Investigation of Thermophysical Properties and Thermal Performance and Pressure Drop of of Nanofluid including Functionalized Graphene with Polyvinyl Alcohol

The lack of an appropriate dispersibility of Graphene Nanoplatelets (GNP) in different hydrophilic and hydrophobic media and their poor interaction to form bundles is one of the most important problems of this material. Therefore, in the present study, in order to perform covalent functionalization of GNP as well as increase the dispersibility in aqueous media, firstly it is created carboxylated with oxidation method on the GNP (Gr). Then, polyvinyl alchol (PVA) with the long chain can be a good candidate to functionalize on the surface of Gr for decorating divalent cations as a linkage and/or bridge and to solve the problem of lack of dispersibility. Also, it can provide good colloidal stability in aqueous media. So, after performing a reaction between PVA and Gr structure, structure and morphology of functionalized PVA-Gr to covalently were investigated by Raman spectroscopy and transmission electron microscopy (TEM), respectively. after covalently-functionalized nanofluids (PVA-Gr/water), with different weight concentrations of 0.025%, 0.05% and 0.1% were prepared. The stability and thermophysical properties such as thermal conductivity, viscosity and density of the above nanofluids have been studied. Then, the convective heat transfer coefficient, pressure drop, performance index and pumping power of the prepared nanofluids for different weight concentrations under turbulent flow regime (0.03-0.12 lit/s) were studied. The results show that as the flow rate and weight concentration of PVA-Gr in nanofluids increase, the convective heat transfer coefficient enhances, which PVA-Gr/water nanofluids illustrate the maximum enhancement in the heat transfer coefficient for all weight concentrations in comparison with pure water.