Heat transfer efficiency of Al2O3-MWCNT/thermal oil hybrid nanofluid as a cooling fluid in thermal and energy management applications: An experimental and theoretical investigation

The main objective of the present study is to assess the heat transfer efficiency of Al2O3-MWCNT/thermal oil hybrid nanofluid over different temperatures (25–50 °C) and solid concentrations (0.125%–1.5%). To this end, first of all, the stability of the nano-oil has been studied through the Zeta potential analysis. Then, the dynamic viscosity and thermal conductivity of the nanofluid have been experimentally investigated. It was found that the nanofluid showed Newtonian behavior over the studied range of temperatures and solid concentrations. The dynamic viscosity showed increasing trend as the solid concentration increased. It is found that the minimum increase in dynamic viscosity is at the temperature of 50 °C in all the studied solid concentrations except 0.5% and 1%. As for the thermal conductivity, it showed increasing trend as the temperature and solid concentration increased. The maximum enhancement was at the temperature of 50 °C and solid concentration 1.5% by approximately 45%. Based on the experimental data, two new highly precise correlations to predict the dynamic viscosity and thermal conductivity of the studied nanofluid have been proposed. Moreover, the heat transfer efficiency of the nanofluid has been evaluated based on different figures of merit. It is revealed that using this nanofluid instead of the base fluid can be beneficial in all the studied solid concentrations and temperatures for both the internal laminar and turbulent flow regimes except the solid concentrations of 1 and 1.5% in internal turbulent flow regimes. The effect of adding nanoparticles on pumping power and convective heat transfer coefficient has also been theoretically investigated.