Abstract:

Using latent heat thermal energy storage (LHTES) system can alleviate the mismatch between the energy supply and demand. In this paper, a vertical shell and tube LHTES unit was designed, and multiple layer phase change materials (PCMs) with melting temperatures of 35℃, 42℃, and 50℃ were filled. The nanoparticle of Al₂O₃ was added in PCM and heat transfer fluid for heat transfer enhancement. The thermal energy and exergy performance of the multiple LHTES unit were compared with the single layer unit. The thermal energy and exergy density evaluation criteria that comprehensively considered the volume of the composite PCM and the heat storage time were proposed. The effects of different nanoparticle volume fractions (1%, 3%, 5%, 7%, 9%, and 11%) on the performance of the multiple LHTES unit were analyzed. The results showed that compared to the single layer unit with a melting temperature of 50℃ of composite PCM, the heat storage time of the multiple LHTES unit was reduced by 29.81% under the same condition. Moreover, the multiple LHTES unit simultaneously presented higher thermal energy and exergy storage amounts. When the volume fraction of nanoparticles increased from 1% to 11%, the heat storage rate of the multiple LHTES unit could be improved by 21.31%, the thermal energy storage density increased by 15.61%, and the thermal exergy density decreased after reaching the maximum value of 3086J/(m³·s) at the volume fraction of the nanoparticle of 7%. Considering the volume of composite PCM, heat storage time, and total thermal energy and exergy storage amounts, the multiple LHTES unit presented the best performance with a nanoparticle volume fraction of 7%. Compared with the nanoparticle volume fraction of 1%, the thermal energy and exergy storage densities increased by 11.57% and 12.96%, respectively. This paper provided a theoretical reference for the application and optimization of multiple LHTES systems.

Key words: latent heat thermal energy storage, phase change material, nanomaterials, heat transfer, exergy, numerical simulation

摘要：

利用潜热储热（latent heat thermal energy storage，LHTES）系统能够缓解能源供需不匹配的问题。本文设计一种垂直管壳式LHTES储热单元，多级填充熔点为35℃、42℃和50℃的相变材料（phase change material, PCM），Al₂O₃纳米颗粒分别添加至PCM和换热流体中强化传热。对比多级与单级LHTES储热单元的储热及储㶲性能；提出考虑复合PCM体积和储热时间的储热储㶲密度评价标准，分析不同纳米颗粒体积分数（1%、3%、5%、7%、9%、11%）对多级储热单元性能的影响。结果表明：相同工况下，相较于单级填充熔点50℃复合PCM的储热单元，多级复合PCM的使用可将储热时间缩短29.81%，且多级储热单元同时表现出较高的储热量和储㶲量；纳米颗粒体积分数从1%增加至11%时，多级储热单元的储热速率提高21.31%，储热密度增大15.61%，而储㶲密度在体积分数为7%时达到最大值3086J/(m³·s)后逐渐降低。综合考虑复合PCM体积、储热时间以及总储热和储㶲量，填充纳米颗粒体积分数为7%的多级储热单元性能最优，相较于纳米颗粒体积分数为1%时，储热和储㶲密度分别提升11.57%和12.96%。本文可为多级LHTES系统的应用与优化提供理论参考。

关键词: 潜热储热, 相变材料, 纳米材料, 传热, ?, 数值模拟