Entropy generation analysis of turbulent convection flow of Al2O3-water nanofluid in a circular tube subjected to constant wall heat flux

A parametric investigation of entropy generation of nanofluid turbulent forced convection inside a circular section tube subjected to constant wall heat flux is presented. The analysis is developed for different inlet conditions (i.e. constant Re, fixed mass flow rate and constant velocity) and in a concentration range from 0% up to 6%. The impact of the dispersed nanoparticles on total, thermal and frictional entropy generation is investigated and optimal working conditions are highlighted. The study shows that at the increase of Re, the optimal particles concentration to minimize entropy generation decreases. The impact of nanoparticles dimension is also taken into account, showing that its effect depends on the flow conditions. When working with constant mass flow rate, an optimal concentration is determined to minimize the frictional entropy generation, whereas thermal entropy generation results to increase. The study shows that to minimize total entropy generation when velocity is kept constant, a low concentration of nanoparticles is necessary. (C) 2013 Elsevier Ltd. All rights reserved.