Experimental investigation and modeling of the viscosity of some water-based nanofluids

The kinematic viscosity of three kinds of nanofluids namely Al₂O₃/water, TiO₂/water, and graphene/water was measured at different temperatures. Concentration of the metallic oxide nanoparticles in water ranged from 0.01 to 0.04 wt% with 0.01 wt% steps while the concentrations of graphene/water nanofluids were 0.05, 0.25, 0.5, 0.75, 1 wt%. The viscosity of the studied nanofluids was measured at five temperatures ranging from 25 to 65 °C with 10 °C steps. The viscosity of DI water was measured at these temperatures as well. The viscosity ratios of all the studied nanofluids were calculated and compared with the prediction of nine well-known models proposed by former researchers. The percent error of these models in predicting the viscosity ratio of the studied nanofluids varied between 1.13% and 19.51% for Al₂O₃/water; 0.01% and 21.94% for TiO₂/water, and 0.14% and 68.78% for graphene/water nanofluid. Polynomial models were proposed for each nanofluid as these had lower percent errors in calculating viscosity ratios. The percent errors of the proposed models were 0.06 − 5.36% for Al₂O₃/water; 0.12 − 3.35% for TiO₂/water, and 0.15 − 55.74% for graphene/water nanofluid. Two overall models were also proposed for the viscosity ratio of all the studied nanofluids, one of which was temperature independent while the other had a functionality of temperature. The percent errors of the overall proposed models were observed to vary from 0.1% to 49.21% and from 0.02% to 36.83%, respectively which shows higher level of accuracy in predicting the viscosity ratio of the studied nanofluids when compared with the previous models.