Abstract:

Nanomaterials could improve the heat transfer and thermal heat storage performance of molten salts and further increase the efficiency of heat transfer and thermal heat storage systems greatly. To find efficient method for large-scale production of molten salt nanofluids, both the high-temperature melting method and the aqueous solution method were employed to prepare molten salt nanofluids by adding SiO₂ nanoparticles to a binary nitrate salt. Then, methods of differential scanning calorimetry, thermogravimetric analysis and micromorphology analysis were used to investigate the enhancement of latent heat and sensible heat, change of micromorphology of molten salt nanofluids prepared by the two methods. Results show that molten salt nanofluids with optimal performance were observed under the mixing time of 90 minutes for both preparation methods when heat of fusion and specific heat of molten salt nanofluid prepared by the high-temperature melting method are 2.6% and 28.18% higher than those by the aqueous solution method; Effect of preparation methods on melting point is weak but is apparent on micromorphology of molten salt nanofluids. Formation process and structure of cloud nuclei determine the thermal storage performance of molten salt nanofluids. In addition, preparation process of the high-temperature melting method is simple and energy-saving, which is suitable for large-scale production and engineering application of molten salt nanofluids.

Key words: molten salt nanofluid, large-scale production, high-temperature melting method, aqueous solution method, cloud nuclei, thermal energy storage

摘要：

纳米材料能够改善高温熔盐的传热储热性能，提升大规模储热系统的储热和热交换效率，但目前仍未找到纳米熔盐的高效大规模制备方法。为优选纳米熔盐的高效大规模制备方法，以二元混合盐为基盐，采用高温熔融法和水溶液法分别制备纳米熔盐，用差示扫描量热法、热重分析法和微观形貌分析法，研究制备方法对纳米熔盐显热和储热性能提升、微观结构的影响，探索纳米熔盐形成机理。结果表明，两种制备方法均在搅拌90 min时制备的纳米熔盐性能达到最优，且高温熔融法制备纳米熔盐的熔化潜热和比热容分别比水溶液法高2.6%和28.18%；两种方法制备纳米熔盐的熔点较小，但对纳米熔盐的微观形貌存在明显影响，云核的形成与结构影响着纳米熔盐的储热性能。相比水溶液法，高温熔融法工艺简单，过程能耗低，纳米熔盐储热性能更好，适用于纳米熔盐的大规模生产和工程应用。

关键词: 纳米熔盐, 大规模生产, 高温熔融法, 水溶液法, 云核, 储热