基于截面气含率的文丘里湿气压降模型

运用两相流理论对湿气中的气相与液相流动进行分析,在分层流与环雾状流的条件下推导了两相流通过水平标准文丘里流量计的理论模型.通过分别考虑截面气含率、相间摩擦以及液滴夹带等因素,在文丘里轴向对湿气流动中的气相动量方程进行求解.通过对水平直管中的截面气含率公式进行修正,建立了适用于收缩管道的截面气含率模型,并在此基础上模拟了湿气流经标准文丘里时其两个取压孔之间的轴向静压分布.实验证实,使用修正后的截面气含率公式将使模型对文丘里压降的预测准确度明显提升,其相对误差在15%以内.该模型以湿气两相流在水平文丘里中的流动形态为依据,具有较充分的物理背景,而且在推导过程中较少依赖特定实验装置与数据,为建立具有一定普适性的文丘里湿气计量模型奠定了基础.     

Z法气体超声波流量计湿气测量的虚高预测模型

引言湿气通常是指气相为连续相,液相为离散相的气液两相流。美国机械工程师学会ASME将其界定为Lockhart-Martinelli参数(L-M参数)X<0.3的气液两相流[1]。湿气普遍存在于自然界与工业现场中,如常规天然气田井口产出气(湿天然气)、煤层气、湿饱和蒸汽以及页岩气等均属湿气。随着工业生产的发展,对湿气不分离计量的要求越     

A study on the modeling of static pressure distribution of wet gas in Venturi

A model for gas–liquid annular and stratified flow through a standard Venturi meter is investigated, using the two‐phase hydrokinetics theory. The one‐dimensional momentum equation for gas has been solved in the axial direction of Venturi meters, taking into consideration the factors including the void fraction, the friction between the two phases and the entrainment in the gas core. The distribution of wet gas static pressure between the two pressure tapings of the Venturi meters has been modeled in the pressure range of 0.1–0.6 MPa. Compared with the experimental data, all the relative deviations of the predicted points by the model were within ±15%. As the model is less dependent on the specific empirical apparatus and data, it provides the basis for further establishing a flow measurement model of wet gas which will produce fewer biases in results when it is extrapolated. © 2014 American Institute of Chemical Engineers AIChE J, 61: 699–708, 2015     

湿气流量测量新方法

基于均相流假设,根据文丘里管两相流流量测量模型和空隙率定义式,结合气液两相流的差压瞬时值、流量瞬时值和空隙率瞬时值间存在的时间平均值关系,推导了湿气流量测量机理模型,并根据Froude准数对模型进行了修正。本文建立的湿气流量测量模型形式上为一经气、液密度和Froude准数修正的节流式流量测量关系式,该关系式将为湿气流动机理的研究提供有益的借鉴。实验结果表明,本文建立的湿气流量测量模型可用于湿气流量的测量,流量测量误差小于5%,满足实际测量的要求。     

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.     

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.     

On the prediction of the phase distribution of bubbly flow in a horizontal pipe

Horizontal bubbly flow is widely encountered in various industrial systems because of its ability to provide large interfacial areas for heat and mass transfer. Nonetheless, this particular flow orientation has received less attention when compared to vertical bubbly flow. Owing to the strong influence due to buoyancy, the migration of dispersed bubbles towards the top wall of the horizontal pipe generally causes a highly asymmetrical internal phase distributions, which are not experienced in vertical bubbly flow. In this study, the internal phase distribution of air-water bubbly flow in a long horizontal pipe with an inner diameter of 50.3 mm has been predicted using the population balance model based on direct quadrature method of moments (DQMOM) and multiple-size group (MUSIG) model. The predicted local radial distributions of gas void fraction, liquid velocity and interfacial area concentration have been validated against the experimental data of Kocamustafaogullari and Huang (1994). In general, satisfactory agreements between predicted and measured results were achieved. The numerical results indicated that the gas void fraction and interfacial area concentration have a unique internal structure with a prevailing maximum peak near the top wall of the pipe due to buoyancy effect.     

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.     

CFD modeling and validation for two-phase medium viscosity oil-air flow in horizontal pipes

This study presents the results of a Computational Fluid Dynamics (CFD) simulation of two-phase medium viscosity oil-air flow in a 50.8?mm internal diameter horizontal pipe. Void fraction and pressure gradient predictions were validated using experimental data for four different oil viscosities (0.039, 0.06, 0.108 and 0.166?Pa s) and different flow rates varying from 0.1 to 2.9?m/s for the gas phase and from 0.01 to 2.95?m/s for the liquid phase, where four flow patterns were predicted (stratified, dispersed bubble, bubble elongated and slug flow). The obtained results of void fraction and pressure gradient presented a mean relative error of 30.04 and 21.38%, respectively. Furthermore, the CFD results were compared against 66 empirical correlations and predictions from OLGA. It was found that between the three studied methods (CFD, OLGA and empirical correlations) the CFD model outperformed the other two methods regarding the predicted flow patterns, pressure gradients and void fractions on most cases.     

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…     

Equilibrium and non‐equilibrium gas–liquid two phase flow in long and short pipelines following a rupture

The two‐phase flow following the blowdown of pipeline carrying flashing liquid is numerically investigated by using thermodynamic equilibrium and non‐equilibrium models. Model equations are solved numerically by the finite volume method. The values of fluxes at cell boundaries are obtained by AUSM+‐up. To obtain proper values for the coefficients of dissipation, both single phase liquid and two phase shock tube problems are investigated. The transient release from the pressurized pipeline is studied for two cases of long and short pipes. Comparison of the predictions against experimental data reveals non‐equilibrium model performs a little better than equilibrium model in the prediction of temporal variations of pressure and void fraction of the long pipe. However, equilibrium model totally overestimates pressure and void fraction of the short pipe. The relative error of equilibrium model in the prediction of pressure variation with time exceeds 50% and it is 20% for non‐equilibrium model. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3214–3223, 2017     

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.     

垂直管内通气空泡掺气过程仿真分析简

A semi-empirical gas entrainment model was proposed for the ventilated cavity in vertical pipe, based on which, a complete numerical scheme was established by coupling with the Eulerian-Eulerian two-fluid model to predict the multiscale flow field created by ventilated cavity. Model predictions were validated against experimental measurements on void fraction and bubble size distributions. Simulations were carried out to explore the effect of ventilation rate and inlet turbulence intensity on the macroscale cavity shape and the bubbly flow downstream of the ventilated cavity. As the ventilation rate increasing, a reverse trend was observed for the void fraction and bub- ble size distributions. It is concluded that the average void fraction in the pipe flow region is determined by the volumetric ratio between liquid and gas. However, the bubble size evolution is dominated by the breakage effect induced by turbulence in the vortex region. Furthermore, simulations were conducted to analyze geometric scale effect based upon Froude similitude. The results imply that the velocity distributions were properly scaled. Slight scale effect was seen for the void fraction caused by faster dispersion of bubbles in the larger size model. The com- paratively greater bubble size was predicted in the smaller model, implying significant scale effects in terms of tur- bulence and surface tension effect. It reveals that empirical correlations valid in wide range are required for the ex- trapolation from small-size laboratory models.     

A new mechanistic model to predict gas–liquid interface shape of gas–liquid flow through pipes with low liquid loading

Devising a new mechanistic method to predict gas–liquid interface shape in horizontal pipes is concerned in this article. An experiment was conducted to find the pressure gradients of air–water flow through a 1‐in. pipe diameter. Comparing results of model with some experimental data available in the literature demonstrates that the model provides quite better predictions than existed models do. This model also predicts flow regime transition from stratified to annular flow better than Apparent Rough Surface and Modified Apparent Rough Surface models for both 1‐ and 2‐in. pipe diameters. The model also leads to reliable predictions of wetted wall fraction experimental data. Although one parameter of new model was evaluated based on air–water flow pressure loss experimental data for 1 in. pipe, it was considerably successful to predict pressure drop, liquid holdup, stratified‐annular transition and wetted wall fraction for other gas–liquid systems and pipe diameters. © 2014 American Institute of Chemical Engineers AIChE J, 61: 1043–1053, 2015     

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.     

Comparative study of gas–oil and gas–water two-phase flow in a vertical pipe

A wire-mesh sensor has been employed to study air/water and air/silicone oil two-phase flow in a vertical pipe of 67 mm diameter and 6 m length. The sensor was operated with a conductivity-measuring electronics for air/water flow and a permittivity-measuring one for air/silicone oil flow. The experimental setup enabled a direct comparison of both two-phase flow types for the given pipe geometry and volumetric flow rates of the flow constituents. The data have been interrogated at a number of levels. The time series of cross-sectionally averaged void fraction was used to determine characteristics in amplitude and frequency space. In a more three-dimensional examination, radial gas volume fraction profiles and bubble size distributions were processed from the wire-mesh sensor data and compared for both flow types. Information from time series and bubble size distribution data was used to identify flow patterns for each of the flow rates studied.     

水平管泡状流相分布特性

<正>气液两相泡状流的主要特征是连续液相中携带散布其中的细小气泡,气泡的存在不仅对气液两相流的传热、传质及阻力特性有很大的影响,而且对两相流动的稳定性也有很大的影响.前人有关泡状流的研究大多偏重于两相流的平均参数,对于两相流局部统计参数如局部空隙率等参数的变化规律是近年来两相流研究的新趋势.对于垂直管内的流动已经积累了相当数量的数据,而同样有广泛应用的水平管内相分布规律还知之甚少.气泡对气液两相流的传热、传质及流动结构影响机理的研究必须以了解相分布及气泡的局部统计参数为前提,同时对相分布特性的深人研究也为气液两相流的数学模型化提供实验依据.本文以空气、水为工质,研究水平管内气液两相流的相分布特性,给出了典型泡状流的时域信号图,研究了相分布随气液两相流量的规律变化,并与前人的有关结果进行了比较.     

用改进ECT技术测定油气两相流中空泡分数的测量研究

To measure the void fraction online in oil-gas pipeline, an improved electrical capacitance tomography (ECT) system has been designed. The capacitance sensor with new structure has twelve internal electrodes and overcomes the influence of the pipe wall. The data collection system is improved by using high performance IC (integrated circuit). Static tests of bubble flow, stratified flow and annular flow regime are carried out. Measurements are taken on bubble flow, stratified flow and slug flow. Results show that the new ECT system performs well on void fraction measurement of bubble flow and stratified flow, but the error of measurement for slug flow is more than 10%.     

A Simple Model for Predicting the Two-Phase Heavy Crude Oil Horizontal Flow with Low Gas Fraction

A two-phase heavy crude oil flow with low gas fraction is common in the oil transportation process. However, most of the studies of a gas–liquid flow are based on low viscosity fluid, such as water and light oil; as a result, the results cannot be introduced successfully into the mixture flow of gas and heavy crude oil. In this work, a two-phase flow of gas and heavy crude oil, which originated from the Bo-hai oilfield in China, was investigated in a horizontal pipe with 47-mm inner diameter. Data were acquired for the oil flow rate ranging from 2 m³/h to 10 m³/h, the input gas volume fraction ranging from 0.01 to 0.15, and the viscosity of crude oil ranging from 2.41 Pa·s to 0.34 Pa · s. Based on the drift-flux model, a new simplified correlation was developed to predict the void fraction and the pressure gradient. A comparison between the predicted and measured data demonstrates a reasonable agreement, and the correlation might be helpful for practical application in industry, especially in initially estimating the flow characteristic parameters.     

Experimental Study of Two-Phase Air–Water Flow in Large-Diameter Vertical Pipes

Recently, due to an increase in production demand in nuclear and oil and gas industries, the requirement to migrate toward larger pipe sizes for future developments has become essential. However, it is interesting to note that almost all the research on two-phase gas–liquid flow in vertical pipe upflow is based on small-diameter pipes (D ≤ 100 mm), and the experimental work on the two-phase gas–liquid flow in large-diameter (D > 100 mm) vertical pipes is scarce. Under the above circumstances, the application of modeling tools/correlations based on small-diameter pipes in predicting flow behavior (flow pattern, void fraction, and pressure gradient) poses severe challenges in terms of accuracy. The results presented in this article are motivated by the need to introduce the research work done to the industries where the data pertaining to large-diameter vertical pipes are scarce and there is a lack of understanding of two-phase gas-liquid flow behavior in large-diameter (D > 100 mm) vertical pipes.

The unique aspect of the results presented here is that the experimental data have been generated for a 254-mm inner diameter vertical pipe that forms an excellent basis for the assessment of modeling tools/correlations. This article (i) presents the results of a systematic investigation of the flow patterns in large-diameter vertical pipes and identifies the transition between subsequent flow patterns, (ii) compares it directly with the existing large- (150 mm) and small-diameter data (28 mm and 32 mm) in the same air–water superficial velocity range, (iii) exemplifies that the existing available empirical correlations/models/codes are significantly in error when applied to large-diameter vertical pipes for predictions, and last (iv) assesses the predictive capability of a well-known commercial multiphase flow simulator.