Heat Transfer in Horizontal Annulus Saturated with Copper Nanofluid under Various Boundary Conditions

The natural convection heat transfer of laminar nanofluid flow is investigated numerically taking copper as nano particles and the water as based fluid in a three dimensional annulus enclosure filled with porous media between two horizontal concentric cylinders.12 annular fins of 3mm length and 2.4 mm thickness attached to the inner cylinder under steady state condition and different wall temperature boundary conditions. The governing equations used Darcy law and Boussinesqs approximation is transformed to dimensionless equations, then the finite difference approach is used to obtain the results using the MATLAB. The parameters affected on the system are modified Rayleigh number (10 Ra* 500), the copper volume fraction and for the sinusoidal temperature boundary condition, the parameters are the dimensionless amplitude, the constant dimensionless time =0.2 and dimensionless period (0.005 0.05). The results show that For Ra*=500, adding Cu nanoparticles with = 0.3 cause 268.18 % enhancement in heat transfer and For Ra*=500, adding Cu nanoparticles with = 0.3 cause 268.18 % enhancement in heat transfer and applying sinusoidal temperature boundary condition causes 1.7 % increase in heat transfer than that of constant wall temperature. A correlation for Nu in terms of Ra*, volume fraction () and amplitude (a) has been developed.