Correlations for thermal conductivity and viscosity of water based nanofluids

The thermo-physical properties of nanofluids such as thermal conductivity, viscosity, density and specific heat of nanofluids are required for the analysis of convection heat transfer coefficients. The density and specific heat of nanofluids can be estimated with the mixture relations in literature. Information regarding the properties at different volume concentration and temperature is required for the estimation of heat transfer coefficient. The two most fundamental properties which are, experimentally, determined, are viscosity and thermal conductivity. Investigators have been determining the properties of nanofluids at different temperatures and base liquids. The present work is an attempt to analyze the available data to develop a non-linear regression equation for the estimation of thermal conductivity and viscosity of water based nanofluids. In the present study, nanofluids are considered as a homogenous medium and the parameters influencing the thermo physical properties identified. Equations are developed for the analysis of thermo-physical properties of nanofluids as a function of parameters viz., material, concentration, temperature and particle size useful for designer. The opposing nature of thermal conductivity rise and viscosity decrease with temperature; dependence of nanofluid thermal conductivity on material properties alters the range of applicability of nanofluids for heat transfer applications. The thermal conductivity and viscosity of Al2O3, ZnO and TiO2 dispersed in water are measured to validate the proposed equations. The result shows that the equations are able to predict the thermal conductivity and viscosity of different types of nanofluids of different particle diameters closely.