Numerical Study on Flow and Heat Transfer Characteristics of the Molten Salt Single Tank Heat Storage Process
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摘要: 针对储热技术在新能源消纳领域的应用背景，该文设计了一种储换热一体式熔盐单罐，通过数值模拟研究了单罐蓄热特性及熔盐在蓄热过程中的传热规律，探讨了螺旋管间距、布置位置等对蓄热过程的影响规律. 研究结果表明：熔盐温度在蓄热过程中逐渐上升，密度减小，使得熔盐在罐内形成自然对流，螺旋管结构的布置形式使得罐内熔盐流场呈现三处旋涡；当螺旋管布置位置接近罐内底部时，由于底部熔盐密度较小，自然对流更为强烈，蓄热完成时间相对于布置在罐内中上部时可缩短34.1%；螺旋管内径的增大使得换热面积增加，加快了熔盐升温速率；螺旋管间距的增大会使熔盐加热范围变大，小幅度缩短蓄热完成时间；下进上出的进汽方式由于进口位置更靠近底部，使得罐内熔盐自然对流更强.Abstract: Aimed at the application of heat storage technology in the field of new energy consumption, a molten salt single tank integrating the heat storage and the heat exchange was proposed. The single tank heat storage characteristics and molten salt heat transfer laws during the heat storage process were numerically simulated and analyzed. The effects of spiral tube spacings and inlet/outlet layout positions on the heat storage process were discussed. The results show that, the molten salt temperature increases gradually in the heat storage process, while the molten salt density decreases and the natural convection forms in the tank. The spiral structure of the tube makes 3 vortices be formed in the flow field of the molten salt. With the spiral tube positioned at the bottom of the tank, the heat storage completion time can be shortened by 34.1% due to a stronger natural convection, compared with the cases at the center and the top of the tank. The increase of the spiral tube diameter may enlarge the heat transfer area and speed up the heating rate of the molten salt. With the increase of the spiral tube spacing, the heating range of the molten salt will be larger, and the heat storage completion time will be shortened slightly. The natural convection of the molten salt is stronger in the inlet-down and outlet-up case since the inlet position is closer to the tank bottom.
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Key words:
- molten salt single tank /
- heat storage completion time /
- molten salt temperature /
- natural convection /
- spiral tube
edited-byedited-by1) 我刊青年编委李勇来稿 -
图 1 熔盐单罐原理示意图
Figure 1. Schematic diagram of the single tank principle for molten salt
图 5 熔盐平均温度、蒸汽出口温度和熔盐侧对流换热系数随蓄热时间变化曲线
Figure 5. Variation curves of the average temperature of molten salt, the steam outlet temperature and the convective heat transfer coefficient on the molten salt side with the heat storage time
图 6 熔盐罐中心垂直截面(y=0)在不同时间点的流场和温度场分布
Figure 6. Flow field and temperature distributions of the vertical cross section (y=0) at different moments in the center of the molten salt tank
图 7 不同布置位置时，熔盐平均温度、熔盐侧对流换热系数随蓄热时间变化曲线
Figure 7. Average temperatures of the molten salt and convective heat transfer coefficients on the molten salt side with the heat storage time in different positions
图 8 不同布置位置时，中心垂直截面(y=0)处熔盐流场对比(τ=12 000 s)
Figure 8. Comparison of molten salt flow fields at the center vertical section (y=0) at different positions(τ=12 000 s)
图 9 不同管内径时，熔盐平均温度、熔盐侧对流换热系数随蓄热时间变化曲线
Figure 9. Average temperatures of the molten salt and convective heat transfer coefficients on the molten salt side varying with the heat storage time under different inner diameters of pipes
图 10 不同管内径时，中心垂直截面(y=0)处熔盐流场对比(τ=12 000 s)
Figure 10. Comparison of molten salt flow fields at the center vertical section (y=0) under different inner diameters of pipes(τ=12 000 s)
图 11 不同管间距时，熔盐平均温度、熔盐侧对流换热系数随蓄热时间变化曲线
Figure 11. Average temperatures of the molten salt and convective heat transfer coefficients on the molten salt side with respect to the heat storage time with different pipe spacings
图 12 不同管间距下，中心垂直截面(y=0)处熔盐流场对比(τ=12 000 s)
Figure 12. Comparison of molten salt flow fields at the center vertical section (y=0) under different pipe spacings (τ=12 000 s)
图 14 不同进汽方式时，熔盐平均温度、熔盐侧对流换热系数随蓄热时间的变化曲线
Figure 14. Average temperatures of the molten salt and convective heat transfer coefficients on the molten salt side varying with the heat storage time under different steam inlet layouts
图 15 不同进汽方式时，中心垂直截面(y=0)处熔盐流场对比(τ=12 000 s)
Figure 15. Comparison of molten salt flow fields at the center vertical section (y=0) under different steam inlet layouts (τ=12 000 s)
表 1 三元熔盐物性参数
Table 1. Physical parameters of the ternary molten salt
parameter value upper limit temperature/℃ 535 thermal conductivity/(W/(m·℃)) 0.571 specific heat/(J/(kg·K)) 1 550 dynamic viscosity/(mPa·s) 0.000 131T2-0.177 26T+61.764 melting point/℃ 142 density/(kg/m3) 2 317.5-0.787 8T 
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表 2 网格及时间步长独立性校核
Table 2. Mesh and time step independence checks
grid number time step /s molten salt temperature /℃ relative error /% 1 153 615 1 67.622 - 1 393 601 1 67.711 0.131 1 850 900 1 67.691 0.029 2 275 841 1 67.701 0.014 1 850 900 10 68.016 - 1 850 900 1 67.691 0.477 1 850 900 0.1 67.681 0.014
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