Decrease In Bubble Size Research Articles

The influence of wire orientation during nucleate pool boiling in subcooled dodecane

Experiments were performed to examine the influence of thin wire heater orientation (φ = 0° (horizontal), 22°, 33°, 44°, 49.5°, 74° and 90° (vertical)) on nucleate boiling in subcooled dodecane. Variations of both heat flux (q̇″) and temperature difference (ΔT) along with φ change were analyzed. The number, velocity, and size of bubbles (whose size were larger than the wire diameter) were recorded, and their influence on critical heat flux (CHF) at different orientation angles were discussed. As φ increased, CHF variations decreased slowly at first and then quickly. The decrease in CHF was accompanied by decrease of bubble number and size, but increase of bubble speed along the wire. A critical angle of φ = 22° shows the highest heat transfer coefficient (HTC).

Computational modeling of the electrostatic charge build-up in fluidized beds

Coupled computational fluid dynamics and discrete element method was used to investigate the electrostatic charge build-up in fluidized beds. The charge transfer among particles and particles-wall collision was considered. The repulsive electrostatic force among particles increases the bed voidage and bubble size decreases. The average charge of particles linearly increases with time and the slope of this line increases at higher gas velocities. There is a lack of experimental data on charge transfer and effect of electrostatic charge of particles on the hydrodynamics of fluidized beds and this work provides a first insight into the charge transfer on bubble behaviors.

Improvement of flotation recovery using oscillatory air supply

The present work compares the flotation recoveries of silica at different particle sizes with oscillatory air supply and conventional steady air supply. The flotation tests were carried out at continuous mode using a 50 mm diameter column equipped with a sparger. Bubble size and gas holdup were measured in the presence and absence of silica particles. The results showed that converting steady air supply to oscillatory air supply could lead to significant improvement of flotation recovery at all particle size fractions tested in the present work, including a 54% increase in flotation recovery for ultrafine particles (−10 μm) and an extension of the upper limit of particle size. The improvement of flotation recovery was linked to decreased bubble size and increased gas holdup. The present study has important implications for research on fine and coarse particle flotation.

The Effect of Soundwaves on Foamability Properties and Sensory of Beers with a Machine Learning Modeling Approach

The use of ultrasounds has been implemented to increase yeast viability, de-foaming, and cavitation in foods and beverages. However, the application of low frequency audible sound to decrease bubble size and improve foamability has not been explored. In this study, three treatments using India Pale Ale beers were tested, which include (1) a control, (2) the application of audible sound during fermentation, and (3) the application of audible sound during natural carbonation. Five different audible frequencies (20 Hz, 30 Hz, 45 Hz, 55 Hz, and 75 Hz) were applied daily for one minute each (starting from the lowest frequency) during fermentation (11 days, treatment 2) and carbonation (22 days, treatment 3). Samples were measured in triplicates using the RoboBEER to assess color and foam-related parameters. A trained panel (n = 10) evaluated the intensity of sensory descriptors. Results showed that samples with sonication treatment had significant differences in the number of small bubbles, alcohol, and viscosity compared to the control. Furthermore, except for foam texture, foam height, and viscosity, there were non-significant differences in the intensity of any sensory descriptor, according to the rating from the trained sensory panel. The use of soundwaves is a potential treatment for brewing to improve beer quality by increasing the number of small bubbles and foamability without disrupting yeast or modifying the aroma and flavor profile.

Bubble propagation in Hele-Shaw channels with centred constrictions

We study the propagation of finite bubbles in a Hele-Shaw channel, where a centred occlusion (termed a rail) is introduced to provide a small axially uniform depth constriction. For bubbles wide enough to span the channel, the system’s behaviour is similar to that of semi-infinite fingers and a symmetric static solution is stable. Here, we focus on smaller bubbles, in which case the symmetric static solution is unstable and the static bubble is displaced towards one of the deeper regions of the channel on either side of the rail. Using a combination of experiments and numerical simulations of a depth-averaged model, we show that a bubble propagating axially due to a small imposed flow rate can be stabilised in a steady symmetric mode centred on the rail through a subtle interaction between stabilising viscous forces and destabilising surface tension forces. However, for sufficiently large capillary numbers Ca, the ratio of viscous to surface tension forces, viscous forces in turn become destabilising thus returning the bubble to an off-centred propagation regime. With decreasing bubble size, the range of Ca for which steady centred propagation is stable decreases, and eventually vanishes through the coalescence of two supercritical pitchfork bifurcations. The depth-averaged model is found to accurately predict all the steady modes of propagation observed experimentally, and provides a comprehensive picture of the underlying steady bifurcation structure. However, for sufficiently large imposed flow rates, we find that initially centred bubbles do not converge onto a steady mode of propagation. Instead they transiently explore weakly unstable steady modes, an evolution which results in their break-up and eventual settling into a steady propagating state of changed topology.

Characterizing gas bubble size distribution of laboratory foamed cement using X-ray micro-CT

The objectives of this study are to use micro-computed tomography (micro-CT) to elucidate the influencing factors of the microstructure of laboratory foamed cement and develop statistical models to quantify the gas bubble size distributions. During this study, foamed cement slurries were prepared using sealed foam cement mixers at various operating conditions. The influences of shear rate, mixing energy, base cement slurry composition, blender geometry, and applied pressure on the gas bubble size distribution of set foamed cement were investigated. Test results indicate foam quality and gas pressure are the primary determining factors of gas bubble size in foamed cement. The gas bubble size in foamed cement produced by a sealed foam mixer approximately follows the normal distribution. For samples generated with a standard multiblade blender at atmospheric condition, the mean and standard deviation of gas bubble size distribution increase exponentially with increasing foam quality. A dramatic decrease in gas bubble size is observed with increasing gas pressure. On the other hand, variations in mixing energy, shear rate, base slurry composition, and blender geometry have relatively little effect on the microstructure of the foamed cement within the range investigated.

The influence of low-energy helium plasma on bubble formation in micro-engineered tungsten

Four different types of micro-engineered tungsten surfaces were exposed to low energy helium plasma, with a planar surface as control. These samples include two surfaces covered with uniform W-coated rhenium micro-pillars; one with cylindrical pillars 1 μm in diameter and 25 μm in height, and one with dendritic conical pillars 4–10 μm in diameter and 20 μm in height. Additionally, two samples with reticulated open-cell foam geometry, one at 45 pores per inch (PPI), and the other at 80 PPI were fabricated with Chemical Vapor Deposition (CVD). The samples were exposed to helium plasma at 30–100 eV ion energy, 823–1123 K temperature, and 5 × 1025 - 2 × 1026 m−2 ion fluence. It is shown that the formation of nanometer-scale tendrils (fuzz) on micro-engineered W surfaces is greatly reduced as compared to planar surfaces. This is attributed to more significant ion backscattering and the increased effective surface area that intercept incident ions in micro-engineered W. A 20% decrease in the average ion incident angle on pillar type surfaces leads to ∼30% decrease in bubble size, down to 30 nm in diameter. W fuzz was found to be absent from pillar sides due to high ion backscattering rates from pillar sides. In foam samples, 28% higher PPI is observed to have 24.7%–36.7% taller fuzz, and 17.0%–25.0% larger subsurface bubbles. These are found to be an order of magnitude smaller than those found in planar surfaces of similar environment. The helium bubble density was found to increase with ion energy in pillars, roughly from 8.2% to 48.4%, and to increase with increasing PPI, from 36.4% to 116.2%, and with bubble concentrations up to 9.1 × 1021 m−3. Geometric shadowing effects in or near surface ligaments are observed in all foam samples, with near absence of helium bubbles or fuzz in deeper layers of the foam.

A perspective on flotation: a review

AbstractThe problem of fine particles processing has become important both in mineral processing and also for water and wastewater engineering. It is accepted, on the other hand, that the bubble–particle collection efficiency increases with decreasing bubble size. A decrease in bubble size can be obtained using different methods (dispersed‐air, where electroflotation is included, and/or dissolved‐air flotation), as discussed. Following an introduction of the subject, older laboratory results are presented in this review paper (based on 4 decades of experience), explaining the above, giving further ideas and possibly, assisting future researchers in the area. Examples given are: separation of fine mineral particles (such as pyrite and magnesite), and of metal ions (as chromium, arsenic, copper, zinc, germanium and so on); among the various available techniques, mention is given to ion, precipitate, adsorbing colloid, sorptive and biosorptive flotation ‐ including certain comparisons for the same application. The metal ion flotation application deserves further study and work, mainly for selective removal. © 2017 Society of Chemical Industry

Effect of bubble size on bubble-particle attachment and film drainage kinetics - A theoretical study

Effect of bubble size on bubble-particle attachment and film drainage was studied based on the extended Derjaguin-Landau-Verwey-Overbeek theory and the Stefan-Reynolds flat film model. The disjoining pressure isotherms and wetting film drainage kinetics between a bubble and an model silica with different hydrophobic force decay lengths were calculated theoretically. It is found that the results depend on the shapes of total disjoining pressure isotherms. Film formed between a small bubble and silica surface always has faster drainage kinetics compared to that formed between a big bubble and silica surface due to the high Laplace pressure. For a monotonic repulsive total disjoining pressure, the wetting film is thermodynamically stable and the final equilibrium film thickness decreases with decreasing bubble size. In presence of a pressure barrier in total disjoining pressure, whether or not the film can rupture is determined by the magnitude between Laplace pressure and the pressure barrier. A small bubble is beneficial to the recovery of particles with weak and moderate floatability since the high Laplace pressure can drive the film to the range of hydrophobic force or even overcome the pressure barrier resulting in successful attachment. In flotation practice, much attention should be paid on bubble size since it not only affects collision efficiency but also influences the attachment behaviour.

Effect of Surfactant on Bubble Size and Air Holdup on Column Flotation

Flotation is a complex process in which is present physicochemical and hydrodynamic phenomena. The flotation performance is related to the probability of bubble-particle collisions and stability of aggregate formed. The collision efficiency is a function of particle and bubble diameters. Currently one of the biggest challenges of the mining industry is the flotation of fine and ultrafine particles and a possible solution to increase the recovery of these fine particles is the use of bubbles with intermediate size (100-1000μm). Therefore, determining and controlling the bubble size is very important for further recoveries in the flotation of fine particles. It is known that the bubble size and air holdup are influenced by variations on the superficial gas velocity and by addition of surfactants. Thus this work aimed to study the effect of adding surfactants on bubbles formation. The results showed that the addition of surfactant was a good alternative to decrease bubble size and increase the air holdup in a bubble column. Three different surfactants had similar behavior on bubble size and holdup. It was possible to define the range of concentration values which are sufficient for forming bubbles with intermediate size and holdup within the range recommended for mineral flotation.

Electroflotation of precipitated phosphate from synthetic solution

ABSTRACT The phosphate recovery from a 20 mg L-1 Na2HPO4 solution through precipitation with Ca(OH)2 followed by electroflotation was evaluated. X-ray diffraction and particle size measurements indicated that the precipitates were a mixture of hydroxyapatite and calcium-deficient hydroxyapatite, with size ranging from 3 to 10 μm. Electroflotation with Na-oleate as surfactant was used to recover the precipitates. The surfactant adsorption was evaluated through zeta potential measurements. The influence of Na-oleate concentration, pH and bubble size on phosphate recovery was investigated. In the absence of Na-oleate, a phosphate recovery of 50% was achieved, while in the presence of 20 mg L-1 of Na-oleate it was increased to 90%, at pH 11. The phosphate recovery also increased with Ca(OH)2 concentration increase and bubble size decrease, reaching 100% at 300 mg L-1 Ca(OH)2 and bubble size around 39 µm.

Performance Evaluation of Underwater Wireless Optical Communications Links in the Presence of Different Air Bubble Populations

We experimentally evaluate the performance of underwater wireless optical communication (UWOC) links in the presence of different air bubbles. Air bubbles of different sizes and densities are generated by using an air pipe in conjunction with a submersible water pump of variable flow rate that helps break up large bubbles into smaller bubbles. Received signal intensity measurements show that bubbles significantly degrade the performance of UWOC links. Large bubbles completely obstruct the optical beam and cause a deep fade. However, as the bubble size decreases, the level of deep fade also decreases because the optical beam is less susceptible to complete obstruction, and more light reaches the detector. We also show that beam expansion could help mitigate the performance degradation due to the deep fade caused by air bubbles scatters in the channel.

Bubble size distribution in cyclonic zone of a novel flotation column

ABSTRACTIn order to investigate bubble size distribution (BSD) in the cyclonic flotation column, a series of tests were conducted to study flow velocity distribution (FVD) and BSD by using the method of particle image velocimetry (PIV). Foaming performance of the n-octyl alcohol is more applicable than both of n-butyl alcohol and terpenic oil. At different circulation volume conditions, BSD range lies in 0–800 μm, and a large number of tiny bubbles (<90 μm) are generated. Besides, the curve presents a normal distribution in 90–180 μm. With the increase in circulation volume, bubble size decreases. BSD determined by cyclonic flow effect plays a crucial role on bubble mineralization with fine particle in cyclonic zone of the flotation column.

Enhanced hydrodynamics in a novel external-loop airlift reactor with self-agitated impellers

In the present work, self-agitated impellers, as a novel type of internals, have been proposed for improving hydrodynamic and mass transfer characteristics of external-loop airlift reactors. The influence of inserted self-agitated impellers, in the riser section, in various liquid phases and with different sparger types, on main hydrodynamic parameters, was studied. The results show that the insertion of impellers led to significant bubble breakage and decrease in mean bubble size, particularly in pseudoplastic liquid. Obtained riser gas holdup values were up to 47% higher, in comparison to the configuration without impellers. Higher improvements were obtained with single orifice, given that this is the least effective gas distributor. Even though impellers represent an obstacle to the flow, relatively low reduction (about 10%) in downcomer liquid velocity was observed, for all investigated cases. Having this in mind, the benefit of inserting self-agitated impellers for improving the performance of external-loop airlift reactors was apparent.

Synthesis and characterization of alkyl, propoxy, ethoxy-based frothers

In this paper we describe the synthesis and characterization of a homologous series of linear polyglycol-based frothers comprising alkyl, propoxy (propylene oxide, PO), and ethoxy (ethylene oxide, EO) groups. The identities were confirmed by proton nuclear magnetic resonance spectroscopy and total organic carbon analysis. Characterization used three parameters, bubble size, gas holdup and water overflow rate, measured in a bubble column. The results indicate that increasing number of PO groups led to significant decrease in bubble size, and increase in gas holdup and water overflow rate. Increasing the alkyl chain length, gave similar but less pronounced trends; the least effect was increasing the number of EO groups. Changing the relative position of the PO and EO group had a significant effect on all three parameters. To account for the effect of PO/EO position, a mechanism based on effect of structure on molecule packing at the air/water interface is proposed.

Influence of bubble size on the fluid dynamic behavior of a DAF tank: A 3D numerical investigation

Abstract With computational fluid dynamics (CFD) methods, the influence of bubble size on the fluid dynamic behavior in a dissolved air flotation tank is investigated in this study. The choice of multiphase flow model between Euler–Euler and Euler–Lagrange approach is first addressed by comparing with the experimental results. The results indicate that Euler–Euler multiphase model is more suitable for the simulation of air/water flow in the DAF tank as it makes better performance in predicting air distribution. With the aid of Euler–Euler model, a systematic study was carried out to investigate the flow pattern and air distribution in the separation zone under bubble diameter from 30 μm to 70 μm. The results demonstrate that larger bubbles are conducive to the formation of stratified flow when bubble diameter ranges from 30 μm to 50 μm and show little impact on flow patterns when bubble diameter exceeds 50 μm. Bubble size has a significant influence on air distribution. Decreasing bubble size enlarges the height of “white water zone”.

Study on the High Shear Degassing Process with Water Simulation

Hydrogen as the main cause of the gas porosity in aluminium alloys should be removed before casting. The degassing process with intensive melt shearing shows a high efficiency. In the present work, the water simulation was used to study the high shear degassing process and the effect of rotation speed on the size and distribution of inert gas bubbles. The results show that with the increase of rotation speed, the bubble size decreases and the affected region becomes larger. The proper rotation speed of the rotor for the rotor-stator high shear degassing process is 5000-6000 RPM.

Delayed recompression for decompression sickness: retrospective analysis.

IntroductionMost cases of decompression sickness (DCS) occur soon after surfacing, with 98% within 24 hours. Recompression using hyperbaric chamber should be administrated as soon as feasible in order to decrease bubble size and avoid further tissue injury. Unfortunately, there may be a significant time delay from surfacing to recompression. The time beyond which hyperbaric treatment is non effective is unclear. The aims of the study were first to evaluate the effect of delayed hyperbaric treatment, initiated more than 48h after surfacing for DCS and second, to evaluate the different treatment protocols.MethodsFrom January 2000 to February 2014, 76 divers had delayed hyperbaric treatment (≥48h) for DCS in the Sagol center for Hyperbaric medicine and Research, Assaf-Harofeh Medical Center, Israel. Data were collected from their medical records and compared to data of 128 patients treated earlier than 48h after surfacing at the same hyperbaric institute.ResultsThere was no significant difference, as to any of the baseline characteristics, between the delayed and early treatment groups. With respect to treatment results, at the delayed treatment divers, complete recovery was achieved in 76% of the divers, partial recovery in 17.1% and no improvement in 6.6%. Similar results were achieved when treatment started early, where 78% of the divers had complete recovery, 15.6% partial recovery and 6.2% no recovery. Delayed hyperbaric treatment using US Navy Table 6 protocol trended toward a better clinical outcome yet not statistically significant (OR=2.786, CI95%[0.896-8.66], p=0.07) compared to standard hyperbaric oxygen therapy of 90 minutes at 2 ATA, irrespective of the symptoms severity at presentation.ConclusionsLate recompression for DCS, 48 hours or more after surfacing, has clinical value and when applied can achieve complete recovery in 76% of the divers. It seems that the preferred hyperbaric treatment protocol should be based on US Navy Table 6.

Assessing the Sensory Profiles of Sparkling Wine over Time

Sparkling wine sensory properties are driven by many factors, including the amount of CO₂ and pressure in the bottle. We were interested in characterizing the sensory attributes of California blanc de blanc sparkling wine and the sensory impact of various effervescence conditions, such as artificial nucleation points, on the aroma and flavor. Beginning with the effect of effervescence conditions on the aroma and flavor intensity, three different nucleation treatments (air-dried glasses, paper towel-dried glasses, and glasses with an etched nucleation point) were compared. Thirty-three panelists assessed overall aroma and flavor intensity for each treatment in triplicate. No statistically significant differences in aroma and flavor intensity were found. Following this, the sensory profiles of eight Californian blanc de blanc sparkling wines were determined using a generic descriptive analysis. Eleven trained judges used visual, aroma, taste, mouthfeel, and bubble descriptors to characterize the sensory differences among the sparkling wines. The characterization was done at both 1 and 5 min after pouring, using the same descriptors, to assess temporal variation. In addition, the atmospheric pressure of each wine bottle was measured to determine the influence of pressure on taste and aroma over time. Sparkling wines assessed at 1 and 5 min showed a significant difference in all wines. This difference was characterized by a decrease in bubble size and concentration and allowed for greater differences within the sample set; thus, at 5 min there was a greater differentiation among the wines. No correlations between bottle pressure and sensory attributes were found.

Oil–water separation property of polymer-contained wastewater from polymer-flooding oilfields in Bohai Bay, China

In this study, the effects of gravitational settling time, temperature, speed and time of centrifugation, flocculant type and dosage, bubble size and gas amount were investigated. The results show that the simple increase in settling time and temperature is of no use for oil–water separation of the three wastewater samples. As far as oil–water separation efficiency is concerned, increasing centrifugal speed and centrifugal time is highly effective for L sample, and has a certain effect on J sample, but is not valid for S sample. The flocculants are highly effective for S and L samples, and the oil–water separation efficiency increases with an increase in the concentration of inorganic cationic flocculants. There exist critical reagent concentrations for the organic cationic and the nonionic flocculants, wherein a higher or lower concentration of flocculant would cause a decrease in the treatment efficiency. Flotation is an effective approach for oil–water separation of polymer-contained wastewater from the three oilfields. The oil–water separation efficiency can be enhanced by increasing floatation agent concentration, flotation time and gas amount, and by decreasing bubble size.