Ram Mohan
The University of Tulsa, Mechanical Engineering, Faculty Member
The purpose of the present study is to improve the current prediction capabilities of the entrainment fraction in horizontal gas-liquid flow. Since it is recognized that waves at the gas-liquid interface are the main source of... more
The purpose of the present study is to improve the current prediction capabilities of the entrainment fraction in horizontal gas-liquid flow. Since it is recognized that waves at the gas-liquid interface are the main source of entrainment, an experimental and theoretical work has been carried out to characterize the waves at the gas-liquid interface and to develop a model for entrainment calculations based on such characteristics. The model consists of three sub-models, namely, onset of entrainment, maximum entrainment and entrainment values in between. The onset of entrainment model determines the conditions at which the gas starts shearing the wave crests through a force balance between drag and surface tension forces. The maximum entrainment model provides the maximum fraction of liquid that can be entrained at high gas velocities by integration of the turbulent velocity profile to a determined dimensionless film thickness within the buffer sub layer. The entrainment fraction in between onset and maximum boundaries is calculated from an equilibrium between atomization and deposition rates. The atomization rate is calculated by first determining the wave mass flux in the liquid film and second by calculating the fraction of a single wave that is sheared by the gas through a force balance. The deposition rate is calculated as a linear function of the droplet concentration in the gas. Closure relationships have been developed from data for wave celerity, frequency, amplitude and width which are used in the entrainment model. A review of the most used correlations for calculating the entrainment fraction is presented and their performance evaluated. The present model shows better prediction than available models when compared to the acquired experimental data and the available experimental data in the literature.
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ABSTRACT
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ABSTRACT
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Sand transport in multiphase flow has recently gained keen attention of the oil and gas industry owing to the negative effects associated with it. These include partial pipe blockage, pipe corrosion, excessive pressure drop and production... more
Sand transport in multiphase flow has recently gained keen attention of the oil and gas industry owing to the negative effects associated with it. These include partial pipe blockage, pipe corrosion, excessive pressure drop and production decline. To date, no comprehensive literature review and models evaluation have been published, which compare the experimental data collected for the prediction of the critical sand deposition velocity under intermittent flow with the related model predictions. This study can be used by engineers and researchers to determine the conditions under which the developed models perform the best. The intermittent flow critical sand deposition velocity data acquired by Najmi (2015) are presented in detail. Next, the effects of important parameters such as phase velocities, liquid viscosity as well as particle size and concentration on the critical velocity are investigated. The collected data are utilized to evaluate the performance of the models developed by Salama (1998), Hill (2011), Stevenson et al. (2001) and Danielson (2007), in order to determine the best model for the prediction of the sand critical velocity. The experimental data of Najmi (2015) indicate that higher critical velocities are required with increasing the liquid viscosity, particle size and particle concentration. However, the predictions of the models of Salama (1998), Stevenson et al. (2001) and Danielson (2007) demonstrate that these models do not take into account the effect of particle concentration. Depending on the liquid viscosity, Stevenson et al. (2001) model significantly over-predicts or under-predicts the critical velocity over different ranges of the phase velocities, while Salama (1998) model under-predicts the critical velocity under all experimental conditions. An overall comparison of the data with the published model predictions confirms that the Hill (2011) model has the best performance capturing the physical phenomena, including the effects of phase velocities, particle size, particle concentration and liquid viscosity.
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Gas Carry-Under (GCU) is one of the two undesirable phenomena that occur in the GLCC©,1 (Gas-Liquid Cylindrical Cyclone) separators when it operates even within the Operational Envelope (OPEN). Earlier studies have shown that maintaining... more
Gas Carry-Under (GCU) is one of the two undesirable phenomena that occur in the GLCC©,1 (Gas-Liquid Cylindrical Cyclone) separators when it operates even within the Operational Envelope (OPEN). Earlier studies have shown that maintaining a liquid level below the inlet of the GLCC under control configuration affects the GCU in GLCC. It has been identified that the tangential wall jet is the cause of gas entrainment within the GLCC and has been understood to change with liquid level maintained at the inlet. Also, it has been theorized that effective formation of the vortex formed in the lower part of the GLCC, or a stable gas core enhances the separation of gas entrained in the liquid. At present, there is no mechanistic model which captures these complex physical phenomena in the GLCC. This paper presents a newly developed mechanistic model which can predict the GCU for different flow conditions, fluid properties, and various liquid levels. The proposed model captures the various physical phenomena namely: saturated flow at the inlet, tangential wall jet phenomena, gas entrainment and vortex flow that results in separation of gas. The developed model has been compared with the extensive experimental data and is said to be in good agreement.
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Slug flow, which commonly occurs in the petroleum industry, is not always a desired flow pattern due to production operation problems it may cause in pipelines and processing facilities. To mitigate these problems, flow conditioning... more
Slug flow, which commonly occurs in the petroleum industry, is not always a desired flow pattern due to production operation problems it may cause in pipelines and processing facilities. To mitigate these problems, flow conditioning devices such as multiphase flow manifolds and slug catchers are used, where dissipation of slugs occurs in downward flow or in larger diameter pipe sections. Tee-junctions are important parts of these flow conditioning devices. In this work, Computational Fluid Dynamics (CFD) simulations are conducted using ANSYS/FLUENT 17.2 to investigate slug dissipation in an Enlarged Impacting Tee-Junction (EIT). An Eulerian–Eulerian MultiFluid VOF transient model in conjunction with the standard k-ε turbulent model is used to simulate slug dissipation in an EIT geometry. The EIT consists of a 0.05 m ID 10 m long inlet, which is connected to the center of a 0.074 m ID 5.5 m long section that forms the EIT branches. Moreover, experimental data are acquired on slug dissipation lengths in a horizontal EIT with a similar geometry as in the CFD simulations. The CFD results include the mean void fraction and cross-sectionally averaged void fraction time series in the EIT for different gas and liquid velocities. These results provide the inlet slug length and dissipation length in the EIT branches. The CFD results are evaluated against the experimental data demonstrating that the slug dissipation occurring in EIT branches can be predicted by simulation.
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The gas-liquid cylindrical cyclone (GLCC©) is a simple, compact and low-cost separator, which provides an economically attractive alternative to conventional gravity based separators over a wide range of applications. As shown in Figure... more
The gas-liquid cylindrical cyclone (GLCC©) is a simple, compact and low-cost separator, which provides an economically attractive alternative to conventional gravity based separators over a wide range of applications. As shown in Figure 1, over the past 20 years more than 6,000 GLCC’s have been installed around the world by the Petroleum and related industries. However, to-date no systematic study has been carried out on its structural integrity. The GLCC inlet section design is a key parameter, which is crucial for its performance and proper operation. This paper presents Finite Element Analysis (FEA) simulation results aimed at investigating the effect of various parameters on the inlet section structural integrity. Finally, recommendations on design modifications are presented, directed at strengthening the inlet section.
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In order to assess the critical sand deposition condition, a unique 4-in ID test facility was designed and constructed, which enables the pipe to be inclined 1.5 deg upward. Experiments were conducted with air–water-glass beads at low... more
In order to assess the critical sand deposition condition, a unique 4-in ID test facility was designed and constructed, which enables the pipe to be inclined 1.5 deg upward. Experiments were conducted with air–water-glass beads at low sand concentrations (< 10,000 ppm), and the air and water flow rates were selected to ensure stratified flow regime along the pipe. At constant superficial liquid velocity, the gas velocity was reduced to find the critical sand deposition velocity. Six sand flow regimes are identified, namely, fully dispersed solid flow, dilute solids at the wall, concentrated solids at the wall, moving dunes, stationary dunes, and stationary bed. The experimental results reveal that sand flow regimes under air–water stratified flow are strong functions of phase velocities, particle size, and particle concentration. Also, the results show that air–water flow regime plays an important role in particle transport; slug flow has high capability to transport particles at the pipe bottom, while the stratified flow has high risk of sand deposition. As long as the sand dunes are observed at the pipe bottom, the critical sand deposition velocities slightly increase with concentrations, while for stationary bed, the critical velocity increases exponentially with concentration.
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This paper presents the comparative study of experimental, modeling, and simulation results that are performed using commercially available ANSYS Fluent software to analyze the separation kinetics of oil and water in a horizontal... more
This paper presents the comparative study of experimental, modeling, and simulation results that are performed using commercially available ANSYS Fluent software to analyze the separation kinetics of oil and water in a horizontal separator at various velocities and watercuts. The horizontal pipe separator used in this study has an internal diameter of 0.0762 m and a length of 10.3 m separating oil and water with specific gravities of 1.0 and 0.857 and watercuts ranging from 20 to 90%. The mixture velocities studied are 0.08, 0.13, and 0.20 m/s. Numerical simulations are done using the hybrid Eulerian-Eulerian multifluid VOF model to study the effect of watercut on the creaming of the oil layer and sedimentation of the water layer respectively. As the mixture velocities increased, the initial length of separation increased like experimental results. As the watercut increased, the separation of water enhanced, while the oil creaming improved with the lowering of the watercut as expected. Numerical results showed good agreement for water/dispersion interface predictions for all the conditions studied. The CFD results are compared against experimental results obtained by Othman in 2010 and agree with the trend of separation. The numerical simulations gave insights into the velocity profiles in each of the layers such as creamed oil, sedimented water, and the layer of emulsion that is not separated. Also, the numerical results are validated against the extended Gassies (2008) model incorporating correlation for turbulent time decay and oil volume fraction proposed by Dabirian et al in 2018.
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Gas Carry-Under (GCU) is one of the undesirable phenomena that exist in the Gas-Liquid Cylindrical Cyclone (GLCC) separators even within the liquid carry-over Operational Envelope (OE). In order to quantify the GCU, it is important to... more
Gas Carry-Under (GCU) is one of the undesirable phenomena that exist in the Gas-Liquid Cylindrical Cyclone (GLCC) separators even within the liquid carry-over Operational Envelope (OE). In order to quantify the GCU, it is important to understand the cause of gas entrainment that occurs in the GLCC other than the incoming entrained gas within the liquid medium. The tangential inclined inlet of 27° with reduced area allows the stratified liquid flow to exit the inlet nozzle tangentially along the wall into the vertical lower part of the GLCC, whereby the liquid film spreads along the wall in an asymmetrical shape. The gas moves to the center of the GLCC and escapes through the gas leg. The liquid film flow is complex and turbulent exhibiting unevenness of the film thickness and asymmetrical velocity distribution. Experimental investigations show that the magnitude of liquid wall jet film tangential and axial velocity change as a function of length along the GLCC below the inlet of the GLCC. This wall jet film flowing down along the wall is the cause for gas entrainment and GCU. The experimental results show that the gas entrainment mechanism is not like the conventional jet entrainment as expected to be occurring in GLCC. The change in velocities of the wall jet film at various liquid heights maintained below the inlet results in varying gas entrainment at various inlet liquid levels and for fluid properties. The wall jet phenomena that takes places at the inlet has been discussed in detail and a mechanistic model capable of predicting the wall jet parameters has been presented in this paper. Further, a novel mechanistic model that is developed for the first time is also presented which can predict the gas entrainment at various liquid levels and flow conditions using the wall jet parameters as an input condition.
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Horizontal Pipe Separators (HPS©) are used for separation of oil and water especially in subsea environment owing to its simplicity, installation, and operation. In the present work, the flow phenomena in the HPS with 0.0762m ID and 10.3... more
Horizontal Pipe Separators (HPS©) are used for separation of oil and water especially in subsea environment owing to its simplicity, installation, and operation. In the present work, the flow phenomena in the HPS with 0.0762m ID and 10.3 m long separating oil and water with specific gravities of 1 and 0.857 is simulated and analyzed using ANSYS Fluent 16. Hexahedral mesh with boundary layers has been done utilizing ANSYS design modeler for this analysis. A grid independence study is performed on 3 different mesh grids using grid convergence index. 3-D simulations are carried out using a Hybrid Eulerian-Eulerian Multifluid VOF model for watercuts ranging from 20 to 80% and a mixture velocity of 0.08 m/s. The CFD simulations analyzed the effect of watercut on the oil-water mixture flow behavior and the entry region required for the oil and water to separate in the HPS. These simulation results are validated against acquired experimental data by Othman in 2010. These simulations provide an insight to understand the effects of diameter, watercut, and mixture velocities on the performance of HPS to aid in its design and scale up/down studies.
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A novel non-fibrous filter media is evaluated for in-line oil-water separation. Outside-in-crossflow configuration incorporating the filter media is utilized in order to test the filter. All experiments are conducted with a... more
A novel non-fibrous filter media is evaluated for in-line oil-water separation. Outside-in-crossflow configuration incorporating the filter media is utilized in order to test the filter. All experiments are conducted with a hydrophilic-olephobic filter for water-continuous flow with low oil concentrations. The collected experimental data include permeate flow rate and purity as well as pressure drop. Values of permeate flow rate and pressure drop are averaged over the duration of the experiments, which is about 5 minutes, constituting the “initial average” of the permeate flow rate and the corresponding pressure drop. Totally twelve experimental runs are conducted for mixture velocities of 0.038 m/s, 0.055 m/s and 0.066 m/s, and oil concentrations of 0.6%, 0.83%, 1.1%, 7.9% and 9.1%. Permeate samples are analyzed for oil content, demonstrating a high separation efficiency of 98 ± 2%. The permeate flux across the filter cartridge ranges between 0.0739 (L/h)/cm2 to 0.216 (L/h)/cm2 owing to the low pressure drop across to filter. Oil concentration in to permeate water samples shows consistently increasing trend with an increase in inlet oil content, while maintaining high separation efficiency for all runs. The pressure drop across the membrane under flowing conditions ranges from 0.35 psid to 0.6 psid for flow rates between 0.1 L/min and 0.29 L/min, respectively. Also the data confirm that the filter membrane breakthrough pressure is 0.35 psid.
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Gas Carry-Under (GCU) is one of the undesirable phenomena that exists in the GLCC©1 even within the Operational Envelope (OPEN) for liquid carry-over. Few studies that are available on GLCC© GCU have been carried out when the GLCC© is... more
Gas Carry-Under (GCU) is one of the undesirable phenomena that exists in the GLCC©1 even within the Operational Envelope (OPEN) for liquid carry-over. Few studies that are available on GLCC© GCU have been carried out when the GLCC© is operated in a metering loop configuration characterized by recombined outlets. In such configurations the gas and the liquid outlets of the GLCC are recombined downstream which acts as passive level control. However, studies have shown that the GLCC© OPEN increases significantly when active control strategies are employed. There has not been a systematic study aimed at analyzing the effect of control on the GCU in the GLCC. This study compares the previously published GLCC GCU swirling flow mechanism under recombination outlet configuration with data taken under the separated outlet configuration (control configuration). Experimental investigations for GCU are conducted in a state-of-the-art test facility for air-water and air-oil flow incorporating pressure and level control configurations. The experiments are carried out using a 3″ diameter GLCC© equipped with 3 sequential trap sections to measure simultaneously the Gas Volume Fraction (GVF) and gas evolution in the lower part of the GLCC. Also, gas trap sections are installed in the liquid leg of the GLCC© to measure simultaneously the overall GCU. The liquid level was controlled at 6″ below the GLCC© inlet for all experiments using various control strategies. Tangential wall jet impingement is the cause for entrainment of gas, thereby leading to GCU. 3 different flow mechanisms have been identified in the lower part of the GLCC and have significant effect on the GCU. Viscosity and surface tension are observed to affect the GCU. The extensive acquired data shed light on the complex flow behavior in the lower part of the GLCC© and its effect on the GCU of the GLCC©.
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A novel and unique experimental facility was design, constructed and instrumented, enabling slug flow splitting data acquisition in both parallel and looped lines. A total of 81 experimental test runs were carried out for various... more
A novel and unique experimental facility was design, constructed and instrumented, enabling slug flow splitting data acquisition in both parallel and looped lines. A total of 81 experimental test runs were carried out for various superficial gas and liquid velocity combinations. Uneven split conditions data were acquired by utilizing either a choke valve on one of the lines or different pipe diameters. For the symmetrical configurations of both parallel and looped equal diameter lines, the phases split equally in the lines. When the parallel and looped lines are of different resistance to flow (utilizing a choke installed on one of the lines or different line diameters), uneven split of the phases occurs. The gas-phase flows preferentially into the smaller resistance line. This results in different gas–liquid ratios in the two lines, which are different from the gas–liquid ratio at the inlet. A mechanistic model has been developed for the prediction of the uneven gas and liquid splitting and the pressure drop in two-phase looped lines. Good agreement is observed between the model predictions and the experimental data, with an average error of about 15 % in the phase splitting and pressure drop.
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A dynamic model and a simulator have been developed for the Gas-Liquid Cylindrical Cyclone/Slug Damper (GLCC©-SD) system, for the prediction of its flow behavior under transient slugging flow conditions. Separate dynamic models and... more
A dynamic model and a simulator have been developed for the Gas-Liquid Cylindrical Cyclone/Slug Damper (GLCC©-SD) system, for the prediction of its flow behavior under transient slugging flow conditions. Separate dynamic models and simulators are developed for the GLCC© and the SD units, which are integrated together with a slug generator model/simulator into an overall model/simulator for the GLCC©-SD system. Two numerical schemes are utilized for the developed integrated simulator, namely, fixed time step and variable time step schemes. Simulation examples are presented for the GLCC©, SD and integrated GLCC©-SD system, for the prediction of their performance under transient flow conditions. The GLCC©-SD simulation results demonstrate clearly the advantage of this system in dampening and smoothing the liquid flow rate under slug flow conditions, providing fairly constant flow rate at the GLCC© outlet liquid leg. The developed GLCC©-SD simulator can be extended to other separators, such as the gravity vessel separators and liquid hydrocyclones.
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Gas-Liquid Cylindrical Cyclone (GLCC©) Separators have been in use in petroleum and other related industries for over two decades. Prediction of Liquid Carry-Over Operational Envelope (LCO-OE) is essential for designing and proper... more
Gas-Liquid Cylindrical Cyclone (GLCC©) Separators have been in use in petroleum and other related industries for over two decades. Prediction of Liquid Carry-Over Operational Envelope (LCO-OE) is essential for designing and proper operation of GLCC©. Earlier mechanistic models for predicting LCO-OE were based on gas-liquid phase flow. A new mechanistic model has been developed for the prediction of the LCO-OE incorporating the effect of watercut and fluid properties for a GLCC© under liquid level and pressure control configuration. The new model captures the effect of viscosity and surface tension on the LCO-OE and the effect of water cut on the onset of annular mist velocity. Comparison between the developed mechanistic model predictions for LCO-OE with the experimental data show a good agreement.
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Foaming can hinder gas-liquid separation, therefore, it is desirable to break the foam upstream of separation facilities. There are different methods to breakup foam, including chemical (utilizing defoaming agent), mechanical (such as... more
Foaming can hinder gas-liquid separation, therefore, it is desirable to break the foam upstream of separation facilities. There are different methods to breakup foam, including chemical (utilizing defoaming agent), mechanical (such as cyclones), and thermal (by increasing temperature). Foam stability and breakup are studied in a standalone Churn Flow Coalescer (CFC) and in a Churn Flow Coalescer/Gas-Liquid Cylindrical Cyclone© (CFC/GLCC©) system. The goal is to investigate the possible improvement of the foam breakup efficiency in the GLCC© by installing a CFC upstream of the GLCC©. Testing the standalone CFC, it was found that the CFC generates more, but less stable, foam that can be broken more easily. Three different CFC’s are tested with diameters of 1″, 2″ and 3″. For the same inlet conditions, the 3″ CFC with tangential inlet was found to be the most efficient for generating less stable foam. The optimal operating conditions for this CFC are at low superficial gas velocities, namely, vsg(CFC) between 0.1 to 0.3 m/s. Higher flow rates generate smaller bubbles and more stable foam. From testing the CFC/GLCC© system, it is found that foam breakup in this system is more efficient than that of the standalone GLCC©, under the same flow conditions. The operational envelope of the CFC is predicted based on the transition boundary to churn flow developed by Taitel et al. (1980), as a function of the CFC aspect ratio (LE/D). The analysis of transition boundary between slug and churn confirm that less stable foam occurs at the left of churn flow transition boundary.
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A slurry jet driller is a novel drilling method, which delivers an abrasive slurry and supercritical gas mixture, to an expander nozzle. The expanded fluids flowing out of the nozzle, energize the particles, which hit the target material... more
A slurry jet driller is a novel drilling method, which delivers an abrasive slurry and supercritical gas mixture, to an expander nozzle. The expanded fluids flowing out of the nozzle, energize the particles, which hit the target material and erode it, achieving drilling. The expansion of the gas from a super critical state to in situ pressure and temperature conditions is the driving mechanism of the drilling operation. The primary objective of this paper is to evaluate the feasibility of the novel slurry jet drilling system. An experimental program is carried out for testing the performance of a slurry jet driller. The slurry is formed by mixing water with garnet particles, and a super critical carbon dioxide as the gas phase. The purpose of experiments is to evaluate the erosive nature of garnet rocks and to test the cutting efficiency of the nozzle. The acquired data show that the material removal rate increases with increase in the gas-slurry flow ratio, until a ratio of 1.5. A further increase in the flow ratio results in a reduction of the rate of material removal. Improved nozzle geometry was obtained using a program written in MATLAB. Criteria used for geometry improvement was the force applied to the bottom of the drilled bore. A rudimentary model is developed for the prediction of material removal rate utilizing a slurry jet driller, which is presented in a dimensionless form. The model incorporates the important variables affecting the jet driller system performance, including fluid and target material properties, and particle velocity. A fair agreement is observed between model predictions and experimental data, exhibiting a 20% deviation.
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A novel and systematic experimental investigation was conducted on droplet deposition and coalescence in curved pipes. Various curved pipe bends, to be utilized as flow conditioning devices upstream of wet gas separators, were tested.... more
A novel and systematic experimental investigation was conducted on droplet deposition and coalescence in curved pipes. Various curved pipe bends, to be utilized as flow conditioning devices upstream of wet gas separators, were tested. Data were collected for about 200 experimental runs, varying v ratio up to 4.5, for two liquid loadings of 700 and 1400 m3∕MMsm3. The results show that the 180∘ pipe bend and the long elbow bend performances are similar, which are the best among the curved pipes tested. The long elbow bend is recommended for field applications for its performance, availability, and ease of installation. A model for the prediction of droplet deposition in a long elbow bend was developed, based on the physical phenomena, consisting of a force balance and a conservation of angular momentum on a droplet. The model enables tracking the droplet movement in the elbow and identifying the depositing droplets. A comparison between the model predictions and experimental data shows a good agreement with average error about 20%.
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Petroleum industry uses shear devices such as chokes, valves, orifices and pumps, which cause droplet coalescence and breakup making the downstream separation process very challenging. Droplet-droplet coalescence leads to formation of... more
Petroleum industry uses shear devices such as chokes, valves, orifices and pumps, which cause droplet coalescence and breakup making the downstream separation process very challenging. Droplet-droplet coalescence leads to formation of larger droplets, which accelerate the phase separation, whereas the breakup of larger droplets into smaller ones delays the separation process. Computational Fluid Dynamic (CFD) simulations are conducted by ANSYS-Fluent software to track the droplet breakup and droplet-droplet coalescence, where the interfaces between the two phases are tracked by the Volume of Fluid (VOF) model. The material of droplet is water, while the continuous phase is oil. In this study, the effect of variables such as droplet diameter, droplet relative velocities as well as droplet motion directions on the time evolution of droplet-droplet coalescence and breakup is evaluated. The simulation results confirm that smaller droplet collisions lead to coalescence under wide ranges of droplet relative velocities, while larger droplet collisions result in droplet breakup at higher relative velocities. During coalescence, two droplets combine into one droplet, which deform in several times from one direction to orthogonal direction until recovering its shape or breakup. In addition, the simulation results show that fastest coalescence takes place when droplet collisions occur at optimum relative velocity, whereas droplet breakup occurs at higher velocities than the optimum velocity, and delay in coalescence happens at lower velocity. Furthermore, the simulation results clearly show that droplet moving direction play an important role in the occurrence of droplet coalescence and breakup. Comparison of the simulation results with the collected experimental data from literature confirm that the simulations are capable of predicting the evolution time of the droplet coalescence and breakup with high accuracy.
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Gas carry-under (GCU) and the corresponding gas volume fraction (GVF) in the gas–liquid cylindrical cyclone (GLCC©)2 liquid outlet occurs even within its normal operational envelope (OPEN). Few studies are available on GLCC, GCU, and GVF,... more
Gas carry-under (GCU) and the corresponding gas volume fraction (GVF) in the gas–liquid cylindrical cyclone (GLCC©)2 liquid outlet occurs even within its normal operational envelope (OPEN). Few studies are available on GLCC, GCU, and GVF, which have been carried out in a GLCC operated in a metering loop configuration. This study focuses on GLCC GCU and GVF in swirling flow under separated outlet configuration with active control, which increases the GLCC OPEN significantly. A state-of-the-art test facility is used to acquire extensive GCU and GVF data for both air–water and air–oil flow in a 3″ diameter GLCC. The GLCC is equipped with three sequential trap sections to measure the instantaneous GVF and gas evolution in its lower part below the inlet. Also, gas trap sections are installed in the GLCC liquid outlet leg to measure the overall time-averaged GCU and GVF. The extensive acquired data shed light on the complex flow behavior in the lower part of the GLCC and its effect on the GCU and GVF in the GLCC. Tangential wall jet impingement from the GLCC inlet is the cause of gas entrainment and swirling in the lower GLCC body. The swirling flow mechanisms in the lower part of the GLCC are identified, which affect the GCU and GVF. The liquid viscosity and surface tension also affect the results. The GCU and GVF in the GLCC liquid outlet reduce as the superficial liquid velocities are increased for both air–oil and air–water flows, whereby the superficial gas velocities do not have a significant effect. The GCU and GVF for air–water flow are three orders of magnitude lower as compared to the air–oil flow.
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Efficient transport of sand or cuttings is of great importance in oil and gas industry and the fluid velocity in these processes should be high enough to keep particles continuously moving along the pipe. This minimum fluid velocity below... more
Efficient transport of sand or cuttings is of great importance in oil and gas industry and the fluid velocity in these processes should be high enough to keep particles continuously moving along the pipe. This minimum fluid velocity below which particles deposit, defined as the critical velocity, depends on various factors including flow regime, particle size, particle concentration, phase velocities and fluid viscosity. The objective of this study is to investigate the effect of parameters such as particle size and liquid viscosity on solid particle transport in horizontal pipelines using Computational Fluid Dynamics (CFD) simulations and validate the numerical model predictions with experimental data. CFD simulations have been conducted with a commercially available software, ANSYS-FLUENT. Eulerian model with k-ω SST turbulence closure model is used to simulate the fluid flow while particles are tracked as the Lagrangian phase. In these simulations eddy interaction model is included to consider the effect of flow turbulence on the particle track. The simulations are created for 0.05 m pipe diameter with 4 m length. The simulations are initialized at relatively high fluid velocity, which is gradually reduced until the particle velocity drops below the acceptable critical velocity. The CFD simulation results are validated with experimental data from literature, Najmi (2015) and Najmi et al. (2016) for two particle sizes and multiple liquid viscosities. It was observed that the critical velocity values for liquid flows are comparable with CFD simulation results. The simulation results show that depending on the flow regimes (laminar or turbulent) and particle size, the critical velocity can demonstrate similar trend with carrier liquid viscosity as that of the experimental data. Also the CFD simulations and experiment results are compared with three models currently used in industry, namely Oroskar and Turian (1980) model, Salama (2000) model and Danielson (2007) model.
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Prediction of the Operational Envelope (OPEN) for liquid carry-over is essential for optimized performance of Gas-Liquid Cylindrical Cyclone (GLCC©1) compact separators. This study extends the previous GLCC liquid carry-over studies from... more
Prediction of the Operational Envelope (OPEN) for liquid carry-over is essential for optimized performance of Gas-Liquid Cylindrical Cyclone (GLCC©1) compact separators. This study extends the previous GLCC liquid carry-over studies from 2-phase flow to 3-phase gas-oil-water flow incorporating pressure and level control configurations. A series of experiments were conducted to evaluate the performance of a 3″ diameter GLCC in terms of OPEN for liquid carry-over. Both light oil and heavy oil were utilized, with watercuts ranging from 0 to 100%. The liquid level was controlled at 6″ below the GLCC inlet. A significant effect of watercut on the OPEN for liquid carry-over for three-phase flow was observed. As the watercut reduces, the OPEN for liquid carry-over reduces too. Also, the OPEN for heavy oil reduces as compared to light oil, which could be primary due to the effect of viscosity. Finally, the annular mist velocity increases with the increment of watercut and viscosity.Copyright © 2016 by ASME
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Novel experimental and theoretical investigations are carried out on Zero Net Liquid Flow (ZNLF) in the upper part of the Gas-Liquid Cylindrical Cyclone (GLCC©) separator. Experimental data are acquired for the variation of the Zero Net... more
Novel experimental and theoretical investigations are carried out on Zero Net Liquid Flow (ZNLF) in the upper part of the Gas-Liquid Cylindrical Cyclone (GLCC©) separator. Experimental data are acquired for the variation of the Zero Net Liquid Holdup (ZNLH) and the associated Churn region height for air-oil and air-water flow. The experiments are carried out at normal operating conditions below the GLCC Operational Envelope (OPEN) for Liquid Carry-Over (LCO). The ZNLH measurements for air-oil flow are higher than those for air-water flow. The Churn region height is higher for air-oil flow, as compared to the air-water flow, for the same operating conditions. The higher oil viscosity, which results in higher frictional and drag forces, leads to greater ZNLH for air-oil flow. The Churn region height is sensitive to the superficial gas velocity, whereby a small increase of gas velocity results in exponential growth of the Churn region height. The model developed by Karpurapu et al. (2018) for predicting the ZNLH at specific operational conditions just below the OPEN for LCO is extended to predict the ZNLH variation along the upper part of the GLCC below the OPEN for LCO, as well as the associated Churn region height. The predictions of the developed extended model for the ZNLH variation compared to the acquired experimental data showing discrepancies of 8% and 3%, respectively, for air-oil and air-water flows.
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Foaming is a common phenomenon in the petroleum industry. Foams can be desirable for drilling applications, whereby the cutting bits are lubricated, and cuttings are carried up to the surface. However, foam can be undesirable for... more
Foaming is a common phenomenon in the petroleum industry. Foams can be desirable for drilling applications, whereby the cutting bits are lubricated, and cuttings are carried up to the surface. However, foam can be undesirable for production operation, which hinders the gas-liquid separation process. Experimental investigation has been conducted on foam break-up in a standalone Churn Flow Coalescer (CFC), a standalone Gas Liquid Cylindrical Cyclone (GLCC©) and a combined CFC/GLCC© system. A 1-inch Foam Characterization Rig (FCR) is utilized. The FCR is equipped with a 3-inch diameter CFC, which is connected in series to a 2-inch diameter GLCC©. A total of 30 experimental runs are conducted for both Gas Mode (GM) and Liquid Mode (LM) operations. A surfactant (SI-403) with concentration of 0.025%, superficial liquid velocities of 0.1 and 0.15 m/s and superficial gas velocities of 0.5, 1, and 1.5 m/s are used in the experiments. The experimental results show that for the GM operation, the foam break-up in combined CFC/GLCC© system is more efficient than that in the standalone GLCC©, for the same flow conditions. Lowering the superficial gas velocity or increasing the superficial liquid velocity produce less stable foam, larger gas bubbles and lower half-life time. The outlet clear liquid flow rate (with no foam) under the LM operation increases with increasing superficial liquid velocity or decreasing superficial gas velocity. The recommended operational conditions for the CFC are at low superficial gas velocities, lower than the transition boundary to churn flow in the CFC.
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Oil-water dispersed flow, in which one of the phases either water or oil is dispersed into the other phase, which is the continuous phase, occurs commonly in Petroleum Industry during the production and transportation of crudes. Phase... more
Oil-water dispersed flow, in which one of the phases either water or oil is dispersed into the other phase, which is the continuous phase, occurs commonly in Petroleum Industry during the production and transportation of crudes. Phase inversion occurs when the dispersed phase grows into the continuous phase and the continuous phase becomes the dispersed phase caused by changes in the composition, interfacial properties and other factors. Production equipment, such as pumps and chokes, generate shear in oil-water mixture flow, which has a strong effect on phase inversion phenomena. In this study, based on the newly acquired data on a gear pump, the relationship between phase inversion region and shear intensity are discussed and the limitation of current phase inversion prediction model is presented.
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Research Interests:
Sand transport in multiphase flow has recently gained particular attention of many companies in oil and gas industry owing to unpleasant circumstances that particle deposition accompanying. The main objective of this study is to evaluate... more
Sand transport in multiphase flow has recently gained particular attention of many companies in oil and gas industry owing to unpleasant circumstances that particle deposition accompanying. The main objective of this study is to evaluate the performance of some existing models for the prediction of the critical sand deposition velocity under gas-liquid stratified flow against acquired experimental data. Experimental data are acquired under stratified flow regime with the air as gas phase, and the water as liquid phase. Spherical glass bead with three particle sizes of 70, 185 and 510 μm with concentrations less than 0.0045 vol/vol are utilized as solid phase. A horizontal 0.1 m ID test facility is designed and constructed in order to investigate the effects of parameters such as phase velocities, particle concentration and particle size on the critical sand deposition velocity. The acquired data are compared with previous models developed by Salama (1998), Stevenson and Thorpe (2002), Hill (2011), Ibarra et al. (2014) and Dabirian et al. (2017) to determine the most reliable model for the prediction of the critical sand deposition velocity. The experimental data show that depending on the particle size and concentration, the critical velocity can change either linearly or exponentially with particle concentration. The evaluation of the previous models with acquired experimental data confirm that Ibarra et al. (2014) and Dabirian et al. (2017) models generally show better performance for the predictions of the critical velocity. Models proposed by Salama (1998) and Hill (2011), respectively, under-predicts and over-predicts the critical velocities under various experimental conditions. Also, the comparison of Stevenson & Thorpe (2002) model and the experimental data corroborates that the model is not an accurate predictive tool for the critical velocity.
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Horizontal Pipe Separators (HPS©) are used for separation of oil from oil-water mixture. It can be an attractive alternative to the vessel type separator owing to its simplicity, ease of construction, installation and operation and its... more
Horizontal Pipe Separators (HPS©) are used for separation of oil from oil-water mixture. It can be an attractive alternative to the vessel type separator owing to its simplicity, ease of construction, installation and operation and its lower price. An experimental and theoretical investigation on the (HPS©) were conducted. New experimental data and mechanistic modeling are presented to show the effect of different variables such as mixture velocity and water cut on the performance of the separator. A HPS facility, consisting of a 0.0762 m ID 10.3 m long horizontal pipe has been designed and constructed. Five observation boxes are installed along the horizontal pipe to observe the development of the oil/dispersion and water/dispersion interfaces throughout the pipe. A wide range of experimental data was acquired for oil-water mixture flow behavior, and length of entry region for the oil and water separation in the Horizontal Pipe Separator was also investigated. A total of 34 runs were conducted for mixture velocities of 0.08, 0.13, 0.20 and 0.30 m/s with water cuts between 10 to 90%. The experimental data confirm that the higher the mixture velocity, the longer is the entry region required for separation. On the other hand, when increasing the water cut, the water separation is more efficient. Similarly, decreasing the watercut results in an easier separation of the oil phase. For low water cuts (10 to 30%) and higher mixture velocities (>0.3 m/s), no separation between the phases was observed. The Gassies (2008) model has been validated and improved for water continuous flow by developing correlations for two of the Gassies model's input variables, namely, the turbulent decay time and the oil volume fraction in the dense packed zone. For water continuous phase, the comparison between the improved model prediction and the experimental data shows very good agreement for the water/dispersion interface and also for the oil/dispersion interface at low mixture velocities.