Preparation, Structure Analysis Of Functionalized Graphene And Investigation Of Its Nanolfuids

Graphene is a flat monolayer of sp2-bonded carbon atoms tightly packed into a honeycomb lattice. Graphene has many remarkable properties because of its special structure, especially specific surface area (2630m2/g in theory) and high values of thermal conductivity (about5000W/m·K), which is potential to be an excellent additive used in nanofluids. In this paper functionalized graphene (FG) as additive and silicone oil and ethylene glycol (EG) as base fluids, nanofluids were studied. The detail research contents and results are summarized as follows:FG was prepared by oxide-reduction method. At first graphene oxide was prepared by Hummers method, and then was modified by introducing3-glycidoxypropyltrimethoxysilane (KH-570), finally FG was prepared in the presence of hydrazine hydrate. FG can be stably dispersed in ethanol/H2O(9:1, volume), acetone/H2O(9:1, volume) or N,N-dimethyl formamide(DMF)/H2O(9:1, volume). The results shows that FG has irregular shape, and the size of FG nanosheets ranges from200nm to400nm, and the thickness of FG nanosheets is between1.1nm and2.3nm.FG-silicone oil nanofluid was prepared by using two-step method. FG has good compatibility with silicone oil, and it can be dispersed well in silicone oil without any surfatant or additives. The relative concentrations are maitained over60%of the initial concentration after setting10days. The results show that FG-silicone oil nanofluids behave in Newtonian manner. The viscosity of the nanofluids increases with increasing FG concentration, and decreases with increasing temperature. Thermal conductivity depends strongly on temperature as well as concentration. Thermal conductivity of nanofluids increases with increasing FG concentration, and the enhancement ratio of thermal conductivity at30℃for a mass fraction of0.01%is about2.2%, while for a mass fraction of0.07%, enhancement ratio of thermal conductivity raises to7.8%. Thermal conductivity also increases with increasing temperature, and enhancement ratio of thermal conductivity at20℃for a mass fraction of0.07%is about5.7%, while as at60℃, the enhancement ratio raises to18.9%. An enhancement ratio of electrical conductivity at25℃for a mass fraction of0.07%is about1400%.FG-EG nanofluid was also prepared by using two-step method. The result shows that FG-EG nanofluids are stable with the pH previously adjusted to8.5. FG-EG nanofluids behave in pseudoplastic fluid, and viscosity reduces with increasing shear rate. Different with FG-silicone oil nanofluids, thermal conductivity of FG-EG nanofluids are constant with increasing temperature. Thermal conductivity of FG-EG nanofluids depends strongly on FG concentration, and increases with increasing FG concentration. Thermal conductivity of FG-EG nanofluids shows an enhancement ratio of15.9%with0.01wt%FG loading, and enhancement ratio raises to63.0%with0.07wt%FG loading, which shows that heat transfer efficiency increases obviously. Moreover, the electrical conductivity shows an enhancement ratio of49.1%with0.07wt%FG loading at25℃.