Photo-thermal characteristics of water-based Fe₃O₄@SiO₂nanofluid for solar-thermal applications

This work proposes and demonstrates the novel idea of using Fe _3 O _4 @SiO _2 core/shell structure nanoparticles (NPs) to improve the solar thermal conversion efficiency. Magnetite (Fe _3 O _4 ) NPs are synthesized by controlled co-precipitation method. Fe _3 O _4 @SiO _2 NPs are prepared based on sol–gel approach, then characterized. Water-based Fe _3 O _4 @SiO _2 nanofluid is prepared and usedto 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 Fe _3 O _4 @SiO _2 NPs have a core/shell structure with spherical morphology and size of about 400 nm. Fe _3 O _4 @SiO _2 /H _2 O nanofluid enhances the photo-thermal conversion efficiency compared with base fluid and Fe _3 O _4 /H _2 O 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 Fe _3 O _4 @SiO _2 /H _2 O, 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.