Increase In Bubble Size Research Articles

Investigation on the Properties of Aqueous Foams Stabilized by Cetyltrimethylammonium Bromide in Terms of Free Drainage and Bubble Size

AbstractAlthough foams stabilized by surfactants have been the subject of massive investigations and great achievements were made over the past few years, many questions concerning their properties are still not well understood. The aim of this study is to examine the effect of the cetyltrimethylammonium bromide (CTAB) concentration on the foam properties and illustrate the interaction between liquid drainage and bubble size evolution. Experiments were carried out at varying CTAB concentrations ranging from 0.1 to 5.0 times the critical micelle concentration (CMC), where the variation of the liquid content of foam and bubble size was simultaneously determined using a commercially available FoamScan device. The results showed that the foam properties (both foamability and foam stability) of CTAB were largely dependent on the surfactant concentration when concentrations c < CMC but this effect did not scale linearly with concentration. When c ≥ CMC, both foamablity and foam stability were nearly concentration independent, while the latter showed a small decrease due to the formation of micelles. In addition, the correlation between free drainage and bubble size evolution indicated that the increase of bubble size could indeed enhance the foam drainage.

Effects of initial bubble size on geometric and motion characteristics of bubble released in water

To seek and describe the influence of bubble size on geometric and motion characteristics of the bubble, six nozzles with different outlet diameters were selected to inject air into water and to produce different bubble sizes. High-speed photography in conjunction with an in-house bubble image processing code was used. During the evolution of the bubble, bubble shape, traveling trajectory and the variation of bubble velocity were obtained. Bubble sizes acquired varied from 0.25 to 8.69 mm. The results show that after the bubble is separated from the nozzle, bubble shape sequentially experiences ellipsoidal shape, hat shape, mushroom shape and eventually the stable ellipsoidal shape. As the bubble size increases, the oscillation of the bubble surface is intensified. At the stabilization stage of bubble motion, bubble trajectories conform approximately to the sinusoidal function. Meanwhile, with the increase in bubble size, the bubble trajectory tends to be straightened and the influence of the horizontal bubble velocity component on the bubble trajectory attenuates. The present results explain the phenomena related to relatively large bubble size, which extends the existing relationship between the bubble terminal velocity and the equivalent bubble diameter.

Investigation of trajectory and rise velocity of loaded and bare single bubbles in flotation process using video processing technique

ABSTRACTIn flotation, among the key parameters that dictate the hydrodynamic characteristics are bubble rising velocity and trajectory. This study aims to investigate the trajectory and rise velocity of loaded and bare bubbles using an experimental setup and video processing technique. After acquiring the videos of rising bubbles, using the background subtraction algorithm, bubbles were detected and their rise velocity and trajectory were determined with regard to the changes in the coordinates of bubbles’ centers. It was shown that bare bubbles have a zigzag trajectory, while for loaded bubbles the trajectory was close to the straight vertical path. In addition, with increasing bubble size, the rise velocity and the deviation from the straight path increase.

Impact of fish feeds, fish oils, and amino acids on the performance of airlift pumps

The impact of the addition of a wide variety of commercial, experimental, and larval feeds as well as fish oils, specific lipid products, amino acids, and surfactants on airlift pumping rates were documented. At 250 min after addition, the airlift flow rate varied from 12% to 102% of baseflow for diffuser injection but only 77 to 85% of base flow for direct injection. As a group, the fish and algal-based oils had the greatest impact on airlift flow rate. It is hypothesized that the impact of feed addition is due to lipids and surface-active compounds leaching out of the feed and increasing bubble size. There was a significant correlation between gas holdup and airlift pumping rate. Higher gas holdup was positively correlated with higher water flows. There was also a wide range in speed and range of flow rate recovery; flow recovery may depend on adsorption of lipids on the tank walls or chemical reactions. There was a positive correlation between lipid content and flow reduction, but the physical characteristics of the feed and specific fatty acid profiles of the feed may be important. The use of performance information based on clean water tests may significantly over-estimate pumping rates of airlift pumps. For critical applications, on-site evaluation using actual airlift pumps and feeds may be needed. While feed addition had much more impact on the performance of airlift pumps using diffuser injection compared to direct injection, the significantly higher efficiency of diffuser injection makes this injector type a better choice for many applications.

Enhanced mass transfer from the installation of a sieve tray subject to the variation of liquid heights and flow regimes in a bubble column

This work addressed the gas–liquid (G/L) mass transfer limitation coming from the increasing liquid height and the circumvention of the limitation by introducing a sieve tray in a bubble column. Either monoethylene glycol (MEG) solution or n-hexane was adopted as a liquid phase and argon was used as a gas phase in the bubble column. The gas holdup and the mass transfer coefficient became lowered by the static liquid height increase due to the increase of bubble size. The loss of mass transfer was overcome by installing a sieve tray inside the column. The two sieve trays with different hole sizes were employed and both bubble diameter and standard deviation of pressure were investigated to understand the effect of the sieve tray on the mass transfer. With a smaller size hole sieve (1mm), the mass transfer deteriorated in both liquid systems (MEG and n-hexane) due to the formation of gas cap below the sieve while with a larger hole sieve (3mm), it was enhanced because of the reduction of bubble diameters without any gas cap formation. However, it was found that the sieve tray effect was weakened when the flow regime changes from homogeneous to heterogeneous.

CFD model simulation of bubble surface area flux in flotation column reactor in presence of minerals

Bubble surface area flux (Sb) is one of the main design parameter in flotation column that typically employed to describe the gas dispersion properties, and it has a strong correlation with the flotation rate constant. There is a limited information available in the literature regarding the effect of particle type, density, wettability and concentration on Sb. In this paper, computational fluid dynamics (CFD) simulations are performed to study the gas–liquid–solid three-phase flow dynamics in flotation column by employing the Eulerian–Eulerian formulation with k-ε turbulence model. The model is developed by writing Fortran subroutine and incorporating then into the commercial CFD code AVL FIRE, v.2014. This paper studies the effects of superficial gas velocities and particle type, density, wettability and concentration on Sb and bubble concentration in the flotation column. The model has been validated against published experimental data. It was found that the CFD model was able to predict, where the response variable as indicated by R-Square value of 0.98. These results suggest that the developed CFD model is reasonable to describe the flotation column reactor. From the CFD results, it is also found that Sb decreased with increasing solid concentration and hydrophobicity, but increased with increasing superficial gas velocity. For example, approximately 28% reduction in the surface area flux is observed when coal concentration is increased from 0 to 10%, by volume. While for the same solid concentration and gas flow rate, the bubble surface area flux is approximately increased by 7% in the presences of sphalerite. A possible explanation for this might be that increasing solid concentration and hydrophobicity promotes the bubble coalescence rate leading to the increase in bubble size. Also, it was found that the bubble concentration would decrease with addition of hydrophobic particle (i.e., coal). For instance, under the same operating conditions, approximately 23% reduction in the bubble concentration is predicted when the system was working with hydrophobic particles. The results presented are useful for understanding flow dynamics of three-phase system and provide a basis for further development of CFD model for flotation column.

Prediction of Cavitation Depth in an Al-Cu Alloy Melt with Bubble Characteristics Based on Synchrotron X-ray Radiography

The size of cavitation region is a key parameter to estimate the metallurgical effect of ultrasonic melt treatment (UST) on preferential structure refinement. We present a simple numerical model to predict the characteristic length of the cavitation region, termed cavitation depth, in a metal melt. The model is based on wave propagation with acoustic attenuation caused by cavitation bubbles which are dependent on bubble characteristics and ultrasonic intensity. In situ synchrotron X-ray imaging of cavitation bubbles has been made to quantitatively measure the size of cavitation region and volume fraction and size distribution of cavitation bubbles in an Al-Cu melt. The results show that cavitation bubbles maintain a log-normal size distribution, and the volume fraction of cavitation bubbles obeys a tanh function with the applied ultrasonic intensity. Using the experimental values of bubble characteristics as input, the predicted cavitation depth agrees well with observations except for a slight deviation at higher acoustic intensities. Further analysis shows that the increase of bubble volume and bubble size both leads to higher attenuation by cavitation bubbles, and hence, smaller cavitation depth. The current model offers a guideline to implement UST, especially for structural refinement.

Comparative scaling analysis of two different sized pilot-scale fluidized bed reactors operating with biomass substrates

This paper presents a comparative scaling analysis of two different sized pilot-scale fluidized bed reactors operating with biomass substrates. A multiphase Eulerian-Eulerian 2-D mathematical model was implemented, coupled with in-house user-defined functions (UDF) built to enhance hydrodynamics and heat transfer phenomena. The model validation was attained by comparison to experimental data gathered from both reactors. A grid refinement study was carried out for both geometries to achieve an appropriate computational domain. Hydrodynamics was deeply studied for both reactors concerning the scale-up effect. Mixing and segregation phenomena, solid particle distribution and biomass velocity were matters of great concern. Results showed that UDF implementation successfully minimized deviations and increased the model’s predictability. The largest deviations measured between experimental and numerical results for syngas composition were of about 20%. Solids mixing and segregation was found to be directly affected by the particles size, density, and superficial gas velocity, with the larger reactor revealing improved mixing ability. Improved mixing occurred for smaller particles size ratio (dbiomass = 3 mm), smaller particles density ratio (ρbiomass = 950 kg/m3), and higher dimensionless superficial gas velocities (U0/Umf=3.5). The larger unit showed an increase in near-wall velocity, lateral dispersion, and bubble size. As for the smaller reactor, higher velocities were obtained at the center region due to a more pronounced wall boundary layer. Similarities were found between the two reactors regarding the bubble distribution, dimensionless average bed pressure drop and biomass velocity vector profiles when dimensionless parameters were employed.

Gas Bubble Migration and Trapping in Porous Media: Pore‐Scale Simulation

AbstractGas bubbles can be naturally generated or intentionally introduced in sediments. Gas bubble migration and trapping affect the rate of gas emission into the atmosphere or modify the sediment properties such as hydraulic and mechanical properties. In this study, the migration and trapping of gas bubbles are simulated using the pore‐network model extracted from the 3D X‐ray image of in situ sediment. Two types of bubble size distribution (mono‐sized and distributed‐sized cases) are used in the simulation. The spatial and statistical bubble size distribution, residual gas saturation, and hydraulic conductivity reduction due to the bubble trapping are investigated. The results show that the bubble size distribution becomes wider during the gas bubble migration due to bubble coalescence for both mono‐sized and distributed‐sized cases. And the trapped bubble fraction and the residual gas saturation increase as the bubble size increases. The hydraulic conductivity is reduced as a result of the gas bubble trapping. The reduction in hydraulic conductivity is apparently observed as bubble size and the number of nucleation points increase.

Investigation of the induction time of low-rank coal particles on rising bubble surfaces

ABSTRACT In this paper, the back-calculated induction times of low-rank coal particles on the rising bubble with mobile surfaces were back-calculated from the micro-flotation rate constants. The back-calculated induction times slightly increased with the flotation recovery increase or the surfactant concentration decrease. It is because the drainage time accounting for most of the induction time is affected by the force exerted on the wetting film. Moreover, the force exerted on the wetting film is characterized by the Reynolds number. Furthermore, the Reynolds number increased with increasing bubble rising velocity due to an increase in bubble size as a result of decreasing surfactant concentration. Therefore, the back-calculated induction times could reflect the difference in the flotation recoveries at the same surfactant concentration. Meanwhile, it indicated that the hydrodynamic condition in the flotation process had a significant effect on the back-calculated results of induction times. From this investigation, it can be speculated that the back-calculated induction time of particles sliding on the rising bubble with mobile bubble surfaces is greatly influenced by the Reynolds number.

Radiation damage in helium ion–irradiated reduced activation ferritic/martensitic steel

Abstract Nanocrystalline reduced activation ferritic/martensitic (RAFM) steel samples were prepared using surface mechanical attrition treatment (SMAT). Un-SMATed and SMATed reduced activation ferritic/martensitic samples were irradiated by helium ions at 200°C and 350°C with 2 dpa and 8 dpa, respectively, to investigate the effects of grain boundaries (GBs) and temperature on the formation of He bubbles during irradiation. Experimental results show that He bubbles are preferentially trapped at GBs in all the irradiated samples. Bubble denuded zones are clearly observed near the GBs at 350°C, whereas the bubble denuded zones are not obvious in the samples irradiated at 200°C. The average bubble size increases and the bubble density decreases with an increasing irradiation temperature from 200°C to 350°C. Both the average size and density of the bubbles increase with an increasing irradiation dose from 2 dpa to 8 dpa. Bubbles with smaller size and lower density were observed in the SMATed samples but not in the un-SMATed samples irradiated in the same conditions, which indicate that GBs play an important role during irradiation, and sink strength increases as grain size decreases.

Influence of the Physical Properties of Liquids and Diameter of Bubble on the Formation of Liquid Column at the Interface of Two Liquid Phases by the Rising Bubble

The formation of metal emulsion in a steel-making process enhances the reaction between metal and slag. A part of the metal emulsion is formed by a bubble passing through the interface between the metal and slag phases. In a previous study, it was determined that the formation of metal column by the bubble is related to the formation of metal droplets. In this research, the effects of bubble particle size, interfacial tension, viscosity of upper layer, and lower layer density on the formation of lower liquid column were investigated. In order to conduct an in situ observation of gas and liquid behaviors, aqueous solution and silicon oil systems were employed. It was determined that a narrow and elongated column forms liquid droplets in the upper liquid layer and contributes to the formation of droplets. The height of the column and the volume of droplets increase with the increase in bubble size. The influence of interfacial tension of the two liquid phases on the column height and the formation of droplet is slight. The height of the formed column decreases with the increase in the density of lower liquid.

Helium bubbles aggravated defects production in self-irradiated copper

Under the environment of high radiation, materials used in fission and fusion reactors will internally accumulate numerous lattice defects and bubbles. With extensive studies focused on bubble resolution under irradiation, the mutually effects between helium bubbles and displacement cascades in irradiated materials remain unaddressed. Therefore, the defects production and microstructure evolution under self-irradiation events in vicinity of helium bubbles are investigated by preforming large scale molecular dynamics simulations in single-crystal copper. When subjected to displacement cascades, distinguished bubble resolution categories dependent on bubble size are observed. With the existence of bubbles, radiation damage is aggravated with the increasing bubble size, represented as the promotion of point defects and dislocations. The atomic mechanisms of heterogeneous dislocation structures are attributed to different helium-vacancy cluster modes, transforming from the resolved gas trapped with vacancies to the biased absorption of vacancies by the over-pressured bubble. In both cases, helium impedes the recombination of point defects, leading to the accelerated formation of interstitial loops. The results and insight obtained here might contribute to understand the underlying mechanism of transmutant solute on the long-term evolution of irradiated materials.

Increase of bubble size playing a critical role in foam-induced protein aggregation: Aggregation of BSA in foam fractionation

In this work, the role of increase of bubble size in foam-induced protein aggregation was investigated using bovine serum albumin (BSA) asa model protein. Firstly, different increases of bubble size were obtained by varying the height of rising foam. Then, the effects of increase of bubble size on the desorption of BSA molecules from the interface, and the aggregation of desorbed BSA molecules in the rising foam and during the defoaming process were studied. Finally, the effects of the foam-induced aggregation on the performances of foam fractionation of BSA were studied. The results show that by reducing the flux of the gas-liquid interfacial area, the increase of bubble size desorbed BSA molecules from the interface to cause protein aggregation. By promoting the increase of bubble size, foam drainage intensified the foam-induced BSA aggregation, and increased the production of BSA aggregates with larger-sizes. For a slight increase in bubble size, most of the BSA aggregates were produced during the defoaming process, so both the enrichment ratio and recovery percentage of BSA monomer reduced. Whereas for more significant increase of bubble size, most of the BSA aggregates were produced in the rising foam and companied with enhanced foam drainage, they decreased both the recovery percentages of BSA overall and BSA monomer.

Dense gas–liquid–solid flow in a slurry bubble column: Measurements of dynamic characteristics, gas volume fraction and bubble size distribution

Dense three-phase slurry flows are important in several industrial processes (e.g., Methanol/ DME synthesis, Fischer Tropsch synthesis). In the present work, gas–liquid–solid flow in a pseudo 3D slurry bubble column is characterized under dense flow conditions for superficial gas velocity (UG) of 5–30cms-1 and overall solid loading (αS) of 0–40vol.%. In-house developed voidage probes were used to measure local gas volume fraction fluctuations. The high frequency fluctuations (∼1–10Hz) caused by individual bubbles or swarms of bubbles were found to increase with increase in αS and UG. The low frequency oscillations (∼<1Hz) corresponding to column-scale recirculating flow were found to decrease with increase in αS. Importantly, time-averaged gas volume fraction and its internal composition (i.e. gas volume fraction contained in different bubble size groups) and bubble size distribution were measured at different locations in the slurry bubble column. With an increase in αS, local gas volume fraction was found to decrease, accompanied by an increase in bubble size. Based on the distribution of bubble chord lengths, the gas volume fraction contained in different bubble size groups was measured for different αS and UG. With increase in αS, the gas volume fraction for small bubbles was found to decrease while that for large bubbles was found to increase. Under the dense flow conditions (at high UG and αS), while small bubbles were found to accumulate near the column walls, as indicated by the wall peaking in α‾G profiles, large bubbles/gas slugs were found to flow predominantly through the column center. In addition to the new experimental data, the present work helps to improve the understanding of dense slurry flows that will aid the development and verification of Eulerian multiphase models.

Effects of bubbles on high-temperature corrosion of helium ion-irradiated Ni-based alloy in fluoride molten salt

Samples of a Ni-Mo-Cr-Fe-Si alloy subject to helium ion irradiation damage were corroded in a eutectic mixture of FLiNaK at 750°C. It was found that the helium bubbles that formed increased the number of surface defects so greatly increasing the physical contact area between the alloy and the molten salt, resulting in acceleration of corrosion damage. Segregation and depletion of chemical elements at bubble surfaces were also identified, and became more severe with increasing bubble size. Significant segregation of Si resulted in the formation of Ni-Si precipitates at large bubbles. This segregation enhanced the chemical corrosion damage to the alloy.

Study of air-core vortical flow structure induced by a plughole vortex

This paper describes a study of the generation of a plughole vortex and its consequences in a drainpipe during drainage of water from a stationary rectangular tank. The critical and minimum depths of water above the inlet of the drainpipe, where a surface dip starts to develop for drainpipes of various diameters, were examined parametrically. This study explored the following naturally occurring phenomena arising from a plughole vortex. (i) A plughole vortex initially causes a surface dip to develop towards the inlet of the drainpipe and as the surface dip approaches the inlet of the drainpipe it creates a droplet-shaped air bubble. (ii) A unique bubble transformation, i.e. from a droplet-shaped to a donut-shaped bubble ring, occurs just after the separation of the droplet-shaped air bubble from the surface dip. (iii) The donut-shaped bubble ring flows with the drain water and initially causes bubbly flow in the drainpipe. (iv) As the water head above the inlet of the drainpipe decreases, the droplet-shaped bubble size increases, and consequently, the bubble ring size increases and causes slug flow in the drainpipe. (v) As the slugs combine, the flow of the draining water eventually becomes annular flow in the drainpipe. Sounds, such as that of instantaneous fizz and bubble sink draining, were observed to be produced as a result of the bubble formation process. Temporal changes in the shape and size of the air bubbles were studied. Within the range of 0.45–0.6, the ratio of the bubble diameter to the bubble length was found to be linearly proportional to the ratio of the water depth to the diameter of the drainpipe. Several drainage cases were simulated numerically to observe the physics of these naturally occurring phenomena. The shapes and sizes of the vortices induced by plugholes have been visualised and analysed using the vortex core method.

Bubble size and flow characteristics of bubbly flow downstream of a ventilated cylinder

Bubbly flows downstream of a ventilated cylinder in a water tunnel are experimentally studied. Emphasis is placed upon the relationship between bubble property and carrier flow parameters. Under no-ventilation condition, the pure-water wake flow is measured with particle image velocimetry technique. Bubbles are generated with ventilation and the bubbly flow is visualized using shadow image velocimetry. The separation and statistical treatment of bubbles in the captured images are accomplished with an in-house code. The influence of upstream flow velocity and air flow rate is examined. Sauter mean diameter of the bubbles and bubble velocity distribution are obtained. Instantaneous bubbly flow pattern is in accordance with the carrier flow characteristics. Across the high-vorticity region, bubbles experience a remarkable bubble size variation, large bubbles are annihilated. As for cross-sectional bubble size distribution, the tendency obtained with image processing agrees with the result obtained with the formula associating turbulent kinetic energy dissipation with bubble size. As upstream velocity increases, the percentage of small bubbles increases. Both bubble volume fraction and the most predominant bubble size increase with air flow rate. The percentage of large bubbles varies slightly with air flow rate.

Characterization of aerosol emissions from single bubble bursting

• The bubble film thickness increased dramatically with increasing bubble size and exponentially with increasing surface tension.

Mechanistic modeling and numerical simulation of in-situ gas void fraction inside ESP impeller

When gas is entrained with liquid into an electrical submersible pump (ESP), the in-situ gas void fraction (αG) inside the ESP impeller is closely related to its pressure boosting ability. Due to complex pump geometries, the direct measurement of αG is very difficult to carry out. In this study, a mechanistic model for predicting the in-situ αG inside an ESP impeller is developed and validated by three-dimensional (3D) computational fluid dynamics (CFD) simulations. The pressure increment of ESP obtained from single-phase numerical simulations matches experimental measurement well. With a new bubble size prediction model implemented into multiphase CFD simulations, the calculated ESP pressure increments under gassy flow conditions also agree with experimental pump performance curves. As the inlet gas volumetric fraction (GVF) increases, the ESP boosting pressure deteriorates. The simulated in-situ αG, which is used to verify mechanistic model predictions, increases with bubble size increase and gas density or rotational speed decrease. Based on the radial velocity slippage between gas and liquid phases, the in-situ αG can be determined with GVF, rotational speed, bubble size, and fluid properties etc. Compared with empirical correlations, the proposed mechanistic model can predict in-situ αG better by accounting for the gas-liquid phase interaction using the radial force balance between centrifugal buoyancy and drag forces exerted on a stable bubble.