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.     

Horizontal air–water flow in a square cross‐section channel: Pseudo‐slug flow regime

New experimental data for air–water flow in a horizontal square cross‐section channel (H = 24.25 mm) is presented, including data on liquid hold‐up, gas and liquid velocities, and wave velocities and frequencies. For the majority of gas and liquid flow rates studied, the regime observed was pseudo‐slug. Using visualization studies it was possible to identify wavy‐stratified and pseudo‐slug flows. For the pseudo‐slug regime new correlations were obtained for liquid hold‐up, for gas and liquid velocities as a function of the ratio between gas and liquid mass flow rates, and for the frequency of roll‐waves as a function of gas and liquid mass flow rates.     

Experimental study on severe slugging mitigation by applying wavy pipes

Wavy pipes were installed in the pipeline for mitigating severe slugging in pipeline/riser systems. Experimental results have revealed that: with a wavy pipe applied, the operating region of severe slugging is reduced; the severity of severe slugging and oscillation flow is mitigated; the wavy pipe performs better with its outlet located upstream of the riser base. The wavy pipe is essentially reducing the slug length. For severe slugging the wavy pipe works by accelerating the movement of the gas in the pipeline to the riser base; for the oscillation flow it works by mixing the gas/liquid two phases.     

Electrical capacitance tomography measurements on vertical and inclined pneumatic conveying of granular solids

Pneumatic conveying of granular solids in vertical and inclined risers was studied using electrical capacitance tomography (ECT). The focus of the study was on flow development past a smooth bend connecting the riser to a horizontal duct which brought the gas-particle mixture to the riser. In the vertical riser, dispersed flow manifested a core-annular structure, whose development is discussed. Three different time-dependent flow patterns were imaged. Slugging flow, which appeared to be intrinsic to riser flow, took the form of alternating bands of core-annular disperse flow and a slug with a particle-rich core. Averaging over these two structures yielded a composite distribution with high particle concentration both at the axis and the wall region. Pulsing flow, whose ECT fingerprint was similar to that of slugging flow, was largely an entrance effect. Stationary and moving annular capsules with a dilute core were also observed, and such flow patterns do not appear to have been reported previously. Our ECT measurements probing the development of disperse flow in an inclined riser past a bend revealed that the particle loading initially decreased, subsequently increased and then leveled off. Regimes such as eroding dune flow and flow over a settled layer could be easily imaged using ECT. The surface of the settled layer had a concave shape, suggesting that the particles were picked up from the settled layer by airflow at the center and deposited on the sides of the tube.     

水平与微倾斜管内间歇流中长气泡的形态特征

利用双平行探针技术和摄像方法对水平和近水平微倾斜管内长气泡的形态特征进行了实验研究.实验结果表明气泡头部以及气泡体的形态特征取决于气液混合Froude数和管道倾角,而尾部特征还与气泡长度有关;小气泡通过单纯水跃面的长气泡尾部向液塞区弥散,而具有阶梯状尾部结构的长气泡并不向液塞区弥散小气泡,所以气泡尾部结构特征的变化决定了弹状流向段塞流的转变;管道倾角对长气泡形态特征有显著的影响,下倾管内的长气泡在低Froude数时出现头尾倒置现象,同时下倾管内的长气泡比上倾管更易保持阶梯状的尾部结构,所以下倾管的弹状流区比上倾管宽.     

水平管道油气二相段塞流稳态流动特性

使用通过自行设计并搭建的实验装置,对水平管道油气二相段塞流稳态流动特性进行了实验研究。采用压力信号互相关方法测量了段塞流平均液塞速度,通过分析得到了液塞速度、液塞长度和液塞频率随气、液相折算速度的变化规律。结果表明,当液相折算速度恒定时,随着气相折算速度的增大,液塞速度基本上呈线性增大,而液塞长度呈双曲线减小;当气相折算速度恒定时,随着液相折算速度的增大,液塞频率基本呈线性增大,而液塞长度呈双曲线减小。     

Behavior of Pressure Gradient and Transient Pressure Signals during Liquid‐Liquid Two‐Phase Flow

Liquid‐liquid two‐phase flows are encountered in several process industries, multiphase reactors and oil industries. In each of these applications, identification of flow patterns poses a challenging problem and many efforts are directed towards developing suitable devices for this purpose. In the present work, attempts have been made to use pressure gradient and transient pressure signals to study flow patterns during the simultaneous flow of two liquids through a horizontal pipe. It is observed that the slope of the pressure gradient curves as a function of fluid superficial velocities is a weak function of the flow pattern. However, the variation of the slope with the pattern transition is much more significant when the pressure gradient is normalized with respect to only kerosene flow through the pipe (Δp_TP/Δp_KO). Further attempts have been made to identify flow patterns from transient pressure signals and the statistical analysis of these random signals has been undertaken. The PDF analysis and the wavelet multiresolution technique have been adapted to explain the signals in detail. The flow regimes identified are smooth stratified, wavy stratified, plug flow, ‘three‐layer' flow, ‘oil dispersed in water and water' and ‘oil and water in oil' flow patterns. The signal characteristics are depicted for each flow pattern.     

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%.     

水平管内气液段塞流液塞发展特性实验研究

Slug initiation and subsequem evolution along a 5.0 cm ID, 16m long horizomal pipe are experimentally studied. The transient characteristics of interfacial structures are described by using simultaneous measuremeres of the liquid height at multiple locations along the pipe. Various effects of superficial gas and liquid velocities and pressure oscillation on the slug initiation and evolution along the pipe are illustrated. It is found that the slug is initiated by a deterministic orocess with reolenishmem and deoletion of liquid near the inlet for the superficial gas velocity USG〈3.0m·s^-1 and by a stochastic process with wave coalescence along the pipe for USG〉3.0m·s^-1.The evolution of the slugs is strongly attected by superhclal gas and liquid veloclties for USG〈3.0m·s^-1 but weakly affected by the superficial gas velocity for USG〉3.0 m·s . The suppression of pressure oscillation at the pipe inlet significantly delays the onset of slugging, with slugs forming postponed further downstream. The slug frequency at the outlet is, however, not affected by the variation in the pressure oscillation.     

Investigating the liquid film characteristics of gas–liquid swirling flow using ultrasound doppler velocimetry

A novel gas–liquid two‐phase flow metering method was proposed. A spiral vane mounted in the inner pipe was used to transform inlet flow patterns into gas–liquid swirling annular flow. The thickness and velocity profile of liquid film were measured by ultrasound Doppler velocimetry. The liquid flow rates were obtained by integrating of velocity profile during the liquid film zone. Experiments were carried out in an air–water two‐phase flow loop and an ultrasonic transducer was installed under the bottom of the test section with the Doppler angle of 70°. The flow patterns included stratified wavy, annular, and slug flows. Compared with non‐swirling flow, the liquid film thickness at the bottom reduces greatly. The measurement accuracy of liquid flow rate was independent of inlet flow patterns, gas and liquid velocities. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2348–2357, 2017     

Development of kerosene–water two‐phase up‐flow in a vertical pipe downstream of A 90° bend

The development of kerosene–water up‐flow in a vertical pipe of 77.8 mm inner diameter and 4500 mm, length downstream of a 90° bend, has been investigated using a Pitot tube and dual optical probe. The CFD ANSYS Fluent 12.0 is used to model the flow and the results are compared with experimental data. The CFD provides detailed information on flow structure which is difficult to obtain in experiments. The experimental measurements of the local parameters demonstrate that the single phase and two‐phase flows reached the fully developed axisymmetrical conditions at L/D = 54. These results also show the severe asymmetry distributions of the two‐phase flow parameters at the entrance region (L/D = 1). The predictions from Fluent are found to be in close agreement with experimental data for L/D ≥ 16 but there is a significant discrepancy at L/D = 1. © 2011 Canadian Society for Chemical Engineering     

柔性立管管径对严重段塞流特性的影响

用于将海底原油及天然气举升到海上平台的S型柔性立管是海洋石油工业中的重要设备.为研究柔性立管尺寸对严重段塞流特性的影响,在集输-S型柔性立管系统上分别实验研究了立管内径等于和大于集输管道内径时严重段塞流的特征参数规律.该实验环路内径为50 mm,由水平环路、倾角为-2°的下倾段和S型柔性立管组成,其中水平段长为114 ...     

垂直U型管两相流流型和传热研究(I)——U型管弯管段两相流流型转变

对垂直U型管弯管段空气-水同向流动时气液两相流在不同速度范围内流型间转变进行了试验,试验用内径21.5mm有机玻璃管,弯管半径分别为694、500和320mm.流型采用直接观察法及电导探针法确定.所得数据与Mandbane等人及Weiman等人的水平管转变关系式作了比较.根据试验结果,给出了以折算气体和液体速度V_(SG)及V_(SL)为座标的总流型图,提出了计算流型转变的关联式.     

Estimation of particulate velocity components in pneumatic transport using pixel based correlation with dual plane ECT

This article presents a technique developed to estimate the velocity components of two phase solid/gas flow using electrical capacitance tomography (ECT). The pixel by pixel correlation method for consecutive frames in a given sensor plane has been used to trace the particle velocity profile in the transverse direction. The transverse movement of solid particles in slug flows has been reported recently in the literature. The transverse velocity of the particles is probably caused by the picking up mechanism experienced by single particles, to form a slug body. Rest of the particles following the slug forms a stationary layer thus exhibiting no transverse component. These phenomena have also been observed in earlier studies using high-speed video camera. The pixel-based correlation using ECT confirms these observations and also helps to detect the slugging phenomena. The same technique is implemented to trace the path of rotational motion of an object inside the sensor plane and also to detect the transverse motion of particulates in dilute phase vertical pneumatic conveying system. Both axial and transverse velocity components estimated by ECT are verified using Laser Doppler Anemometer (LDA).     

垂直管内气液两相弹状流含气率研究

In order to investigate the influence of the entrance effect on the spatial distribution of phases, the experiments on gas-liquid two-phase slug flow in a vertical pipe of 0.03m ID were carried out by using optical probes and an EKTAPRO 1000 high speed motion analyzer. It demonstrates that the radial profile of slug flow void fraction is parabolic. Influenced by the falling liquid film, the radial profile curve of liquid slug void fraction in the wake region is also parabolic. Since fully turbulent velocity distribution is built up in the developed region,the void fraction profile in this region is the saddle type. At given superficial liquid velocity, the liquid slug void fraction increases with gas velocity. The radial profiles of liquid slug void fraction at different axial locations are all saddle curves, but void fraction is obviously high around the centerline in the entrance region. The nearer the measuring station is from the entrance, the farther the peak location is away from the wall.     

Slug flow characterization in horizontal annulus

To characterize slug flows in annuli channels and highlight the effect of the eccentricity on the flow behaviors, experiments were conducted in two horizontal annuli setups (a) concentric and (b) fully eccentric using air and water as the testing fluids. The range of air and water superficial velocities investigated were 0.45–3.49 m/s and 0.15–2.77 m/s, respectively. Slug parameters measured using conductance probes designed for this study include slug length, translational velocity, slug frequency, and slug holdup. It is found that the slug translational velocity is unaffected by the annulus eccentricity; however, parameters including slug frequency, slug holdup, and slug lengths have a higher value in the fully eccentric annulus when compared with the concentric one. We introduced a new definition of hydraulic diameter, which reconciles the correlation between the dimensionless mean slug length and the mixture velocity of the horizontal annuli with different setups.     

On the electrostatics of pneumatic conveying of granular materials using electrical capacitance tomography

In this work the electrostatics of the pneumatic conveying of granular materials in a non-conducting (PVC) pipe is studied using Electrical Capacitance Tomography (ECT) system. The non-conducting wall in general attains static charges arising from particle-wall collisions in the initial periods of conveying process and then reaches equilibrium with the surroundings. The polarity of particles and conveying pipe inner wall agrees reasonably well with the contact potential difference measurements. The perturbations in the capacitance signal due to charge accumulation are larger with smaller air superficial velocity. The denser flow regimes give larger wall residual charge. Wall charging process shows similar trend described by surface potential taken from electrostatic voltmeter to that revealed by ECT measurements. Also the addition of small amount (0.5% by weight) of anti-static agent (Larostat-519) in the powder form decreases the electrostatic charge generation by altering the dynamics of particle-particle and the particle-wall collisions.     

Coupled DEM‐CFD Simulation of Pneumatically Conveyed Granular Media

A DEM‐CFD coupling for the simulation of gas‐solid flows was successfully implemented and simulations were performed for the application to industrial‐scale pneumatic conveying. Therefore, all particle collisions and phase interactions were considered and porosity determination was optimized. The aim of this work is to show the applicability of the presented simulation model to the different regimes of pneumatic conveying systems. As a first test case a dense vertical pneumatic conveying system was chosen and an individual plug was investigated in detail. Variations of the conveying air velocity were also considered. As a second test case dilute conveying in a horizontal‐to‐vertical pipe bend was simulated. The occurrence of roping and the reduction of particle velocity is of high interest for the design of specific pneumatic systems. It is shown that both regimes can be captured reasonably well and the results are rich in details.     

下倾管段塞流液塞频率波动的非线性分析

利用非线性分析技术中的分形理论,在长24.73 m、内径0.05 m的小型气液两相流实验装置上对下倾管空气-水段塞流中的液塞频率波动特性进行了研究.结果表明,液塞频率的波动是对初始条件敏感的混沌振荡,遵循分形统计规律,具有持久性.折算液速小时,液塞频率波动的长程相关性随着混合速度的增大而减弱,液塞频率波动对初始条件的敏感程度增强,折算液速较大时则相反.管线倾角越大,液塞频率对初始条件的敏感程度受混合速度的影响越小.折算液速和混合速度均较大时,液塞频率的混沌程度受管线倾角的影响较小.