Al2O3-water Nanofluid in a Square Cavity with Curved Boundaries

In this research, natural convection of Al2O3-water nanofluid in a square cavity with top and bottom curved boundaries has been investigated using lattice Boltzmann method. A D2Q9 single relaxation time model has been used for both the hydrodynamic and thermal equations. Furthermore, in order to study the effect of nanoparticle size on the average Nusselt number, a two-component model has been used and two separate equations (one for each component) have been solved. Drag and buoyancy forces are included for coupling of these equations. Rayleigh number has been varied from 10^3 to 10^6 while volume fraction of nanoparticles is selected between 0 to 0.05 (six values including pure water). Three nanoparticle sizes, namely 20, 50 and 100nm, have been used in our simulations. Results show that the main factor for controlling the effectiveness of average Nusselt number of nanofluids compared to the base fluid is the volume fraction of nanoparticles. Results also reveal that nanoparticle size has a deteriorating effect on the Nusselt number enhancement of nanofluid. Effect of utilizing nanoparticles on the temperature and velocity contours are presented and showed that the effect of nanoparticles can be seen in increasing the effective Rayleigh number of the flow. A correlation is then presented to predict the average Nusselt number of Al2O3-water nanofluid in the investigated criteria for Rayleigh number, volume fraction and size of nanoparticles.