Energy-efficient automotive thermal management using mono and hybrid nanofluids with SDS surfactant: Experimental heat-rejection enhancement in a flat-tube radiator with water–ethylene glycol coolant

Improving energy efficiency in automotive systems requires effective thermal management that maintains engine temperatures while reducing parasitic power losses and enabling lighter, more compact heat-rejection hardware. Conventional water/ethylene-glycol coolants are limited by modest thermophysical properties, which can constrain radiator performance and increase the energy demand of auxiliary components like fans and pumps. In this study, the energy-relevant potential of mono and hybrid nanofluid coolants to intensify radiator heat rejection is evaluated experimentally under practical operating conditions. A commercial Hyundai Verna aluminium flat-tube, louvered-fin radiator was tested using ZnO, Al₂O₃, and CuO mono-nanofluids and a ZnO–Al₂O₃ hybrid nanofluid prepared at equal total mass fractions for consistent benchmarking. Nanoparticles ZnO (≈60 nm), Al₂O₃ (≈30 nm), and CuO (≈15 nm) were dispersed in a 70% water–30% ethylene glycol base fluid at mass fractions of 0–0.4 wt.%. Experiments were conducted on a dedicated rig at inlet temperatures of 60–80 °C, flow rates of 2–6 L/min, and various fan speeds. Heat transfer rates, convective coefficients, Reynolds and Nusselt numbers, and temperature-dependent properties were measured. Radiator performance improved with increasing coolant flow rate and nanoparticle concentration, primarily through an increase in the overall heat transfer coefficient. The Al₂O₃ nanofluid achieved the highest enhancement, reaching a 57.4% improvement, while the ZnO–Al₂O₃ hybrid yielded a 32.2% improvement at the same loading. These experimentally demonstrated heat transfer gains, together with a calculated fan power reduction estimate based on standard fan affinity law scaling, indicate that nanofluid based coolants are a promising pathway toward higher heat rejection or equivalent cooling with potentially reduced fan power and more compact radiator sizing implications for vehicle energy efficiency that warrant direct experimental validation at the fan and vehicle level in future work.