Thermal conductivity of nanofluids containing microwave hydrothermal reactor reduced graphene oxide nanosheets

Graphene oxide nanosheets (GONs) were synthesized using Hummer's method. It was reduced applying microwave hydrothermal reactor (MHR). X- ray photoelectron spectroscopy (XPS) was utilized to study the chemical state variations of the GONs under applying the MHR. The reduction of GONs (RGONs) was confirmed using Energy Dispersive X- ray analysis (EDAX) analysis and photoluminescence (PL) spectrophotometer. By dispersing RGONs in ethylene glycol (EG), stable homogeneous nanofluids were prepared (RGONs- EG). The concentrations of RGONs in nanofluids were maintained at 0.01, 0.03 and 0.05 wt.% at the temperature range of 10 degrees C up to 55 degrees C. Zeta potential was utilized to clarify the stability of nanofluids. DLS analysis illustrated the size of RGONs nanosheets. The measurements of RGONs- EG thermal conductivity indicated that the nanofluids have significantly higher thermal conductivities than the base fluid. The thermal conductivity increased by enhancement of RGONs nanosheets concentration and strongly depended on the temperature. The highest enhancement was obtained to be about 17.8% for 0.05 wt.% of RGONs nanosheets at 55 degrees C. The thermal conductivity of the fluids remained almost constant for ten days, indicating high stability. These types of nanofluids including RGONs show prominent potential for substitutions as advanced heat transfer fluids in medium temperature applications such as solar collectors and heat exchanger systems.