矩形通道中两相流变密度模型空泡份额计算

基于Bankoff的圆管内和无限长平板间两相流变密度模型空泡份额计算式的推导，结合流体在管道中的流场分布特征，建立了矩形通道中两相流流场分布规律方程，导出了变密度模型在矩形通道中空泡份额的计算式，并对3种通道计算的结果进行了对比分析。计算结果与原有Bankoff模型符合得很好。     

Characteristics of Counter current Gas-Liquid Two-Phase Flow in Vertical Tubes

Investigations into the flow pattern and the void fraction for countercurrent air-water flow in vertical tubes of diameter D = 40 and 80 mm were reported. The flow maps were presented and showed slug flow regime occupied larger portion on them. The void fraction was measured by the quick-closing valve technique, in bubbly and slug flow regime.

The void fraction data available in the literatures as well as present work for counter- current flow in vertical tubes were correlated in terms of dimensionless groups. The experimental results of the present work were also compared with the drift flux model.     

较大管径中两相流动漂移流模型研究

漂移流模型作为一种简单实用的模型,在反应堆热工水力及安全分析,特别是在空泡份额的计算方面,应用非常广泛。针对不同的通道及流型,研究者提出了多种基于漂移流模型的计算方法。通过较大通道中两相流动过程的实验研究,对5种空泡份额计算模型进行评价分析。结果表明,基于常规通道的Hibiki-Ishii模型与实验值吻合较好,平均相对误差为14.1%。结合对气泡运动过程的研究,发现在〈J_g〉β<0.027区,分布参数C₀<1,据此,给出了在较大管径通道中计算精度更高的模型关系式。     

Void Fraction and Pressure Drop in Liquid Metal Two-Phase Flow

This paper describes a new correlation for predicting a two-phase frictional pressure drop multiplier, and discusses the pressure level effects and the mass velocity effects. This correlation predicts satisfactorily the frictional pressure drop not only for liquid metals but also for ordinary fluid two-phase flow in a wide range of flow variables.

The authors' void fraction correlation previously proposed is also compared with published data of void fraction for liquid metal two-phase flow, and is found to represent well the mass velocity effects. Wettability and magnetohydrodynamic effects are discussed briefly in relation to the hydrodynamic characteristics of liquid metal two-phase flow.     

垂直上升两相流漂移流模型研究

漂移流模型在两相流空泡率计算中处于非常重要的地位,长期以来,研究者对模型中分布参数及漂移速度的确定持不同的观点.本文采用理论分析与实验研究相结合的方法,总结了分布参数和漂移速度的一般规律,提出了垂直上升两相流漂移流模型分布参数和漂移速度必须满足的限制条件,根据理论分析以及实验数据的验证,得出了漂移流模型推荐关系式.     

气液两相流的网络模型探讨

运用网络理论 ,针对气液两相管网流动进行了机理上的探讨。并基于均相流模型 ,推导出无损管路和平均摩擦管路条件下气液两相流的网络参数———阻抗和导纳的表达式。对于不适于均相流模型的流型的模型给出了一些建议。     

Vertically Downward Two-Phase Flow, (I)

Fully developed vertically downward two-phase flow of air-water mixture was investigated on void distribution and average void fraction among the three basic flow regimes; bubbly, slug and annular flows. The annular flow further was divided into two regimes of falling film flow and annular drop flow. Test channel is in form of inverted U-tube and tests were carried out at 100 tube diameters downstream from the curved part. Distributions of local void fraction were measured by means of a conductance needle probe method and the average void fraction was obtained from numerical integration of the measured local void fraction According to the results, profiles of local void fraction in bubby and slug flows showed characteristic natures with a peak in the middle region between the center and the wall of tube The average void fraction in downward flow depended greatly on the flow regimes. Accordingly correlation for each flow regime was developed to predict the average void fraction, based on flow mechanisms and experiments. The correlations were compared with experimental results for atmospheric air-water flow and showed satisfactory agreement.     

摇摆对垂直上升管内气液两相流截面含气率影响的研究

对垂直上升管内气液两相流在摇摆状态下和非摇摆状态下分别做了截面含气率的实验研究,发现在水流量较小时,两相流在摇摆状态下的截面含气率小于非摇摆状态下的截面含气率.通过对实验现象的观察和对单相液体在两种状态下摩阻系数的分析,合理解释了产生这种结果的原因.     

Safety Relief Valve Performance for Two-Phase Flow

The performance of main steam safety relief valve has been evaluated with respect only to the steam. In the present study, two-phase flow and subcooled water blow-out tests with model valves were performed in order to evaluate the valve's characteristics and performance. From the test results, it was made clear that not only for the steam but also for the two-phase flow the measurement data were hardly affected by scaling and also that the reaction force of the fluid to the valve stem was hardly dependent upon the void fraction. Analytical study was performed using the two-phase flow model in the valve. The results of the analysis showed good agreement with the test data. It was shown from the test and analysis results that the reaction force of the two-phase flow and subcooled water to the valve stem was almost as much as that of the steam flow, and the integrity of the safety relief valve could be maintained.     

Hydrodynamic and Hydraulic Studies on Void Fractions in Two-Phase Flow

For gas-liquid two-phase flow, two kinds of fundamental equations have been proposed by the methods of hydrodynamics and hydraulics. The hydrodynamic equation, to avoid analytical difficulties, does not deal with two-phase flow itself, but with a hypothetical liquid flow which has actual physical quantities in the region where the liquid phase really exists and has the imaginary physical quantities of liquid in the region where the gas exists, for each instant, and with a hypothetical gas flow similarly. The hydraulic equation differs from the usual form in the treatment of friction term or interaction, and has better physical insight. These equations are analyzed mathematically and some relationship between physical quantities centering void fraction are discussed. Hydrodynamic equation shows the void fraction distribution to have relation to pressure loss and velocity distributions, and, for the case of laminar two-phase flow with axial symmetry, explicit expression is presented. By hydraulic equation, the relation between void fraction and other variables are discussed. For the upward two-phase flow with constant flow area, gas-liquid interaction force is discussed theoretically and experimentally.     

蒸汽发生器二次侧汽液两相流数值模拟

以大亚湾核电站蒸汽发生器为原型,在相似原理的指导下,建立了蒸汽发生器“单元管”三维物理模型,采用Particle模型和热力学相变模型,并基于CFX软件实现了蒸汽发生器二回路侧两相流流动与沸腾换热特性数值模拟。计算结果表明：满负荷运行时,沿传热管高度升高,蒸汽发生器的传热系数及截面含汽率均呈上升趋势,其平均传热系数的数值模拟结果与Rohsenow经验关联式计算结果间的误差为8.4%,出口质量含汽率与大亚湾核电站实际运行参数相符。热相变模型在蒸汽发生器两相流数值模拟中的成功应用,可为蒸汽发生器热工水力的准确分析提供参考。     

Vertically Downward Two-Phase Flow, (II)

Following Part (I) of the present paper, which presented the experimental results obtained on the void distribution and average void fraction shown by nearly fully-developed, vertically downward two-phase flow of air-water mixture, this Part (?) covers the flow regime transition criteria among the three basic flow regimes : bubbly, slug and annular flows. The annular flow further was divided into two subregions of falling film flow and annular drop flow. The general situation of the transition criteria is as follows : (1) bubbly-to-slug flow transition occurs when the local void fraction in the central region of the tube is 0.3; (2) slug-to-annular drop flow transition criterion is given as a case which equations giving average void fraction for the slug flow and the annular flow are simultaneously satisfied; (3) slug-to-falling film flow transition occurs when the pressure difference between the crest of large wave and the bottom overcomes the surface tension; (4) the occurrence of liquid droplets from wave crests gives the transition criterion between the falling film flow and the annular drop flow.

These criteria were correlated to predict each flow regime boundary respectively considering flow mechanisms or from experimental results. The correlations obtained were compared with published flow regime maps for atmospheric air-water flow and showed satisfactory agreement.     

Flow Behavior and Phase Distribution in Two-Phase Flow around Inverted U-Bend

Experimental results are presented on the flow behavior, phase distribution, average void fraction and slip ratio in air-water two-phase mixture flowing through an inverted U-bend. The curved test section of transparent acrylic resin tubing with 24 mm I. D. was used, comprising a riser, an inverted U-bend with radius of 96 mm, and a downcomer. From the visual observation, a flow map was derived, which indicates the relation between the flow patterns and velocities. Distributions of local void fraction along a diameter lying in the central plane of the bend and over the whole cross section of bend tube were measured, and those distribution mechanisms were explained by the effect of centrifugal and gravitational forces. The average void fraction around the bend was obtained by numerical integration of the measured local void fraction, and the slip ratio was calculated using the average void fraction.     

基于漂移流模型的矩形通道内泡状流-弹状流转变准则

以空气和水为工质,对竖直向上矩形通道(40 mm×1.41 mm,40 mm×10 mm)两相流流型特性进行了可视化研究。气液相表观速度分别为0.01~0.59 m/s和0.02~3.72 m/s。基于3个经典的泡状流向弹状流转变准则,考虑矩形通道的尺寸效应,导出了泡状流向弹状流转变时的临界空泡份额为0.23。以窄边宽度2.5 mm为界,将矩形通道分为小通道和常规通道两类,对泡状流向弹状流转变准则进行修正,修正准则能很好地预测实验值。为进一步验证修正准则的准确性和适用性,将修正准则与Mishima、Wilmarth和Sadatomi等的实验数据进行了对比,结果显示修正准则同样具有较好的预测效果。     

Flow Regime Transition to Wavy Dispersed Flow for High-Pressure Steam/Water Two-Phase Flow in Horizontal Pipe

A wavy-dispersed flow regime was observed between slug and annular-dispersed flow regimes in TPTF high-pressure steam/water horizontal pipe experiments, employing the video probe visual observation. The onset OF entrainment was identified to cause slug to wavy-dispersed flow transition. The wavy-dispersed flow regime extended towards lower gas flow rates as pressure was increased. Furthermore, it was found that the gas-liquid relative velocity for the onset of entrainment decreases significantly, resulting in decrease in the minimum void fraction. Consequently, the slug flow regime was found to disappear for pressures above 8.6MPa, as observed in the previous TPTF experiments. Applicability of available models and correlations on the onset of entrainment was assessed against the TPTF data. Steen-Wallis parameter correlated the data well when the superficial gas velocity term in this parameter 1s replaced by the gas-liquid relative velocity.     

Experimental Study on Gas Carry-Under in Liquid Down Flow from a Two-Phase Mixture

The gas carry-under characteristics in liquid down flow from a two-phase mixture flow have been studied for various flow parameters, based on experiments with a small scale air- water system simulating the concept of a natural circulation BWR with no separators. For high void fraction in the riser, as the liquid superficial velocity jf increased to 0.17 m/s, the void fraction in the lower part of the downcomer αd increased sharply due to the descent of comparatively large bubbles (diameter: about 4–6mm). In the region of jf> 0.17m/s, on increasing jf, the void fraction αd increased until it reached a maximum value at jf.3. For liquid descending velocities higher than 0.3 m/s, αd became almost constant and the level of the mixture above the riser had little effect on the void fraction ad due to the phase separation of the large bubbles formed by bubble coalescence in the upper part of the downcomer. The void fraction αd increased as the void fraction αr increased until bubble coalescence occurred in the upper part of the downcomer, and αd became constant and independent of αr after the occurrence of bubble coalescence. Under the conditions of high void fractions in the riser, 0.4<αr<0.64 (upper limit of the tests), and high liquid descending velocities in the down-comer, 0.3 m/s<jf.<0.4 m/s (upper limit of the tests), the void fraction αd was represented by a dimensionless number (G = η⁴ g/σ³ pf) and by the upper limit of void fractions in bubbly flow, αd=0.3.     

矩形小通道内空气-水两相流动均相流模型研究

在机玻璃竖直矩形通道内,以空气和去离子水为工质获得实验数据。据此对竖直矩形小通道内均相流模型的适用性进行评价。结果表明,采用McAdams两相粘度时均相流模型及Chen等提出的修正均相流模型能较好用于1.41 mm间隙通道压降的预测,平均绝对误差分别为10.92%和12.20%;采用McAdams两相粘度时均相流模型对于3 mm间隙通道在两相雷诺数Re大于6000时平均绝对误差为10.04%,但气-液两相Re较低时预测偏差较大。通过实验数据分析得到了均相流模型适用于3 mm间隙通道的范围;针对两相Re较低的区域拟合得到了新的经验关系式,其预测值与实验值符合较好。     

Experimental Study on Gas Carry-Under in Down Flow from Two-Phase Mixture

In this paper, simultaneous optimization is carried out for successive two cycles of pressurized water reactors. At first, a simplified problem of the simultaneous optimization was studied by assuming the batch-wise power sharing as independent variable, i.e., batch-wise power sharing was optimized without considering corresponding loading patterns. The optimization of the batch-wise power sharing was carried out for the conventional single cycle, the equilibrium cycle and the two successive (tandem) cycles. The analysis indicated that the tandem cycle optimization well reproduce that of the equilibrium cycle optimization, which is considered as a typical case of the true multicycle optimization. Next, simultaneous optimization of loading patterns for tandem cycles is carried out using the simulated annealing method. Since the design space of the tandem cycles optimization is much larger than that of the conventional single cycle optimization, the optimization condition (i.e., number of calculated patterns) are established through sensitivity study. The optimization results are compared with those obtained by the successive single cycle optimizations and it is clarified that the successive single cycle optimization well reproduces the optimization results obtained by the simultaneous optimization if objective functions are appropriately chosen. The above result will be encouraging for the current in-core optimization method since single cycle optimization is utilized due to limitation of computation time.