Experimental Study of Thermal Conductivity and Viscosity of Water-Based MWCNT-Y₂O₃ Hybrid Nanofluid with Surfactant

There is an overwhelming demand in many solar applications to evaluate and improve the thermal properties (dynamic viscosity and thermal conductivity) of working fluids to ensure that those fluids are the most efficient. This can be achieved via scattering of tiny solid (mono or hybrid) nanomaterials into conventional fluids. In this experimental study, the thermal properties of a distilled water-based MWCNT+Y₂O₃ combination with a 20:80 weight ratio were experimentally investigated. The proposed hybrid nanofluid, prepared by a two-step method, with Gum Arabic as a surfactant, had half total volume concentrations of (0.01–0.2% vol) in the temperature range of 20–60°C, where stability has been reached and checked with various technics. The results demonstrate that the thermal conductivity coefficient increases with both temperature and concentration, especially at high concentrations and high temperatures. The maximum enhancement observed reaches 13% at a volume concentration of 0.2% and temperature of 60°C. As for the viscosity, the relative viscosity was obtained for various temperatures and concentrations, the maximum results reaching 8.85 at a concentration equal to 0.2%. Finally, correlations for the hybrid nanofluid thermal conductivity ratio and relative viscosity were suggested under the mentioned limitations, and the calculated experimental results demonstrate good accuracy with the proposed correlations with R² = 0.99 for the thermal conductivity ratio and R² = 0.95 for the relative viscosity.