Experimental Investigation of Convective Heat-Transfer Performance of Graphite and SiO2-Graphite Nanofluids for Automotive Radiator Applications

Efficient heat transfers in radiators are vital for the life of the engine, to avoid being overheated. Conventional fluids are inefficient in engine cooling, and alternate solutions to prolong engine life must capture enhanced heat transfer, including the application of nanofluids. Despite growing interest in nanofluid-based radiator cooling, limited studies have quantified the comparative performance of base fluids, Gr/Water-EG single nanofluid and SiO2-Gr/Water-EG hybrid nanofluids under varying concentrations, individually. This study experimentally examined their thermophysical and convective heat-transfer behaviour in a radiator channel flow using thermal conductivity, viscosity, inlet temperature, Nusselt number and Reynolds number as performance indicators. Increasing nanoparticle volumetric fraction enhanced the thermal conductivity of both graphite and SiO2-Gr nanofluids, whereas increasing ethylene glycol (EG) fraction in the Water-EG base fluid reduced thermal conductivity. Viscosity also increased with volumetric fraction for all fluids, confirming the concentration-induced trade-off between heat-transfer enhancement and flow resistance. The Nusselt number increased with inlet temperature for the Water-EG base fluid and graphite nanofluid, indicating improved convective heat-transfer response at elevated temperature. Conversely, the SiO2-Gr composite nanofluid showed a reduction in Nusselt number with increasing inlet temperature, suggesting temperature-sensitive transport behaviour; however, at 51 °C, its Nusselt number remained approximately 26% higher than Gr/Water-EG. Reynolds number increased with inlet temperature for the base fluid and graphite nanofluid, indicating stronger inertial flow. Although the hybrid SiO2-graphite nanofluid exhibited higher Reynolds numbers than the graphite nanofluid under the tested conditions, the observed reduction in Nusselt number with increasing inlet temperature suggests that the thermal enhancement mechanism may be influenced by alterations in fluid properties and particle interactions. Nevertheless, the SiO2-Gr nanofluid maintained a Reynolds number 66.7% higher than Gr/Water-EG at 51 °C. Overall, the hybrid nanofluid improved heat-transfer performance, although viscosity and flow penalties require optimization for radiators in automotive application.