Intermittent Flow Research Articles

A Review of the Measurement of the Multiphase Slug Frequency

The slug frequency (SF), which refers to the number of liquid slugs passing through a pipe during a specific time, is an important parameter for characterizing the multiphase intermittent flows and monitoring some process involving this kind of flow. The simplicity of the definition of SF contrasts with the difficulty of correctly measuring it. This manuscript aims to review and discuss the various techniques and methods developed to determine the slug frequency experimentally. This review significantly reveals the absence of a universal measurement method applicable to a wide range of operating conditions. Thus, the recourse to recording videos with high-speed cameras, which can be used only at a laboratory scale, remains often necessary. From the summarized state-of-the-art, it appears that correctly defining the threshold values for detecting the liquid slugs/elongated bubbles interface from physical parameters time series, increasing the applicability of instrumentations at industrial scales, and properly estimating the uncertainties are the challenges that have to be faced to advance in the measurement of SF.

Intermittent Flow Control Schemes for Heat Stress Mitigation in Lactating Sows on a Floor Cooling Pad

The Purdue hog cooling pad has previously been demonstrated to mitigate heat stress in lactating sows by conductively transferring heat from a sow to cool water running through an integral heat exchanger. Coolant effectiveness, which describes how much heat is removed per volume of water flushed through the cooling pad, is used to compare the operation under varying conditions. Past studies have indicated that the intermittent flow of cooling water achieves a greater coolant effectiveness than continuous flow operational schemes. An electronic control system was implemented with the current cooling pad design to allow for the automated control of a solenoid valve to create the intermittent flow conditions. All testing was performed using 18 ± 1 °C inlet water. Potential control schemes were categorized into two groups, temporal and temperature threshold. The temporal schemes opened the solenoid for 30 s, enough time to flush the entire contents of the cooling coils, before closing for 3, 6, or 9 min. The temperature threshold control schemes utilized feedback from thermal probes embedded beneath the surface of the cooling pad to open the solenoid for 30 s, when a maximum surface temperature was detected. Trigger temperatures of 28.0, 29.5, or 31.0 °C were used. The temperature threshold control schemes achieved greater heat transfer rates (348, 383, 268 W) compared to the temporal control schemes (324, 128, 84 W). The cooling effectiveness for all control schemes ranged from 46.6 to 64.7 kJ/L. The tested intermittent flow control schemes in this study achieved greater cooling effectiveness than continuous flow systems from previous studies (time: 51 kJ/L; temperature: 61 kJ/L; steady: 5.8 kJ/L), although the temporal control schemes exhibited lower heat transfer rates (time: 180 W; temperature: 330 W; steady: 305 W).

Management and Performance Analysis of Textile Effluent Treatment Plants in Laundries of The Local Productive Arrangement of Pernambuco

Objective: The present study aimed to assess 10 laundries for compliance with Brazilian legislation Theoretical Framework: The Local Productive Arrangement (APL) of Pernambuco plays a crucial role in job creation and economic growth in the state. However, the jeans beneficiation process consumes a significant amount of water and involves the use of various chemicals, which generate effluents with high organic loads, color, and toxicity. This has caused serious environmental problems. The issue is exacerbated during prolonged drought periods and by intermittent river flows, which reduce the natural self-purification capacity of the rivers. Method: A total of 334 influent and effluent samples were collected. All the laundries studied employed physicochemical treatment processes (flocculation followed by sedimentation). Results and Discussion: The WWTPs proved to be efficient in the removal of settleable solids, demonstrating that the coagulation and flocculation processes are effective for this purpose, even in scenarios with management deficiencies. On the other hand, poor operation of the treatment plants has resulted in other parameters, such as pH, oils, and greases, being out of compliance with current legislation. The efficiency in reducing BOD was highly inconsistent, with fluctuations ranging from over 90% efficiency to negative values, indicating significant operational issues. High concentrations of organic matter can compromise oxygen levels in the receiving bodies. It is essential to intensify monitoring and improve treatment processes to mitigate negative environmental impacts.

Experimental study on condensing flow and heat transfer characteristics in minichannels under mechanical vibration conditions

Minichannel heat exchangers are often used in the condensers of vehicle air conditioners, and vibration is inevitable in vehicle driving. However, the influence of mechanical vibration on the characteristics of minichannel condensing flow and heat transfer has been rarely studied. Therefore, the experimental study of condensing flow and heat transfer in minichannels under mechanical vibration was carried out in this paper. With R134a as the working medium, the condensation heat transfer coefficient, frictional pressure drop and flow pattern images were measured in the saturation temperature of 40 °C, mass flux density of 200 kg/(m2·s), vapor quality range of 0–1, vibration frequency of 15–50 Hz and amplitude of 0–2.4 mm. For annular flow, intermittent flow and bubble flow, the vibration can enhance the wave of gas-liquid interface, and promote the breakup of long bubbles and the polymerization of small bubbles. Vibration enhances heat transfer in most cases, but weakens heat transfer in some specific cases. The frictional pressure drops under vibration conditions are greater than those under static conditions, which indicates that the influence mechanism of vibration on heat transfer and pressure drop is different. This paper attempts to analyze the complex mechanism of vibration affecting minichannel condensing heat transfer and pressure drop, which provides theoretical support for further study of condenser optimization design under vibration conditions.

Investigation on intermittent flow characteristics in horizontal pipe by visualization measurement method

Accurate measurement and prediction of the intermittent flow characteristics in horizontal pipes is important for constructing multiphase flow models and ensuring pipe flow safety. In this paper, a quantitative image post-processing technique for intermittent flow characteristics based on gray histogram image similarity is proposed, which can realize the measurement of slug frequency. In addition, the technique also has the ability to classify a large number of images, and can quickly find the elongated bubble head, liquid film area and liquid slug area of intermittent flow. On the basis of this technique, combined with image post-processing methods such as gas–liquid interface feature analysis, a set of intermittent flow image processing technique with perfect route is formed. Based on this post-processing technique, the similarity image oscillation trajectories of plug flow and slug flow are obtained. There are differences in the similarity image oscillation trajectories of the two intermittent sub-flow patterns, and the similarity image of the plug flow has an obvious platform period and trailing rising line, which can be used as a basis for the classification of the two intermittent sub-flow patterns. A correlation for predicting the slug frequency of intermittent sub-flow patterns is developed. The accuracy of this slug frequency prediction correlation can be improved by about 10 % compared to not dividing the sub-flow patterns. When the mixture Froude number Frm is less than 5.0, the radial position of the elongated bubble head decreases linearly as the Frm increases. When the Frm is greater than 5.0, the elongated bubble head oscillates near the middle of the pipe. Prediction correlations for the radial position of the elongated bubble head and the slug velocity are established separately, and the maximum error is ± 10 %. The modified mixed Froude number is proposed, and based on this, a new prediction model for the transition from plug flow to slug flow is established.

Efficient cooling strategies for liquid hydrogen pipelines: A comparative analysis

Liquid hydrogen (LH2) stands out for its high energy density, efficient transportation, and safe low-pressure storage. However, the challenge lies in achieving rapid cooling of LH2 pipelines while minimizing hydrogen loss. This paper introduces a robust three-dimensional model for simulating the unsteady-state heat transfer and the gas-liquid two-phase flow within LH2 pipelines. Throughout the cooling cycle, the pipe undergoes transitions in flow patterns, including stratified smooth flow, wavy flow, and intermittent flow, in which wavy flow dominates due to the extremely low liquid-to-gas density ratio of hydrogen. A comprehensive comparative analysis is conducted for three cooling modes: constant flow, variable flow, and pulsing flow. Finally, an evaluative framework for distinct pipeline cooling modes has been proposed. A reasonable variable flow cooling mode exhibits certain advantages in both cooling time and liquid hydrogen consumption when compared with the constant flow cooling mode, and the pulse flow cooling method adeptly capitalizes on the performance benefits derived from intermittent flow. Specifically, within the cooling range of 40 K–20 K, it substantially economizes liquid hydrogen consumption (15%–20 %), albeit concomitant with an extended total cooling time (40%–60 %). This study can offer theoretical insights to guide the high-efficiency cooling of liquid hydrogen pipelines.

Experimental study on flow patterns and pressure gradient of decaying swirling gas-liquid flow in a horizontal pipe

The utilization of swirling flow in multiphase flow devices is prevalent for purposes such as mixing, separation, stabilization, and heat transfer enhancement, primarily owing to its characteristic of inducing low-pressure drop. In the nuclear industry, for example, two-phase swirling flow is applied in the nuclear gas generator to improve gas quality. In this study, an experimental investigation was conducted on the decaying swirling flow of gas-liquid in a horizontal pipe equipped with a vane-type swirler. The flow patterns were visually examined, and the pressure gradients along the test pipe and across the swirler were measured. The findings suggest the presence of four distinct swirling flow patterns at the swirler outlet (z/D = 0), namely chain flow, swirling gas column flow, swirling intermittent flow, and swirling annular flow. Because of swirl decay, these swirling flows recover their original pattern approximately 70D downstream from the swirler, with the exception of the swirling gas column flow. The flow regime maps at z/D = 10, 40, 70 and 100 are proposed and the pattern-based pressure gradient characteristics are analyzed. It is shown that the pressure gradient rises as both gas superficial velocity (jg) and liquid superficial velocity (jl) increase. The largest pressure gradient occurs within the swirler section, while the lowest is found upstream of the swirler. Near the swirler outlet (z/D = 0–33), the pressure gradient is approximately 1.5–2.3 times higher than at z/D = 33–67. Further downstream, at z/D = 67–100, it is 2.2–3.5 times greater, depending on the flow patterns.

Efficacy of Transarterial Embolization Using Intermittent Flow Control for Tentorial Dural Arteriovenous Fistula Presenting as Myelopathy: A Technical Report

BackgroundTransarterial embolization (TAE) is generally the endovascular treatment of choice for tentorial dural arteriovenous fistula (dAVF). Although flow control of the feeder vessel has been reported to achieve complete shunt blockade, flow control in the absence of ischemia tolerance of ICA as a feeder has not been reported. we present a case in which treatment by Onyx TAE with intermittent flow control of the meningohypophyseal trunk (MHT) as the feeder was successful for a tentorial dAVF presenting with myelopathy without tolerance of ischemia. MethodsThe intermittent flow control is presented for a tentorial dAVF presenting with myelopathy without tolerance for ischemia. An inflation of the balloon in the internal carotid artery was set for 5 minutes, and the Onyx injection was repeated at intervals of at least 2 minutes. Injections and pauses were repeated to allow Onyx to reach the shunt pouch. ResultsThe patient underwent successful TAE with intermittent flow control for a tentorial dAVF presenting with myelopathy. The disappearance of the shunt was confirmed with gait disturbance resolution postoperatively. ConclusionIntermittent flow control of the MHT using a balloon may be safe and effective for cases showing no tolerance for ischemia.

Experimental study on effect of pressure on ADS-4 liquid entrainment characteristics in T-junction

Liquid entrainment phenomenon can occur in the T-junction formed by the vertical ADS-4 pipeline and the hot pipe section during SBLOCA process in AP1000 reactor. At present, most of the studies on the liquid entrainment phenomenon in T-junction with large branch pipe concentrate on the atmospheric pressure condition, which is difficult to accurately reflect the real state of the accident process. The liquid entrainment experiments were carried out at 0.1–0.4 MPa on ADETEL facility. The results show that there will be obvious reverse flow phenomenon in the branch at 0.1 MPa and the phenomenon disappears gradually with the increase of pressure. Furthermore, the occurrence of intermittent two-phase slug flow in the horizontal tube was observed at lower pressures. As pressure increases, the entrainment process will become more continuous and stable, with a concomitant reduction in intermittency. The steady-state entrainment liquid level and the onset of entrainment liquid level both decrease with increasing pressure, indicating that increasing pressure can facilitate the liquid entrainment amount. The existing correlations cannot accurately estimate the entrainment amount during SBLOCA in nuclear reactor with a deviation of more than +100% between the predictions and experimental data.

An investigation on hydrodynamic behavior of horizontal gas–liquid intermittent flow by S-PLIF and parallel-wire conductance sensors

Horizontal gas–liquid two-phase flows widely exist in a variety of industrial fields such as the environment, chemical industry and energy. Intermittent flow, characterized by the quasi-periodic alternation motion of liquid slugs and large-scale Taylor bubbles, is the most prevalent flow pattern in horizontal gas–liquid two-phase flows. Comprehensive research on the hydrodynamic behavior of gas–liquid intermittent flow is essential for revealing the mass and heat transfer characteristics between phases, thereby establishing physical models of flow parameters. In this study, a structured planar laser-induced fluorescence (S-PLIF) system and paired parallel-wire conductance sensors (PWCSs) are designed to detect the gas–liquid interface structures and the hydrodynamic parameters. The S-PLIF system consists of a laser, a visualization box, a Ronchi ruling-plate and a pair of high-speed cameras. An optical linear prism forms a laser sheet in the transverse direction and the middle of the test section, and the cameras are positioned at 70° and 90° respectively to the plane of the laser sheet, referred to as S-PLIF70 and S-PLIF90. Under the laser excitation, bright and dark stripes generated by the Ronchi ruling-plate are deflected at the gas–liquid interface. The influence of total reflection can be effectively avoided by identifying the deflection position of the stripes, allowing for accurate detection of the gas–liquid interfacial structures. The effects of the interface fluctuations and detached bubbles on the S-PLIF70&90 results are investigated. Fluctuation and evolution characteristics of the gas–liquid interface are analyzed by probability density function (PDF) and power spectral density (PSD). Meanwhile, hydrodynamic parameters, i.e., Taylor bubble nose and tail velocity, Taylor bubble and slug length, and slug frequency, are detected by the PWCSs, and compared with previous correlations. The evolution characteristics of the interfacial structures and hydrodynamic parameters are uncovered as the flow condition changes.

Numerical investigation of the multiphase flow and loading state of underwater semiclosed initial interrupted bubbles

The pulsation of bubbles and the impact load from reverse flow, generated by the evolution of semiclosed initial intermittent bubble multiphase flow during underwater launches, are crucial factors affecting launch safety. This paper employs the mixture multiphase flow model and the interphase heat and mass transfer model to simulate the interaction between the gas inside a partially enclosed cylinder and the water medium outside the cylinder, combined with simulation and piggybacking experiments, to analyze the flow process and load state. The numerical model is further utilized to study the evolution of the multiphase flow field of the semienclosed initial intermittent bubble, the pulsating load of the bubble, the impact load of the inverted water flow, and the influence of structural dimensions on the load. The results show that the initial intermittent bubble in the mouth of the cylinder experiences an expansion–contraction–expansion pulsation process, and as the migration of the interface between the phases results in significant pressure pulsation, the peak pulsation can exceed twice the pressure difference between the initial gas pressure inside the cylinder and the hydrostatic pressure at the mouth of the cylinder. At the late stage of bubble pulsation, a large amount of water with pulsating bubbles flows into the semiclosed cylinder, and the pulsation-induced velocity and gravity are used to form a high-speed inverted water flow. The interaction between the inverted water and the gas inside the cylinder generates an oscillating shock load where the maximum shock load is significantly greater than the ambient pressure load. Additionally, the effect of structural dimensions on the load state under the same intermittent conditions is examined.

Experimental investigation of different sub-regimes in horizontal stratified and intermittent gas-liquid two-phase flow: Flow map and analysis of pressure drop fluctuations

Horizontal stratified and intermittent gas-liquid two-phase flows exhibit several sub-regimes. Identifying these correctly would enable the development of more robust predictive models. This study reports on experimental investigation, based on observations and the collection of time series of pressure drop in a 40 mm ID pipe. Nine different sub-regimes (SS, 2D wave, 3D wave, RW, ED+RW, PS+RW, plug, LAS, HAS) were revealed. An original flow pattern map for this diameter is proposed including transitory regions between the sub-regime. Comparison of experimental observations with existing flow maps has highlighted the effect of pipe diameter on transition of sub-regimes. As reported in literature the sub-regimes, could be identified by direct visualization of the pressure drop time series obtained from differential pressure sensor a swell as using Probability Density Function. Furthermore, statistical analysis of standard deviation as function of gas superficial velocity enabled detection of the transition of various sub-regimes. Finally, a space feature based on standard deviation and mixture Froude number is proposed as an identification tool between the different sub-regimes investigated.

Novel dimensionless predictive flow pattern map for HFOs inside microscale enhanced tubes

Models designated to predict flow patterns in microscale geometries with enhanced surfaces such as micro-finned tubes are scarce in the literature and new low-GWP HFOs could benefit from the utilization of such geometries. Therefore, HFO1234ze(E)’s condensation flow patterns were subjected to visualization inside micro-finned tubes ranging from 4 to 7 mm outer diameters with various geometrical figures. The saturation temperature was set to 30 °C, vapor qualities ranged in the scope of 0.01 to 0.9, and mass fluxes in the magnitude of 100 to 400 kg m-2 s-1. Four distinctive flow patterns are observed, namely intermittent, annular, wavy-stratified, and transitional. Stratification only transpired at low mass fluxes (mainly below 100 kg m-2 s-1) and intermittent flow was only present at vapor qualities close to full condensation. The range in which transitional flow is observable shrinks with a progressive trend of mass flux. The impact of diameter was observed to be negligible, however, a more meticulous assessment highlights smaller ranges of vapor qualities in which transitional flow is present for the tube of 5 mm OD whose helix angle is substantially larger. Datapoints were juxtaposed to previous models of Doretti et al., Chen et al., Mandhane et al., and Jige et al. and the results attested to an inadequacy of accurate predictions made for tube of 4 mm OD. Noting the absence of surface tension force in the aforementioned maps, a novel flow pattern map based on modified Froude versus modified Weber numbers provided an accurate prediction for the three cases under study. Ultimately the model was also deemed fairly suitable for visualization datasets collected from literature.

POD Analysis of the Wake of Two Tandem Square Cylinders

This study aims to investigate the wake of two tandem square cylinders based on the Proper Orthogonal Decomposition (POD) analyses of the PIV and hotwire data. The cylinder centre-to-centre spacing ratio L/w examined is from 1.2 to 4.2, covering the four flow regimes, i.e., extended body, reattachment, transition and co-shedding. The Reynolds number examined was 1.3 × 104. A novel Proper Orthogonal Decomposition (POD) technique (hereafter referred to as PODHW) is developed to analyse data from single point hotwire measurements, offering a new perspective compared to the conventional POD analysis (PODPIV) based on Particle Image Velocimetry (PIV) data. A key finding is the identification of two distinct states, reattachment and co-shedding, within the transition flow regime at L/w = 2.8, which PODPIV fails to capture due to the limited duration of the PIV data obtained. This study confirms, for the first time, the existence of these states as proposed by Zhou et al. (2024), highlighting the advantage of using PODHW for capturing intermittent flow phenomena. Furthermore, the analysis reveals how the predominant coherent structures contribute to the total fluctuating velocity energy in each individual regime. Other aspects of the flow are also discussed, including the Strouhal numbers, the contribution to the total fluctuating energy of the flow from the first four POD modes, and a comparison between different regimes.

Deep Low‐Frequency Earthquake Reveals Unsteady Fluid Flow Beneath Tengchong Volcano Field in Southeast Tibet

AbstractDeep low‐frequency earthquakes (DLFE) are observed beneath volcanoes worldwide but are limited to island arc volcanoes, hotspot volcanoes, and rift zones. Here we show DLFEs in the Tengchong Volcano Field, southeast Tibet, located ∼300 km from the Indo‐Burma volcanic arc, by analyzing a 12‐year continuous seismic data set. The earthquakes were at a depth of ∼12 km, near the sidewall of the magma body detected by the magnetotelluric survey. The features of isotropic focal mechanism, episodic occurrence, and possible non‐power‐law scaling, with no detectable geodetic deformation, as well as the petrological signatures of the Holocene eruption product, suggest that the earthquakes were likely associated with the weak intermittent magma flows near the magma body. This finding may demonstrate the existence of unsteady magmatic processes in the margin of the Indo‐Eurasia collision zone, which could indicate unneglectable volcanic hazards, underestimated geothermal resources, and mineralization processes in similar regions.

Comparative Genomics Supports Ecologically Induced Selection as a Putative Driver of Banded Penguin Diversification.

The relative importance of genetic drift and local adaptation in facilitating speciation remains unclear. This is particularly true for seabirds, which can disperse over large geographic distances, providing opportunities for intermittent gene flow among distant colonies that span the temperature and salinity gradients of the oceans. Here, we delve into the genomic basis of adaptation and speciation of banded penguins, Galápagos (Spheniscus mendiculus), Humboldt (Spheniscus humboldti), Magellanic (Spheniscus magellanicus), and African penguins (Spheniscus demersus), by analyzing 114 genomes from the main 16 breeding colonies. We aim to identify the molecular mechanism and genomic adaptive traits that have facilitated their diversifications. Through positive selection and gene family expansion analyses, we identified candidate genes that may be related to reproductive isolation processes mediated by ecological thermal niche divergence. We recover signals of positive selection on key loci associated with spermatogenesis, especially during the recent peripatric divergence of the Galápagos penguin from the Humboldt penguin. High temperatures in tropical habitats may have favored selection on loci associated with spermatogenesis to maintain sperm viability, leading to reproductive isolation among young species. Our results suggest that genome-wide selection on loci associated with molecular pathways that underpin thermoregulation, osmoregulation, hypoxia, and social behavior appears to have been crucial in local adaptation of banded penguins. Overall, these results contribute to our understanding of how the complexity of biotic, but especially abiotic, factors, along with the high dispersal capabilities of these marine species, may promote both neutral and adaptive lineage divergence even in the presence of gene flow.

Influence of hydrological variability and life history strategy on riverine fish assemblages in the Australian wet‐dry tropics

AbstractRiverine fish assemblages are strongly influenced by attributes of the flow regime. Tropical savannah river systems have distinct and predictable hydrologic seasonality, reflecting the wet‐dry climate, but can vary substantially in terms of dry season flow permanency and wet season flow‐pulse characteristics. Understanding how flow permanence and variability influence fish assemblages, and whether these factors can be used to predict responses to future hydrological change, are key knowledge gaps that impede effective management. We examined the influence of hydrological variability on the structure and diversity of freshwater fish assemblages across rivers of the wet‐dry tropics of northern Australia. We found distinct fish assemblages that varied predictably across three hydrological river types: Intermittent, Perennial Stable and Perennial Flashy flow regimes. This distinction emerged despite a common species pool across the region. Species richness was greatest in rivers with Perennial Stable flow regimes, whereas beta‐diversity was greatest in Intermittent rivers. However, life history strategies of constituent species were generally poor predictors of species abundances within each hydrological river type. The distinct fish assemblages evident among hydrological classes may provide some cautious ability to both predict potential fish assemblage changes with future hydrological changes (e.g. if perennial streams became more flashy or intermittent), and to predict fish assemblages expected in unsampled rivers with particular hydrological characteristics. Our findings provide further support for the importance of maintaining regional flow‐habitat heterogeneity and the connectivity between hydrological river types, and their essential role for conserving tropical fish species diversity into an uncertain hydrological future.

Numerical modeling and experimental validation of fluid flow in micro- and meso-fluidic siphons

Siphons have been used for thousands of years to transfer fluids without the use of pumps or power and are present in our daily lives. Paradoxically, it is only in recent decades that the operation of siphons has been fully clarified, which is now understood to be exclusively linked to gravity and molecular cohesion. Siphons are uniquely able to offer automatic, intermittent flow, yet present the main drawback of requiring a source of energy to induce initial flow. Our research team has recently disclosed a microfluidic siphon able to self-prime and deliver a sequence of bioanalytical reagents, previously demonstrated for high-performance, multi-reagents diagnostic testing. Here we show for the first time 2D and 3D computational fluid dynamics (CFD) modeling and the experimental characterization of fluid flow in a range of miniaturized hydrophilic siphons of varying hydraulic liquid height-to-length ratios, ΔH/LT = 0–0.9, using fluids of varying viscosities. CFD simulations using velocity- and pressure-driven inlet boundary conditions were generally in good agreement with experimental fluid flow rates and pressure-balance predictions for plastic ∼0.2 mm and glass ∼0.6 mm internal diameter microfluidic siphons. CFD predictions of fluid flow in “meso-scale” siphons with 1 and 2 mm internal diameters also fully matched normalized experimental data, suggesting that miniaturized siphons are scalable. Their discharge rate and pressure drop are readily predicted and fine-tunable through the physical properties of the fluid and some design parameters of the siphon. The wide range of experimental and numerical parameters studied here provide an important framework for the design and application of gravity-driven micro- and meso-fluidic siphons in many applications, including but not limited to life sciences, clinical diagnostics, and process intensification.

Bubble Separation in a Gas–Liquid Swirling Pipe Flow

Gas–liquid swirling pipe flow plays an essential role in phase separators. Bubble motions and flow patterns transitions in the flow are crucial for further investigation of this flow. However, much attention has been paid to these in non-swirl flow instead of swirl flow. In this work, bubble separation generated by a vane-typed swirler in a vertical pipe with an inner diameter of 62 mm was experimentally studied. Superficial air velocities (0.036 − 1.41 m/s) and superficial water velocities (0.02 − 0.95 m/s). The results show that dispersed bubbles gradually transform to gas column flow with increasing superficial water velocities (0.093 − 0.640 m/s) in the swirl flow; gas column flow gradually transforms to swirling intermittent flow with increasing superficial air velocities (0.05 − 0.40 m/s), and one peak increases to two peaks in the probability density function curve of pressure drop; slug flow can transform to swirling intermittent flow. Finally, transition criteria for bubble separation were proposed: when the turbulent fluctuations are strong enough to overcome centrifugal force, then the bubbles move to the pipe center and coalescence with each other, lead to the transition of gas column flow/swirling intermittent flow.

A novel laser interferometric method for thin film thickness measurement in gas–liquid intermittent flow

Abstract In horizontal intermittent flow, the long bubbles move toward the center of the pipe due to inertia, forming the thin liquid film above the long bubbles. Accurate measurement of the liquid film thickness is crucial for heat and mass transfer. In this paper, laser interferometric technology is innovatively introduced to measure the film thickness of the intermittent flow, and the thin liquid film is detected with a resolution of 100 nm. Considering the curvature of the circular pipe wall, which leads to divergent reflected light, the effect of the pipe wall on the interference pattern is explored by the ray tracing technique. A two-dimensional interpolation phase retrieval algorithm based on light intensity is proposed to reconstruct the thickness of the liquid film, and the average error is less than 1.86%. Benefiting from the exceptionally high resolution, research is conducted on the thin liquid film at the top of the horizontal intermittent flow, revealing its dependence on the sub-regimes and gas–liquid velocities.