Effect of suspending hybrid nano-additives on rheological behavior of engine oil and pumping power

•Preparing SAE40 based nanofluids containing Al2O3-MWCNTs hybrid nano-additives.•Performing tests in concentration range of 0-1.0% and temperature range of 25-50 °C.•All hybrid nanofluid samples were Newtonian fluid at all temperatures considered.•Performing sensitivity analysis for viscosity using experimental findings.•Proposing a new correlation to predict the viscosity of the hybrid nanofluid.

In this paper, the rheological behavior of engine oil containing various quantities of hybrid nano-additives has been examined. The experiments were performed in the solid volume fraction range of 0-1.0% and temperatures ranging from 25 °C to 50 °C. Viscosity measurements, at the shear rate range of 1333-13,333 s−1, showed that Al2O3-MWCNTs/SAE40 hybrid nanofluid had a Newtonian behavior at all solid volume fractions and temperatures considered. Experimental results also indicated that the viscosity of the hybrid nanofluid increased with increasing nano-additives concentration and decreasing temperature. Results of relative viscosity of the hybrid nanofluid showed that the maximum augmentation of the viscosity was about 46%. Results from sensitivity analysis of viscosity revealed that the viscosity sensitivity to temperature variation is minor, while it is more sensitive to the variations of solid volume fraction. Furthermore, an accurate correlation was proposed to predict the viscosity of the hybrid nanofluids for application in thermal engineering. Finally, the effects of nano-additives on the pumping power for the oil flow have been reported.