Photo-thermal characteristics of water-based Fe₃O₄@SiO₂ nanofluid for solar-thermal applications

This work proposes and demonstrates the novel idea of using Fe₃O₄@SiO₂ core/shell structure nanoparticles (NPs) to improve the solar thermal conversion efficiency. Magnetite (Fe₃O₄) NPs are synthesized by controlled co-precipitation method. Fe₃O₄@SiO₂ NPs are prepared based on sol-gel approach, then characterized. Water-based Fe₃O₄@SiO₂ nanofluid is prepared and used to illustrate the photo-thermal conversion characteristics of a solar collector under solar simulator. The temperature rise characteristics of the nanofluids are investigated at different heights of the solar collector, for duration of 300 min, under a solar intensity of 1000 W m-2. The experimental results show that Fe₃O₄@SiO₂ NPs have a core/shell structure with spherical morphology and size of about 400 nm. Fe₃O₄@SiO₂/H₂O nanofluid enhances the photo-thermal conversion efficiency compared with base fluid and Fe₃O₄/H₂O nanofluid, since the silica coating improves both the thermodynamic stability of the nanofluid and the light absorption effectiveness of the NPs. At a concentration of 1 mg/1 ml of Fe₃O₄@SiO₂/H₂O, and with the utilization of kerosene into the solar collector, and exposure for radiation for 5 min, the photo-thermal conversion efficiency has shown an enhancement at the bottom of the collector of about 32.9% compared to the base fluid.