硝酸盐/膨胀石墨复合相变材料的热性能

Thermal Properties of Nitrate/Expanded Graphite Composite Phase-Change Materials

选用熔点为131．1℃、相变潜热值为170．2J／g的40％（质量分数，下同）LiNO3-60％KNO3二元混合硝酸盐作为相变材料，选用高导热性、高比表面积、化学稳定性及热稳定性良好的膨胀石墨（EG）作为载体材料，采用磁力搅拌疰去制备得到LiNO3-KNO3／EG复合相变储热材料，并对其进行微观形貌表征、热物理性能测试、热稳定性研究及热性能分析。结果表明：混合熔盐较好地渗入到EG的多孔骨架结构中，且整体分散较为均匀，未出现混合熔盐团聚的现象；由于EG的强化传热、异相成核作用和微孔内压力变化的综合作用，导致样品的熔点和凝固点均有所降低，其中凝固点温度降低较多；EG的加入显著提高了样品的热导率；10％EG的加入使复合材料中较易分解的KNO，的分解温度由380℃上升到430℃，扩大了相变材料的应用范围。

Lithium nitrate （LiNO3） of 40% （mass fraction, the same below） and potassium nitrate （KNO3） of 60% were chosen as a phase change material （PCM） with the melting point of 131.1℃ and the latent heat value of 170.2 J/g. Expanded graphite （EG） was used as a carrier material with high thermal conductivity, high surface area, good chemical stability and thermal stability. The LiNO3-KNO3/EG composite phase-change heat storage material was prepared by a magnetic stirring method. The microstructures, thermal properties and thermal stabilities of different LiNO3-KNO3/EG samples were analyzed. The results show that the mixed molten salt is well infiltrated into EG porous skeleton structure, and the overall dispersion is relatively uniform without agglomeration The melting and freezing points reduce, and the freezing point temperature decreases more. It is the combined effect of strengthening heat transfer and heterogeneous nucleation of the EG and the pressure changes in the micro holes. The addition of EG increases the thermal conductivity of the sample. Based on the results of pyrolysis experiment, the decomposition temperature of KNO3 increases from 380℃ to 430℃, expanding the application range of phase change material.