Bubble Capture Research Articles

Three-Dimensional Distribution of Hooks in Al-Killed Low-Carbon Continuous Casting Steel Slabs

In the current study, steel samples were etched and hooks on several successive layers of longitudinal and transverse slab sections were obtained to investigate the three-dimensional (3-D) distribution of hooks in low-carbon continuous casting slabs. The data from industrial trials and numerical calculation were used to explain the variation in the distribution and morphology of hooks. Around the slab perimeter, the mean depth of hooks at the center and edge of the wide face and the edge of the narrow face was larger than that of other locations. The 3-D hook demonstrated a varied characteristic on different layers, as the observed surface changed in the longitudinal direction. By several layers of the transverse section being polished off, hooks in the transverse direction below the slab surface were obtained, in which the truncated hook and the joint hook between the wide face and narrow face were observed at the slab corner. The same oscillation mark could show as hook type and depression type, depending on the occurrence of the overflow between the solidified meniscus and the copper plate. Industrial trials and the numerical calculation illustrated that the transient variation of hooks in the 3-D space was related to the level fluctuation of molten steel in the mold and temperature fluctuation with casting time and the fluid flow and temperature near the meniscus. Finally, the influence area and volume of hooks on the capture of inclusions and bubbles were discussed.

Large Eddy Simulations of Electromagnetic Braking Effects on Argon Bubble Transport and Capture in a Steel Continuous Casting Mold

In continuous casting of steel, argon gas is often injected to prevent clogging of the nozzle, but the bubbles affect the flow pattern, and may become entrapped to form defects in the final product. Further, an electromagnetic field is frequently applied to induce a braking effect on the flow field and modify the inclusion transport. In this study, a previously validated GPU-based in-house code CUFLOW is used to investigate the effect of electromagnetic braking on turbulent flow, bubble transport, and capture. Well-resolved large eddy simulations are combined with two-way coupled Lagrangian computations of the bubbles. The drag coefficient on the bubbles is modified to account for the effects of the magnetic field. The distribution of the argon bubbles, capture, and escape rates, are presented and compared with and without the magnetic field. The bubble capture patterns are also compared with results of a previous RANS model as well as with plant measurements.

Bubble adhesion on hydrophobic surfaces in solutions of pure and technical grade ionic surfactants

The attachment of bubbles onto a collecting surface plays a critical role in many industrial processes. Here, the bubble behaviour is crucially influenced by the presence of surface active agents, where the ionic surfactants are the most common agents. The ionic surfactants very often contain contaminants which, even in trace amounts, could unexpectedly influence the bubble adhesion. This work is focused on an experimental study of bubble adhesion onto the hydrophobic surface in solutions of two ionic surface-active agents (DTAB and SDS) of pure and technical grade purity. The diameters of the three-phase contact line together with bubble dynamic contact angles, dynamic surface tension and dynamic drop contact angles are measured. It was observed that the contaminants decrease the ability of bubbles to attach to solid surfaces when compared with the mono-surfactant solution. The influence of contaminants is crucial below the critical micelle concentration of the main surfactant and it may even happen that the capture of bubbles is avoided.

Numerical study of gravity effects on phase separation in a swirl chamber

The effects of gravity on a phase separator are studied numerically using an Eulerian/Lagrangian two-phase flow approach. The separator utilizes high intensity swirl to separate bubbles from the liquid. The two-phase flow enters tangentially a cylindrical swirl chamber and rotate around the cylinder axis. On earth, as the bubbles are captured by the vortex formed inside the swirl chamber due to the centripetal force, they also experience the buoyancy force due to gravity. In a reduced or zero gravity environment buoyancy is reduced or inexistent and capture of the bubbles by the vortex is modified. The present numerical simulations enable study of the relative importance of the acceleration of gravity on the bubble capture by the swirl flow in the separator. In absence of gravity, the bubbles get stratified depending on their sizes, with the larger bubbles entering the core region earlier than the smaller ones. However, in presence of gravity, stratification is more complex as the two acceleration fields – due to gravity and to rotation – compete or combine during the bubble capture.

Effects of Purge-Flow Rate on Microbubble Capture in Radial Arterial-Line Filters

The process of microbubble filtration from blood is complex and highly dependent on the forces of flow and buoyancy. To protect the patient from air emboli, arterial-line filters commonly use a micropore screen, a large volume housing with purpose-built shape, and a purge port to trap, separate, and remove circulating microbubbles. Although it has been proposed that an insufficient buoyancy force renders the purge port ineffective at removing microbubbles smaller than 500 μm, this research attempts to investigate the purge flow of an arterial-line filter to better understand the microbubble removal function in a typical radial filter design. As its primary objective, the study aims to determine the effect of purge-flow rate on bubble capture using air bolus injections from a syringe pump with 22-gauge needle and Doppler ultrasound bubble detection. The measureable bubble size generated in the test circuit ranged between 30 and 500 μm, while purge flow was varied between .1 and .5 L/min for testing. Statistical analysis of the test data was handled using a repeated measures design with significance set atp< .05 level. Outcomes demonstrated that higher purge flows yielded higher bubble counts, but the effect of purge-flow rate on bubble capture decreased as bubble size increased. Results also showed that purge flow from the test filter was capable of capturing all bubble sizes being generated over the entire flow range tested, and confirms utility of the purge port in removing microbubbles smaller than 500 μm. By analyzing bubble counts in the purge flow of a typical radial-filter design, this study demonstrates that currently available micropore filter technology is capable of removing the size range of bubbles that commonly pass through modern pump-oxygenator systems and should continue to be considered during extracorporeal circulation as a measure to improve patient safety.

Numerical study of gravity effects on phase separation in a swirl chamber.

The effects of gravity on a phase separator are studied numerically using an Eulerian/Lagrangian two-phase flow approach. The separator utilizes high intensity swirl to separate bubbles from the liquid. The two-phase flow enters tangentially a cylindrical swirl chamber and rotate around the cylinder axis. On earth, as the bubbles are captured by the vortex formed inside the swirl chamber due to the centripetal force, they also experience the buoyancy force due to gravity. In a reduced or zero gravity environment buoyancy is reduced or inexistent and capture of the bubbles by the vortex is modified. The present numerical simulations enable study of the relative importance of the acceleration of gravity on the bubble capture by the swirl flow in the separator. In absence of gravity, the bubbles get stratified depending on their sizes, with the larger bubbles entering the core region earlier than the smaller ones. However, in presence of gravity, stratification is more complex as the two acceleration fields - due to gravity and to rotation - compete or combine during the bubble capture.

Modeling and Measurements of Multiphase Flow and Bubble Entrapment in Steel Continuous Casting

In steel continuous casting, argon gas is usually injected to prevent clogging, but the bubbles also affect the flow pattern, and may become entrapped to form defects in the final product. To investigate this behavior, plant measurements were conducted, and a computational model was applied to simulate turbulent flow of the molten steel and the transport and capture of argon gas bubbles into the solidifying shell in a continuous slab caster. First, the flow field was solved with an Eulerian k–e model of the steel, which was two-way coupled with a Lagrangian model of the large bubbles using a discrete random walk method to simulate their turbulent dispersion. The flow predicted on the top surface agreed well with nailboard measurements and indicated strong cross flow caused by biased flow of Ar gas due to the slide-gate orientation. Then, the trajectories and capture of over two million bubbles (25 μm to 5 mm diameter range) were simulated using two different capture criteria (simple and advanced). Results with the advanced capture criterion agreed well with measurements of the number, locations, and sizes of captured bubbles, especially for larger bubbles. The relative capture fraction of 0.3 pct was close to the measured 0.4 pct for 1 mm bubbles and occurred mainly near the top surface. About 85 pct of smaller bubbles were captured, mostly deeper down in the caster. Due to the biased flow, more bubbles were captured on the inner radius, especially near the nozzle. On the outer radius, more bubbles were captured near to narrow face. The model presented here is an efficient tool to study the capture of bubbles and inclusion particles in solidification processes.

Simulation and validation of two-phase turbulent flow and particle transport in continuous casting of steel slabs

In continuous steel casting, argon gas is usually injected at the slide gate or stopper rod to prevent clogging, but entrapped bubbles may cause defects in the final product. To better understand this, the flow of molten steel and the transport and capture of argon gas bubbles have been simulated and compared with plant measurements. First, the flow field was solved with an Eulerian k-s model of the steel, which was two-way coupled with a Lagrangian model of the large bubbles using a Discrete Random Walk method to include dispersion of bubbles due to turbulence. The asymmetrical flow pattern predicted on the top surface agreed well with nailboard measurements. Then, the motion and capture of over two million bubbles were simulated using two different capture criteria. Results with the advanced capture criterion agreed well with measurements of the number, locations, and sizes of captured bubbles, especially for larger bubbles. The relative capture fraction of 0.3% was close to the measured 0.2% for 1mm bubbles, and occurred very near the top surface. The model presented here is an efficient tool to study the capture of bubbles and inclusion particles in solidification processes.

Improving the Current Stability through the Bubbles-Free Microfluidic Electro-Spray Ionizing Chip

The bubbles in the microfluidic based electro-spray ionizing chips seriously affect the performance of the system. This paper presents a bubble capture method to stabilize the current of the microfluidic based electro-spray ionizing sources. A bubble capture structure was introduced to collect the bubbles. A normal close clamp valve assured a suitable pressure in the bubble capture structure that no liquid in the microfluidic channel can enter; when the bubble capture structure was filled with gas bubbles, the clamp valve was opened to release the bubble and balance the pressure. The results indicated that the current fluctuation, which reflects the stability of the electro-spray ionizing devices, was below 1.8% during the stable cone-jet electro-spray stage (2000V~4500V) for the proposed system, which was a notable improvement comparing with normal microfluidic-based electro-spray ionizing chip without the bubble capture structure.

The shape of non-axisymmetric bubbles on inclined planar surfaces

Bubble-particle interaction is a common phenomenon that is used in numerous industrial applications, and the knowledge of contact angles is important for the description of the expansion of the three-phase contact line. In contrast to drops, the capture of bubbles adhering to a solid surface is an extremely rapid process, and the image quality that can be achieved is worse. For bubble adhesion on a slightly inclined plane, different curvature radii should be considered on the upper and lower bubble sections of the three-phase contact line. The method proposed here is based on the assumption that the ADSA-P approach could be used separately for both bubble parts.Bubble motion during the adhesion process was recorded using a high-speed digital camera, and points located on the bubble boundary were detected using image analysis. The bubble was divided into two independent parts, and the ADSA-P technique for contact angles of greater and less than 90° was applied to describe the bubble shape.The calculated coordinates of the bubble profile were compared to the experimental data, and an excellent agreement was obtained. The proposed methodology could improve and simplify the description of bubble-particle interactions on non-horizontal surfaces.

Properties of Ti-sapphire as laser material

The optical quality of sapphire doped with 0.03–0.12 mass.% of titanium was investigated. The crystals are obtained by Czochralski method from Mo crucible in crystallization medium with the reductive chemical potential ɛ ≈ −250 kJ/mole. The as-grown crystals are characterized by absence of optical IR-absorption typical of Ti-sapphire, but at 206, 255 and 268 nm observed is UV-absorption connected with the violation of the anionic stoichiometry of the matrix and with the formation of F, F+ and [F+-Ti3+]-centers. Coagulation of excessive aluminum and Schottky defects may give rise to the formation of submicron-size inclusions in the form of 70–400 nm pores which contain atoms of aluminum and its suboxides. The photo- and X-ray luminescence of Ti-sapphire was investigated. The centers of emission at 310–330 nm and at 350–550 nm are according to activator-vacancy complexes based on the anionic and cationic vacancies. Treatment of the melt with ultrasound with a frequency 350–400 kHz in the process of crystallization decreases the efficiency of the capture of gaseous bubbles by the growing crystal by a factor of 2–2.5, not changing the crystal structure.

Behavioural traits of competent Concholepas concholepas (loco) larvae

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 430:207-221 (2011) - DOI: https://doi.org/10.3354/meps09153 Behavioural traits of competent Concholepas concholepas (loco) larvae Patricio H. Manríquez1,2,*, Juan Carlos Castilla3 1Laboratorio Costero de Recursos Acuáticos de Calfuco and 2Instituto de Ciencias Marinas y Limnológicas (formerly Instituto de Biología Marina ‘Dr. Jürgen Winter’), Universidad Austral de Chile, Casilla 567, Valdivia, Chile 3Estación Costeras de Investigaciones Marinas (ECIM, Las Cruces) and Centre for Advanced Studies in Ecology & ­Biodiversity, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Casilla 114–D, Santiago, Chile *Email: pmanriquez@uach.cl ABSTRACT: Swimming activity of competent Concholepas concholepas (Bruguière, 1789) larvae, under different photoperiod, water turbulence and settlement cues were investigated in laboratory experiments. At night, larvae mainly swam to the water surface and then sank passively to the bottom. During the day, regardless of the photoperiod, larvae mainly stayed on the bottom, occasionally exhibiting upward movements. During the swimming period, larvae displayed the capacity to adhere to floating substrata through several mechanisms, including the secretion of a long and sticky mucous thread, air bubble capture or taking advantage of the water tension. The presence of C. ­concholepas prey, such as the mussel Semimytilus algosus and the chthamaloid barnacle Notoch­thamalus scabrosus, significantly influenced the swimming activity of competent C. concholepas ­larvae, inducing them to stay close to the bottom where prey were present. C. concholepas prey also triggered the initiation of larvae crawling, a characteristic of the early benthic life of C. concholepas. Although our laboratory experiments are proxies of nature, they are in good agreement with field observations in shallow nearshore areas (< ca. 0.5 km from shore) that recorded higher abundances of competent C. concholepas larvae (which are often associated with floating substrata) captured by surface planktonic tows during the night rather than day. Similarly, competent C. concholepas larvae abundances were higher in tows through inner nearshore foam slicks than in non-slick areas. The results suggest that the presence of endogenous swimming behaviour in these larvae may be a key factor enhancing adherence to floating substrata. The laboratory discovery of vertical buoyancy provides new information leading to a better understanding of the distribution and abundance patterns of these larvae in inner nearshore waters. KEY WORDS: Chile · Concholepas concholepas · Larval distribution and transport · Swimming behaviour · Rafting · Mucous thread · Stickiness · Foam slicks Full text in pdf format PreviousNextCite this article as: Manríquez PH, Castilla JC (2011) Behavioural traits of competent Concholepas concholepas (loco) larvae. Mar Ecol Prog Ser 430:207-221. https://doi.org/10.3354/meps09153 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 430. Online publication date: May 26, 2011 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2011 Inter-Research.

A new experimental method for determining particle capture efficiency in flotation

A single bubble experiment has been developed for the determination of the capture efficiency of particles by bubbles in flotation under well-controlled hydrodynamics and physico-chemical conditions. In a glass column, small single bubbles ( d b =0.22−1.16 mm) are produced in pure water and then rise at their terminal velocity through a suspension consisting of spherical glass particles ( d p = 5 – 56 μ m ) where bubble–particle capture takes place. The capture efficiency E capt is calculated as the ratio of the number of particles captured by one bubble to the number of particles present in the volume swept out by this bubble. Images recorded at high optical magnification show that particles slip on the interface, then adhere to air bubbles individually or as aggregates and cover the rear part of bubble surface. The bubble's effective density and interface contamination level are increased by captured particles. As a result, bubble's rising velocity U b is reduced along the experimental device. By establishing the relationship between capture efficiency E capt , bubble rise velocity U b and bubble clean angle θ clean , a new approach to measure particle–bubble capture efficiency is proposed. This new experimental technique is applied to provide a new set of data for capture efficiency in the case of bubbles with a clean interface. E capt is found to grow as d b decreases and d p increases, within the range between 0.02 and 0.20, which is in the order of magnitude of experimental results of Ralston and Dukhin (1999) as well as of numerical results of Sarrot et al. (2005). These data are favorably compared to numerical modeling of collision efficiency.

The limits of fine particle flotation

Understanding the limits of fine particle flotation is the key to the selective separation of fine mineral particles. Fine particles have low collision efficiencies with gas bubbles and float slowly. There has been a great deal of work aimed at overcoming the inefficient collision of small particles with rising air bubbles. This review deals with the influence of bubble size, particle aggregation, different flow conditions, particle induction time, as well as the action of surface and capillary forces on fine particle–bubble capture. Recommendations for practice are given.

Electrostatic attraction between a hydrophilic solid and a bubble

The contact between fine hydrophilic α-Al(2)O(3) particles and nitrogen bubbles was studied as a function of solution composition in single bubble capture experiments, where the bubble collection efficiency was measured. The surface charges of both bubble and particle were controlled by varying the electrolyte concentration and pH of the solution. In all experiments the bubbles were negatively charged while the α-Al(2)O(3) particles were either negatively (above pH of the isoelectric point, pH(IEP)) or positively (below pH(IEP)) charged. The collection efficiency was found to be strongly influenced by the surface charge of the particles. The maximum collection efficiency occurred when the bubble and particle were oppositely charged (at low pH values) and at low salt concentration, i.e. when a long range attractive electrostatic interaction is present. In the case where both bubble and particle were of the same charge, the collection efficiency was near to zero within experimental error and was not influenced by either salt concentration or pH. This is the first experimental proof of the concept of 'contactless flotation', first proposed by Derjaguin and Dukhin in 1960, with far reaching implications from minerals processing to biology.

Prevention of air bubble formation in a microfluidic perfusion cell culture system using a microscale bubble trap

Formation of air bubbles is a serious obstacle to a successful operation of a long-term microfluidic systems using cell culture. We developed a microscale bubble trap that can be integrated with a microfluidic device to prevent air bubbles from entering the device. It consists of two PDMS (polydimethyldisiloxane) layers, a top layer providing barriers for blocking bubbles and a bottom layer providing alternative fluidic paths. Rather than relying solely on the buoyancy of air bubbles, bubbles are physically trapped and prevented from entering a microfluidic device. Two different modes of a bubble trap were fabricated, an independent module that is connected to the main microfluidic system by tubes, and a bubble trap integrated with a main system. The bubble trap was tested for the efficiency of bubble capture, and for potential effects a bubble trap may have on fluid flow pattern. The bubble trap was able to efficiently trap air bubbles of up to 10 mul volume, and the presence of captured air bubbles did not cause alterations in the flow pattern. The performance of the bubble trap in a long-term cell culture with medium recirculation was examined by culturing a hepatoma cell line in a microfluidic cell culture device. This bubble trap can be useful for enhancing the consistency of microfluidic perfusion cell culture operation.

Bubble migration in a turbulent boundary layer

The wall void peaking distribution observed in an upward turbulent bubbly boundary layer along a flat plate is generated by bubbles that move towards the plate, come into contact with the wall and then slide along it. This transverse ‘migration’ has been studied using flow visualization, high speed video and particle tracking techniques to measure the trajectories of mono-disperse air bubbles at very low void fractions. Investigations have been performed at four Reynolds numbers in the range 280 < Re θ < 3000, covering both the laminar and turbulent regimes, with mono-disperse bubbles of mean equivalent diameter between 2 mm and 6 mm. Lagrangian statistics calculated from hundreds of trajectories show that the migration only occurs in the turbulent regime and for bubble diameters below some critical value: 3.5 mm < d eqcrit < 4 mm. Above this size ( We > 3), the interface deformation is such that bubbles do not remain at the wall, even when they are released at the surface. Also, bubble migration is shown to be non-systematic, to have a non-deterministic character in the sense that trajectories differ significantly, to increase with Reynolds number and to take place on a short time scale. A series of experiments with isolated bubbles demonstrates that these results are not influenced by bubble–bubble interactions and confirm that two-way coupling in the flow is limited. Flow visualizations show that the migration originates with the capture of bubbles inside the large turbulent structures of the boundary layer (‘bulges’). The bubbles begin to move towards the wall as they cross these structures, and the point at which they reach the wall is strongly correlated with the position of the deep ‘valleys’ which separate the turbulent ‘bulges’. The analysis of the mean Lagrangian trajectories of migrating bubbles confirms these observations. Firstly, the average time of migration calculated from these trajectories coincides with the mean transit time of the bubbles across the structures. Secondly, once the trajectories have been scaled by this transit time and the boundary layer thickness δ, they all have the same form in the region y/ δ < 0.4, independent of the Reynolds number.

Bubble capture by a propeller

A small air bubble (radius a) is injected in water (kinematic viscosity v) in the vicinity (distance r 0 ) of a propeller (radius r p , angular frequency ω). We study experimentally and theoretically the conditions under which the bubble can be 'captured', i.e. deviated from its vertical trajectory (imposed by gravity g) and moved toward the centre of the propeller (r =0). We show that the capture frequency ω capt follows the relationship where β is a dimensionless parameter characterizing the propeller, f(Re b ) is an empirical correction to Stokes' drag law which accounts for finite-Reynolds-number effects and π/2 -φ 0 is the angle between the axis of the propeller and the line between the centre of the propeller and the point where the bubble is injected. This law is found to be valid as long as the distance d between the propeller and the water surface is larger than 3r 0 . For smaller distances, the capture frequency increases; using an image technique, we show how the above expression is modified by the presence of the surface.

A degassing plate with hydrophobic bubble capture and distributed venting for microfluidic devices

This paper introduces a microfluidic wall plate that allows the removal of gas bubbles from a gas/liquid mixture in a distributed fashion, i.e., throughout the flow path, eliminating the need for discrete separators common in macroscopic practice. Integrated into a microfluidic system at critical locations, such a degassing plate prevents the build up of gas bubbles in microchannels so as to maximize the effective reaction area, decrease the flow resistance and keep the chamber pressure under check. Furthermore, the plate surface is designed to capture the gas bubbles preferentially on designated venting sites, so that the rest of the surface can be dedicated to other functions, such as the catalyst or electrodes. The mechanism of bubble capture is explained by surface energy minimization, and two types of bubble sinks are proposed and verified. Once captured, the bubbles can be vented out through hydrophobic venting holes small enough (e.g. sub-micron) to block the liquid by surface tension. By chemically generating CO2 inside a small chamber (30 mm × 50 mm × 1.5 mm) sealed by the degassing plate, the process of bubble capture and removal is visually demonstrated. A porous polypropylene membrane with ∼0.2 µm diameter holes shows that gas can be removed with only several kPa of internal pressure while water stays free of leakage even under 2.4 × 105 Pa (35 psi). Venting is effective in any gravitational orientation, paving the way for portable microfluidic devices.

Capture and inception of bubbles near line vortices

Motivated by the need to predict vortex cavitation inception, a study has been conducted to investigate bubble capture by a concentrated line vortex of core size rc and circulation Γ0 under noncavitating and cavitating conditions. Direct numerical simulations that solve simultaneously for the two phase flow field, as well as a simpler one-way coupled point-particle-tracking model (PTM) were used to investigate the capture process. The capture times were compared to experimental observations. It was found that the point-particle-tracking model can successfully predict the capture of noncavitating small nuclei by a line vortex released far from the vortex axis. The nucleus grows very slowly during capture until the late stages of the process, where bubble/vortex interaction and bubble deformation become important. Consequently, PTM can be used to study the capture of cavitating nuclei by dividing the process into the noncavitating capture of the nucleus, and then the growth of the nucleus in the low-pressure core region. Bubble growth and deformation act to speed up the capture process.