Effect of Al₂O₃ nanoparticle dispersion on the thermophysical properties of an ethylene glycol-water coolant for automotive applications

Abstract

This experimental study evaluates Al₂O₃ nanoparticles dispersed in a 50:50 ethylene glycol–water (EG/W) mixture as an automotive coolant. Nanofluids containing 0.5–3.0 wt% Al₂O₃ were prepared by a two-step method and tested at 30–90 °C. FE-SEM, TEM, and XRD were used for particle characterization; dispersion stability was assessed by sedimentation and zeta-potential measurements. Thermal conductivity, dynamic viscosity, density, and specific heat capacity were measured experimentally. The dispersions remained visually stable for more than 200 h, with zeta potentials of −35 to −42 mV. Thermal conductivity increased with temperature and particle loading, reaching 0.640 W·m⁻¹·K⁻¹ at 3.0 wt% and 90 °C, 21.7% above the base fluid. At 30 °C, viscosity rose from 4.20 to 6.05 mPa·s at 3.0 wt%, while density increased slightly and specific heat decreased by 2.6–2.8%. The results show a clear conductivity–viscosity trade-off and indicate 1.5–2.0 wt% as a practical range for subsequent radiator-level testing.