Liquid entrainment, droplet concentration and pressure gradient at the onset of annular flow in a vertical pipe

Experimental investigation of drag reduction in vertical two-phase annular flow is presented. The work is a feasibility test for applying drag reducing additives (DRAs) in high production-rate gas-condensate wells where friction in the production tubing limits the production rate. The DRAs are intended to reduce the overall pressure gradient and thereby increase the production rate. Since such wells typically operate in the annular-entrained flow regime, the gas and liquid velocities were chosen such that the experiments were in a vertical two-phase annular flow. The drag reducers had two main effects on the flow. As expected, they reduced the frictional component of the pressure gradient by up to 74%. However, they also resulted in a significant increase in the liquid holdup by up to 27%. This phenomenon is identified as “DRA-induced flooding.” Since the flow was vertical, the increase in the liquid holdup increased the hydrostatic component of the pressure gradient by up to 25%, offsetting some of reduction in the frictional component of the pressure gradient. The DRA-induced flooding was most pronounced at the lowest gas velocities. However, the results show that in the annular flow the net effect will generally be a reduction in the overall pressure gradient by up to 82%. The findings here help to establish an envelope of operations for the application of multiphase drag reduction in vertical flows and indicate the conditions where a significant net reduction of the pressure gradient may be expected.

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CFD Simulation of Two-Phase Vertical Annular Flow in Both Upward and Downward Direction in a Small Pipe

Volume 8: Polar and Arctic Sciences and Technology; Petroleum Technology ◽

10.1115/omae2019-96311 ◽

2019 ◽

Author(s):

Ekhwaiter Abobaker ◽

Abadelhalim Elsanoose ◽

John Shirokoff ◽

Mohammad Azizur Rahman

Keyword(s):

Film Thickness ◽

Multiphase Flow ◽

Pressure Gradient ◽

Annular Flow ◽

Cfd Simulation ◽

Flow Direction ◽

Flow Behavior ◽

Two Phase ◽

Downward Flow ◽

Disturbance Wave

Abstract Computational fluid dynamics (CFD) simulation is presented to investigate the annular flow behavior in the vertical pipe by using ANSYS Fluent platform 17.2. The study was analyzed complex behavior of annular flow in two cases (upward and downward flow) for different air superficial velocities and range of Reynolds number for water, in order to obtain the effect of orientation flow and increasing superficial gas and liquid velocities on the base film, mean disturbance wave thickness, the average longitudinal size of disturbance wave as well as pressure gradient. For multiphase flow model, the volume of fluid method (VOF) for two-phase flow modelling was used and coupled with RNG k-ε turbulence model to predict fully annular flow structures in the upward and downward flow direction. From CFD simulation results, it is clear to see how increases in air velocity result in reductions in film thickness and increase in pressure gradient. Additionally, the results showed monotonic enhancement of film thickness occurring in tandem with increases in the liquid flow rate. However, due to the effect of gravitational force and interfacial friction, the film thickness and pressure gradient are slightly larger for the upward flow than for the downward flow. The results agree with the recent experimental data that studied the annular flow behavior and pressure drop in the upward and downward flow direction. This study will be very helpful in understanding multiphase flow behavior in natural gas wells.

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Effect of virtual mass force on prediction of pressure changes in condensing tubes

Thermal Science ◽

10.2298/tsci1202613s ◽

2012 ◽

Vol 16 (2) ◽

pp. 613-622 ◽

Cited By ~ 2

Author(s):

Hamid Saffari ◽

Nemat Daur

Keyword(s):

Experimental Data ◽

Annular Flow ◽

Fluid Model ◽

Mass Force ◽

Virtual Mass ◽

Vertical Pipe ◽

Pressure Drops ◽

Factors Affecting ◽

Pressure Changes ◽

Significant Factors

Three-fluid model is used to calculate the pressure drops in a vertical pipe with the annular flow pattern for condensing steam. The three-fluid models are based on the mass, momentum, and energy balance equations for each of the fluid streams in the annular flow. There are discrepancies between predictions of three-fluid model for pressure drops and the experimental data for pressure drops when using the avail?able correlations for steam-film interfacial friction. The correlation by Stevanovic et at provides good match with experimental data, but it does not take into account some important factors affecting the pressure drops in its three-fluid model. One of these significant factors which is considered in the three fluid model used in the present paper is virtual mass (added mass) force term. Inclusion of the virtual mass force improves the pressure drop predictions such that they agree much better with the experiments.

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The Effect of Surfactants on Vertical Air/Water Flow for Prevention of Liquid Loading

SPE Journal ◽

10.2118/164095-pa ◽

2016 ◽

Vol 21 (02) ◽

pp. 488-500 ◽

Cited By ~ 4

Author(s):

A. T. van Nimwegen ◽

L. M. Portela ◽

R. A. Henkes

Keyword(s):

Surface Tension ◽

Pressure Gradient ◽

Water Flow ◽

Annular Flow ◽

Surfactant Concentration ◽

Gas Flow ◽

Liquid Loading ◽

Dynamic Surface ◽

Flow Rates ◽

Churn Flow

Summary From field experience in the gas industry, it is known that injecting surfactants at the bottom of a gas well can prevent liquid loading. To better understand how the selection of the surfactant influences the deliquification performance, laboratory experiments of air/water flow at atmospheric conditions were performed, in which two different surfactants (a pure surfactant, sodium dodecyl sulfate, and a commercial surfactant blend) were added to the water. In the experiments, a high-speed camera was used to visualize the flow, and pressure-gradient measurements were performed. Both surfactants increase the pressure gradient at high gas-flow rates and decrease the pressure gradient at low gas-flow rates. The minimum in the pressure gradient moves to lower gas-flow rates with increasing surfactant concentration. This is related to the transition between annular flow and churn flow, which is shifted to lower gas-flow rates because of the formation of an almost stagnant foam substrate at the wall of the pipe. At high surfactant concentration, it appears that the churn flow regime is no longer present at all and that there is a direct transition from annular flow to slug flow. The results also show that the critical micelle concentration, the equilibrium surface tension, the dynamic surface tension, and the surface elasticity are poor predictors of the effect of the surfactant on the flow.

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Effects of Liquid Velocity on Pressure Gradient, Slip and Interfacial Friction Factor in Annular Flow in Horizontal Pipe

European Journal of Engineering Research and Science ◽

10.24018/ejers.2018.3.8.819 ◽

2018 ◽

Vol 3 (8) ◽

pp. 5

Author(s):

Uche Osokogwu

Keyword(s):

Pressure Gradient ◽

Friction Factor ◽

Annular Flow ◽

Liquid Velocity ◽

Interfacial Friction ◽

Gas Velocity ◽

Horizontal Pipe ◽

Mixture Density ◽

Superficial Gas Velocity ◽

Superficial Liquid Velocity

Experimental investigations on annular flow behaviour in two-phase (air/water) flow in horizontal pipe were conducted using 2-inch (0.0504m) with a total length of 28.68m closed loop system. The emphasis from the experiments were on pressure gradient, slip and interfacial friction factor in annular flow. For interfacial friction factor, the entrainment, gas quality, the droplets and slip mixture density values were obtained through the experimental results which were substituted to determine it. In all, effects of liquid velocity were felt, as increase in superficial liquid velocity, increases the interfacial friction factor and pressure gradient in annular flow in horizontal pipes. More so, increase in superficial gas velocity, reduces the interfacial friction factor. Thus, interfacial friction factor decreases with increases in superficial gas velocity, while the pressure gradient increases with increase in superficial liquid velocity. The lower the superficial liquid velocity, the higher the slip but the lower the pressure gradient. Likewise, the lower the superficial liquid velocity, the more ripple waves obtained while the higher the superficial liquid velocity, the more disturbance waves in annular flow in horizontal pipe from the experiments.

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Direct numerical simulation of a turbulent core-annular flow with water-lubricated high viscosity oil in a vertical pipe

Journal of Fluid Mechanics ◽

10.1017/jfm.2018.408 ◽

2018 ◽

Vol 849 ◽

pp. 419-447 ◽

Cited By ~ 1

Author(s):

Kiyoung Kim ◽

Haecheon Choi

Keyword(s):

Numerical Simulation ◽

Direct Numerical Simulation ◽

Pipe Flow ◽

Annular Flow ◽

Volume Fraction ◽

Phase Interface ◽

High Viscosity ◽

Vertical Pipe ◽

The Core ◽

High Viscosity Oil

The characteristics of a turbulent core-annular flow with water-lubricated high viscosity oil in a vertical pipe are investigated using direct numerical simulation, in conjunction with a level-set method to track the phase interface between oil and water. At a given mean wall friction ($Re_{\unicode[STIX]{x1D70F}}=u_{\unicode[STIX]{x1D70F}}R/\unicode[STIX]{x1D708}_{w}=720$, where $u_{\unicode[STIX]{x1D70F}}$ is the friction velocity, $R$ is the pipe radius and $\unicode[STIX]{x1D708}_{w}$ is the kinematic viscosity of water), the total volume flow rate of a core-annular flow is similar to that of a turbulent single-phase pipe flow of water, indicating that water lubrication is an effective tool to transport high viscosity oil in a pipe. The high viscosity oil flow in the core region is almost a plug flow due to its high viscosity, and the water flow in the annular region is turbulent except for the case of large oil volume fraction (e.g. 0.91 in the present study). With decreasing oil volume fraction, the mean velocity profile in the annulus becomes more like that of turbulent pipe flow, but the streamwise evolution of vortical structures is obstructed by the phase interface wave. In a reference frame moving with the core velocity, water is observed to be trapped inside the wave valley in the annulus, and only a small amount of water runs through the wave crest. The phase interface of the core-annular flow consists of different streamwise and azimuthal wavenumber components for different oil holdups. The azimuthal wavenumber spectra of the phase interface amplitude have largest power at the smallest wavenumber whose corresponding wavelength is the pipe circumference, while the streamwise wavenumber having the largest power decreases with decreasing oil volume fraction. The overall convection velocity of the phase interface is slightly lower than the core velocity. Finally, we suggest a predictive oil holdup model by defining the displacement thickness in the annulus and considering the boundary layer characteristics of water flow. This model predicts the variation of the oil holdup with the superficial velocity ratio very well.

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Effect of Drag-Reducing Agents in Multiphase Flow Pipelines

Journal of Energy Resources Technology ◽

10.1115/1.2795002 ◽

1998 ◽

Vol 120 (1) ◽

pp. 15-19 ◽

Cited By ~ 18

Author(s):

C. Kang ◽

R. M. Vancko ◽

A. S. Green ◽

H. Kerr ◽

W. P. Jepson

Keyword(s):

Multiphase Flow ◽

Pressure Gradient ◽

Slug Flow ◽

Annular Flow ◽

Flow Regimes ◽

Reducing Agents ◽

Pressure Gradients ◽

Horizontal Pipes ◽

Flow Pressure ◽

Inclined Pipes

The effect of drag-reducing agents (DRA) on pressure gradient and flow regime has been studied in horizontal and 2-deg upward inclined pipes. Experiments were conducted for different flow regimes in a 10-cm i.d., 18-m long plexiglass system. The effectiveness of DRA was examined for concentrations ranging from 0 to 75 ppm. Studies were done for superficial liquid velocities between 0.03 and 1.5 m/s and superficial gas velocities between 1 and 14 m/s. The results indicate that DRA was effective in reducing the pressure gradients in single and multiphase flow. The DRA was more effective for lower superficial liquid and gas velocities for both single and multiphase flow. Pressure gradient reductions of up to 42 percent for full pipe flow, 81 percent for stratified flow, and 35 percent for annular flow were achieved in horizontal pipes. In 2 deg upward inclination, the pressure gradient reduction for slug flow, with a concentration of 50 ppm DRA, was found to be 28 and 38 percent at superficial gas velocities of 2 and 6 m/s, respectively. Flow regimes maps with DRA were constructed in horizontal pipes. Transition to slug flow with addition of DRA was observed to occur at higher superficial liquid velocities.

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Coanda Effect on the Impact of Distribution Characteristics of Oil-Air Annular Flow

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.620.166 ◽

2014 ◽

Vol 620 ◽

pp. 166-170

Author(s):

Qi Guo Sun ◽

Dong Xu Chen ◽

Xiong Shi Wang ◽

Zheng Hui Zhou

Keyword(s):

Pressure Gradient ◽

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Annular Flow ◽

Branch Pipe ◽

Coanda Effect ◽

Distribution Characteristics ◽

Coandǎ Effect ◽

The Impact

The T-junction model is simulated in Fluent by changing the curvature of branch pipe, and then the distribution characteristics of the annular flow was studied in T-junction distributor. The mass flow and pressure of the annular flow in this T-junction are studied, and the impact of Coanda Effect on the annular flow distribution characteristic is analyzed in oil-air two phases flow. The results show that, Coanda Effect affects the distribution of oil-air annular flow unevenly. The mass flow rate of air phase and the air velocity of outlet increase with decreasing the curvature, while the mass flow rate of liquid decrease with decreasing the curvature of the branch pipe connection; T-shaped junction inlet pressure is high, but the pressure gradient is small, the pressure gradient in the small curvature manifold is larger than that in the large curvature manifold.

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Modeling Transient Churn-Annular Flows in a Long Vertical Pipe

Volume 8C: Heat Transfer and Thermal Engineering ◽

10.1115/imece2013-64534 ◽

2013 ◽

Author(s):

M. V. C. Alves ◽

J. R. Barbosa ◽

P. J. Waltrich ◽

G. Falcone

Keyword(s):

Annular Flow ◽

Large Scale ◽

Coefficient Matrix ◽

Vertical Tube ◽

Flow Conditions ◽

Vertical Pipe ◽

One Dimensional ◽

The One ◽

Energy Equations ◽

Liquid Flows

A mathematical model is presented to describe the behavior of transient gas-liquid flows involving the churn and annular flow patterns in a long vertical tube. The HyTAF (Hyperbolic Transient Annular Flow) code, developed specifically for this study, is based on the one-dimensional multi-fluid formulation and takes account of hydrodynamic non-equilibrium flow conditions by means of relationships for the rates of droplet entrainment and deposition. A finite difference algorithm is employed to solve the hyperbolic system of mass, momentum and energy equations via the Split Coefficient Matrix Method. The modeling results are compared with experimental data for steady-state annular and churn flows obtained from the literature and with pressure and flow rate induced transient churn-annular flow data generated in a large scale facility (48-mm ID, 42-m long test section).

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Pressure Effects on Low-Liquid-Loading Oil/Gas Flow in Slightly Upward Inclined Pipes: Flow Pattern, Pressure Gradient, and Liquid Holdup

SPE Journal ◽

10.2118/191543-pa ◽

2019 ◽

Vol 24 (05) ◽

pp. 2221-2238 ◽

Cited By ~ 2

Author(s):

Hendy T. Rodrigues ◽

Eduardo Pereyra ◽

Cem Sarica

Keyword(s):

Pressure Gradient ◽

Flow Pattern ◽

Slug Flow ◽

Annular Flow ◽

Flow Patterns ◽

Pressure Effects ◽

Liquid Holdup ◽

Liquid Loading ◽

Interfacial Roughness ◽

Oil Gas

Summary This paper studied the effects of system pressure on oil/gas low–liquid–loading flow in a slightly upward inclined pipe configuration using new experimental data acquired in a high–pressure flow loop. Flow rates are representative of the flow in wet–gas transport pipelines. Results for flow pattern observations, pressure gradient, liquid holdup, and interfacial–roughness measurements were calculated and compared to available predictive models. The experiments were carried out at three system pressures (1.48, 2.17, and 2.86 MPa) in a 0.155–m–inside diameter (ID) pipe inclined at 2° from the horizontal. Isopar™ L oil and nitrogen gas were the working fluids. Liquid superficial velocities ranged from 0.01 to 0.05 m/s, while gas superficial velocities ranged from 1.5 to 16 m/s. Measurements included pressure gradient and liquid holdup. Flow visualization and wire–mesh–sensor (WMS) data were used to identify the flow patterns. Interfacial roughness was obtained from the WMS data. Three flow patterns were observed: pseudo-slug, stratified, and annular. Pseudo-slug is characterized as an intermittent flow where the liquid does not occupy the whole pipe cross section as does a traditional slug flow. In the annular flow pattern, the bulk of the liquid was observed to flow at the pipe bottom in a stratified configuration; however, a thin liquid film covered the whole pipe circumference. In both stratified and annular flow patterns, the interface between the gas core and the bottom liquid film presented a flat shape. The superficial gas Froude number, FrSg, was found to be an important dimensionless parameter to scale the pressure effects on the measured parameters. In the pseudo-slug flow pattern, the flow is gravity–dominated. Pressure gradient is a function of FrSg and liquid superficial velocity, vSL. Liquid holdup is independent of vSL and a function of FrSg. In the stratified and annular flow patterns, the flow is friction–dominated. Both pressure gradient and liquid holdup are functions of FrSg and vSL. Interfacial–roughness measurements showed a small variation in the stratified and annular flow patterns. Model comparison produced mixed results, depending on the specific flow conditions. A relation between the measured interfacial roughness and the interfacial friction factor was proposed, and the results agreed with the existing measurements.

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