Characteristic Analysis on Distribution of Void Fraction during Stable Flow Flashing Process under Low Pressure
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摘要: 以低压自然循环系统内产生的闪蒸现象为研究对象，对闪蒸驱动的稳定两相自然循环流动阶段的空泡份额变化规律进行分析，通过分析发现上升段入口流体温度及水箱液位高度都会对流动闪蒸汽化过程的规律产生影响，使得空泡份额径向和轴向分布不一样。通过分析，得出影响汽化过程的主要因素是流体过热度，可知减小上升段入口流体过热度，闪蒸起始点会下移，闪蒸两相段变长；随着闪蒸汽化的不断进行，流体过热度逐渐减小，轴向空泡份额先迅速增加而后逐渐变缓，径向空泡份额分布由“壁峰”型衍变成“核峰”型。然后，然后基于流体当地过热度变化，拟合给出了不同工况下轴向空泡份额计算关系式，与实验数据对比符合较好，相对误差在±15%以内。Abstract: Taking the flashing phenomenon in the low pressure natural circulation system as the research object, the change law of void fraction in the stage of stable two-phase natural circulation flow driven by flashing is analyzed. Through the analysis, the following law is found that the inlet fluid temperature of the rising section and the liquid level height of the water tank will cause the flow to affect the flashing vaporization process, which makes the radial and axial distribution of the void fraction different. Through the analysis, it is concluded that the main factor affecting the vaporization process is the fluid superheat degree. It is known that reducing the fluid degree of subcooling at the inlet of the rising section, the flashing starting point will move down, and the flashing two-phase section will become longer. Along with the continuous flashing vaporization, the fluid degree of subcooling decreases gradually, the axial void fraction distribution increases rapidly first and then gradually slows down, and the radial void fraction changes from “wall peak” type to “nuclear peak” type. Then, based on the change of local fluid degree of subcooling, fitting gives the calculation formula of axial void fraction under different cases. By comparing with the experimental data, it is found that the fitting is good, and the relative error is within ±15%.
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Key words:
- Low pressure /
- Natural circulation /
- Flashing /
- Void fraction /
- Superheat degree
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图 1 实验系统示意图
T1~T9—热电偶；ΔP1、ΔP2 —差压传感器；P1~P3 —压力传感器；TA1~TA3 —温度测点
Figure 1. Schematic Diagram of Experimental System
图 2 WMS处时均空泡份额沿径向分布图
Tin, 上升段—上升段入口温度；α—时均空泡份额，r—径向位置
Figure 2. Radial Distribution of Time-averaged Void Fraction at WMS Position at Different Fluid inlet Temperatures
图 3 不同流体入口温度轴向中心位置处时均空泡份额分布
Z—轴向位置；L—上升段长度
Figure 3. Distribution of Time-averaged Void Fraction at Axial Center Position at Different Fluid inlet Temperatures
图 4 上升段底部静压变化曲线
Figure 4. Variation Curve of Static Pressure at Bottom of Rising Section
图 5 不同水箱液位下WMS处时均空泡份额变化曲线
Figure 5. Variation Curve of Void Fraction at WMS Position at Different Tank Levels
图 8 不同流体过热度下计算值与实验值的比值
Figure 8. Ratio of Calculated Values to Experimental Values for Different Fluid Superheat Degree
表 1 实验测量参数的不确定度
Table 1. Uncertainty of Parameters Measured in Experiment
测量参数 A类不确定度/% B类不确定度/% 总不确定度/% 温度 0.53~7.22 0.363 0.64~7.23 压力 5.25~15.83 0.283 5.26~15.83 压差 0.12~13.64 0.207 0.24~13.64 体积流量 0.59~6.68 0.205 0.62~6.68 
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