▎ 摘　　要

The present work is focused on the development of surfactant-free, highly stable thermally conducting nanofluid by employing in-house synthesized 'Silver decorated functionalized reduced graphene oxide' nanoflakes. The optical and thermophysical properties to structure relationships have been studied by varying sizes of silver nanoparticles decorated over functionalized reduced graphene oxide. Raman spectroscopic studies show 'Surface Enhanced Raman Spectroscopy' (SERS) properties, which is highly dependent on the size of silver nanoparticles. The reduced graphene oxide and its hybrid are effective photocatalysts for the degradation of harmful water-soluble azo dye tartrazine. Since the present coolant is aqueous-based hence this is the additional advantage we got by using reduced graphene oxide in the coolant. The synthesized material based surfactant-free nanofluids has been prepared. The enormous enhancement in the thermal conductivity is observed [similar to 24%, for 0.25% (w/v) additive] for the prepared nanofluid as compared to the base fluid and the thermal conductivity analysis was further correlated with Raman spectroscopic results. The nanofluid has been employed on the custom-made engine test rig and a reduction in the total fuel consumption is observed by 15-17% and other important performance parameters were significantly enhanced which promises its applications as a potential nanocoolant.