Abstract:

Phase separation and supercooling are common phenomenon of salt hydrates, which is a key problem affecting the thermal stability and thermal performance of phase change material. Sodium acetate trihydrate (SAT), as a low and medium temperature hydrate salt, is the main study object. Carboxyl methyl cellulose (CMC) and disodium hydrogen phosphate dodecahydrate (DHPD) were firstly used to modify SAT by melt blending method. A high-performance composite phase change material (PCM) was prepared by optimizing the ratio of the additives. The thermophysical properties and stable performance of different samples were tested by using differential scanning calorimetry (DSC) and a melting-freezing setup. The effects of the additives on phase change enthalpy, phase transition temperature, supercooling and phase separation were analyzed. Finally, a high-density heat reservoir was built by using the modified PCM and a latent heat storage water system was set up. The charging and discharging performance of the system under different working conditions were analyzed. The results showed that adding 0.5% CMC as the thickening agent and 2% DHPD as the nuclear agent could avoid phase separation and decrease supercooling degree. The phase change enthalpy and temperature range of modified SAT were 258 kJ·kg^-1 and 57℃,respectively. The modified PCM had good cycling stability and its supercooling degree was smaller than 2℃. In addition, the output water temperature of the latent heat storage system under different cooling conditions can be heated up to over 50℃. The efficiency was higher than 90% and the heating power was as high as 10 kW. The heating power, energy storage capacity and thermal storage efficiency increased with the decrease of the inlet water temperature. The system has good charging and discharging performance and its volume heat storage density is 2.6 times as higher as traditional water tank.

Key words: salt hydrate, sodium acetate trihydrate, composite phase change thermal energy storage material, supercooling, thermal stability, charge and discharge

摘要：

水合盐相变储热材料普遍存在的过冷和相分离现象是影响其热稳定性和热性能的关键问题。以中低温水合盐相变储热材料三水醋酸钠（SAT）为研究对象，采用熔融共混法将羧甲基纤维素（CMC）和十二水磷酸氢二钠（DHPD）作为添加剂对三水醋酸钠进行了改性研究，通过各成分的配比优化制备了高性能相变储热复合材料，利用DSC及熔融-凝固装置对改性材料进行了热物性和稳定性的测试，分析了不同质量分数的添加剂对相变储热复合材料的相变焓、相变温度、过冷度及相分离现象的影响；在此基础上采用改性的SAT相变储热复合材料构建了高密度储热器并搭建了相变储能热水实验系统，研究了不同运行工况下相变储热器的储/放热性能。结果表明：添加0.5% CMC和2% DHPD的相变储热复合材料有效改善了纯SAT的相分离严重和过冷度大的问题，具有良好的热稳定性，多次循环后复合样品的相变焓为258 kJ·kg^-1，相变温度为57℃，过冷度在2℃以内；相变储能热水系统在不同放热工况下出口水温度均超过50℃，放热过程中相变材料温度变化平稳，储热器的储放热效率高于90%，放热功率大于10 kW，且随着入口水温下降，放热功率、放热量及储放热效率都提高，相变储热器的储能密度是传统水箱的2.6倍。

关键词: 水合盐, 三水醋酸钠, 复合相变储热材料, 过冷度, 热稳定性, 储放热