Eccentricity effects of heat source inside a porous annulus on the natural convection heat transfer and entropy generation of Cu-water nanofluid

This study presents a numerical investigation on free convection heat transfer and entropy generation of Cu-water nanofluid inside an annulus, fully filled with a porous foam, in presence of a cylindrical heat source. For accurate nanofluid flow simulation, the two-phase mixture model is applied, and the viscosity and thermal conductivity of the mixture are computed based on the empirical Corcione's models. The effects of the vertical and horizontal heat source eccentricity (- 0.4 <= xi <= 0.4) and nanoparticles volume fraction (0 <= phi <= 0.04) for different values of Darcy (10(-4) <= Da <= 10(-1)) and Rayleigh (10(3) <= Ra <= 10(6)) numbers on the heat transfer and entropy generation are discussed. Results indicate that for various figures of eccentricity, heat transfer can be improved or deteriorated, depending on the value of Da, Ra and direction of the inner cylinder movement. Consequently, for each Rayleigh number, optimal values of Da and xi exist to meet the maximum average Nu number. In addition, an appropriate eccentricity - around xi = 0.1 and 0.2 - exists to minimize the total entropy generation. Moreover, the downward eccentric annulus expresses the best performance in which the highest heat transfer and lowest entropy generation occur.