Air Bubble Size Distribution Research Articles

A Method of Analysis of Independent Components for Hydro-Acoustic Control of the Flotation Process

The application of algorithms for the analysis of independent components together with a hydroacoustic method for determining the disperse composition of the gas phase in water is proposed. Mathematical modeling of the effect of emission of acoustic waves by bubbles demonstrated the principle of blind separation of the measured signals into components and the possibility of determining the size distribution of air bubbles without taking into account the geometry of the relative position of the flow of bubbles and measuring points. It is proposed to use signal spectra, rather than temporal signals as initial mixtures for decomposition.

Bayesian estimation of the size distribution of air bubbles in water

Bayesian estimation of the size distribution of air bubbles in water

Measurement of the air bubble size and velocity from micro air bubble generation (MBG) in diesel using optical methods

In this paper, we determine the bubble size and velocity from air bubble generation (MBG) in a diesel using optical methods. A KTM Series Pump was used to generate micro air bubbles in diesel. The air bubble radius and velocity measurements can be useful parameters to optimize the bubble generation process. Two optical systems were used for measurement air bubble sizes and their velocities in diesel. First, the optical system without an objective lens was used to determine the velocity of air bubbles in diesel. Another optical system with a 10× objective lens was used to obtain the size distribution of air bubbles generated in diesel. An available optical system with a 10× objective lens can detect a bubble diameter greater than 3.3 µm that air bubble images were processed using the ImageJ program. We measured the size distribution of air bubbles generated using the ImageJ program. The micro air bubble radius measured in diesel was found to be 6.26 µm in the sample after a month from air bubble generation. In addition, the particle image velocimetry (PIV) technique was used to measure the velocity field. Then, we used the OpenPIV program for PIV image processing. The highest velocity distribution was determined to be 90 mm/s for diesel without air bubbles and 20 mm/s for diesel with air bubbles after a month of the bubble generation.

Air Entrainment and Surface Fluctuations in a Turbulent Ship Hull Boundary Layer

Air entrainment due to turbulence in a free-surface boundary layer shear flow created by a horizontally moving vertical surface-piercing wall is studied through experiments and direct numerical simulations (DNS). In the experiments, the moving wall is created by a laboratory-scale device composed of a surface-piercing stainless steel belt that travels in a loop around two vertical rollers; one length of the belt between the rollers simulates the moving wall. The belt accelerates suddenly from rest until reaching constant speed and creates a temporally evolving boundary layer analogous to the spatially evolving boundary layer that would exist along a surface-piercing towed flat plate. We report cinematic laser-induced fluorescence measurements of water surface profile histories, cinematic observations and measurements of air entrainment events, and air bubble size distributions and motions. To complement the experiments, DNS of the temporally evolving turbulent boundary layer were conducted, considering both the air and water phases. Because of cost considerations, only a portion of the belt was simulated at a lower Reynolds number, keeping the Froude number, however, at the same levels as in the experiments. The results of the experiments and DNS are found to be in qualitative agreement and are used synergistically to explore the physics of the air entrainment process; quantitative agreement is not to be expected given the differences in setup and Reynolds numbers. In the experiments and DNS, the free-surface motion is found to consist of a region near the belt with fast-moving uncorrelated large-amplitude ripples and an outer region of small-amplitude propagating waves. Entrainment events similar to plunging breaking waves are found in the experiments, and these and other entrainment mechanisms are examined in detail in the DNS. The spatial distributions of bubble numbers and velocities are reported along with their diameter distributions.

Air Entrainment and Surface Fluctuations in a Turbulent Ship Hull Boundary Layer

The air entrainment due to the turbulence in a free surface boundary layer shear flow created by a horizontally moving vertical surface-piercing wall is studied through experiments and direct numerical simulations. In the experiments, a laboratory-scale device was built that utilizes a surface-piercing stainless steel belt that travels in a loop around two vertical rollers, with one length of the belt between the rollers acting as a horizontally-moving flat wall. To complement the experiments, Direct Numerical Simulations (DNS) of the two-phase boundary layer problem were carried out with the domain including a streamwise belt section simulated with periodic boundary conditions. Cinematic Laser-Induced Fluorescence (LIF) measurements of water surface profiles in two vertical planes oriented parallel to the belt surface (wall-parallel profiles) are presented and compared to previous measurements of profiles in a vertical plane oriented normal to the belt surface (wall-normal profiles). Additionally, photographic observations of air entrainment and measurements of air bubble size distributions and motions are reported herein. The bubble entrainment mechanisms are studied in detail through the results obtained by the DNS simulations. Free surface features resembling breaking waves and traveling parallel to the belt are observed in the wall-parallel LIF movies. These breaking events are thought to be one of the mechanisms by which the air is entrained into the underlying flow. The bubble size distribution is found to have a characteristic break in slope, similar to the Hinze scale previously observed in breaking waves. Finally, several entrainment mechanisms are found in the simulations and their prevalence in the free surface boundary layer is assessed.

Evaluation of Gas Phase Dispersion in Flotation under Predetermined Hydrodynamic Conditions

Results of various investigations shows the relationship between the flotation parameters and gas distribution in a flotation cell. The size of gas bubbles is a random variable with a specific distribution. The analysis of this distribution is useful to make mathematical description of the flotation process. The flotation process depends on many variable factors. These are mainly occurrences like collision of single particle with gas bubble, adhesion of particle to the surface of bubble and detachment process. These factors are characterized by randomness. Because of that it is only possible to talk about the probability of occurence of one of these events which directly affects the speed of the process, thus a constant speed of flotation process. Probability of the bubble-particle collision in the flotation chamber with mechanical pulp agitation depends on the surface tension of the solution, air consumption, degree of pul aeration, energy dissipation and average feed particle size. Appropriate identification and description of the parameters of the dispersion of gas bubbles helps to complete the analysis of the flotation process in a specific physicochemical conditions and hydrodynamic for any raw material. The article presents the results of measurements and analysis of the gas phase dispersion by the size distribution of air bubbles in a flotation chamber under fixed hydrodynamic conditions. The tests were carried out in the Laboratory of Instrumental Methods in Department of Environmental Engineering and Mineral Processing, Faculty of Mining and Geoengineerin, AGH Univeristy of Science and Technology in Krakow.

Economic impact of spargers degradation in flotation columns

Flotation is a very complex process, where many variables interact to produce different metallurgic results. These characteristics pose a challenging problem to evaluate the economic impact of deviations of a normal condition. For example, what is the value of a calibration plan to assure the quality of a measurement of froth depth in a cell? Specific experiments designed to evaluate this deviations cannot be implemented in practice, since there are many independent variables changing simultaneously with unknown values.In this paper a methodology applied to estimate the economic impact of spargers degradation in flotation columns is presented. Four pieces of information are required. First, we need to express the association of the deviation from a normal condition with specific characteristics of process variables. In this case how the change in orifice diameter in the sparger affects the air bubble size distribution produced. Second, we need to relate this physical change with the process metallurgic. One way of doing this is to develop a phenomenological model that includes the effect of such variable. Third, we need to relate the metallurgical losses to economic losses. In this case we need to know how the metallurgic changes will affect the value of a concentrate and the extra cost of posterior treatment due to the changed characteristics of this product. Finally the information of how fast a sparger is degraded over time is needed.The methodology is applied to an industrial flotation column, discussing the assumptions made because of the lack of some precise information. The idea is that in spite these uncertainties, at least the most conservative economic evaluation can be made. If one need more precise evaluation to make decisions, then the characteristics of the extra information needed and how to obtain it in an industrial environment is suggested.

Dispersion of air bubbles in a flotation cell under predetermined hydrodynamic conditions

From a practical point of view the most important stage in flotation is a mineralization of gas bubbles, where the bubbles size is an important factor. Numerous studies and models show the relationship between the flotation parameters and gas distribution in a flotation cell. The size of gas bubbles is a random variable with a specific distribution [1] and analysis of this distribution is useful to make mathematical description of the flotation process. The article presents the results of measurements and analysis of the gas phase dispersion by the size distribution of air bubbles in a flotation chamber under fixed hydrodynamic conditions.

Size distribution of air bubbles entering the brain during cardiac surgery.

BackgroundThousands of air bubbles enter the cerebral circulation during cardiac surgery, but whether high numbers of bubbles explain post-operative cognitive decline is currently controversial. This study estimates the size distribution of air bubbles and volume of air entering the cerebral arteries intra-operatively based on analysis of transcranial Doppler ultrasound data.MethodsTranscranial Doppler ultrasound recordings from ten patients undergoing heart surgery were analysed for the presence of embolic signals. The backscattered intensity of each embolic signal was modelled based on ultrasound scattering theory to provide an estimate of bubble diameter. The impact of showers of bubbles on cerebral blood-flow was then investigated using patient-specific Monte-Carlo simulations to model the accumulation and clearance of bubbles within a model vasculature.ResultsAnalysis of Doppler ultrasound recordings revealed a minimum of 371 and maximum of 6476 bubbles entering the middle cerebral artery territories during surgery. This was estimated to correspond to a total volume of air ranging between 0.003 and 0.12 mL. Based on analysis of a total of 18667 embolic signals, the median diameter of bubbles entering the cerebral arteries was 33 μm (IQR: 18 to 69 μm). Although bubble diameters ranged from ~5 μm to 3.5 mm, the majority (85%) were less than 100 μm. Numerous small bubbles detected during cardiopulmonary bypass were estimated by Monte-Carlo simulation to be benign. However, during weaning from bypass, showers containing large macro-bubbles were observed, which were estimated to transiently affect up to 2.2% of arterioles.ConclusionsDetailed analysis of Doppler ultrasound data can be used to provide an estimate of bubble diameter, total volume of air, and the likely impact of embolic showers on cerebral blood flow. Although bubbles are alarmingly numerous during surgery, our simulations suggest that the majority of bubbles are too small to be harmful.

Steady-state size distribution of air bubbles in polar ice

Between the close-off depth and the bubble-to-hydrate transition zone in polar ice sheets, the geometrical properties of air bubbles, such as number concentration and size of bubbles, are mainly controlled by firn temperature and ice accumulation rate prevailing during the snow to ice transformation [3], and by the bubble compression in the course of bubbly ice densification [13]. This implies that the data on the bubble properties can be used for reconstruction of the past climate change. On the basis of our earlier studies of bubbly ice densification and the new measurements of air bubbles in the Antarctic ice cores, we have developed a theory of bubble evolution in polar ice and propose an inverse procedure for bubble size conversion to specified conditions at the close-off depth. Both outcomes of the research contribute to elaboration of the new paleoclimatological tool based on the bubble properties.

Air Bubble Size Measurement in a Laboratory Flotation Cell

Air bubble size distribution in a laboratory flotation cell was investigated by using of image analysis technology in this paper. Results showed that it was feasible to determine the air bubble size according to image analysis software. For a porous media-aerated flotation cell, bubble size was dependent on poles size of porous media. Furthermore, operating parameters of the cell could affect the size. Mean bubble diameters increased with increasing of air flow rate. In contrast, it decreased when adding deinking agent. Its decreasing with increasing pulp flow rate under given conditions illustrated the fact that proper turbulence strength at the inlet of air bubbles was favorable for reducing bubble size. Gas holdup increased with increasing air flow rate to some extent, but it had a peak value. Gas holdup would rise obviously when deinking agent existed. An efficient approach to enhancing bubble surface area flux was to increase air flow rate and keep small bubble size at the same time.

Visualisation of foam microstructure when subject to pressure change

We report the development of a methodology to study the static and dynamic effects of pressure on the stability of air bubbles to coalescence in process and formulation regimes that are relevant to much of the food industry. In this initial work a model food foam was studied using a combination of a Linkam pressure cell and direct in situ imaging of the foam by confocal scanning laser microscopy (CSLM). Observations were made during pressure changes from 11 bar absolute to 1 bar, from 11 to 6 bar, and from 6 to 1 bar and the resulting changes in the foam microstructure were captured. Analysis of the digital images obtained was then used to quantify the effects of pressure on bubble size distribution. The results obtained show that the foam under study was relatively stable under quiescent conditions but could de-stabilise when subject to a pressure change similar to that of a typical industrial process. The larger the pressure change that was applied to the foam, the more coalescence resulted. However, most of the coalescence events were noted to take place over a small pressure window. The resulting change in the air bubble size distribution through pressure changes must be directly related to the nature of the air/water surface and how this responds to a change in surface area. It is also likely to relate to the solubility of the gas in the continuous phase as a function of dynamic change.

Transient development of whipped cream properties

Commercially available UHT cream was tempered at 4 °C for 24 h and whipped for different times: 3, 6, 9 and 12 min. The following properties of cream were measured: rheological and interfacial properties, overrun and size distribution of air bubbles. The whipping process changes the properties of cream, which exhibits viscoelastic behaviour with a high influence of elastic component. The air bubbles incorporated during the process result in forming stronger foam containing smaller bubbles, and also give a higher overrun. These changes are observed around 9 min of whipping, when the amount of air is sufficient to create a stable structure. Further whipping reduces the overrun and the foam partly collapses; this may be caused by aggregation of fat droplets.

Composition of Interfacial Layers in Complex Food Emulsions Before and After Aeration: Effect of Egg to Milk Protein Ratio

Whipped emulsions were prepared at pilot scale from fresh milk, whole egg, and other ingredients, for example, sugars and stabilizers (starch, polysaccharides). Egg content was varied: 4 recipes were studied differing in their egg to milk protein ratio (0, 0.25, 0.38, and 0.68). Protein and fat contents were kept constant by adjusting the recipes with skim-milk powder and fresh cream. Emulsions were prepared by high-pressure homogenization and whipped on a pilot plant. Particle-size distribution determined by laser-light scattering showed an extensive aggregation of fat globules in both mix and whipped emulsions, regardless of recipe. Amount of protein adsorbed at the oil-water interface and protein composition of adsorbed layer were determined after isolation of fat globules. Protein load is strongly increased by the presence of egg in formula. Values obtained for the whipped emulsions were dramatically lower than those obtained for the mix by a factor of 2 to 3. Sodium dodecyl sulfate-PAGE indicated a preferential adsorption of egg proteins over milk proteins at the oil-water interface, regardless of recipe. This phenomenon was more marked in aerated than in unaerated emulsions, showing evidence for desorption of some milk proteins during whipping. Egg proteins stabilize mainly the fat globule surface and ensure emulsion stability before whipping. Air bubble size distribution in whipped emulsions was measured after 15 d storage. When the egg to milk protein ratio is decreased to 0.25, large air cells appear in whipped emulsions during storage, indicating mousse destabilization. The present work allows linking the protein composition of adsorbed layers at the fat globule surface to mousse formula and mousse stability.

Images acquisition of multiphase dispersions in fermentation processes

Multiphase mixing is a common operation in fermentation process. However, one of the main problems for online automatic monitoring of dispersions occurring in microbial cultures in a mechanically stirred bioreactor, is the difficulty in acquiring images (in motion) clear enough to characterize its elements (mainly air, water, oil and biomass) and their interactions during cultivation. Once the images to be analyzed have been acquired, other problems arise related to the complexity and diversity of objects/artifacts captured in the visual field. The heterogeneous transparency of some objects, low contrast and similarity between different classes of objects are, among others, major problems for the automation of image analysis procedures. The purpose of this work is to present a system that allows the on-line acquisition of images inside a mechanically stirred tank.The images are digitally obtained by connecting a TV camera to a stereomicroscope. The scanning of the camera is synchronized to the flashing of a stroboscope, which acts as the light source and is equipped with a submergible probe. These illumination conditions allow obtaining high quality images that can be further analyzed to quantify size distributions of air bubbles and oil drops in multiphase dispersion, and to observe the dynamics of phase interactions (solid, liquid and gaseous) in a model culture.

Study on Characteristics of Air Entrapment into Seawater Due to Nappe for Design of De-Aeration Chamber : Volume and Size Distribution of Air Bubbles Generated in Seawater Due to Nappe from Weir

Study on Characteristics of Air Entrapment into Seawater Due to Nappe for Design of De-Aeration Chamber : Volume and Size Distribution of Air Bubbles Generated in Seawater Due to Nappe from Weir

Ultrasonic-induced nucleation of ice in water containing air bubbles

Cavitation induced by ultrasonic vibrations can cause nucleation of ice in supercooled water. In this study, the time required for ultrasonic-induced nucleation of ice was measured for water containing two different size distributions of air bubbles. When the water was supersaturated with air bubbles, there was a time lag of about 0.5 s between the onset of ultrasonic irradiation and the onset of ice nucleation, and the probability of ice nucleation was unusually high within 0.5–1.1 s after the onset of ultrasonic irradiation. These results cannot be explained by conventional models alone, in which the collapse of a cavitation bubble triggers the nucleation of ice. Secondary effects appear to also influence ice nucleation.

Bubble measurements downstream of hydraulic jumps

A phase Doppler anemometer (PDA) system was used to measure the velocity profiles and air bubble size distributions downstream of two-dimensional hydraulic jumps for different upstream flow conditions in a 1.92 m long laboratory flume. The PDA detected bubbles from 1 to 500 μm in diameter, and more were found at the bottom of the downstream flow near the elevation of the upstream free surface. This distribution was more marked for smaller bubbles, those with diameters less than 100 μm . The migration of the bubbles is controlled by the effects of buoyancy and by turbulent mixing; the relative magnitude of their effects on bubble distribution depends strongly on bubble size, and also on the energy of the upstream flow.

Effects of System Parameters on the Physical Characteristics of Bubbles Produced through Air Sparging

Air sparging is a relatively new, cost-effective technology for the remediation of soil and groundwater contaminated with volatile organic compounds (VOCs). While the method has met with reasonable success at a large number of field sites, implementation of the technique is restricted to relatively coarse-grained soils with large values of air permeability, which significantly limits its applicability. An understanding of the fundamental parameters that control the formation and distribution of air in the sparging process is useful for optimizing the system implementation and extending its range of applicability. This work presents the results of an experimental investigation into the effect of process control parameters on the size and size distribution of air bubbles produced in aqueous and idealized saturated porous media systems. The experiments used digital image analysis to image and quantify the physical characteristics of the bubbles generated in a bench scale test cell. Results demonstrated that the average bubble size and range of size distribution increased as the injection pressure and size of the injection orifice were increased. Larger diameter bubbles with wider size distributions were produced in the presence of particles when compared to aqueous systems. As the particle size was decreased, the size of bubbles produced increased. Finally, the presence of trace quantities of the surfactant Triton X100 led to uniformly small diameter bubbles under all experimental conditions. The presence of the surfactant coating produced bubbles with physical characteristics that are more suited to in situ stripping of VOCs than the bubbles produced in the absence of a surfactant.

Study of drop and bubble sizes in a simulated mycelial fermentation broth of up to four phases.

The mean sizes and size distributions of air bubbles and viscous castor oil drops were studied in a salt-rich aqueous solution (medium), first separately, and then simultaneously as a three-phase system. The dispersion was created in a 150-mm-diameter stirred tank equipped with a Rushton turbine, and the sizes were measured using an advanced video technique. Trichoderma harzianum biomass was added in some experiments to study the effect of a solid phase under unaerated and aerated conditions to give either three-or four-phase systems. In all cases, the different dispersed phases could be clearly seen. Such photoimages have never been obtained previously. For the three phases, air-oil-medium, aeration caused a drastic increase in Sauter mean drop diameter, which was greater than could be accounted for by the reduction in energy dissipation on aeration. Also, as in the unaerated case, larger drops were observed as the oil content increased. On the other hand, mean bubble sizes were significantly reduced with increasing oil phase up to 15% with bubbles inside many of the viscous drops. With the introduction of fungal biomass of increasing concentration (0.5 to 5 g L(-1)) under unaerated conditions, the Sauter mean drop diameter decreased. Finally, in the four-phase system (oil [10%]-medium-air-biomass) as found in many fermentations, all the phases (plus bubbles in drops) could clearly be seen and, as the biomass increased, a decrease in both the bubble and the drop mean diameters was found. The reduction in size of bubbles (and therefore increase in interfacial area) as the oil and bio- mass concentration increased provides a possible explanation as to why the addition of an oil phase has been reported to enhance oxygen transfer during many fermentations.