Volume Concentration Of Bubbles Research Articles

Reflection of sound pulses from an inhomogeneous bubble medium

The effect of changes in the volume concentration of bubbles in the boundary zone of the bubble medium on the nature of reflection and radiation of the excited bubble medium is studied. The spectral characteristics of the radiation of a bubble medium are obtained at the initial stage of transition radiation and at large times when the radiation is stationary. It is shown that in the initial phase the emission spectrum is broadband and is located in the absorption band of the bubble medium, and at large times the emission spectrum is located outside this band.

Feasibility Evaluation on Single-Collector Collision Model to Separate Microplastics in Micro Bubble Flotation Process

Objectives:The single collector collision (SCC) model is a model that predicts the separation efficiency of particles based on the collision efficiency between microbubbles and particles in the particle separation process. In order to remove micro-plastics (MPs) particles, which have recently been known to be harmful, we tried to analyze the impact and separation efficiency of MPs based on the SCC model and evaluate its application feasibility.Methods:Based on the SCC model, the collision efficiency prediction for MPs particle removal was simulated and the separation efficiency was evaluated. In addition, a series of flotation experiments were conducted using a flotation device that injects microbubbles to remove MPs particles suspended in water, and the experimental results and predicted values were compared.Results and Discussion:Using the SCC model, the collision efficiency according to the size distribution of MPs particles was not significantly different from that of typical particles (clay, kaolin) in water. Based on this collision efficiency, the maximum removal efficiency of MPs particles separated from the water body is predicted to reach about 90%. On the other hand, the initial collision-adhesion coefficient () of the MPs particles based on the SCC model was 0.03 to 0.1, showing a slight difference from the clay particles having the range of 0.3 to 0.4. The flotation separation efficiency of the MPs particles evaluated and predicted by applying this initial collision-adhesion coefficient showed a range similar to the measured value. In addition, the particle separation efficiency according to the increase of the measured bubble volume concentration to improve the particle separation efficiency also showed a pattern similar to the predicted value.Conclusions:In the flotation process, the initial collision-adhesion efficiency of the MPs particles predicted by the SCC model was lower than that of the kaolin particles. Based on the simple and simple model SCC theory, it was confirmed that it can be applied to the flotation separation analysis of MPs particles.

The formation of nonlinear sound fields in the boundary region of the bubble medium

The formation of sound fields in the boundary region of a bubble medium under the influence of a powerful sound pulse for different volume concentrations of bubbles is studied. Two characteristic ranges of the volume concentration of bubbles, to the limits of which different types of wave fields are formed, are determined. At low values of volume concentrations in the boundary region, a long-lived space-limited standing sound wave is formed. A standing sound wave contains an order of magnitude more energy than other areas of the bubble medium. At large values of the volume concentration of bubbles in the boundary region of the bubble medium, an excitation zone forms. The structure of the zone is a periodic wave propagating deep into the bubble medium. The wavelength in the excitation zone increases with increasing distance from the boundary.

Reflection of sound pulses from the boundary of the bubble medium

The reflection of sound and radiation of a bubble medium under excitation by a short sound wave are studied for different values of the volume concentration of bubbles. It is shown that at the beginning of the interaction of the wave with the medium, reflection occurs as from a structureless soft boundary, which at the end of the interaction is replaced by radiation from an excited medium. The dependences of the reflection coefficient are obtained and the spectral characteristics of the radiation of the bubble medium are determined at the initial stage of the process and at large times when the radiation is steady-state. It is shown that the emission spectrum of the layer is continuous with a maximum in the frequency range of volume pulsations of free bubbles.

Cool White Polymer Coatings based on Glass Bubbles for Buildings

While most selective emitter materials are inadequate or inappropriate for building applications, here we present a techno-economically viable optical coating by integrating glass bubbles within a polymer film. A controlled glass bubble volume concentration from 0 to 70% leads to a selective solar reflectivity increase from 0.06 to 0.92 while the mid-infrared emissivity remains above 0.85. Outdoor measurements show the polymer coating on a concrete surface can provide a temperature reduction up to 25 °C during the day when conduction and convection are limited and a net cooling power greater than 78 W/m2 at a cost less than $0.005/W. The impact of polymer coating on common buildings is estimated as potential annual energy savings of 2–12 MJ/m2 and CO2 emission savings of 0.3–1.5 kg/m2. More savings are expected for higher surface-area-to-volume-ratio buildings, and the polymer coating is also expected to resolve cooling issues for old buildings with no air conditioning.

Unraveling the mystery of ultrafine bubbles: Establishment of thermodynamic equilibrium for sub-micron bubbles and its implications

HypothesisWe test the validity of the Young-Laplace equation and Henry’s law for sub-micron bubble suspensions, which has long been a questionable issue. Application of the two theories allows characterization of bubble diameter and gas molecule partitioning between gaseous and dissolved phases using two easily measurable variables: total gas content (CT) and bubble volume concentration (BVC). ExperimentsWe measure CT and BVC for sub-micron bubble suspensions generated from three pure gases, which allows calculation of bubble diameter for each suspension using the Young-Laplace equation and Henry’s law. Uncertainties involved in the experimental measurements are assessed. Bubble size for each suspension is also directly measured using a dynamic light scattering (DLS) technique for comparison. FindingsApplying the two theories we calculate that the bubble diameters are in the range of 304–518 nm, which correspond very well with the DLS-measured diameters. Sensitivity analyses demonstrate that the correspondence of the calculated and DLS-measured bubble diameters should take place only if the two theories are valid. The gas molecule partitioning analysis shows that >96% of gas molecules in the suspension exist as dissolved phase, which suggests the significance of the dissolved phase for applications of the bubble suspensions.

Sound waves in multifractional liquids with bubbles

The propagation of sound waves in multifractional mixtures of liquid with vapor–gas and gas bubbles of different sizes and different compositions with phase transitions is studied. The dispersed phase consists of N+M fractions having various gases in bubbles and different in the bubbles radii. Phase transitions accounted for N fractions. The total bubble volume concentration is small (less than 1%). The dispersion relation is derived and dispersion curves is built. The evolution of the weak pulsed perturbations of the pressure in this mixture was calculated numerically.

Weak waves in multifractional liquids with bubbles

The propagation of weak waves in multifractional mixtures of liquid with vapor-gas and gas bubbles of different sizes and different compositions with phase transitions is studied. The dispersed phase consists of N+M fractions having various gases in bubbles and different in the bubbles radii. Phase transitions accounted for N fractions. The total bubble volume concentration is small (less than 1%). The dispersion relation is derived and dispersion curves is built. Influence of the mass concentration is shown. It is shown that dispersion and dissipation of acoustic waves depends significantly on presence of different bubbles in fractions of the dispersed phase.

Acoustic waves in multifractional bubbly liquids

The propagation of acoustic waves in multifractional mixtures of a liquid with vapor-gas and gas bubbles of different sizes and different compositions with phase transitions is investigated. The dispersed phase consists of N + M fractions having various gases in bubbles and different in the bubble radii. Phase transitions accounted for N fractions. The total bubble volume concentration is small (less than 1%). A system of differential equations of the mixture motion is developed, and the dispersion relation is derived. It is shown that the dispersion and dissipation of acoustic waves depends largely on the presence of bubbles of various proportions in the composition of the disperse phase. It is found that the replacement of a fraction of vaporgas bubbles in the monodisperse bubbly mixture with phase transitions for gas bubbles with different thermophysical properties, depending on the type of gas, can lead to both a decrease and an increase in the attenuation coefficient in the low-frequency region.

Comparative evaluation of particle separation efficiency based on carbon dioxide and air bubble sizes in flotation separation processes

Micro-sized carbon dioxide gas bubbles can be applied as alternatives to air bubbles in flotation separation processes, which can reduce CO2 emissions as well as decrease energy consumption. CO2 and air bubbles were used as particle collectors in the flotation process to investigate and compare the collision efficiency and particle separation characteristics. This study measured bubble size distributions and simulated the single-collector collision (SCC) model that has been applied extensively to flotation processes. The diameter of the air bubbles was found to decrease as the saturator pressure increased, but the size of the CO2 bubbles increased when the pressure exceeded 151.99–202.65kPa. When using CO2 bubbles as collectors to separate particles in water, the simulation results from the SCC model expressed in terms of bubble volume concentration (BVC) was related to the lower collision efficiency of CO2 bubbles, and the bubble number concentration (BNC) rather than the BVC to the effects of macrobubbles. The findings of this study suggest that the advantages of CO2 bubbles used as collectors in particle separations would be lower operating costs and reduced greenhouse gas emissions from water and wastewater treatment plants.

해수담수화 전처리로서 DAF공정에서 고온의 해수에 대한 영향 특성

Flocculation and flotation are used as pretreatment steps prior to the reverse osmosis (RO) process. During seawater treatment, high temperature can change the water chemistry of seawater during the process of coagulation. It also affects bubble volume concentration (BVC) and bubble characteristics. Coagulants such as alum and ferric salts at <TEX>$40^{\circ}C$</TEX> can also change flux rates in the seawater reverse osmosis (SWRO) process. In this study, the bubble characteristics in dissolved air flotation (DAF), used as a SWRO pretreatment process, were studied in synthetic seawater at <TEX>$20^{\circ}C$</TEX> and <TEX>$40^{\circ}C$</TEX>. The flux of an RO membrane was monitored after dosing the synthetic seawater with coagulants at different temperatures. Results showed that BVC increases as the operating pressure increases and as the salt concentration decreases. The bubble size released at <TEX>$40^{\circ}C$</TEX> is far smaller than that at <TEX>$20^{\circ}C$</TEX>The addition of a ferric salt is effective for turbidity removal in synthetic seawater at <TEX>$20^{\circ}C$</TEX>; it is more effective than alum. When synthetic seawater was dosed with a ferric salt, the RO membrane flux increased by 27 % at <TEX>$40^{\circ}C$</TEX>.

Evaluation of Transfection Efficiency in Skeletal Muscle Using Nano/Microbubbles and Ultrasound

Recent studies have revealed that ultrasound contrast agents with low-intensity ultrasound, namely, sonoporation, can noninvasively deliver therapeutic molecules into target sites. However, the efficiency of molecular delivery is relatively low and the methodology requires optimization. Here, we investigated three types of nano/microbubbles (NMBs)—human albumin shell bubbles, lipid bubbles and acoustic liposomes—to evaluate the efficiency of gene expression in skeletal muscle as a function of their physicochemical properties and the number of bubbles in solution. We found that acoustic liposomes showed the highest transfection and gene expression efficiency among the three types of NMBs under ultrasound-optimized conditions. Liposome transfection efficiency increased with bubble volume concentration; however, neither bubble volume concentration nor their physicochemical properties were related to the tissue damage detected in the skeletal muscle, which was primarily caused by needle injection. (E-mail: kodama@bme.tohoku.ac.jp)

Effects of floc and bubble size on the efficiency of the dissolved air flotation (DAF) process

Dissolved air flotation (DAF) is a method for removing particles from water using micro bubbles instead of settlement. The process has proved to be successful and, since the 1960s, accepted as an alternative to the conventional sedimentation process for water and wastewater treatment. However, limited research into the process, especially the fundamental characteristics of bubbles and particles, has been carried out. The single collector collision model is not capable of determining the effects of particular characteristics, such as the size and surface charge of bubbles and particles. Han has published a set of modeling results after calculating the collision efficiency between bubbles and particles by trajectory analysis. His major conclusion was that collision efficiency is maximum when the bubbles and particles are nearly the same size but have opposite charge. However, experimental verification of this conclusion has not been carried out yet. This paper describes a new method for measuring the size of particles and bubbles developed using computational image analysis. DAF efficiency is influenced by the effect of the recycle ratio on various average floc sizes. The larger the recycle ratio, the higher the DAF efficiency at the same pressure and particle size. The treatment efficiency is also affected by the saturation pressure, because the bubble size and bubble volume concentration are controlled by the pressure. The highest efficiency is obtained when the floc size is larger than the bubble size. These results, namely that the highest collision efficiency occurs when the particles and bubbles are about the same size, are more in accordance with the trajectory model than with the white water collector model, which implies that the larger the particles, the higher is the collision efficiency.

Implementation of the Laser Diffraction Technique for Acoustic Cavitation Bubble Investigations

Knowledge of the acoustic cavitation cloud would be useful for improving ultrasound reactor design. Among the characterisation techniques, few are adapted to bubble investigations in an intense ultrasound field. Some problems raised by these measurements result from interactions between the acoustic pressure wave and the measuring light wave. This paper reports the implementation of the laser diffraction technique to determine the size and volume concentration of bubbles generated by a dipping horn operating at 20 kHz. Measurements were performed with a Malvern 2600 instrument. The size distribution, deduced from the diffraction pattern scattered by the bubble cloud crossed by a laser beam, is disturbed by the acoustic pressure wave involving deviation of a light beam at low diffusion angles (acousto-optic effect). A bubble size correction procedure based on the subtraction of the light energy due to the ultrasound wave is described. The size measurements, and thus the correction procedure, were validated by a second laser technique based on a different measuring principle: phase Doppler interferometry. The measurement reliability was further confirmed by an original application of laser diffraction based on measurements performed just after sonication. These three methods lead to a mean bubble size (Sauter mean diameter) of about 10 μm at a high ultrasound power input. Concerning the void fraction, only measurements achieved after sonication and by laser diffraction predict a correct estimation of this parameter.

Mathematical Model of a Mass-Transfer Apparatus for Producing a Foamed Liquid with a Desired Microstructure

A mathematical model is developed to describe the bubble formation from a gas outflowing through microholes into a liquid. The model is valid over wide ranges of gas-flow rates, gas/liquid pressure drops, and the thermophysical properties of the liquid. The calculated results agree well with the observed data. A model is proposed to characterize the hydrodynamics of and mass transfer in laminar liquid flow in a coaxial mass-transfer apparatus with a gas-permeable inner tube. Numerical data are reported for the effect of the operating parameters of the mass-transfer apparatus with a specified matrix (inner tube) microstructure on the bubble- size distribution and the volume concentration of bubbles in the liquid.

Original Article

This paper presents the mathematical formulation of a model for bubble–floc agglomeration in the contact zone of dissolved air flotation (DAF). It also contains rising velocity formulae for a bubble–floc agglomerate in the separation zone of DAF. The bubble–floc agglomeration model is based on the population balance of air bubbles, particles, and bubble–particle agglomerates, and the rate of bubble–floc collision and attachment. The model has been designed for two cases: where particles are larger than bubbles and vice versa. The requirements of pre-treatment (coagulation and flocculation) and the amount of air as bubbles are discussed, with the support of a model simulation. The air supply–consumption ratio (Asc) is derived as an important static parameter determining DAF performance, and should be greater than 1. The traditional DAF parameter, the air–solid ratio (As), is proportional to the air supply–consumption ratio. The DAF model parameter evaluation suggested that it should be on the order of 0.01 or more. To ensure a sufficient bubble–floc collision rate, the DAF model simulation revealed, the kinetic parameter (bubble volume concentration times floc diameter, φbd) should be greater than 6.0 × 10−8 m. The performance of DAF in treating a high concentration suspension (>100 mg/L) is dependent mainly on the air–solid ratio (or the air supply–consumption ratio). For low concentration suspensions (≪100 mg/L), φbd instead of the air–solid ratio is a dominant operational parameter in ensuring an acceptable bubble–floc collision frequency. The bubble volume concentration required for treating a low concentration suspension can be reduced with the increase of floc size by pre-flocculation.

Modeling, simulation and operational parameters of dissolved air flotation

This paper presents the mathematical formulation of a model for bubble–floc agglomeration in the contact zone of dissolved air flotation (DAF). It also contains rising velocity formulae for a bubble–floc agglomerate in the separation zone of DAF. The bubble–floc agglomeration model is based on the population balance of air bubbles, particles, and bubble–particle agglomerates, and the rate of bubble–floc collision and attachment. The model has been designed for two cases: where particles are larger than bubbles and vice versa. The requirements of pre-treatment (coagulation and flocculation) and the amount of air as bubbles are discussed, with the support of a model simulation. The air supply–consumption ratio ( A sc ) is derived as an important static parameter determining DAF performance, and should be greater than 1. The traditional DAF parameter, the air–solid ratio ( A s ), is proportional to the air supply–consumption ratio. The DAF model parameter evaluation suggested that it should be on the order of 0.01 or more. To ensure a sufficient bubble–floc collision rate, the DAF model simulation revealed, the kinetic parameter (bubble volume concentration times floc diameter, φ b d ) should be greater than 6.0 × 10 −8 m. The performance of DAF in treating a high concentration suspension (>100 mg/L) is dependent mainly on the air–solid ratio (or the air supply–consumption ratio). For low concentration suspensions (≪100 mg/L), φ b d instead of the air–solid ratio is a dominant operational parameter in ensuring an acceptable bubble–floc collision frequency. The bubble volume concentration required for treating a low concentration suspension can be reduced with the increase of floc size by pre-flocculation.

Cavitation phenomena in pulse modulated ultrasound fields

Sonoluminescence (SL), subharmonic generation (SH) and ultrasound absorption in a cavitation zone generated by pulse modulated fields were studied. It has been shown that SL intensity may be increased due to pulse modulation of an ultrasound field by more than two orders of magnitude as compared to the SL intensity obtained by continuous irradiation. The achieved increase in the erosion rate is smaller with pulse modulation. The ultrasound absorption decreases with the inverse pulse duty ratio (or off/on factor), i.e. clarification effect is found to exist in pulsed fields. The thresholds of studied phenomena increase with inverse pulse duty ratio. The intensity of the subharmonic and of other low-frequency components of the cavitation noise decreases; this allows us to conclude that the decreased bubble volume concentration is mainly caused by a decrease of the large bubbles that have low energy concentration efficiency and make little contribution to the cavitation effects.

Rheological model of volume stretching of newtonian liquids

An equation of state for a volumetrically stretched cavitating liquid medium that holds in the entire span of volume concentrations of bubbles ranging from cavitation nuclei to the stage of formation of a cellular foam structure is obtained based on a proposed macrorheological model. The dependence of the modulus of volume elasticity of a liquid on the volume concentration of bubbles is plotted, and a method for estimating the relaxation time for tensile stresses in cavitating liquid media is proposed.

Flocculation and Air Requirements for Dissolved Air Flotation

Bench‐scale and pilot‐plant studies were used to investigate the effects of flocculation time and floe size on the performance of dissolved air flotation and to determine air requirements for three different types of water supplies. The results show that long flocculation periods are not needed and suggest that floe particles of 10–30 μm should be prepared for flotation. Two measures of the air supplied were examined: percentage recycle and the bubble volume concentration or the volume of air released per volume of water treated. Bubble volume concentrations of 4,600 ppm or 8 percent recycle were sufficient to effectively treat all the waters tested.