Experimental research on viscosity of Al2O3-H2O nanofluids.

Viscosity of Al2O3-H2O nanofluids under different temperatures, concentrations and particle sizes is studied in this paper. A digital viscosimeter is used to measure the viscosity of four kinds of particle sizes (10 nm, 20 nm, 50 nm, 100 nm), five different volume fractions (0.25%, 1%, 1.5%, 2%, 2.5%) of nanofluids with the temperature ranging from 18°C to 40°C. And we calculated the relative viscosity of the nanofluids and its base fluid (deionized water). The result suggests that the viscosity of Al2O3-H2O nanofluids decreses with the increase of temperature, while the relative viscosity increases with the increase of volume fraction, and there exists a critical value of the volume fraction of 1.5% relating to the increasing rate of relative viscosity. It is also found that the smaller the particle size, the greater the influence of nanoparticles on the base fluid viscosity, namely the smaller nanopaticles have more obvious effect on base fluids’ viscosity. Our experimental viscosity values are in high agreement with the calculation value of Khanafer ‘s model at the volume fraction of 1%. But with the increase of volume fraction, the difference gets bigger between them. This may be associated with the different preparation methods of nanofluids. In addition, unknown surfactants in nanofluids have unknown effect on its viscosity.