Experimental investigation of thermo-physical and tribological properties of oil-based graphene oxide nano-fluid using two types of polysorbate (tween 20 and tween 80)

In this paper, the effect of adding Reduced Graphene Oxide (RGO) nano-particles to engine base oil (Poly-Alpha-Olefin-PAO) on the thermo-physical properties of nano-fluid such as viscosity, thermal conductivity, and friction coefficient, are investigated numerically and experimentally. To keep the nano-fluid stable, before using ultrasonic waves, two types of polysorbate (tween 20 and tween 80) as surfactants were added to four concentrations of 0.01, 0.02, 0.0375, and 0.05 wt%, and the effects of nano-particles were studied to find the best combination in terms of viscosity, thermal conductivity, and friction coefficient, which made the nan-fluid quite stable during the tests procedure. The results showed with good accuracy that the final nano-fluid was Newtonian and its viscosity was very similar to the base oil. An increase of 7% was observed between 25 °C and 75 °C and for the concentration of 0.02 wt%. Thermal conductivity was raised in all states with an increase in concentration and the highest effect was 8% in the concentration of 0.05 wt%. The friction tests proved a desirable decrease of as much as 45% in friction coefficient compared to base oil and 28% compared to common anti-friction material used in industry for the optimum concentration which was 0.02 wt%. In addition, experimental data were compared to the models presented in the literature and the models that could describe the behavior of this nano-fluid in the best way were reported, and an empirical equation (for each surfactant) is developed to show the variation of COF with nano-particles weight fraction in the nano-fluid.