Slug Flow Regime Research Articles

Elucidating flow-directed 98% CO2 absorption using millimeter-sized coiled flow inverters: Nanocellulose-aided sustainable scope

The Sustainable Development Goals (SDGs) adopted by the United Nations drive the global efforts to discover a sustainable carbon capture method for the reduction of anthropogenic CO2 emissions. Concentrated alkanolamine solutions are being used as CO2 capture mediums for batch processes amid several disadvantages, such as energy intensiveness and poor efficiency. In this work, millimeter-sized coiled flow inverters (CFI) have been explored as a point-source CO2 capture tool for highly efficient, continuous operations. Solvent and CO2 gas flow rates are found to dictate the slug flow regime and, more specfically, slug lengths. High interfacial area and residence time remain the driving factors for enhanced CO2 capture using CFI. About 98% CO2 absorption efficiency has been achieved for 3% aqueous diethanolamine solution in CFI . The efficacy of nanocellulose, a sustainable nanomaterial has been unearthed for CO2 capture at low flow rate.

Detection of Two-Phase Slug Flow Film Thickness by Ultrasonic Reflection

Slug flow is a common phenomenon in closed pipes, occurring in two-phase flow where liquid and gas phases mix, impacting the custody transfer or the efficiency of chemical reactions. This study aims to detect and analyze slug flow film thickness in two-phase flow, providing detailed structural flow information. The ultrasonic or Doppler reflection method is employed to identify slug flow and detect detailed thickness. Additionally, electrical resistance tomography (ERT) is used to image and confirm the presence of slug flow. A high-speed camera records the slug flow's shape in real time, validating its existence. The ultrasonic reflection method offers high accuracy, with a measurement error rate of less than 1% based on experimental results. The study uses a homogeneous block calibration method to measure slug flow thickness. Graphical results reveal clear differences between the slug flow regime, inner pipe wall, and outer pipe wall, with the first echo of slug flow being easily observable. The accuracy of results is attributed to the combination of FPGA (Field-Programmable-Gate-Array) instruments and measurement methods, showcasing the study's novel approach. This research introduces a new perspective or novelty on slug flow in multiphase flow studies, highlighting an innovative method for detecting film thickness.

Characterization of the oil water two phase flow in a novel microchannel contactor equipped with helical wire static mixer

This study investigates an oil/water two-phase system to assess the potential efficacy of a novel passive mixer in enhancing the liquid-liquid interfacial area within a micro-channel contactor. In this system, two fluids are introduced into a microchannel with a diameter of 800 μm and a length of 20 cm, which is equipped with a stainless-steel helical wire measuring 250 μm in diameter. Throughout the experiments, both fluids are supplied at equal flow rates, and the dominant forces, including attachment and detachment forces, are examined. The results reveal a critical Weber number of 3.8 × 10−³, at which the first detachment occurs. A comparison between microchannels with and without the passive micromixer demonstrates that greater slug breakup occurs in the system incorporating the helical wire micromixer. This innovative configuration results in a significant reduction in slug/droplet size compared to a microchannel without a barrier, decreasing from approximately 600 μm to 390 μm at a flow rate of 0.8 mL/min. Additionally, a flow map is presented, illustrating three distinct flow regimes: flow contains long slug, Slug-droplet flow, and droplet flow regimes, with the droplet flow regime covering the largest area. The findings indicate that the implementation of this innovative passive mixer substantially increases the interfacial area, providing significant advantages for mass transfer applications.

Advancing oil and gas pipeline monitoring with fast phase fraction sensor

Abstract In the oil and gas sector, the design of monitoring equipment usually prioritizes durability and long-term reliability. However, such equipment does not provide resolution for scientific research, where capturing transient and dynamic events is crucial to enhancing flow understanding. This work describes the development of a capacitive sensor system optimized for phase fraction measurements in oil-gas industrial environments. The sensor features high sensitivity and temporal resolution to meet flow measurement investigative requirements. The measurement technique is based on the electrical capacitance variations of the flowing media and was validated with reference equipment. Six sensors were deployed across multiple test stations to analyze the slug flow regime and its evolution along the pipe. The data collected from these experiments were processed, and flow parameters were compared with a model that describes the elongated bubble shape found in the slug flow pattern. Results show a good agreement between the experimental data and the model, validating its capability to track the fast-changing phases of multiphase flow. The uncertainty analysis revealed a maximum absolute uncertainty of 1.65% for the gas fraction measurements. Further, the gas flow rate was evaluated with a good agreement against the reference gas flow meter, ensuring the sensor's reliability in dynamic multiphase flow environments. By providing accurate experimental data from real-world industrial conditions, the developed sensor can significantly enhance the precision of flow models, thereby improving the understanding of complex flow phenomena.

Effect of high solids loading on gas–liquid mass transfer in an oscillatory flow reactor for process intensification

A wide range of chemical processes involves three phases, where common systems have inefficient mixing and mass transfer is limited. This study uses the oscillatory flow reactor with smooth periodic constrictions (OFR-SPC) according to the patent EP3057694 (B1) to evaluate its potential on O2 mass transfer at high solids loading (10–50 % (v/v)). For that, the effect of solids (EPS, PVC) properties (concentration, density, and size) on the performance of the volumetric liquid-side mass transfer coefficient (kLa), gas holdup (εG) and Sauter mean bubble diameter (d32) using several operational conditions (oscillation amplitude and frequency, superficial gas velocity) was assessed. Results show that oscillatory conditions can influence the solids effect on kLa. At solid load (≥ 30 % (v/v)) under low oscillations, kLa decreased, εG and d32 increased, slug flow regime emerged and the OFR-SPC behaved as fixed bed reactor. Contrary, no significant influence of solid properties on kLa, and εG was observed at higher oscillations, where the reactor behaved as fluidized bed in a homogeneous flow regime. Notably, solids’ concentration (<30 % (v/v)), size and density revealed a negligible influence on mass transfer for all range of oscillations, contrary to the widespread consensus where kLa tends to decrease in conventional reactors at lower solid’s load (<15 % (v/v)), making the OFR-SPC a valuable resource for catalytic processes. The OFR-SPC demonstrated higher mass transfer rates (∼3 − fold) than conventional multiphase devices with reasonable power consumption (∼100 W/m−3(−|-)). These are remarkable results, which indicate the OFR-SPC for three-phase industrial processes intensification.

One‐dimensional kinetic model with novel bubble size equation in molten‐metal bubble column reactors for CH4 pyrolysis

AbstractNon‐oxidative methane pyrolysis produces hydrogen and solid carbon without CO2 in molten‐metal bubble column reactors (MMBCRs). One‐dimensional MMBCR models, which involve bubble hydrodynamics, reactions, heat transfer, and axial dispersion, have been developed for reactor design; however, empirical equations of the mean bubble size derived from bench‐scale experiments have also been used for industrial‐scale MMBCRs. In this study, a novel bubble size equation based on dimensionless numbers was proposed for the bubbling, transient, and slugging flow regimes, which is applicable to both bench‐ and industrial‐scale reactors. Using the MMBCR model coupled with the new bubble size, reaction kinetic parameters were identified for four bench‐scale MMBCRs with Te‐based alloys in the bubbling flow regime. In four industrial‐scale MMBCRs at 980°C, belonging to the transient flow regime for an H2 production of 10,000 Nm3/h, the bubble size and methane conversion were approximately 40 mm and under 35%, respectively.

Experimental design and manufacturing of a smart control system for horizontal separator based on PID controller and integrated production model

During oil production, the reservoir pressure declines, causing changes in the hydrocarbon components. To ensure better separation of produced phases, separator dimensions should also be adjusted. It is not possible to change the dimensions of the separator during production. Therefore, to improve the separation of the phases, the level of the separator needs to be adjusted. An intelligent system is required to ensure that the liquid level is maintained at the desired level for optimal phase separation during changes in reservoir pressure. In this study, a novel correlation is presented to measure the desired liquid level using new separator pressures. For this purpose, an intelligent system was built in the laboratory and tested in different operational conditions. The intelligent system effectively maintained the desired liquid level of the separator through a new correlation technique. The system accomplished this by acquiring new separator pressure readings collected by installed sensors. This approach helped mitigate the negative effects of the slug flow regime and minimized issues such as foam formation and over-flushing of the separator. It could achieve a 99.1% separation efficiency between gas and liquid phases. This was possible during liquid and gas flow rates ranging from 0 to 2.35 and 8–17 m3/h, respectively. The system could operate under bubble, stratified, plug, and slug flow regimes. Then the intelligent model obtained from lab experiments was integrated into the production model for the southern Iranian oil field. The smart model increased oil production by 13% and prevented the separator from over-flushing in 840 days.

Investigation of the Static Pressure Drop and Production that Occurs due to Flow Patterns in a Perforated Horizontal Wellbore

This study examined the intricate interaction between flow patterns and production within a perforated horizontal wellbore. The study precisely assessed the behavior of static pressure drop by utilizing an array of flow regimes encompassing bubble, dispersed bubble, transitional bubble/slug, slug, stratified, transitional slug/stratified wave, and stratified wave. Remarkably, an upward trend in static pressure drop was observed with increasing water phase presence, while the converse was true for the air phase. Besides, the air phase superficial velocity exhibited a direct correlation with the magnitude of pressure drop fluctuations. The liquid production demonstrated a peak during bubble and slug flow regimes, followed by a descent during the transition to stratified and stratified wave flow. This decline can be attributed to mixing pressure drops localized during the perforations. Furthermore, an upward trend in average liquid production was observed with increasing mixture superficial velocity, primarily due to the dominant presence of the water phase. Additionally, the percentage of liquid production was positively associated with the water's superficial velocity when the air's superficial velocity was held constant. While the experimental and numerical results were in agreement for slugs and structured flows, there were discrepancies in the behavior of static pressure for bubbles, small bubbles, and structured waves.

Effect of slug characteristics on the nonlinear dynamic response of a long flexible fluid-conveying cylinder

Hydrocarbon flows in a marine riser may appear in multiple phases with varying flow patterns, among which, slug flows are known to exhibit complex flow characteristics due to fluctuations in multiphase mass, velocities, and pressure changes. Bulk of the literature concerning internal single and two-phase flow induced vibrations have largely focused on the use of a linearized tension beam model. In this study, the fluid-structure interaction phenomena of a submerged long flexible cylinder conveying two-phase slug flows is investigated taking into account the geometric and hydrodynamic nonlinearities. A semi-empirical theoretical model which consists of nonlinear structural equations of coupled out-of-plane, in-plane and axial structural motions is presented for the analysis and prediction of two-phase slug flow induced vibrations (SIV). The model includes equations involving centrifugal and Coriolis forces to capture mass variations in the slug flow regime. A numerical space-time finite difference approach combined with a frequency domain analysis is used for analyzing the highly nonlinear three-dimensional responses. The model assumes constant geometric properties across the span of the cylinder and utilizes an idealized slug unit concept, wherein slug properties are considered to be fully developed and undisturbed by pipe oscillations. Model validations are performed through comparisons with published experimental internal flow-induced vibration results. Parametric study captures the effects of several key slug characteristics on the vibration responses of a fluid-conveying cylinder. The results demonstrate amplitude-modulation response, mean displacements, three-dimensional cylinder displacements due to geometric nonlinear couplings and the influence of internal flow velocities. Higher dominant modes and oscillation frequencies were observed when the cylinder experiences large amplitude motions at specific slug formations. A new dimensionless parameter is introduced to predict scenarios of high amplitude oscillations for long flexible cylinders carrying two-phase slug flows.

Research on void drift between rod bundle subchannels

Void drift between subchannels in a rod bundle is a crucial phenomenon affecting the calculation accuracy of thermal-hydraulic parameters in SMRs. It holds significant importance in enhancing the precision of safety analysis for SMRs. Existing research on experiment and model of void drift between rod bundle subchannels is relatively rare, and the accuracy of model calculations requires improvement. In this study, experiments on gas-liquid two-phase non-equilibrium flow were conducted to measure the redistribution of two-phase flow induced by void drift in a 1 × 2 rod bundle. The experiment results indicated that in bubby flow regime with void fraction less than 0.3, the void diffusion coefficient showed little variation with changes in void fraction. However, in slug flow and annular flow regimes with void fraction exceeding 0.3, the void diffusion coefficient significantly increased with an increase in void fraction. Furthermore, a new void drift model was developed and validated based on a subchannel code. The overall predicted uncertainty for the outlet void fraction in the rod bundle benchmark was less than 13%.

Influence of slug flow on sand dune transport in a 3.6° upward inclined pipeline

AbstractThis study presents an experimental investigation of sand conveying from a stationary flatbed through two‐phase liquid–gas flows as a function of the fluids flow rates and pipeline orientation (α = 0°, and α = +3.6°). The characteristics of sand particle transportation by saltation, sand dune formation process and morphologies are visualized using a transparent cylindrical acrylic pipeline and digital photography. It was observed that slug flow regime was the dominant mechanism to lift the sand particles for both horizontal and upward inclinations. It was also found that sand dunes deconstructed more quickly at an upward inclination than horizontal position. For the upward inclination, the conveying phenomenon is characterized by sand bed lifting, suspension, and backward entrainment below the air bubble in the water film. Due to the increased liquid flow rates, higher dune velocity is recorded for the inclined condition. The dune pitch length grew for the horizontal configuration after the transient phase, as a result of the gravitational force effect, while it remained constant for the inclined orientation. In both conditions the slip face angle decreased with time; however, for the inclined configuration, this angle was lower because of the higher upstream liquid flow rate. These results provide important insights into the effect of pipe inclination on bed‐load mode solid transport by two‐phase flow inside a closed circular conduit. The obtained experimental data can be used to validate future numerical investigations.

CO2 capture using gas-lift pumps operating under two-phase flow conditions

CO2 capture through dissolution in water offers environmental benefits and industry applications. However, current studies mostly focus on CO2 extraction into solvents, overlooking its direct solubility in water. Alternatively, gas-lift pumps may hold significant potential for capturing and storing CO2 in water; but this ability remains unexplored. Therefore, this study experimentally delves into the CO2 capture capacity and hydraulic performance of a dual injection gas-lift pump with a 25.4 mm riser diameter. Operating at a constant submergence ratio of 70 %, the pump is fed with simulated flue gas with flow rates within 5–30 LPM at volumetric CO2 concentrations of 10 %, 15 %, and 25 %, and temperatures of 22 °C (isothermal operation) and 110 °C (non-isothermal operation). Two-phase flow hydrodynamics is also evaluated using high-speed imaging in conjunction with time-series void fraction measurements. Within the riser pipe, three distinct two-phase flow patterns — slug, intermittent, and churn flows — are identified. The results reveal that under both isothermal and non-isothermal operations and across all volumetric CO2 concentration levels, churn flow demonstrates superior mass transfer coefficient and lifted liquid flow rate, while slug flow achieves minimum energy consumption per ton of captured CO2, highest CO2 capture degree, and maximum lifting efficiency. Also, the highest degrees of sensitivity to inlet gas flow rate for volumetric mass transfer coefficient, delivered liquid flow rate, and void fraction were observed in slug flow regime. Both gas temperature and volumetric CO2 concentration positively impacted the mass transfer performance. However, the pump showed remarkably higher lifting efficiencies under isothermal operation conditions. Moreover, compared to four established CO2 capture methods (absorption, adsorption, cryogenic distillation, and membrane diffusion), the gas-lift pump exhibits moderately lower energy consumption, at 38-266 kWh/tonCO2, but with lower CO2 capture degree of 2.3 % to 6.7 %.

A novel recurrence-based approach for investigating multiphase flow dynamics in bubble column reactors.

In chemical industries, multiphase flows in a bubble column reactor are frequently observed. The nonlinearity associated with bubble hydrodynamics, such as bubble-bubble and bubble-liquid interactions, gives rise to complex spatiotemporal patterns with increased gas or liquid velocities, which are extremely difficult to model and predict. In the current study, we propose a new, computationally efficient recurrence-based approach involving the angular separation between suitably defined state vectors and implement it on the experimental multiphase flow variables. The experimental dataset that consists of image frames obtained using a high-speed imaging system is generated by varying air and water flow rates in a bubble column reactor setup. The recurrence plots using the new approach are compared with those derived from conventional recurrence, considering standard benchmark problems. Further, using the recurrence plots and recurrence quantification from the new recurrence methodology, we discover a transition from a high recurrence state to a complex regime with very low recurrence for an increase in airflow rate. Determinism exhibits a rise for the decrease in airflow rate. A sharp decline in determinism and laminarity, signifying the quick shift to complex dynamics, is more prominent for spatial recurrence than temporal recurrence, indicating that the rise in airflow rate significantly impacts the spatial location of bubbles. We identify three regimes that appeared as distinct clusters in the determinism-laminarity plane. The bubbly regime, characterized by high values of determinism and laminarity, is separated by an intermediate regime from the slug flow regime, which has low determinism and laminarity.

MODELING OF TWO-PHASE GAS-LIQUID SLUG FLOWS IN MICROCHANNELS

Even though numerical simulation of two-phase flows in microchannels has been attempted by many investigators, most efforts seem to have failed in correctly capturing the flow physics, especially the slug-flow regime characteristics. The presence of a thin liquid film in the order of 10 &amp;mu;m around the bubble (sometimes called gas pocket or gas slug) may be a contributing factor to the above difficulty. Typically, liquid films have a significant effect on the flow field. Thus, there is a strong motivation to employ numerical simulation methods to avoid some of the experimental difficulties. In this paper, the characteristics of two-phase slug flows in microchannels are calculated with the help of the volume-of-fluid (VOF) method. Formation of the slugs for different superficial velocities, capillary numbers, and gas volume fractions are investigated. The minimum mesh resolution required to capture the liquid film surrounding the gas bubble is reported employing a dynamic mesh adaptation methodology with interface tracking. Results are shown to be in good agreement with experimental data and empirical correlations.

Multiphase Flow Behavior Prediction and Optimal Correlation Selection for Vertical Lift Performance in Faihaa Oil Field, Iraq

In the petroleum industry, multiphase flow dynamics within the tubing string have gained significant attention due to associated challenges. Accurately predicting pressure drops and wellbore pressures is crucial for the effective modeling of vertical lift performance (VLP). This study focuses on predicting the multiphase flow behavior in four wells located in the Faihaa oil field in southern Iraq, utilizing PIPESIM software. The process of selecting the most appropriate multiphase correlation was performed by utilizing production test data to construct a comprehensive survey data catalog. Subsequently, the results were compared with the correlations available within the PIPESIM software. The outcomes reveal that the Hagedorn and Brown (HB) correlation provides the most accurate correlation for calculating pressure in FH-1 and FH-3 while the Beggs and Brill original (BBO) correlation proves to be the optimal fit for wells FH-2 and Gomez mechanistic model for FH-4. These correlations show the lowest root mean square (RMS) values of 11.5, 7.56, 8.889, and 6.622 for the four wells, respectively, accompanied by the lowest error ratios of 0.00692%, 0.00033%, 0.00787%, and 0.0011%, respectively. Conversely, Beggs and Brill original (BBO) correlation yields less accurate results in predicting pressure drop for FH-1 compared with other correlations. Similarly, correlations, such as Orkiszewski for FH-2, Duns and Ros for FH-3, and ANSARI for FH-4, also display less accuracy level. Notably, the study also identifies that single-phase flow dominates within the tubing string until a depth of 6000 feet in most wells, beyond which slug flow emerges, introducing significant production challenges. As a result, the study recommends carefully selecting optimal operational conditions encompassing variables such as wellhead pressure, tubing dimensions, and other pertinent parameters. This approach is crucial to prevent the onset of slug flow regime and thus mitigate associated production challenges.

Numerical simulation of two-phase slug flows in horizontal pipelines: A 3-D smoothed particle hydrodynamics application

A fundamental difficulty of studying gas–liquid pipe flows is the prediction of the occurrence and characteristics of the slug flow regime, which plays a crucial role in the safety design of oil pipelines. Current empirical methods and one-dimensional computational models only achieve limited success. While 3-D numerical simulations are highly recommended, they have been very seldom used. We perform 3-D Lagrangian numerical simulations of gas–liquid pipe flows by adapting an existing multi-phase smoothed particle hydrodynamics (SPH) method based on a Riemann solver to achieve an efficient solver. To realize the high inlet velocities of gas and liquid an in- and outlet boundary condition is presented. The results are validated against existing experimental data, numerical simulations and analytical solutions. Multiple gas–liquid pipe flow patterns are predicted, namely, smooth stratified, stratified wavy, bubble flow, slug flow and bubble flow. Several principle characteristics of slug flows, e.g., pressure gradient, slug development and slug frequency are analyzed in a 3-D fully Lagrangian framework.

Understanding differential microemulsion polymerization in continuous slug flow through kinetic Monte Carlo simulation

Microreactors have been universal in polymerization and will help mitigate the residence time distribution and viscosity if conducted in a slug flow regime. The numerical simulation of this practice remains uncharted. Herein, based on our previous study, we proposed a kinetic Monte Carlo algorithm to describe the differential microemulsion polymerization in a biphasic slug flow. Propelled by an automatically spaced refreshment method and other accelerating approaches, the performance of the algorithm was boosted by over forty times. The sensitivity to the model-fitting parameters was analyzed to help understand the underlying mechanisms. After a thorough investigation on the effects of miscellaneous operating conditions regulatable in the continuous slug flow regime, the feasibility of product customization was demonstrated with case studies. Bridging the studies upon kinetics of microemulsion polymerization and interphase mass transfer in microreactors, this work should be able to provide deeper understanding of the process and guide the actual operation.

Correction: Experimental and numerical study of forced convection heat transfer in a upward two-phase flow of air–water/SiO2 nanofluid with slug flow regime

Correction: Experimental and numerical study of forced convection heat transfer in a upward two-phase flow of air–water/SiO2 nanofluid with slug flow regime

Effect of flow direction on evaporation flow regime of R32/R1234ze(E) mixture inside multiple rectangular minichannels

This study visualized the evaporation flow regime of a non-azeotropic mixture R32/R1234ze(E) inside multiple vertical-upward and horizontal rectangular minichannels with a hydraulic diameter of 2 mm. The effects of the mass flux, vapor quality, heat flux, flow direction, and test refrigerant on the flow regime characteristics were explored. The flow regimes of the mixture were compared to those of R1234ze(E). The effect of flow direction on the flow regime was examined under low mass flux conditions. In the vertical-upward flow, three flow regimes: slug, slug-annular, and annular flow regimes were observed. The flow regime transition boundary of R1234ze(E) shifted to lower mass flux and vapor quality conditions compared to the mixture because of the higher vapor velocity of R1234ze(E). Boiling bubbles were generated in the liquid slug and channel corners around the vapor plug, and the number of boiling bubbles increased with an increasing heat flux. The size of the boiling bubble of the mixture was smaller than that of R1234ze(E), which is attributed to the mass transfer resistance of the non-azeotropic mixture. Only in the vertical-upward flow, the reverse flow was observed in some channels, where the slug flow was observed, because of the effect of gravity. The number of channels with reverse flow decreased with increasing vapor velocity. The annular flow did not appear in the horizontal flow, and the flow regime was observed only in two regimes: slug and slug-annular flow regimes. No difference in flow regime transition boundary between R1234ze(E) and R32/R1234ze(E) was observed.

Intensification of extractive desulfurization in micro-channels using triethylamine/propionic acid as deep eutectic solvent

In this study, the extractive desulfurization from the model fuel was investigated in different micro-channels using triethylamine/propionic acid with the molar ratio of 1 to 3 ([TEA:3Pr]) as DES. In this regard, the effect of operating parameters (i.e., extraction time, temperature, and fuel to DES volume ratio) and micro-channel geometrical parameters (i.e., the diameter of the micro-channel, and length of the micro-channel) on the sulfur removal and volumetric mass transfer coefficient was investigated. Moreover, the effect multiple extractive desulfurization cycles, regeneration of spent [TEA:3Pr] has been also investigated. It was found that the best geometry for the micro-channel is 0.6 mm in the diameter and 20 cm in length considering the sulfur removal and mass transfer. The slug and throat-annular flow regimes were observed in the different micro-channels through two-phase flow visualization. The achieved sulfur removal was 70.8%, 68.7%, and 44.4% from the model fuels containing dibenzothiophene (DBT), benzothiophene (BT), and thiophene (Th) in a very short residence time of 17 s, respectively. The overall volumetric mass transfer coefficient in the micro-channel was 0.679 s−1 in the fuel to DES volume ratio of 5. It was also found that deep sulfur removal can be achieved using multiple-extraction cycles.