Influence of Inlet and Outlet Resistance on the Characteristics of Backflow in Inverted U-tube Bundle
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摘要: 蒸汽发生器（SG）倒U型管束内倒流问题增大了自然循环条件下SG的流动阻力，降低了系统自然循环能力，对反应堆安全产生了负面影响。针对上述问题，以船用SG为研究对象，分别采用理论分析和计算流体动力学（CFD）数值模拟方法，通过修圆并联倒U型管束内管板开孔，研究了采用改进方案前后管板的流量分配和倒流特性。结果表明，通过修圆短管管板开孔，在自然循环工况下能有效降低SG流动阻力，增大短管的流量分配，从而降低倒流临界流量，延缓倒流现象的发生。研究结论为SG倒U型管束内倒流问题提供了一种可行的解决方案，可以为解决倒流问题研究提供支持。Abstract: The inverted U-tube bundle backflow problem of the steam generator (SG), which increases the flow resistance of SG under natural circulation conditions and reduces the natural circulation capacity of the system, has a negative impact on reactor safety. In view of the above problems, taking the marine SG as the research object, the flow distribution and backflow characteristics of the tube plate before and after the improvement scheme are studied by using the methods of theoretical analysis and computational fluid dynamics (CFD) numerical simulation and by rounding the tube plate opening in the parallel inverted U-tube bundle. The results show that by rounding the tube plate opening of the short tube, the flow resistance of SG can be effectively reduced and the flow distribution of the short tube can be increased under the natural cycle condition, so as to reduce the critical flow of backflow and delay the occurrence of backflow. The research conclusion provides a feasible solution for the backflow problem in the SG inverted U-tube bundle, and can provide support for the research on solving the backflow problem.
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图 1 流量分配管板的改进示意图
Figure 1. Improvement Schematic Diagram of Flow Distribution Tube Plate
图 2 改进前后各组U型管平均流量占比随总流量变化
Figure 2. Average Flow Proportion of U-tubes in Each Group Changing with the Total Flow Before and After Improvement
图 3 SG腔室的进出口压降随流量变化曲线
Figure 3. Variation Curve of Inlet and Outlet Pressure Drop of SG Chamber with Flow Rate
图 4 SG正流和倒流时的温度分布
Figure 4. Temperature Distribution of SG under Forward Flow and Backflow
图 6 SG并联倒U型管束内流速矢量图
Figure 6. Vector Diagram of Flow Velocity in SG Parallel Inverted U-tube Bundle
图 7 改进后SG腔室的进出口压降随流量下降曲线
Figure 7. Inlet and Outlet Pressure Drop Curve of SG Chamber with Flow after Improvement
表 1 并联倒U型管束内流量分配
Table 1. Flow Distribution in Parallel Inverted U-tube Bundle
流动状态 管板结构 流量分配/% 第1组 第3组 第5组 低流量 改进前 31.07 33.96 34.97 改进后 42.05 33.04 24.91 较高流量 改进前 33.17 33.33 33.50 改进后 35.22 32.26 32.52 
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