Abstract:

Latent heat thermal energy storage using phase change materials is an effective approach to address the intermittency issues of renewable energy sources. Nano-scale phase change microcapsules were prepared by interfacial hydrolysis condensation method using tetrabutyl titanate (TBT) as the precursor. The average thermal conductivity is enhanced to 215%, reaching approximately 0.43 W/(m·K). The phase change temperature is found to be 42.4℃. The latent heat of nano-encapsulated phase change materials is about 234.7 J/g. The nano-scale phase change microcapsules improved heat transfer performance and are suitable for heat storage of solar thermal water heating systems. A three-dimensional computational model was established, and numerical simulations were conducted on the packed bed using Fluent software to study the heat storage/release performance of the sequential structure (SS) and cross compound structure (CS) packed bed. The analysis focused on examining the variations in liquid fraction, temperature distribution, and thermal storage/release power for both SS and CS under different flow rate. The results show that the melting/solidification rates increase with increasing flow rate. At the same flow rate, CS exhibited faster melting/solidification compared to SS. The temperature variation of CS was more uniform than that of SS at different stages. At lower flow rate (2 L/min), both SS and CS exhibit longer and more stable periods of thermal storage/release. Under different flow rate (2, 4, and 6 L/min), the peak thermal storage power of CS is 1.7—1.9 times that of SS, and peak thermal release power is 1.8—2.0 times that of SS.

Key words: phase change, nano-scale phase change microcapsule, packed bed, numerical simulation, sequential structure, cross compound structure, thermal storage/release performance

摘要：

利用相变材料的潜热储能，是解决可再生能源不连续问题的有效途径之一。以钛酸四丁酯（TBT）为前体，采用界面水解-缩聚法制备了纳米相变微胶囊。纳米相变微胶囊的热导率提高到原材料的215%，约为0.43 W/（m·K），相变温度为42.4℃，相变潜热达到234.7 J/g，纳米相变微胶囊强化了相变材料的传热性能蓄热，适用于太阳能热水系统。建立了三维计算模型，利用Fluent软件对填充床进行了数值模拟，研究了顺排结构（SS）和叉排结构（CS）填充床的蓄/放热性能。分析了两种结构化填充床在不同流速下，液相率、温度场和蓄/放热功率的变化情况。结果表明，随着流速的增大，SS和CS的熔化/凝固速率均加快。在相同流速下，CS比SS熔化/凝固更快。SS和CS在不同的阶段升温速率不同，与SS相比，CS的温度变化更加均匀。在较低流速（2 L/min）下，SS和CS蓄/放热持续时间较长，变化较小。在不同的流速（2、4和6 L/min）下，CS的峰值蓄热功率是SS的1.7倍~1.9倍，峰值放热功率是SS的1.8倍~2.0倍。

关键词: 相变, 纳米相变微胶囊, 填充床, 数值模拟, 顺排结构, 叉排结构, 蓄/放热性能