Analysis of HTFs, PCMs and fins effects on the thermal performance of shell–tube thermal energy storage units
Analysis of HTFs, PCMs and fins effects on the thermal performance of shell–tube thermal energy storage units
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DOI：
10.1016/j.solener.2015.09.019
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发表时间：
2015-12
期刊：
影响因子：
6.7
通讯作者：
Zhuo Li;Zhi-Gen Wu
中科院分区：
文献类型：
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作者：
Zhuo Li;Zhi-Gen Wu
在太阳能热电厂中，蓄热系统是一个关键部件，它包括蓄热单元、蓄热材料和传热流体。我们数值模拟了具有不同几何构型、相变材料（PCMs）（包括纯纳米3和纳米3/膨胀石墨（EG）的复合材料）以及HTFs（如合成油和熔盐）的壳管式TES装置的动态热性能。在充放电过程中，特别关注蓄热单元与热输送通道之间的共轭传热行为。利用总热流密度和有效努塞尔数对扩展翅片、PCMs和HTFs对热流性能的改善效果进行了研究和量化。结合所提出的PCM相演化图，清楚地揭示了热传导和自然对流对TES单元热行为的影响。由于自然对流，PCM的相位分布不均匀，导致在充放电过程结束时花费相当长的时间。结果表明，采用扩展翅片和复合材料可使完全熔化时间和凝固时间至少缩短14%。本研究可望对热输运机制提供更全面的解释，并为TES系统的优化运行提供合理的建议。
In solar thermal power plant, the thermal energy storage (TES) system is a key component which includes thermal energy storage unit, thermal energy storage material and heat transfer fluid (HTF). We numerically simulate the dynamical thermal performances of shell–tube TES units with diverse geometric configurations, phase change materials (PCMs) including pure NaNO3and a composite of NaNO3/expanded graphite (EG), and HTFs such as synthetic oil and molten salts. In the charging/discharging process, the conjugated heat transfer behavior between the thermal storage unit and thermal carriage channel is specially concerned. Effects of the extended fin, PCMs and HTFs on improving heat performance are examined and quantified with total heat flux and effective Nusselt numbers. Together with the presented diagrams of PCM phase evolution, the roles of heat conduction and natural convection in influencing the thermal behavior of the TES units are clearly revealed. The nonuniform phase distribution of PCM due to natural convection results in a considerable time spent in the end of the charging/discharging processes. The results show that both the full melting time and solidification time can be shortened at least 14%, benefited from using the extended fins and the composite. This study is expected to provide an apprehensive interpretation of thermal transport mechanism and rational advices in optimizing the TES system operation.