Bubble Surface Area Research Articles

Process intensification of cooling crystallization of cholesterol from acetone solution using CO2 gas bubbles: Experiments and modeling

The present work investigates dependence of heterogeneous nucleation of solids on the gas bubble-solution interface in a process termed as "Precipitation by Gas-Bubbling" (PGB), through experiments and modeling. This process involves bubbling of CO2 gas at ambient condition through a solution of cholesterol in acetone, which is simultaneously cooled by an external coolant. The process parameters selected are coolant temperature, initial solution concentration, and CO2 flow rate. The flowing CO2 gas bubbles facilitate reduction in metastable zone width and induction time for cholesterol precipitation, rendering more efficient surface-mediated crystallization, thereby enabling process intensification of cooling crystallization. Faster precipitation of cholesterol at higher CO2 flow rate, i.e., higher CO2 bubble-solution interfacial area, demonstrates gas bubble-solution interface acting as a substrate for heterogeneous nucleation. Accordingly a mechanism for heterogeneous nucleation of cholesterol is proposed and validated by developing a model for prediction of final average particle size. The kinetic model parameters, namely, the pre-exponential factor as per the classical nucleation theory, and the crystal growth coefficient are regressed by comparing the predicted values of average particle size with the corresponding experimental data, and are found to be proportional to the surface area of gas bubbles and in turn on CO2 flow rate.

A flexible image processing technique for measuring bubble parameters based on a neural network

The main parameters in a liquid-gas system are the size, shape, and kinetic parameters of bubbles, which affect the mass transfer process. To describe the mass transfer process accurately, it is necessary to characterize bubble parameters such as bubble volume and surface area under different experimental conditions. However, these bubble parameters are not accurately assessable by conventional methods, which are limited by poor robustness and flexibility, including numerical methods and conventional neural networks. Based on the neural network technique, we propose a flexible method for measuring bubble parameters in three steps: segmentation of bubble images, segmentation of overlapping bubbles, and extraction of bubble feature parameters. This technique combines geometric, optical, and topological information. To verify the effectiveness of our method, we considered a gas-liquid reactor and microbubble radiosensitizer for brachytherapy as testing scenarios and used several groups of experimental images and synthetic images as testing sets. In the first step, the accuracy of the segmentation of bubble images was greater than 90% in all scenes and reached 99% in some scenes. In the second step, the proposed method was capable of segmenting overlapping bubbles and avoiding excessive segmentation. In the final step, our approach considers the geometric shape and deflection angle of bubbles. Therefore, the bubble parameters of largely deformed and deflected bubbles were obtained with high flexibility. Our method is a powerful tool with robustness and flexibility for the study of gas-liquid interface measurements in chemical and biochemical processes.

Effect of Closure Characteristics of Annular Jet Mixed Zone on Inspiratory Performance and Bubble System

In the flotation process, gas-liquid properties and the bubble system greatly influence bubble mineralization. In order to clarify how the mechanism applies to the closure characteristics of an annular jet mixed flow zone on the inspiratory performance and the bubble system, different degrees of closure on the velocity field and gas-liquid ratio in the mixed flow zone were investigated using numerical simulation. The variations in the characteristics of bubble size distribution, rising velocity, and gas content under different closure levels were measured with a high-speed dynamic camera technology. The results confirmed that when the closure degrees of the mixed flow zone improved, the inlet jet could gradually overcome the static pressure outside the nozzle effectively. It formed a gas-liquid mixing zone with high turbulence first, and a large pressure difference at the gas-liquid junction second. This helped to increase the inspiratory capacity. At the same time, the gas-liquid ratio rose gradually under conditions of constant flow. When the nozzle outlet was completely closed, the gas-liquid ratio gradually stabilized. For the bubble distribution system, an enhancement in the closure degrees can effectively reduce the bubble size, and subsequently, the bubble size distribution became more uniform. Due to the improved gas-liquid shear mixing, the aspect ratio of the bubbles can be effectively changed, consequently reducing the bubble rising speed and increasing the gas content and bubble surface area flux of the liquid.

The Effect of Hydrodynamic Conditions on the Selective Flotation of Fully Liberated Low Grade Copper-Nickel Ore

Low grade sulfide ores are difficult to process due to their composite mineralogy and their fine grained dissemination with gangue minerals. Therefore, fine grinding of such ores becomes essential to liberate valuable minerals. In this research, selective flotation was carried out using two pitched blade turbine impellers with diameters of 6 cm and 7 cm to float copper and nickel. The main focus of this research was to generate optimum hydrodynamic conditions that can effectively separate nickel and copper from gangue minerals. In addition, we investigated the effects of superficial gas velocity, impeller speed, bubble size distribution, and bubble surface area flux on the flotation recovery and rate constant. The results demonstrated that a 7 cm impeller comparatively produced optimum hydrodynamic conditions that improved Cu-Ni recovery and the rate constant. The maximum copper and nickel recoveries in the 7 cm impeller tests were observed at 93.1% and 72.5%, respectively. However, a significant decrease in the flotation rate of nickel was observed, due to entrainment of nickel in copper concentrate and the slime coating of gangue minerals on the nickel particle surfaces.

Simulation of the method of excitation of pulsations in a moving fluid flow

The article deals with an important issue of efficiency of using energy supplied into each of the elements of the Venturi-type pipe, i.e. the value of energy efficiency coefficient. The issue coverage requires conducting comparative studies of the specific surface area of bubbles in a gas-liquid system and the mass transfer coefficients in a pipe with a periodically changing cross-section and in a cylindrical pipe with other conditions being equal. The proposed method of excitation of pulsations in a moving fluid flow can be used for the processes of splitting droplets and bubbles in a continuous liquid phase, since this creates favorable conditions - significant amplitudes of pressure, speed and acceleration at a frequency of about dozens of Hertz.

Influence of Aeration Microporous Aperture on Oxygen Mass Transfer Efficiency in Terms of Bubble Motion Flow Field

Microporous aeration has been widely used to restore eutrophic water bodies. The gas–liquid mass transfer in the aeration process has a significant influence on the improvement of water quality. Therefore, the influence mechanism of oxygen mass transfer is worth studying. However, the influence of bubble movement characteristics on oxygen mass transfer has not been systematically studied. Thus, the present study explored the influence mechanism of microporous apertures on oxygen mass transfer in terms of bubble motion characteristics by investigating the oxygen mass transfer process and the feature of bubble movement under different aeration microporous aperture sizes. The results showed that the mass transfer efficiency was reduced as the micropore aperture increased from 200 to 400 μm. and the reduction rate was 7.17% when the aperture increased from 200 to 300 μm, which was lower than that from 300 to 400 μm (19.17%). Furthermore, the micropore aperture showed a positive correlation with the time-averaged velocity field. With the increase in aperture, the bubble velocity gradient (from the center to both sides of the edge) increased from about 0.2 to 0.4 m/s, which increased the oxygen mass transfer effect. The increase of micropore aperture caused the increase of average Sauter bubble diameter and the decrease of specific surface area of bubbles. In addition, the negative effects of the reduction of specific surface area and the shortening of bubble residence time on oxygen mass transfer efficiency were greater than the positive effects of the increase of turbulent kinetic energy. When the aperture changes from 300 to 400 μm, the shortening of bubble residence time should have played a major role. This study provides some theoretical parameters for investigating the mechanism of oxygen mass transfer in microporous aeration.

Importance of gas input in aqueous two-phase flotation (ATPF)

Aqueous two-phase flotation (ATPF) is a new method for separation of biotechnological products like enzymes from crude bio-suspensions. However, more research is needed to develop ATPF on its way to industrial use. Especially the gas input has to meet several demands.An appropriate bubble introduction could be realized via porous media. Bubble sizes were measured using image analysis methods. Impacts of system and flotation parameters on bubble size were monitored. The passage of bubbles through aqueous phase boundary was characterized and an appropriate bubble size window was found for efficient flotation and preventing phase mixing. Increasing the bubble surface area flux led to higher flotation rates and thus faster separation. A linear dependency of flotation rate constant and bubble surface area flux could be determined for ATPF of model enzyme phospholipase A2. The bubble surface area flux was found to be a key parameter for evaluating gas input.

Dynamics of Gas Bubbles From a Submarine Hydrocarbon Seep Within the Hydrate Stability Zone

AbstractWe validate a new model for mass transfer and bubble transport for natural seeps on the continental margins using an integrated observation of a seep at 883 m in the Northern Gulf of Mexico. In the model, mass transfer is assumed to transition from clean to dirty bubble mass transfer rates following a characteristic hydrate formation time that depends on the initial bubble surface area and the hydrate subcooling. We show that buoyancy‐induced upwelling is negligible for the bubble stream. We initialize the model using precise data observed at the seafloor and validate the model results to optical and acoustic measurements within the bubble stream. The model accurately predicts the acoustic attenuation of the bubble flare by lateral spreading and bubble shrinkage throughout the water column. The model shows that up to 99.4% by mass of the released gases from this seep dissolves into the ocean within the hydrate stability zone.

Influence of methylated milk casein flocculant dosage on removal rate of oil droplet removal from o/w in flotation

In previous study, we conducted removal of oil droplets in o/w emulsion by flotation involving addition of methylated milk casein (MeCS) as a flocculant in a batch system and proposed a simple kinetic model to evaluate the removal rate constant, K, which is proportional with two adsorption parameters and one experimental conditional parameter. The formers are adsorption rate constant, ka, of oil droplet and its floc onto bubble surface and the saturated adsorption density, Xs, the latter is the specific surface area per unit column volume, which is expressed as a product, (Sbτ)/V, where Sb, τ, and V are bubble surface production rate, bubble residence time within the column and the treated volume of o/w emulsion. This proportional relationship was verified from flotation experiments at the optimum dosage of MeCS, which was determined by the clarification experiment of flocculation. In this study, especially, the influence of MeCS dosage on the removal kinetics of the flotation and the variation of K was investigated. The result suggested that the flotation efficiency in the case of varying MeCS dosage was mainly controlled by the specific surface area of bubbles and the flocculation condition within the flotation column.

To a question of temperature driven gas swelling in helium doped ferritic alloys

Samples of three different ferritic steels: conventional AISI410S and two experimental oxide dispersion-strengthened alloys Сr16ODS and EP450ODS, were uniformly ion-doped with helium to concentrations of 0.2 and 1 at% and annealed in vacuum at 1023K. Subsequent TEM studies revealed various patterns of gas porosity development in them: a bimodal distribution of gas bubbles near the grain boundaries in the AISI410S and Сr16ODS alloys and a uniform growth of bubbles within the entire volume of grains in EP450ODS alloy. Measurements of bubbles from different samplings depending on the mode of growth, type of alloy and the doping level showed that the surface area of bubbles does not change during thermal growth of gas porosity, but remains proportional to a concentration of implanted helium, and for all alloys is within the range from 1×104 to 2×104 m2/mole. Regardless the type of material the coarsening of the bubbles occurs according to the mechanism of migration and coalescence. The volume of gas porosity increases during the growth of bubbles approximately in proportion to their size. It is determined that the gas pressure inside the bubbles is not equal to the surface tension pressure. The dependence of pressure on the bubble size at a constant temperature repeats the isotherm for real gas and is much stronger than previously thought. It is concluded that all the bubbles, regardless of the gas pressure inside, are in a state of thermodynamic equilibrium.

Potential of flotation as alternative separation process in biotechnology with focus on cost and energy efficiency

Flotation is a density separation process which is influenced by physico-chemical interaction between a particle and a bubble. In biotechnology, it finds application in the solid-liquid separation of biomass. The process mechanism depends on the formation of stable microorganism-bubble-complexes by collision and adsorption. The difference in density of these complexes and the surrounding liquid medium causes them to rise to the liquid surface, where a foam develops. This microorganism enriched foam can then be removed. An economical comparison of the separation technologies centrifugation, cross-flow-filtration and flotation showed, that flotation is a financially and energetically interesting alternative process step for the harvest of microorganisms. In this work separation results with a model microorganism S. cerevisiae are presented. Experiments were conducted batch-wise in a 6L-laboratory dissolved air flotation setup, where bubble generation classically results from expanding air from supersaturated medium. Goal was the optimization of the flotation rate and the energy efficiency of the flotation process by adaptation of operational parameters, such as gas- and recycle flow rate and saturation pressure. Flotation models show proportional dependency between the flotation rate and the bubble size and bubble surface area flow rate. Therefore, the effect of operational parameters, such as saturation pressure, recycle and gas flow rate, on the bubble size and surface area flow rate was analyzed. The positive effect of an increasing bubble surface area was possible with increasing gas flow rate, recycle flow rate and saturation pressure. Decreasing bubble sizes were measured for increasing recycle flow rate and saturation pressure, meanwhile the contrary was the case with an increasing gas flow rate. Evaluation of the flotation rate and flotation energy efficiency showed, increasing the recycle flow rate and the saturation pressure both improved the flotation rate, but had low effect on the energy efficiency. Increasing the gas flow rate improved both flotation rate and energy efficiency. It is the most interesting operational parameter for enhancing the process efficacy.

Imaging method for mass transport measurements in a two-phase bubbly flow of supercritical CO2 and viscous liquids in a static mixer

In this work, a simple optical measurement method for two-phase bubbly flow investigations was developed using backlight imaging and particle image velocimetry techniques. Besides information about bubble sizes, surface area and volumes, the mean dispersed phase mass flow rate and the mean dissolution of the dispersed phase in the continuous phase at the end of a static mixer were accurately estimated. The method was validated with air-in-glycerol and water-in-oil systems, and then proven with CO2-glycerol and CO2-PEG6000 dispersions under high pressure. A 30-element SMX4 plus static mixer with a nominal outer diameter of 4.8 mm was used for all mass transfer investigations. Measurements of the dispersed phase mass flow and the dissolution of the dispersed phase at the end of the mixer are reported with combined uncertainties of 8.1 % and 1.0 wt-%. The first experiments with CO2-glycerol and CO2-PEG6000 prove the applicability of this method for systems under high pressure.

Flotation froth feature analysis using computer vision technology

The possibility of machine vision application in the field of flotation efficiency evaluation was studied. Algorithm for froth image analysis was developed with aim of obtaining bubble’s size distribution. Algorithm consists of two parts: image processing and object detection. Algorithm’s work was verified on the sulfide flotation froth. As result, mathematical correlations for air flow rate, mean bubble diameter and surface area bubble flux were established.

Application of flotation column for Cl‐ and N, N′‐bis (2‐hydroxyethyl) piperazine separation in gas sweetening unit

The degradation of amine solvents leads to increasing costs and deterioration in long term performance. Therefore, the purification of the solvents is needed to guarantee smoother operations. In this research, the flotation setup was investigated by means of laboratory and pilot‐scale experiments in the amine reclamation for chloride and N, N′‐bis (2‐hydroxyethyl) piperazine (BHEP) separation. The maximum removal efficiency recorded was 51% for the largest chloride concentration of 7091 mg/l and 37% for the lowest chloride concentration of 1536 mg/l. The mass transfer coefficient was hence correlated with the hydrodynamic parameters, including chloride reduction rate, bubble surface area, and gas and liquid phase concentration. The average chloride removal efficiency for the monoethanolamine (MEA) was more than 61% due to a better dispersion of pure nitrogen gas bubbles and formation of the tiny bubbles provided in the column. The results indicated that a higher chloride initial concentration corresponded to better performance of the setup. Under the typical column operating conditions, it was concluded that a collection zone H:D of 10:1 was a reasonable compromise. The flotation setup results in BHEP separation, known as amine degradation product showed about 24% average amine recovery.

Separation Between Silicon and Aluminum Powders Contained Within Pulverized Scraped Silicon-Based Waste Solar Cells by Flotation Method

There are few study examples on the separation of metals by floating method. In this study, separation of silicon and aluminum, which are the main components of silicon-based solar cell module, was carried out by floating method in order to purify silicon from waste solar cell module. The selection of surfactant, control of electric charge, wettability of the solid particles, surface tensions, and bubble surface area are important for separation of solids by floating method. Sodium dodecyl sulfate (SDS) can increase the hydrophobicity of aluminum powder due to the difference of surface potentials between silicon and aluminum. SDS behaves as a collector of aluminum as well as a frothing agent to decrease the bubble size. At a SDS concentration of 2 g/L and sample dipping time of 10 min, 80.1 mass% of aluminum was floated and separated, and the sedimentary silicon reached a purity of 90.7% from a mixture of 50 mass% aluminum and 50 mass% silicon. Finally, at a pH value of 7.0, SDS concentration between 1.0 and 2.5 g/L and air flow rate of 2.5 L/min (STP) were suitable experimental conditions to purify silicon from a mixture of silicon and aluminum by flotation separation method.

Single bubble breakup in the flow field induced by a horizontal jet—The numerical simulation

AbstractBubble breakup is a common in the multiphase flow, and the breakup result will influence the performance of the gas–liquid reactor, in which liquid jetting is a typical way in breaking the bubble. In present work, based on the comparison with the experimental results, large eddy simulation and volume of fluid method are coupled to simulate processes of the deformation and breakup of a single bubble in the liquid jet flow. The trajectory of mother bubble, number of daughter bubbles, variation of bubble surface area, and the forces acting on the bubble surface were analyzed. It was found that the shear force at the bubble neck was significantly larger compared with that in the stage of undeformed, and the critical condition for bubble breakup was when the total turbulent pressure on bubble surface was greater than the surface force of bubble. Based on the velocity difference on the upstream and downstream of the bubble, a modified critical Weber number was proposed for a better description of the breakup condition of the single bubble in the liquid jet flow.

Hydrodynamics and simulation of air–water homogeneous bubble column under elevated pressure

AbstractA gas–liquid Eulerian computational fluid dynamics (CFD) model coupled with a population balance equation (PBE) was presented to investigate hydrodynamics of an air–water bubble column (1.8 m in height and 0.1 m in inner diameter) under elevated pressure in terms of pressure drop, gas holdup, mean bubble size, and bubble surface area. The CFD‐PBE model was modified with three pressure correction factors to predict both the total gas holdup and the mean bubble size in the homogeneous bubbly flow regime. The three correction factors were optimized compared to experimental data. Increasing the pressure led to increasing the density, reducing the bubble size, and increasing the gas holdup. The bubble size distribution moved toward a smaller bubble size, as the pressure increased. The modified CFD‐PBE model validated with experimental data and empirical models represented well hydrodynamics of the bubble column at P = 0.1, 1.5, and 3.5 MPa.

Kinetics and Recovery of Xanthate-Copper Compounds by Ion Flotation Techniques

The recovery of copper in aqueous media by ion flotation in a laboratory flotation cell was carried out. Hydrodynamics and gas dispersion parameters were obtained. The results show that the increase of potassium amyl xanthate concentration above the stoichiometric amount considerably affects the efficiency of the separation of copper. In a stage of flotation with recirculation, recoveries of 58% and 66 % were obtained with the flat and the cylindrical spargers respectively. The dispersion parameters and bubble surface area flux (Sb) show a good relation with the apparent flotation rate constant (k), even when the superficial gas velocity is 0.8 cm/s, where we can find the appropriate hydrodynamic conditions to carry out the ion flotation. The system subsequently changes from a homogeneous bubble flux to a turbulent flux. Gas dispersion results show that superficial gas velocity, superficial liquid velocity, dispersion system geometry and the simulated malfunction of spargers considerably affect the recovery of copper in a multi stage system of five flotation cells. The best recoveries were obtained at low superficial gas velocities, achieving efficiencies of 94%, 90% and 95 % with the flat, cylindrical and battery of four spargers respectively.

Use of oscillatory air supply for improving the throughput and carrying capacity of column flotation

Column flotation is widely used for material separation such as coal cleaning, mineral beneficiation, water purification and oil recovery. Flotation columns typically have small diameter-to-height ratios, posing a severe limit on their throughput and carrying capacity. This paper addresses this issue. A fast-switching solenoid valve was added to the air intake line of a 5-cm diameter flotation column equipped with a sparger to change the flow pattern of air supply from steady to rapidly oscillatory. The flotation tests were carried out at semi-continuous mode for a coking coal sample at various throughput levels controlled by adjusting the solids content or volumetric flowrate of the feed slurry. It was found that use of oscillatory air supply to replace steady air supply could significantly improve the throughput without sacrificing product yield and increase the carrying capacity of the column, which was consistent with the enhanced bubble surface area flux in the column.

The effects of froth depth and impeller speed on gas dispersion properties and metallurgical performance of an industrial self-aerated flotation machine

In self-aerated flotation machines, the gas rate depends on operational variables (e.g. froth depth and impeller speed), pulp properties (e.g. solid content and viscosity), and reagent addition (e.g. type and concentration of frother). The gas rate has a strong correlation with the flotation performance by influencing the gas dispersion properties and froth retention time. A factorial experimental design was used to study how the gas dispersion properties, the froth retention time, and the flotation performance respond to changes in froth depth and impeller speed (as the most common operational variables). An in-depth understanding of the effects of impeller speed and froth depth on the gas dispersion properties, especially the bubble surface area flux and froth retention time, is necessary to improve operating strategies for self-aerated flotation machines. All experiments were carried out in a 50 m(3) self-aerated flotation cell in an iron ore processing plant. The results showed that the froth depth affected the metallurgical performance mostly via changing the froth retention time. The impeller speed had two important impacts on the metallurgical performance via varying both the froth retention time and the bubble surface area flux in the froth and pulp zones, respectively. The interaction effects of the froth depth and impeller speed were also established. This allowed us to develop a strategy for operating self-aerated flotation machines based on varying the froth depth and impeller speed with regard to the cell duty.