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Journal of Zhejiang University SCIENCE A
ISSN 1673-565X(Print), 1862-1775(Online), Monthly
2025 Vol.26 No.4 P.339-358
Thermocline performance in a molten salt thermocline energy storage tank with annular-arranged and cross-arranged diffusers
Abstract: The thermocline energy storage tank (TEST) serves as a crucial component in thermal energy storage systems, utilizing the working fluid that enters through a diffuser to store and harness energy. However, the conventional double-plate radial diffuser is ill-suited for a single-medium TEST’s full tank storage due to its unidirectional fluid inflow. There has been a notable lack of optimization analysis of diffusers. Two innovative tubular diffuser designs with reduced cross-sectional areas have been introduced: the annular-arranged diffuser (AAD) and the cross-arranged diffuser (CAD). To elucidate the impact of diffuser designs on energy storage efficiency, a 3D transient computational fluid dynamics (CFD) model was established to simulate a thermocline formation under two diffuser types. The model was validated against experimental data. Results showed that the thermocline of AAD was 11.39% thinner than that of a traditional double-plate diffuser. In the process of charging and discharging, the time-varying thermocline and factors influencing thermocline thickness were analyzed. Results indicate that in the mixed dominant region, increased turbulent kinetic energy correlates with reduced thermocline thickness. Notably, the AAD’s stable thermocline was 4.23% and 5.41% thinner than the CAD’s during charging and discharging, respectively, making the AAD preferable for engineering applications. The effects of tube diameter and orifice opening angle on temperature stratification performance were also examined. The findings suggest that an inclined impact jet and large-diameter tubes are more conducive to temperature stratification. Moreover, an orifice diameter optimization method was developed, which can decrease the thermocline by 6.78%.
Key words: Molten salt; Thermocline; Computational fluid dynamics (CFD); Diffuser; Thermal energy storage
机构：1浙江大学，流体动力基础件与机电系统全国重点实验室，中国杭州，310058；2浙江大学，机械工程学院，中国杭州，310058；3西子清洁能源装备制造股份有限公司，中国杭州，310021
目的：温跃层储能单罐储放热过程中易出现黏性指进等现象，影响热分层效率，且缺少对扩散器的优化分析。传统双盘径向流扩散器在单工质满罐储热应用中存在局限性且缺乏优化分析。本文旨在研究和比较环形布置扩散器和十字布置扩散器在熔盐储热罐中的性能，分析不同扩散器设计、结构参数（管径、开孔角度）对熔盐储罐温跃层性能的影响，并提出优化方法以提高储能效率。
创新点：1.提出了两种适用于单工质熔盐储罐且具有较小截面积比的新型管式扩散器（环形布置扩散器和十字布置扩散器），并比较了不同扩散器结构参数对温跃层厚度的影响；2.开发了一种针对管式扩散器开孔直径的优化算法，成功改善了射流均匀性，进一步减小了温跃层厚度。
方法：1.建立考虑真实工况的三维瞬态计算流体动力学模型，用于模拟熔盐储罐在不同扩散器配置下的储放热过程和温跃层的形成与演变（图1）；2.应用开发的迭代优化算法，调整扩散器上各开孔的直径，并通过最小化各孔口出流流量的标准差，达到优化目的（图2）；3.通过仿真模拟，得到不同结构参数对温跃层性能的影响（图19和20）。
结论：1.环形扩散器性能更优，且温跃层厚度比交叉扩散器在储热和放热工况下分别减少4.23%和5.41%，更适合工程应用。2.冲击射流对温跃层厚度有显著影响，且斜向射流效果最佳；45°~60°孔口角度可平衡水平与垂直热交换，减少冷热流体混合。3.大管径扩散器可降低湍流扰动，改善温度分层。4.扩散器孔口尺寸的优化增强了熔盐储罐内温度分布的均匀性，且所提出的优化方法可使温跃层的厚度减少6.78%。
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DOI:
10.1631/jzus.A2400359
CLC number:
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On-line Access:
2025-04-30
Received:
2024-07-19
Revision Accepted:
2024-08-12
Crosschecked:
2025-04-30