Experimental study of viscosity characteristics of graphite/engine oil (5 W-40) nanofluids

Viscosity characteristics of graphite/engine oil nanofluids is experimentally studied by the present work. Factors of temperature, particle concentration, and shear rate were investigated with ranges of 5-45 degrees C, 1-5.5 vol% and 17-5333 s(-1), respectively. Results reveal that addition of graphite nanoparticles does not perform much influence on the viscosity of base oil, which is unusual but indicates graphite as a promising nanoparticle addition. Besides, a maximum increase of 593% of viscosity was observed when decreasing temperature from 45 to 5 degrees C. From the results of ANOVA analysis, it showed the dominant effect of temperature which occupies more than 97% contribution to viscosity, overshadowing the effect of other factors. What's more, a time-dependent behavior of viscosity measurement was observed in the condition of low temperature and high shear rate. Test (background) temperature is supposedly attributed to such phenomenon. In the lower range of shear rate (17-68 s(-1)), nanofluids behaved as Newtonian fluid, while in the higher range of shear rate (667-3333 s(-1)) they performed as non-Newtonian fluid. Besides, using a power law model, simulation results indicate that particle volume fraction and temperature have little effect on power law index, but increase in temperature resulted in evident decline of consistency index.