Synthesis of Compact and Porous SiO2 Nanoparticles and Their Effect on Thermal Conductivity Enhancement of Water-Based Nanofluids

In this work, compact and porous SiO2 nanoparticles (NPs) were synthesized using the Stober and the modified Stober methods. Water-based nanofluids were characterized by dynamic light scattering, scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction, and the porosity of the compact and porous SiO2 samples was measured by N-2 adsorption-desorption isotherms. Thermal wave resonator cavity and inverse photopyroelectric configuration novel techniques were used for the first time to obtain the porous nanoparticles thermal diffusivity (D) and effusivity (e), respectively. Thermal conductivity (k) was obtained from the relationship between them k = e root D. An increase in the thermal conductivity of the porous SiO2 NPs was obtained compared to the thermal conductivity of the compact NPs fluids with an enrichment of 14.7 %. Our results are supported by a theoretical model with a thermodynamic approach adapted for the thermal conductivity of porous SiO2 governed by the parameters of the porosity and nanoparticle size.