In this study, nanofluids of tungsten oxide (WO3) nanoparticles (0.5–4 % mass fractions) in ethylene glycol (EG) and glycerol (G) as base fluids were prepared and their rheological properties were measured as functions of mass fraction, temperature, and shear rate. G and WO3–G fluids show nearly Newtonian behavior while EG and WO3–EG fluids display shear-thinning behavior especially at higher temperatures. The experimental data were fitted to classical fluid models (power law, Bingham plastic, and Herschel–Bulkley models). The rheological behavior of both nanofluids and base fluids was fitted well with the Herschel–Bulkley model. A 9 and 14 % increase in viscosity of ethylene glycol and glycerol was observed when 4 % WO3 nanoparticles were loaded at 20 °C and shear rates of 105 and 4 s−1, respectively. The viscosity of the nanofluids decreases exponentially with increasing temperature. The viscosity data as a function of temperature were fitted with six empirical models. To the best of our knowledge, this research is the first report on the rheological properties of nanofluids of tungsten oxide nanoparticles in EG and G. The colloidal stability of both WO3–EG and WO3–G nanofluids was measured using UV–Vis method. It was found that the stability of WO3–G is more than that of WO3–EG nanofluids. The WO3 nanoparticles with an average particle size of 22 nm were prepared using hydrothermal method and subsequently characterized using seven techniques including X-ray diffraction, transmission electronic microscopy (TEM), high-resolution TEM, energy-dispersive X-ray spectroscopy, UV–Vis, FT-IR spectroscopy, and Doppler light scattering technique.

Keywords