Performance Investigation on the Heat Transfer of Composite rGO-SiO₂ Nanofluid in a Radiator

High-performing cooling fluids are increasingly gaining prominence in thermal applications due to their superior heat transfer (HT) features compared to conventional coolants. This is attributed to the sub-optimal cooling and heat transfer limitations by conventional coolants. Reports reveal that HT enhancement includes different modifications to the radiator for effective heat dissipation, engineered suspensions of nanoparticles in base fluids ensures the direct deployment of existing radiators. In this study, reduced graphene oxide (rGO) nanoparticle was prepared by modified Hummer’s technique via reduction process, with graphite powder as starting material, while silicon dioxide (SiO₂) was commercially sought. A comparative study was conducted to investigate the heat transfer of de-ionised (DI) water-based rGO-SiO₂ against its individual make-ups (rGO and SiO₂). At different volumetric concentrations (0.1%–0.3%) and temperature (20-60°C), SiO₂-rGO|0.3 composite nanofluid achieved a thermal conductivity (TC) enhancement of 16.8%, 9.4%, 7.1%, and 1.8% over the DI-Water, SiO₂|0.1, rGO|0.1, and SiO₂|0.3, which suggest a quick temperature equalization and better heat dissipation potential via Brownian motion, but 0.6% lower Tc compared to rGO|0.3 nanofluid. The viscosities of SiO₂|0.1, rGO|0.1, SiO₂|0.3, rGO|0.3 and SiO₂-rGO|0.3 nanofluids increased by 4.5%, 8.8%, 12.2%, 17.0%, and 14.0%, respectively, which may lead to an increase in pumping power demand, however, the positive figure of merit (TCR>1.0) justifies the nanofluids as better alternative to the basefluid. Furthermore, the Nu values of DI-Water/rGO SiO₂|0.3 was enhanced by 27.4%, 11.6%, 13.2%, 7.6% and 3.9% over the basefluid, SiO₂|0.1, rGO|0.1, SiO₂|0.3 and rGO|0.3 nanofluids, with an observable Nu increment of 3.71% and 8.87% of SiO|0.3 and rGO|0.3 compared to SiO|0.1 and rGO|0.1, respectively. In conclusion, TC ratio of the nanofluids were above unity, indicating enhanced heat transfer capability of the nanofluids compared to the base-fluid, and the MATLAB implementation of the proposed nusselt number correlation, fitted from experimental data achieved an R2 = 0.964.