Flow In Vertical Pipe Research Articles

A finite-element algorithm for Stokes flow through oil and gas production tubing of uniform diameter

Stokes flow of a Newtonian fluid through oil and gas production tubing of uniform diameter is studied. Using a direct simulation on computer-aided design of discretised conduits, velocity profiles with gravitational effect and pressure fields are obtained for production tubing of different inner but uniform diameter. The results obtained with this new technique are compared with the integrated form of the Hagen–Poiseuille equation (i.e., lubrication approximation) and data obtained from experimental and numerical studies for flow in vertical pipes. Good agreement is found in the creeping flow regime between the computed and measured pressure fields with a coefficient of correlation of 0.97. Further, computed velocity field was benchmarked againstANSYS Fluent; a finite element commercial software package, in a single-phase flow simulation using the axial velocity profile computed at predefined locations along the geometric domains. This method offers an improved solution approach over other existing methods both in terms of computational speed and accuracy.

Метод расчета гидравлического уклона при движении двухфазной смеси в наклонных трубопроводах

The paper investigates two-phase mixture flows in sloping pipes employing two computational methods in the transitional region of pipe slope angle. We used methods of computing two-mixture flows in horizontal and vertical pipes as the basis for our equations. When flowing downwards through a sloping pipe, the solid phase volume ratio distribution changes most significantly: an axisymmetric flow through a vertical pipe transforms into a flow featuring a markedly non-uniform distribution of the solid phase along the vertical plane in the sloping pipe. When flowing upwards, the solid phase volume ratio profile is inversely transformed. Comparison of the experimental and computational data showed that the datasets are in a sufficiently good agreement. The computational method developed is semi-empirical and may be recommended for calculating hydraulic gradient in sloping pipes.

Polydisperse bubble flows: a study of the bubble cloud evolution by CFD methods

The evolution of a polydisperse bubble cloud is analyzed by means of computational fluid dynamics. Gravity-driven bubble flows in a column with a circular cross-section as well as a downward flow in a long vertical pipe are numerically investigated. A method employed in the simulations is based on the Euler-Euler description of the multiphase medium. An inhomogeneous multiple-size group (MUSIG) model is used to describe the bubble size distribution. The formulated approach provides detailed description of the bubble flow structure including variation of the bubble size distribution.

Experimental investigations of kerosene-water two-phase flow in vertical pipe

Oil and water two-phase flow studies are important to the oil industries. This paper aims to determine the flow patterns, holdup, pressure losses, phase inversion, drift flux parameters and mixture properties in vertical upward kerosene and water flow. The experiment was conducted in a 26 mm i.d duct with phase velocities spanning from 0.1 to 1.0 m/s. The averaged holdup was measured using quick close valves in a 1.16 m long test section. The same test section was used to measure the pressure drop. A local impedance probe and high-speed films were used to determine the flow patterns. Six different flow patterns was identified: dispersed bubbly (DB), core annular (CA), bubbly (B), churn turbulent (CT), and elongated water drop (EWD). The kerosene holdup was highest for EWD, spanning from 0.8 to 0.9, followed by CT and CA, which spans from 0.35 to 0.75. The kerosene holdup for bubbly spans from 0.12 to 0.6, being the highest range for all patterns. The phase inversion occurs when the kerosene input fraction is βK = 0.35. There is no evidence of slippage between the dispersed and continuous phases. The drift velocity is due to the misalignment of the dispersed fraction and the mixture velocity profile and the distribution parameter is C0 = 1.10. The pressure loss showed a good agreement with Blasius correlation. The exception is for the bubbly and churn turbulent. The density was determined using the homogeneous model and five different mixture viscosity models were investigated. The pressure loss deviation using (Mukhaimer et al., 2015) mixture viscosity spans from 5 to 25%. The drift-flux correlation increase the predictive capability of the oil fractions in oil pipelines, which contribute to the operational security. In addition, a better pressure drop losses estimative provide in this study helps to a better oil pipeline design.

CFD modelling of two-phase gas–liquid annular flow in terms of void fraction for vertical down- and up-ward flow

Two-phase flows are present in all the value chain of the oil industry, being of significant interest in pipeline transportation. They are essential for the calculation of production rates or separation process design; therefore, multiphase flows have been studied for several years, and numerous models, data banks and computational software have been developed to design more efficient processes. For this reason, the purpose of this study is to develop a CFD numerical model capable of predicting air–oil and air–water annular flow for up- and down-ward flows in vertical pipes with the objective of present a methodology to develop a reliable numerical model and present CFD tools as an alternative to the empirical models, or other commercial computational codes such as the dynamic multiphase flow simulators, for the study of multiphase flow. To achieve this objective, 36 simulations using CFD were compared against 150 simulations using OLGA and 66 different empirical correlations to predict void fraction and compare the obtained results against experimental data. Different liquid viscosities (0.00089, 0.127, 0.213, 0.408 and 0.586 Pa s) and three different pipelines were used: a 22.72 m long and 0.0508 m ID pipe, a 15.24 m long and 0.0508 m ID pipe, and a 15.24 m long and 0.1016 m ID pipe. The obtained results showed that the CFD model accurately predicts the void fraction for both down- and up-ward cases, while the obtained results using OLGA and the empirical correlations showed a lower accuracy.

One-dimensional turbulence investigation of variable density effects due to heat transfer in a low Mach number internal air flow

A novel spatial formulation of the One-Dimensional Turbulence (ODT) model is applied to a vertical pipe-flow with heat transfer, analogous to the Direct Numerical Simulation (DNS) performed by Bae et al. [Phys. Fluids 18, (075102) (2006)]. The framework presented here is an extension for radially confined domains of the cylindrical ODT spatial formulation for low Mach number flows with variable density. The variable density simulations for air (Prandtl number Pr=0.71) are performed at an initial bulk Reynolds number Reb,0,DNS=6000 and Grashof number Gr0,DNS=6.78×106. ODT results are presented for both the spatial formulation introduced in this work and the standard temporal formulation for cylindrical flows introduced by Lignell et al. [Theor. Comput. Fluid Dyn. 32, 4 (2018), pp. 495–20]. Streamwise bulk profiles and radial profiles at specific streamwise positions for the temporal and spatial formulations are in good agreement with the DNS results from Bae et al. For the present application, the spatial formulation yields physically better results in comparison to the temporal formulation. Overall, the findings in the original work of Bae et al. were corroborated with ODT. Although the framework proposed in this work is not a compressible framework and has some clear limitations regarding conservation properties, we suggest its use for future studies in the low Mach number variable density regime.

Upward interfacial friction factor in gas and high-viscosity liquid flows in vertical pipes

In this study, experiments were carried out in a vertical 60-mm internal diameter pipe with air and oil (viscosities 100–330 mPa s) constituting the gas and liquid phases. Superficial air and oil velocity ranges used were 9.81–59.06 m/s and 0.024–0.165 m/s, respectively. Visual observations and change in slope of pressure drop– plot were used to identify flow pattern transition to annular flow. Using the experimental data as well as other reported data, a new correlation to predict interfacial friction factor in upward gas–viscous liquid annular flow regime was developed. Compared to the performance of 16 existing correlations using higher viscosity liquids, that of the new correlation was better. The performance of another correlation we derived for predictions at both low and higher low viscous showed good agreement with measurements. In addition, a neural network model to predict the interfacial friction factor involving both low and high viscous liquids was developed and it excellently described the experimental data.

Experimental study on interfacial and wall friction factors under counter-current flow limitation in vertical pipes with sharp-edged lower ends

Experiments on air-water counter-current annular flows in circular vertical pipes of 20 and 40 mm in diameter were carried out to obtain databases of the interfacial and wall friction factors. The pipes were made of transparent acrylic resin to observe counter-current flow limitation (CCFL) in the pipe. The vertical pipe was connected to an upper and a lower tank. The liquid and gas phases were supplied to the upper and lower tanks, respectively. The liquid volume flow rate, the pressure gradient and the liquid volume fraction were measured to evaluate the friction factors. The flows in the pipe were observed using a high-speed video camera and the flow pattern under CCFL was identified using the time-strip visualization technique. The main conclusions obtained under the present experimental conditions are as follows: (1) the flows under CCFL condition can be classified into four regimes, i.e. the smooth film, the transition from smooth film to rough film regimes, the rough film with large amplitude disturbance waves forming at the lower pipe end, and the rough film with simultaneous onsets of disturbance waves inside the pipe, (2) the slope of the CCFL diagram depends on the flow regimes, (3) the flow structure strongly affects the friction factors, and therefore, available correlations of friction factors not accounting for their dependences on the flow regimes cannot give good evaluations, (4) the wall friction factor can be correlated in terms only of the liquid Reynolds number, (5) the interfacial friction factor in the rough film regimes can be well correlated in terms of the gas Wallis parameter (Froude number) since the interface structure strongly depends on the Wallis parameter, and (6) the CCFL model derived using the present empirical correlations of friction factors agrees well with the CCFL characteristics data.

The effect of swirl on transition from churn flow to annular flow in an intermediate diameter pipe

Swirling annular flow has been widely used in industries. The transition boundary of swirling annular flow which is important for its application in practice is rarely studied in published works. In this work, the effect of swirl on transition from churn flow to annular flow in an intermediate diameter pipe has been investigated by experimentation and modelling. The experiments were conducted with air–water two-phase flow in an 11-m vertical pipe (D = 62 mm) at the range of the test conditions: the liquid superficial velocity ranges from 0.0039 to 0.95 m/s and the gas superficial velocity ranges from 1.22 to 32.49 m/s. The experimental results showed that the churn flow can be transformed to swirling annular flow under the effect of swirl, and the gas velocity required for the transition from churn flow to swirling annular flow in a swirling flow is lower compared with that for the transition from churn flow to annular flow in a non-swirling flow. Then a theoretical model based on separated flow model was established to predict the transition boundary between churn flow and swirling annular flow in a vertical pipe. Calculated results were in good agreements with experimental results.

CFD modeling of liquid film reversal of two-phase flow in vertical pipes

The phenomenon of two-phase flows is characterized by its wide range of presence in nature and industrial applications. In gas and oil production, the simultaneous two-phase flow of gases and liquids often occurs in gas wells. The produced gases flow rate decreases over the years until reaching a critical flow rate when they lose their ability to lift the associated liquids upward and the liquid film reverses direction, which triggers liquid loading. Liquid loading causes the produced liquids to accumulate in the bottom of the wellbore, which causes a high back pressure that reduces the well production rate till production is ceased eventually. The critical gas velocity exists in the churn flow regime which is mainly characterized by the oscillatory behavior of the liquids flow field. This study employs CFD techniques to model the churn flow in a 3-inch-diameter vertical pipe near the critical gas flow rate for different liquid flow rates. This work utilizes the two-fluid Eulerian model along with the RNG (Re-Normalization Group) k-ε turbulence model to investigate the behavior of the flow field in a two-dimensional axisymmetric computational domain. Simulations were carried out using the commercial software ANSYS Fluent 18.2 with air and water as the two working fluids. The model results showed a good agreement with the experimental data and proved the mesh and time independence of the model. Oscillatory behaviors of the liquid film flow rate, shear stress, and pressure were observed along with the formation of interfacial waves. Detailed information about the velocity, shear stress, and pressure behaviors is presented. Accordingly, recommendations are suggested for future considerations.

Water–air flow in straight pipes and across 90∘ sharp-angled mitre elbows

Water–air flow in horizontal and vertical straight pipes and through 90∘ sharp-angled mitre elbows is investigated by visualizing the flow patterns by means of a high-precision camera and by measuring the pressure drop. The flow is studied in pipes with three diameters for about six hundred conditions of water–air flows, characterized by superficial velocities in the ranges of jL* = 0.3–1 m/s for water and jG* = 0.15–34 m/s for air. The portion of the pipe upstream of the elbow is always positioned horizontally, while the portion of the pipe downstream of the sharp bend is oriented horizontally or vertically with the flow moving upward. Plug, slug, slug-annular, and annular flows are visualized in horizontal straight pipes, while slug, churn, and annular regimes are recorded in vertical straight pipes downstream of the sharp bend. These patterns are well predicted by the Mandhane map (Mandhane et al., 1974) for horizontally oriented straight pipes and by the Hewitt–Roberts map (Hewitt and Roberts, 1969) for vertically oriented straight pipes. The changes of the flow patterns as the fluids pass through the mitre elbows are discussed. A multiple membrane flow structure is observed in the vertical upward flow at much higher Reynolds numbers based on the water superficial velocity than in the vertical downward case previously reported in the literature. A dimensional analysis is employed to obtain the non-dimensional parameters that describe the flows through the straight pipes and across the elbows. It is proved that a rigorous way to present the flow regimes and the pressure-drop coefficients of the water–air flow for a given geometry is the space of the Reynolds numbers based on the superficial velocities of air and water for fixed Froude number because the flow is incompressible and isothermal. By expressing the maps in scaled form, the prediction of the flow patterns along the straight portions of the pipe improves. The flow patterns through the elbows are expressed in terms of rescaled Mandhane maps, which, for the first time, simultaneously represent the flow patterns both upstream and downstream of the elbows. New pattern-based empirical correlations are obtained for the scaled pressure drops for the water–air flows through the horizontal and vertical pipes and through the elbows. The correlations are based on the flow patterns and do not rely on widely used prediction models, thereby predicting the pressure drop more accurately than the models presently available in the literature.

Experimental investigation of gas\u2013oil\u2013water phase flow in vertical pipes: influence of gas injection on the total pressure gradient

Experimental work has been conducted to study the influence of gas injection on the phase inversion between oil and water flowing in a vertical pipe. A vertical transparent pipe test section line of 40 mm ID and 50 cm length was used. The test fluids used were synthetic oil and filtered tap water. Measurements were taken for mixture velocity, superficial water velocity, superficial gas velocity, and input superficial oil velocity ranging from 0.4 to 3 m/s, 0.18 to 2 m/s, 0 to 0.9 m/s, and 0 to 1.1 m/s. Most of the experiments were conducted more than two times, and the reproducibility of the experiments was quite good. Special attention was given to the effect of oil and water concentration where phase inversion took place with and without gas injection. The results showed that the phase inversion point was close to water fraction of ~ 30%, for both water friction direction changes (from water to oil or from oil to water) and that the effective viscosity increases once the mixture velocity increases. On the other hand, the results with gas injection showed that gas injection had no effect on the oil or water concentration where phase inversion occurred. Furthermore, the study investigated the effect of gas–oil–water superficial velocity on the total pressure gradient in the vertical pipe. It was found that the total pressure gradient was fast and increased at high superficial gas velocity but was slow at low superficial gas velocity. When the superficial oil velocity increased, the total pressure gradient approached the pressure gradient of an oil–water two-phase flow. The obtained results were compared with few correlations found in the literature, and the comparison showed that the uncertainty of the flow pattern transition peak in this study is very low.

Numerical Simulations of Subcooled Boiling Flow in Vertical Pipe at High Pressure

The results of numerical modeling of hydrodynamics and heat and mass transfer at boiling of subcooled liquids in conditions of forced flow in vertical heated pipes are presented. The mathematical model is based on the use of Euler’s description of mass, motion and energy conservation for liquid and gas phases, recorded within the framework of the theory of interacting continua. The turbulent characteristics of the fluid are calculated using a modified model of transfer of components of the Reynolds stress tensor, taking into account the presence of the gaseous phase in the medium. For an approximate calculation of the heat transfer coefficient for bubble boiling of a liquid near the heat-generating wall, generalized empirical dependences are used, taking into account the various mechanisms of heat transfer in a two-phase vapor-liquid medium. Comparison of the results of numerical modeling with experimental data has shown that the proposed approach allows to simulate bubble boiling modes in a wide range of pressure values, mass flow rates, heating modes of subcooled liquids during forced turbulent fluid flow in vertical pipes.

Experimental study on the effect of surfactants on the characteristics of gas carrying liquid in vertical churn and annular flows

In this paper, air-water and air-SDBS solution vertical pipe flow experiments were carried out at room temperature and pressure. The purpose of this work is to study the effect of surfactants on the characteristics of gas carrying liquid in churn and annular flows by a high-speed camera. The results show that surfactants significantly affect the gas-liquid distribution characteristics in churn and annular flows. The process and degree of momentum transfer between the gas phase and liquid phase also change. With the introduction of surfactants, the bubble entrainment is enhanced while the droplet entrainment is inhibited. In churn flow, surfactants make the way of gas carrying liquid change from the accelerated migration of entrained liquid blocks to the one-way migration of stable waves. In annular flow, surfactants make the way of gas carrying liquid change from the accelerated migration of entrained liquid droplets and wave unidirectional migration to the migration of waves with uniform circumferential and axial distribution. The change of the way of gas carrying liquid caused by surfactants increases the momentum transfer between the gas phase and liquid phase, leading to a significant increase in the pressure drop gradient. The foaming of the liquid film is due to the fact that the wave growing from the liquid inlet can more easily satisfy the conditions of bubble entrainment than droplet entrainment. The gas and liquid flow rates determine the growth characteristics of the wave at the liquid inlet, thus determine the degree of change in the way of gas carrying liquid by surfactants.

Experimental study of slug and churn flows in a vertical pipe using plug-in optical fiber and conductance sensors

It is of great significance to explore the flow structures in gas-liquid slug and churn flows. Aiming at this purpose, a novel plug-in optical probe combined with conductance sensors are designed. Furthermore, we perform experimental study of gas-liquid flows in vertical upward pipe with 20 mm inner diameter. Simultaneously, the local time average of void fraction in axial direction, cross-correlation velocity and instantaneous bubble chord distribution in slug and churn flows at seven radial positions are obtained. The research results show that big deformed bubbles in churn flow spiral up in test pipe, but sometimes they rise along pipe center just as gas slugs in slug flow. Besides, bubble chord length distributions in liquid slug of slug and churn flows are analyzed in this study.

Experimental investigation of high-viscosity oil\u2013water flow in vertical pipes: flow patterns and pressure gradient

Flow experiments have been conducted for two-phase flow in a vertical pipe. The experiments were made for highly viscous oil–water in a stainless pipe at 250 psig pressure through the laboratory-scale flow test equipment. The test section used is a vertical transparent tube of 50 cm length and 40 mm ID. The test fluid utilized in this experiments is synthetic oil (viscosity = 35 mPas, density = 860 kg/m3) and filtered tap water (interfacial tension 31 mN/m at 20 °C, viscosity 0.95 mPas at 25 °C). The measurements of superficial velocities of oil and water were varied between 0.01 to 3 m/s. According to the experimental observations using audiovisual recordings, a flow pattern map was identified at different condition. Measuring the variations in pressure gradient and flow patterns at different superficial velocities of two-phase flow, six typical flow patterns were categorized and mapped under two groups, oil-dominant region and water-dominant region, and categorized based on the variations of oil and water superficial velocities, and mixture fluid velocity, at different amount of the water holdup in the vertical tubing. The measurements of the total pressure gradient at five different mixture fluid velocities were conducted verses water holdup in vertical tubing. The results show that all the upward flows show an identical flow pattern, where the pressure gradients increase with increasing mixture fluid velocity and water cut with similar trend. The experiments show a clear peak in the pressure gradient as a result of the frictional factor, specifically at the point of flow patterns occurs (i.e., water holdup ~ 30%). The results concluded that the pressure gradient is significantly influenced by flow patterns and flow rates. Besides, the oil viscosity has a high effect on the pressure gradients; however, it is observed that at similar water and oil superficial velocities, there is a subsequent increase in the pressure gradient due to the increase in oil viscosity.

Experimental study on entrained droplets in vertical two-phase churn and annular flows

In this paper, the air-water vertical two-phase pipe flow experiment was carried out at room temperature and pressure to study the characteristics of entrained droplets in churn and annular flows with the high-speed camera and phase Doppler anemometry. The results show that there are five kinds of droplet entrainment modes in churn and annular flows, namely shearing-off of waves, bag break-up of waves, ligament break-up of waves, droplet impacting liquid film, and burst of bubbles. With the flow pattern transition from churn flow to annular flow, the dominant droplet entrainment changes from shearing-off of waves to ligament break-up of waves. The gas superficial velocity plays a decisive role in determining the characteristics of entrained droplets, while the effect of the liquid superficial velocity can be neglected. In churn flow, the shearing-off of waves produces a small amount of entrained droplets with low sphericity and initial velocity. Large droplets tend to deposit, and small droplets undergo a certain degree of fragmentation and coalescence during the accelerated migrating in the gas core. In annular flow, the ligament break-up of waves produces a large amount of entrained droplets with high sphericity and initial velocity. Droplet size presents continuous distribution. The size of droplets increases slightly due to the coalescence of small droplets during the accelerated migrating in the gas core. Compared with churn flow, the momentum exchange between the gas phase and droplets is greater in annular flow, which leads to a significant increase in droplet momentum. The size distribution of the entrained droplets determines the momentum exchange between the gas core and the entrained droplets to a certain extent.

Characteristics and formation mechanism of plug flow in the industrial vertical pipeline of dense-phase pneumatic conveying of pulverized coal

Plug flow, which affects the reliable feeding of pulverized coal, is one of flow patterns in dense-phase pneumatic conveying of pulverized coal. The control and formation mechanism of plug flow are very important for the industrial application and theoretical research. In this work, experiments were carried out on a pneumatic conveying test platform in the Key Lab of Coal Gasification and Energy Chemical Engineering of Ministry of Education, ECUST, to study on the plug flow in the industrial vertical pipe under a low superficial gas velocity. All the flow states and flow patterns of the dense-phase pneumatic conveying process were analyzed. The present study shows that five different particle velocity distributions were found in the plug flow. However, the time series of the pressure and solid concentration signal are almost the same. What’s more, the power spectral density function analysis provides the relationship of the solid concentration signal of the cross-section by the electrical capacitance tomography (ECT) between all four operational cases and five different kinds of plug flows. From the point view of application, five different kinds of the plug flow were characterized by the plug length, fluctuation parameter of the plug flow (the Strouhal number) and the operational parameters (Lockhart–Martinelli parameter and the Froude number of the gas phase and the solid phase). Based on the phase diagram constructed using the Strouhal number and Lockhart-Martinelli parameter, five types of plug flow could be predicted. A larger Strouhal number indicates the poorer stability of the plug flow. Moreover, the formation mechanism of the plug flow was analyzed by the Janssen equation. Finally, we found that all types of the plug flow have the same unit friction force based on a statistical discussion. Through this work, we wish that our research will give a deeper understanding of the formation and control of the plug flow in the dense-phase pneumatic conveying of pulverized coal.

110th Anniversary: Numerical Simulations of Gas–Liquid Two-Phase Flow in Vertical Pipe Implementing Population Balance Modeling

Population balance modeling in a gas–liquid two-phase bubbly flow allows us to predict the bubble size distribution. The prediction of bubble size distribution is of utmost importance as it prevails the heat, mass, and momentum transport mechanisms. In the present work, numerical simulations of gas–liquid two-phase flow in a vertical pipe have been performed using population balance modeling. The effects of different coalescence and breakage models have been studied. The wall peak and core peak case in the bubbly flow regime is considered for the prediction of the radial distribution of the gas void fraction, interfacial area concentration, bubble size distribution, Sauter mean diameter, and gas and liquid velocities. Numerical simulations were performed with the Euler–Euler two-fluid model and the k–ω SST turbulence model. The population balance equation is solved using the traditional class method. The combination of Brownian coalescence and Ghadiri breakage model is recommended for the prediction of th...

A Mechanistic Model of Liquid Film Movements in Pipe Elbows for Annular Flow

A mechanistic model of film movements is developed based on the treatments on the annular flow field. The initial conditions at the inlet are determined by adopting a validated film thickness correlation of fully developed upward annular flow in vertical pipes. The overall pressure gradient is assumed to be uniform all along the axial distance within the elbow and the static pressure is also uniform on every cross section. The axial velocities of the liquid film and the core region are both uniform on the cross-sectional plane. The droplets are assumed to travel in straight lines normal to the inlet plane until colliding on and absorbed by the liquid film surface. The liquid film motion is divided into the axial and radial directions. Energy conservation law and Newton's second law are, respectively, used in the two directions. The film motion calculation is executed by using a discrete method with an explicit solution. The average film thickness and the circumferential thickness distribution on an arbitrary cross section can be obtained for the given flow conditions. The mechanistic model is verified by comparing the predicted circumferential distribution of film thickness with three series of experimental data from the literature. Parametric studies are also conducted to investigate the parameter effects and the range of application. The present work proves that the variation and distribution of film thickness within the elbows can be efficiently described by the mechanistic model.