Investigation of thermal properties of SiO₂ and TiO₂ composite nanofluids synthesized using sol–gel method for solar thermal applications

This study investigates the thermal properties of hybrid nanofluids composed of titanium dioxide (TiO2) and silicon dioxide (SiO2), synthesized via the sol–gel method at varying pH levels. The nanofluids, with concentrations between 0.1 and 0.5%, were prepared using a two-step process and characterized using a hydrometer, viscometer and rapid hot-wire technique. FTIR (Fourier transform infrared spectra) analysis confirmed the formation of Ti–O and Ti–O–Si bonds, enhancing TiO2's structural and thermal properties due to SiO2 incorporation. The results showed significant thermal conductivity improvements, even at low concentrations, with performance increasing as concentration rises. Notably, a maximum specific heat capacity of 4177.02 J kg⁻¹ K⁻¹ was achieved at a 0.1% volume concentration, while thermal conductivity reached 0.62 W m⁻¹ K⁻¹ at a 0.5% volume concentration. Overall, the TiO2–SiO2 nanofluids demonstrated exceptional thermal properties, particularly under high-solar-energy conditions, making them promising for efficient thermal management applications.