Effect of Shear Rate, Temperature, and Particle Concentration on the Rheological Properties of ZnO and ZrO2Nanofluids

The rheological behavior of ZnO and ZrO2 nanoparticle suspensions in a polyalphaolefin (PAO 6) was investigated at high shear rates. Nanoparticles were dispersed at 0.5, 1.0, and 2.0 wt% in PAO 6 using an ultrasonic probe to produce nanofluids whose viscosity was determined over shear rates and temperatures ranging from 106 to 107 s−1 and 40 to 100°C, respectively. For the particle concentrations tested, the nanofluids exhibited a shear-thinning rheological behavior. The classical models typically used to predict nanofluid viscosity failed under these conditions because the viscosity depends not only on the temperature but also on the shear rate imposed. Two new experimental viscosity models were developed and validated for the studied nanofluids and constitute a practical tool to estimate the tribological behavior in lubricated pairs.