Experimental investigation of a novel Al₂O₃–TiO₂–CuO– Fe₃O₄/water–EG quadri hybrid nanofluid: Effects of temperature and nanoparticle concentration on thermophysical properties

This study experimentally investigates the thermophysical properties of a novel quadri-hybrid nanofluid consisting of Al₂O₃, TiO₂, CuO, and Fe₃O₄ nanoparticles dispersed in a 50:50 (v/v) water-ethylene glycol base fluid. The suspension was stabilized with oleic acid and sodium dodecyl sulfonate as surfactants. The nanoparticles were characterized by SEM and XRD analyses. The dynamic viscosity, electrical conductivity, and surface tension were measured in the temperature range of 298–340 K at nanoparticle volume fractions between 0.1–1%. The results showed that the electrical conductivity increased monotonically with nanoparticle concentration, with a maximum increase of ~ 170% at 1% loading. Surface tension exhibited a U-shaped profile, decreasing by up to 29% at a concentration of 0.1% before partially recovering at higher concentrations. Viscosity analysis revealed two distinct regimes: a low-shear Newtonian plateau and a high-shear shear-thickening behavior, where viscosity increased by almost an order of magnitude at T ≥ 325 K and γ̇ ≥ 0.8 s-¹. To capture this complex behavior, a new RBF (Radial Basis Function) correlation was developed that reproduced all experimental viscosity data with a 3% deviation. These results demonstrate the strong coupling of temperature, shear rate, and nanoparticle concentration and emphasize the potential of quadri-hybrid nanofluids for advanced thermal management in aerospace, cryogenic cooling, and de/anti-icing applications.