Two-phase slug flow in vertical and inclined tubes

Gas-liquid slug flow is investigated experimentally in vertical and inclined tubes.The non-invasive measuremnts of the gas-liquid slug flow are taken by using the EKTAPRO 1000 High Speed Motion Analyzer.The information on the velocity of the Talyor bubble,the size distribution of the dispersed bubbles in the liquid slugs and some characteristics of the liquid film around the Taylor bubble are obtained.The experimental results are in good agreement with the available data.     

Gamma-ray attenuation technique for measuring void fraction in horizontal gas-liquid two-phase flow

The measurement of void fraction is of importance to the oil industry and chemical industry. In this article, the principle and mathematical method of determining the void fraction of horizontal gas-liquid flow by using a single-energy γ-ray system is described. The γ-ray source is the radioactive isotope of 241Am with γ-ray energy of 59.5 keV. The time-averaged value of the void fraction in a 50.0-mm i.d. transparent horizontal pipeline is measured under various combinations of the liquid flow and gas flow. It is found that increasing the gas flow rate at a fixed liquid flow rate would increase the void fraction. Test data are compared with the predictions of the correlations and a good agreement is found. The result shows that the designed γ-ray system can be used for measuring the void fraction in a horizontal gas-liquid two-phase flow with high accuracy.     

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.     

Influences of physical properties of two-phase mixture on voidfraction in an annular vessel

To keep the void fraction of two-phase hydrogen in the moderator cell of the cold neutron source (CNS) of China Advanced Research Reactor (CARR) to a specified range, an annular vessel with the same size as the actual moderator cell was used as test section. Deionized water and alcohol, sucrose, and sodium chloride solutions with different concentrations were used as working fluid to find out influences of physical properties, such as density, viscosity and surface tension, of the two-phase mixture on void fraction. The tests proved that the ratio of surface tension to density of liquid phase has great influence on void fraction: the larger the ratio, the smaller the void fraction. Since the ratio of surface tension to density of Freon 113 is lower than that of liquid hydrogen, Freon 113 can be used as a working fluid to study the void fraction in the two-phase hydrogen thermosiphon loop in the CNS of CARR and the results will be conservative.     

低质量流速绝热管内截面平均空泡率实验研究

汽液两相流空泡率实验与计算方法研究对于反应堆自然循环及事故分析具有重要意义,然而现有研究主要以高质量流速工况为主,已有的空泡率公式预测结果在低质量流速条件下也存在较大差异。为此,本文以单探头光学探针为主要测量手段,进行了低质量流速绝热工况空泡率实验研究,截面平均空泡率根据探针测量得出的局部空泡率在流道截面上积分计算得出。实验数据与已有空泡率计算公式进行了比较,表明低质量流速工况下多数公式预测结果偏高,而Chexal et al．、GE—Ramp以及Dix公式可得出非常满意的预测结果。综合Vijayan的研究结果,本文建议低质量流速空泡率计算中采用Chexal et al．的公式。     

Measurement of void fraction in bubbly-slug flow with a constant electric current method

In several void fraction measurement methods, a constant electric current method which is one of conductance methods is focused in the present study. By using this method, void fraction can be measured with higher temporal resolution. However, it has been mainly applied to annular flow in previous studies. In the present study, Maxwell's estimation, Bruggemann's estimation, low void fraction approximation and new estimations which consider the bubble shape are applied in order to measure more accurately void fraction of dispersed bubbly flow and slug flow. To understand the effect of bubble shapes and flow patterns, void fraction was measured by the constant electric current method for a rising single spherical bubble and a rising single slug bubble without a forced convection. In addition, void fraction was also measured in bubbly flow and bubbly-slug flow with a forced convection. Then, effects of flow patterns on the proposed estimations of void fraction and the accuracy of their estimations were discussed with the measurement results. From the result, the new estimations which consider a bubble shape are more accurate than the previous estimation in a slug bubble and bubbly-slug flow.     

倾斜圆管内泡状流空泡份额特性实验研究

采用光纤探针测量方法对倾斜圆管(内径为50 mm)内空气-水两相泡状流空泡份额分布特性进行实验研究。结果表明,截面平均空泡份额随倾斜角度的增加而减小,倾斜角度大于5°时减小速率明显减慢;竖直条件下空泡份额径向分布呈"马鞍形",即空泡份额除在近壁区出现峰值然后迅速降低到最小值外,在其他区域几乎不随位置发生变化;倾斜条件下气泡明显向上壁面聚集,中心线上方近壁区空泡份额峰值增加,中心线下方近壁区空泡份额峰值被削弱,倾斜角度较大时甚至消失。     

Influence of void fraction change on plutonium and minor actinides recycling in BWR with equilibrium burnup

A study on the influence of void fraction change on plutonium and minor actinides recycling in standard boiling water reactor (BWR) with equilibrium burnup model has been conducted. We considered the equilibrium burnup model since it is a simple time independent burnup method that can handle all possible produced nuclides in any nuclear system.

The uranium enrichment for the criticality of the reactor diminishes significantly for the plutonium and minor actinides recycling case compared to that of the once-through cycle of BWR case. This parameter decreases much lower with the increasing of the void fraction. A similar propensity was also shown in the required natural uranium per annum. The annual required natural uranium was calculated by assuming that the uranium concentration in the tail of the enrichment plant is 0.25 w%. The amount of loaded fuel reduces slightly with the increment of the void fraction for plutonium and minor recycling in BWR.     

向上倾斜管内气-水两相流流型转变分析

对管径15 mm,管长6 m的有机玻璃管,在两种不同的向上倾斜角度(15°、30°)下,同向通过的气水两相流流型转变进行了分析,列出相应的转变准则关系式。结果显示,弹状流向泡状流转变界限的实验值与计算符合较好,间歇流向环状流的转变界限在低液体流速下符合较好。     

Three-dimensional time-averaged void fraction distribution measurement technique for BWR thermal hydraulic conditions using an X-ray CT system

We have developed a void fraction distribution measurement technique using the three-dimensional (3D) time-averaged X-ray computed tomography (CT) system to understand two-phase flow behavior inside a fuel bundle for boiling water reactor (BWR) thermal hydraulic conditions of 7.2 MPa and 288 °C. As a first step, we measured the 3D void fraction distribution in a vertical square (5?×?5) rod array that simulated a BWR fuel bundle in the air–water test. A comparison of the volume-averaged void fractions evaluated by the developed X-ray CT system with those evaluated by a differential pressure transducer showed satisfactory agreement within a difference of 0.03. Thus, we confirmed that the developed system could be used to get 3D imaging of the vertical square rod array used in the test under the BWR operating pressure condition. In the next step, we did a verification test using the vertical pipe (11.3 mm ID) for BWR thermal hydraulic conditions. A comparison of the cross-sectional-averaged void fractions evaluated by the X-ray CT system with those evaluated by the drift-flux model showed good agreement within a difference of 0.05. We confirmed that the evaluated void fraction distribution forms in the horizontal cross section changed with the quality in response to the flow regime transition.     

竖直圆管中泡状流含汽率径向分布的统计测量方法

为了研究竖直圆管中高含汽率泡状流的含汽率径向分布,设计了一种测量含汽率径向分布的方法.该方法通过统计投影视图中的像素信息得到泡状流的投影含汽率,根据汽泡投影重叠概率计算出截面含汽率在投影面上的边缘分布;再基于竖直圆管中含汽率分布轴对称的假设,使用改进的傅里叶级数展开方法求解Abel逆变换,计算出含汽率沿圆管径向的分布.为验证该方法的有效性,测量了较低含汽率时的泡状流径向含汽率,并与匹配方法的测量结果进行比较.实验结果表明:此方法能得到高含汽率或含汽率近壁分布等其他方法难以测量的含汽率分布.     

垂直上升管内两相流空泡份额径向分布

对于两相流空泡份额分布的实验研究,通常只能在有限工况下进行,而对其基本现象的描述也仅局限于特定的实验工况。为此,本文总结分析了以往一些研究者的实验结果,对圆管内垂直上升两相流空泡份额的径向分布情况进行了比较系统的描述。根据这些结果,进一步分析得出了典型的垂直上升流中空泡份额径向分布曲线与流型的对应关系,通过与已有实验结果的比较,说明该对应关系无论从实验结果还是机理解释上都是可信的。     

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.     

Study theoretically on two-phase circulation flow characteristics under ERVC condition in advanced PWR

For the problem of two-phase natural circulation flow in gap clearance between reactor vessel lower head and insulator in the condition of severe accident, one-dimensional steady-state natural flow analysis code was written by utilizing FORTRAN. Based on the code, the effects of different correlations for friction coefficient and the number of nodes of heating section on mass flow rate of two-phase natural circulation flow were studied. And the results are compared with that of Chinese REPEC experiment and simulation using RELAP5 program so as to verify the rationality and correctness of the code. Based on the experiment data, simulation results and the model, friction coefficient and the void fraction condition under ERVC correlation are obtained by fitting. The results calculated by the model using fitting friction coefficient correlation agree well with ULPU V test data. Furthermore, the effect of power, pressure, inlet area, gap diameter, flooding level and inlet water subcooling on mass flow rate and void fraction of two-phase natural circulation were studied utilizing this code.     

摇摆状态下竖直管内弹状流单元物理模型解析

通过建立质量守恒方程和弹状流稳定存在条件等方程,对摇摆状态下竖直管内充分发展的弹状流单元物理模型进行解析.在此基础上,给出摇摆状态下弹状流平均空泡份额计算关系式,并与实验值进行比较,结果符合较好.因此,该弹状流单元物理模型是进一步分析摇摆状态下弹状流流动特性的基础.     

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。     

Flow patterns and their transition characteristicsof the air-water two-phase flow in a horizontal pipe with asudden-changed cross-section area

Flow patterns in upstream and downstream straight tubes of suddenchanged areas in a horizontal straight pipe were experimentally examined.Both sudden-expansion cross-section(SECS)and sudden-contraction cross-section(SCCS) were inverstigated.The flow pattern maps upstream and downstream were delineated and compared with those in straight tubes with uniform cross-sections.The effects of the SECS and SCCS on flow patterns were discussed and analyzed.Furthermore.flow pattern transition mechanisms resulting in occurrences of different flow patterns were simply discussed and some transition criteria for the flow pattern transitions were deduced by using the non-dimensionlized analysis method.     

垂直上升横掠水平管束的两相流空泡份额模型研究

与管内两相流空泡份额模型相比,垂直上升横掠水平管束的两相流空泡份额研究成果相对有限。利用垂直上升的气-水两相流横掠水平管束的实验数据,对现有的空泡份额计算模型进行对比分析,并对2种现有模型的拟合公式进行修正。采用其他实验结果对本文重新修正的空泡份额模型进行验证,结果表明:与原始模型相比,修正的空泡份额计算模型给出的空泡份额预测值更好。     

外加扰动下垂直管内气-液两相流空隙波特性

采用双环电导探针技术实验研究了外加扰动对垂直上升管内气-液两相流空隙波特征的影响。研究结果表明,气-液两相流空隙波对外加周期性扰动具有频率选择性。在泡状流区,低频扰动能诱发与扰动等频的空隙波;在泡状流／弹状流转变区,低频扰动能加速气泡合并,促进泡状流向弹状流转变;而在弹状流区空隙波特征对外界扰动并不敏感。空隙波的传播速度受外界扰动频率的影响,随着扰动频率的增大,空隙波波速先减少又增大。本文的实验研究发现,存在对气-液两相流空隙波特征影响最为显著的临界扰动频率,在本实验条件和参数范围内,该临界扰动频率为20Hz。     

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。