Bubbles Of Different Sizes Research Articles

Thermodynamics of the inception and interactions of multiple laser-produced cavitation bubbles using the lattice Boltzmann method

Understanding the thermodynamics associated with the inception and interactions of multiple cavitation bubbles is vital in developing deeper insights into the flow field and temperature properties of cavitation bubble clouds. This paper describes a double-distribution-function thermal lattice Boltzmann method for investigating the thermodynamics of multiple-bubble interactions, and proposes a new two-dimensional method for cavitation bubble inception without the initialization of gas nuclei. This approach is validated by simulating the evolution of a laser-produced bubble. The interaction between two vapor bubbles is simulated, and the hydrodynamics and thermodynamics of cavitation bubbles are systematically investigated. Both weak and strong interactions among bubbles of equal size are accurately reproduced. The coalescence mode is further categorized according to differences in the collapse behaviors: the remaining parts collapse away from each other for coalescence in the collapse stage, but collapse toward each other for coalescence in the growth stage. Interactions among bubbles of different sizes are also explored and the different morphologies for various interaction modes are reported. In the case of small distances between bubbles under the weak interaction regime, the smaller bubble is pushed away from the symmetry axis, leading to an initial decrease in collapse intensity and then an increase as the distance between the two bubbles increases. Finally, the thermodynamics of a bubble cluster are investigated. The hydrodynamic and thermodynamic processes in different regions of the cavitation bubble cluster are determined, and the toroidal shape in the final stage is reproduced. The results demonstrate that the proposed model accurately simulates the complex interactions among multiple cavitation bubbles.

Mechanism of bottom-blown bubble coalescence in narrow channels

The coalescence of bottom-blown bubbles moving in narrow channels was studied using digital image-processing techniques. The effects of the gas flow and NaCl concentration on the shape, size, motion orbits, velocity, and vertical distance between the bubbles were comparatively analyzed, and a mathematical model for the coalescence of irregularly shaped bubbles of different sizes was established. The mechanism of bubble coalescence under bottom-blown stirring was investigated, and the consistency between the model-predicted and experimental results was analyzed to determine the ranges where the model can be applied. At a high gas flow rate, low liquid concentration, and high velocities of the first and following bubbles, the gas-liquid two-phase flow was more chaotic and the probability of collision between the bubbles was larger; hence, coalescence occurred earlier. A mathematical model of bubble coalescence was established to analyze the motion of bubbles after coalescence. The results predicted using the model were 70–78% consistent with the experimental results. Our model exhibited higher computational accuracy than Li Shaobai's model and is applicable to laminar fluids but not turbulent fluids. These findings offer basic data for quantifying bubble strengthening and blending effects in narrow channels.

The interaction of multiple bubbles in a Hele-Shaw channel

We study the dynamics of two air bubbles driven by the motion of a suspending viscous fluid in a Hele-Shaw channel with a small elevation along its centreline via physical experiment and numerical simulation of a depth-averaged model. For a single-bubble system we establish that, in general, the bubble propagation speed monotonically increases with bubble volume so that two bubbles of different sizes, in the absence of any hydrodynamic interactions, will either coalesce or separate in a finite time. However, our experiments indicate that the bubbles interact and that an unstable two-bubble state is responsible for the eventual dynamical outcome: coalescence or separation. These results motivate us to develop an edge-tracking routine and to calculate these weakly unstable two-bubble steady states from the governing equations. The steady states consist of pairs of ‘aligned’ bubbles that appear on the same side of the centreline with the larger bubble leading. We also discover, through time-dependent simulations and physical experiment, another class of two-bubble states that, surprisingly, are stable. In contrast to the ‘aligned’ steady states, these bubbles appear on either side of the centreline and are ‘offset’ from each other. We calculate the bifurcation structures of both classes of steady states as the flow rate and bubble volume ratio are varied. We find that they exhibit intriguing similarities to the single-bubble bifurcation structure, which has implications for the existence of $n$ -bubble steady states.

New multi-fluid model of pool scrubbing in bubble rise region

A theoretical simulation model of solid particles behaviour inside a scrubbing pool was developed, with the purpose to evaluate the particles decontamination factor. A three-step approach to describe pool scrubbing on the local instantaneous scale, using Computational Fluid Dynamics, is proposed. A subgrid model for particle decontamination, based on simulation of particle flow within individual bubbles of different sizes, is introduced first. Experimental data from the literature were then used to first validate the used open-source numerical solver’s gas–liquid flow part with the implemented drag model, and then to assess the results of pool scrubbing simulations using the implemented decontamination model.

Underwater Transmitted Wavefront Manipulation Based on Bubble-Arrayed Acoustic Metasurfaces

Manipulating underwater acoustic waves along the prescribed trajectory has great potential for various applications. Traditional metasurfaces for underwater acoustic modulation usually have complex structural designs and are complicated to manufacture. Here, we propose a simple strategy of embedding air bubbles of different sizes inside the polymer to freely manipulate the transmitted underwater acoustic wavefields. The transmitted phase shift covers the entire 2π range by adjusting the diameter of the bubbles. Utilizing the air-bubble array with precisely designed phase profiles, the abnormal refraction, self-bending beams, and bottle beams are univocally demonstrated based on the generalized Snell’s law. Our study can be used for designing waterborne metasurfaces with simple structures to freely manipulate the transmitted wavefronts and inspire lots of applications for underwater explorations.

Numerical and Experimental Investigation of the Hydrodynamics in the Single-Use Bioreactor Mobius® CellReady 3 L.

Two-way Euler-Lagrange simulations are performed to characterize the hydrodynamics in the single-use bioreactor Mobius® CellReady 3 L. The hydrodynamics in stirred tank bioreactors are frequently modeled with the Euler–Euler approach, which cannot capture the trajectories of single bubbles. The present study employs the two-way coupled Euler–Lagrange approach, which accounts for the individual bubble trajectories through Langrangian equations and considers their impact on the Eulerian liquid phase equations. Hydrodynamic process characteristics that are relevant for cell cultivation including the oxygen mass transfer coefficient, the mixing time, and the hydrodynamic stress are evaluated for different working volumes, sparger types, impeller speeds, and sparging rates. A microporous sparger and an open pipe sparger are considered where bubbles of different sizes are generated, which has a pronounced impact on the bubble dispersion and the volumetric oxygen mass transfer coefficient. It is found that only the microporous sparger provides sufficiently high oxygen transfer to support typical suspended mammalian cell lines. The simulated mixing time and the volumetric oxygen mass transfer coefficient are successfully validated with experimental results. Due to the small reactor size, mixing times are below 25 s across all tested conditions. For the highest sparging rate of 100 mL min, the mixing time is found to be two seconds shorter than for a sparging rate of 50 mL min, which again, is 0.1 s longer than for a sparging rate of 10 mL min at the same impeller speed of 100 rpm and the working volume of 1.7 L. The hydrodynamic stress in this bioreactor is found to be below critical levels for all investigated impeller speeds of up to 150 rpm, where the maximum levels are found in the region where the bubbles pass behind the impeller blades.

Time-domain simulation of acoustic scattering and internal propagation from multiple gas bubbles

Acoustic scattering and resonance responses from multiple gas bubbles are computed using a time-domain simulation based on the numerical solutions of the conservation laws. The time histories of scattered pressure and velocity, both outside and inside the bubbles, are obtained simultaneously from an immersed-boundary method facilitating the investigation of both exterior and interior acoustic fields for non-spherical bubbles. Agreement is found with both analytical scattering solutions and those from empirical shape factors in limiting cases. In addition, the time-domain method allows for the study of the transient acoustic scattering from pulse forcing (Gaussian). In this case, the interior gas oscillates in an off-center, non-uniform manner compared to the steady state forcing cases. The time history and the interior gas behavior are presented in detail for combinations of two bubbles of different sizes and shapes (spherical, prolate, oblate). A comparison and analysis of this immersed-boundary method to the finite element method and boundary element methods is provided. Also, the increasingly important role of computational acoustics in the study scattering of multiple targets of diverse sizes and shapes is highlighted.

Coalescence preference in surfactant-laden bubbles of equal size

Coalescence preference is the tendency of a bubble merged from two parent bubbles to be placed closer to one of the parents. Coalescence preference has been extensively studied for parent bubbles of different size, but mechanism of coalescence preference in bubbles of equal size have not yet been fully characterized. Here, we use high-fidelity simulations to investigate potential coalescence preference in contaminated bubbles of equal size. Results show that when a clean bubble merges with a surfactant-contaminated bubble of the same size, the merged bubble tends to be closer to the contaminated parent. By analyzing the coalescence events at different surfactant concentrations we also identify a novel preference mechanism characterized by spontaneous self-propulsion of the merged bubble. Elucidating mechanisms of coalescence in surfactant-contaminated bubbles has implications for technological processes involving bubble dispersions in the food and chemical industries where the presence of surfactants is ubiquitous.

Distributed Acoustic Sensing (DAS) Response of Rising Taylor Bubbles in Slug Flow.

Slug flow is one of the most common flow types encountered in surface facilities, pipelines, and wellbores. The intermittent gas phase, in the form of a Taylor bubble, followed by the liquid phase can be destructive to equipment. However, commonly used point flow sensors have significant limitations for flow analysis. Distributed acoustic sensing (DAS) can turn optical fibers into an array of distributed strain rate sensors and provide substantial insights into flow characterization. We built a 10 m vertical laboratory flow loop equipped with wrapped fiber optic cables to study the DAS response of rising Taylor bubbles. Low-passed DAS data allow for velocity tracking of Taylor bubbles of different sizes and water velocities. Moreover, we measured the velocity of the wake region following the Taylor bubble and explored the process of Taylor bubbles merging. The amplitude analysis of DAS data allows for the estimation of Taylor bubble size. We conclude that DAS is a promising tool for understanding Taylor bubble properties in a laboratory environment and monitoring destructive flow in facilities across different industries to ensure operations are safe and cost-effective.

Removal of organics from Bayer liquors via foam flotation

Rich foam is often formed in Bayer liquors, providing a promising short green process for the removal of organics by foam flotation. In this study, foam flotation of sodium oxalate (SO), sodium benzoate (SB), sodium citrate (SC), and sodium stearate (SS) was investigated using sodium dodecyl sulfate (SDS) as a frother and collector in a synthetic sodium aluminate solution. The feasibility of foam flotation in industrial production was then verified using Bayer liquor from alumina refineries. Low molecular weight organics achieved high maximum surface excesses, and elevated temperatures reduced them in the synthetic solution. Foams containing bubbles of different sizes were generated in the synthetic solution, and the stability of the foam increased with decreasing temperature. Medium molecular weight organics readily adhered to the bubble surface owing to their good surface activities, and the removal rate followed the order SO < SB < SS < SC. Increasing the temperature increased the removal rate of organics in both the synthetic solution and the Bayer liquor. Additionally, two types of Bayer liquor with a high total organic carbon (TOC) concentration produced a rich foam consisting of small, uniform bubbles. Over 31% of the removed organics were enriched in the foam for the Bayer liquor with TOC above 9 g L−1. A concentration coefficient of 3.46 could be achieved, resulting in a TOC greater than 51.9 g L−1 in the foam. These foam enrichment results were mainly attributed to small bubbles, high TOC concentrations, and multilayer adsorption.

Influence of surfactant contaminations on the lift force of ellipsoidal bubbles in water

The shear-induced lift force is known to influence the lateral distribution of gas bubbles in bubbly flows. Although the hydrodynamic behavior of a bubble can be greatly affected by surfactants that are present in the liquid bulk, their influence on the lift force has only been investigated to a limited extent. In our previous work we investigated the influence of impurities on the lift force in air-water flows and could reveal non-negligible changes even without a modification of the bubble drag or shape. To bring further insight on changes caused by higher surfactant concentrations, the lift coefficient of single ellipsoidal bubbles of different sizes, which rise in water with varying degree of contamination are experimentally determined in this work. For this purpose, different amounts of 1-Pentanol as well as Triton X-100 were added to the flow. The results reveal a strong dependency of the lift coefficient on the bubble shape, where different findings in the literature for bubbles with lower Reynolds numbers could also be observed for ellipsoidal bubbles in water.

Морфологічна характеристика еритроцитів сечі в дітей з еритроцитурією

Актуальність. Визначення походження еритроцитурії в практиці педіатра є важливим завданням, воно дозволяє сформувати правильний діагноз. Розглянуто можливість застосування фазово-контрастної мікроскопії (ФКМ) для виявлення гломерулярної та негломерулярної еритроцитурії. Метою роботи було визначення морфологічної характеристики еритроцитів сечі в дітей з еритроцитурією для покращення якості диференціальної діагностики. Матеріали та методи. Дослідження морфологічної характеристики еритроцитів сечі методом ФКМ проведено 73 пацієнтам віком від 1 до 18 років, із них 45 (61,6 %) хворим на гематуричну форму гломерулонефриту, 23 (31,5 %) хворим на спадковий нефрит та 5 (6,8 %) хворим на дисметаболічну нефропатію. Результати. У дітей із клінічно встановленим діагнозом «гломерулонефрит, гематурична форма» виявлено незмінені еритроцити в 44,4 % пацієнтів, у 42,2 % випадків еритроцити були дисморфними, і в 13,4 % випадків виявлено акантоцити. Серед дітей з еритроцитурією, яким було клінічно встановлено діагноз «спадковий нефрит», переважали пацієнти з дисморфними еритроцитами — 52,2 %, у 26,1 % хворих еритроцити не були зміненими, і в 21,7 % виявлено акантоцити. У дітей з еритроцитурією, хворих на дисметаболічну нефропатію, еритроцити осаду сечі були незмінені й простежувались кристали солей. Висновки. Метод ФКМ можна використовувати в сукупності із загальноклінічними методами в рутинній практиці для визначення подальшої тактики обстеження та лікування дітей з еритроцитурією.

Dynamic behaviors of anisodiametric bubbles under effects of horizontal attraction and vertical wake

The present study aims to describe the interaction between rising bubbles of different sizes. Coaxial and triangle bubble configurations were investigated. Bubble sizes ranged from 4.0 mm to 10.0 mm. Three-dimensional unsteady numerical simulations were performed and the volume of fluid multiphase model was employed. The numerical scheme was validated through experimental results. Time-dependent bubble geometry, bubble velocity, and near-bubble flow patterns were obtained. The results show that the participation of lateral bubbles causes coalescence delay. The mergence of bubbles is followed by an immediate decrease in bubble velocity. Liquid flow structures tend to be combined accordingly as the bubbles coalesce. For the triangle configuration, the first coalescence of small bubbles takes place between the trailing bubbles. As bubble size increases, the first coalescence arises between the leading bubble and the left trailing bubble.

Interaction of two approximately equal-size bubbles produced by sparks in a free field

A series of experiments are performed to study the interaction of two bubbles of approximately equal size in free-field water for different parameter combinations (i.e., the phase difference θ and the initial distance d*). First, a high-voltage discharge device that can generate multiple bubbles of different sizes in water and accurately control the time of bubble generation is introduced. For different discharge voltages, the maximum radius and the first oscillation period of a single bubble and the shock wave energy and bubble energy conversion rate are studied through high-speed photography, current monitoring, voltage probes, and an underwater free-field pressure sensor. Then the distance of the center of mass and average radius of two bubbles generated at different distances at the same time are compared with a theoretical model and good consistency is obtained when the initial distance is greater than the bubble diameter. Finally, the interaction phenomena of two bubbles generated with different initial distances and phase differences are divided into five categories, namely, coalescence, failed catapult, piercing jet, jet toward, and jet away, and the boundary conditions used to distinguish different phenomena are given. For the piercing jet, a high-speed fine jet will be generated in the bubble generated later. The jet will penetrate the wall of the bubble and propagate steadily in the water at high speed (∼79 m/s). The velocity of the jet in the bubble and in water generated with different parameter combinations is statistically analyzed, and the velocity distribution cloud diagrams are given.

Oil droplets dispersion under a deep-water plunging breaker: Experimental measurements and numerical modeling

Abstract (1141370) Wave tank experiments were performed to measure the droplets size distribution under the plunging breaking wave. A deep-water plunging breaker of height 20 cm was generated using the dispersive focusing method, and a shadowgraph camera was used to take images of droplets and bubbles of different sizes. For droplets smaller than the 1000 microns, the number-based DSD matched the DS correlation (Delvigne and Sweeney 1988), which gives N(d) ~ d−2.3, but N(d) ~ d−9.7 for diameters larger than 1000 microns. A numerical method was designed to study the oil dispersion under breaking waves by coupling the computational fluid dynamic (CFD) with the Lagrangian particle tracking code (NEMO3D) and population balance model (VDROP). The wave hydrodynamics was reproduced using the Reynolds-averaged Navier Stokes approach within a commercial CFD code ANSYS Fluent. The obtained wave hydrodynamics was then used as inputs for the NEM3D code and VDROP model. The numerical results show reasonable agreement with our experimental observation. The approach adopted to produce the DSD reduces the empiricism of the DS correlation, as the approach uses oil properties and measurable wave properties. The proposed numerical method was ready to be used in other scenarios of oil spills (i.e., oil jets in deep oceans and oil dispersion in riverine systems). It could also be potentially used in large scale forecast and hindcast simulations for oil spill response and research.

A microscopic study of the corneal stromal lenticules extracted during femtosecond laser-assisted small incision lenticule extraction.

The aim of the present study was to investigate the histological and morphological characteristics of corneal stromal lenticules extracted during femtosecond laser-assisted small incision lenticule extraction (SMILE) surgery by light and electron microscopy. A total of 20 human corneal stromal lenticules extracted during SMILE surgery were sent for microscopic examination immediately after surgery. Of these, six were observed under a light microscope and 14 were observed under an electron microscope. The smoothness of the front and rear surface of the lenticules observed under an electron microscope was rated on a scale of 0 to 4 according to unified evaluation criteria and the scores were statistically compared. Under the light microscope, the edge of the cross section of the corneal stromal lenticules was deeply stained and certain burrs and broken collagen fibers were observed. The swollen corneal stromal fibers were distributed irregularly, with a few bubbles of different sizes. Under the electron microscope, the surface of the lenticules ablated using a femtosecond laser was not perfectly smooth and the front surface was smoother than the rear surface. The side edge of the lenticules ablated using a femtosecond laser was not as regular as the edge cut using microscissors. Necrosis and dissolution of collagen fibers were observed near the surface of the lenticules. In conclusion, the surface quality of corneal stromal lenticules ablated using a femtosecond laser was not optimal when observed under a microscope. Increased attention should be paid to the histology and morphology of the corneal surface following laser ablation.

Acoustic backscattering observations from non-spherical gas bubbles with ka between 0.03 and 4.4.

The study of gas bubbles in liquid media is of importance in many areas of research. Gas bubbles are often studied using in situ measurement techniques; however, acoustic inversion techniques have also been used to extract physical properties of gas bubbles. These inversion techniques rely on existing analytical scattering models; however, these models often assume that the gas bubbles are spherical in shape and have an equivalent bubble radius, a, that is small compared to the incident acoustic wavelength (ka ≪ 1), which is not always valid. This study aims to understand how the departure from these assumptions affects the acoustic backscattering cross section, σbs, of non-spherical gas bubbles. Experimental estimates of σbs of non-spherical gas bubbles of different sizes, with ka values ranging between 0.03 and 4.4, were compared to four commonly known analytical σbs models. All models performed equally at predicting σbs for ka smaller than 0.5; however, there was no model that better predicted the experimental estimates of σbs for ka larger than 0.5, regardless of bubble shape. Large variabilities in the experimental estimates of σbs are observed for ka larger than 0.5, which are caused by the variability in bubble shape and size, as well as the bubble's orientation.

Adsorption Kinetics of Various Frothers on Rising Bubbles of Different Sizes under Flotation Conditions

This paper studies the effect of the type and concentration of selected frothers, the gas flowrate, and the pore size of the porous frit on the bubble sizes (Sauter mean diameter, SMD) of bubbling flow produced in a micro-flotation cell, and the determination of bubble size distribution (BSD) in the presence of the frothers. The commercial frothers polypropylene glycols (PPG 200, 400, and 600), tri propylene glycol (BTPG), triethylene glycol (BTEG), dipropylene glycol (BDPG), and Methyl Isobutyl Carbinol (MIBC) were used in the present investigation. The frother concentration varied from 1 to 1000 ppm. The flow rate varied in the range of 25 to 100 cm3/min. The pore sizes of the frit were selected as 10–16 μm, 16–40 μm, and 40–100 μm. Each frother exhibited its own unique ability in preventing coalescence of the bubbles in the order of BTEG &lt; BDPG &lt; PPG 200 &lt; MIBC &lt; BTPG &lt; PPG 400 &lt; PPG 600. The factorial experiments established that the type of the frother and its concentration have a major effect on the size of the bubbles. The bubbles decreased twice their size when the frother concentration was increased from 1 ppm to 1000 ppm. The pore size of the frit is a significant factor as well. The size of the bubbles can be reduced from about 10% to about 40% by decreasing the pores from 40–100 μm to 10–16 μm but the level of this decrease depends on the type of the frother. The increase of the flowrate from 25 cm3/min to 100 cm3/min produced bubbles smaller by 25% to 50% for the case of BTEG, BDPG, PPG 200, MIBC, BTPG, while a minimum of the bubble sizes was reached for the case of PPG 400 and PPG 600, beyond which the bubbles enlarged their size. The BSD in the presence of PPG 600 varied around 0.3 mm, whereas BTEG gave a wider BSD which indicated that the type of frother affected the bubble production. Our analysis shows that the first group of frothers adsorbs instantly on the bubbles, once they leave the porous frit, thus reaching equilibrium. PPG 400 and PPG 600 adsorb significantly slower on the bubbles, possibly not reaching equilibrium during their resident time.

An experimental study of two identical air bubbles rising side-by-side in water

We experimentally study the dynamics of two identical air bubbles rising side-by-side in water by varying two parameters, namely, the radius of the bubble and center to center distance between them. The bubbles follow a three-dimensional spiraling motion, and their path and shape oscillations are observed in both the front and top views by using a high speed camera with a back-lit illumination and a mirror arrangement. Bubbles of different sizes are created by using a dumping cup mechanism, and the center to center distance between the two bubbles is varied by using telescopic joints. The dynamics of the two side-by-side bubbles is compared and contrasted with that of a single rising bubble. We found that the bubbles act independent of each other, like a single bubble, when the center to center distance is greater than seven times the radius of the bubbles. For similar separation distances, increasing the size of the bubbles results in a smaller terminal velocity and also lesser deviation from a spiral path due to high inertia.

A lattice Boltzmann modeling of the bubble velocity discontinuity (BVD) in shear-thinning viscoelastic fluids

The bubble velocity discontinuity (BVD), when single bubble rising in shear-thinning viscoelastic fluids, is studied numerically. Our three-dimensional numerical scheme employs a phase-field lattice Boltzmann method together with a lattice Boltzmann advection-diffusion scheme, the former to model the macroscopic hydrodynamic equations for multiphase fluids, and the latter to describe the polymer dynamics modeled by the exponential Phan–Thien–Tanner (ePTT) constitutive model. An adaptive mesh refinement technique is implemented to reduce computational cost. The multiphase solver is validated by simulating the buoyant rise of single bubble in a Newtonian fluid. The critical bubble size for the existence of the BVD and the velocity-increasing factor of the BVD are accurately predicted, and the results are consistent with the available experiments. Bubbles of different sizes are characterized as subcritical (smaller than critical size) and supercritical (larger than critical size) according to their transient rising velocity behaviors, and the polymeric stress evolution affecting the local flow pattern and bubble deformation is discussed. Pseudo-supercritical bubbles are observed with transition behaviors in bubble velocity, and their sizes are smaller than the critical value. The formation of bubble cusp and the existence of negative wake are observed for both the pseudo-supercritical and the supercritical bubbles. For the supercritical bubble, the trailing edge cusp and the negative wake arise much earlier. The link between the BVD, the bubble cusp, and the negative wake is discussed, and the mechanism of the BVD is explained.