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。     

起伏振动状态下倾斜管气液两相流型实验研究

在起伏振动状态下对倾斜管内气液两相流进行了实验研究。将振动装置与两相流实验回路相结合,改变管道倾角和振动频率、振幅,分析其对流型转变的影响。研究发现振动条件下的流型与稳态下相比有较大区别,通过对流型分类发现两种新流型为珠状流、起伏弹状流。绘制流型转换边界图结果表明,倾角的增加使起伏弹状流在流型图中的区域扩张,其他流型的区域相对减小。振动频率和振幅对流型转换边界的影响相似,振动频率和振幅增加会使珠状流和准弹状流区域有所增加。3种变化因素中振动频率对流型转变的影响最大。     

非线性振动下水平通道内气液两相流动研究

在地震等行为产生的非线性振动下,两相流体会影响回路传热并对装置结构进行冲击,因此对气液界面行为的把握对核安全具有十分重要的意义。本文通过将振动装置与两相流实验回路相结合的方法,对非线性振动下水平通道内气液两相流问题进行了实验研究。基于FLUENT平台,结合动网格模型及UDF编程手段建立了数学模型,并对数学模型进行验证。研究结果表明：模拟结果与实验结果具有很好的一致性;振动工况下气液两相流动形式不同于稳态工况,会出现更复杂的气液界面,主要流型有泡状流、弹状流、搅拌流、波状流及环状流;瞬时摩擦压降的波动幅度随振动幅度和频率的增大而增大,且与振动幅度相比,振动频率对其影响更大。     

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.     

摇摆状态下气液两相流流型转变的实验研究

通过可视化观察和数码照片对摇摆状态下光滑有机玻璃管内气液两相流流型进行分类和定义,并分析了不同管径、摇摆角度以及摇摆周期对流型之间转变的影响.结果表明:在液相折算流速一样的情况下,管径增加、摇摆周期缩短或摇摆角度减小会使得环状流形成需要更高的气体折算流速;弹状流向搅混流转变所需气相流量则随着管径的减小、摇摆周期的增加或摇摆角度的减小而增加.而在气相折算流速一样的条件下,管径增加、摇摆周期缩短或摇摆角度增大会使泡状流产生需要更高的液相流量.     

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。      

通道尺寸对竖直向上气-水两相流流型影响实验研究

本文以空气和水为工质,对竖直向上矩形通道(40 mm×1.41 mm,40 mm×10 mm)和圆形通道(D=25 mm)内的两相流流型特性进行了可视化研究。气液两相的表观速度分别为：0.03～24.71 m/s和0.03～3.73 m/s。3个实验段内均出现了泡状流、弹状流、搅混流和环状流4种流型,40 mm×10 mm和圆形通道中流型特征较为接近,与40 mm×1.41 mm通道中流型相比存在明显差别。此外,绘制出了3种通道详细的流型图。对比结果显示,矩形通道窄边宽度对流型转变有显著的影响,随着矩形通道窄边宽度的增加,其流型转变边界更加趋近于圆形通道。     

空气-水在垂直非圆截面通道内流型研究

采用可视化方法研究了水力直径分别为15mm和10mm的两种正方形截面、14.43mm的三角形截面以及14mm的圆形截面通道内空气-水垂直上升流动,表观气速0.04～80m/s,表观水速0.001～6m/s.观察到了泡状流、弹状流、块状流、环状流和弥散泡状流等常见流型.此外,在表观气速很大而表观水速很小时,在非圆截面通道内发现了爬动流,证实了非圆截面直通道内存在"二次流"现象,且对气-液两相流动的相分布有较大影响,证明截面形状对两相流流型及其转变具有重要影响.由实验得到了流型转变界限,并首次获得了包括爬动流的两相流流型图.比较本文的实验结果及与前人的研究结果对比发现,水力直径的大小对两相流流型的转变具有一定影响.     

Distribution of void fraction for gas-liquid slug flow in an inclined pipe

In order to investigate the effect of inclination angle on the spatial distribution of phases,experiments on gas-liquid two-phase slug flow in an inclined pipe were carried out by using the optical probe and an EKTAPRO 1000 high speed motion analyzer.It has been demonstrated that the inclination angle and the mixture velocity are important parameters to influence the distribution of void fraction for upward slug flow in the inclined pipe.At high mixture velocity,the gas phase profile is axial symmetry in the cross-section of the pipe.This is similar to that for vertical slug flow.In contrast.most of the gas phase is located near the upper pipe wall at low mixture velocity.By measuring the axial variation of void fraction along the liquid slug.it can be concluded that there is a high void fraction wake region with length of 3-4D in the front of liquid slug.In the fully developed zone of liquid slug.the peak value of the void fraction is near the upper wall.     

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.     

Direct Measurement of Neutron Flux

An experimental study was carried out on steady-state boiling of sodium flowing in the annular channel formed around an electrically heated simulation of a fuel pin. In the present experiment, the inlet temperature and flow rate were held constant, and the heat flux was gradually increased up to the inception of boiling. Thereafter, the heat flux was further increased step by step until the surface temperature of the heater pin marked a sharp rise, indicating the occurrence of dry-out. Records were obtained of the changes brought by the increasing heat flux to boiling phenomena, with particular reference to the behavior of the two-phase flow pattern and to the characteristics of boiling noise, as well as of the frequency of bubble formation.

It was made clear that there exists a region in which steady-state boiling will be established, and under these conditions the two-phase flow pattern changes sequentially from bubbly flow to slug flow and then to annular flow. This behavior of sodium boiling in a narrow channel is quite similar to the case of water.

With rising heat flux, the level of noise intensity associated with boiling first increased sharply to attain a maximum point, then decreased somewhat and remained constant thereafter until dry-out.

The frequency of bubble formation depended on the size of the bubble. The product of bubble frequency and equivalent diameter was found to be constant.     

竖直窄矩形通道气液两相流流型识别研究

在实验研究的基础上,采用小波分析的方法对窄矩形通道内两相流的流型进行有效的识别,为在不可视或不能进行摄影测试技术特殊情况下提供了有效识别方法。通过可视化观察发现,窄矩形通道内两相流流型主要有泡状流、弹状流、搅混流和环状流。采用小波分析法给出了4种流型的功率密度图,并结合每种流型的特征及压差波动特性,对每种流型的频率分布范围及最大能量分布范围给出了界定。因此,利用频率分布特征值及最大能量分布值可对流型进行有效的识别和判定。     

铅铋合金冷却反应堆内气泡提升泵提升自然循环能力的理论研究

液态金属冷却核反应堆采用气泡提升泵的概念设计来提升堆芯自然循环能力。液态金属和惰性气体两相流动特性显著影响自然循环能力和系统安全性。本工作对铅铋合金冷却反应堆中气泡提升泵提升自然循环能力进行数值模拟研究。基于漂移流模型,采用空泡份额预测模型和摩擦压降预测模型分析了气体质量流量、质量含气率、气泡直径、上升管道高度对气泡提升泵提升自然循环能力的影响。结果表明：泡状流区域中,对于给定的气体质量流量,随着充入气泡直径减小,自然循环能力呈增加趋势。在泡状流、弹状流、乳状流和环状流等流型中,随着气体质量流量、质量含气率增加,自然循环能力先增大后减小。随着上升管道高度增加,自然循环流量增大。可见,流动参数显著影响堆芯热工水力特性。现有工作有助于优化带有气泡提升泵的自然循环冷却系统设计。     

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.     

单棒通道流动振荡诱发沸腾临界可视化实验研究

为深入分析沸腾两相流动振荡诱发沸腾临界的影响特性,本文以去离子水为工质,横截面19 mm×19 mm、中心为外径9.5 mm的单棒通道为研究对象,通过在不同热工参数下开展沸腾两相流动特性可视化实验研究,结合汽泡行为和汽-液界面特性,分析流动振荡诱发沸腾临界的影响特性。研究结果表明,低压力、低质量流速和低入口过冷度下,极易出现流动振荡,并导致沸腾临界提前发生,此时的临界热流密度与稳定工况下相比明显偏低;随着壁面热流密度不断增加,流道中两相流型先后出现泡状流、弹状流、合并弹状流、搅混流、剧烈搅混流、不稳定环状流;当流动出现剧烈振荡时,流道存在回流;发生沸腾临界时流道压降波动最大,对应的流型为不稳定环状流。因此,单棒通道内流动振荡可能会导致沸腾临界提前发生。      

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.     

基于图像法的气液两相稀疏泡状流气泡参数分析

采用图像法对垂直上升管气液两相流中稀疏上升气泡进行实验测量研究。该方法使用高速摄像机拍摄气泡运动图像,经图像处理后,提取气泡的特征参数,分别绘制稀疏气泡上升过程中速度变化曲线和单个气泡上升过程中面积变化及形心位置变化曲线,分析气泡参数,总结运动规律。实验结果表明,采用图像法可以很好地完成对气泡参数的分析。     

Natural Convection Sodium Boiling Experiments in 37-Pin Bundle Geometry

Decay heat removal capability under boiling condition was studied using an LMFBR fuel subassembly mockup loop. The sodium flow was driven by natural convection through the loop in which was installed a 37-pin bundle heated electrically over a length of 45 cm.

The heat flux furnished by the pins was increased stepwise, upon which the two-phase flow regime changed from bubble to slug flow and then to annular or annular mist flow. Dryout occurred even in slug flow regime, but only momentarily, and permanent dryout was not observed before establichment of annular flow. A suitable criterion for permanent dryout is considered to be 0.5 average exit sodium vapor quality. The results indicated that upon occurrence of sodium boiling, the coolability of fuel subassembly would be maintained by natural convection after reactor shutdown.     

R134a卧式螺旋管内沸腾两相流型与传热特性实验研究

在蒸发温度为5～15 ℃、热流密度范围为5～20 kW·m^-2、工质质量流速变化范围为50～500 kg·m^-2·s^-1和干度范围为0.01～0.9的条件下,对R134a在卧式螺旋管内的沸腾两相流型及传热特性进行了实验研究。利用可视化技术对流型进行了观察分析,发现在相同工况条件下,卧式螺旋管上升段和下降段的流型有所不同,特别是形成环状流之前存在明显不同的过渡流型,分别为波环状流型和超大气弹流型,因此,对上升段和下降段分别建立了流型图。获得了传热系数随工质的干度、质量流速和热流密度等参数的变化关系,发展了R134a在卧式螺旋管内流动沸腾传热系数的计算关联式。     

摇摆状态下窄矩形通道内两相流流型特性研究

以空气和水为工质,在40mm×1.6mm的窄矩形通道内对竖直状态和摇摆状态下两相流流型进行了研究。流型由拍摄照片辨别,实验通道内观察到的流型有泡状流、弹状流、搅混流和环状流,绘制出窄矩形通道内的流型图,并与常规尺寸圆管内两相流型进行了对比。摇摆对窄矩形通道内流型的影响与常规尺寸圆管相似,但由于狭小空间的限制及表面张力的作用,摇摆对两相流动并无明显影响。