纳米相变微胶囊在蓄热结构化填充床中的应用模拟

Simulation of the application of nano-scale phase change microcapsules forthermal storage in structured packed bed

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。

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.