Bubble Diameter Distribution Research Articles

Experimental and numerical simulation research on the transport process of bubble clusters in aeration system

Improving gas-liquid mass transfer efficiency in aeration systems contributes to energy savings, cost reduction, and enhanced efficiency in wastewater treatment. However, due to the complex nonlinear interactions among bubbles in turbulence, understanding the transport mechanisms of non-uniform bubble clusters in turbulence remains unclear. This study employs a combined approach of experimental research and numerical simulations to investigate the shape, diameter distribution, trajectory, and velocity of bubbles under different aeration port sizes and flow rates. The diameter distribution of bubble clusters exhibits a bimodal distribution. Bubble trajectories during ascent mainly exhibit two types of motion patterns: “Z” shaped and linear. Increasing aeration port size and flow rate both lead to an increase in the maximum bubble diameter. Higher initial flow rates and smaller port sizes induce greater lateral velocity fluctuations in bubbles. The proposed numerical simulation method serves as a reference for simulating the transport of non-uniform bubble clusters.

Radial bubble size distributions in a rising foam column

The diameter distribution of bubbles in foam is one of the most important features in foam-based separation processes like foam fractionation and froth flotation.In this study the bubble size at different radial positions of pneumatically produced foams without coalescence and coarsening of bubbles is investigated in a cylindrical column by employing an invasive sampling probe. It is shown that pronounced differences of the local Sauter-mean diameter of the bubbles can appear in radial direction. Oftentimes a parabolic profile with the largest mean bubble diameter in the center of the column is found. The difference of the Sauter-mean diameter between wall- and center region is in the order of up to 60%. Experiments on foams produced with different spargers, gas flow rates and liquid filling levels reveal that the actual degree of the inhomogeniety depends on the specific bubble size distribution that is produced by the sparger, and becomes more pronounced if the range of bubble diameters in the foam increases. As an explanation for the observations, hydrodynamic interactions in the liquid phase, as well as the behavior of different sized bubbles close to the liquid/foam interface are proposed.The observed existence of local differences of the bubble diameters can have a strong influence the dynamic behavior, like liquid drainage, and measurement methods of pneumatic foams. In particular it can limit the applicability of surface-based bubble size measurements.

Study on the bubble breakup and internal flow characteristics in the pulsed jet ejector

To intensify the bubble breakup in the ejector, a novel pulsed jet ejector is designed in this work. The pulsed jet is introduced into the ejector by one fluidic oscillator. A high-speed camera experiment is conducted to capture the progress of bubble breakup. The intensification mechanism of pulsed jet on bubble breakup in ejector is investigated by numerical simulation. The experimental results indicate that the introduction of the pulsed jet effectively induces the occurrences of pressure fluctuations and vortex collision, prompting the deformation of bubbles to produce microbubbles. It is also found that the bubble diameter and number of microbubbles mainly depend on the process of bubble breakup in the divergent section, and the bubble diameter distribution is significantly influenced by the variation of Reynolds number. The variations of the vortex structure are induced by the pulsed jet, which is a key factor influencing mixing efficiency and bubble breakup effects. In addition, pulsed jet ejectors have superior mixing performance compared to conventional ejectors.

Effect of bubble properties and dispersion characteristics in microbubble counter-current collision flotation column

ABSTRACT Cationic collectors are widely used in the flotation of hematite, silicate, oxides, etc. GE-601, as a new type of cationic collector, which was used in various mineral flotation process, has achieved excellent selection indexes. In order to study foaming performance of GE-601, the bubble characteristics are studied in an experimental scale two-phase flotation column. A high-speed camera recorder is used to take bubbles’ images and the distribution of bubble diameter under different conditions is measured by image analysis. Moreover, the surface tension of bubbles under different reagent concentrations is measured by a surface tension meter. Studies show that as GE-601 concentration increases, d 32 gradually decreases and after exceeding CCC, Sauter mean diameter (d 32) stabilizes at 0.562 mm. When the bubble diameter decay degree is 99%, 90% and 50%, GE-601 concentration reaches 0.112 mol/m3, 0.0643 mol/m3, and 0.0295 mol/m3, respectively. The adsorption concentration of GE-601 is about 0.0254 μmol·m−2. GE-601 reduces pulsation on the surface of bubbles in flowing liquid. During the rise of bubbles, d 32 is approximately linearly related to measured height, but the concentration of d 32 and GE-601 decrease varies linearly.

Effect of gas flow rate and nozzle diameter on bubble size and shape distributions in bubble column

The influence of gas flow rates and nozzle diameters on bubble size and aspect ratio distributions was studied using high-speed photography with an image processing algorithm. Results reveal bimodal probability density distributions (PDD) of bubble diameter under all nozzle diameters, with one peak near 1.5–2 mm and the another in the larger bubble range. Increasing gas flow rates from 0.1 to 0.2 L/min leads to a higher probability density of large bubbles, indicating prevalent bubble coalescence. As the gas flow rate rises to 1.2 L/min, the peak shifts to smaller bubble diameters, and the bubble breakage becomes dominant. For 1–2 mm bubbles, shape is less influenced by gas flow rates, while 3–9 mm bubbles exhibit aspect ratio PDD peaks at an aspect ratio (E) of 0.5 across all gas flow rates. The Iguchi and Chihara model can better predict the variation of bubble departure diameter with increasing gas flow rates.

Investigation of aerosol transportation phenomena in pool scrubbing by combining bubble plume measurements and single-bubble mass transfer analysis

The fission product filtration capability of pool scrubbing is an uncertain factor in severe accident risk analysis. Limited discussions on aerosol transportation phenomena exist due to insufficient understanding of aerosol mass transfer from single bubbles and bubble plume behavior. This study aims to investigate aerosol transportation during pool scrubbing by integrating individual bubble mass transfer into the overall bubble plume.Decontamination factor (DF) measurements were conducted for various nozzle submergences, followed by analysis of bubble diameter distributions in the corresponding bubble plume. Findings revealed that the MELCOR model overestimates bubble break-up, contrary to the expected positive impact on DF. To address this discrepancy, a computational fluid dynamics simulation was employed to analyze mass transfer coefficients considering different bubble diameters and aerosol properties. By integrating the mass transfer of single bubbles, the discrepancy in the DF tendencies was attributed to the underestimation of aerosol mass transfer coefficients in individual bubbles.

Parametric study of population balance model on the DEBORA flow boiling experiment

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.

Experimental investigation on the characteristics of XG/GG/HPAM gel foam and prevention of coal spontaneous combustion

Polymer gel foam shows excellent development potential and application prospects in the prevention of coal spontaneous combustion. To reveal the relationship between the characteristics of gel foam and the prevention of coal spontaneous combustion, XG/GG/HPAM gel foam consisting of polymer xanthan gum (XG), guar gum (GG), and polyacrylamide (HPAM) is prepared. The characteristics of gel foam are investigated in terms of microstructure, viscosity, thermal stability, and film-forming. The effects of gel foam on gas products, characteristic temperature, combustion characteristics parameters, and functional groups during coal oxidation are studied. The results show that polymer delays the foam coarsening and improves the foam stability. XG/GG/HPAM gel foam exhibits a slow foam coarsening process, concentrated bubble diameter distribution, shear-thinning behavior, excellent thermal stability, and film-forming properties. Moreover, the inhibition rate of XG/GG/HPAM gel foam on coal is 43.63% higher than that of ordinary foam. XG/GG/HPAM gel foam effectively improves the apparent activation energy of coal, the maximum weight loss rate of the coal is decreased by 7.55%, and the combustibility, combustion stability, and comprehensive combustion index are diminished by 8.50%, 7.64%, and 10.17%, respectively. Simultaneously, XG/GG/HPAM gel foam reduces the oxidation activity of aliphatic hydrocarbons and oxygen-containing functional groups in coal, blocks the chain reaction, and thus inhibits coal spontaneous combustion. The results provide support for achieving efficient fire prevention performance of gel foam.

Effects of pressure and particle size on bubble behaviors in a pseudo 2D pressured fluidized bed with Geldart A/B, B and D particles

Bubble behaviors of three types of particles from Geldart A/B, B and D groups were comprehensively investigated in a pseudo 2D pressurized fluidized bed via digital image analysis. Based on the analysis of a large quantity of experimental data, the effects of pressure and particle size on the spatial distribution of bubbles, bubble diameter, rise velocity, bubble fraction and flow regimes were obtained. Results show that bubbles are smaller and uniformly dispersed throughout the bed of Geldart A/B particles, while they become densely populated and grow into much larger sizes in the bed of Geldart B particles. A single peak of large bubbles in the center and emptying of bubble near the walls is formed in the bed of Geldart D particles due to the preferable rising path of bubbles towards the center and the significant coalescence of bubbles. Bubble diameter decreases with increasing pressure, and the effect of pressure is more pronounced on Geldart D particles. Bubble rise velocity increases with the increasing particle size and decreases as pressure rises. Large bubbles/slugs hardly appear in the bed of Geldart A/B particles, while they are clearly visible in the bed of Geldart B and D particles. The flow regime transition from slugging to fast fluidization shifts to the lower gas velocity for Geldart D particles compared with Geldart B particles.

Carbon dioxide-water bubbly flow in a vertical pipe with or without chemical absorption

CO2 bubbly pipe flows with or without chemical absorption were measured to obtain spatial evolution of dissolving bubbly flows. The experiments were carried out using pure water and aqueous NaOH solution of pH = 13 at two gas volume fluxes. The spatial evolutions of flow patterns, mean void fractions and bubble diameter distributions were obtained using an image processing method. The enhancement factor correlation proposed in our previous study was implemented into a three-dimensional one-way bubble tracking method to examine its applicability to CO2-water bubbly flow with chemical absorption. The numerical prediction agreed well with the measured spatial evolutions with or without chemical absorption, which confirmed the applicability of the enhancement factor correlation to bubbly pipe flows.

Investigations of bubble size distribution on swirl effervescent atomizer flotation

Atomizer flotation has the advantages of low cost, low energy consumption, adjustable, and long cycle life in industrial applications. The bubble diameter is an important parameter for floatation. The smaller the bubble diameter, the better the flotation effect. However, the bubble diameter produced by the atomizer during flotation separation is large at present. In this paper, a swirl effervescent atomizer is designed and experimental diagnosis through a spray measurement system and submerged spray visualization system. The diameter and size distribution of bubbles in 5 mm from the atomizer outlet to the jet cross-section spray were discussed. The results showed that the swirl effervescent atomizer obtained a fine Sauter mean diameter (SMD is 13–25 μm) compared with the traditional atomizer. Three flow patterns were observed at the submerged spray system: large bubbly flow, discrete bubbly flow, and slug flow. A statistical method of bubbles under high injection pressure was proposed. The effects of the operating conditions of the effervescent atomizer on the bubble diameter were investigated. The average bubble diameter decreased with the increase in injection pressure and gas–liquid mass flow ratios (GLR). However, with the GLR being increased to 0.15, the influence of injection pressure on bubble diameter was reduced. The backpressures (Liquid level heights) have less effect on bubbles compared with injection pressure and GLR. This paper has great significance for the sustainable development of the atomizer in the flotation separation application.

Experimental study of gas-lift systems with inclined gas jets

The focus of the present research is on the optical measurements of gas jets in liquid cross flows in vertical pipes. Three distinct injection angles (-45°, 0°, 45°), two orifice diameters (2 and 5 mm) and air and water flow rates varying respectively between 0.57 to 2.15 m3h−1 and 2 to 5 m3h−1 were investigated. To characterize the continuous and dispersed flow phases, shadow sizing and particle image velocimetry (two well-established optical measurement techniques) were employed. Global and local measurements provide data on the bubble diameter distribution, bubble shapes, air jet deflection angles, mean velocity profiles in the continuous phase and pressure distributions. The work compares the different features associated with the three angles of injection to determine the most appropriate geometry for a desired application. The diameter distributions for small bubbles appear to be insensitive to the liquid and gas flow rates and to the diameter and angle of the gas injector. The size distributions of the large bubbles, however, depend strongly on the flow parameters and the geometry of the injector (diameter and angle). The measured mean velocity profiles illustrate the complex interactions between the continuous and dispersed phases and the pipe wall.

다상유동 RANS법을 이용한 수상 함정 주위 기포 층 두께 예측

This paper shows the numerical analysis of bubbly flows generated by an air bubble masking belt installed in the midships of a surface ship. Numerical simulations were performed using the Reynolds Averaged Navier-Stokes(RANS) Eulerian multiphase(EMP) flow method and the bubble layer thickness around the model and full scale ship, bubble diameter distribution, and changes in hull resistance were investigated. The layer of bubbles became thicker downstream of the both hulls as the air flow rate increased. Since the large bubbles moving downstream of the hulls rose to the free surface due to the buoyancy, the average diameter of the bubbles inside the bubble layers tended to decrease as it went downstream. Although the thickness of bubble layers according to the air flow rates at the model and full scale conditions showed a tendency to roughly follow the scale ratio, a further study on the accurate correlation should be conducted in the future. Both the model and full scale ship showed an increase in pressure resistance after air injection, and a decrease in friction resistance. The distribution of air bubbles in the propeller planes followed the nominal wake characteristics, showing more bubbles at the full scale conditions.

Computational Fluid Dynamics Modeling of the Pressure Drop of an Iso-Thermal and Turbulent Upward Bubbly Flow Through a Vertical Pipeline Using Population Balance Modeling Approach

Abstract A computational fluid dynamics (CFD) model of the two-phase flow is presented to simulate isothermal, turbulent, upward bubbly flow in a pipeline for the purpose of forecasting a mean pressure reduction along the pipe (a three-dimensional (3D) multiphase flow, by Eulerian–Eulerian strategy combined with population balance model (PBM)). A set of experimental data from the literature for water (liquid) and air (gas) in an isothermal pipe is used where the internal diameter of which is 200 mm; it tends to analyze radial void fraction and bubble diameter distributions as well as the axial pressure distribution of fluid flow. The CFD model is applied to grids of minimum control volumes. The interfacial forces, including nondrag and drag forces, where the former can be categorized into turbulent scattering, lift, and wall lubrication, have been noticed in simulations. The comparison between CFD forecasts with experimental data demonstrates that the coring phenomena plus observed wall peaking could be predicted with this CFD-PBM modeling approach. The primary aim of this study was to anticipate the axial pressure distribution of bubbly flow in the pipe by CFD modeling in a large vertical pipe. Acceptable agreement between models predictions and experimental data indicates that CFD can be a beneficial method for investigating pressure drop of an upward and multiphase flow.

Improvement of pressurized dissolution method nozzle and various characteristics of generated bubbles

In recent years, it has been confirmed that micro bubbles are effective in various industries such as aquaculture and hydroponics. It is expected that the required micro bubble diameter distribution and void fraction of micro bubble water are different in each industry. Therefore, we focused on micro bubble generated by pressurized dissolution method and an experimental study on how micro bubble diameter distribution and void fraction of micro bubble water was affected by a change of a shape of a micro bubble generating nozzle was carried out. One of the important elements that make up the nozzle is clearance part. We conducted experiments using several nozzles with various clearance widths. (clearance widths x = 0.135, 0165, 0.180, 0.210, 0.260, 0.310, 0.365 mm) As a result, we found that changes in the nozzle clearance width affect the micro bubble diameter distribution and void fraction of micro bubble water.

Pore-scale mechanisms and simulations for gas–water two-phase transport processes in natural gas reservoirs

During the development of natural gas reservoirs, predicting the bubble size distribution and transport velocity in the study of gas-water two-phase flow through porous media is extremely important in natural gas recovery. Considering the different forces that act on small and elongated bubbles, a double-bubble phase population balance model was introduced to establish an improved bubble flow model. Accordingly, a two-dimensional visualized model was designed to analyze the bubble diameter distribution and average velocity of bubbles. Dominant bubble coalescence, breakup, and coexistence flows were simulated to evaluate the uniqueness of the diameter distribution of bubbles, the change in the median bubble size at different dimensionless distances, and the average velocity distribution. The peak distribution of the bubble diameter was different in the three flow conditions. Owing to the difference in the bubble breakup and coalescence rates, the peak values of bubbles varied with the increase in the dimensionless distance. Higher bubble breakup or coalescence rates were accompanied by a rapid change in the median bubble size. Furthermore, the average velocity of the transition from small bubbles to elongated bubbles decreased significantly. Thus, the proposed pore-scale gas-water two-phase model can effectively predict the occurrence and transport processes in natural gas reservoirs.

Investigation on Bubble Diameter Distribution in Upward Flow by the Two-Fluid and Multi-Fluid Models

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.

Beyond time-averaged measurement of bubble parameters in steam-water flows with conductivity probes

Two-phase data from flashing experiments are presented beyond the traditional time-averaged approach in this work. Probability density functions of parameters such as bubble duration, velocity, chord length, and number frequency are obtained from four-sensor conductivity probes and presented here. The axial evolution of the distributions is discussed in detail along with high-speed videos for a qualitative description of the flow field. The distributions of bubble parameters are observed to be positive-skewed with a long tail, and the shape of the distributions is analyzed in terms of the skewness and kurtosis. The number frequency of spherical and cap bubbles in the liquid slug is studied, as well as the number ratios of each bubble type in the flow. Parametric studies are carried out to investigate the effects of mass flux and system pressure on the distributions of bubble parameters. Bubble diameter distribution functions such as the Nukiyama-Tanasawa, Weibull, and lognormal distributions are validated with the chord length data of spherical bubbles where the Nukiyama-Tanasawa distribution appears to fit the chord length data the best. Sensitivity study is performed to investigate the effects of the adjusting parameters on the accuracy of the fits. The data are potentially useful for the benchmark and validation of high-fidelity simulation tools and the development of modeling approaches for phase-change flows. This work also provides a template for reporting beyond-time averaged measurements in future datasets generated with conductivity probes.

Benchmarking of computational fluid dynamic models for bubbly flows

Eulerian-Eulerian computational fluid dynamic (CFD) models allow the prediction of complex and large-scale industrial multiphase gas–liquid bubbly flows with a relatively limited computational load. However, the interfacial transfer processes are entirely modelled, with closure relations that often dictate the accuracy of the entire model. Numerous sets of closures have been developed, often optimized over few experimental data sets and achieving remarkable accuracy that, however, becomes difficult to replicate outside of the range of the selected data. This makes a reliable comparison of available model capabilities difficult and obstructs their further development. In this paper, the CFD models developed at the University of Leeds and the Helmholtz-Zentrum Dresden-Rossendorf are benchmarked against a large database of bubbly flows in vertical pipes. The research groups adopt a similar modelling strategy, aimed at identifying a single universal set of widely applicable closures. The main focus of the paper is interfacial momentum transfer, which essentially governs the void fraction distribution in the flow, and turbulence modelling closures. To focus on these aspects, the validation database is limited to experiments with a monodispersed bubble diameter distribution. Overall, the models prove to be reliable and robust and can be applied with confidence over the range of parameters tested. Areas are identified where further development is needed, such as the modelling of bubble-induced turbulence and the near-wall region, as well as the best features of both models to be combined in a future harmonized model. A benchmark is also established and is available for the testing of other models. Similar exercises are encouraged to support the confident application of multiphase CFD models, together with the definition of a set of experiments accepted community-wide for model benchmarking.

Simulation and experimental study of working characteristics of an improved bioreactor for degrading oily sludge

The degradation characteristics of oily sludge in the bioreactor were studied by using Euler-multiphase flow method, in which the gas-liquid two-phase and gas-liquid-solid three-phase flow field dynamics model was established. The working characteristics of the conventional bioreactor and the proposed new bioreactor were simulated via FLUENT software respectively, and the distribution of bubble diameter and the accumulation and dispersion phenomenon of the oily sludge particles were studied. The experimental results showed that compared with the conventional bioreactor, the proposed one can significantly improve the degradation efficiency of oily sludge and greatly reduce energy consumption.