液相物性对壳侧不互溶双组分两相流截面含气率及两相压降的影响

在用空气-水、空气-0号柴油研究的基础上,用空气和质量浓度为30％的甘油水溶液研究了理想管壳式换热器壳侧平均截面含气率和两相压降,以期进一步考察不同液相物性的影响.研究表明,液相物性对两者均有一定影响.提出了不同液相物性时截面含气率的通用关联式.根据流型整理了两相摩擦因子.并提出了一种新的两相摩擦压降关联式,它能较好地预测不同液相物性时两相压降的实验数据.     

Effects of sparger geometry on the mechanism of flow pattern transition in a bubble column

Electrical resistance tomography (ERT) is used to measure void fraction wave characteristics and to identify flow pattern in a bubble column reactor (0.24 m diameter, 2.75 m height). The effects of column pressure and superficial gas velocities for different sparger geometry and for different flow pattern have been investigated. The ERT sensor can distinguish the void fraction disturbances in different flow regimes with a good clarity. The holdup derived from ERT is in good agreement with the hold-up values measured by pressure transmitters. Different flow regimes have been identified based on void fraction properties and wall pressure fluctuations. The spectral analysis of ERT measurements yields quantitative information, such as a characteristic time and a characteristic frequency of void fraction waves, which are closely related to flow structure in the prevailing regime. The experimental observations are compared with the literature.     

垂直同心环形管内上升气液两相环状流含气率与压降预测

对垂直同心环形管内上升气液环状流的截面含气率及压降预测进行了研究.根据Kelessidis有关团状流向环状流转换的思路以及Wallis有关圆管内环状流积分分析的方法,考虑环形管的结构特征及环状流的流型特征,通过两相动力学理论建立了新的预测截面含气率及总压降的模型.将新模型及现有模型与实验数据的分析比较表明新模型对于总压降的预测效果较好.     

Void fraction in vertical gas-liquid slug flow: Influence of liquid slug content

In this study we develop a model for computing the mean void fraction and the liquid slug void fraction in vertical upward gas-liquid intermittent flow. A new model for the rate of gas entrained from the Taylor bubble to the liquid slug is formulated. It uses the work done by the pressure force at the rear of the Taylor bubble. Then an iterative approach is employed for equating the gas entrainment flux and the gas flux obtained via conservation equations. Model predictions are compared with experimental data. The developed iterative method is found to provide reasonable quantitative predictions of the entrainment flux and of the void fraction at low and moderate liquid slug void fraction conditions. However, with an increased liquid slug void fraction experimental data indicate that the flow in the liquid slug transits to churn-heterogeneous bubbly flow thus gas entrainment flux tends to zero. Considering this effect in the iterative model significantly improved the predictions for large liquid slug void fraction conditions.     

基于ECT和蚂蚁算法的油气两相流空隙率在线测量

基于电容层析成像系统（ECT）和蚂蚁算法,提出了一种油气两相流空隙率在线测量的新方法。该方法利用电容层析成像系统12电极电容传感器所获取的66个测量电容信息,首先根据电容层析成像系统所获取的流型辨识结果确定对应流型下的实际空隙率测量模型参数f和b,然后利用蚂蚁算法的信息素信息,找到当前测量状态下对空隙率起主要作用的组合电容集合和相应的权重系数,从而实现空隙率测量。与流型相对应的空隙率测量线性模型参数f和b基于先验数据通过最小二乘方法确定。油气两相流的实验结果表明,该方法对空隙率的在线测量是有效的,避免了复杂的图像重建计算,实时性能佳,测量时间小于0.08 s。在几种典型流型下,提出的空隙率测量方法与常用的快关阀方法相比最大测量偏差小于5.5%。     

Void fraction measurement and calculation model of vertical upward co-current air–water slug flow

The focus of this paper is on the measurement and calculation model of void fraction for the vertical upward co-current air–water slug flow in a circular tube of 15 mm inner diameter. High-speed photography and optical probes were utilized, with water superficial velocity ranging from 0.089 to 0.65 m·s^-1 and gas superficial velocity ranging from 0.049 to 0.65 m·s^-1. A new void fraction model based on the local parameters was proposed, disposing the slug flow as a combination of Taylor bubbles and liquid slugs. In the Taylor bubble region, correction factors of liquid film thickness C_δ and nose shape C_Z^* were proposed to calculate α_TB. In the liquid slug region, the radial void fraction distribution profiles were obtained to calculate α_LS, by employing the image processing technique based on supervised machine learning. Results showed that the void fraction proportion in Taylor bubbles occupied crucial contribution to the overall void fraction. Multiple types of void fraction predictive correlations were assessed using the present data. The performance of the Schmidt model was optimal, while some models for slug flow performed not outstanding. Additionally, a predictive correlation was correlated between the central local void fraction and the cross-sectional averaged void fraction, as a straightforward form of the void fraction calculation model. The predictive correlation showed a good agreement with the present experimental data, as well as the data of Olerni et al., indicating that the new model was effective and applicable under the slug flow conditions.     

Interfacial Shear Stress of Stratified Flow in a Horizontal Pipe

Experimented data are presented for the void fraction aud the shear stresses of stratified gas-liquid flow in a pipe, A new technique was used to measure the interface shear strew. The interfacial shear stress was determined by using two methods: a momentum balance of gas and an extrapolation of the Reynolds shear stress prone at the gas-liquld interface. A new formula ,relatiog to the interfacial friction factor with the void fraction and superficiol gas Rcynold number, was dewloped to predict the interface shear stress. The predicted values are in good agreement with experimental data.     

Two‐Phase Bubbly Flow Structure in Large‐Diameter Vertical Pipes

The two‐phase flow structure of an air‐water, bubbly, upward flow in a 20 cm diameter pipe is presented with particular emphasis on the local interfacial area concentration. The radial distribution of void fraction, bubble velocity, bubble size, bubble frequency, and interfacial area concentration were measured using a local dual‐optical probe. The experimental results showed that the saddle‐type distribution of void fraction and interfacial area concentration, which are common for bubbly flow in small diameter pipes, only appeared in the present experiments under conditions of very low area‐averaged void fraction (<?> < 0.04). The values for the interfacial area concentration were higher in large diameter pipes when compared with data obtained under the same flow conditions in small pipes. The area‐averaged void fraction data were correlated using the drift‐flux model.     

BUBBLE AND SLUG FLOW AT MICROGRAVITY CONDITIONS: STATE OF KNOWLEDGE AND OPEN QUESTIONS

Based on the experiments carried out over the past decade at microgravity conditions, an overview of our current knowledge of bubbly and slug flows is presented. The transition from bubble to slug flow, the void fraction and the pressure drop are discussed from the data collected in the literature. The transition from bubble to slug flow may be predicted by introducing a critical void fraction that depends on the fluid properties and the pipe diameter: however, the role of coalescence which controls this transition is not clearly understood. The void fraction may be accurately calculated using a drift-flux model: it is shown from local measurements that the drift of the gas with respect to the mixture is due to the non uniform radial distribution of void fraction. The pressuredrop happens to be controlled by the liquid flow for bubbly flow whereas for slug flow the experimental results show that pressure drops is larger than expected. From this study, the guidelines for future research in microgravity are given.     

电阻层析成象技术在两相管流测量中的应用

介绍应用电阻层析成象 (ERT)技术测量两相流中的基本原理和ERT系统的基本结构 ;描述应用天津大学过程层析成象研究室开发的ERT系统样机 ,在实验装置上进行两相流流型识别的实验研究。提出应用ERT系统进行流型识别的基本方法 ;并通过重建图像和分析测量数据实现两相流流型的识别。实验结果证明应用ERT系统实现两相流流型和参数测量的可能性     

Destabilisation of homogeneous bubbly flow in an annular gap bubble column

Experimental results are presented to show that there are very significant differences in the mean gas void fractions measured in an open tube and a annular gap bubble column, when operated at the same gas superficial velocity, using a porous sparger. Measurements were carried out in a vertical 0.102 m internal diameter column, with a range of concentric inner tubes to form an annular gap, giving diameter ratios from 0.25 to 0.69; gas superficial velocities in the range 0.014–0.200 m/s were investigated. The mean gas void fraction decreases with increasing ratio of the inner to outer diameter of the annular gap column and the transition to heterogeneous flow occurs at lower gas superficial velocities and lower void fractions. Two reasons are proposed and validated by experimental investigations: (1) the presence of the inner tube causes large bubbles to form near the sparger, which destabilise the homogeneous bubbly flow and reduce the mean void fraction; this was confirmed by deliberately injecting large bubbles into a homogeneous dispersion of smaller bubbles, and (2) the shape of the void fraction profiles changes with gap geometry and this affects the distribution parameter in the drift‐flux model. Both of these effects serve to reduce the mean gas void fraction in an annular gap bubble column compared to an open tube at the same gas superficial velocity.     

水平管道气液两相流中空隙率对动态压降信号的影响

引　言在化工、石油及动力等工程中 ,气液两相流动现象极为普遍 ,其研究得到了人们的广泛重视 .气液两相流动中的管道平均压降与其他流动条件及参数之间的关系已有较多的研究 ,得到了大量数学模型和经验公式可资工程设计应用[1,2 ],但对管道压降动态特性的研究还不多见 .而对于两相流系统安全性能的设计和运行状态监控等方面 ,管道压降的动态特性无疑是极为重要的参数 .另一方面 ,气液两相流动体系中的空隙率是表示气相浓度 (含气率 )的常用指标之一 ,它对确定气液两相流系统的流型、气液分相流量以及管道中的摩擦压降、重力压降和惯性压降…     

Experimental investigation of cocurrent two-phase flow in a vertical rectangular channel

New time averaged data of two-phase flow in bubbly and slug regimes are presented. A modified dual spherical tipped optical fiber probe is used to measure local void fractions, gas velocity and bubble sizes. Hot film anemometry was used to measure the local mean liquid velocity axially. The void fraction, gas and liquid velocities values were presented as averages over the long and short dimensions respectively. Also core values of these variables are presented along the smaller dimension of 12.7 mm, near the plane of symmetry of the longer dimension, to show the most general trend of the different bubbly and slug flow runs. Bubble sizes obtained experimentally were compared with predictive models applied to circular geometries and were found to have a reasonable agreement. It was also interesting to find that local void fractions measured using hot film anemometers were comparable to those found by optical fiber probes. Frequencies of interfacial passage of bubbles and slugs are presented which show rather flat profiles across the channel. It is hoped that these data can be further used in predictive two-phase two-fluid models in the future. Lastly of interest is the fact that slip values near the boundaries were shown to be less than 1.0 for some cases in bubbly flow similar to those observed in circular geometries.     

基于ERT传感器和数据挖掘技术的空气水两相流空隙率测量(英文)

Based on an electrical resistance tomography(ERT) sensor and the data mining technology,a new voidage measurement method is proposed for air-water two-phase flow.The data mining technology used in this work is a least squares support vector machine(LS-SVM) algorithm together with the feature extraction method,and three feature extraction methods are tested:principal component analysis(PCA),partial least squares(PLS) and independent component analysis(ICA).In the practical voidage measurement process,the flow pattern is firstly identified directly from the conductance values obtained by the ERT sensor.Then,the appropriate voidage measurement model is selected according to the flow pattern identification result.Finally,the voidage is calculated.Experimental results show that the proposed method can measure the voidage effectively,and the measurement accuracy and speed are satisfactory.Compared with the conventional voidage measurement methods based on ERT,the proposed method doesn’t need any image reconstruction process,so it has the advantage of good real-time performance.Due to the introduction of flow pattern identification,the influence of flow pattern on the voidage measurement is overcome.Besides,it is demonstrated that the LS-SVM method with PLS feature extraction presents the best measurement performance among the tested methods.     

The Measurement of Oil, Gas and Water Flowrates in Three-Phase Slug Flow

Three-sphase flow invo1ving oil-water two immiscible liquids and gas which is often foundin the fields of petroleum production has been studied in this paper.A new method with thecombination of a horizontal tube,a downward flow vertica1 tube and an orifice to measure theflowrates is presented.In this method the frictional pressure drop in the downward vertical tube isreplaced by that in the horizontal tube,the void fraction is derived from the gravitational pressuredrop,then the volume fraction of the individual phase can also be obtained.The individual flowratescan be calculated when the water fraction is known.This method is applicable for many kinds ofoil-wells to measure the flowrates of crude oil,natural gas and water.Compared with other methods,the presented method involves fewer measuring parameters.The experimental results proved quitegood accuracy of the method,with measurement deviation within 10%,and reliable results wereobtained under high Dressure conditions.     

气液两相垂直管流中弹状流型数学模型

本文对气液两相垂直管流的弹状流型的流动机理进行了分析,建立了数学模型。模型的特点是采用了以弹状气泡速度运动的相对座标系,在弹状气泡周围下落液膜流动、液体段空隙率计算和压降计算等方面部提出了新的观点。在两种管径中用空气-水系统进行了实验以验证模型,与一些其他作者的实验数据和理论模型也进行了比较,结果都表明这个机理模型计算的弹状流型的各种流体力学参数值与实验值吻合良好,也优于其他作者提出的模型。     

Investigating the effect of pressure on a vertical two-phase upward flow with a high viscosity liquid

This article presents void fraction and pressure gradient data for sulfur hexafluoride (SF₆) with gas densities of 28 and 45 kg/m³ and oil (with viscosity 35 times that for water) in a 127 mm diameter pipe. The superficial velocities of gas ranged from 0.1 to 3 m/s and those for liquid from 0.1 to 1 m/s, respectively. Measurements of void fraction data were recorded using a capacitance wire mesh sensor (WMS) system, which permits the 3D visualization of the flow patterns. All the data were obtained with a data acquisition frequency of 1,000 Hz. A differential pressure transducer was used to measure the pressure drops along the length of the pipe. The WMS provide time and cross-sectionally resolved data on void fraction and from an analysis of its output, flow patterns were identified using the characteristic signatures of probability density function (PDF) plot of time series of void fraction. The PDF plots showed the single peak shapes associated with bubbly and churn flows but not the twin-peaked shape usually seen in slug flows. This confirms previous work in larger diameter pipes but with less viscous liquids. For the bubble and churn flows investigated, the pressure gradient was observed to decrease with an increase in gas superficial velocity. Nevertheless, there was an insignificant observed effect of pressure on void fraction below certain transitional flow rates, the effect however became significant beyond these values. In the present work, wisps appear to be smaller, which might be due to the different fluid properties of the working fluids employed. In addition, wisps are easily revealed as long as there is a transition between churn and annular flows regardless of the pressure. Experimental data on void fraction and pressure gradient are compared against existing data. Reasonably good agreements were observed from the results of the comparison.     

Modeling the pressure drop of wet gas in horizontal pipe

A model for gas-liquid annular and stratified flow through a horizontal pipe is investigated,using the two-phase hydrokinetics theory.Taking into consideration the flow factors including the void fraction,the friction between the two phases and the entrainment in the gas core,the one-dimensional momentum equation for gas has been solved.The differential pressure of the wet gas between the two tapings in the straight pipe has been modeled in the pressure range of 0.1-0.8 MPa.In addition a more objective iteration approach to determine the local void fraction is proposed.Compared with the experimental data,more than 83％ deviation of the test data distributed evenly within the band of ± 10％.Since the model is less dependent on the specific empirical apparatus and data,it forms the foundation for further establishing a flow measurement model of wet gas which will produce fewer biases in results when it is extrapolated.     

水平管束间气液两相流局部含气率分布的实验研究

在废热锅炉火管管束间的气液两相流中,局部含气率的分布直接影响管束间流场、温度场的均匀性以及火管壁温工况.使用单纤光纤探针对水平管束间含气率的分布进行测量.实验沿管周方向以5度的间隔布置测点,得出含气率随径向、角度、气量、液量等参数变化的分布规律.同时通过分析得到了平均截面含气率的计算式.     

Improved Void Fraction Correlation for Two‐Phase Flow in Large‐Diameter Annuli

A flow pattern‐independent void fraction correlation for gas‐liquid two‐phase flow in vertical large‐diameter annuli is established. Two equations are proposed for the parameters of a drift flux model‐based correlation: the distribution parameter and the drift flux velocity. These equations are expressed as a function of two‐phase flow variables including void fraction, fluid properties, pipe geometry, and phase flow rates. Experiments were performed to study the void fraction of vertical air‐water two‐phase flow in large‐diameter annuli. The obtained experimental data along with the literature data of Caetano are used to verify the performance of the proposed void fraction correlation. The accuracy of this correlation is compared with nineteen frequently used correlations in literature. The proposed correlation was found to predict the void fraction consistently with a better accuracy.