Gas-liquid Flow Regime Research Articles

Gas-liquid flow regimes identification using non-intrusive Doppler ultrasonic sensor and convolutional recurrent neural networks in an s-shaped riser

The problem of gas-liquid (two-phase) flow regime identification in an S-shaped riser using an ultrasonic sensor and convolutional recurrent neural networks (CRNN) is addressed. This research systematically evaluates three different schemes with four CRNN-based classifiers over fourteen experiments. Four metrics are used as the evaluation criteria: categorical accuracy, categorical cross-entropy, mean square error (MSE), and computation graph complexity. Compared with existing results, a compatible performance is achieved while considerably reducing the model complexity. The testing and validation accuracies were 98.13% and 98.06%, while the complexity decreased by 98.4% (only 117,702 parameters). The proposed approach is i) accurate, low complexity, and non-intrusive and hence suitable for industry, and ii) could provide a benchmark for flow regime identification.

Comparative Performance of Machine Learning and Deep Learning Algorithms in Predicting Gas-Liquid Flow Regimes

Comparative Performance of Machine Learning and Deep Learning Algorithms in Predicting Gas-Liquid Flow Regimes

Influence of Liquid Properties on Gas-Liquid Flow Regimes and Pressure Drop in a Flat Microchannel

Influence of Liquid Properties on Gas-Liquid Flow Regimes and Pressure Drop in a Flat Microchannel

Non-thermal plasma-based inactivation of bacteria in water using a microfluidic reactor

Failure of conventional water treatment systems may lead to the contamination of water sources, which can cause outbreaks of waterborne healthcare associated infections. Advanced oxidation processing by non-thermal plasma has the potential to treat water without the addition of chemicals. Antibiotic resistant Pseudomonas aeruginosa and Escherichia coli were chosen to investigate the use of non-thermal plasma generated in a microfluidic reactor to disinfect bacteria contaminated water. The microfluidic reactor used in this study utilized a dielectric barrier discharge, in a gas-liquid phase annular flow regime. Microbiological analysis of water inoculated with P. aeruginosa and E. coli was carried out before and after plasma treatment. Using air as the carrier gas, effective disinfection of water was achieved. At the lowest flow rate (35 µL/min), P. aeruginosa and E. coli viability were drastically reduced, with an approximate 8 log maximum decrease in viability following an estimated residence time of 5 s of plasma treatment. Scanning electron microscopy indicated changes in cell morphology due to the plasma treatment. Live/Dead assays revealed that the membranes of the cells had been damaged after plasma treatment. This work demonstrated that non-thermal plasma has the potential to disinfect against microbial contamination in water.

Gas-Liquid Flow Regime Identification Via a Non-Intrusive Optical Sensor Combined with Polynomial Regression and Linear Discriminant Analysis

Gas-Liquid Flow Regime Identification Via a Non-Intrusive Optical Sensor Combined with Polynomial Regression and Linear Discriminant Analysis

Gas-Liquid Flow and Interphase Mass Transfer in LL Microreactors

This work investigates the impact of fluid (CO2(g), water) flow rates, channel geometry, and the presence of a surfactant (ethanol) on the resulting gas–liquid flow regime (bubble, slug, annular), pressure drop, and interphase mass transfer coefficient (kla) in the FlowPlateTM LL (liquid-liquid) microreactor, which was originally designed for immiscible liquid systems. The flow regime map generated by the complex mixer geometry is compared to that obtained in straight channels of a similar characteristic length, while the pressure drop is fitted to the separated flows model of Lockhart–Martinelli, and the kla in the bubble flow regime is fitted to a power dissipation model based on isotropic turbulent bubble breakup. The LL-Rhombus configuration yielded higher kla values for an equivalent pressure drop when compared to the LL-Triangle geometry. The Lockhart–Martinelli model provided good pressure drop predictions for the entire range of experimental data (AARE < 8.1%), but the fitting parameters are dependent on the mixing unit geometry and fluid phase properties. The correlation of kla with the energy dissipation rate provided a good fit for the experimental data in the bubble flow regime (AARE < 13.9%). The presented experimental data and correlations further characterize LL microreactors, which are part of a toolbox for fine chemical synthesis involving immiscible fluids for applications involving reactive gas–liquid flows.

Flow Regime Identification in Vertical Upward Gas–Liquid Flow Using an Optical Sensor With Linear and Quadratic Discriminant Analysis

Abstract The accurate identification of gas–liquid flow regimes in pipes remains a challenge for the chemical process industries. This paper proposes a method for flow regime identification that combines responses from a nonintrusive optical sensor with linear discriminant analysis (LDA) and quadratic discriminant analysis (QDA) for vertical upward gas–liquid flow of air and water. A total of 165 flow conditions make up the dataset, collected from an experimental air–water flow loop with a transparent test section (TS) of 27.3 mm inner diameter and 5 m length. Selected features extracted from the sensor response are categorized into feature group 1, average sensor response and standard deviation, and feature group 2 that also includes percentage counts of the calibrated responses for water and air. The selected features are used to train, cross validate, and test four model cases (LDA1, LDA2, QDA1, and QDA2). The LDA models produce higher average test classification accuracies (both 95%) than the QDA models (80% QDA1 and 45% QDA2) due to misclassification associated with the slug and churn flow regimes. Results suggest that the LDA1 model case is the most stable with the lowest average performance loss and is therefore considered superior for flow regime identification. In future studies, a larger dataset may improve stability and accuracy of the QDA models, and an extension of the conditions and parameters would be a useful test of applicability.

Non-intrusive classification of gas-liquid flow regimes in an S-shaped pipeline riser using a Doppler ultrasonic sensor and deep neural networks

The problem of predicting the regime of a two-phase flow is considered. An approach is proposed that classifies the flow regime using Deep Neural Networks (DNNs) operating on features extracted from Doppler ultrasonic signals of the flow using the Fast Fourier Transform (FFT) is proposed. The features extracted are categorised into one of the four flow regime classes: the annular, churn, slug, and bubbly flow regimes. The scheme was tested on signals from an experimental facility. To increase the number of samples without losing key classification information, this paper proposes a Twin-window Feature Extraction (TFE) technique. To further distinguish the performance of the proposed approach, the classifier was compared to four conventional machine learning classifiers: namely, the AdaBoost classifier, bagging classifier, extra trees classifier, and decision tree classifier. Using the TFE features, the DNNs classifier achieved a higher recognition accuracy of 99.01% and greater robustness for the overfitting challenge, thereby showing the superiority of the DNNs in flow regime classification when compared to the four conventional machine-learning classifiers, which had classification accuracies of 55.35%, 86.21%, 82.41%, and 80.03%, respectively. This approach demonstrates the application of DNNs for flow regime classification in chemical and petroleum engineering fields, using a clamp-on Doppler ultrasonic sensor. This appears to be the first known successful attempt to identify gas–liquid flow regimes in an S-shaped riser using Continuous Wave Doppler Ultrasound (CWDU) and DNNs.

Study of intermittent flow characteristics experimentally and numerically in a horizontal pipeline

The gas-liquid intermittent flow regime is the dominant flow pattern, which significantly occurs in the oil and gas industries. The intermittent flow is challenging in the hydrocarbon transportation systems and separators operation. The present investigation aims to comprehend the behavior of intermittent flow characteristics using experimental and numerical methods simultaneously. Superficial velocities of water and air were set in ranges of (0.18–0.84 m/s) and (1.22–4.9 m/s), respectively. The research was conducted in a horizontal pipe with a diameter of 44 mm and 147D long to study slug frequency, slug length, translational slug velocity, pressure drops, as well as slug's initiation location using static pressure data and high-speed camera tools. In this regard, the volume of fluid (VoF) method and SST k-ω model were also applied to specify film thickness, maximum Taylor bubble velocity, and to grasp behaviors of the flow field in more detail. The results revealed that liquid superficial velocity has more effects on slug frequencies than gas superficial velocity. On the other hand, slug initiation location, as well as slug fully developed length, is affected by the gas superficial velocity more than liquid superficial velocity. Moreover, both the gas and liquid superficial velocities have the same effects on translational slug velocities. The obtained experimental results were also employed to define a distinctive inlet boundary condition in the numerical simulation, which leads to a 65 percent reduction in the computational domain.

Gas–Liquid Flow Regime Prediction in Minichannels: A Dimensionless, Universally Applicable Approach

Apparatus containing micro- or minichannels are seen as promising tools to intensify several chemical engineering processes. For gas–liquid systems, the apparatus should operate in the Taylor flow ...

Experimental Investigation of Adiabatic Gas-Liquid Flow Regimes and Pressure Drop in Slit Microchannel

The flow regimes and pressure drop in a slit microchannel with a height of 164 μm and width of 10 mm are studied experimentally. The boundaries between the regimes are precisely determined using the developed procedure. The homogeneous flow model and the separated flow model are considered for determining the frictional pressure drop. Experimental data are compared with theoretical models. For the homogeneous flow model, the Dukler correlation gives good agreement with experimental data with a mean absolute error of 12%. A new correlation, which describes the experimental data with a mean absolute error of 8.1%, is proposed for the homogeneous flow model. For the separated flow model, the Hwang and Kim correlation gives the best agreement with a mean absolute error of 12.8%. The dependence of the pressure drop in the film flows (annular and stratified regimes) on the mass gas quality has been investigated. It is shown that the minimal pressure drop for the film flows is achieved in the stratified regime; thus, it is the most promising for the use in technical applications.

Experimental study of gas-liquid two-phase wavy stratified flow in horizontal pipe at high pressure

The regimes of gas-liquid two-phase flow in horizontal pipe at high pressure were experimentally investigated, and characteristics of wave stratified flow, such as wave length, wave height and propagation speed were calculated. The pressure drop was analyzed and friction factors, such as gas-wall, liquid-wall and interfacial friction factors, were calculated and new correlations were deduced. Influence of interface wave on interfacial friction factor was studied, and characteristics of interface wave were included to deduce new correlation for it, and good accuracy was proved. For the gas-water two-phase flow at 2 MPa, transition from wave stratified to annular flow appears with smaller gas superficial velocity compared with that at atmosphere, and intermittent flow appears with greater liquid superficial velocity. Regime transition models are tested, for the gas-liquid two-phase flow at atmosphere the sheltering coefficient with value of 0.01 is appropriate. However, it is promoted to be 0.06 at 2 MPa, and good performance of regime transition model was reached.

A high-pressure visual flow loop for hydrate blockage detection and observation.

More than 65% of the worldwide natural gas is transported through pipelines. Gas hydrate formation and blockage in the pipeline are commonly encountered, causing significant problems in safe and efficient transportation. Yet the instrument simulating the high-pressure multiphase flow and demonstrating the hydrate blocking behavior at flowing conditions is not available. In this work, a high-pressure visual flow loop is developed to detect and observe the hydrate nucleation, growth, and deposition during the multiphase flow. The pressure limit is designed to be 8 MPa, and the temperature can go down to -20 °C. This device allows a direct observation of the gas-liquid flow regime during transportation; investigations on the initiation and evolution of hydrate blockage in the dead-leg section, U-shaped region, and rising pipes are now possible. Sensors are distributed along the pipelines to detect the pressure and temperature change; the differential pressure is used to effectively detect the degree of hydrate blockage, which increases upon hydrate formation. The visual flow loop could also help examine the effect of shut-down and restart of the pump on the flow behavior. The system has been verified feasible demonstrating the flow behavior and predict hydrate blockage. The developed device would help understand the mechanism of hydrate blockage in the transportation pipelines and provide guidance to efficiently avoid such problems.

Identification of gas-liquid flow regimes using a non-intrusive Doppler ultrasonic sensor and virtual flow regime maps

The accurate prediction of flow regimes is vital for the analysis of behaviour and operation of gas/liquid two-phase systems in industrial processes. This paper investigates the feasibility of a non-radioactive and non-intrusive method for the objective identification of two-phase gas/liquid flow regimes using a Doppler ultrasonic sensor and machine learning approaches. The experimental data is acquired from a 16.2-m long S-shaped riser, connected to a 40-m horizontal pipe with an internal diameter of 50.4 mm. The tests cover the bubbly, slug, churn and annular flow regimes. The power spectral density (PSD) method is applied to the flow modulated ultrasound signals in order to extract frequency-domain features of the two-phase flow. Principal Component Analysis (PCA) is then used to reduce the dimensionality of the data so as to enable visualisation in the form of a virtual flow regime map. Finally, a support vector machine (SVM) is deployed to develop an objective classifier in the reduced space. The classifier attained 85.7% accuracy on training samples and 84.6% accuracy on test samples. Our approach has shown the success of the ultrasound sensor, PCA-SVM, and virtual flow regime maps for objective two-phase flow regime classification on pipeline-riser systems, which is beneficial to operators in industrial practice. The use of a non-radioactive and non-intrusive sensor also makes it more favorable than other existing techniques.

Bubble mapping: three-dimensional visualisation of gas–liquid flow regimes using electrical tomography

It is well known that electrical tomography is capable of ‘seeing’ through opaque pipe walls and flow media. However, due to the relatively low spatial resolution, electrical tomograms are ineffective on visualisation of small bubbles or sharp interfaces between large bubbles and the liquid. These limitations give rise to ambiguity in human and/or machine perception of flow dynamics from presenting bubble cluster and blurry boundaries of large bubbles in faint colour or grey. In this paper, a binary approach, called bubble mapping, is proposed to enhance the visibility of flow regime in gas–liquid pipeline flows. With the input gas concentration tomograms reconstructed by an electrical tomography, the method takes the major visual characteristics of typical flow regimes in common recognition as a prior knowledge and replaces the conventional colour mapping with a number of bubbles and their mergence with a thresholding value. With this approach, a stack of cross-sectional tomograms by electrical tomography is transformed and displayed as a collection of individual gas bubbles. The transformation is done with the help of a lookup table indexed by bubble size and an enhanced isosurface algorithm for vivid three-dimensional visualisation. This new approach has been applied to a gas-in-water flow rig and its performance is compared with photo images taken by a high-speed camera. Reasonable agreements have been obtained for common flow regimes including bubbly flow, stratified flow, plug flow, slug flow and annular flow in horizontal pipe and bubbly flow, slug flow and annular flow in vertical pipe. Results evidence the method can provide a photorealistic flow visualisation and therefore enhance the visibility of electrical tomograms for visual identification of flow regime, particularly for opaque media in industrial flows.

Bioprocess Intensification Using Flow Reactors: Stereoselective Oxidation of Achiral 1,3-diols with Immobilized Acetobacter Aceti

Enantiomerically enriched 2-hydroxymethylalkanoic acids were prepared by oxidative desymmetrisation of achiral 1,3-diols using immobilized cells of Acetobacter aceti in water at 28 °C. The biotransformations were first performed in batch mode with cells immobilized in dry alginate, furnishing the desired products with high molar conversion and reaction times ranging from 2 to 6 h. The biocatalytic process was intensified using a multiphasic flow reactor, where a segmented gas–liquid flow regime was applied for achieving an efficient O2-liquid transfer; the continuous flow systems allowed for high yields and high biocatalyst productivity.

Gas-liquid flow regimes in horizontal annulus

Gas-liquid flows in annulus channels are frequently encountered in the underbalanced drilling operation when the gasified drilling fluid is used. Accurate characterization of two-phase flow regimes in such conduits is critically important in order to gain a better understanding of the flow behaviours in the channels, thus to ensure a successful drilling operation achieved. In this paper experimental studies regarding gas-liquid flows in a concentric and fully eccentric horizontal annulus were reported. The test section setups of the flow loop have a length of 10.8 m, with outer and inner pipe diameters of 0.0768 m and 0.060 m respectively. Air and water at atmospheric pressure constituted the gas and liquid phases and the range of gas and liquid superficial velocities investigated during this study was 0.14–24 m/s and 0.15–2.78 m/s respectively. Flow regimes observed in both annulus setups by high speed camera imaging were dispersed bubble, elongated bubble, slug, wavy slug, churn, wavy annular and annular. A detailed description of the flow regimes with different features are presented together with high quality images. The local liquid holdup time series together with its probability density function (PDF) are used to gain more insights about the characteristics of the observed flow regimes. Effects of the annulus eccentricity on the observed flow regimes are also investigated. It is found that the annulus eccentricity affects the shape and structure of the elongated bubble, wavy annular and annular flow regimes. It is also observed that the annulus eccentricity causes the transition from elongated bubble to dispersed bubble to take place at higher liquid superficial velocities. It is also found that in the fully eccentric annulus causes transitions between different flow regimes to occur at higher liquid and lower gas superficial velocities when compared with that of concentric ones. An improved flow regime map is proposed based on gas and liquid Froude numbers by integrating the test results from this study with over 1000 data points found in literature.

An experimental investigation of gas-liquid flowcharacteristics in the microchannel

The two-phase gas-liquid flow regimes in the horizontal rectangular microchannel using the high-speed video camera and dual-laser scanning were studied. Experiments were carried out in the microchannel with cross section 217x370 μm for the water-nitrogen mixture. The T-shaped mixer was used for gas-liquid flow formation. The influence of T-shaped entrance on the length of a gas and liquid bridges in the microchannel was established. The total pressure drop was measured in the microchannel taking into account the distribution of the gas and liquid bridges.

Axial development of gas-liquid flow regime maps in a vertical 5 × 5 rod bundle with prototypic spacer grids

Abstract In relation to the development of flow regime criteria for rod bundle geometry, this paper provides several experimental flow regime maps at different axial locations with simple and prototypic spacer grids, respectively. Experiments with vertical adiabatic air-water flow were conducted under an atmospheric pressure condition. The experiment facility was composed of 5 × 5 rod arranged on a square pitch in a square casing with 9.5 mm outside diameter and 12.6 mm pitch. The inlet superficial gas velocities range from 0.01 to 8.69 m/s, while inlet superficial liquid velocities range from 0.06 to 2.51 m/s. New flow regime maps were acquired at three axial locations of z/DH = 21.9, 58.4 and 107 through high-speed camera images. The experimental maps obtained were compared with the existing analytical models of flow regime transition criteria for vertical rod bundles. A reasonable agreement has been obtained between measured flow regime maps and models of the existing flow regime transition criteria for rod bundles at fully developed flow conditions. The different effects of two types of spacer grids on the flow regime transition were also discussed in this paper.

Sand transport in multiphase flow mixtures in a horizontal pipeline: An experimental investigation

An inherent problem with both oil and natural gas production is the deposition of sand particles in pipeline, which could lead to problems such as excessive pressure drops, equipment failure, pipeline erosion, and production decline. The characterization of sand particles transport and sedimentation in different flow systems such as sand–multiphase mixtures is vital to predict the sand transport velocity and entrainment processes in oil and gas transportation pipelines. However, it seems that no model exists able to accurately characterize the sand transport and deposition in multiphase pipeline. In fact, in the last decade several researchers tried to extend the modeling of liquid-solid flow to gas-liquid-solid flow, but no significant results have been obtained, especially in slug flow condition due to the complexity of the phenomenon. In order to develop and validate a mathematical model properly formulated for the calculation of the sand critical deposition velocity in gas-liquid flow, more and more experimental data are necessary. This paper presents a preliminary experimental study of three phase flows (air-water-sand) inside a horizontal pipe and the application of the sand-liquid models present in literature. Significant observations were made during the experimental study from which several conclusions were drawn. Different sand flow regimes were established by physical observation and data analysis: fully dispersed solid flow, moving dunes and stationary bed. The critical deposition velocities were determined at different sand concentrations. It was concluded that sand transport characteristics and the critical deposition velocity are strongly dependent on the gas-liquid flow regime and on sand concentration.