Effect of nanoparticles Brownian motion and uniform sinusoidal roughness elements on natural convection in an enclosure

The aim of the present study is to examine natural convection heat transfer in a square cavity filled with Al 2 O 3 –water nanofluid using lattice Boltzmann method. Right and left walls are kept at hot and cold constant temperatures, respectively, while uniform sinusoidal roughness elements are placed on both walls. Effective viscosity and thermal conductivity of nanofluid are obtained using Koo–Kleinstreuer model implementing Brownian motion of nanoparticles. The influence of pertinent parameters, such as Rayleigh number, solid volume fraction of nanoparticles, frequency and dimensionless amplitude of uniform sinusoidal roughness elements, on flow and heat transfer fields is investigated in the present paper. Results show an increase in Nusselt number with increasing nanoparticles volume fraction for various Rayleigh numbers with their most prominent effect at φ = 0.04 for Ra = 10 3 . Moreover, it was observed that mean Nusselt number decreases by increasing frequency and dimensionless amplitude of roughness elements for the whole range of Rayleigh numbers. In general, effect of nanoparticles on heat transfer enhancement is more highlighted by considering the role of Brownian motion.