Rheological behaviour of eutectic nanofluids containing a low fraction of GO/TiO2 hybrid nanoparticles

Abstract

In this study, rheological properties of hybrid eutectic nanofluids were investigated. The eutectic salt mixture was prepared using nitrate salts in varying proportions, and eutectic nanofluid was prepared by dispersing low fractions of graphene oxide/titanium oxide (GO/TiO2) hybrid nanoparticles in the eutectic salt mixture. The material characterisation was performed using environmental scanning electron microscopy. Viscosity was measured by varying shear rates and temperatures from 0.001 to 1000 s−1 and 70–190 °C, respectively. Results show the effect of GO/TiO2 concentration (0.01, 0.05, and 0.1 wt%) reduced the viscosity by − 2.29%~22.63% at a higher shear rate (1000 s−1) and temperature (190 °C). Moreover, the eutectic nanofluid displayed strong Newtonian behaviour and was directly related to temperature and nanoparticle concentration. Herschel Bulkley model displayed the best fit and predicted all data points accurately even at higher temperatures with the coefficient of determination, R2 of 0.9987 (0.01 wt%), 0.9999 (0.05 wt%), 0.9999 (0.1 wt%) with standard deviation of 0.02 (0.01 wt%), 0.0018 (0.05 wt%), and 0.0027 (0.1 wt%), respectively. Viscoelastic studies of eutectic nanofluid at different wt% showed a slight thixotropic behaviour at 0.1 wt%, indicating the presence of nanostructures that is primarily responsible for the Newtonian behaviour of eutectic nanofluids. The proposed correlation predicts R between 0.873 and 0.878 while P-values < 0.05 at 190 °C, which is in good agreement with the statistical data. The variation in viscosity with temperature is better studied with a second-order polynomial function and the behaviour is explained with the proposed equations.