Numerical Study of Turbulent Mixed Convection of Nanofluids in Three-Dimensional Horizontal Concentric Annuli

Three-dimensional turbulent mixed convection flow using nanofluids in horizontal concentric annuli is numerically simulated. The continuity, Navier-Stokes and energy equations are solved using finite volume method (FVM) and the SIMPLE algorithm scheme is applied to examine the effects of turbulent flow on heat transfer characteristics. In this study, several parameters such as different types of nanoparticles (Al2O3, CuO, SiO2 and ZnO), different volume fractions in the range of 1% to 4%, different nanoparticles diameter in the range of 20 to 80 nm were used. Reynolds numbers are considered in the turbulent range of 6000 <= Re <= 18000. Different nanoparticle shapes (i.e., blades, platelets, cylindrical, bricks, and spherical), and effects of inner cylinder and outer cylinder heat fluxes were analyzed. Hydraulic diameter ratio was also examined. The numerical results indicate that the nanofluid with SiO2 has the highest Nusselt number and pressure drop compared with other nanofluids types. Heat transfer characteristic increases as the volume fraction of nanoparticles increases while it decreases as the nanoparticles diameter increases. Effects of hydraulic diameter ratio, nanoparticle shapes and location of applying heat flux on heat transfer characteristics are significant.