A state of art review of the viscosity behavior of nano-lubricants containing MWCNT nanoparticles: Focusing on engine lubrication goals

• Study on rheological behavior of industrial oils enriched by multi wall carbon nanotube. • Presenting dedicated rheological characteristics of single degree oils. • Presenting rheological characteristics differences between single degree and multi degree oils. This study is conducted to investigate the rheological behavior of hybrid nano-lubricants with a focus on viscosity. Fluid viscosity influences pumping force, pressure drop, engine oil, and heating and cooling devices and, many factors affect the viscosity of nanofluids. In the present study, the effect of two parameters of solid volume fraction of nanoparticles ( φ ) in base fluids and temperature is studied and, all nano-lubricants discussed in this study are enriched with MWCNT nanoparticles. Also, the study of the rheological behavior of single-grade and multi-grade lubricants containing different nanoparticles is compared. Parameters such as consistency index, power-law index, temperature, φ , type of engine oil, and type and composition of nanoparticles are studied statistically and, the results from past research are organized. In fact, in this study, there is a good summary of the researchers' views about the proposed parameters. The studied nano-lubricants include a review of the types of engine oils which are used in the market.