LAUSR

Abstract Viscosity behavior of MWCNT (30%)-Al2O3 (70%)/5W50 nanofluid was investigated in temperature range of 5–55 °C, concentrations of 0.05%, to 1% and shear rate range of 666.5–11,997 S−1. Viscosity measurements showed pseudo-plastic behavior in all temperatures and concentrations of nanoparticles. Results revealed that viscosity of nanofluid decreases when temperature increases and it increases when volume fraction increases. Experimental data of MWCNT (30%)-Al2O3 (70%)/5W50 nanofluid was compared to data reported in other researches. An empirical correlation was proposed for the prediction of hybrid nanofluid viscosity based on temperature, concentration, and shear rate. R-squared of this correlation is 0.9979, and it means that the proposed correlation is capable of modeling the behavior of the studied hybrid nanofluid with a high level of precision. Moreover, this study proposed an optimized nanoparticles ratio as oil additives to eliminate unwanted viscosity reduction after adding nanoparticles for thermal improvement goals.