Laminar Free Convection of Nanofluid Flow in Horizontal Porous Annulus

A numerical study has been carried out to investigate the heat transfer by natural convection of nanofluid taking Cu as nanoparticles and the water as based fluid in a three dimensional annulus enclosure filled with porous media (silica sand) between two horizontal concentric cylinders with 12 annular fins of 2.4mm thickness attached to the inner cylinder under steady state conditions. The governing equations which used are continuity, momentum and energy equations under an assumptions used Darcy law and Boussinesq’s approximation which are transformed to dimensionless equations. The finite difference approach is used to obtain all the computational results using the MATLAB-7. The parameters affected on the system are modified Rayleigh number (10 ≤Ra≤ 1000), fin length Hf (3, 7 and 11mm), radius ratio Rr (0.293, 0.365 and 0.435) and the volume fraction ( ) 35 . 0 0 ≤ ≤ φ . It was found that the average Nusselt number depends on (Ra, Hf, Rr and φ). The results show that, increasing of fin length decreases the heat transfer rate and for low values of Ra, decreasing Rr cause to decrease Nu while for Ra greater than 100, decreasing Rr cause to increase Nu and adding Cu nanoparticles with 0.35 volume fraction cause 27.9% enhancement in heat transfer. A correlation for Nu in terms of Ra, Hf and φ, has been developed for inner hot cylinder. Keywords—Annular fins, laminar free convection, nanofluid, porous media, three dimensions horizontal annulus.