Thermophysical Properties of Silver/Graphene Hybrid Nanoparticles Reinforced Ethylene Glycol– Glycerol Mixture Based Nanofluids

Abstract

Graphene nanoplatelets (GNPs) based cooling nanofluids have attracted tremendous attention due to low cost and high thermal conductivities. However, GNPs are not stable in common base fluids without proper surface treatments or surfactants. These surfactant or surface treatments impede the potential thermal conduction of GNPs. Several studies have addressed this issue by hybridizing GNP-based nanofluids with different highly thermal conductive materials to overcome that loss of thermal conduction. Besides carbon materials, metal nanoparticles still have higher potential thermal conductivities. Amongst high-conductive metal nanoparticles, silver has the highest proven thermal conductivity and stability. On the other hand, regarding extreme weather or specific industrial conditions ethylene glycol as base fluid has been mostly used, however, it has serious toxicity and environmental concerns. Therefore, in the current work, being the highest conductive and stable metal, silver nanoparticles have been incorporated with GNPs, and the binary mixture of ethylene glycol and glycerol in a ratio of 40:60 has been selected as less toxic and compatible with extreme conditions. The thermophysical properties are optimized based on different GNPs/Ag concentrations. Results showed that at 0.1 vol% of GNPs/Ag nano-additives, the thermal conductivity was significantly increased (102.85%) as compared to the base fluid. The zeta potential was remarkably increased (~100%) after adding T-80 surfactant to the 0.1 vol% GNPs/Ag hybrid nanofluid even after 7 days, where it recorded 35.2 mV compared to 15.7 of that without surfactant. Moreover, a minor increase of 19.84% in viscosity with 0.1 vol% GNPs/Ag hybrid nanofluid was noted relative to the base fluid. The reported hybrid nanofluids have shown potential usage as a cooling fluid in extreme thermal conditions.