▎ 摘　　要

Thermal and rheological behaviors of the graphene-water nanofluids are investigated experimentally, focusing on the hysteresis phenomenon. Nanofluids with particle mass fraction from 0.1 to 2.0% are prepared by using PVP as surface-active material and ultrasonication. Morphological, material and stability characterization are carried out by STEM imaging, Raman spectroscopy, and zeta potential measurements. Rheological behavior of the prepared samples is analyzed at different temperatures and shear rates. Maximum viscosity increase is observed to be 45% for the 2.0% mass concentration at 25 degrees C. The relative viscosity does not change with temperature, unlike the absolute viscosity that decreases with temperature due to the viscosity change of the base fluid. Moreover, the relative viscosity is nearly constant at low concentrations for all shear rates, and it decreases with increasing shear rate for the mass fractions higher than 1.0%. Therefore, graphene-water nanofluids exhibit Newtonian behavior for particle mass fractions below 1.0% and shear thinning behavior at higher concentrations. Hysteresis is observed when increasing and reducing the shear rates within the same speed ranges for the samples higher than 1% particle mass fraction and above 40 degrees C. Thermal conductivity is enhanced with increasing concentration and maximum augmentation is observed to be 96% for a mass fraction of 2.0%. (C) 2019 Elsevier Ltd. All rights reserved.