A Review on Recent Progress in Preparation of Medium-Temperature Solar-Thermal Nanofluids with Stable Dispersion

Abstract

Direct absorption of sunlight and conversion into heat by uniformly dispersed photothermal nanofluids has emerged as a facile way to efficiently harness abundant renewable solar-thermal energy for a variety of heating-related applications. As the key component of the direct absorption solar collectors, solar-thermal nanofluids, however, generally suffer from poor dispersion and tend to aggregate, and the aggregation and precipitation tendency becomes even stronger at elevated temperatures. In this review, we overview recent research efforts and progresses in preparing solar-thermal nanofluids that can be stably and homogeneously dispersed under medium temperatures. We provide detailed description on the dispersion challenges and the governing dispersion mechanisms, and introduce representative dispersion strategies that are applicable to ethylene glycol, oil, ionic liquid, and molten salt-based medium-temperature solar-thermal nanofluids. The applicability and advantages of four categories of stabilization strategies including hydrogen bonding, electrostatic stabilization, steric stabilization, and self-dispersion stabilization in improving the dispersion stability of different type of thermal storage fluids are discussed. Among them, recently emerged self-dispersible nanofluids hold the potential for practical medium-temperature direct absorption solar-thermal energy harvesting. In the end, the exciting research opportunities, on-going research need and possible future research directions are also discussed. It is anticipated that the overview of recent progress in improving dispersion stability of medium-temperature solar-thermal nanofluids can not only stimulate exploration of direct absorption solar-thermal energy harvesting applications, but also provide a promising means to solve the fundamental limiting issue for general nanofluid technologies.

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“…The better dispersibility contributes greatly to higher photothermal conversion efficiency . The photothermal performance of OA-Ag@Fe 3 O 4 CSNWs shows a maximum temperature of approximately 60 °C within 8 min due to its better dispersibility (Figure c).…”

“…Figure 3b shows the zeta potential of Ag@Fe The better dispersibility contributes greatly to higher photothermal conversion efficiency. 39 The photothermal performance of OA-Ag@Fe 3 O 4 CSNWs shows a maximum temperature of approximately 60 °C within 8 min due to its better dispersibility (Figure 3c). This temperature increase induced by photothermal effects of OA-Ag@Fe 3 O 4 CSNWs is lethal to bacteria.…”

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“…Hu et al [4] provided an overview of the latest advancements in the development of solar thermal nanofluids capable of achieving homogeneous and stable dispersion at moderate temperatures. The authors comprehensively examined the issues associated with dispersion in several media, including ionic liquid, oil, molten salt-based, mediumtemperature solar thermal nanofluids, and ethylene glycol.…”