Investigation effect of nanoparticle mean diameter on mixed convection Al2O3-water nanofluid flow in an annulus by two phase mixture model

In this paper, laminar mixed convection of nanofluid (Al₂O₃–water) in horizontal concentric annulus with constant heat flux boundary condition has been studied. Two thermal boundary conditions were investigated, one in which a uniform heat flux at the inner wall and an adiabatic at the other wall, and the other inner and outer walls were heated in a same heat flux. Two phase mixture model employed to investigate effect of mean diameter of nanoparticle on the hydrodynamics and thermal characteristic. The fluid flow properties are assumed constant except for the density in the body force, which varies linearly with the temperature (Boussinesq's hypothesis), thus the fluid flow characteristics are affected by the buoyancy force. Three dimensional elliptical governing equations have been discretized using the finite volume approach (FVM) using SIMPELC algorithm to investigate fluid flow throughout of an annulus duct. Numerical simulations have been carried out for the nanoparticle volume fraction (? = 0.02) and various mean diameters of nanoparticles (d_p) between 13 and 72 nm and different values of the Grashof and Reynolds numbers. The calculated results demonstrate that Nusselt number decreases with increasing nanoparticle mean diameter while it does not influence significantly the hydrodynamic parameters. Also this results show that nanoparticle distribution at the annuluses cross section is non-uniformity.