the importance of natural convection relative to the forced convection is set to Ri = 1, 5, and 10. Numerical results show that the convective heat transfer effects of nanofluids are higher than that of the base fluid. Increasing the nanoparticle volume fraction up to 4% can cause the averaged Nusselt number of the hot wall an increase about 5–7% in natural convection and 9–13% in mixed convection respectively. In natural convection, the streamlines and temperature contours are found to be slightly changed by adding nanoparticles into water. But in mixed convection, significant differences are obtained because the influence of adding nanoparticles on the properties of nanofluids is enlarged by the force convection effects.