Pool boiling heat transfer characteristics of graphene-based aqueous nanofluids

In the present study, experiments on pool boiling heat transfer of graphene nanofluids on a flat heater surface (40 mm diameter) were conducted under the saturated boiling and atmospheric pressure. This study also examined the thermal conductivity behavior of nanofluids based on graphene and functionalized graphene (PEG-graphene). The characteristics of pool boiling heat transfer such as boiling heat transfer coefficient (HTC), critical heat flux (CHF) as a function of heat flux and mass fraction of graphene sheets water-based graphene nanofluids have been measured and discussed. In addition, effective thermal conductivities versus temperatures for different concentrations of graphene were determined. From the boiling experimental results, it was indicated that the enhancement of boiling HTC and CHF changes considerably via increasing the concentration of graphene sheets. The results demonstrated that at the same temperature and concentration, thermal conductivity of nanofluid including PEG-graphene was significantly higher than that of one including pure graphene. In PEG-graphene/water nanofluids, CHF increased as the concentration increased. The results indicated that the enhancement in CHF was above 72% at the concentration of 0.1 mass%. The results demonstrated that PEG-graphene nanofluids at all concentrations (0.01, 0.05 and 0.1 mass%) have a suitable dispersion and fewer tendencies for agglomeration and precipitation, compared to graphene without functionalization.