Slug Flow Pattern Research Articles

Recurrence analysis of pressure signals for identification of intermittent flow sub-regimes

Recurrence analysis of pressure signals measured from the pipe wall simultaneously with flow visualization is used to depict a methodology for identifying intermittent flow sub-regimes through opaque pipes. Pressure signal alone is not sufficient to differentiate two-phase flow regimes in an opaque pipe. Hence, the phase space trajectory of pressure signals is used to develop a recurrence plot for each sub-regime. It is observed that a homogeneously dispersed type of recurrence plot is obtained for plug flow which changes to a checkerboard-like structure for the slug flow pattern. This depicts the chaotic nature of slug flow. The chaos increases with further increase in gas superficial Reynolds number when aeration in slug flow enhances, leading to highly aerated slug flow. It is established that the recurrence plot and recurrence quantification parameters change as the flow transits from plug to less aerated slug and highly aerated slug regime. Thus the recurrence analysis of pressure signals has shown potentials to be used as a technique to identify different intermittent flow sub-regimes. • Recurrence analysis for predicting intermittent flow sub-regimes through petroleum pipes. • Pressure signals are measured simultaneously with flow visualization. • Recurrence analysis of pressure signals is used to identify intermittent flow sub-regimes. • Homogeneous type of recurrence plot for plug flow while rectangular structure for slug flow. • Rectangles formed checkerboard configuration depicting the chaotic nature of slug flow.

A Review on the Hydrodynamics of the Liquid–Liquid Two-Phase Flow in the Microchannels

The ability of small and microchannels to enhance mass transfer, reduce diffusional limitations, and create a safer process has made them the best choice for process intensification. This study provides a review of the available experimental and computational literature on the hydrodynamics of liquid–liquid two-phase flow in microscale, namely, flow regimes, pressure drop, and flow structure. When two immiscible liquids flow in small channels, various flow patterns can be observed, with the development of those patterns being influenced by several parameters, such as the geometry of the mixing junction and channel, the channel material, the fluids properties, and the orientation of the flow. As part of the flow patterns observations and measurement, the velocity fields and internal circulation reported in the literature were reviewed in the context of the microparticle velocimetry (μPIV) implementation. Also, relevant to our study is the literature outlining, pressure drop, and the available models that have been used to predict it. These models are discussed in detail with special reference to flow patterns and fluids viscosities. Moreover, the numerical studies results using computational fluid dynamics (CFD) have also been reviewed and discussed, in terms of the validity of the simulation and the different parameters affecting slug formation and flow patterns. Each section of the discussion also points out the gaps in the research and proposes future work that could further develop the technology under a review of liquid–liquid two-phase flow in microchannels.

Liquid–Liquid Microfluidic Flows for Ultrafast 5-Hydroxymethyl Furfural Extraction

We study the effects of liquid–liquid flow patterns on the extraction of 5-hydroxymethyl furfural from the aqueous phase into an organic phase (methyl isobutyl ketone, ethyl acetate, and 2-pentanol) at ultrashort residence times of 0.2–20 s in a coiled capillary microchannel. Slug, droplet, slug-droplet, dispersed, parallel, annular, and irregular two-phase flow patterns are generated. We evaluate the extraction efficiency and the volumetric mass transfer coefficient via experiments and computational fluid dynamics (CFD). The CFD predictions are in quantitative agreement with the experimental data. The convective and diffusive contributions to the mass transfer of different flow patterns are analyzed. For all solvent pairs, the extraction efficiency varies irregularly with increasing flow rate due to changes in the mass transfer mechanism caused by a transition between flow regimes. Overall, we demonstrate >90% extraction efficiencies with high volumetric mass transfer coefficients ranging from 0.006 to 2.17 s–1. Furthermore, a merit index is defined to assess the trade-off between the fast mass transfer and the pressure drop in biphasic microchannels. In general, the mass transfer rate increases significantly at high flow rates at the expense of a high-pressure drop. The ethyl acetate/water irregular flow pattern is optimal due to a large throughput, extraction efficiency, and mass transfer coefficient, with a minimal pressure drop.

Flow induced vibration of two-phase flow passing through orifices under slug pattern conditions

Flow restricting orifices are important components for flow and pressure control in the oil, gas, and power generation industries. In many situations, the piping systems are operating under two-phase flow conditions. These orifices affect the redistribution of the two phases and induce vibrations in the piping structures. These vibrations often occur during a slug flow pattern and can severely affect the integrity of a structure; therefore, in the present work, both the vibrations of the piping structure and the characteristics of the two-phase flow dynamics are experimentally investigated in the presence of an orifice. In this study, an air–water​ two-phase flow mixture was utilized at different superficial velocities ranging from 0.12 m/s to 1.7 m/s for air and 0.46 m/s to 1.3 m/s for water. Synchronized flow visualization images, along with local void fraction and vibration measurements, were used to evaluate the response of the structure as the slug flow passed through the orifices. Detailed instantaneous local void fraction measurements were carried out to understand the underlying physics of the phenomenon and their effect on the vibration response of the structure. The results showed that not all slug flow cases excited the piping at the slug frequency. The amplitude of vibration around the slug frequency was found to increase as the superficial velocity of the gas phase increased.

Experimental Investigation of Two-Phase Flow Patterns in a Vertical to Horizontal Bend Pipe Using Wire-Mesh Sensor

The air-water two-phase flow plays an important role in many applications of industry fields. Usually, a 90-degree bend is used to connect pipes for changing the direction of flow which influences the two-phase flow pattern. In this paper, the effect of 90-degree bend under different ranges of gas and liquid superficial velocities on the two-phase flow patterns in the horizontal pipe located after the bend was experimentally investigated, and then results were presented and compared in a two-phase flow pattern map. Also, tomographic images and probability density functions were used to capture the cross-section void fraction and its distribution for the two-phase flow patterns. The results revealed that at low liquid and gas flow rates, a stratified-wavy flow pattern was observed as a dominant flow pattern. While the wavy-annular and semiannular flow patterns were observed at a high range of gas flow rates in the horizontal pipe. The results also showed that at the high range of liquid flow rate, bubbly, plug, slug, stratified-wavy, and wavy-annular flow patterns were observed in the horizontal pipe when the gas flow increased. The tomographic images and probability density functions gave good agreement with the experimental observations and results.

A numerical investigation on a capsule-intake of the electrical submersible pump in skid

The Electrical Submersible Pumping (ESP) system is one of the most commonly used artificial lift methods in the petroleum industry and one recent breakthrough in this system is enclosed in a capsule and positioned on the seabed in a skid. As it is a recent technology, with only a small amount of equipment currently in operation, there is a clear need for a greater understanding of the flow within this geometry with the objective of perfecting the design of this promising submarine boosting system. This paper presents a numerical investigation of single-phase flow within the scaled capsule-intake of an ESP system in the Skid considering a model with geometric and dynamic similarities in relation to a real equipment in operation in the Espadarte field, located in the Campos Basin, Brazil. The tridimensional and transient simulation for a case for one mass flow rate and inclination angles are investigated. While neglecting the effects of the diffuser and impeller in the system, the flow field features, axial and radial velocity profiles in the intake region were computed. The numerical results show that the flow in the intake region is dominated by the secondary flow, leading to the formation of bathtub vortex. It is expected that the vortices influence the flow pattern in the intake region, breaking the larger bubbles into smaller bubbles, making the transition from the slug flow pattern to the dispersed bubbles or bubbly pattern in which it would be more difficult to be dragged into the intake.

Pengaruh Liquid Hold-Up terhadap Transisi Pola Aliran 2 Fasa Air-Udara dari Stratified Ke Slug pada Pipa 50 mm

The slug flow pattern is one of the most avoiding factors in piping systems due to its destructive characteristics. Research on the criteria of the slug formation is still the concern. The present study focused on finding out the influence of liquid hold-up toward the transition of the flow pattern from stratified to slug pattern. It was conducted on a 50 mm-diameter horizontal acrylic pipe. The visual data was obtained from a fully developed area (180-210 D) by variations of liquid superficial rate (JL) of 0,03-0,3 m/s and gas superficial rate (JG) from 0,7 to 3,77 m/s. The high-speed camera with 2000 fps recording speed was the instrument to obtain the visual data. The measurement of the liquid hold-up is made by Constant Electric Current Method (CECM). The drastic decrement of liquid hold-up value on the wave growth mechanism (JG ≤ 1,88 m/s) indicated the changes in flow patterns from the stratified to the slug pattern, while on the wave coalescence mechanism (JG > 1,88 m/s) the liquid hold-up remains increases. The pattern change from pseudo slug to the slug pattern was not decreasing on its film thickness, yet, it tends to increase the frequency and the liquid slug length.

Identification of coherent structures in horizontal slug flow

Multiphase flow measurement devices are significantly affected by the flow pattern, such as, e.g., slug flow, leading to large uncertainties. In this context, the slug flow pattern in horizontal pipes is investigated with the aim of finding a statistical characterization of the structures in space and time. For this, two different instances of slug flow are analyzed with a snapshot proper orthogonal decomposition and an additional mode coupling algorithm, which provides an energy-ranked mode basis of the underlying coherent structures. For the considered flows, the most energetic mode pair has been identified with the corresponding slugging structures. Thereby, the temporal and spatial information of these mode pairs enables a statistical characterization of the slugs. In this context, a length scale, a dominant frequency, and an energy representation of the slugging structures are obtained from this method.

Characteristics of horizontal gas-liquid two-phase flow measurement in a medium-sized pipe using gamma densitometry

Two-phase flows are common occurrences in many industrial applications. The understanding of their characteristics in industrial piping systems is vital for the efficient design, optimization, and operation of industrial processes. Most of the previous experimental studies involving the use of gamma densitometers for holdup measurements in air-water mixtures are limited to smaller diameter pipes (generally regarded as those with < 50 mm in nominal diameter). Further, very few literature report experimental data obtained using gamma desitometers. This paper presents an application of a gamma densitometer in the measurement of two-phase flow characteristics in an intermediate diameter pipe (nominal diameter between 50 mm and 100 mm). Scaled air-water experiments were performed in a 17-m long, 0.0764-m internal diameter horizontal pipe. Liquid superficial velocity ranged between 0.1–0.4 m/s while gas superficial velocity ranged from 0.3 to 10.0 m/s. The measured parameters include liquid holdup, pressure gradient, flow pattern, and slug flow features. The flow patterns observed were stratified, stratified-wavy, plug, slug, and annular flows. Plug and slug flow patterns showed good agreement with established flow pattern maps. Furthermore, the slug translational velocity was observed to increase with increasing mixture velocity, as reported by previous authors, hence establishing the reliability of the instrumentation employed. The slug body length was also measured using the gamma densitometer and was found to be within the range 24–36D with a mean length of 30.6D.

Experimental study of the flow structure around Taylor bubbles in the presence of dispersed bubbles

This work presents an experimental study focusing on the interactions between the dispersed and Taylor bubbles in a slug flow pattern. In order to better investigate these interactions, a quasi-real slug flow was studied, where a single Taylor bubble is injected in a bubbly flow background stream, under controlled and repeatable conditions, controlling the bubbly flow superficial gas and liquid velocity, and also the Taylor bubble length. In this way, ensemble averaged results can be obtained over several Taylor bubbles. The flow was analyzed through the laser diode photocell, high-speed camera imaging and PIV techniques. Results revealed that the terminal Taylor bubble velocity is affected by the gas volume fraction of the bubbly background flow. Ensemble average velocity profiles are presented for Taylor bubble nose and tail regions. Since the experimental apparatus used in the present work allowed a large number of instantaneous PIV acquisitions, the turbulent statistics around the Taylor bubble can also be calculated. These experimental results can be used for the implementation and validation of multidimensional CFD models for flows with different interface length scales.

Effect of flow patterns on bovine serum albumin and ampicillin partitioning using aqueous two-phase systems in microdevice

The separation and purification of biomolecules via aqueous two-phase extraction (ATPE) has encountered a series of obstacles to its industrial implementation. Recently, the miniaturization of ATPE has attracted interest due to the increase of performance, the possibility of operating in a continuous mode, and easy to scale-up by numbering-up approach. However, there is a gap in the literature with regard to the effects of flow patterns on the partitioning of biomolecules using microdevices. Thus, the present study investigated the ATPE of bovine serum albumin (BSA) and ampicillin, a beta-lactam antibiotic, under different flow patterns (slug, droplet and parallel) by means of microdevices. The microdevices were manufactured with circular tubes in a senoidal shape and the ATPE were prepared from the mixture between aqueous solutions of polyethylene glycol (PEG) and dibasic potassium phosphate. Using 1.80 mm tubes, slug, droplet and parallel flow patterns were observed only in the PEG 1500/dibasic potassium phosphate system, while the parallel flow pattern was not stabilized in systems involving PEG 4000 and PEG 6000. Experiments using a droplet flow pattern showed higher values of recovery (56% after 10 min) and partition coefficient of BSA compared to the slug and parallel flow patterns. In experiments involving ampicillin, the extraction performance was practically independent of the flow patterns. The BSA recovery behaved as an inverse function of the diameter tubes, which achieved slightly superior performance than the batch experiment (67% after 10 min) using droplet flow pattern, 0.51 mm tubes and residence time of 10 min (69%).

Statistical features of the flow evolution in horizontal liquid-gas slug flow

The occurrence of the slug flow pattern is frequently detected in the petroleum industry. Theoretical and experimental works on the complex behaviour of this flow pattern are abundantly found, and their aim is to advance the state-of-the-technique on the behaviour of this kind of flow. The goal of the present work is to provide experimental data collected in five probing stations with resistive sensors mounted on a horizontal air–water slug flow in a 25.8-mm ID pipe. A signal processing technique provides the translational velocities, frequencies and void fractions that arise from different gas and liquid volumetric flow rates. Based on the obtained results, the effects of the liquid and gas superficial velocities were correlated with the probability density functions (PDFs) of the parameters variations observed in the slug flow development along the pipe. A quantitative criteria based on maximum likelihood estimates is used to determine the Weibull distribution for the translational velocity and the lognormal distribution type for the slug frequency distribution type.

Two-phase flow regimes of refrigerant R134a in an oscillating horizontal rectangular minichannel conduit

ABSTRACT In this study, refrigerant R134a experiments were carried out to observe two-phase flow in an oscillating horizontal rectangular minichannel conduit at refrigerant mass flux of approximately 30 kg•m − 2•s − 1 to 300 kg•m − 2•s − 1, saturation temperature of approximately 30 °C, and average vapor quality in the test section inlet of approximately 0.05 to 0.9. The test section was made from quartz and consists of a visible rectangular minichannel with a hydraulic diameter of 0.84 mm. The test section was oscillated vertically using a reciprocating motor. The effects of oscillation on slug and stratified flow patterns were investigated. The experimental observation was compared with an existing flow pattern map. The thin liquid film around the vapor of slug flow mostly moved up and down when the test section oscillated. As a result, a dry surface was not observed around the vapor due to the lower heat transfer coefficient. When the test section oscillated, the stratified flow changed to annular flow, and a dry surface was also not observed on the upper side of the minichannel conduit.

Capillary microbioreactors for VOC vapor treatment: Impacts of operating conditions

Micro-capillary bioreactors (1 mm ID, 10 cm long) were investigated for the biodegradation of toluene vapors as a model volatile organic compound (VOC). The intended application is the removal of VOCs from indoor air, when such microbioreactor is coupled with a microconcentrator that intermittently delivers high concentrations of VOCs to the bioreactor for effective treatment. The effects of key operating conditions were investigated. Specifically, gas film and liquid film mass transfer coefficients were determined for different gas and liquid velocities. Both mass transfer coefficients increased with gas or liquid velocity, respectively, and the overall gas-liquid mass transfer was dominated by the liquid-side resistance. Experiments with the microbioreactors focused on the effects of gas velocity, liquid velocity and mineral medium renewal rate on the treatment of toluene vapors at different inlet concentrations. The best performance in terms of toluene removal and mineralization to CO2 was obtained when the gas and liquid velocity ratio was close to one and achieving Taylor or slug flow pattern. Sustained treatment over extended periods of time with toluene elimination capacities ranging from 4000 to over 9000 g m−3 h−1 were obtained, which is orders of magnitude greater than conventional biofilters and biotrickling filters. Biological limitations generally played a more important role than mass transfer limitation. Continuous mineral medium supply at a high rate (10 h liquid retention time) enabled pH control and provided ample nutrient supply and therefore resulted in better toluene elimination and mineralization. Overall, these studies helped select the most suitable conditions for high performance and sustained operation.

Flow pattern classification in water-air vertical flows using a single ultrasonic transducer

Researchers around the world have proposed different methodologies for flow-pattern identification in multiphase flows. The most common explored techniques are based on optical imaging, pressure fluctuation, electrical impedance, radiation absorption, and ultrasound. Because the ultrasonic technique is relatively low in cost, easy to conduct, accurate, nonintrusive, and suitable for opaque systems, this paper presents a flow-pattern classifier based on ultrasound for two-phase vertical water–air flows. It is based on the coefficient of variation of the energy of the pulses reflected by the dispersed phase. Also, it uses just one ultrasonic transducer. An experimental plant was built to develop two-phase water–air flows to evaluate the proposed technique performance by comparing it to the visual analysis of the recorded image of the flow. A total of 102 different experimental points were collected and evaluated. The results have shown that the method was capable to distinguish dispersed bubbles, slug and churn flow patterns.

Effect of slug flow pattern on supercritical extraction of phenolic compounds from aqueous solutions

This study mainly aims to correlate the effect of high-pressure CO2−Water slug flow formed by microfluidic mixing on the extraction of phenolic compounds (gallic acid, protocetechuic acid, cafeic acid, syringic acid, ferulic acid, and benzoic acid) from its multi-component aqueous solutions. Both slug flow observation and extraction performances were experimentally conducted at different CO2 flow rates (100–650) ml min−1, temperatures (25–60) oC, and pressures (8.0–20.0) MPa. The slug flow patterns are affected by all CO2 flow rates, temperatures, and pressures. The slug flow patterns have a strong correlation with the extraction efficiencies of phenolic compounds from the aqueous solutions. Using slug flow process, benzoic acid can be completely purified from the multi-component aqueous solutions by supercritical CO2 extraction.

Evaluating the two-phase flow development through orifices using a synchronised multi-channel void fraction sensor

Understating two-phase flow through flow restricting orifices is critical in evaluating the piping degradation mechanisms in nuclear power generation systems. Characterizing the instantaneous changes of the two-phase local parameters across flow restricting orifices is critical in evaluating the piping structure dynamics. A multi-channel void fraction sensor was developed to investigate the effect of flow restricting orifices on flow pattern development in a 25.4 mm horizontal pipe. Instantaneous void fraction measurements were obtained at multiple locations upstream and downstream of the flow restricting orifices with area ratios of 0.062, 0.14, 0.25, and 0.56. Additionally, pressure measurements and flow visualizations were carried out to investigate the dynamics flow characteristics through the orifice. A liquid superficial velocity of 0.526, and 1.08 m/s and a gas superficial velocity ranging from 0.164 to 2.795 m/s were selected to represent the intermittent flow pattern. The results revealed that as the gas superficial velocity increased, the flow pattern downstream of the restriction changed to dispersed bubbly, or liquid jet and annular-dispersed liquid for an intermittent flow upstream of the orifice. The flow pattern development along the test section was affected significantly in the region close to the orifice, especially at a lower area ratio. Analysis of statistical characteristics of the slug flow pattern such as slug velocity, elongated bubble length and slug frequency were determined from the void fraction data and presented. The slug velocity upstream of the orifice decreased non-linearly as the area of the flow restriction decreased for the same flow condition upstream. The pressure variations along the pipe for different two-phase flow conditions across the orifices were obtained and different correlations to predict pressure drop across the orifices were evaluated. The Simpson et al. [1] correlation was the best as it predicted 93% of the experimental data with a 25% error.

Flow Regime, Slug Frequency and Wavelet Analysis of Air/Newtonian and Air/non-Newtonian Two-Phase Flow

This study focused on gas/Newtonian and gas/non-Newtonian two-phase horizontal fluid flow behavior by analyzing their flow regime identification and flow structural analysis on a horizontal flow loop apparatus. This involved the recognition of two-phase flow regimes for this flow loop and validation with existing flow maps in the literature. In addition, the study included flow pattern identification via wavelet analysis for gas/Newtonian and gas/non-Newtonian two-phase fluid flow in a horizontal flow loop apparatus. Furthermore, the study was extended to the detailed examination of slug frequency in the presence of air/Newtonian and air/non-Newtonian fluid flow, and the predicted slug frequency model was applied to the studied systems. The obtained results suggest that the flow regime maps and slug frequency analysis have a significant impact. The obtained pressure sensor results indicate that the experimental setup could not provide high-frequency and high-resolution data; nevertheless, wavelet decomposition and wavelet norm entropy were calculated. It offered recognizable flow characteristics for bubble, bubble-elongated bubble, and slug flow patterns. Therefore, this study can provide deep insight into intricate multiphase flow patterns, and the wavelet could potentially be applied for flow analysis in oil and gas pipelines.

A case study on internal flow patterns of the two-phase closed thermosyphon (TPCT)

This study investigates types of two-phase flow patterns that affect the heat transfer rate which occurs within the two - phase closed thermosyphon (TPCT) made of heat-resistant glass tube with inner diameters of 7 and 25.2 mm. Aspect ratio was 5 while the inclination angels were 0°, 80° and 90°, and the evaporator temperature were 50, 70 and 90 °C. Furthermore, the addition rate of chemical reactants was 50% by volume of the evaporator component whilst the water temperature within the condensation unit was maintained at 20 °C. From the experimental results, the TPCT's inner diameter was 7 mm, the inclination angels were at 80° and 90°. There were four types of flow pattern including; bubble flow pattern, slug flow pattern, churn flow pattern and annular flow pattern. Churn flow pattern and the annular flow pattern affected the heat transfer rate of the TPCT with the inner diameter of 7 mm at the inclination angels of 80 and 90° respectively. As for the TPCT test, the inner diameter of 25.2 mm with the inclination angels of 80° resulted in four types of the flow patterns, including the bubble flow pattern, slug flow pattern, churn flow pattern and stratified flow pattern respectively. According to the results, churn and stratified flow patterns, were the types of flow that affected the heat transfer rate. According to the experiment of TPCT with inner diameter of 25.2 mm at the inclination angels of 90°, four flow patterns including the bubble pattern, slug flow pattern, churn flow pattern and the vortex flow pattern were found. The vertex flow pattern was initiated when the temperature of the evaporator section was raised from 70 to 90 °C. According to this experiment, the churn flow and the vortex flow patterns were able to affect the heat transfer rates. Furthermore, the experiment revealed that heat flux that was obtained from the experiments of TPCT with the inner diameter of 7 and 25.2 mm showed the highest heat transfer rate at evaporation temperature of 90 °C and the inclination angels of 80° which were 31.88 and 58.15 W, respectively.

Pola Aliran Dua Fase Gas - Fluida Non Newtonian Melalui Belokan Pipa

Two-phase flow applications can be used in chemical reactors, fuel cell and a cooler of electronic devices. Nowadays, the study on multiphase flow is concern with the gas-non Newtonian liquids flow. Since, non-Newtonian liquids commonly used in both industrial and medical applications such as blood flow, polymer and chemical solutions. The viscosity of a non-Newtonian liquid cannot be described by Newton’s law viscosity. The viscosity will affect flow behavior in pipes depends on the rheology of the fluid. The purpose of this study is to further investigate the flow pattern characteristic of gas-Newtonian/non-Newtonian liquid two-phase flows in a normal channel. Ultrapure water, polyacrylamide aqueous solutions (PAM) were used as test fluids, while argon gas as the test gas. Liquid and gas were introduced in T-junction, which placed on the upstream of the test section. In this study, the polyacrylamide concentration was variated on 0.1% wt and 0.4% wt. Moreover, the flow rate of liquids tested were variated on 0.1167 m 3 /s, 0.183 m 3 /s, 0.25 m 3 /s; and 0.283 m 3 /s. Therefore, the gas tested was variated on 0.083 m 3 /s, 0.167 m 3 /s, and 0.25 m 3 /s. The circular channel and bend pipe were used in this study, which has hydraulic diameter of 25.4 mm. The high-speed video camera was used to record the flow patterns in the bend as the test section. The flow pattern, bubble length, bubble velocity and void fraction were determined by analyzing the video image of the flows. Slug and plug flow patterns mostly appear in this study for each variation of liquids tested. Increasing gas superficial velocity induced the longer bubble. Furthermore, because of the higher viscosity of the non-Newtonian liquid, the bubble nose of gas-non Newtonian liquid two-phase flow becomes sharper than the bubble nose of gas-Newtonian liquid two-phase flow.