An Analysis of Pressure Drop and Holdup for Liquid‐Liquid Upflow through Vertical Pipes

The present study has attempted to investigate pressure drop and holdup during simultaneous flow of two liquids through a vertical pipe. The liquids selected were kerosene and water. The measurements were made for phase velocities varying from 0.05–1.2 m/s for both liquids. The pressure drop was measured with a differential pressure transducer while the quick closing valve (QCV) technique was adopted for the measurement of liquid holdup. The measured holdup and pressure drop were analyzed with suitable theoretical models according to the existing flow patterns. The analysis reveals that the homogeneous model is suitable for dispersed bubbly flow whereas bubbly and churn‐turbulent flow pattern is better predicted by the drift flux model. On the other hand, the two fluid flow model accurately predicts the pressure drop in core annular flow.     

Flow pattern transition in gas‐liquid downflow through narrow vertical tubes

The present report studies on the flow pattern transitions during vertical air water downflow through millichannels (0.83 ≤ Eötvös no. ≤ 20.63). Four basic flow patterns namely falling film flow, slug flow, bubbly flow, and annular flow are observed in the range of experimental conditions studied and their range of existence has been noted to vary with tube diameter and phase velocities. Based on experimental observations, phenomenological models are proposed to predict the transition boundaries between adjacent patterns. These have been validated with experimental flow pattern maps from the present experiments. Thus the study formalizes procedure for developing a generalized flow pattern map for gas‐liquid downflow in narrow tubes. © 2016 American Institute of Chemical Engineers AIChE J, 63: 792–800, 2017     

Sensor‐based flow pattern detection—gas–liquid–liquid upflow through a vertical pipe

Flow distribution during gas–liquid–liquid upflow through a vertical pipe is investigated. The optical probe technique has been adopted for an objective identification of flow patterns. The probability density function (PDF) analysis of the probe signals has been used to identify the range of existence of the different patterns. Dispersed and slug flow have been identified from the nature of the PDF, which is bimodal for slug flow and unimodal for dispersed flow. The water continuous, oil continuous, and emulsion type flow distributions are distinguished on the basis of the PDF moments. The method is particularly useful at high flow rates where visualization techniques fail. Based on this, a flow pattern detection algorithm has been presented. Two different representations of flow pattern maps have been suggested for gas–liquid–liquid three phase flow. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3362–3375, 2014     

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.     

Inception and termination of the core‐annular flow pattern for oil‐water downflow through a vertical pipe

Different flow patterns for lube oil–water and for kerosene‐water downflow through a vertical glass tube have been analyzed with the help of flow visualization. Core‐annular flow is the dominant flow regime, with oil forming the core, and water is forming the wall film. When the velocities are increased, transition to slug flow and transition to dispersed flow are found. The waves found during the transition to slug flow depend on oil viscosity: axisymmetric bamboo waves are seen in kerosene‐water downflow and the waves are asymmetric in case of lube oil–water flow where they have a cork‐screw shape. Based on the experimental observations, simple mathematical models have been proposed for predicting the flow pattern transition curves. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Effect of oil viscosity on the flow structure and pressure gradient in horizontal oil–water flow

The flow patterns and pressure gradient of immiscible liquids are still subject of immense research interest. This is partly because fluids with different properties exhibit different flow behaviours in different pipe's configurations under different operating conditions. In this study, a combination of oil–water properties (σ = 20.1 mN/m) not previously reported was used in a 25.4 mm acrylic pipe. Experimental data of flow patterns, pressure gradient and phase inversion in horizontal oil–water flow are presented and analyzed together with comprehensive comments. The effect of oil viscosity on flow structure was assessed by comparing the present work data with those of Angeli and Hewitt (2000) and Raj et al. (2005). The comparison revealed several important findings. For example, the water velocity required to initiate the transition to non-stratified flow at low oil velocities increased as the oil viscosity increased while it decreased at higher oil velocities. The formation of bubbly and annular flows and the extent of dual continuous region were found to increase as the oil–water viscosity ratio increased. Dispersed oil in water appeared earlier when oil viscosity decreased.     

Identification of stratified liquid-liquid flow through horizontal pipes by a non-intrusive optical probe

The stratification during the simultaneous flow of two immiscible liquids through a horizontal conduit has been investigated. For the identification of different flow patterns, an indigenously developed unique optical probe has been used. The presence of different phase contents and various interfacial features along the optical path gives rise to attenuation and scattering and makes the identification possible. The probability density function (PDF) analysis and the wavelet multiresolution technique have been adopted for development of an objective flow-pattern indicator. The range of existence of the different stratified distributions as predicted by the indicator is in close agreement with the maps reported in literature.     

Pressure Drop in Liquid‐liquid Two Phase Horizontal Flow: Experiment and Prediction

The present study is aimed at an investigation of the pressure drop characteristics during the simultaneous flow of a kerosene‐water mixture through a horizontal pipe of 0.025 m diameter. Measurements of pressure gradient were made for different combinations of phase superficial velocities ranging from 0.03–2 m/s such that the regimes encountered were smooth stratified, wavy stratified, three layer flow, plug flow and oil dispersed in water, and water flow patterns. A model was developed, which considered the energy minimization and pressure equalization of both phases.     

顺错列管束流型及其压差波动信号的递归特性研究

对气液两相向上横掠节距比为1.3的顺列与错列两种排列方式管束进行流型图像与压差数据采集,基于气相与液相折算速度绘制流型图.分析了管束排列方式对流型的影响,用非线性递归分析方法分别绘制了两种排列方式管束不同流型的递归纹理图,并结合递归特征量对比分析了两种排列方式管束气液两相流的流动特性.研究结果表明：在实验范围内,两种排列方式管束中均出现泡状流、间歇流和雾状流3种流型.错列管束较顺列管束中间歇流流型范围小,泡状流与雾状流流型范围大;错列管束中从泡状流起各流型就具备周期性特点,而顺列管束中间歇流流型才出现周期性,泡状流时流型呈明显的随机特征.     

Effect of tube diameter on two‐phase flow patterns in mini tubes

The effect of tube diameter on two‐phase flow patterns was investigated in circular tubes with inner diameters of 0.6, 1.2, 1.7, 2.6, and 3.4 mm using air and water. The gas and liquid superficial velocity ranges were 0.01–50 and 0.01–3 m/s, respectively. The gas and liquid flow rates were measured and the two‐phase flow pattern images were recorded using high‐speed CMOS camera. The flow patterns observed were dispersed bubbly, bubbly, slug, slug‐annular, wavy‐annular, stratified, and annular flows. These flow patterns were not observed in all the test diameters, but were found to be unique to particular tube diameters, confirming the effect of tube diameter on the flow pattern. The data obtained were compared to existing experimental data and flow regime transition maps which show generally reasonable overall agreement at the larger diameters, but significant differences were observed with the smaller diameter tubes.     

Experimental studies on phase inversion in a small diameter horizontal pipe

The present work describes phase inversion during kerosene–water flow through a 0.012 m diameter horizontal pipe. The phenomenon has been identified using three techniques namely the optical probe technique, pressure drop measurements and an isokinetic sampling technique. Since repeated experiments have reveled dispersed flow to occur at high mixture velocities (>1 m/s), the studies have been conducted for mixer velocity ranging from 1 m/s to 2.5 m/s. The observations have shown that the transition from oil-in-water to water-in-oil dispersion occurs via an emulsified homogenous mixture at high mixture velocities while several different flow patterns mark the transition at lower flow rates of the two phases.     

Influence of an orifice on liquid–liquid two phase flow

The present study aims an in depth investigation of liquid–liquid horizontal flow through an orifice. Initial studies have been directed to observe the influence of the orifice plate on the phase distribution of the two liquids in the pipe. The flow patterns have been identified using an optical probe along with photographic technique. The probability density function (PDF) analysis of the random signals obtained from the optical probe has been adopted to quantify the observations. The cross‐correlation function between the probe signals upstream and downstream of the orifice has been estimated to check the repeatability of the phenomenon. The inception of dispersion in the downstream section has been observed to occur in the stratified region of the upstream. The use of an orifice as a homogenizer as well as a feasible flow‐metering device for liquid–liquid flow has been encouraged by experimental results.     

液体粘度,表面张力与管径对池式两相流型的影响

在不同直径的垂直玻璃管中盛装着不同物性(粘度与表面张力)的液体,空气经分配器注入静止的液体中,对两相流型的变化进行了观察研究。流型的确定采用了高速录相机系统,也同时进行肉眼观察,并测量了不同流型的空隙度。实验表明:空气-高粘性液体和空气-起泡液体的气、液两相流型与通常的空气-水系统的流型极不相同。其空隙度也在较广泛范围内变化。     

Inline Concentration Monitoring of Binary Liquid Mixtures in the Presence of a Dispersed Gas Phase with a Modified Speed of Sound Immersion Probe

A commercial speed of sound (SOS) immersion probe has been modified in order to permit concentration measurements of liquid mixtures in the presence of dispersed gas phases. Experiments were performed in which water was removed from a polymer/water mixture via evaporation and stripping in mixed vessels of different flow patterns. The original and modified SOS immersion probe was used to monitor the water concentration. In the stripping stage, where a persistent gas phase of high volume fraction is generated, the original SOS immersion probe fails to measure the water concentration. This drawback has been successfully eliminated by means of a special SOS probe housing. The modified SOS immersion probe showed reliable inline water concentration monitoring for directed (draft tube reactor) and undirected flow pattern (ordinary stirred reactor) under boiling and stripping conditions.     

Liquid‐liquid two‐phase flow patterns in a new helical microchannel device

Flow patterns of liquid‐liquid two‐phase fluids in a new helical microchannel device were presented in this paper. Three conventional systems were considered: kerosene‐water, n‐butyl acetate‐water, and butanol‐water. Six different flow patterns, slug flow, continuous parallel flow, discontinuous deformation parallel flow, discontinuous deformation parallel‐droplet flow, droplet‐slug flow, and filiform‐droplet flow, were observed. The influence of interfacial tension, microchannel structure, and rotation rate on two‐phase flow patterns were studied, and a universal flow pattern map was presented and discussed. The systems without mass transfer (0.1 g/g (10 %) tri‐n‐butyl phosphate (TBP)‐water, 0.2 g/g (20 %) TBP‐water, and 0.8 g/g (80 %) TBP‐water) and the system with mass transfer (0.8 g/g (80 %) TBP‐0.62 g/g (62 %) H₃PO₄) were used to verify the validity of the proposed universal flow pattern map in predicting flow patterns. The results showed that the former compared with the latter can be predicted more accurately by the universal flow pattern map.     

垂直上升管内有水平柱体时气液两相局部流型转变的研究

1 INTRODUCTION Gas-liquid two-phase cross flow and heat transfer exists in oil production and chemical facilities. With the rapid development of the technology of modern industry, the gas-liquid two-phase flow across a rod and heat transfer characteristics are studied more ex- tensively, and its thorough understanding is of great importance to the design and operation of processing equipment. Flow pattern and its transition are important in the study of multiphase flow. Because of the com…     

BUBBLE MEASUREMENTS IN A GAS-LIQUID JET

Measurements have been carried out in the developing and fully developed regions of a free, axisymmetric, isothermal, air-water, bubbly jet. Three experiments have been conducted at a fixed jet-exit Reynolds number and gas superficial velocity using three different bubble injector assemblies producing bubbles of moderately different average sizes and size distributions. The volume fraction of the bubbly jet flow examined in this study is low and the resulting dispersed flow is dilute. A one-component Phase-Doppler Velocimetry system has been employed to measure bubble size and velocity non-intrusively. Visual data collected simultaneously with the light-scattering measurements were analyzed with the aid of image processing and used to verify the trends portrayed by the light-scattering measurements and to determine average bubble size. Our measurements show that, even in the dilute flow examined here, differences in initial bubble-size and size distribution can influence the RMS velocity fluctuations of the bubbles, particularly in the jet development region. The average bubble velocities are less sensitive. Evidence that the development pattern of the jet near the exit is affected by the presence of the bubbles is also presented. Near the exit of the jet, bubbles are shown to be ejected laterally outside the jet due to the significant lift force caused by the high velocity gradient in the axisymmetric shear layer. The observed sensitivity of the bubble flow to size-related parameters and initial conditions in this dilute case, indicates that discrepancies in previous measurements of dispersed, bubbly flows could be attributed to different size characteristics and/or initial conditions.     

AN EXPERIMENTAL STUDY OF GAS HOLDUP IN TWO-PHASE BUBBLE COLUMNS WITH FOAMING LIQUIDS

Gas-liquid upward flow experiments have been performed in two bubble columns of different diameters (0.10 and 0.29 m,) using air as gas phase and several liquids: water, aqueous solutions of ethanol and glycerine, kerosene, and a solution of a surfactant in kerosene. The main goal of the study is the analysis of foaming systems, including the comparison of their behavior with respect to non-foaming systems. The gas holdup was determined experimentally as a function of the gas and liquid superficial velocities in bubbling, churn-turbulent and foaming regimes. It was found that, for foaming systems, semi-batch operation enhances foam formation, yielding higher holdups than those obtained in continuous operation at very low liquid velocities. Opposite to what is observed in non-foaming systems, the liquid superficial velocity affects the gas holdup appreciably in foaming systems. An increase in column diameter results in a decrease in gas holdup for all the systems studied. In aqueous foaming systems, this trend is more drastic since foam is inhibited as the column diameter increases.     

Hydrodynamics and liquid phase axial mixing in orifice pipe reactor

Two phase flow in a horizontal pipe, with orifice plates placed at regular intervals as obstructions, was studied for the effect of phase velocities on flow patterns, fractional phase hold-ups, pressure drop and liquid phase axial dispersion. Radioactive technetium-99m (as an aqueous solution of sodium pertechnatate) was used as tracer. A pulse injection technique with two point measurements was employed. Three different orifice diameters were used (8 mm, 16 mm, and 20 mm) in a pipe diameter of 32 mm. The orifice spacing was 500 mm in all cases. Superficial gas (air) velocity was varied over a range from 0.02 m/s to 1.0 m/s and superficial liquid (water) velocity from 0.03 m/s to 0.85 m/s. Different flow patterns under different flow conditions were identified and a generalised flow map is presented. Variations in hold-ups and pressure drop with flow patterns have been explained. Rational correlations have been developed for fractional phase hold-ups and pressure drop. A preliminary comparison of two phase gas-liquid flow in a horizontal pipe with orifice obstructions (to be called orifice pipe reactor), as a gas-liquid contacting device, is made with a conventional bubble column reactor. Recommendations have been made for future work.     

注气孔位置对文丘里管式微气泡发生器成泡特性的影响分析

尽管文丘里管式微气泡发生器的注气口位置会对气泡在文丘里流道内的碎化特征产生直接影响,但迄今缺乏针对性的深入研究。通过可视化实验方法,对比分析了注气口分别位于喉管处（结构1型）和进水管处（结构2型）时的气液流型、气泡破碎特征以及成泡特性。实验表明,气、液相流量对结构1型微气泡发生器内的气液流型影响显著,初始成泡区域随液相流量增加,环状流或泡状流向弹状流转变,而随气相流量增加则由泡状流或弹状流向环状流转变;结构2型微气泡发生器则在此过程中始终为泡状流,其对操作工况的适应范围大于结构1型。在相同工况下,结构1型微气泡发生器的成泡Sauter平均粒径小于结构2型,但随着液相Reynolds数的增大,二者间的成泡平均粒径差值随之减小。分析原因是由于弹状流流型下,延伸至扩张段区域的弹型泡的表面积更大,能量转化率更高,气泡界面失稳碎化的程度更显著。随着液相Reynolds数的增大,初始成泡体积减小,湍流破碎机理作用占据主导,掩盖了由于界面失稳引起的气泡破碎。结构1型微气泡发生器的成泡能耗高于结构2型,并且随液相Reynolds数的增大,两者之间的差值随之增大。综合来看,结构2型微气泡发生器能够在低能耗下实现高效成泡,面向工程应用将更具优势。