Investigation of Viscosity and Rheological Properties of Copper/Ethylene Glycol Nanofluid

In recent years, significant attention has been devoted to nanofluids to improve the thermal efficiency of conventional cooling fluids. Copper nanoparticles are a proper candidate for this purpose due to their high thermal conductivity. In this study, stable copper nanoparticles with a 34.5 nm average diameter were synthesized via chemical reduction without an inert environment. The synthesized copper nanoparticles and also commercial copper nanoparticles with a 40 nm average size were used in ethylene glycol as the base fluid. Viscosity and rheological behavior of these nanofluids as important factors for assessment of flow behavior in heat exchange equipment were also investigated experimentally. The effects of volume fraction and temperature on nanofluid viscosity were investigated. Viscosity was measured in a 29.5-60 °C temperature range at low weight fractions of 0.0001, 0.0003, and 0.0005. The results were compared with the proposed models for the prediction of nanofluid viscosity, suggesting a correlation. The results show the Newtonian behavior of both nanofluids. Based on the results of a previous study, the heat transfer coefficient and thermal conductivity increased significantly (38.2 % for 0.03 wt. % nanofluid at Re=68 and 39.4% for 0.01 wt. %, respectively). Also, for both cases, nanofluid viscosity was smaller than the base fluid (for nanofluid B, 12.8% reduction at 1.06 vol. %). These results suggest copper nanofluid as an appropriate alternative for application in heat exchange equipment.