Two-phase Slug Flow Research Articles

Mass-Transfer Enhancement in Large-Diameter Pipeline under Water/Gas Stationary Slug Flow

In multiphase flow, gas bubbles are produced that collapse at the liquid/solid interface. In order to examine such effects, mass-transfer studies have been performed in an electrochemical cell and in a large-diameter flow loop under water/gas two-phase stationary slug flow. A limiting current density technique was used for oxidation of or reduction of in concentrated NaOH solutions. High-frequency and high-magnitude, instantaneous mass-transfer coefficients were found by potentiostatic measurements and may account for the corrosion rate enhancement in water/gas slug flow. A physical model of the stationary slug flow is proposed to explain the mechanism of gas bubble formation and bubble distribution. The effect of the gas bubbles on the mass-transfer enhancement is reported and a mechanism for the mass-transfer coefficient fluctuations is proposed. This study demonstrates that gas bubbles produced in stationary slug flow have a direct enhancement impact on the mass-transfer and corrosion rate of carbon steel pipeline. © 2004 The Electrochemical Society. All rights reserved.

A model for simulating gas bubble entrainment in two-phase horizontal slug flow

In an earlier paper it was shown that the basic one-dimensional transient two-fluid model is capable of capturing horizontal and near-horizontal slug flow automatically. However, that work did not account for the effect of gas entrainment into the liquid slug body which is deemed to be an important phenomenon. In this paper, a mathematical model to account for the entrainment of gas bubbles into liquid slugs is proposed, implemented and validated. The model is cast in the framework of the existing two-fluid model and is incorporated in a computational procedure, which is applied to the prediction of slug flow in horizontal and slightly inclined pipes. The model entails the introduction of a scalar equation for the transport of the dispersed gas bubbles within the liquid. The rate of entrainment of gas at the slug front is supplied as a closure relation, the expression for which is obtained from existing correlations. The model is validated against experimental data and the comparison shows satisfactory agreement. However, the inclusion of the aeration model appears to yield marginal differences when compared to predictions which ignore entrainment in the horizontal pipe flow cases studied. More significant differences are obtained in the case of the flow in a V-section pipeline.

On the simulation of three-phase slug flow in nearly horizontal pipes using the multi-fluid model

The article presents a mathematical model to simulate three-phase (liquid/liquid/gas) stratified and slug flows. The approach is based on the one-dimensional transient two-fluid model in which the two-phases consist of the gas and the mixture of the two liquids, with the motion of the liquid phases relative to each other being modelled via a drift–flux model. In order to close the model, a scalar transport equation for the conservation of mass for one of the liquid phases is introduced. Other closure models incorporated relate to the liquid–liquid flow pattern (stratified or fully dispersed), the phase inversion point (when the continuous liquid phase becomes dispersed in the other and vice-versa), the slip between the liquid phases and the mixture viscosity (which changes abruptly when phase inversion occurs). The equations are solved numerically using a previously developed finite volume methodology that had been applied to the prediction of two-phase slug flow and by which liquid slugs are automatically captured as an outcome of the numerical integration. The new method is applied to the study of the flow of oil, water and air in horizontal pipes. The method is shown to be able to predict locally whether the two liquids form a dispersion (of either oil droplets in water continuous flow (O/W) or water droplets in oil continuous flow (W/O)) or flow in stratified layers. It is demonstrated that the developed model is capable of correctly predicting slugging, and is moreover able to reproduce successfully observed experimental trends for the major slug properties, such as pressure gradient, slug frequency, and total liquid hold-up. The study revealed that the slip between the two liquid phases plays a major role in determining the slug characteristics in three-phase flow.

Modeling of Slug Dissipation and Generation in Gas-Liquid Hilly-Terrain Pipe Flow

Hilly-terrain pipelines consist of interconnected horizontal, uphill and downhill sections. Slug flow experiences a transition from one state to another as the pipe inclination angle changes. Normally, slugs dissipate if the upward inclination becomes smaller or the downward inclination becomes larger, and slug generation occurs vice versa. Appropriate prediction of the slug characteristics is crucial for the design of pipeline and downstream facilities. In this study, slug dissipation and generation in a valley pipeline configuration (horizontal-downhill-uphill-horizontal) were modeled by use of the method proposed by Zhang et al. The method was developed from the unsteady continuity and momentum equations for two-phase slug flow by considering the entire film zone as the control volume. Computed results are compared with experimental measurements at different air-mineral oil flow rate combinations. Good agreement is observed for the change of slug body length to slug unit length ratio.

Hydrodynamic and statistical parameters of slug flow

In two-phase slug flow pattern, the bulk of the gas is trapped inside large bubbles that are separated by liquid slugs, which may contain small dispersed bubbles. The unsteady nature of slug flow makes the prediction of pressure drop and heat and mass transfer a difficult task. Earlier models that deal with steady slug flow assume constant lengths and shapes of liquid slugs and elongated bubbles, as well as a constant elongated bubble propagation velocity. However, due to the intrinsically irregular character of slug flow, statistical means are required for its proper description. Variation of the flow parameters along the pipes of various diameters and inclinations may strongly affect the resulting flow pattern and should thus be taken into account in modeling the flow. The development of slug flow along the pipe is mainly governed by the interaction between consecutive elongated bubbles. To gain a better insight into the mechanisms that govern slug flow evolution along pipes, experiments with controlled injection of consecutive elongated bubbles were performed in recent years. Due to the complexity of both the continuous slug flow and the liquid flow around injected bubbles, sophisticated experimental methods are required. The latest works regarding the hydrodynamic and statistics of naturally occurring continuous slug flow in pipes, as well as the results of experiments with controlled injection of elongated bubbles are reviewed. It is demonstrated how the information obtained in the controlled experiments can be applied to improve the performance of slug flow and slug tracking models.

Effect of Mixed Fine Particles on the Characteristics of Gas-Liquid Two-Phase Slug Flow in a Vertical Pipe

Among the recent measuring methods of multiphase flows, there are some methods in which we must mix fine particles into fluid as tracer or scattering particles ; for example, LDV, PIV and some methods using ultrasonic sound. The effect of fine particles mixed in on the flow characteristics is, however, not examined in detail. Therefore, in this study, we measured some parameters to investigate the effect of fine particles mixed into gas-liquid two-phase slug flows in a vertical pipe. Polyethylene particles of 10.6 and 160 μm mean diameter were used. The effects of particle mixing on average void fraction, large bubble and slug length, large bubble rising velocity and shape are discussed.

고주파 삼각파 여자법을 사용한 실시간 슬러그 유동 측정용 전자기유량계

In order to investigate the characteristics of two-phase slug flow. an electromagnetic flowmeter with 240Hz triangular AC excitation was designed and manufactured. The signals and noise from the flowmeter were obtained. and analyzed in comparison with the observations with a high speed CCO camera. The uncertainty of the flowmeter under single-phase flow was:!: 2.24% in real-time. For two-phase slug flow. electromagnetic flowmeter provided real-time simultaneous measurements of the mean film velocity around Taylor bubble and thc relative location and the length of the bubble. Besides. it is an easier and cheaper method for measuring mean tilm velocity than others such as photochromic dye activation method or particle image velocimetry.br/

Flow measurement with an electromagnetic flowmeter in two-phase bubbly and slug flow regimes

In order to investigate the characteristics of an electromagnetic flowmeter in two-phase flow, an alternating-current electromagnetic flowmeter was designed and manufactured. The signals and noise from the flowmeter under various flow conditions were obtained, and analyzed in comparison with the flow patterns observed with a high-speed charge-coupled device camera. An experiment with void simulators, in which a rod-shaped non-conducting material was used, was carried out to investigate the effect of bubble position and void fraction on the flowmeter. Two-phase flow experiments, encompassing bubbly to slug flow regimes, were conducted with a water–air mixture. The simple relation Δ U TP=Δ U SP/(1− α), relating the flowmeter signal between single-phase flow and two-phase flow, was verified with measurements of the potential difference and the void fraction for a bubbly flow regime. Due to the lack of homogeneity in a real two-phase flow, the discrepancy between the relation and the present measurement increased slightly with increasing void fraction and superficial liquid velocity j f. Whereas there is no difference in the shape of the raw signal between single-phase flow and bubbly flow, the signal amplitude for bubbly flow is higher than that for single-phase flow at the same water flow rate, since the passage area of the water flow is reduced. In the case of slug flow, the phase and the amplitude of the flowmeter output show dramatically the flow characteristics around each slug bubble and the position of the slug bubble itself. Therefore, the electromagnetic flowmeter shows a good possibility of being useful for identifying the flow regimes.

901 超音波流速分布計による静止水中大気泡周囲の液速度分布の測定

Various methods are used for the velocity measurement of the gas-liquid two-phase flows, for example, Particle Image Velocimetry (PIV) or Laser Doppler Velocimetry (LDV), and ect. The Ultrasonic Velocity Profile monitor (UVP) has a unique feature that it can obtain an instantaneous velocity profile on a line. However, it has not been so far applied to the measurement of the multiphase flow in circular pipes. In this study, velocity distribution of a liquid film arround a large bubble in stagnant water which seems to be a simple type of gas-liquid two-phase slug flow in a vertical pipe was measured using UVP. It was found that the velocity distribution can be almost approximated by the profile curve of a general falling liquid film, while a liquid film receives the effect of tube wall especially near the nose.

On the interaction of Taylor bubbles rising in two-phase co-current slug flow in vertical columns: turbulent wakes

An experimental study on the interaction between Taylor bubbles rising through a co-current flowing liquid in a vertical tube with 32 mm of internal diameter is reported. The flow pattern in the bubble's wake was turbulent and the flow regime in the liquid slug was either turbulent or laminar. When the flow regime in the liquid slug is turbulent (i) the minimum distance between bubbles above which there is no interaction is 5D-6D; (ii) the bubble's rising velocity is in excellent agreement with the Nicklin relation; (iii) the experimental values of the bubble length compare well with theoretical predictions (Barnea 1990); (iv) the distance between consecutive bubbles varied from 13D to 16D and is insensitive to the liquid Reynolds number. When the flow regime in the liquid slug is laminar (i) the wake length is about 5D-6D; (ii) the minimum distance between bubbles above which there is no interaction is higher than 25D; (iii) the bubble's rising velocity is significantly smaller than theoretical predictions. These results were explained in the light of the findings of Pinto et al. (1998) on coalescence of two Taylor bubbles rising through a co-current liquid.

鉛直管内気液二相スラグ流における大気泡長さ，液体スラグ長さ，スラグユニット長さ並びにスラグ周期の推算式

Fundamental forms of correlations are proposed for large bubble lengths, liquid slug lengths and slug unit lengths, and slug periods of gas-liquid two-phase slug flow in vertical pipes. The empirical correlations for each length are derived using 337 experimental data obtained from water-air, water solution containing NaOH, K3Fe(CN)6 and K4Fe(CN)6- air and water-carbon dioxide two-phase slug flows in pipes of their diameter 8-50.8mm, and volumetric fluxes JG=0.0256−3.42m/s, JL=0.0390−1.50m/s, JT=0.0847−4.40 m/s. They are shown below. For large bubble length LLB: LLB=0.121D(JG/JT)1.70(JL/JT)-0.408(JT/(gD)0.5)0.582(ρLDJT/μL)0.149(ρLDJT2/σ)-0.207(μG/μL)0.291(ρG/ρL)-0.831+0.00186. For liquid slug length LLS: LLS=534000D(JG/JT)0.415(JL/JT)0.143(JT/(gD)0.5)0.143(ρLDJT/μL)0.0983(ρLDJT2/σ)-0.119(μG/μL)1.34(ρG/ρL)0.753−0.124. For slug unit length LSU: LSU=19700D(JG/JT)0.305(JL/JT)-0.340(JT/(gD)0.5)0.393(ρLDJT/μL)0.0275(ρLDJT2/σ)-0.154(μG/μL)0.944(ρG/ρL)0.346−0.291. The similar method is applied to derive the correlation for the slug period. The following correlation is obtained using 205 experimental data. TB=16100(D/JT)(JG/JT)1.38(JL/JT)-0.166(JT(gD)0.5)-0.317(ρLDJT/μL)1.61(ρLDJT2/σ)-0.564(μG/μL)0.333(ρG/ρL)3.04+0.0870. These empirical correlations are applicable for gas-liquid two-phase slug flow under nearly room temperature and at atmospheric pressure.

00/03189 Gas industry development in Egypt

This study uses high-speed imaging to characterize microchannel slug flow boiling using a novel experimental test facility that generates an archetypal flow regime suitable for high-fidelity characterization of key hydrodynamic and heat transfer parameters. Vapor and liquid phases of the fluorinated dielectric fluid HFE-7100 are independently injected into a T-junction to create a saturated two-phase slug flow, thereby eliminating the flow instabilities and flow-regime transitions that would otherwise result from stochastic generation of vapor bubbles by nucleation from a superheated channel wall. Slug flow boiling is characterized in a heated, 500 μm-diameter borosilicate glass microchannel. A thin layer of optically transparent and electrically conductive indium tin oxide coated on the outside surface of the microchannel provides a uniform heat flux via Joule heating. High-speed flow visualization images are analyzed to quantify the uniformity of the vapor bubbles and liquid slugs generated, as well as the growth of vapor bubbles under heat fluxes ranging from 30 W/m2 to 5160 W/m2. A method is demonstrated for measuring liquid film thickness from the visualizations using a ray-tracing procedure to correct for optical distortions. Characterization of the slug flow boiling regime that is generated demonstrates the unique ability of the facility to precisely control and quantify hydrodynamic and heat transfer characteristics. The experimental approach demonstrated in this study provides a unique platform for the investigation of microchannel slug flow boiling transport under controlled, stable conditions suitable for model validation.

Liquid slug holdup in horizontal and slightly inclined two-phase slug flow

A new empirical equation for estimating liquid slug holdup in horizontal and slightly inclined two-phase flow is developed as a function of mixture velocity, liquid viscosity and inclination angle. The proposed equation is based on measured data consists of 316 data points for horizontal flow and 107 data points for inclined flow, with inclination angles ranging from −10° to 9° from horizontal. Based on the present measured data and data from other sources, the new equation is shown to be a significant improvement over the published models for both the horizontal and inclined slug flow.

A mechanistic model for vertical and inclined two-phase slug flow

This work proposes a mechanistic model for predicting the flow behavior for upward vertical and inclined two-phase slug flow. Expressions for bubble rise velocity, liquid film velocity, liquid holdup around the Taylor bubble, and liquid slug void fraction are derived from the relationships between the two-phase velocities. Based on measured void fraction data, the proposed liquid slug void fraction equation exhibits better performance than the existing models. The proposed mechanistic model and twelve commonly used slug models are compared with the Tulsa University Fluid Flow Projects data bank (1052 well cases). This data covers a wide range of the flow conditions, well geometry and fluid properties. The comparison indicates that: (1) the new model is straightforward and is therefore easier to apply than other models, (2) the model is in very good agreement with the measured data and (3) the model performs best and clearly outperforms all other models.

Structure and Void Fraction of Liquid Slug in Gas-Liquid Two-Phase Slug Flow.

The distribution of gas and liquid in gas-liquid two-phase slug flow was measured using semi-supermultiple point-electrode probes. Based on the measurements, the wake zone behind the gas slug and the low void fraction zone in the liquid slug are defined and the void fractions of the two zones are determined. The data reveals that the void fraction of the wake zone increases according to Jg, while there is little dependence. On jι. Non-dimensional head is proposed in consideration of the momentum change of the liquid in the wake zone. It is clarified that non-dimensional head is closely related to the void fraction of the wake zone. A good practical relationship is found between non-dimensional head and the lengths of the swelling liquid front zone and the wake zone, and empirical correlations are proposed for the void fraction in the wake zone, the mean void fraction in the liquid slug, and the lengths of the swelling liquid front zone and the wake zone.

Tomographic imaging of the phase distribution in two-phase slug flow

A new tomographic measurement technique for the spatial imaging of the phase distribution in horizontal slug flow is presented. The features of the new technique are a high spatial and temporal resolution. The measurement principle is based on the measurement of the conductivity between parallel wires. It is a function of the liquid hold-up between the wires. Using three different measurement directions, projections with linearly independent integral measurements of the phase distribution are obtained. These are processed using an iterative series expansion method based on the algebraic reconstruction technique (ART). The quality of the reconstruction is increased using a priori knowledge of the flow regime. The maximum temporal resolution is 5 ms and the spatial resolution is smaller than 1% of the cross-sectional area of the pipe.

Flow Control Characteristics of Gas-Magnetic Fluid Two-Phase Flow by the Application of a Magnetic Field.

The magnetic flow control characteristics of magnetic fluid two-phase slug flow in a vertical pipe was examined from measured void fractions and pressure drops together with the two-fluid model. The axial pressure distribution was primarily dominated by magnetic pressure rise and drop, and acceleration loss both of which depended on the axial distribution of void fraction. As the interaction between gas and liquid flows, the virtual mass force was remarkably large near the position of maximum magnetic field strength. The drag force acted on gas phase greatly due to large slip ratio which was caused by the magnetic force.

Shape of Taylor bubbles in vertical tubes

The shape of a Taylor bubble in a vertical downward slug flow in a pipe is studied. The phase distribution in the Taylor bubble region is investigated by still pictures and video film. The shape of the Taylor bubble is reported for different condition. These experimental results consists of the position of the interface x( r) obtained using image processing and represents the new view to the shape of the Taylor Bubble and gives some light on the basic phenomena for the hydrodynamics of the two-phase slug flow.

Heat transfer to two-phase slug flows under reduced-gravity conditions

New hydrodynamic and heat transfer measurements are presented for two-phase slug flows in a reduced gravity environment. Air and two liquids, water and 50% aqueous glycerine were used to obtain a range of liquid Reynolds numbers from 1000 to 20,000 in a 25.4 mm i.d. tube. The measurements include void fraction, pressure gradient, and heat transfer coefficient. The enhancement of the heat transfer coefficient over single-phase liquid flow increases with increasing void fraction and is somewhat larger for the 50% glycerine solution than for water. Based on a comparison to normal-gravity correlations, the heat transfer coefficients are smaller at reduced-gravity than at normal-gravity under the same flow conditions. This can be explained by smaller liquid-phase turbulence levels in the absence of buoyancy-induced slip between the gas and liquid.

Heat resistance of Talaromyces flavus ascospores as determined by a two phase slug flow heat exchanger

Heat resistance of Talaromyces flavus was determined using two methods. Standard thermal death time vials were used to determine the heat resistance of T. flavus ascospores, from 80 to 90 °C with a decimal reduction time D 90 of 6.2 min. A continuous two-phase slug flow heat exchanger System with heating, holding and cooling sections was used to determine the heat resistance from 90 to 100 °C. Inoculated heating medium was pumped through 1.85 mm ID tubing in ‘slugs’ separated by air bubbles to interrupt laminar flow. Varying pump speed, length of tubing in the heating bath and temperature allowed collection of data under varied heating conditions. D 90 with the slug flow heat exchanger system was 6.4 min, indicating the two methods were comparable, z values were 6.7 and 6.4 °C, respectively. The slug flow heat exchanger system permits rapid determination of heat resistance over a range of temperatures. Because of minimum come-up time the slug flow heat exchanger can be used at temperatures near the upper limit of heat resistance for the microorganism being tested.