Entropy Generation Analysis of Nanofluid Flow in Turbulent and Laminar Regimes

Entropy generation analysis is one of the most powerful tools to investigate the performance of thermal systems. Many researchers have studied entropy generation of thermal systems to find the optimum operating conditions. This paper numerically investigates the effects of Al2O3 nanoparticle concentration on the entropy generation of water-Al2O3 nanofluid flow through a circular pipe under constant wall heat flux boundary condition in laminar and turbulent regimes. The nanofluid flow is simulated using a CFD (Computational Fluid Dynamics) finite volume code and the k - epsilon model is applied to simulate the turbulent flow. The code which is employed for the simulation of the nanofluid flow is validated with the available empirical correlations. Approved formulations are used to model the density, specific heat, viscosity and conductivity of the nanofluid. It is observed that adding nanoparticles to the slurry results in a decrease in the heat transfer entropy generation and an increase in the friction entropy generation. In the turbulent flow both of the friction and thermal entropy generation terms are of the same order of magnitude, while in the laminar regime the effect of the heat transfer entropy generation strongly outweighs that of the friction entropy generation. In this article, the total entropy generation is plotted versus Reynolds number for laminar and turbulent regimes and the optimum Reynolds number minimizing the entropy generation is obtained. Moreover, the contours of the friction, thermal and total entropy generations are displayed in laminar and turbulent regimes. It is found that application of Al2O3 nanofluid slurry instead of pure water in low Reynolds numbers decreases the entropy generation and is beneficial.