Investigation of Heat Transfer Coefficient of Ethylene Glycol/ Graphenenanofluid in Turbulent Flow Regime

In the present work, graphene was synthesized by chemical vapor deposition (CVD) method. The structure of graphene was then confirmed by X-Ray diffraction (XRD) and scanning electron microscope (TEM) images. After that, mixed acid method (H2SO4/HNO3) was used to make the structure of synthesized graphenehydrophilic. In this method, carboxylate and hydroxide groups were linked to the edges of graphenenano sheets. The hydrophilic graphene was added to ethylene glycol (EG) with the concentrations of 0.100, 0.125, and 0.150 wt%, and the mixtures were sonicated at 60°C for 3hours to prepare the ethylene glycol/ graphenenano fluid. The thermal conductivity of samples was measured by KD2, while thermophysical properties of were estimated by valid theoretical equations. Then heat transfer coefficient of the samples was measured by using a straight pipe under constant heat flux and a turbulent flow regime. According to the obtained results, thermal conductivity and heat transfer coefficient increased by 21.2% and 42.4%, respectively, only by the addition of 0.15wt % of graphene in to ethylene glycol. Also thermal conductivity and heat transfer coefficient were improved by increasing the temperature and concentration of graphene.