A correlation approach for the calculation of thermal conductivity of nanofluids as a function of dynamic viscosity

Abstract

A correlation approach for the calculation of thermal conductivity of nanofluids as a function of dynamic viscosity is presented in this paper due to the significance of the nanofluids in energy systems. Available experimental data of relevant literature are used in terms of second order polynomial fit of the least-squares sense through the commercial software of MATLAB. The data belong to a variety of nanoparticles used in water (W) and ethylene glycol (EG)/ethylene glycol-water (EG-W) base fluids. Graphical plots of relative thermal conductivity, k(r) and relative dynamic viscosity, mu (r) are given as a function of nanoparticle volume fraction phi as a common route. The fitted equations are used to calculate k(r) and mu (r) in an extended range of 0%<= phi <= 55%. The validity range is given as a temperature range T of 20-50 degrees C and nanoparticle size range of 5-100 nm. The proposed non-dimensional equations of k(r)=k(r) (mu (r)) for W-based and EG/EG-W-based nanofluids have a severe difference indicating the major influence of base fluid. It is possible to calculate k(r) with the known or estimated value of mu (r) or vice versa as a solid contribution the state of art. The correlations also reflect the influence of viscosity on thermal enhancement of nanofluids as a physical fact of practice provided.