Characterization, Preparation and Thermophysical Properties Investigations of Aqueous AgNO3–Graphene Hybrid Nanofluids for Heat Transfer Applications

The comprehensive characterization of AgNO₃/graphene nanoparticles, preparation of their hybrid nanofluids and important thermophysical properties investigations have not been done so far to identify their potential application in heat transfer. Hence, current study attempts to characterize AgNO₃ and graphene nanoparticles by employing SEM, X-ray diffraction and FT-IR spectrum. Various concentrations of AgNO₃–graphene/water hybrid nanofluids (HNFs) are prepared. Two-step preparation process for HNFs involve magnetic stirring followed by probe sonication. Further, HNFs are characterized by particle size analysis and UV-spectroscopy. Additionally, thermal conductivity, specific heat, viscosity and density of HNFs are investigated experimentally with varying temperature ranges 25 °C to 75 °C and concentration ranges 0.01 vol % to 0.03 vol %. AgNO₃ and graphene structures peak are obtained at position 2θ = 35.58° and 2θ = 26.42° respectively and both the NPs features slight narrowing peaks. Experimental results reveal that, thermal conductivity improves with increasing temperature and found enhanced by 8.21 % for 0.01 vol %, 15.37 % for 0.02 vol % and 23.59 % for 0.03 vol % concentration at 75 °C compared to water. Specific heat of the HNFs rises with rising temperature whereas at a particular temperature it decreases with increasing NPs concentration. Dynamics viscosity decreases with increasing temperature for all prepared HNFs. The density exhibits no significant variation with the increase in concentration and temperature. Prepared HNFs are recommended as heat transfer fluid in various applications.