The effect of Al2O3-water nanofluid on the heat transfer and entropy generation of laminar forced convection through isotropic porous media

Abstract

Forced convection of Al2O3-water nanofluid through isotropic porous media consisting of two arrangements of square pillars, i.e., staggered and in-line, were investigated from the perspective of the first and second laws of thermodynamics. To describe the thermophysical properties of the nanofluid, experimentally verified correlations and temperature-dependent thermal conductivity values were utilized. Assuming symmetrical boundary condition for the upper and lower lines and a constant longitudinal distance between the square pillars in both arrangements, different porosities were considered for the channels. Using similar thermophysical conditions for the two arrangements investigated, the temperature contours revealed that thermal equilibrium between the nanofluid and square pillars was reached in a shorter flow distance for the in-line arrangement. While the heat flux increased with increases in the nanofluid volume fraction, a decreasing trend was observed for the Nusselt number. The results further indicated that regardless of the arrangement of the square pillars, the dimensionless surface averaged entropy generation rate was reduced with increases in the nanofluid volume fraction. Concurrently, as the nanofluid volume fraction increased the Bejan number also increased. A comprehensive performance evaluation revealed that the in-line arrangement is the superior configuration, when both the first and second laws of thermodynamics are utilized in the evaluation process.