光学探针测点位置对受热工况两相流流型识别的影响

采用汽泡尺寸概率密度函数(PDF)分析的方法，研究了探测点径向位置对流型识别的影响。结果表明，受热工况下该影响不可忽视。考虑到探测点空间位置对受热工况流型识别的影响，同时为了简化测量与分析，本文提出了“两点判别法”。实验结果表明，该方法对于垂直受热圆管可以得出准确的流型识别结果。     

中压沸腾工况相径向分布实验研究

采用高温高压单探头光学探针．在中压沸腾工况下进行了局部空泡率与汽泡频率径向分布特性实验研究,并根据探针信号对两相流流型进行了识别,分析了中压沸腾工况下空泡率径向分布与流型的关系。研究结果表明：随热平衡含汽率增加,整个直径方向上空泡率分布从近U形向鞍形和弧形发展;汽泡频率则以近U形分布为主;泡状流工况下,空泡率呈U形或近壁区显著高于中心区的鞍形分布,弹状流工况下,中心区空泡率略低于近壁区。整个直径上空泡率呈弧形分布。     

受热管内空泡率空间分布与流型的关系

介绍了运用RBI双探头光学探针,在加热上升管内对蒸汽-水两相流空泡率径向分布测量的情况,同时对不同实验工况下两相流流型进行了识别。根据实验结果,总结出加热上升管内空泡率径向分布与流型的关系。     

用气泡直径概率密度分布和气泡空间频率分析方法识别不可视通道内两相流流型

时域波形及其分析技术是不可视管道内两相流流型识别的常用方法。由于这一技术受到气泡流速的影响,容易造成流型识别的混淆。两相流流型分类的直观物理几何意义在于气泡空间尺度(相对于流道水力学当量直径)及其分布。本文论述了流型识别的空间处理技术(气泡的空间波形、气泡相对直径概率密度分布和空间频谱分析),从而使流型识别建立在流型分类的直观物理意义之上。本文给出了用电导探针作传感器,用空间处理技术识别流型的实验结果。空间处理技术识别流型的显著特点是物理意义上的直观和明晰。     

用气泡直径概率密度分布和气泡空间频率分析方法识别不可视通道内两相流流型

时域波形及其分析技术是不可视管道内两相流流型识别的常用方法。由于这一技术受到气泡流速的影响,容易造成流型识别的混淆。两相流流型分类的直观物理几何意义在于气泡空间尺度(相对于流道水力学当量直径)及其分布。本文论述了流型识别的空间处理技术(气泡的空间波形、气泡相对直径概率密度分布和空间频谱分析),从而使流型识别建立在流型分类的直观物理意义之上。本交给出了用电导探针作传感器,用空间处理技术识别流型的实验结果。空间处理技术识别流型的显著特点是物理意义上的直观和明晰。     

用空泡份额概率密度分布识别承压管道中两相流流型

用局部空泡份额概率密度分布识别流型是一种不可视管道内两相流流型识别的方法，这种流型识别建立在流型分类的直观物理意义之上，并避免了流速的影响。本文给出了用差压传感器信号进行承压管道中局部空泡份额概率密度分布分析，进而识别汽水两相流流型的研究成果，测量仪器装置简单、可靠性高。实验研究是在核供热堆热工水力学实验系统ＨＲＴＬ－５上进行的，试验工作压力为１．５ＭＰａ，工作温度１９０℃。     

低压自然循环系统中的流型实验研究

在5MW低温供热堆热工水力学实验台架HRTL-5上,以水为工质,进行了低压自然循环两相流流型及流型对密度波不稳定性影响的实验研究。结合可视化观察,利用局部差压信号进行流型鉴别。提出了Sr数可以很好地鉴别不同流型,具有明确的物理意义。描述了系统压力为1.5MPa,0.24MPa及0.1MPa下不同工况的流型,认为在1.5MPa工况下发生低干度密度波不稳定时,流型为泡状流,无流型转换,在流型为泡状流向间歇流过渡区时不会引起密度波不稳定。分析了常压稳定闪蒸时上升段出口的流型。在低温供热堆全参数、全尺寸模拟系统中,进行两相流流型的分析研究,对充分认识低温供热堆中各种工况下的流动形态提供了直接的有价值的成果。     

低压自然循环系统中的流型实验研究

在5MW低温供热堆热工水力学实验台架HRT-5上,以水为工质,进行了低压自然循环两相流流型及流型对密度波不稳定性影响的实验研究。结合可视化观察,利用局部差压信号进行流型鉴别。提出了Sr数可以很好地鉴别不同流型,具有明确的物理意义。描述了系统压力为1.5MPa,0.24MPa及0.1MPa下不同工况的流型,认为在1.5MPa工况下发生低干度密度波不稳定时,流型为泡状流,无流型转换,在流型为泡状流向间歇流过渡区时不会引起密度波不稳定。分析了常压稳定闪蒸时上升段出口的流型。在低温供热堆全参数、全尺寸模拟系统中,进行两相流流型的分析研究,对充分认识低温供热堆中各种工况下的流动形态提供了直接的有价值的成果。     

基于非监督机器学习方法的竖直环形流道流动沸腾流型研究

研究流动沸腾两相流动形态对封闭反应堆安全分析程序关键本构模型具有重要意义。本文基于非监督机器学习流型识别方法，提出将两相流物理知识融入数据驱动的机器学习模型，并构建输入特征的挑选原则：(1)机器学习在输入特征中捕捉到的应为流型相关信息；(2)机器学习的聚类准则应包络该流型下输入特征的所有可能性。依据挑选原则分析电导探针信号生成的汽泡分布特征，确定汽泡弦长累积分布函数数据可用于非监督机器学习流型判断。依据流型识别结果，获得了竖直环形流道内流动沸腾的二维局部流型特性，发现高位局部流型出现在流道中心位置并偏向内加热壁面；并判别了流道截面的全局流型，结果表明流动沸腾泡状流至弹状流的流型转变出现在空泡份额约为0.14位置。     

用差压信号空间特征频率Sr鉴别两相流流型

压差脉动分析方法是两相流流型识别的常用方法,通过频域特征峰辨识流型会受到气泡速度的影响,而混淆泡状流和间歇流。从两相流流型的空间几何意义出发,利用差压计作传感器,提出用标准空间特征频率斯特罗哈尔数Sr作流型识别的定量依据,斯特罗哈尔数Sr识别流型具有明确的物理意义。给出了这一空间处理技术辨识流型的实验结果。     

基于竖直圆管空气-水两相流实验的相间曳力模型研究

研究两相流相间阻力特性对系统程序关键本构模型封闭具有重要意义。本文基于竖直圆管开展了空气-水两相流实验,采用四探头电导探针对空泡份额、气泡弦长和界面面积浓度等气泡参数的径向分布进行了测量。结果表明空泡份额和气泡弦长呈现“核峰型”分布,而界面面积浓度并没有表现出随流速的单调关系。进一步开发了泡状流和弹状流的相间曳力模型,考虑了液相表观流速与管径对气泡尺寸分布的影响,建立了临界韦伯数与不同液相流速的关系。计算得到的空泡份额和界面面积浓度与实验数据整体符合较好,验证了模型的可靠性,为两相流相间阻力特性研究提供参考意义。     

Upward vertical two-phase flow local flow regime identification using neural network techniques

Traditionally, the flow regimes in two-phase flow are considered in a global sense. However, a local flow regime is required to understand and model the interfacial structures present in the flow. In this work, a new approach has been used to identify both global and local flow regimes in a two-phase upward flow in a 50.8 mm internal diameter pipe under adiabatic conditions. In the present method, the bubble chord length distributions, which are measured simultaneously with three double-sensor conductivity probes, have been used to feed a self-organized neural network. The global flow regime identification results show a reasonable agreement with the visual observation for all the flow conditions. Nonetheless, only the local flow regimes measured at the center of the pipe agree with the global ones. The local flow regime combinations found are analyzed using the flow map information, cross-correlations between the probe signals, and previous correlations. In this way, it is possible to identify eight different global flow regime configurations.     

Interfacial area density, mean radius and number density measurements in bubbly two-phase flow

This paper presents a new experimental method for measuring the local interfacial area density, average bubble radius and number density for bubbly two-phase flow. Experiments were performed using a KfK dual-sensor resistivity probe. The results obtained for interfacial area density using this method agreed with other methods previously proposed, except for high void fractions, close to the transition to slug flow, where prior methods are known to no longer be valid.     

竖直下降两相流相界面结构输运特性

竖直下降两相流具有与竖直上升两相流不同的相界面结构特征及输运特性。本文对竖直下降管内的气水两相流进行了实验研究,运用微型四头电导探针对7.5、31.5及55.5倍管径横截面处的空泡份额、相界面浓度、气泡直径、气泡频率及气泡速度等相界面结构参数的局部分布进行了测量。分析获得了相界面结构参数的沿程变化规律,并研究了气相表观流速对相界面结构发展的影响及一维相界面结构输运特性。发现竖直下降泡状流的升力指向管中心,导致相界面结构参数基本呈中心峰值分布;气相表观流速的增大会提高空泡份额和相界面浓度分布的峰度;竖直下降两相流在距入口31.5倍管径处基本达到充分发展。     

光纤双探针法测量液液两相流液滴直径

作为设计脉冲筛板柱的重要水力学特性参数,分散相液滴尺寸和液滴速率有重要的研究价值。使用内径为38mm的标准脉冲筛板柱,以水为连续相,纯煤油为分散相,利用光纤双探针法测量分散相表观流速、连续相表观流速和脉冲强度等因素对分散相液滴尺寸的影响。结果表明,光纤两相流参数测量系统能够很好地识别液液两相中的不同相,验证了光纤探针法应用于液液两相流的可行性。     

管束间空气-水两相流激振力特性及归一化方法研究

利用管束间空气-水两相流激振力的实验数据,研究了两相流激振力的部分特性,分析了混合物流速、空泡特征长度等两相流参数对两相流激振力的影响。结果表明,两相流激振力约与界面流速、混合物密度和混合物运动黏度呈正比,泡状流下激振力随气泡直径线性增长,证明两相流激振力的无量纲归一化可采用气泡数率作为频率缩比参数。基于上述两相流激振力的特性,从方便工程应用角度给出了两相流激振力的无量纲归一化方法,获得了较好的归一化效果。     

Simulation of a Single Bubble Rising with Hybrid Particle-Mesh Method

A computational study of the dynamics on a gas bubble rising in a viscous liquid by a hybrid particle-mesh method is presented. The hybrid particle-mesh method has been developed for the simulation of a two-phase flow. One phase is represented by moving particles and the other phase is defined on a stationary mesh. The flow field is discretized by conservative finite volume approximation on the stationary mesh, and the interface is automatically captured by the distribution of particles moving through the stationary mesh. The moving particles are calculated by Moving Particle Semi-implicit (MPS) method. The effect of surface tension is evaluated by the continuum surface force model. In this study, we simulate the motion of a gas bubble rising in a viscous liquid. The buoyancy driven motion of the bubble in a wide range of flow regimes is simulated successfully by the present method. The deforming interface of the bubble is captured effectively by the moving particles although significant density and viscosity differences exist. By comparing the simulation results with experimental ones, we approve the possibility of applying the hybrid method to the two-phase flow with particles representing the gas phase and mesh representing the liquid phase.     

Flow regime identification methodology with neural networks and two-phase flow models

Vertical two-phase flows often need to be categorized into flow regimes. In each flow regime, flow conditions share similar geometric and hydrodynamic characteristics. Previously, flow regime identification was carried out by flow visualization or instrumental indicators. In this research, to avoid any instrumentation errors and any subjective judgments involved, vertical flow regime identification was performed based on theoretical two-phase flow simulation with supervised and self-organizing neural network systems. Statistics of the two-phase flow impedance were used as input to these systems. They were trained with results from an idealized simulation that was mainly based on Mishima and Ishii's flow regime map, the drift flux model, and the newly developed model of slug flow. These trained systems were verified with impedance signals measured by an impedance void-meter. The results conclusively demonstrate that the neural network systems are appropriate classifiers of vertical flow regimes. The theoretical models and experimental databases used in the simulation are shown to be reliable.     

New Interfacial Drag Force Model Including Effect of Bubble Wake, (II)

In the previous study, we proposed a new interfacial drag force model based on experimental data of steam-water bubbly flow in a large-diameter pipe. This is because our experimental results had suggested that effect of bubble wake should be included in the interfacial drag force model, although it had not been taken into account in the existing models. A preliminary method for including the effect of bubble wake was hence developed and used in the new model. A new bubble size prediction method was also adopted in the model. In the present study, after improving the measuring equipment and signal processing procedure, another series of experiments was carried out. Using the new experimental data, the methods of predicting bubble size and effect of bubble wake were slightly modified. To test the validity of the new model, predicted results were compared with available experimental data sets of steam-water bubbly two-phase flow in large-diameter pipes. One-dimensional and two-dimensional two-fluid models were used for the calculation. Comparisons showed that the new model is in good agreement with the experimental data, whereas the model which does not take into account the effect of bubble wake overestimated the void fractions.     

压差波动特性识别流型研究

提出了一种基于小波分析的气液两相流流型模糊识别的新方法。该方法以加热段管程压降ΔP的波动信号作为测试信号,进行基于三阶的Daubechies小波二尺度分解,根据所得的二尺度细节系数的均方值确定了流型的识别方法。研究结果表明,这种识别方法能有效地实现气液两相流中泡状流、弹状流的识别。