Effective viscosities and thermal conductivities of aqueous nanofluids containing low volume concentrations of Al2O3 nanoparticles

Aqueous nanofluids containing low volume concentrations of Al2O3 nanoparticles in the 0.01–0.3 vol.% range were produced and characterized. Measurements of zeta potential and TEM micrograph of the alumina nanoparticles in the Al2O3–water nanofluids show that the alumina nanoparticles can be best dispersed and stabilized in DI water with little evidence of aggregation at 5 h of ultrasonic vibration. Viscosity measurements show that the viscosity of the Al2O3–water nanofluids significantly decreases with increasing temperature. Furthermore, the measured viscosities of the Al2O3–water nanofluids show a nonlinear relation with the concentration even in the low volume concentration (0.01%–0.3%) range, while the Einstein viscosity model clearly predicts a linear relation, and exceed the Einstein model predictions. In contrast to viscosity, the measured thermal conductivities of the dilute Al2O3–water nanofluids increase nearly linearly with the concentration, agree well with the predicted values by the Jang and Choi model, and are consistent in their overall trend with previous data at higher concentrations.