Experimental investigation on non-Newtonian behavior of Al2O3-MWCNT/5W50 hybrid nano-lubricant affected by alterations of temperature, concentration and shear rate for engine applications

In the present study, rheological behavior of Al2O3-MWCNT (65%-35%)/5W50 hybrid nano-lubricant is experimentally evaluated with the aim of facilitating its applications in automotive industry. Aluminum oxide (Al2O3) nanoparticles with the mean diameter of 50 nm along with multi-walled carbon nanotubes (MWCNTs) with inner diameter of 3-5 nm and outer diameter of 5-15 nm were used as nano-dispersants. Dynamic viscosity of samples of hybrid nano-lubricant composed out of 0% up to 1% solid volume fraction was measured at temperatures between 5 and 55 °C and shear rates between 666.5 and 10,664 s− 1. As a result it was revealed that the hybrid nano-lubricant is a non-Newtonian fluid, also power law index signified shear thinning (pseudoplastic) behavior of the fluid. It was observed that increasing of solid volume fraction aggravates non-Newtonian behavior of the nano-lubricant; on the contrary, temperature increment had the reverse effect. For the purpose of forecasting viscosity of the hybrid nano-lubricant, a new correlation is proposed which is based on temperature and solid volume fraction. R-squared of the correlation outputs is 0.9923, this means that the correlation is capable of modeling viscosity behavior of the hybrid nano-lubricant.