Abstract:

Molten salt as phase change materials can be used as thermal storage medium in concentrating solar power (CSP) system. It is possible to significantly improve the thermal properties of molten salt by adding nanoparticles to molten salt. Nanofluids were synthesized by dispersing 20 nm SiO₂ particles to potassium nitrate, sodium nitrate, and solar salt (60% NaNO₃ and 40% KNO₃, mass fraction) respectively. Nanofluids were prepared by water-solution, sonication, and evaporation. The thermo-physical properties (latent heat, specific heat and molting point) of nonofluids were characterized by DSC method, and the thermal diffusivity was analyzed by laser flash apparatus (LFA). Results show that mass fraction of 20 nm SiO₂ particles significantly enhanced latent heat, specific heat and thermal conductivities of potassium nitrate, sodium nitrate, and solar salt. Compared with base salt, the average specific heat improved of solar salt,potassium nitrate,sodium nitrate with 20 nm SiO₂ nanoparticles was found to be 4.7%-15.89%, 3.9%-33.5%, 1.9%-11.86% in liquid, and the maximum thermal conductivity increased by a maximum of 17.16%, 39.7%, and 9.5%, respectively.

Key words: nanofluids, phase-change temperature, specific heat capacity, melting latent heat, thermal conductivities, decomposition temperature

摘要：

熔盐作为相变材料，可以用作聚热太阳能电站中的储热介质，通过向基盐中添加不同比例的纳米材料可以显著增强熔盐的热物性。将20 nm的SiO₂纳米颗粒分别分散到硝酸钾、硝酸钠和solar salt （60% NaNO₃，40% KNO₃，均为质量分数）中制备成稳定的纳米流体，制备的每一种纳米流体都经过溶解、超生、干燥蒸发等过程。采用差式扫描量热法测量熔盐的比热容、熔化潜热、熔点等热物理性质，并采用激光闪射法对基盐和纳米熔盐的热扩散系数进行测量和分析。结果表明，SiO₂颗粒的添加对硝酸钠、硝酸钾和solar salt的熔化潜热、比热容和热导率等热物理性质有显著的影响。与基盐相比，solar salt、硝酸钾和硝酸钠在液态的比热容值分别增加了4.7%～15.89%、3.9%～33.5%、1.9%～11.86%；测得的热导率分别最大增加了17.16%、39.7%、9.5%。

关键词: 纳米流体, 相变温度, 比热容, 熔化潜热, 热导率, 分解温度