非等距螺旋管壳式相变系统的蓄热性能研究

Heat storage performance investigation of non-isometric spiral shell-and-tube phase change system

针对垂直等螺距螺旋管壳式相变蓄热系统中相变材料上下受热不均匀的问题,首先,提出了3种不同压缩比的变螺距螺旋换热管结构;其次,数值模拟了不同压缩比螺旋管蓄热单元中相变材料加载过程;再次,讨论了4个蓄热罐中温度场和相界面的变化趋势,分析了液相分数与斯蒂芬数随傅里叶数的变化规律;最后,对比了不同配置下相变材料的加载时间、平均储能速率和储能量。研究结果表明:压缩后的换热管可以有效促进圆柱形蓄热罐底部沉降相变材料的熔化,减轻蓄热罐内温度垂直分层现象,强化液体相变材料之间的自然对流,提升等距螺旋管壳式潜热蓄热系统的热性能;与同等条件下的等距螺旋管相比,使用压缩比为2和3的螺旋管,其完全熔化时间分别减少了10.2%和16.6%,平均储能速率分别提高了16.1%和22.6%。此外,当压缩比增加到5时,系统加载时间不降反增,平均储能速率略有下降。

In order to optimize the phenomenon of uneven heating of the top and bottom of the phase change materials in a vertical equal-pitch spiral shell-and-tube type phase change heat storage system, three structures of variable-pitch spiral heat exchange tubes with different compression ratios were firstly proposed. Secondly, the loading process of phase change material in the spiral tube heat storage unit with different compression ratios was numerically simulated. Subsequently, the variation trend of temperature distribution and phase interface in four heat storage tanks was discussed, and the variation of liquid fraction and Stefan number with Fourier number were investigated. Finally, the loading time, average energy storage rate, and energy storage of phase change materials with different configurations were compared. The results show that the compressed heat flow tube can effectively promote the melting of the settling phase change materials at the bottom of the cylindrical heat storage tanks,reduce the vertical stratification of temperature in the thermal storage tanks, strengthen natural convection between liquid phase change materials, and improve the thermal performance of isometric spiral tube-and-shell latent heat storage system. Compared with the isometric spiral tube under the same conditions, the melting time of the spiral tube with compression ratio of 2 and 3 decrease by 10.2% and 16.6%, respectively, and the average energy storage rate increase by 16.1% and 22.6%, respectively. Moreover, when the compression ratio increases to 5, the loading time increases instead of decreases and the average energy storage rate decreases slightly.