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The influence of circulating liquid velocity on bubble size distribution (BSD) and turbulence characteristics of an external loop airlift reactor was studied in this paper. The instantaneous and time‐averaged velocity in the riser were studied using particle image velocimetry (PIV), and BSDs were measured by digital image analysis technique based on machine learning. Then turbulence kinetic energy (TKE) and energy dissipation rate (EDR) were calculated through the velocity field. The results indicate that as the circulating liquid velocity increased, the peak value of BSD rapidly decreased from nearly 6 mm to approximately 2 mm. The radial velocity of the liquid gradually decreased and changed direction, eventually increasing again. TKE first decreased and then increased. Compared with bubble flow with a BSD peak of 2–6 mm, bubble flow with a BSD peak of 2 mm had larger TKE. The radial movement of bubbles had great influence on the turbulence characteristics. This study demonstrates that selecting an appropriate circulating liquid velocity can reduce the diameter of bubbles while obtaining greater TKE, thereby improving the mass transfer and reaction efficiency in external loop airlift reactors (EL‐ALR). [ABSTRACT FROM AUTHOR]

High expansion (Hi‐Ex) foam is recommended to suppress the leakage and diffusion of cryogenic liquid due to its light weight and large volume. However, the disadvantages of low stability and high break rate under environmental conditions are all limited the further application in vapor mitigation and fire extinguishing. So that, this paper focus on the effect and mechanism of nanoparticles in stabilizing Hi‐Ex foam. Three kinds of nanoparticles with different concentration were selected to evaluate the effect of foam half‐life and the mechanism of particles on improving the foam stability. The results indicated that different particle concentrations can improve the foam stability to a specific extent, and the maximum improving of half‐life can increase by 95.4% in the presence of the hydrophilic SiO2 at .5 wt%. Meanwhile, the hydrophilicity, size, and morphology of the particles have a specific impact on the foam stability. The foam expansion rate first increased and then decreased. From the microscopic point of view, the bubble size gradually increases with time by two processes of ripening and coalescence and satisfied in a logarithmic distribution. While, the liquid film thickness remarkably decreases due to foam drainage without particles and the adsorption and accumulation of nanoparticles on foam lamella can provide a spatial barrier for the film thinning and the inter bubble diffusion. Finally, the microscopic interaction mechanism on improving the foam stability has been further explored and revealed in these two aspects. [ABSTRACT FROM AUTHOR]

A one‐dimensional (1D) multifluid population balance model approach is presented as a compromise between computational effort and accuracy. The approach is used to test process scenarios, perform sensitivity analysis, and provide a reliable reactor scale‐up and optimization tool. The article focuses on a mini‐plant batch bubble column, where the scale‐up behavior in terms of bubble column height, gas flux, and composition of the liquid phase is investigated. Although simplifications were made, the model requires calibration to experimental data using different calibration methods. An optimal calibration procedure is found that minimizes experimental effort while maximizing scalability. The model was tested on various liquid‐phase compositions, and it was found to reproduce experimental data accurately. However, the model cannot reproduce flow regime changes and does not perform well across substance systems. The study shows that the applied 1D multifluid population balance approach is a valuable and reliable tool in multiphase reactor scale‐up and optimization. [ABSTRACT FROM AUTHOR]

A computational fluid dynamics coupled population balance model (CFD-PBM) was used to numerically simulate the fluid dynamics of bubble swarms in a bubble column containing non-Newtonian fluids. The effects of superficial gas velocity (Ug), the consistency index (K), and the flow index (n) on bubble size distribution (BSD), gas holdup, and fluid dynamic viscosity in a bubble column were analyzed at both local and overall scales. As Ug increases, the bubble breakup occurs excessively, the gas holdup increases, and the dynamic viscosity decreases. K and n were used to characterize the rheological properties of power law fluid. As K increases, fluid viscosity increases, bubble breakup rate decreases, gas holdup in the top zone is slightly lower than in the middle zone, and dynamic viscosity increases. Within the range of n from 0.45 to 1.07, when n is smallest, the relative frequency of bubbles smaller than the initial size is relatively large, and the overall and local gas holdup are the highest. When n = 1.07, the fluid exhibits shear-thickening properties, and the dynamic viscosity variations are significant. [ABSTRACT FROM AUTHOR]

Bubbles of different sizes exhibit distinct hydrodynamic behaviors and their dense coexistence complicates seriously the multiphase flow. The commonly‐used arithmetic average method (e.g., PIV) treats every bubble equally and consequently erases many physical details. In this study, a polydisperse particle inline image method is developed to simultaneously measure comprehensive feature set of every bubble in bubble swarms and carrier phase velocity. By harnessing the optimal frame rate capture alongside assigning IDs for tracking, complete identification of polydisperse swarm in single frame is integrated with the accurate acquisition of transient dynamics across multiple frames. In gas–liquid stirred tanks, the bubble deformation is notably intensified owing to the presence of collisions driven by velocity differences. A novel analysis of bubble hydrodynamics decomposed by bubble size reveals they are jointly commanded by the inertial effect and size effect. Actual flow regime of the system is essentially the superposition of multiple dissimilar flow patterns. [ABSTRACT FROM AUTHOR]

The flow generated in a gas-liquid stirred tank reactor highly depends on the design of the impeller and sparger. To better understand the contact between the phases and the mass and heat transfer rates, especially when the mass transfer is the limiting step, it is crucial to investigate the hydrodynamics generated by the impellers and its impact on the bubble size and their distribution, and gas volume fraction. In this work, experimental and numerical studies are performed with a novel mixed impeller in a pilot scale (T = 0.486 m) gas-liquid stirred tank reactor. The Sauter mean diameter, mean bubble diameter and bubble size distribution is determined at the different radial and axial regions by using high-speed imaging technique. Further, Euler-Euler simulations are performed to find the detailed flow field of novel mixed impeller used in the current study. Finally, the gassed power to impeller swept volume ratio is determined from the CFD and correlated with the Sauter mean diameter measured in the experiment in the impeller discharge region. It is found that the novel mixed impeller used in current work shows the similar behavior as the Rushton impeller in the impeller discharge region and it also provide good axial mixing. [ABSTRACT FROM AUTHOR]

In two-fluid simulations of flow boiling, the modeling of the mean bubble diameter is a key parameter in the closure relations governing the intefacial transfer of mass, momentum, and energy. Monodispersed approach proved to be insufficient to describe the significant variation in bubble size during flow boiling in a heated pipe. A population balance model (PBM) has been employed to address these shortcomings. During nucleate boiling, vapor bubbles of a certain size are formed on the heated wall, detach and migrate into the bulk flow. These bubbles then grow, shrink or disintegrate by evaporation, condensation, breakage and aggregation. In this study, a parametric analysis of the PBM aggregation and breakage models has been performed to investigate their effect on the radial distribution of the mean bubble diameter and vapor volume fraction. The simulation results are compared with the DEBORA experiments (Garnier et al., 2001). In addition, the influence of PBM parameters on the local distribution of individual bubble size groups was also studied. The results have shown that the modeling of aggregation process has the largest influence on the results and is mainly dictated by the collisions due to flow turbulence.

A particle size inversion method based on whale optimization algorithm (WOA) is presented. In the experiment, the small angle forward scattering measurement system is used to conduct experimental research on the inversion of bubble particle size. WOA is used to invert and simulate the bubbles that follow a certain distribution, adding different levels of random noise to verify the stability of the algorithm. The results verify the feasibility and stability of applying WOA to particle size inversion.

A three-dimensional model is established to investigate the effect of argon injection mode, argon flow rate and casting speed on the gas–liquid two-phase flow behavior inside a slab continuous casting mold. The Eulerian–Eulerian model is employed to simulate the gas–liquid flow, and the population balance model is applied to describe the bubble breakage and coalescence process in the mold. The numerical simulation results of the bubble size distribution are verified using the water model experiment. The results show that the flow field and bubble distribution are similar between the argon injection at the upper submerged entry nozzle (SEN) and tundish upper nozzle (TUN), while the number density is larger for the argon injection of TUN. The coalescence rate of bubbles and the bubble size inside the mold increase with increasing argon flow rate. When the argon flow rate exceeds 4 L/min, the flow pattern of liquid steel changes from double-roll flow to complex flow, with aggravation of the level fluctuation of the top surface near the SEN. When the casting speed increases, the bubble breakup rate increases and results in a decrease in the size of bubbles inside the mold. At a high casting speed, the flow pattern tends to form double-roll flow, and the liquid level at the narrow face of the top surface increases. [ABSTRACT FROM AUTHOR]

Hypothesis: One of the existing challenges in the foam production industry is to achieve the desired mechanical and thermal insulation properties required, which are directly related to cellular density, size, and distribution of bubbles. Therefore, predicting the bubble size distribution in each foam production system significantly contributes to the final properties of the desired foam. Nucleation, growth, coalescence of bubbles, and their final stabilization are influential stages in the ultimate properties of the foam that should be considered in predicting the bubble size distribution and laboratory testing phase.Methods: Initially, a modified classical nucleation model was used for predicting cell nucleation, and then a population balance model was employed to predict the size distribution of bubbles in a batch system for the production of polystyrene foam. The modeling of this process was one-dimensional, and changes in bubble diameter were included as the characteristic variable of the system's equations. The foam production stage was carried out at temperatures of 70°C, 90°C, and 110°C, under a pressure of 20 MPa, and the consolidation stage was performed within 0.1 s and 1 s and without consolidation. To calculate the average cell size and size distribution, SEM images and software tools such as Axiovision.v4.82.SP2 and SPSS 26 were used, and the results were compared with the modeling outcomes.Finding: Using the bubble size distribution obtained from modeling, the average bubble size at a saturation temperature of 70°C and a consolidation time of 1 s was 4.3 µm. With an increase in temperature from 70°C to 90°C, the average bubble size increased to 36.7 µm due to the higher rate of gas diffusion into the bubbles. With an increase in the amount of gas in polystyrene, the free volume increased, and glass transition temperature decreased. At 110°C, the average size of bubble cells increased to 78.1 µm. Since this temperature was higher than the glass transition temperature of polystyrene, in addition to the high gas diffusion rate into the bubble cells, the growth process did not stop, and gas diffusion and coalescence between the bubbles continued. Finally, the model predictions were compared with experiments under various conditions and demonstrated acceptable agreement.

Dissolved air flotation (DAF) is an important water treatment process for removing suspended solids. Understanding the characteristic size and spatial distribution of both bubbles and suspended solids, including their hydrodynamics, within flotation tanks is key to optimising flotation performance. In this study, a continuously operating lab scale DAF tank was constructed to simultaneously monitor size distributions and motions of microbubbles (Ø = 67–86 ± 13–19 µm) and spherical polyethylene microplastic particles (Ø = 69.8 ± 5.3 µm) in unbuffered water at circumneutral pH without salt addition and with 0.5 g L−1 sodium chloride (NaCl) added. Microplastic particles were used for the first time in such a setup. Particle tracking showed different flow regimes in the separation zone, with short-circuiting flow paths varying at different flow rates. Within the range of flowrates employed, the bubble bed that formed was not prominent enough to promote stratified flow. The addition of NaCl greatly reduced microplastic particle counts within the separation zone during flotation. This new multi-factorial approach provides critical insights into the variations in DAF performance. • Method for monitoring several factors simultaneously in DAF developed. • Image analysis observes flow patterns, particle and bubble size distribution. • First time microplastics particle removal in a DAF tank design investigated. [ABSTRACT FROM AUTHOR]

Background and Objective: For control of bread quality to achieve high loaf volume and uniform crumb structure, gas bubble dynamics in dough needs to be better understood throughout different breadmaking processes. The objective of this review was to establish a solid theoretical basis on how flour type, water and salt content, and mixing conditions affected the incorporation, evolution, and stabilization of gas bubbles in a dough. Findings: Bubble dynamics including entrainment, disentrainment, break‐up, disproportionation, growth, and coalescence were outlined and their effects on the gas phase of the dough were assessed. The application, advantages, and disadvantages of microscopy, magnetic resonance imaging (MRI) and X‐ray microtomography techniques for qualitatively or quantitatively characterizing the void fraction and bubble size distribution (BSD) in the dough at various stages of the breadmaking process have been discussed. Conclusions: Since the BSD evolution in bread dough is associated with the quality of the resultant products, to devise strategies for improving the product quality, dough formulation, and mixing conditions need to be considered. Significance and Novelty: Due to the obvious challenges of monitoring the fast evolution of BSD in yeasted dough, future research needs to focus on the effects of yeast activity on dough's BSD. [ABSTRACT FROM AUTHOR]

The paper describes a study of wet foams in microgravity whose bubble size distribution evolves due to diffusive gas exchange. We focus on the comparison between the size of bubbles determined from images of the foam surface and the size of bubbles in the bulk foam, determined from Diffuse Transmission Spectroscopy (DTS). Extracting the bubble size distribution from images of a foam surface is difficult so we have used three different procedures: manual analysis, automatic analysis with a customized Python script and machine learning analysis. Once various pitfalls were identified and taken into account, all the three procedures yield identical results within error bars. DTS only allows the determination of an average bubble radius which is proportional to the photon transport mean free path $\ell ^*$. The relation between the measured diffuse transmitted light intensity and $\ell ^*$ previously derived for slab-shaped samples of infinite lateral extent does not apply to the cuboid geometry of the cells used in the microgravity experiment. A new more general expression of the diffuse intensity transmitted with specific optical boundary conditions has been derived and applied to determine the average bubble radius. The temporal evolution of the average bubble radii deduced from DTS and of the same average radii of the bubbles measured at the sample surface is the same (to a factor probably close to one) throughout the coarsening. Finally, ground experiments were performed to compare bubble size distributions in a bulk wet foam and at its surface at times so short that diffusive gas exchange is insignificant. They were found to be similar, confirming that bubbles seen at the surface are representative of the bulk foam bubbles.

A numerical simulation based on computational fluid dynamics and population balance model has been accomplished to analyze the gas-liquid-solid three phases in molten salt chlorination furnace. A two-way coupled model considering the influence of the bubble size distribution (BSD) on the flow field by transmitting the data of the Sauter mean diameter is firstly set up and validated with the experimental and simulation results. Based on the mechanisms of bubble coalescence and breakup induced by the turbulence and the bubble-particle interaction, some factors like the velocity field, volume fraction, turbulence dissipation rate, BSD, bubble number density and particle distribution are discussed. The results show that 40 m/s is an appropriate operation parameter for the inlet velocity of molten salt chlorination furnace, for the reason that the large bubble in the upper part of the furnace can break up into fine bubbles distributed uniformly in the whole furnace. It is conducive to the increase the interaction opportunity among phases, promote the chemical reactions, and reduce the area of "dead zone", providing theoretical support and engineering design basis for the production of large-scale molten salt chlorination furnace. [Display omitted] • The influence of bubble size distribution is modeled with two-way coupled CFD-PBM considering particle effects. • The performance of gas stirring is well predicted and analyzed in the molten salt furnace. • The appropriate operation parameter (40 m/s) for the inlet velocity of molten salt chlorination furnace is proposed. • The efficiency of bubble-particle entrainment and gas stirring are studied by discussing the turbulence dissipation rate. [ABSTRACT FROM AUTHOR]

Although thermoplastics possess many desirable traits as solidified materials, they are combustible and burn readily. Post burning samples of polymethylmethacrylate (PMMA) are the focus of this study. During flame spread, PMMA forms a bubble containing molten surface layer that influences the spread rate and the surface mass efflux. This study examines the formation and distribution of bubbles inside a PMMA sample that has previously been subjected to flame spread and then re‐hardened into its solid state. Experiments discussed herein were conducted in a Narrow Channel Apparatus (NCA), which reduces the influences of gravitation (buoyancy) on flame spread. Bubble sizes and counts were determined using digital image analysis (DIA). The burnt samples were analyzed by dividing sample images into eight equal area sections. Frequency distributions of bubble size (area) were compared. Distribution functions were fitted against the empirical probability density function (PDF) for the bubble size distribution. The log‐normal distribution predicts the bubble size distribution for all segments. The bubble distribution function can be used to describe physical processes inside the polymeric material as it undergoes thermal transformation by the spreading flame. [ABSTRACT FROM AUTHOR]

Accurate measurements of the bubble size distribution (BSD) are crucial for investigating gas–liquid mass transfer mechanisms and describing the characteristics of chemical production. However, measuring the BSD in high-density bubbly flows remains challenging due to limited image algorithms and high data densities. Therefore, an end-to-end BSD detection method in dense bubbly flows based on deep learning is proposed in this paper. The bubble detector locates the positions of dense bubbles utilizing objection detection networks and simultaneously performs ellipse parameter fitting to measure the size of the bubbles. Different You Only Look Once (YOLO) architectures are compared, and YOLOv7 is selected as the backbone network. The complete intersection over union calculation method is modified by the circumferential horizontal rectangle of bubbles, and the loss function is optimized by adding L 2 constraints of ellipse size parameters. The experimental results show that the proposed technique surpasses existing methods in terms of precision, recall, and mean square error, achieving values of 0.9871, 0.8725, and 3.8299, respectively. The proposed technique demonstrates high efficiency and accuracy when measuring BSDs in high-density bubbly flows and has the potential for practical applications. [ABSTRACT FROM AUTHOR]

In this work, we present the results collected in a gas-liquid stirred tank by a combination of experimental and computational methods, with the aim of presenting original data on the bubbles size distribution and contributing to the development of fully predictive methods for the design and the scale-up of chemical and biochemical gas-liquid reactors. Basic variables which affect mass transfer and consequently the performances of industrial aerobic fermentations are discussed, with special focus on the bubble size distribution, the gassed power consumption and the gas cavities. The current developments of Two Fluid and Population Balance models for obtaining fully predictive results on gas-liquid mixing in stirred tanks are discussed. The results confirm that the correct prediction of the bubble size in the impeller zone is a crucial prerequisite for obtaining reliable results of the hydrodynamics of aerated stirred tanks. • Measurement of bubble size distribution, gassed power consumption and gas cavities. • Fully predictive methods for design and scale-up of sparged gas-liquid reactors. • Assessment of Two-Fluid and Population Balance models. • Bubble size in the impeller zone crucial for reliable hydrodynamics predictions. [ABSTRACT FROM AUTHOR]

Venturi bubble generators have been extensively studied because of having a simple structure and high foaming efficiency, while producing a uniform bubble size. The effect of a noncondensable gas on hydraulic cavitation was considered to improve the Zwart-Gerber-Belamri cavitation model. This improved model and a population balance model were used to study the effect of cavitation on bubble fragmentation. The CFD-PBM results were compared with experimental results, and the accuracy of the improved calculation method was verified in terms of the distributions for the cavitation cavity, gas phase, and bubble size. The calculation results showed that increasing the noncondensable gas content over a certain range promoted the development of hydraulic cavitation, and the cavitation intensity could be indirectly controlled by adjusting the noncondensable gas content. With increasing cavitation intensity, the average bubble size decreased, and the bubble size distribution became narrower. Therefore, a high-pressure pulse generated by cavitation could effectively break bubbles. The development process of microbubbles was studied. The main controlling factors for bubble formation were determined to be the turbulent shear force of the fluid and the collapse impact force of the cavitation group, which provides a theoretical basis for optimizing the design of bubble generators.

Fluids incorporating carbon dioxide (CO2) microbubbles have been utilized to promote enhanced oil recovery from hydrocarbon reservoirs. The performance of such fluids in porous media is greatly affected by both the bubble size and stability. On this basis, the present study evaluated the effects of varying the concentrations of a xanthan gum (XG) polymer, a surfactant (sodium dodecyl sulfate: SDS) and sodium chloride (NaCl) on both the stability and bubble size distribution (BSD) of CO2 microbubbles. CO2 microbubble dispersions were prepared using a high-speed homogenizer in conjunction with the diffusion of gaseous CO2 through aqueous solutions. The stability of each dispersion was ascertained using a drainage test, while the BSD was determined by optical microscopy and fitted to either normal, log-normal or Weibull functions. The results showed that a Weibull distribution gave the most accurate fit for all experimental data. Increases in either the SDS or XG polymer concentration were found to decrease the microbubble size. However, these same changes increased the microbubble stability as a consequence of structural enhancement. The addition of NaCl up to a concentration of 10 g/L (10 g/1000g) decreased the average bubble size by approximately 2.7%. Stability was also reduced as the NaCl concentration was increased because of the gravitational effect and coalescence. [ABSTRACT FROM AUTHOR]

A comprehensive experimental characterization of a small‐scale bubble column bioreactor (60 mL) is presented. Bubble size distribution (BSD), gas holdup, and kLa were determined for different types of liquids, relevant fermentation conditions and superficial gas velocities uG. The specific interfacial area a and liquid mass transfer coefficient kL have been identified independent of each other to unravel their individual impact on kLa. Results show that increasing uG leads to larger bubbles and higher gas holdup. As both parameters influence a in opposite ways, no increase of a with uG is found. Furthermore, kL increases with increasing bubble size outlining that improved oxygen transfer is not the result of higher a but of risen kL instead. The results build the foundation for further simulative investigations. [ABSTRACT FROM AUTHOR]

Venturi bubble generators have been extensively studied because of having a simple structure and high foaming efficiency, while producing a uniform bubble size. The effect of a noncondensable gas on hydraulic cavitation was considered to improve the Zwart-Gerber-Belamri cavitation model. This improved model and a population balance model were used to study the effect of cavitation on bubble fragmentation. The CFD-PBM results were compared with experimental results, and the accuracy of the improved calculation method was verified in terms of the distributions for the cavitation cavity, gas phase, and bubble size. The calculation results showed that increasing the noncondensable gas content over a certain range promoted the development of hydraulic cavitation, and the cavitation intensity could be indirectly controlled by adjusting the noncondensable gas content. With increasing cavitation intensity, the average bubble size decreased, and the bubble size distribution became narrower. Therefore, a high-pressure pulse generated by cavitation could effectively break bubbles. The development process of microbubbles was studied. The main controlling factors for bubble formation were determined to be the turbulent shear force of the fluid and the collapse impact force of the cavitation group, which provides a theoretical basis for optimizing the design of bubble generators. [ABSTRACT FROM AUTHOR]

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The Spallation Neutron Source (SNS) creates neutrons by striking a liquid mercury target with short pulses of high-energy protons. SNS targets have been operated with helium microbubble gas injection into portions of the flowing mercury since 2017. The measurements during in situ testing showed that the strain response of the stainless steel target vessel significantly decreased with gas injection. Strain reductions ranged from 40% to 75% for targets operating with gas-injection rates between 2 and 3 standard liters per minute. These strain reductions have allowed SNS to operate reliably at 1.4 MW over the last few years and are expected to significantly improve the fatigue life of the target vessel. The achieved mitigation of the pulse response and the associated cavitation damage with gas injection is a cornerstone of the upgrade basis to the redesigned mercury vessel for planned higher power operation.Existing methods can simulate the structural response of the target operated without gas injection. Developing simulation techniques that account for the benefits of gas injection adds a considerable challenge. A combined mercury/bubble material model based on the Rayleigh–Plesset equation was developed to improve simulation of the response of a structure containing liquid and gas by incorporating bubble growth volume feedback. This paper details the implementation of the mercury/bubble material model in the pulse simulation of an existing target design. The newly developed simulation technique combines the current no-gas mercury material model for no-gas regions and the bubbly mercury material model for the regions with gas bubbles. The results of the strain response simulation using the new techniques are promising. The challenges of the technique development are also discussed. For example, the bubble size distributions are crucial for the simulations but remain an area of active research.

A three-dimensional model is established to investigate the effect of argon injection mode, argon flow rate and casting speed on the gas–liquid two-phase flow behavior inside a slab continuous casting mold. The Eulerian–Eulerian model is employed to simulate the gas–liquid flow, and the population balance model is applied to describe the bubble breakage and coalescence process in the mold. The numerical simulation results of the bubble size distribution are verified using the water model experiment. The results show that the flow field and bubble distribution are similar between the argon injection at the upper submerged entry nozzle (SEN) and tundish upper nozzle (TUN), while the number density is larger for the argon injection of TUN. The coalescence rate of bubbles and the bubble size inside the mold increase with increasing argon flow rate. When the argon flow rate exceeds 4 L/min, the flow pattern of liquid steel changes from double-roll flow to complex flow, with aggravation of the level fluctuation of the top surface near the SEN. When the casting speed increases, the bubble breakup rate increases and results in a decrease in the size of bubbles inside the mold. At a high casting speed, the flow pattern tends to form double-roll flow, and the liquid level at the narrow face of the top surface increases.

[Display omitted] • Effect of surfactant concentration, brine, and oil on the stability of CO 2 microbubbles. • Higher Acacia concinna surfactant concentration enhances foam stability. • Higher gas flow rates lead to faster foam collapse, emphasizing the need for optimal rates. • Drainage stability kinetics provides crucial insights into the foam behavior over time. • A log-normal distribution effectively described bubble size distribution in emulsions, aiding in optimizing microbubble size. This study addresses the challenge of CO 2 microbubble stability in enhanced oil recovery (EOR), with a focus on the combined effects of surfactant concentration, brine concentration, brine-oil ratio, and gas flow rate. Microbubble destabilization, driven by phase separation and improper brine-oil ratios, is a critical issue in EOR. The novelty of this research lies in the use of Acacia concinna, a natural, non-ionic surfactant, to enhance microbubble stability sustainably. The study systematically investigates foamability, drainage kinetics, surface tension, rheology, and bubble size distribution to assess microbubble stability. The results showed that increasing surfactant concentration and brine-oil ratio significantly impacted foam stability and bubble size distribution, with optimal stability conditions observed at 2 wt% surfactant concentration (53.6 min), 5000 ppm brine concentration (47.6 min), a brine-oil ratio of 1:2 (52.4 min), and a CO 2 gas flow rate of 1 lpm. Key findings also indicate that increasing NaCl concentration from 5000 to 20,000 ppm caused an increase in microbubble diameter, while higher gas flow rates reduced bubble size. The work introduces new empirical correlations for predicting bubble size distribution based on column diameter, surfactant and brine concentrations, viscosity, density, and gas superficial velocity. These correlations provide a more accurate means of optimizing EOR processes, improving oil recovery efficiency while enhancing CO 2 sequestration, contributing to both energy production and environmental sustainability. [ABSTRACT FROM AUTHOR]

A new model to predict the breakup of gaseous bubbles in a continuous liquid phase is developed. In the model each bubble is modelled as a spring–damper system, namely a Kelvin–Voigt element, while the outer force is derived by a Lagrangian analysis determining the largest stretching rate of the flow field below. The developed model is based on physical principles and no further arbitrary parameters have to be adjusted. Each bubble is observed on its way through the bubbly flow individually, taking into account its history along its respective path. With the implemented model numerical simulations in a wide range of scales are conducted, ranging from the laboratory scale of a vessel of 3 L to the large industrial scale of 15 m 3 . The simplicity of the model allows for a good cost to benefit ratio. In the present work, the achieved results are compared to experimental data obtained from optical measurements in a replica of a 200 L aerated stirred tank reactor for various stirrer frequencies. [Display omitted] • A novel model to predict bubble breakup is formulated. • The model is implemented in M-Star CFD and tested for a wide range of scales. • The history of each bubble is accounted for individually. • The results are validated with experimental data. [ABSTRACT FROM AUTHOR]

[Display omitted] • Multiple sensors collectively measured gas dispersion in a lab-scale flotation cell. • Spatial distribution of hydrodynamics in a 3-phase binary flotation system was resolved. • In situ bubble size is determined using a high-resolution in-line endoscope at high particle loading. • Highest local bubble surface area flux close to the rotor. Improvement in resolving hydrodynamic variables in multiphase flows is key to optimizing flotation performance. However, due to equipment complexity and opacity of three-phase systems, in situ measurements become challenging. Therefore, by using a novel multi-sensor approach, the aim of this study is to spatially resolve key hydrodynamic and gas dispersion parameters in a mechanical flotation cell such as superficial gas velocity (J g), gas holdup (ε g), bubble size distribution (BSD), and bubble surface area flux (S b). A high-resolution inline endoscope (SOPAT), J g and ε g sensors were fixed at multiple axial positions in a 6L nextSTEP™ flotation cell. This multi-sensor concept has been applied to a simplified benchmark flotation scenario, as part of a binary (pyrite-quartz) flotation test campaign (30 % solid load). Varying operating conditions include tip speed (4.7 – 5.5 m/s), air flow (0.4 – 0.5 cm/s), frother (MIBC: 30 – 60 g/ton), and collector concentrations (PAX: 30 – 60 g/ton). S b is a good indicator of gas dispersion efficiency in flotation, and local measurements indicated that there are significant differences in the local superficial gas velocities which can be measured with our adapted sensor. Real-time bubble size measurements reflected the high shear rates near the rotor–stator region. Overall, the gas flow rate and frother concentration were shown to have the most significant effect on the gas dispersion in the benchmark flotation tests. [ABSTRACT FROM AUTHOR]

Artificial or natural processes can cause underwater gas leakage, which often forms upwelling bubbly plume. The interaction of gaseous plume with acoustic waves would result in the variation of sound speed, which makes it possible to monitor the upwelling process via active acoustics. In this work, we build a numerical model to simulate the transport of gaseous bubbles and the sound speed response to the plume in the acoustic channel. The effectiveness of the model is validated by conducting a tank-based experiment, in which the sound speed variations were measured by varying gas flow rates. Meanwhile, signals at six frequencies (1 to 8 kHz) were transmitted and propagated through the medium part of which was occupied by the gaseous plume. Moreover, the comparison results also give a matched bubble size distribution (BSD), which further confirms the validity of the proposed model. [ABSTRACT FROM AUTHOR]

The hydrodynamics involved with the rise of air bubbles in shear‐thinning non‐Newtonian liquids in bubble columns was investigated using computational fluid dynamics (CFD). In bubble columns, the bubble size distribution (BSD) and gas holdup significantly affect the mass transfer rates and the reactor design. Consequently, the influence of superficial gas velocity, flow index, consistency index, sparger bubble size, and yield stress were analyzed on a local and global scale. The bubble sizes and the coalescence and breakage phenomena were incorporated using the homogeneous discrete method of the population balance model (PBM). The bubbles underwent coalescence during ascent and exhibited bimodal distribution. The radial homogeneity of the gas phase increased axially. Moreover, the zones of low liquid dynamic viscosity produced zones of a high gas holdup. Though the dual effect of viscosity on gas holdup was non‐existent, the gas holdup surged after 35.1 mPa s at the mid‐zone and remained constant thereafter. The noteworthy differences in simulation results put further emphasis upon the importance of sparger bubble size in CFD modelling. A decrease in the overall gas holdup and the axial air velocity with yield stress was observed. CFD simulation proved capable of providing results in reasonable agreement with experiments. [ABSTRACT FROM AUTHOR]

Knowledge of bubble size distribution (BSD) is critical for controlling mass transfer and reaction in bubble column reactors. Installation of internals further complicates this issue. The effects of internals on BSD were systematically investigated through experiments and computational fluid dynamics‐population balance model simulations. The experiments show a bimodal distribution of the volume‐based BSD except at low superficial gas velocity of 0.01 m/s. Addition of 20% internals increases the small‐bubbles fraction, making the first BSD peak more evident. Correspondingly, the simulation reveals a prominent decrease of turbulent dissipation rate and turbulent kinetic energy. Moreover, while the unresolved turbulent kinetic energy dominates in the empty columns, the resolved portion becomes the major component in the presence of internals. This suggests that internals may redistribute turbulent kinetic energy in each scale, which provides more insights into the complex flow characteristics in the presence of internals and process intensification. [ABSTRACT FROM AUTHOR]

Accurate measurements of the bubble size distribution (BSD) are crucial for investigating gas–liquid mass transfer mechanisms and describing the characteristics of chemical production. However, measuring the BSD in high-density bubbly flows remains challenging due to limited image algorithms and high data densities. Therefore, an end-to-end BSD detection method in dense bubbly flows based on deep learning is proposed in this paper. The bubble detector locates the positions of dense bubbles utilizing objection detection networks and simultaneously performs ellipse parameter fitting to measure the size of the bubbles. Different You Only Look Once (YOLO) architectures are compared, and YOLOv7 is selected as the backbone network. The complete intersection over union calculation method is modified by the circumferential horizontal rectangle of bubbles, and the loss function is optimized by adding L2 constraints of ellipse size parameters. The experimental results show that the proposed technique surpasses existing methods in terms of precision, recall, and mean square error, achieving values of 0.9871, 0.8725, and 3.8299, respectively. The proposed technique demonstrates high efficiency and accuracy when measuring BSDs in high-density bubbly flows and has the potential for practical applications.

Bubble size and its distribution are the important parameters which have a direct impact on mass transfer in bubble column reactors. For this, a new robust image processing technique was presented for investigating hydrodynamic aspects and bubble behavior in real chemical or biochemical processes. The experiments were performed in a small-scale bubble column. The study was conducted for the wide range of clear liquid heights and superficial gas velocities. However, a major challenge in image analysis techniques is identification of overlapping or cluster bubbles. This problem can be overcome with the help of the proposed algorithm. In this respect, large numbers of videos were recorded using a high-speed camera. Based on detailed experiments, the gas–liquid dispersion area was divided into different zones. A foam region width was found as inversely proportional to the clear liquid height. An entry region width was found as directly proportional to the clear liquid height. Hydrodynamic parameters, including gas holdup, bubble size distribution, and Sauter mean bubble diameter were evaluated and compared for different operating conditions. The gas holdup was calculated from both height measurement and pixel intensity methods, and it was found to be indirectly proportional to clear liquid height. Bubble sizes affect the bubble column performance; therefore, bubbles are tracked to calculate the bubble size distribution. Experimental results proved that the proposed scheme is robust. [ABSTRACT FROM AUTHOR]

Bubble cutting was realized by installing a wire mesh in a micro-structured bubble column (MSBC) and studied experimentally with liquid viscosity range from 1 to 39.6 mPa·s. A non-intrusive high-speed camera method was used to determine bubble size and size distribution. The changes of gas holdup, bubble size, size distribution and Sauter mean diameter before and after cutting were systematically studied with mesh openings of 3.8 mm and 5.5 mm. Three novel bubble cutting behaviors with uniform cutting, detachment cutting and indirect cutting behavior were observed. In the presence of two wire meshes, the bubble size distribution roughly shows a Gaussian curve distribution and the peak tends to shift towards lower diameters. With increasing liquid viscosity and superficial gas velocity, the dominant peak tends to move towards higher diameters, resulting in poor mesh cutting effect. After cutting, in the case of two wire meshes, the Sauter mean diameter decreased by 33.5% and 22.2% and the gas holdup increased by 3.2–12.2% and 1.2–4.4%, respectively. For the case of 3.8 mm mesh opening, the interfacial area increased by 10–26%, which is much better than 5.5 mm mesh. The mean bubble size above the mesh will grow again and its growth rate depends on the liquid viscosity. [ABSTRACT FROM AUTHOR]

Gas embolism is a potentially serious complication of hysteroscopic surgery. It is particularly necessary to monitor bubble parameters in hysteroscopic images by computer vision method for helping develop automatic bubble removal devices. In this work, a framework combining a deep edge-aware network and marker-controlled watershed algorithm is presented to extract bubble parameters from hysteroscopy images. The proposed edge-aware network consists of an encoder-decoder architecture for bubble segmentation and a contour branch which is supervised by edge losses. The post-processing method based on marker-controlled watershed algorithm is used to further separate bubble instances and calculate size distribution. Extensive experiments substantiate that the proposed model achieves better performance than some typical segmentation methods. Accuracy, sensitivity, precision, Dice score, and mean intersection over union (mean IoU) obtained for the proposed edge-aware network are observed as 0.859 ± 0.017, 0.868 ± 0.019, 0.955 ± 0.005, 0.862 ± 0.005, and 0.758 ± 0.007, respectively. This work provides a valuable reference for automatic bubble removal devices in hysteroscopic surgery. [ABSTRACT FROM AUTHOR]

The containment filtered venting system (CFVS) filters the atmosphere of the containment building and discharges a part of it to the outside environment to prevent containment overpressure during severe accidents. The Korean CFVS has a tank that filters fission products from the containment atmosphere by pool scrubbing, which is the primary decontamination process; however, prediction of its performance has been done based on researches conducted under mild conditions than those of severe accidents. Bubble behavior in a pool is a key parameter of pool scrubbing. Therefore, the bubble behavior in the pool was analyzed under various injection flow rates observed at the venturi nozzles used in the Korean CFVS using a wire-mesh sensor. Based on the experimental results, void fraction model was modified using the existing correlation, and a new bubble size prediction model was developed. The modified void fraction model agreed well with the obtained experimental data. However, the newly developed bubble size prediction model showed different results to those established in previous studies because the venturi nozzle diameter considered in this study was larger than those in previous studies. Therefore, this is the first model that reflects actual design of a venturi scrubbing nozzle.

• Bubble dynamics in a pool-scrubbing column is investigated by CFD-PBM method. • Performance of various breakup models is studied based on literature data. • The primary bubble size and breakup rate increases with the injection flow rate. • Various breakup mechanisms and their respective contribution is investigated. • The breakup rate, number of daughter bubbles and their size distribution have a joint effect. Pool scrubbing refers to the process of retention of harmful particles or gaseous components by bubbling in liquid media, which is characterized with high injection velocity and complex bubble dynamics. A comparative study of bubble breakup and coalescence models is performed to investigate the bubble size evolution in a pool-scrubbing column. The bubble size distributions along the column height are obtained by using a CFD (Computational Fluid Dynamics) – PBM (population balance model) coupled method, where the flow field is described by a two-fluid model while bubble size change by the discrete PBM. Various combinations of bubble breakup and coalescence models are investigated, and the bubble size distribution and Sauter mean diameter are compared with the literature data. The results show that under the pool-scrubbing conditions, bubble breakup is dominant compared to coalescence and bubble size decreases continuously, especially in the injection zone. The breakup rate predicted by three breakup models available in the official release of OpenFOAM foundation software is found to differ by several orders of magnitudes, and their daughter size distributions are completely different as well. Some model combinations are able to predict the bubble size more satisfactorily, but there are still biases. For example, the fraction of bubbles is either overestimated or underestimated in certain size ranges compared to the experimental values. Proper description of the breakup rate and daughter bubble size distribution needs further efforts. Additionally, the mechanism governing the breakup is investigated by implementing the breakup model of Liao, which accounts for the effects of turbulence fluctuation, velocity shear in the bulk and eddies as well as interfacial friction. It revealed that both turbulence and interfacial friction contribute to bubble breakup in the pool scrubbing column, and the calibration of each mechanism under different conditions is necessary for future study. Moreover, the assumption of binary or multiple breakup has an obvious effect on the simulation results. Future efforts are needed to model the breakup of gigantic bubbles in the injection zone and turbulence modulation caused by large deformable bubbles. [ABSTRACT FROM AUTHOR]

• Applicability analysis of various breakup and coalescence kernels are studied in CC mold. • The coalescence and breakup mechanisms of bubbles in CC mold was revealed. • A calibration factor of coalescence kernel is proposed to more accurately predict bubble size distribution. Previous studies on polydispersed bubbly flow in continuous casting (CC) mold were mainly attentive to the modeling of shear-induced turbulence, interfacial force, and bubble swarm effects. The current study reveals the coalescence and breakup mechanisms of bubbles in CC mold. Then, a calibration factor of coalescence kernel is proposed based on local gas holdup to harmonize the imbalance between coalescence and breakup rates. The effect of bubble coalescence and breakup models on the Sauter mean diameter, gas holdup, and liquid velocity were studied and against with the experimental data. The results show that the Turbulent and Liao models underestimate the bubbles coalescence rate and the Luo coalescence model overestimates the bubbles coalescence rate. Meanwhile, turbulence shear and surface instability overestimate the bubble breakup frequency, and turbulent impact is the most important mechanism used to describe bubble breakup phenomenon in the CC mold. Furthermore, the turbulent fluctuation, buoyancy driven, and wake entrainment should be considered to define the bubbles collision frequency, while the viscous shear and eddy capture mechanisms could be neglected. The Luo-Prince model could accurately predict the bubble size distribution and the fan-shaped distribution of bubble clusters, which comprehensively considers three collision mechanisms. Finally, the combination form of calibration factors could effectively describe the influence of local gas holdup on bubble collision frequency. The proposed calibration factor can predict bubble size distribution more accurately in the CC mold. The relative error of mean bubble diameter prediction is reduced from 63.53 % to 17.86 %. In turbulent flow, the process of bubble breakup can be divided into two steps. Firstly, bubbles collide with small-scale turbulent eddies. Secondly, the kinetic energy of turbulent eddies is larger than the bubbles surface energy. At present, the main factors leading to bubble breakup can be attributed to turbulence fluctuation intensity, bubble shape, and surface instability for air-water systems. It has been proven that turbulent fluctuations play a role on bubble breakup rate and the shape of bubbles with a diameter less than 10 mm has little effect on the probability of bubble breakup. Meanwhile, small bubbles with a size smaller than the critical diameter and the breakup rate caused by surface instability can be ignored. Therefore, the breakup kernel only considers the influence of turbulent impacts on bubble breakup. Compared to bubble breakup behavior, the coalescence mechanism of bubbles is more complex. The coalescence rate consists of coalescence efficiency and collision frequency between bubbles. Turbulence, eddy capture, viscous shear, wake acceleration, and buoyancy driven have an effect on collision frequency. Due to the complexity of turbulent flow, it is difficult to find a suitable PBM to describe the coalescence and breakup behavior of bubbles. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Sensitivity of local bubble plume hydrodynamics to viscosity and sparger design is examined • Optical Probe and shadowgraph technique revealed strong influence of sparger design on the gas phase • Particle-image velocimetry revealed only a weak influence of sparger design on the liquid phase • Huge sensitivity to viscosity was observed in both phases, regardless of the sparger • Customized phase averaging combined with proper orthogonal decomposition gave access to further insides The present paper provides a complete databank of bubble plume hydrodynamics in various media characterized by different viscosities in the range 1 – 100 mPa. s. Thus, the influence of the viscosity on bubble plume oscillations and on both liquid and gas velocity fields is studied. The role of the bubble size distribution at different viscosities was also analysed by using two different spargers: a membrane to create ellipsoidal millimetrice bubbles and a slugflow tube to create spherical cap bubbles. Mean velocity profiles, averaged over a large number of plume oscillation periods and corresponding root mean square profiles are discussed, in both phases. Furthermore, void fraction profiles, plume oscillation periods, and bubble size distributions are given for all experimental conditions. Finally, probability density functions and phase averaged profiles in the liquid phase provide additional information. The dependence of bubble plume hydrodynamics on liquid viscosity is huge. At large viscosity, the oscillating plume is damped, regardless of the sparger. Concerning the membrane sparger the viscosity increase modifies the plume oscillation period and its lateral plume expansion, whereas, in the case of the slugflow sparger, only the plume expansion is impacted. Liquid phase hyrdodynamics are weakly affected by the choice of sparger, especially at high viscosities. [ABSTRACT FROM AUTHOR]

Subcooled flow boiling was experimentally investigated in a horizontal annulus with a temperature-controlled boiling surface and transparent outer pipe facilitating visualization. Boiling occurs on a copper tube with a diameter of 12 mm in an annulus with a 2 mm gap. Refrigerant R245fa is used as a working fluid. The focus of this study is to explore the effect of heat flux variation on the boiling flow patterns at approximately constant inlet flow conditions of the working fluid (fixed mass flux and inlet fluid temperature). Subcooled flow boiling is recorded by a high-speed camera, images are analyzed by a neural network to determine the bubble size distributions and their variation with the heat flux. The experimental setup being a part of the laboratory THELMA (Thermal Hydraulics experimental Laboratory for Multiphase Applications) at the Reactor Engineering Division of Jožef Stefan Institute, analysis methods and measurement results are presented and discussed. [ABSTRACT FROM AUTHOR]

A population balance model based on the multiple-size-group (MUSIG) approach was developed to investigate the multi-size bubbly flow in a slab continuous casting mold. Firstly, effects of the bubble size group number, the initial bubble diameter, and the calibration factors for breakage and coalescence in MUSIG model on the multi-size bubbly flow were discussed in detail. Then, effects of both the water and gas flow rates on the bubble size distribution, the gas volume fraction, and the turbulence intensity of liquid phase were investigated. A relatively high water flow rate intensified the turbulence in the upper recirculation region of the mold and also eased the turbulence near the submerged entry nozzle (SEN) by promoting the breakage and horizontal transportation of bubbles; thus, an appropriate water flow rate is essential for better stability with a lower turbulence intensity near the SEN to prevent exposed slag eye formation and slag entrainment. With increase in the gas flow rate, the mean bubble diameter and gas volume fraction increased significantly, the turbulence near the SEN was also significantly increased, but this effect was much weaker in the region away from the SEN. [Display omitted] • Bubble initial diameter and size group number in MUSIG model is optimized. • Effects of calibration factors for coalescence and breakage models are discussed. • Bubble redistribution behavior due to variation of operating parameter is revealed. [ABSTRACT FROM AUTHOR]

Oil is a key medium for transmitting power and coupling information in the hydraulic transmission system. Accurate calculation and measurement of the dynamic compressibility of the oil have profound significance to the system performance analysis. The present study primarily focuses on the effect of steady pressure on the bulk modulus of static oil. However, changing pressure and flowing oil are the general working conditions in most of hydraulic apparatus. There are few researchers paying attention to the influence of pressure on the compressibility of flowing oil. Considering the log-normal distribution of bubble size in oil, an improved static oil model (Model B) is developed to calculate the bulk modulus of the motionless oil under the dynamic pressure. Then, by deriving Model B, this paper proposes an original flowing oil model (Model C) to determine the effective bulk modulus of flowing oil. Finally, based on the inherent pressure pulsation of the axial piston pump, an innovative online method for measurement of the bulk modulus of flowing oil is presented as it has the advantage of avoiding interference with flow stability. It has been proved that the changes in the flow velocity corresponds to the crucial effect on the effective bulk modulus of flowing oil, especially under the low-flow and low-pressure operation conditions. Those results and analysis provide promoting support for identifying and determining the effective bulk modulus of oil, analyzing the system stiffness, improving the control accuracy, as well as optimizing the mathematical models.