管内低温两相流液泛发生机理及流型识别方法研究

The onset of flooding is a gas-liquid two-phase countercurrent stability limit, not only destabilizes the flow, but also greatly affects the normal operation of equipments due to the accompanying sharp rise of pressure drop. Since the large differences in thermodynamical properties,application of the correlations obtained from room-temperature fluids to the calculations of the onset of flooding and flow patterns evolution recognition for cryogenic fluids will lead to large errors. This project studies the onset mechanism of flooding of cryogenic fluids in a horizontal or incliend pipe, and gives the evolving nature of the multi-scale unsteady interfacial structure.In theory, through viscous Kelvin-Helmholtz instability analysis, which consideres the interfacial shear stress, and the establishment of dynamic equilibrium equations for single interface wave, to analyze the onset mechanism of flooding. By measuring the dynamic information of the pressure drop and gas fraction, utilizing the signal processing method of PDF,PSD and informative entropy, also through the visual observation using a high-speed camera, to determine the flow pattern transition recognition approach when the flow transits from the interface unsteady to flooding occurred. The influences of the inclinations and pipe diameters on flooding are also investigated in detail, and the flow pattern maps in the horizontal and inclined pipe will be finally drawn. The research results reveal the onset mechanism of flooding of cryogenic two-phase flow in the horizontal and incliend pipe, also obtain quantitative identification method of the flow pattern transition based on the characteristic parameters.

液泛是气液两相逆流的稳定极限，不仅破坏稳定流动，伴随的压降陡升等现象影响设备正常运行。由于热物性差别巨大,基于室温流体得到的关联式用于计算低温流体液泛临界速度和流型识别时误差较大。本项目研究水平管及倾斜管内低温流体液泛发生机理及其多尺度、非定常界面结构的演变特性。构建考虑界面剪切力影响的粘性Kelvin-Helmholtz界面不稳定分析方法以及对单个界面波的动力平衡模型，理论上分析液泛发生机理；通过动态测量压降及相含率等基础信息并基于PDF、PSD及信息熵等信号处理方法，结合高速摄像机可视化观察，获得从界面不稳定到液泛发生过程的流型转变识别方法。系统研究倾角和管径等对液泛发生机理的影响，绘制水平管及倾斜管液泛过程流型图。研究成果揭示管内低温流体液泛发生机理并获得基于特征参数的流型转变定量识别方法。

项目研究低温流体液泛机理及流型转变识别方法，系统探究了液氮/氮蒸汽流型改变条件和特性，特别是研究管内相含率的测量方法。研究成果如下：. 1：理论上：(1) 将二维Kelvin-Helmholtz（K-H）理论，拓展到三维非轴对称模型。K-H理论以往对垂直逆流两相流液泛临界速度的预测，都基于轴对称假设，没有考虑环向界面波。通过建立三维K-H理论并求解，得到与实验更加一致的液泛速度关联式。成果发表于：Annals of Nuclear Energy, 2018, 114: 616-623；（2）基于数学上双曲线方程存在拐点概念，认为拐点对应于物理上的流型转变点的思想，建立了低温流体液泛临界速度预测方法。与液氮/氮蒸汽实验数据对比验证了理论结果。成果发表于：Cryogenics, 2018,93: 41-47. (3) 基于粘性K-H理论，假设界面波达到最危险波长时触发液泛，考虑气液间粘性影响，推导了倾斜管内液泛临界速度预测公式，结果与实验吻合较好，成果发表于：Chemical Engineering Scienc, 2016,144, 395-403. 2：数值上，考虑到两相流发展过程将经历复杂流态改变，将AIAD模型引入到液氮/氮蒸汽的数值模拟中，用以判断流态转换，并考虑液氮/氮蒸汽相对于水的流态改变特点，对原模型系数进行了修正，得到了与实验数据更一致的结果。结果发表于：Cryogenics, 2019,97:100-108. 3:实验上，改进了液泛可视化实验系统，使液氮/氮蒸汽全流程真空绝热，获得了更准确的实验数据，探索了基于激光多普勒测速仪(LDV)测量速度。在两相流空泡率测量上，设计了第三代电容层析成像（ECT）传感器，理论发展了反演算法。相关成果发表于：Cryogenics, 2017, 84: 69-72; 86:97-105; 2019,103: 1-10