Rheological behaviour of nanofluids containing tube / rod-like nanoparticles

Experiments are carried out on the rheological behaviour of ethylene glycol (EG) based titanate nanotubes (TNT) nanofluids containing 0.5, 1.0, 2.0, 4.0 and 8.0 wt.% TNT at 20–60 °C. The results show a very strong shear thinning behaviour of the TNT nanofluids and big influences of particle concentration and temperature on the zero shear viscosity (ZSV) and high shear viscosity (HSV), for which the conventional form of Brenner & Condiff Equation fails to predict. Theoretical analyses show that these experimentally observed phenomena can be well interpreted by the conventional colloid theory if particle shape and aggregation effects are taken into account and different relative importance of the Brownian diffusion and convection at different shear rates. It is suggested that nanofluids containing tube / rod-like nanoparticles with effective aspect ratio (ra) and effective volume fraction (φa) can be classified into dilute nanofluids with 0 < φa < 1/ra2, semi-dilute nanofluids with 1/ra2 < φa < 1/ra, semi-concentrated and concentrated nanofluids with 1/ra < φa.