An Inspection of Viscosity Models for Numerical Simulation of Natural Convection of Al2O3-Water Nanofluid with Variable Properties

Abstract

This paper focuses on the study of natural convection heat transfer characteristics within a square cavity filled with Al2O3-water nanofluid using different viscosity models. The left and right vertical walls of the cavity are maintained at a different constant temperature Th and Tc, respectively, so that Th>Tc, while the bottom and top horizontal walls of the cavity are kept insulated. Finite volume method using SIMPLER algorithm for coupling of pressure velocity are used. In this study, the effects of uncertainties of different viscosity models of Al2O3-water nanofluid, namely, the Brinkman, Corcione, Khanafer & Vafai, and Abu-Nada viscosity models, on natural convection flow and heat transfer have been numerically investigated. Furthermore, the effects of the volume fraction and diameter of nanoparticles as well as the Rayleigh number have been studied. Based on the obtained results, significant differences are found between the magnitudes of heat transfer enhancement in the enclosure for the viscosity models employed. The results indicate that for the Rayleigh numbers of 105 and 106, by increasing the volume fraction of nanoparticles, the average Nusselt number decreases for the Corcione and Khanafer & Vafai models and increases for the Brinkman model, whereas a behavior of increasing in Nusselt number (at low volume fraction of nanoparticles) and decreasing is in average Nusselt number (at high volume fraction of nanoparticles) observed for the Abu-Nada model. In addition, employing the different viscosity models, significant differences at isothermal contours were not noticed.