Research on Influence of Heating Power on Two-Phase Flow Characteristics in Natural Circulation System with Low Height Difference at Low Pressure
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摘要: 对浮动式核电站中一类具有倾斜热管段的低压低高差自然循环系统的两相流动特性进行了实验研究，分析了加热功率对两相流动特性的影响。结果表明，不同功率条件下系统存在两相稳定冷凝和伴随蒸汽冷凝诱发水锤两相振荡2种流动模式，热管段内过冷水倒流和蒸汽与低温过冷水直接接触冷凝是导致2种流动模式的内在机制。此外，蒸汽冷凝诱发水锤的发生会产生较大压力脉冲，并导致过冷水倒流长度显著增加，进而加剧系统流动不稳定。进一步研究表明，加热段出口含气率可以作为流动不稳定判断依据。Abstract: Two-phase flow characteristics of a kind of natural circulation system with low height difference and inclined heat pipe section in floating nuclear power plants are experimentally studied at low pressure. The influences of heating power on the two-phase flow characteristics are analyzed. The results show that there are two flow modes in the system under different power conditions: two-phase stable condensation and two-phase oscillation along with steam condensation induced water hammer. The backflow of subcooled water in the heat pipe section and the direct contact condensation of steam and low-temperature subcooled water are the internal mechanisms resulting in the two flow modes. In addition, the occurrence of steam condensation induced water hammer will generate large pressure pulses and cause a significant increase in the backflow length of subcooled water, which further aggravates flow instability. Further research shows that the gas content at the outlet of the heating section can be used as a basis for judging the flow instability.
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图 2 热管段几何结构和测点布置
Figure 2. Geometric Configuration of Heat Pipe Section and Arrangement of Measuring Points
图 5 不同加热功率下热管段流体温度分布
Figure 5. Fluid Temperature Distribution in Hot Pipe Section at Different Heating Power
图 6 不同加热功率下最大压力峰值分布
Figure 6. Distribution of Maximum Pressure Peaks at Different Heating Power
图 7 加热功率对自然循环流量影响特性
Figure 7. Influence Characteristics of Heating Power on Natural Circulation Flow Rate
图 8 出口热平衡含气率对流动不稳定边界影响
Figure 8. Influence of Outlet Thermal Equilibrium Gas Content on Flow Unstable Boundary
表 1 仪器仪表类型及属性
Table 1. Instrument Type and Property
仪表名称 类别 量程 精度 热电偶 K型 −40~375℃ ±1.5℃ 电磁流量计 DN25 0.1~2 m3/h 1% 压力传感器 动态 −0.1~5 MPa 0.5% 压差计 电容式 −1~2 kPa 0.5% 功率表 有功功率 0~100 kW 0.5% 
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表 2 参数范围及相对不确定度
Table 2. Parameter Range and Relative Uncertainty
参数名 参数范围 相对不确定度/% 温度 24~100℃ 1.97 流量 0.5~1.2 m3/h 2.86 压力 −0.1~2 MPa 1.92 功率 63~87 kW 1.16 压差 0.19~1.06 kPa 1.72
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