小管径气液两相泡状流双电导阵列探针测量方法

针对气液两相流局部流动参数测量问题,采用沿管道径向等间距放置的五路双电导阵列探针测量法。首先,利用有限元法模拟分析了不同尺寸运动气泡对电导探针输出响应影响,发现气泡对探针有效检测域的作用强度明显受气泡大小及其运动轨迹影响;然后,根据双电导探针电场分布特性对其几何尺寸进行了优化,分析了双电导探针的灵敏场分布特性;最后,通过垂直上升气液两相流泡状流动态实验,获得了双电导探针对气液两相流分散相局部体积含率、局部流速及泡径尺寸测量结果。     

空隙率波的波速与气相漂移特性研究

针对垂直上升管内气-水两相泡状流,利用高速数字摄像技术、电导探针和相关性原理,测量了不同气液表现流速下泡状流空隙率波的传播速度,分析了不同扰动频率对空隙率波瞬时波速概率分布的影响,研究了空隙率波的传播相对于两相混合流速的漂移特性．研究结果表明,空隙率波的传播相对于两相混合流速呈正漂移,且飘移速度略大于气相的飘移速度,随两相流混合流速的增大呈线性增大．     

垂直管内油水两相流局部相分布特性实验研究

应用双头电导探针测量系统,对垂直上升管内油水两相分散流局部相分布特性进行了系统测量。得到了油水两相分散流的局部含油率分布类型图。研究结果表明低折算水速和低折算油速条件下,局部含油率在实验段截面上呈抛物线型局部分布特征,局部最大值出现在实验段中心区域。随折算油速增大,油滴受到横向力如升力的作用,逐渐向实验段壁面区域迁移,形成局部含油率的壁面峰值分布特性。当折算水速大于0．8 m／s时,局部含油率在实验段截面上呈均匀分布。     

方管内气液两相流界面波统计特性分析

以空气、水为工质，利用电导探针测量技术结合统计分析理论研究了水平矩形管内气液两相流界面波特性．首先对管内气液两相流的界面波进行了分类和定义；其次研究了气液两相流界面波在幅域、时域和频域的统计特性，同时考察了界面波特性参数（波速、频率和波高）等随气液两相流量的变化规律．     

垂直上升管内气液两相流流型鉴别研究

本文以低压空气一水作介质,进行了垂直上升管内气液两相流流型鉴别的实验研究;采用沿垂直管局部轴向压差信号及压差信号的统计分析并借助高速闪光观测仪进行可视化观察鉴别流型。实验结果发现,利用压差的时域信号和信号的功率谱密度函数（ＰＳＤ）,可以客观地判别垂直上升管内泡状、弹状和环状三种主要流型。     

气液两相流压力波色散特性实验研究

设计了可调频式压力扰动源的气液两相流压力波实验装置,实验研究了垂直上升管内气液两相流泡状流、弹状流压力波的色散规律。实验结果表明,对泡状流,在实验范围内,压力波的传播速度及其衰减跟扰动频率有关,随着扰动频率的增加,波速及其衰减都增加;工质的流速对压力波的色散特性没有影响。结合数值模拟结果,验证了泡状流压力波色散特性的临界频率现象,即高于临界频率,压力波色散特性消失,本文分析了相应的物理机制。对弹状流,压力波同样具有典型的色散特性,已有研究结果还不能预测其色散规律。     

蒸汽-水冷凝泡状流含气率分布

以双流体模型为基础,将前人实验得到的相界面浓度,相界面传热系数,气泡上升速度计算式引入双流体模型用来预测冷凝泡状流沿流动方向的含气率分布。模型预测结果与实验数据的比较结果表明,该模型能较好地模拟蒸汽-水冷凝泡状流含气率沿流动方向分布。     

两相流流型动力学特征多尺度递归定量分析

基于垂直上升管中测取的气液两相流电导波动信号,采用递归定量分析方法,从多尺度角度研究了气液两相流泡状流、段塞流及混状流三种典型流型的动力学运动特征.研究结果表明,低频泡状流及混状流在递归图表现为沿对角线方向比较发育的混沌递归线条纹理特征,表明了低频运动的泡状流及混状流具有较好的确定性运动行为,而随着泡状流及混状流运动频率增加,混沌递归特征变差,其运动特征逐渐向随机方向发展.对于段塞流,在混沌递归图上逐渐呈现间歇的矩形块纹理结构,且段塞流中液塞与气塞的间歇运动特征出现在高频段,而段塞流中的泡状流运动则出现在低频段上,且随着泡状流运动频率增加,泡状流逐渐失去确定性运动行为.表明了基于电导波动信号的多尺度非线性分析方法是理解与表征气液两相流动力学特性的有效途径. 关键词： 两相流 流动特性 多尺度分析 递归分析     

基于非接触电导的气液两相流参数检测系统

研究了电容耦合式非接触电导检测技术(C~4D)应用于气液两相流测量的可行性,建立了一套基于非接触电导的毫米级气液两相流参数检测系统。利用所建立的系统,在内径为5 mm,9 mm的水平管上进行了气液两相流实验,获得了不同流型下的电导测量信号,并对段塞流、波状流、泡状流和环状流四种典型流型下的电导信号进行了分析与比较。研究结果表明,所建立的基于非接触电导的气液两相流参数检测系统是有效的,C~4D技术应用于气液两相流参数测量是可行的。不同流型下所获的电导信号特征均表现出明显差异,有望用于流型辨识。     

两相流流型多尺度熵及动力学特性分析

研究了几种典型非线性时间序列的多尺度熵特征,在此基础上分析了由插入式阵列电导传感器采集的144种流动条件下的垂直上升气液两相流电导波动信号.研究结果表明：利用小尺度下样本熵的变化速率特征可以分辨三种典型流型（泡状流、段塞流、混状流）,而大尺度下样本熵的波动特征可以反映各种流型的动力学特性.泡状流随机可变特性表现为大尺度下样本熵的高值及振荡特征;段塞流气塞与液塞的间歇性运动表现为大尺度下样本熵的低值及平稳性;混状流极不稳定的振荡运动特性表现为介于泡状流及段塞流之间的熵值特点,并在更大尺度时熵值逐渐接近泡状流 关键词： 样本熵 多尺度熵 气液两相流 动力学特性     

油水两相分散流的相界面浓度输运方程研究

通过对连续相湍流导致的油滴聚合和破裂现象的合理模化,本文建立了适用于垂直上升管油水两相分散流的相界面浓度输运方程.其中对连续相湍流驱动油滴随机碰撞引起的聚合现象模化时,考虑了两油滴间连续相液膜排出过程中的凹面膜效应.而在描述油滴与湍流涡随机碰撞导致的破裂现象时,考虑了破裂过程所产生油滴的大小不等的因素.利用所建立的相界面浓度输运方程对沿实验段轴向的相界面浓度变化进行了预测,结果与实验数据比较表明吻合很好.     

泡状流运动的湍流模型及液相速度和湍动能的分布预测

１前言在核能、航天等技术领域和能源、动力、石油化工等工业过程都存在泡状流现象,其中绝大多数的泡状流流动状态为湍流,因此对湍流泡状流进行深入研究极为必要。近年来Ｌｅｅ［１］、Ｌｏｐｅｚ　ｄｅ　Ｂｅｒｔｏｄａｎｏ［２,３］等提出了一些多维的湍流输运的双流...     

Experimental and numerical study of heat transfer enhancement in a turbulent bubbly flow in a sudden pipe expansion

Results of an experimental and numerical simulation of heat transfer in an upward bubbly flowin a sudden pipe expansion are presented. The experimental study of the heat transfer has been performed using infrared thermography. The measurements of the bubble size before the pipe expansion area were carried out by the shadow photographymethod. The numerical simulation of the bubbly flow structure in the sudden pipe expansion has been performed using the Eulerian approach in the presence of heat transfer between the two-phase flow and the wall surface. The model uses the system of Reynolds-averaged Navier–Stokes equations in an axisymmetric approximation, written with consideration of the back effect of bubbles on the averaged and pulsation characteristics of the flow. It has been experimentally and numerically shown that addition of air bubbles causes a significant (up to 3-fold) increase in the heat transfer intensity, these effects growing with bubble concentration. The largest rise in the heat transfer has been revealed in the region of flow relaxation downstream of the flow attachment point.     

水平管液塞区相分布特征研究

设计建造了研究段塞流中液塞卷吸气体的实验装置,采用双头电导探针测量了水平管内固定液塞区域的局部相分布。液塞区含气率的径向分布存在峰值,表明液塞区存在湍流剪切层。随着进入液塞距离增大,含气率峰值减小,峰值对应的径向位置升高。这说明湍流剪切层内的湍流程度减弱,剪切层厚度变大。提出了计算水平管液塞截面平均含气率的方法,发现随着进入液塞距离的增大,截面平均含气率首先迅速减小,然后逐渐趋于稳定。     

Bubble Velocity and Size Measurement with a Four‐Point Optical Fiber Probe

The possibility to measure the velocity and size of individual bubbles in a high‐void fraction bubbly flow is investigated by using a four‐point optical fiber probe. The air bubbles have an initial spherical equivalent diameter ranging from 4 to 10 mm and the void fraction is up to 0.3. Firstly, single bubble experiments show that intrusiveness effects, i.e. bubble deformations due to the probe, are negligible provided that the bubble approaches the probe at the axis of the central fiber. A selection criterion is utilized for multiple bubble experiments. A good compromise can be found between the required accuracy, the duration of the measurements and the number of validated bubbles required for reliable statistical averaging. In an air‐water high‐void fraction vertical bubbly pipe flow, the void fraction obtained with the instrument is found to be in good agreement with both local single‐fiber probe measurements, and with the volume average void fraction obtained from pressure gradient measurements. The area average volumetric gas flow rate, based on the bubble velocity and void fraction as measured with the four‐point probe, agree with the measured gas flow rate. Also, the liquid velocity is measured by means of a laser‐Doppler anemometer, to investigate the slip velocity. The results show that reliable and interesting measurements can be obtained by using a four‐point optical fiber probe in high void fraction flows.     

Gas volume fraction and velocity profiles

Upward inclined gas-liquid flows are frequently encountered in the oil industry and data relating to the local gas volume fraction distribution and the local gas velocity distribution is important, for example, in pressure gradient prediction and in modeling oil well ‘blowouts’. In this paper measurements are presented of the local gas volume fraction distribution and the local axial gas velocity distribution which were taken in bubbly air-water flows in an 80 mm diameter pipe which was inclined at angles of 0°, 15° and 30° to the vertical. Qualitative arguments are presented to explain the influence of the liquid superficial velocity on the local gas volume fraction distribution in inclined flow and also to explain the very high axial gas velocities observed towards the upper side of the inclined pipe.     

EFFECTS OF BOND NUMBERS ON INTERNAL FLOW PATTERNS OF AN INCLINED,CLOSED, TWO-PHASE THERMOSYPHON AT NORMAL OPERATING CONDITIONS

A visual study of internal flow patterns inside an inclined, closed, two-phase thermosyphon at normal operating conditions for several Bond numbers has been conducted. This article describes the effects of varying inclination angles and Bond numbers (Bo) onflow patterns, A copper thermosyphon was used. R123 was selected as the working fluid, with a vapor temperature of 30°C and a filling ratio of 50%. Flow phenomena were observed at selected inclination angles of 90° and 30° from the horizontal axis, with aspect ratios of 30 and 5. The selected external diameters were 12.0 and 28.5 mm. Flow phenomena were also recorded with a standard video camera and a still camera, and the corresponding heat transfer rates were also monitored. It was observed that the basic internal flow patterns could be classified according to the aspect ratios and the Bo as follows: At an aspect ratio of 10 and higher, the annular flow at vertical changes to slug flow in inclined positions for all values of Bo. A thin liquid film always exists in the upper part, promoting heat transfer. In this case, the ratio of heat transfer rates at peak position and those of the vertical (Q / Q90) are almost the same for all Bo. At an aspect ratio of less than 10 and a low Bo, bubbly flow at vertical changes to stratified flow at an inclined position, with bubbly flow in the lower part. Vapor slug is sometimes seen. At an aspect ratio of less than 10 and a high Bo, bubbly flow with a coagulation of bubbles at the vertical position changes to stratified flow with bubbly flow in the upper part, without any vapor slugs. Q / Q90 is comparatively higher than at lower Bo. This result may be attributed to two main factors: (1) there was an area undisturbed by bubbles in the lower part; and (2) no upward vapor slug movement was observed.