低压稳定流动闪蒸过程空泡份额分布特性分析

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。 

Characteristic Analysis on Distribution of Void Fraction during Stable Flow Flashing Process under Low Pressure

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%.