Spectral beam splitting technology based on optical nanofluids (NFs) is a promising field of solar energy research. However, the challenges to optimize the optical properties and enhance the high temperature stability of NFs are always exist. In this study, Indium Tin Oxide (ITO) nanoparticles were selected as the research object because of the excellent optical properties. The Oleylamine-capped ITO nanoparticles were prepared by chemical reduction. A novel NF based on Therminol 66 was successfully prepared. The high temperature stability and optical properties of obtained Oil-based NFs were analyzed by the gravitational sedimentation method and spectrophotometry . Moreover, we experimentally studied the effect of single reaction condition on the morphology and Sn-doping of particles. The results indicated that, at the reaction condition of 320 °C, 5.5 h, and the In/Sn mole ratio of 90:10, the obtained nanoparticles had high monodispersity and crystallinity , and the resulting NF had good stability and dispersion. Furthermore, when tuning single reaction condition, the morphology and Sn doping of nanoparticles tended to be a regular change. However, the change of single reaction condition was not enough to obtain the ITO NFs with good stability and dispersion. The ITO NFs obtained in present study had high thermal stability, and showed different high-temperature characteristics in the Ultraviolet and visible (UV–Vis) and near infrared (NIR) regions.
Junhan Xu,Binghong Chen,Kunpeng Yuan,Jun Shu,Qiguo Yang
Ag@SiO 2 nanofluid is widely used in spectral splitting PV/T system. Its core–shell structure has great influence on the optical properties. In this work, we focus on the comprehensive analysis and structure optimization of Ag@SiO 2 nanofluid to achieve its optimal spectral performance. DDA method is used to predict the optical properties of Ag@SiO 2 nanofluid and an optimization model based on filter efficiency is proposed. The effect of the SiO 2 shell thickness and Ag core mass concentration is analyzed. It indicates that the spectral performance of Ag@SiO 2 nanofluid can be improved with SiO 2 shell thickness of 15–40 nm and Ag core mass concentration of 81–135 mg/L. To achieve the same theoretical merit function of 1.46, the usage of Ag mass can be reduced by 25/33/44/62 % with SiO 2 coating of 10/20/40/70 nm. The optimal structure to achieve the highest filter efficiency η of 37.8 % is with a shell thickness of 20 nm and a mass concentration of 113.9 mg/L. An indoor PV/T operation testing is conducted to verify the optimization results. The merit function of Ag-based nanofluids increases from 1.58 to 1.598 and a reduction in Ag usage of 17 % is achieved with a SiO 2 coating shell of 17.8 nm. Operation stability is also enhanced with no aggregation observed during the working cycle and 7-day static experiment.
In present work, an enhanced solar distillation system that combined a concentrating optical engineering and nanofluid-based spectral splitting PV/T technique is proposed to overcome the drawbacks of conventional solar distillation system. In such a system, gold and silver nanoparticles with selectively spectral absorption are added into water to absorb solar radiation that can’t be efficiently utilized by PV cells, and convert them into heat. The rest of solar radiation through nanofluid is converted into electricity to provide power to a fan, which is used to transport steam to an external condenser. The optical performance of the concentrated distiller is investigated by a simulation and experimental test. The optical and thermal properties of gold and silver nanoparticles are characterized, and the mean absorptivity and transmittance of the nanofluids are calculated and compared with pure water. The experimental results confirmed the improvement of nanofluid-based spectral splitting PV/T technique to solar distillation. In comparison with a conventional system, the water yield of the enhanced systems with gold and silver nanoparticles of mere 26 ppm concentration increase by 79.9% and 69.4%, respectively. The thermal efficiency of the enhanced systems with gold and silver nanoparticles also increase by 6.8% and 4.8%, respectively. Such a performance is mainly owing to two effects in the enhanced system. On the one hand, nanoparticles promote the absorption of water to solar energy, and then raise the temperature of water in the evaporator. On the other hand, the use of an external condenser in the enhanced system not only enhances the condensation of steam, but also improves the transmittance of distiller cover. Moreover, gold nanoparticle has more obvious improvement to water productivity than silver nanoparticle, but the PV efficiency of the enhanced system with gold nanofluid is lower than that of silver nanofluid. Therefore, the spectral characteristics of nanofluid have a significant influence for the performance of the enhanced distillation system.
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