Flow Regime Identification of Gas-liquid Two-phase Flow Based on HHT

A new method to identify flow regime in two-phase flow was presented, based on signal processing of differential pressure using Hilbert Huang transform （HHT）. Signals obtained from a Venturi meter were decomposed into different intrinsic mode functions （IMFs） with HHT, then the energy fraction of each intrinsic mode and the mean value of residual function were calculated, from which the rules of flow regime identification were summarized. Experiments were carried out on two-phase flow in the horizontal tubes with 50mm and 40mm inner diameter, while water flowrate was in the range of 1.3m^3.h^-1 to 10.5m^3.h^-1, oil flowrate was from 4.2m^3.h^-1 to 7.0m^3.h^-1 and gas flowrate from 0 to 15m^3.h^-1. The results show that the proposed rules have high precision for single phase, bubbly, and slug, plug flow regirne identification, which are independent of not only properties of two-phase fluid. In addition, the method can meet the need of industrial application because of its simple calculation.

Identification Method of Gas-Liquid Two-phase Flow Regime Based on Image Multi-feature Fusion and Support Vector Machine

The knowledge of flow regime is very important for quantifying the pressure drop, the stability and safety of two-phase flow systems. Based on image multi-feature fusion and support vector machine, a new method to identify flow regime in two-phase flow was presented. Firstly, gas-liquid two-phase flow images including bub- bly flow, plug flow, slug flow, stratified flow, wavy flow, annular flow and mist flow were captured by digital high speed video systems in the horizontal tube. The image moment invariants and gray level co-occurrence matrix texture features were extracted using image processing techniques. To improve the performance of a multiple classifier system, the rough sets theory was used for reducing the inessential factors. Furthermore, the support vector machine was trained by using these eigenvectors to reduce the dimension as flow regime samples, and the flow regime intelligent identification was realized. The test results showed that image features which were reduced with the rough sets theory could excellently reflect the difference between seven typical flow regimes, and successful training the support vector machine could quickly and accurately identify seven typical flow regimes of gas-liquid two-phase flow in the horizontal tube. Image multi-feature fusion method provided a new way to identify the gas-liquid two-phase flow, and achieved higher identification ability than that of single characteristic. The overall identification accuracy was 100%, and an estimate of the image processing time was 8 ms for online flow regime identification.

An Experimental Study on the Void Fraction for Gas-Liquid Two-Phase Flows in a Horizontal Pipe

The flow patterns and the void fraction related to a gas-liquid two-phase flow in a small channel are experimentally studied.The test channel is a transparent quartz glass circular channel with an inner diameter of 6.68 mm.The working fluids are air and water and their superficial velocities range from 0.014 to 8.127 m/s and from 0.0238 to 0.556 m/s,respectively.The void fraction is determined using the flow pattern images captured by a high-speed camera,while quick closing valves are used for verification.Four flow patterns are analyzed in experiments:slug flow,bubbly flow,annular flow and stratified flow.For intermittent flows(bubbly flow and slug flow),the cross-sectional void fraction is in a borderline condition while its probability distribution function(PDF)image displays a bimodal structure.For continuous flows(annular flow and stratified flow)the cross-sectional void fraction behaves as a fluctuating continuous curve while the(PDF)image displays a single peak structure.The volumetric void fraction data are also compared with available predictive formulas,and the results show that the agreement is very good.An effort is also provided to improve the so-called Gregory and Scott model using the available data.

Branch Quality Control of Gas-Liquid Two-Phase Flow Using a Novel T-Junction Type Distributor

In order to eliminate mal-distribution and ensure the side arm to produce desirable gas quality a special distributor is proposed. The experimental distributor mainly consists of a straight through section,a gas extraction line,a liquid extraction line and a side arm branch. A gas orifice and a liquid orifice are mounted at the gas and liquid extraction line respectively to control the outlet gas quality. The diameter of the liquid orifice was set to 2. 50 mm and three gas orifices with different size( dG= 2. 65,5. 00,10. 00 mm) were tested. The experiments were carried out at an air-water two-phase flow loop. The gas superficial velocity ranged from 6. 0 to 20. 0 m /s and the liquid superficial velocity was in the range of 0. 02- 0. 18 m /s. Flow patterns such as wave flow,slug flow and annular flow were observed. The gas quality of the side arm branch was found mainly determined by the flow area ratio of the gas orifice to the liquid orifice and independent of gas and liquid superficial velocity,flow patterns and extraction flux.

Comparison of One-Dimensional Analysis with Experiment for CO₂Two-Phase Nozzle Flow

The aim of this study is to investigate CO2 two-phase nozzle flow in terms of both experimental and analytical aspects for the optimum design of two-phase flow nozzle of CO2 two-phase flow ejector. In the experiment, it is measured that the temperature profile in the stream-wise direction of a divergent-convergent nozzle through which CO2 in the supercritical pressure condition is blown down into the atmosphere. In the analysis, a one-dimensional model which assumes steady, adiabatic, frictionless, and equilibrium is proposed. In the convergent part of the nozzle the flow is treated as single-phase flow of liquid, whereas in the divergent part the flow is treated as separated two-phase flow with saturated condition. The analytical results indicate that the temperature and the pressure decrease rapidly in the divergent part, and the void fraction increases immediately near the throat. Although this analysis is quite simple, the analytical results can follow the experimental results well within this study.

同轴微通道内管结构对液滴生成的影响规律研究

研究了同轴微通道内水-硅油体系的液滴生成过程。在不同的连续毛细数Ca_(c)和分散相Weber数Wed下,观察到滴出流和喷射流两种不同的流型。实验考察了两相流量、黏度和内管结构对液滴尺寸和液滴生成频率的影响。结果表明液滴尺寸随着分散相流量增加而增大,而随着连续相流量和黏度的增加而降低。此外,随着Wed的增加,流型会从滴出流过渡到喷射流,而更大尺寸的内管会更早过渡到喷射流,从而得到更大的液滴尺寸。对于液滴生成频率,其随Ca_(c)和Wed的增加均呈现先快速增加后变缓的趋势。当内管通道尺寸基本相同时,不同结构的内管通道在固定Ca_(c)时其液滴生成频率相差不大,且随着通道尺寸的减小,液滴生成频率逐渐增加。基于实验结果,建立了液滴尺寸预测模型,预测值与实验值吻合较好。

深部煤层气水平井井筒气液两相流数值模拟

深部煤层气井地层压力高,气液比变化范围大,不同于常规研究中的常压气液两相流,属于中高压的气液两相流流动。通过数值模拟的方法,研究深部煤层气井在高压力范围内、不同气液比下的气液两相流的流型变化、压降流动特性。结果表明:深部煤层气水平井在气液比低或压力高时,主要以弹状流和过渡流为主;气液比高或压力低时主要以环状流为主。深部煤层气实际生产工况中井筒内流体流型主要可划分为弹状流、过渡流、环状流3种区域;压降随着压力升高逐渐增大,相同日产气量的情况下,压降随着日产液量增大而增大,并且压降随压力变化更加剧烈;气液比高时,1 500 m井深以上主要以环状流为主;气液比低时,1 000 m井深以下主要以过渡流为主。

气力提升系统气液两相流流动特性研究

以空气-水作为介质,探究气举泵气液两相流的压力和流量特性,并基于压力信号的时域、功率谱密度函数(power spectral density,PSD)和概率密度函数(probability density function,PDF)分析鉴别流型。结果表明:除了进气喷嘴附近外,其他位置的局部平均压力随气体流速的增大逐渐上升达到峰值后减小,峰值随着浸没比的减小而向右移动且上升速度增大;液体流速随着气体流速增大急剧上升达到峰值后几乎保持不变,最大提升效率约为49%,与最大液体流速并不发生在同一个气体流速下;在不同的气流量下,观测到气泡流、帽弹流、弹状流、搅拌流和环状流的出现,不同流型可通过PSD和PDF估计量进行识别;特别是,浸没比越小越有利于形成大气塞。目前,关于气举泵的研究非常有限,本研究结果可为气液固三相流和气液两相流的研究提供数据和技术支撑。

Performance of a Horizontally Mounted Venturi in Low-pressure Wet Gas Flow

The performance of a Venturi tube used in wet gas flow have been explored mainly under higher-pressure condition, but very often, low-pressure test exists in some oil and gas fields in Tianjin Dagang Oil and Gas Field in China. In this study, the performance of horizontally mounted Venturi meters in low-pressure wet gas flow is discussed. Three 50 mm Venturi meters were tested systematically, with fl values of 0.4048, 0.55 and 0.70, the opera- tion pressure of 0.15 MPa, 0.20 MPa, 0.25 MPa, the gas densiometric Froude number from 0.6 to 2.0, the modified Lockhart-Maretinelli parameter from 0.0022 to 0.06, and the ratio of the gas liquid mass flow rate from 0.5 to 0.99. The effects of modified Lockhart-Maretinelli parameter, pressure, gas densiometric Froude number, diameter ratio, and gas-liquid mass flow rate ratio to the Venturi tube are analyzed with new independent data. Furthermore, low-pressure performance was compared with that under high pressure.

INFLUENCE OF SURFACTANT ON TWO-PHASE FLOW REGIME AND PRESSURE DROP IN UPWARD INCLINED PIPES

The influence of a surfactant on the two-phase flow regime and the pressure drop in upward inclined pipes is investigated for various gas/liquid flow rates.The air/water and air/100 ppm sodium dodecyl sulphate aqueous solution are used as the working fluids.The influence of the surfactant on the two-phase flow regime in upward inclined pipes is investigated using the electrical tomographic technique.For 0o,2.5o and 5o pipe inclinations,the surfactant has obvious effect on the transition from the stratified wavy flow to the annular flow,and the range of the stratified smooth flow regime is also extended to higher gas velocities.For 10o pipe inclination,no stratified flow regime is observed in the air/water flow.In the air/surfactant solution system,however,the stratified flow regime can be found in the range of and.For all inclination angles,the changes of the pressure gradient characteristics are accompanied with the flow pattern transitions.Adding surfactant in a two-phase flow would reduce the pressure gradient significantly in the slug flow and annular flow regimes.In the annular flow regime,the pressure gradient gradually becomes free of the influence of the upward inclined angle,and is only dependent on the property of the two-phase flow.

FLUID DYNAMICS IN A GAS-STIRRED LADLE——A Separated Flow Model with Stochastical Trajectories

A separated flow model with stochastical trajectories has been developed to describe the fluid flow in a bubble stirred ladle.The bubble dispersion,turbulent characteristics and gas-liquid interactions can be predicted by this mathematical model.The bubble flow as a dispersed phase is treated in a Lagrangian frame of reference and the analysis of the turbulent flow for liquid phase is conducted in a Eulerian field.The interactions between bubbles and liquid phases are considered as a bubble source term in the control equation for a continuous phase. The Monte Carlo sampling method is used to determine the bubble trajectories.The homoge- neous flow model is also taken into consideration so that it can be compared with the sepa- rated flow model.Numerical predictions using a water model of a ladle show that the pre- dicted results of the separated flow model agree satisfactorily with the experimental results, but the prediction of the homogeneous flow model are not in good agreement with the experi- mental results.

Classification of flow regimes in gas-liquid horizontal Couette-Taylor flow using dimensionless criteria

In this paper, the flow patterns observed in horizontal Couette-Taylor flow（CTF） were correlated using dimensionless numbers. The analysis of the results showed that the structure of the flow was an outcome of interaction between fluid inertia related to axial and rotational flows and gravitation. Therefore, the flow structures were correlated using axial and angular Reynolds numbers, and Archimedes number for the given value of gas-to-liquid flow ratio. Finally, the correlation for the prediction of the transition to the flow regime observed at high rotational speeds was proposed. The comparison with experiments carried out in the vertical CTF from the literature showed that this correlation can also be useful in the case of vertical flow.

竖直矩形窄通道内流动沸腾研究进展

综述了几何与工况参数变化对竖直矩形窄通道内换热效果影响的传热实验研究,以及窄通道内气泡成核与移动、流型及其转换的研究,从传热模型、核态沸腾起始点、有效空泡起始点、流动不稳定起始点、临界热流密度的研究等方面分析和总结了矩形窄通道内流动沸腾的传热机理研究。结合目前实验与理论研究,总结了现存问题,为矩形窄通道内流动沸腾的进一步研究提供参考。

文丘里气泡发生器内气液两相流流型及压降实验研究

针对一类文丘里气泡发生器内气液两相流动的流型及压降开展了实验研究。通过可视化实验观测区分了气泡发生器内3种基本流型,包括泡状流、弹状流和柱状流。实验发现,随着两相流从弹状流转变为柱状流,气泡发生器内压降迅速增大。通过对压力信号的时频分析,证明气泡发生器出口位置最有利于压力信号的在线监测。从压力信号中提取了与流型转变紧密相关的概率密度函数相对峰度和功率谱密度差异系数,并分别应用于弹状流-柱状流和泡状流-弹状流流型转变的识别。由于已有的压降模型无法准确预测文丘里气泡发生器的整体压降,为此本研究提出了新的压降预测方法。新关联式考虑了气泡发生器内部分单液相流过程以及流型转变对压降预测的影响,预测值与实验测量结果吻合较好,相对均方根偏差约为10.74%。

基于数字图像处理的孔喉内三相接触角自动测量方法

借助数字图像处理技术,以微流控水驱油实验视频为数据源,建立了微流控模型孔喉内三相接触角的自动批量测量计算方法;采用人工测量数据验证了新方法测量结果的可靠性,在此基础上,利用接触角概率密度曲线、均值变化曲线揭示了三相接触角在流动条件下的动态变化规律。研究表明:对于水湿岩石,水驱油过程中,驱替前期接触角均值以锐角为主,随驱替时间的延长,油相受力逐渐由黏滞力为主导向毛细管力为主导过渡,接触角均值不断增大,至驱替中后期以钝角为主。剩余油中的滴状流赋存于孔喉通道中央,不存在三相接触角;多孔流和柱状流在整个驱替过程中接触角变化幅度较小且均值皆为钝角,该类剩余油形成后流动性差,动用难度较大;簇状流在驱替过程中三相接触角均值整体呈上升趋势,剩余油动用难度逐渐升高;膜状流整体呈钝角,水驱后期接触角均值最大,动用难度最大。驱替结束后,不同流态剩余油仅受毛细管力作用的影响,接触角均为钝角,在原油作用下模型孔喉壁润湿性呈油湿特征。

IDENTIFICATION OF GAS LIQUID FLOW REGIMES IN A HORIZONTAL FLOW USING NEURAL NETWORK

The knowledge of flow regimes is very important in the study of a two phase flow system. A new flow regime identification method based on a Probability Density Function (PDF) and a neural network is proposed in this paper. The instantaneous differential pressure signals of a horizontal flow were acquired with a differential pressure sensor. The characters of differential pressure signals for different flow regimes are analyzed with the PDF. Then, four characteristic parameters of the PDF curves are defined, the peak number (K 1 ), the maximum peak value (K 2 ), the peak position (K 3 ) and the PDF variance (K 4 ). The characteristic vectors which consist of the four characteristic parameters as the input vectors train the neural network to classify the flow regimes. Experimental results show that this novel method for identifying air water two phase flow regimes has the advantages with a high accuracy and a fast response. The results clearly demonstrate that this new method could provide an accurate identification of flow regimes.

关于气液两相流流型及其判别的若干问题

气液两相流体系是一个复杂的多变量随机过程体系,流型的定义、流型过渡准则和判别方法等方面的研究是多相流学科目前研究的重点内容．本文就与气液两相流流型及其判别有关的研究状况进行了回顾和评述,力图反映近年来气液两相流流型及其判别问题研究的状态和趋势．

小波变换辨识流型的一种新方法研究

本文提出了一种基于小波分析进行水平管气液两相流流型辨识的新方法。该方法以测试管段的管程压降△P的波动作为测量信号，通过对其小波变换结果的分析，根据不同流型能量分布的定量指标确定了流型判别规则。实验结果表明，这种判别方法能有效地实现对水平管层状流、波状流、塞状流、弹状流等四种典型流型的在线辨识。

汽(气)液两相流流型在线识别的研究进展

综述了根据参数波动过程实现气液两相流流型在线识别的最新研究成果，内容包括两相流参数波动的产生机理，小波分析的应用，两相流参数波动过程的特征提取和特征分析，流型在线识别的特点及各种实现方法等．重点介绍了两相流参数波动过程的统计和非线性特征分析及其与流型之间的关系．深入讨论了流型神经网络识别方法及其存在的问题．从波动参数的选择、数理解释、流型识别方法等不同方面对研究进展进行了讨论．

基于小波分析的气液两相流流型模糊辨识

本文提出了一种基于小波分析进行气液两相流流型模糊辨识的新方法。通过对测试管段的管程压降△P的波动信号的基于Haar基的小波变换结果的分析，根据不同流型能量分布的定量指标确定了流型模糊判别规则。对水平管和5°、15°、25°倾斜上升管的实验结果表明，这种判别方法能较有效地实现气液两相流的气泡流、层状流、波状流、塞状流、弹状流和环状流等典型流型的在线辨识。