Search

An innovative method for bubble detection and characterization in multiphase flows using advanced computer vision and neural network algorithms is introduced. Building on the research group's previous findings, this study combines high-speed video capture with advanced deep learning techniques to enhance bubble detection accuracy and dynamic analysis. In order to further develop a robust framework for detecting and analyzing bubble properties in multiphase flows, enabling accurate estimation of essential mass transfer parameters, a YOLOv9-based neural network was implemented for bubble segmentation and trajectory analysis, achieving high accuracy. Key contributions include the development of an averaged mass transfer model integrating experimental data, neural network outputs, and scaling algorithms, as well as validation of the proposed methodology through experimental studies, including high-speed video imaging and comparisons with mass transfer coefficients obtained via the sulfite method. By precisely characterizing critical parameters, the algorithm enables accurate gas transfer rate calculations, ensuring optimal conditions in various industrial applications. The neural network-based algorithm serves as a non-invasive platform for detailed characterization of bubble media, demonstrating high accuracy in experimental validation and significantly outperforming traditional techniques. This approach provides a robust tool for real-time monitoring and modeling of bubble flows, laying the foundation for novel, non-invasive methods to measure multiphase media properties. [ABSTRACT FROM AUTHOR]

The flow of gas-liquid two-phase flow in reservoir fractures may exhibit various flow regimes, such as bubble flow, slug flow, and annular mist flow. Identifying the conditions for the transition between these flow regime is essential for understanding the formation mechanism of gas-liquid flow and has significant implications for the production pipeline management of natural gas Wells. Based on the flow characteristics of different flow regimes of gas-liquid two-phase flow, combined with the theory of continuous medium control and the principle of momentum conservation, transformation mathematical models between flow regimes such as bubble flow, slug flow, and annular mist flow were established. The decisive conditions and key controlling variable that govern the transitions between various flow regimes have been precisely identified. Furthermore, the precision of the mathematical model was rigorously validated through microscopic physical simulation experiments focused on gas-liquid transportation. The results indicated that, the flow state transition of gas-liquid two-phase flow in fractures was the result of the coupling effect of factors such as the physical properties of the gas/liquid phase, the pore size of the gas injection channel, the pore size of the fracture flow channel, the gas phase fluid velocity, and the liquid phase fluid velocity. The transition between bubble flow and slug flow mainly depended on the size of the initial bubble, the flow channel space, and the height of the liquid phase interface wave. The transition between slug flow and annular mist flow depended on whether the gas phase fluid can break down the liquid phase fluid and suspend it. The main control factors for the transition between different flow states were different. The pore size of the fracture system was one of the most important factors in the mutual transformation of bubble flow and slug flow, when the injection channel aperture was larger and the flow channel aperture was smaller, it was more likely to form slug flow. The mutual transformation between slug flow and annular mist flow was primarily influenced by fluid velocity and the physical properties of gas/liquid phase fluids. A higher relative velocity between the gas-liquid phases, a smaller density difference between the phases, and a lower liquid surface tension all increase the likelihood of forming annular mist flow. These research findings established a theoretical foundation for understanding the mechanism of gas-liquid two-phase flow formation in reservoir fractures and natural gas transport production.

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To address the effect of a ship's rolling on the fluidization quality of fluidized beds, in this study, a simulation of a rolling fluidized bed with longitudinal internal members added (R-FBLIM) was carried out and compared with that of a rolling fluidized bed without internal members added (R-FBWIM). The transient motion, as well as the behavioral characteristics of the bubbles within the R-FBLIM, was analyzed; the variation patterns of the number of bubbles, as well as the equivalent diameter of the bubbles, were compared for different apparent gas velocities, oscillation periods, and amplitudes; and the mechanism of the action of the longitudinal internal members was investigated. The results show that the structural design of the longitudinal internal members can effectively improve the gas–solid fluidization quality of the rolling fluidized bed. The horizontal support plate and the cap hole structure can effectively break the air bubbles, the cap hole structure promotes the radial mixing of the gas–solid fluid, and the internal and outer rings of the curved surface plate roll in rows, which inhibit the aggregation behavior of the gas–solid fluid to the two sides of the oscillating planes, respectively, by cooperating with the cap hole structure. Compared with R-FBWIM, the gas–solid phase within R-FBLIM is more spatially distributed, with the number of bubbles increasing by about 2–4 times and the mean diameter decreasing by about 50–60%. The number of bubbles increases with the gas velocity but decreases with the rolling amplitude; the mean diameter decreases with the gas velocity but responds less to the rolling amplitude change. [ABSTRACT FROM AUTHOR]

An innovative method for bubble detection and characterization in multiphase flows using advanced computer vision and neural network algorithms is introduced. Building on the research group’s previous findings, this study combines high-speed video capture with advanced deep learning techniques to enhance bubble detection accuracy and dynamic analysis. In order to further develop a robust framework for detecting and analyzing bubble properties in multiphase flows, enabling accurate estimation of essential mass transfer parameters, a YOLOv9-based neural network was implemented for bubble segmentation and trajectory analysis, achieving high accuracy. Key contributions include the development of an averaged mass transfer model integrating experimental data, neural network outputs, and scaling algorithms, as well as validation of the proposed methodology through experimental studies, including high-speed video imaging and comparisons with mass transfer coefficients obtained via the sulfite method. By precisely characterizing critical parameters, the algorithm enables accurate gas transfer rate calculations, ensuring optimal conditions in various industrial applications. The neural network-based algorithm serves as a non-invasive platform for detailed characterization of bubble media, demonstrating high accuracy in experimental validation and significantly outperforming traditional techniques. This approach provides a robust tool for real-time monitoring and modeling of bubble flows, laying the foundation for novel, non-invasive methods to measure multiphase media properties.

During a severe accident in nuclear power plant, if passive containment cooling system fails and other pressure relief measures are also useless, the mixed gas in containment can be injected into the spent fuel pool via a injector to reduce the risk of containment overpressure failure and the release of radioactivity to the environment. A aerosol pool scrubbing facility was built to study the factors influencing the effect of aerosol pool scrubbing under the injector. This facility can perform a great variation of experiments using various measurement tools. The aerosol concentration and particle size were monitored by using the spectrometer with a 20% measurement error. TiO2 powder was used as a stimulant for the aerosols in containment, and the mass median diameter ranged from 0.5 to 1.5 μm, the geometric standard deviation ranged from 1.63 to 2.15. According to the different characteristics of gas-liquid hydrodynamic behavior, the pool scrubbing process can be divided into two regions, including injection and rise zones. In the injection zone, with the flow flux increase, the gas regime changed from bubble (We

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The present study shows the applicability of the chemical reactor engineering centre (CREC) Optiprobes engineered with a graded refractive index (GRIN) lens and fibreoptics to establish both the bubble rising velocity (BRV) and the bubble axial chord (BAC) of bubbles in a 240–955 μm sand fluidized bed, filled with different types and loadings of biomasses. It is confirmed via the application of the CREC Optiprobes that the formed bubbles display both BRV and BAC normal probabilistic distributions, leading to characteristic BRV–BAC bands of bubble behaviour, with this being true for an ample range of superficial gas velocities (0.188–0.282 m/s) and broza biomass loadings (0–30 vol.%). It is also proven that the observed BRV and BAC distributions in biomass‐loaded sand fluidized beds are of the quasi‐normal distribution type, as attested by the Shapiro–Wilk test (S–W test). Furthermore, a probabilistic prediction model (PPM) proposed in a previous contribution can be used effectively to predict, in all cases, that a close to 80% of the total bubble population falls within a proposed probabilistic band of bubble behaviour. [ABSTRACT FROM AUTHOR]

This work introduces the development of bubble measurement method utilizing a three-dimensional (3D) reconstruction technique from multi-view images. Multiple synchronized cameras were positioned around a water container, and calibration was performed to obtain external and internal camera parameters. Images of bubbles emerging from a nozzle were captured, and a machine learning technique was used to extract bubble silhouettes as foreground probability distributions, enabling the extraction of bubbles from images obtained with a simple lighting setup. These distributions were then projected onto a 3D voxel space using the visual hull method. It was confirmed that the method can successfully capture bubble generation, detachment, and rise behaviors, offering insights into understanding bubble dynamics and potential applications in 3D computational fluid dynamics validation. • Development of a bubble measurement method using 3D reconstruction from multi-view images. • The method utilizes machine learning and modified Visual Hull, for flexible setups and wide applicability. • Air bubbles emerging from a nozzle at flow rates 1.0 to 10.0 SLPM were reconstructed at 120 frames per second. [ABSTRACT FROM AUTHOR]

Minerals flotation is a widely used process to produce base metal concentrates through the selective capture of particles on the surface of bubbles. The process performance depends on the size distribution of the bubble population generated by gas dispersion, which is characterized by three variables: superficial gas velocity, gas holdup, and bubble size. A literature review revealed that current instrumentation cannot provide reliable on-line measurement of these variables except for gas velocity. There are some promising alternatives for gas holdup, but bubble size measurement will continue to be unavailable. The use of a model that integrates the three gas dispersion variables makes possible the calculation of one of the variables when knowing the values of the other two. Modelling bubble flow has been pursued using two approaches: determining the bubble terminal velocity reduction by the presence of other bubbles and regarding the bubble swarm as a packed bed through which a fluid is allowed to flow. Models based on these approaches (drift-flux and Molerus, respectively) were found in the literature and used to assess their prediction ability. Gas holdup predictions for known values of gas velocity and bubble size showed similar trends for both models; Molerus results were always higher than those obtained with the drift-flux model, and the difference between both predictions increased with bubble size and gas velocity. A relationship between bubble surface area flux and gas holdup was explored (a single line was expected); Molerus values showed a noticeable effect of bubble size, while drift-flux results showed a minor effect of bubble size only for gas holdups below 10%. Model accuracy was established using a data set collected to characterize frother roles in flotation for six commercial frothers, which included values of the three gas dispersion variables measured simultaneously and reported at the same conditions. The results indicate that bubble size predictions obtained from Molerus model are closer to the measured values than those obtained from the drift-flux model. Drift-flux predictions systematically underestimated the measured bubble size, with relative errors between 10 and 30%, while Molerus predictions showed values around the measured size with relative errors not larger than 15% (and in most cases below 10%). The accuracy of the Molerus predictions is acceptable for applications in the control of individual cells and flotation circuits operation. Further testing to assess the performance of Molerus model with data collected in lab and industrial mechanical cells and columns, where conditions in the test volume may not be stable or homogeneous, is recommended. [ABSTRACT FROM AUTHOR]

One of the important tasks in carrying out a computational justification of the reliability and safety of equipment that is part of the projected nuclear power plants today is the modeling of the bubbly regime of the coolant flow. In this regard the aim of this work is the use of extended methods of using matrix conductometric systems which are widespread in research practice for study of gas-liquid flows.The work uses a method of primary processing of experimental data aimed at eliminating of excess conductivity in the cells of the developed wire mesh sensor which makes it possible to obtain the values of the true volumetric gas content in the investigated area.Subsequent analysis of the possibilities to estimate the volumes of registered gas bubbles by the gradient method as well as the size of the interface in the sensor cells which plays a key role in modeling the interfacial heat and mass transfer.Comparison of readings values with the control instruments cues showed a good agreement. The presented work is an adaptation of the use of a conductometric measuring system for the study of multicomponent flows with the aim of further application for the study of two-component flows in the channels of the core simulator using wire mesh sensors.

The key group of research methods used for the analysis of formation and flow of gas bubbles in liquids are those involving digital imaging and shadowgraphy. Despite their frequent use, there is no comprehensive analysis of the compliance of different procedures to determine bubble size based on experimental data. In this work, fifteen different approaches for shape recognition were used to determine the equivalent diameter of a bubble and then the results obtained were compared with bubble equivalent diameters determined experimentally. The experiments concerned bubbles of equivalent diameters in the range of 2.4–5.4 mm which correspond to the size of the bubbles most commonly encountered in industrial practice. Particularly, three algorithms for bubble shape detection were evaluated and then three sets of parameters to express the size of the bubble and two types of bubble equivalent diameter were derived. It was found that the most accurate results are obtained by using image binarization and Canny edge detection for the determination of the bubble shape, combined with the Feret diameter employed to express its size and with the volumetric equivalent diameter instead of the superficial one. As the binarization method is not versatile, we recommend using the Canny edge detector. • Procedures based on shadowgraphy to determine bubble size are compared. • Versatile procedure for determination of bubble equivalent diameter are selected. • Canny edge detector performs best to localize bubble rim in the images of bubbles. • Approximating the bubble with a rotational ellipsoid leads to accurate results. • Determining the bubble shape using Feret diameters leads to accurate results. [ABSTRACT FROM AUTHOR]

The breeding blanket is one of the fundamental components of a nuclear fusion reactor and is responsible for the fuel production, generating tritium through neutronic capture reaction between lithium and neutrons. Lithium is a liquid PbLi alloy and the helium formed as reaction by-product can coalesce into bubbles, generating a two-phase mixture with a high-density ratio ( η ρ ∼ O 5 ). These bubbles can accumulate and stagnate within the blanket channels with potentially harmful consequences. In this work, the interIsoFoam solver of OpenFOAM v2012 is used to simulate bubble motion for a two-phase mixture representative of the He-PbLi system to test its potential for future developments in the field of fusion. In a first phase, several traditional benchmarks were carried out, both 2D and 3D, and considering the two variants of the VOF method implemented in the solver, isoAdvector and plicRDF. Subsequently, He bubbles of different diameters rising in liquid PbLi ( η ρ = 1.2 × 10 5 ) were analysed to investigate different regimes. For a Eötvös number (Eo) greater than 10, it was possible to recreate the axisymmetric, skirted, oscillatory regimes and the peripheral and central breakup regimes. For Eo < 10, non-physical deformations of the interface are observed, probably generated by spurious velocities that have a greater impact on the solution for very small bubbles and rising velocities. [ABSTRACT FROM AUTHOR]

This article investigates the discharge characteristic of the bubble flow in FC-72 under unipolar repetitive pulsed voltage, which supports the insulation design of two-phase cooling in an HV power electronic device. The effect of thermal bubble flow on the insulation of FC-72 refrigerant was evaluated. According to the partial discharge (PD) characteristics, it is found that there are two stages in the discharge characteristics of the bubble flow as voltage rises. Combining the PD inception voltages of FC-72 vapor under unipolar pulse voltage and dc voltage, it reveals the discharge thresholds of the vapor inside the bubble under the transient electric field and the steady electric filed, respectively, which proves the mechanism of the staged PD evolution. Based on the motion calculation of the bubble, the PD probability of the bubble flow within a voltage period is analyzed. It simulates the phase-resolved PD pattern, which reveals the PD mechanism of the bubble flow. The research provides a reference for the insulation design for the two-phase cooling technology in power electronics. [ABSTRACT FROM AUTHOR]

We demonstrate a new image processing methodology for resolving gas bubbles travelling through liquid metal from dynamic neutron radiography images with an intrinsically low signal-to-noise ratio. Image pre-processing, denoising and bubble segmentation are described in detail, with practical recommendations. Experimental validation is presented—stationary and moving reference bodies with neutron-transparent cavities are radiographed with imaging conditions representative of the cases with bubbles in liquid metal. The new methods are applied to our experimental data from previous and recent imaging campaigns, and the performance of the methods proposed in this paper is compared against our previously achieved results. Significant improvements are observed as well as the capacity to reliably extract physically meaningful information from measurements performed under highly adverse imaging conditions. The showcased image processing solution and separate elements thereof are readily extendable beyond the present application, and have been made open-source. [ABSTRACT FROM AUTHOR]

Gas-liquid two-phase flow is widely used in many engineering fields, and bubble dynamics is of vital importance in optimizing the engineering design and operating parameters of various adsorptive bubble systems. The characteristics of gas-liquid two-phase (e.g., bubble size, shape, velocity, and trajectory) remain of interest because they give insight into the dynamics of the system. Bubble plumes are a transport phenomenon caused by the buoyancy of bubbles and are capable of generating large-scale convection. The surface flow generated by bubble plumes has been proposed to collect surface-floating substances (in particular, oil layers formed during large oil spills) to protect marine systems, rivers, and lakes. Furthermore, the surface flows generated by bubble plumes are important in various types of reactors, engineering processes, and industrial processes involving a free surface. The bubble parameters play an important role in generating the surface flow and eventually improving the flow performance. This paper studies the effects of temperature on bubble parameters and bubble motion to better understand the relationship between the various bubble parameters that control bubble motion and how they impact the formation of surface flow, with the ultimate goal of improving the efficiency of the generation of surface flow (i.e., rapidly generate a strong, high, and wide surface flow over the bubble-generation system), and to control the parameters of the surface flow, such as thickness, width, and velocity. Such flow depends on the gas flow rate, bubble size (mean bubble diameter), void fraction, bubble velocity, the distance between bubble generator and free surface (i.e., water height), and water temperature. The experiments were carried out to measure bubble parameters in a water column using the image visualization technique to determine their inter-relationships and improve the characteristics of surface flow. The data were obtained by processing visualized images of bubble flow structure for the different sections of the bubble regions, and the results confirm that temperature, bubble size, and gas flow rate significantly affect the flow structure and bubble parameters. [ABSTRACT FROM AUTHOR]

The present work studies bubble breakup in gas–liquid centrifugal pumps. Different inlet gas-fraction conditions are considered to provoke bubble-to-bubble, slug-to-bubble, and slug-to-slug pattern transitions. Results are presented for different mixture velocities and pump rotation frequencies. Data on mean equivalent bubble diameter and slug unit properties (length, passage frequency) are introduced. For small bubbles, a simple phenomenological theory is developed for the prediction of mean diameters. A discussion on the dynamics of small bubbles in the impeller region is also presented. [Display omitted] • The present work studies the fragmentation of large and small bubbles by a centrifugal pump impeller. • The flow conditions were selected to lie outside the range of other previous works. • Data on mean equivalent bubble diameter and slug unit properties are introduced. • For small bubbles, a simple phenomenological theory is developed for the prediction of mean diameters. • The splitting of large bubbles was shown to be a very complex phenomenon. [ABSTRACT FROM AUTHOR]

• A validated numerical model explores interfacial dynamics during hydrogen reduction. • Periodic patterns in the gas–liquid interface, vorticity distribution asymmetry, and swirling patterns are revealed. • Mass transfer efficiency is higher in the bubble plume, influenced by gas flow in distinct regions. • The study provides insights for optimizing hydrogen reduction processes and enhancing mass transfer efficiency. Hydrogen reduction provides an environmentally friendly alternative to traditional smelting for copper slag. The study investigates the gas–liquid interface dynamics during the process. A numerical model based on Coupled Level Set-Volume of Fluid (CLSVOF) and Large Eddy Simulation (LES) methods has been developed and validated against experimental data. The model accurately depicts bubbling modes and interface characteristics in the reactor. Results indicate periodic self-similar patterns in interfacial area and gas volume signals. The vorticity distribution shows asymmetry and swirling patterns, with higher vorticity in the gas injection and upper liquid surface regions. The mass transfer efficiency is higher in the bubble plume region than in the upper surface. Increasing gas flow rates expands the gas–liquid interface areas but decreases mass transfer efficiency in the bubble plume while increasing it in the upper surface. These findings provide valuable insights into the efficiency of the hydrogen reduction of the copper slag process. [ABSTRACT FROM AUTHOR]

The three-dimensional reconstruction of bubble flow field is of great significance to study the motion of gas-liquid two phase flow. Combined with the abundant information of bubbles in the light field images, a fast and accurate 3D reconstruction method for dilute bubbly flow based on the deep learning algorithm DIF-LeNet (Double Information Fusion with LeNet5 net) is proposed in this work. The calibration method and bubble segmentation algorithm of light field image for data processing is detailed. DIF-LeNet realizes the fusion of different dimension data and regression prediction. By DIF-LeNet, bubble depth could be predicted by fusing the refocused bubble image with the focal distance of the refocused image. Then, the three-dimensional bubble field could be reconstructed with the bubble depth, bubble center and bubble diameter. Comparing with the reconstruction method based on statistics and LeNet5, the reconstruction accuracy and speed of the proposed method based on DIF-LeNet are improved. Especially for the bubble without focused image in the refocused image sequence, the effect of 3D reconstruction based on DIF-LeNet is much prominent. [ABSTRACT FROM AUTHOR]

A passive acoustic method based on synchrosqueezing wavelet transform (SWT) and deep learning was proposed to automatically identify bubble flow regimes in process industries. The method was established on the bijection relationship between bubble flow regime and the time‐frequency (TF) textures of its passive acoustic emission (PAE) signals. Specifically, the PAE signal of the bubble flow was first acquired by hydrophones, then converted into TF representations (TFRs) by SWT and finally used to train convolutional neural network (CNN) to identify bubble flow regimes automatically. The effects of TF analysis method and CNN architecture were studied: the SWT represented TF textures of PAE signals the best, and its combination with ResNet gave the highest identification accuracy of 99.67%. As its main contribution, the method validated the feasibility of PAE and CNN in bubble flow regime identification, and achieved automatic identification of bubble flow regime with high accuracy and barely no subjective interference. [ABSTRACT FROM AUTHOR]

The breeding blanket is one of the fundamental components of a nuclear fusion reactor and is responsible for the fuel production, generating tritium through neutronic capture reaction between lithium and neutrons. Lithium is a liquid PbLi alloy and the helium formed as reaction by-product can coalesce into bubbles, generating a two-phase mixture with a high-density ratio (ηρ∼O5). These bubbles can accumulate and stagnate within the blanket channels with potentially harmful consequences. In this work, the interIsoFoam solver of OpenFOAM v2012 is used to simulate bubble motion for a two-phase mixture representative of the He-PbLi system to test its potential for future developments in the field of fusion. In a first phase, several traditional benchmarks were carried out, both 2D and 3D, and considering the two variants of the VOF method implemented in the solver, isoAdvector and plicRDF. Subsequently, He bubbles of different diameters rising in liquid PbLi (ηρ=1.2×105) were analysed to investigate different regimes. For a Eötvös number (Eo) greater than 10, it was possible to recreate the axisymmetric, skirted, oscillatory regimes and the peripheral and central breakup regimes. For Eo < 10, non-physical deformations of the interface are observed, probably generated by spurious velocities that have a greater impact on the solution for very small bubbles and rising velocities.

Aeration is considered beneficial for hydroponics. However, little information is available on the effects of aeration, and even less on solutions that use bubble flow and their agronomic effects. In this study, the effects of aeration intensity on plants were studied through cultivation experiments and flow field visualization. It was found that the growth of plants did not increase linearly with an increase in aeration intensity. From the results of this study, when the aeration intensity was within the low range (0.07–0.15 L·L−1 NS·min−1), increasing the aeration intensity increased the plant growth. However, after the aeration intensity reached a certain extent (0.15–1.18 L·L−1 NS·min−1), some indicators did not change significantly. When the aeration intensity continued to increase (1.18–2.35 L·L−1 NS·min−1), growth began to decrease. These results show that for increasing dissolved oxygen and promoting plant growth, the rule is not “the higher the aeration intensity, the better”. There is a reasonable range of aeration intensity within which crops grow normally and rapidly. In addition, increasing the aeration intensity means increasing energy utilization and operating costs. In actual hydroponics production, it is very important to find a reasonable aeration intensity range.

We demonstrate a new image processing methodology for resolving gas bubbles travelling through liquid metal from dynamic neutron radiography images with an intrinsically low signal-to-noise ratio. Image pre-processing, denoising and bubble segmentation are described in detail, with practical recommendations. Experimental validation is presented—stationary and moving reference bodies with neutron-transparent cavities are radiographed with imaging conditions representative of the cases with bubbles in liquid metal. The new methods are applied to our experimental data from previous and recent imaging campaigns, and the performance of the methods proposed in this paper is compared against our previously achieved results. Significant improvements are observed as well as the capacity to reliably extract physically meaningful information from measurements performed under highly adverse imaging conditions. The showcased image processing solution and separate elements thereof are readily extendable beyond the present application, and have been made open-source.

Bubble flow can be simulated by the two-fluid model and the multi-fluid model based on the Eulerian method. In this paper, the gas phase was further divided into several groups of dispersed phases according to the diameter by using the Eulerian-Eulerian (E-E) multi-fluid model. The diameters of bubbles in each group were considered to be the same, and their distributions were reorganized according to a specific probability density function. The experimental data of two kinds of bubble flow with different characteristics were used to verify the model. With the help of the open-source CFD software, OpenFOAM-7.x (OpenFOAM-7.0, produced by OpenFOAM foundation, Reading, England), the influences of the group number, the probability distribution function, and the parameters of different bubble diameters on the calculation results were studied. Meanwhile, the numerical simulation results were compared with the two-fluid model and the experimental data. The results show that for the bubble flow with the unimodal distribution, both the multi-fluid model and the two-fluid model can obtain the distribution of gas volume fraction along the pipe radius. The calculation results of the multi-fluid model agree with the experimental data, while those of the two-fluid model differ greatly from the experimental data, which verifies the advantage of the multi-fluid model in calculating the distribution of gas volume fraction in the polydisperse bubble flow. Meanwhile, the multi-fluid model can be used to accurately predict the distribution of the parameters of each phase of the bubble flow if the reasonable bubble diameter distribution is provided and the appropriate interphase force calculation model is determined.

Combining C4D technique and cross-correlation velocity measurement technique, a new measurement method, which is suitable for the bubble/slug velocity measurement in millimeter-scale pipelines, is proposed. Based on the series resonance principle and the simulated inductor technique, a new C4D sensor is developed. With two conductance signals obtained by two new C4D sensors (the upstream sensor and the downstream sensor), the bubble/slug velocity measurement is implemented by the cross-correlation velocity measurement technique. Experiments are carried out in three pipelines with different inner diameters of 4.50, 5.46, and 6.44 mm, respectively. The experimental results show that the proposed bubble/slug velocity measurement method is effective, the development of the new C4D sensor is successful, and the velocity measurement accuracy is satisfactory. The relative error of bubble velocity measurement is less than 5.41% and the relative error of slug flow velocity measurement is less than 4.90%.

Abstract This work presents an enhancement method to improve the synergetic particles removal performance of Wet Flue Gas Desulfurization (WFGD) by adding a Flow Pattern Control (FPC) device. Experimental investigation was carried out to study the collection efficiency improvement with bubble flow formed in a single FPC unit. The results are compared to the collection efficiency with dispersed flow in an open spraying column. The grade and total collection efficiency are measured by ELPI+ and weighting method, respectively. The bubble flow formed in FPC unit is more efficient in collecting fine particles, especially for the conditions with low superficial gas velocity and liquid-to-gas ratio (L/G). The improvement of the collection efficiency at the superficial gas velocity of 3 m/s and 4 m/s is ~21.5% and ~3.1%, respectively, at [ C ] ≈ 100 mg/m3 and L/G = 10 L/m3. Taking the pressure drops into consideration, the performance index (PI) is introduced to evaluate the particle removal effect of FPC column at different operating conditions. For lower flue gas velocities (underload), the improvement on particles removal effect is more obvious and economic. In addition, the simultaneous removal of SO 2 and fine particles with the FPC device were also discussed. Graphical abstract Unlabelled Image Highlights • New internals were proposed to improve desulfurization and particles removal. • Bubble flow is used for improving the particle collection in WFGD. • The improvement of new internals was more significantly with low load. [ABSTRACT FROM AUTHOR]

The bubbles flow in immiscible fluids is widely present in metallurgical and chemical processes, and the investigation of mass transfer characteristics in immiscible fluids is of great importance in bath melting and extraction. The bubble rising process in immiscible fluids is simulated with the phase-field method, different viscosity and density ratios, interfacial tensions and bubble sizes are considered for the study of interface fluctuation behavior. Firstly, whether bubbles can cross the liquid-liquid interface is studied, and the discriminant K 1 of whether bubbles can cross the interface is proposed. When K 1 < 2.0, bubbles are trapped between the interfaces, otherwise, bubbles can successfully cross the interface. Secondly, the fluctuation behavior of bubbles on the interface is investigated after they cross the interface. Finally, the prediction model K 2 for the degree of interface fluctuation is proposed under the condition of K 1 ≥ 2.0. The interface belongs to smaller fluctuation when K 2 < 2.45, and vice versa, it belongs to larger fluctuation. The accuracy of K 2 is 93.39% after verification. [Display omitted] • The bubble rising process in immiscible fluids was simulated with the phase-field method. • The discriminant of whether bubbles can cross the interface (K 1) was proposed. • We put forward the prediction model for the degree of interface fluctuation (K 2). • The accuracy of discriminant K 1 and prediction model K 2 was verified. [ABSTRACT FROM AUTHOR]

A large amount of published data show that particles with diameter above 10% of the turbulence integral length scale (D / l > 0. 1) tend to increase the turbulent kinetic energy of the carrier fluid above the single-phase value, and smaller particles tend to suppress it. We attempted to remove limitations in earlier modeling efforts for solids on the coupling between the particles and turbulence, and better fits to the turbulence modulation amplitude as function of D / l was achieved for a number of data sets. Explicit algebraic forms of the full model were derived using asymptotic analysis, and these are general enough for application to emulsions, bubbles and solids in bulk regions of multiphase turbulent flow. Rigorous particle-kinetic theory was used to derive the work exchanged between the particles and the fluid due to both drag and added mass forces, where the latter is essential for low or moderate particle/fluid density ratios, enabling a well justified model also for emulsions and bubbles. A novel sub-model for turbulence production by vortex shedding due to turbulence-generated slip velocity was incorporated, where earlier models took the slip velocity as an input parameter. The correct asymptotic limit of vanishing turbulence modulation for small tracer particles was also provided, giving better fit to the data for small particles. We found that turbulence augmentation for large diameter solids is due to vortex shedding, and turbulence suppression for small diameters is due to mainly to turbulent drag forces and extra fluid dissipation – a conclusion that agrees with earlier models for solids, despite their possible shortcomings. An important finding is that the mechanisms for turbulence suppression for bubbles and emulsion droplets are similar to those of solids, but with the addition of added mass scaling factors. Another important observation is that augmentation may not occur at all for bubbles or emulsion droplets since the larger diameters require moderate turbulence levels to prevent breakup, so that vortex shedding may be insignificant. [Display omitted] • Solids with diameter above 10% of the turbulence integral length scale increases turbulence. • Bubbles and emulsion droplets may not induce turbulence enhancement by vortex shedding. • Model imitations on coupling between the particles and the turbulence were removed. • Explicit algebraic forms for homogeneous turbulent shear flow were derived. • Improved fits to measured turbulence modulation for varying diameter were achieved. [ABSTRACT FROM AUTHOR]

The synergetic removal of particulate matters (PM) in different wet flue gas desulfurization (WFGD) towers was investigated on a pilot-scale experimental setup with the gas flow up to 6372 m 3 /h. Three types of scrubbing tower, i.e. open scrubbing tower (OST), scrubbing tower with porous tray (TST), and scrubbing tower with a flow pattern control device (FST) were used in this study. The multiphase flow is a counter-current liquid-dispersed flow in OST, while it is an insufficient developed and fully developed bubble flow in TST and FST, respectively. The PM collection efficiency was significantly increased after adding internals (porous tray or flow pattern control device). The total collection efficiency for TST and FST was ~84.3% and ~87.2%, respectively, when using gypsum slurry as recycle liquid at a superficial gas velocity of 3 m/s and L/G  = 10 L/m 3 . Comparing to that of OST, the improvement of the efficiency was ~9.2% and ~13% for TST and FST, respectively. Interestingly, even though the pressure drop of FST is lower than that of TST, the particle removal efficiency of FST is the highest among three scrubbing towers, which means FST is much more cost-effective. The performance index ( PI ) is introduced in this study to evaluate the particle removal effect of different internals. The PI for FST is approximately 4 times larger than that of TST at L/G  = 10 L/m 3 , indicating a much better effect of FST for WFGD, especially for low-load operation in power plant. [ABSTRACT FROM AUTHOR]

Reactions of gases with liquids play a crucial role in the production of many bulk chemicals. Often, the gas is bubbled into the chosen reactor. Most of the processes at the gas-liquid interface of the bubbles and in their tails are not fully understood andwarrant further investigation. For this purpose,NMRimaging or MagneticResonance Imaging has been applied to visualize some of the processes in the bubble tail. To generate sufficient contrast, a magnetogenic gas-liquid reaction associated with a change ofmagnetic state, fromdiamagnetic to paramagnetic, was employed. In this work, a copper(I)-based compound was oxidized to copper(II) to exploit relaxation contrast. To match the speed of the rising bubbles to the acquisition time of the spin-echo imaging sequence, polyethylene glycol was added to increase the viscosity of the reacting solution. Images of the oxygen ingress into a static solution as well as of oxygen bubbles rising in the solution are presented. In both cases, changes in magnetism were observed, which reported the hydrodynamic processes. [ABSTRACT FROM AUTHOR]

The gas hydrate formed in the wellbore or pipeline may pose severe challenges to pressure control and flow assurance. One key issue to address the hydrate problem is the intercoupling of hydrate shell growth characteristics and multiphase flow behaviors, which has not been studied thoroughly in the bubble flow of a water-dominated system. In this study, we develop a fully coupled hydro-thermo-hydrate model considering the interactions of hydrate intrinsic kinetics, mass and heat transfer, and hydrodynamics mechanisms. In the model, the varying concentration of gas on the outside of a hydrate shell, is introduced to describe the dynamic equilibrium between the gas outward diffusion within the hydrate shell, hydrate formation kinetics at the hydrate/liquid interface, and gas dissolution into liquid. The simulation results agree well with the experimental data. Using the proposed model, we study a special kick development mechanism caused by the phase transition of gas traps during deepwater horizontal drilling. The simulated results show that there exists a hydrate phase stability field in the wellbore during deepwater drilling. As the migration of gas traps, the hydrate growth on the bubble surface, which is closely related to the formation and decomposition of hydrate and the dissolution and desolvation of gas, may result in an abrupt and rapid gas kick. The proposed model adds further insights into quantitatively characterizing the hydrate growth and interphase mass transfer rules in the bubble flow of water-dominated systems. [ABSTRACT FROM AUTHOR]