Aqueous hybrid nanofluids containing silver-reduced graphene oxide for improving thermo-physical properties

The main goal of this paper consists in the development of a new solar hybrid nanofluid (synthesis, characterization, and preparation) with improved thermo-physical properties to be used in solar applications in order to enhance the solar efficiency. The modified Hummers' method was employed to synthesize the reduced graphene oxide (rGO), while Ag NPs were synthesized by the reduction in liquid. A Scanning Electron Microscope, Transmission Electron Microscopy and Energy Dispersive X ray Spectroscopy were used to characterize the Ag-rGO/water hybrid nanofluid. Water-based Ag-rGO hybrid nanofluid was prepared with various weight concentrations (0.050, 0.075and 0.1 %). The Zeta Potential and PI index were measured to investigate the stability of the prepared hybrid nanofluid. These parameters exhibit stability in the long term (months). For 0.1 wt% and 50 °C, the thermal conductivity of Ag-rGO/water hybrid nanofluids was enhanced up to 11 %, the viscosity increased approximately 13 % and the density slightly grew with the concentration of Ag-rGO nanofluid up to 0.4 %. Finally, new correlations were developed for every property and the results achieved in this study were compared to existing results in the literature.