A comprehensive study to predict the rheological behavior of different hybrid nano-lubricants: A novel RSM-based analysis

In this study, two hybrid nano-lubricants MWCNT-ZnO (10:90)/oil 5W50 and MWCNT-MgO (35:65)/oil 5W50 are compared in terms of rheological behavior and viscosity. Temperature conditions are 5-55 C and volume fractions are in the range of phi = 0.05-1%. Based on the curve fitting on experimental data by using of the power law model in tau-gamma curves, it is shown that both nano-lubricants are non-Newtonian (shear thinning). Comparison of relative viscosity (mu(r)) and viscosity (mu(nf)) curves in different laboratory conditions shows that the slope of viscosity changes of the two above mentioned nano-lubricants have the same trend and even close values. In addition for time-saving goals and to have higher accuracy for both nano-lubricants, a new viscosity correlation relationship is proposed based on response surface methodology (RSM) with R-2 > 0.999. According to results, the maximum error in prediction of mu nf for MgO-MWCNT (65:35)/oil 5W50 is 8% and on the other hand, maximum 10% error reported for estimating the mu nf of MWCNT-ZnO (10:90)/oil 5W50.