Analysis of the Influence of Viscosity and Thermal Conductivity on Heat Transfer by Al2O3-Water Nanofluid

Abstract

The addition of nanoparticles into liquid, even at low concentrations, leads to an increase in both, dynamic viscosity and thermal conductivity. Furthermore, the increase in temperature causes an increase in thermal conductivity and a decrease in the nanofluid viscosity. In this context, a numerical investigation of the competition between viscosity and thermal conductivity about their effects on heat transfer by Al₂O₃-water nanofluid was conducted. A numerical study of heat transfer in a square cavity, filled with Al₂O₃-water nanofluid and heated from the left side, was presented in this paper. Continuity, momentum, and thermal energy equations are solved by the finite volume method. Regarding the pressure-velocity coupling, the SIMPLER algorithm was used. The working conditions, allowing the increase of heat transfer, are established. In addition, two correlations for viscosity and thermal conductivity of Al₂O₃-water nanofluid as functions of the concentration and diameter size based on experimental measurement are proposed. These correlations were more precisely compared to those given by the theoretical models. Moreover, other models for viscosity and conductivity depending on temperature are used and discussed. The results reveal that heat transfer by Al₂O₃-water nanofluid is enhanced only when the temperature exceeds 40°C and the diameter size does not exceed a certain limit of the order of 45-50 nm depending on temperature.