200MW核供热堆两相流密度波不稳定性实验的Shannon信息熵特性研究

在200MW核供热堆热工实验台架上,利用信息论原理,研究两相流密度波不稳定性的Shannon信息熵特性。通过调节加热功率、运行压力和冷却剂入口过冷度,获得534种工况下加热流道入口压降的实验数据?计算不同工况下的Shannon信息熵,发现具有高的负Shannon信息熵(负熵)的实验工况是不稳定的,而具有低的负熵的实验工况是稳定的。负Shannon信息熵类似很多场合中使用的能量,可以成为衡量系统稳定性的尺度。     

摇摆状态下水平管内气-水两相流流型的判定方法

对摇摆状态下水平管内气-水两相流流型进行了实验研究.实验发现,摇摆状态下两相流的压差波动有明显的周期性.本文根据各流型压差波动的差异判断摇摆状态下水平管内气-水两相流的流型.结果表明:通过与可视化观察和高速摄影观察的流型相比,利用压差特性曲线可以很好地判断摇摆状态下气-水两相流的流动型式.     

矩形通道内两相脉动流平均摩擦压降实验研究

通过对截面为40 mm×3 mm窄矩形通道内不同正弦脉动周期、振幅、平均流量工况下氮气 水两相流（平均分液相雷诺数Re_l<10 000,平均分气相雷诺数Re_g<800）进行实验研究,发现两相脉动流与单相水脉动流的规律不同,平均压差对脉动周期、振幅不敏感。应用各经验公式计算的脉动工况下平均摩擦压降的偏差与稳态工况的计算偏差在数值和分布上均无明显差异,且计算值分布在测量值两侧、相对偏差基本小于20%。其中,Mishima-Hibiki方法和Lee-Lee方法的计算结果与测量结果吻合良好,相对偏差在10%以内,说明两相流摩擦压降经验公式同样适用于脉动工况下平均摩擦压降的计算。     

基于奇异值分解和最小二乘支持向量机的气-液两相流流型识别方法

针对气-液两相流压差波动信号的非平稳特征和BP神经网络学习算法收敛速度慢、易陷入局部极小值等问题,提出了一种基于奇异值分解和最小二乘支持向量机（LS-SVM）的流型识别方法。该方法首先采用经验模态分解将气-液两相流压差波动信号分解为多个平稳的固有模态函数之和,并形成初始特征向量矩阵;对初始特征向量矩阵进行奇异值分解,得到矩阵的奇异值,将其作为流型的特征向量,根据LS—SVM分类器的输出结果来识别流型。对水平管内空气-水两相流4种典型流型进行识别,结果表明,与神经网络相比,该方法具有更高的识别率和识别速度。     

倾斜管内气液两相流流型的实验研究

对空气-水形成的两相流同向通过管径15mm、管长6m,倾斜角为15°和30°两种不同的倾斜角有机玻璃管的流型进行了实验研究。通过可视化观察和压差波动特性对流型进行分类,结合实验数据绘制出不同倾角下的流型图。另外,通过与相同管径下的水平管流型图进行对比以及不同倾角下流型产生范围的比较,发现试验段倾角对流型区间有显著的影响。     

低压系统中非能动虹吸破坏的机理研究

虹吸破坏现象对核安全中的冷却剂丧失事故有重要影响。对非能动空气-水两相流系统中的虹吸破坏过程进行了实验研究,观测了流动过程,对压差、液相流量及液位随时间的变化进行了测量。实验观察到下降管段中的两相流流型随时间变化依次为泡状流、弹状流和降膜流。实验结果表明,非能动虹吸破坏系统能够显著增加压降,降低液相流量。因此,非能动虹吸破坏现象能够减少冷却剂丧失事故中堆芯裸露的风险。     

过冷沸腾自然对流两相CFD模拟及应用

采用计算流体力学（CFD）方法,开展过冷沸腾自然对流两相模拟与应用研究。对侧壁加热圆柱水箱过冷沸腾自然对流实验采用两相CFD瞬态模拟,模拟时间为1 500 s,通过模型设置与模拟方法研究,再现了过冷沸腾发生后实验的温度阶跃,得到与实验较一致的温度分布、气泡产生时间与产生位置,确保了数值计算的合理性与准确性。在此基础上,对以欧洲ESBWR（经济简化沸水堆）非能动安全壳冷却系统（PCCS）为原型的ISP-42实验进行了两相CFD模拟,获得与实验一致的温度分布,确定采用两相CFD数值模拟对非能动安全壳冷却系统及非能动余热排出系统进行应用研究可行,为下一步计算传热系数、构建自然对流传热模型建立了良好基础。该项研究对工程应用中探寻非能动安全壳冷却系统及非能动余热排出系统的两相自然循环传热特性具有较大价值。     

螺旋管直流蒸汽发生器两相流不稳定性

研究了螺旋管直流蒸汽发生器两相流不稳定性。阐述了两相流不稳定性机理。利用线性化频域理论，建立了螺旋管直流蒸汽发生器两相流不稳定性数学模型，编制了计算程序ＨＴＯＴＳＧＩＡ，分析了入口节流圈，系统压力及不同螺旋管圈等因素对螺旋管直流蒸汽发生器两个流不稳定性的影响，给出了螺秘管直流蒸汽发生器两相流稳定区域。计算值与实验值基本一致。     

基于灰色神经网络和支持向量机的两相流流型辨识

两相流流型直接影响两相流的流动特性和传热传质性能。利用小波分析对气液两相流压降实验数据进行处理,提取不同频率的小波系数。以小波能量为特征,输入BP神经网络进行训练,进行流型的初步辨识。将灰色神经网络模型应用于气液两相流的辨识,同时创立将压差波动数据和小波能量数据输入Lib-SVM机分类器的方法,分别对流型进行辨识。结果显示,这三种方法均可进行流型的辨识,小波能量支持向量机的判别结果比灰色神经网络和BP神经网络的判别结果准确。支持向量机对压差信号直接进行流型辨识时准确率达到95.2%。     

功率密度分布对两相流稳定性影响的实验研究

叙述了不同功率密度分布工况下的自然循环两相流稳定性实验研究。实验是在５ＭＷ核从热堆煤水力学模拟实验回路（ＨＲＴＬ－５）上进行的，实验中分别采用了功率密度线性分布和功率密度余弦分布两种加热元件。其结果表明：在低压低干工自然循环系统中，加热元件的功率密度分布形式对两相流稳定性的影响，很小，验证了功率密度线性分布下两相流稳定性实验结果的通用性。     

基于WMS的无旋和螺旋气液两相流流型及空泡份额实验研究

为探究气液两相流流型从无旋状态转变为螺旋状态前后的流型特征及空泡份额时空分布特性,基于高速摄影仪和自主开发的丝网传感器（WMS）测量技术,对内径为30 mm的水平管内起旋装置作用下空气-水两相流的相态时空演变特性进行了可视化实验研究。结果表明,在起旋器诱导的离心力作用下,流场内存在明显的气泡聚并行为和液滴沉积现象,其中,泡状流将转变为螺旋气柱流,塞状流转变为螺旋间歇流,弹状流转变为螺旋环状流,环状流转变为螺旋丝带流;相比于弹状流和环状流,泡状流和塞状流的截面平均空泡份额在起旋器出口波动幅值明显减弱,但离心力场并未明显改变各流型从无旋状态转变为螺旋状态前后的截面平均空泡份额。      

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。     

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.     

Two-phase flow measurements using a photochromic dye activation technique

A novel flow visualization method called photochromic dye activation (PDA) technique has been used to investigate flow structures and mechanisms in various two-phase flow regimes. This non-intrusive flow visualization technique utilizes light activation of a photochromic dye material dissolved in a clear liquid and is a molecular tagging technique, requiring no seed particles. It has been used to yield both quantitative and qualitative flow data in the liquid phase in annular flow, slug flow and stratified-wavy flows.     

Analysis of Gas-liquid Two-phase Flow Pattern Transition in Inclined Rising Pipe under Fluctuant Nonlinear Vibration Condition

The flow pattern and transition law of gas-liquid two-phase flow in inclined rising pipe under different fluctuant nonlinear vibration conditions were studied experimentally. The flow patterns of gas-liquid two-phase flow under fluctuant nonlinear vibration condition were identified by using high-speed camera. The results show that there are four kinds of patterns in inclined rising pipe with diffuse bubble flow, fluctuant slug flow, proto slug flow and liquid-ring annular flow. The mechanisms of the transition from diffuse bubble flow to fluctuant slug flow, proto slug flow to liquid-ring annular flow were derived, the vibration parameter was added on the basis of the steady state transition mechanism and the flow pattern transition formulae considering the vibration acceleration were established. The results show that the flow pattern transition formulae established in this paper agree well with the experimental results.     

起伏非线性振动下倾斜上升管内气液两相流流型转变分析

本文对不同起伏非线性振动条件下倾斜上升管内气液两相流流型及转变规律进行实验研究,借助高速摄影仪对起伏非线性振动状态下气液两相流的流型进行分类。结果表明,倾斜上升管气液两相流有弥散泡状流、起伏弹状流、准弹状流和液环式环状流4种。对弥散泡状流向起伏弹状流和准弹状流向液环式环状流的转变机理进行分析,在稳定状态转变机理的基础上引入振动参数,建立了考虑振动加速度的关系式。本文建立的流型转变关系式与实验结果吻合较好。     

Modeling of bubble coalescence and disintegration in confined upward two-phase flow

This paper presents the modeling of bubble interaction mechanisms in the two-group interfacial area transport equation (IATE) for confined gas–liquid two-phase flow. The transport equation is applicable to bubbly, cap-turbulent, and churn-turbulent flow regimes. In the two-group IATE, bubbles are categorized into two groups: spherical/distorted bubbles as Group 1 and cap/slug/churn-turbulent bubbles as Group 2. Thus, two sets of equations are used to describe the generation and destruction rates of bubble number density, void fraction, and interfacial area concentration for the two groups of bubbles due to bubble expansion and compression, coalescence and disintegration, and phase change. Five major bubble interaction mechanisms are identified for the gas–liquid two-phase flow of interest, and are analytically modeled as the source/sink terms for the transport equation in the confined flow. These models include both intra-group and inter-group bubble interactions.     

双探头光学探针识别受热工况两相流流型的基本方法研究

由于流型识别手段受到限制．目前常用的流型图以及流型转变判据．都是在绝热工况下根据实验得到的；关于受热工况两相流流型还没有足够的实验数据。光学探针的运用为受热工况两相流流型的研究提供了有力的测量手段。本文对双探头光学探针4种流型识别的基本方法进行了研究，包括探针原始电平信号概率密度函数(PDF)分析识别流型、信号时序波形识别流型、空间波形识别流型以及汽泡尺寸PDF分析识别流型。研究结果表明，汽泡贯穿弦长PDF分析可得出满意的流型识别结果。     

Modeling of bubble shape in horizontal and inclined tubes

An experimental and theoretical study on the bubble shape of intermittent flow in the horizontal and inclined pipes has been carried out. The experiment results show that the bubble shape depends on the Froude number, bubble length and pipe inclination. The bubble with staircase pattern tail is observed at low Froude numbers, which is corresponding to plug flow. A model for the prediction of the bubble shape in horizontal and inclined pipes is proposed. The model is able to predict the bubble shape, flow pattern transition between plug and slug flow regimes as well as nose-tail inversion phenomenon observed in the downwardly inclined pipe. Validation shows the model can well predict the bubble shapes in horizontal and inclined pipes. The model discloses that the transition between plug and slug flow regimes occurs within a region. The Froude number range for plug flow regime in the downwardly inclined pipe is much wider than that in the horizontal or upwardly inclined pipe. The assumption of fully developed liquid film under the long bubbles tends to under-estimate the liquid fraction in this part of the slug structure, especially, for the intermittent flow in the upwardly inclined pipe with high Froude numbers.