Measurement of sliding velocity and induction time of a single micro‐bubble under an inclined collector surface

In this study, interactions between a gas bubble and a flat solid surface were investigated by determining two dynamic parameters, bubble sliding velocity underneath an inclined solid surface and induction time of the gas bubble attaching to the solid surface in aqueous solutions. A single micro‐bubble was allowed to move vertically toward an inclined solid surface. After reaching its terminal velocity, the bubble approaches the inclined solid surface and slides underneath it. Complete trajectory of the bubble movement was monitored and recorded by a high‐speed CCD video imaging system. Various types of gas bubbles (CO₂, air, H₂, and O₂) and solid surfaces such as bitumen‐coated Teflon, hydrophobized and hydrophilic silica were used in sliding velocity and induction time measurements. The effect of water chemistry (industrial process water and de‐ionized water) and surface heterogeneity on bubble sliding velocity and induction time was investigated. The results showed that the sliding velocity of micro‐bubbles under an inclined solid surface is a strong function of water chemistry, gas type, temperature and hydrophobicity of the solid surface. This study provides relevant information on bubble–solid interactions that would assist in the understanding of bubble–solid attachment under diverse conditions.     

The effect of different types of micro‐bubbles on the performance of the coagulation flotation process for coke waste‐water

BACKGROUND: Comparison experiments were carried out with three kinds of micro‐bubbles on the coagulation flotation process treatment of coke waste‐water under optimum coagulation conditions obtained from zeta potential measurement. RESULTS: Micro‐bubble flotation with ozone showed the best performance. The ozone micro‐bubbles exhibited high absolute zeta potential values, creating repulsion forces thus avoiding the coalescence of bubbles as well as creating attractive interaction between bubbles and particles in the waste‐water. Moreover, the fluorescence intensity of three micro‐bubble samples showed that the ozone micro‐bubble system produced the most hydroxyl radicals, which contributed to the degradation of organic material in the coke waste‐water. Compared with either air micro‐bubble flotation and oxygen micro‐bubble flotation processes, pyridine removal efficiency of the ozone micro‐bubble flotation process was, respectively, 4.5 and 1.7 times higher, and benzene removal efficiency 3.6 and 1.5 times higher. Finally, drainage models and oxygen diffusion models of the three kinds of micro‐bubble water samples verified the long persistence of the three kinds of micro‐bubbles in the water. CONCLUSION: The application of ozone micro‐bubble technology in coagulation processes may provide an efficient and cost‐effective approach to the treatment of waste‐water containing refractory organic compounds. Copyright © 2011 Society of Chemical Industry     

Attachment of solid particles to air bubbles in surfactant-free aqueous solutions

This paper presents a mechanism to explain the attachment of solid particles to air bubbles in surfactant-free aqueous solutions where both solids and air bubbles have the same sign of zeta potential via investigating the mechanical properties of micro air bubbles and the adsorption of hydroxide on air bubble surfaces.Particle-bubble attachment was measured in a Hallimond tube. The results indicate that purified quartz particles attached to air bubbles in surfactant-free deionised water, and the attachment increased with the pH of the aqueous solutions. The mechanical properties of micro air bubbles in aqueous solutions were measured using a novel micromanipulation technique. It was found that the micro air bubbles were pseudo-elastic and spherical in the solutions. The rigidity of the air bubbles decreased with increasing pH of the solutions. When a moving particle with a certain kinetic energy collided with an air bubble in a surfactant-free aqueous solution, the deformation of the air bubble varied with pH of the solution. In an alkaline solution, the micro air bubble was much softer and the deformation was larger than that in an acidic solution. The larger deformation of the softer air bubble resulted in a large contact area between the solid particle and the air bubble, therefore increasing the attachment, and reducing the rebound.The attachment of purified quartz particles to air bubbles in surfactant-free aqueous solutions was possibly due to hydrogen bond formation. The OH⁻ ions on air bubble surfaces formed hydrogen bonds with silicon and oxygen atoms in ≡Si-O-Si≡ or with the adsorbed OH group on quartz surfaces.     

Effect of Frothers on Bubble Size and Foam Stability in Potash Ore Flotation Systems

The objective of this project was to compare the effect of a selective flotation frother (MIBC) and powerful frothers (DEMPH and DF‐1012) on bubble size and foamability in water and in brine. In water, the bubble size is clearly reduced by flotation frothers which prevent bubbles from coalescing. The present study shows that the bubbles do not coalesce in brine and, therefore, frothers do not affect the size of bubbles in brine. The dynamic foamabality index measured in brine is much lower than that in water for weak frothers (e.g. MIBC); for both tested strong frothers the foamability measurements in brine reveal formation of meta‐stable foams.     

电极上气泡分离行为及其强化技术研究进展

电解水作为大规模生产氢气的途径,增强电解水效率对于氢能源的生产具有十分重要的意义。而如何提高电解水工艺的电解效率是一个被广泛关注的问题。在电解过程中,电极两端产生的气体有三种去向：逸出电解槽、溶解于电解质中、附着在电极上。但在电解过程中,附着在电极上的气泡会严重影响电极与电解质之间的接触面积,直接降低了电解效率。降低气泡在电极上的停留时间能够有效增加电解质与电极的接触时间,提高产氢效率。本工作主要综述了近年来促进电解过程中极板上氢氧气泡从电极分离行为的研究,分别从极板属性、电流、溶液浓度和外加物理场这几个方面对气泡成核、生长、聚结和分离行为进行了具体的归纳总结,讨论了各种强化气泡分离方法的特点,并展望了未来的发展方向和路线,为未来的电解气泡脱离技术的研究提供参考。     

Experimental investigation of interfacial mass transfer mechanisms for a confined high‐reynolds‐number bubble rising in a thin gap

Interfacial mass transfer is known to be enhanced for confined bubbles due to the efficiency of the transfer in the thin liquid films between them and the wall. In the present experimental investigation, the mechanisms of gas–liquid mass transfer are studied for isolated bubbles rising at high Reynolds number in a thin gap. A planar laser induced fluorescence (PLIF) technique is applied with a dye the fluorescence of which is quenched by dissolved oxygen. The aim is to measure the interfacial mass fluxes for pure oxygen bubbles of various shapes and paths rising in water at rest. In the wakes of the bubbles, patterns due to the presence of dissolved oxygen are observed on PLIF images. They reveal the contrasted contributions to mass transfer of two different regions of the interface. The flow around a bubble consists of both two thin liquid films between the bubble and the walls of the cell and an external high‐Reynolds‐number in‐plane flow surrounding the bubble. Mass transfer mechanisms associated to both regions are discussed. Measurement of the concentration of dissolved oxygen is a difficult task due to the nonlinear relation between the fluorescence intensity and the concentration in the gap. It is however possible to accurately measure the global mass flux transferred through the bubble interface. It is determined from the fluorescence intensity recorded in the wakes when the oxygen distribution has been made homogeneous through the gap by diffusion. Assuming a reasonable distribution of oxygen concentration through the gap at short time also allows a measurement of the mass fluxes due to the liquid films. A discussion of the results points out the specific physics of mass transfer for bubbles confined between two plates as compared to bubbles free to move in unconfined flows. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2394–2408, 2017     

Deep ocean bubble transport model coupled with multiple hydrate behavior characteristics

Submarine gas seepage is a widely observed process. In this study, a unified mechanistic model of bubble transport both inside and outside the gas hydrate stability zone (GHSZ) was developed. Multiple hydrate-related behaviors were considered, including hydrate nucleation, hydrate film lateral spread, hydrate shell dynamic growth, hydrate dissolution and decomposition, and collapse and fracture deformation of hydrate-coated bubbles. Using the proposed model, a series of simulation studies about bubble dissolution and rising fate were conducted. The results indicate that the formation of solid hydrates in the deep-sea environment can provide a fairly effective barrier for the dissolution and shrinkage of bubbles, and the deeper the initial release water depth, the smaller the critical size of the bubble required for arriving at the water surface. Furthermore, the majority of gases released from the seafloor would be absorbed by the shallow oceanic layer, but larger bubbles could still pass through the water column to the atmosphere.     

Bubble formation and dynamics in a quiescent high‐density liquid

Gas bubble formation from a submerged orifice under constant‐flow conditions in a quiescent high‐density liquid metal, lead–bismuth eutectic (LBE), at high Reynolds numbers was investigated numerically. The numerical simulation was carried out using a coupled level‐set and volume‐of‐fluid method governed by axisymmetric Navier–Stokes equations. The ratio of liquid density to gas density for the system of interest was about 15,261. The bubble formation regimes varied from quasi‐static to inertia‐dominated and the different bubbling regimes such as period‐1 and period‐2 with pairing and coalescence were described. The volume of the detached bubble was evaluated for various Weber numbers, We, at a given Bond number, Bo, with Reynolds number . It was found that at high values of the Weber number, the computed detached bubble volumes approached a 3/5 power law. The different bubbling regimes were identified quantitatively from the time evolution of the growing bubble volume at the orifice. It was shown that the growing volume of two consecutive bubbles in the period‐2 bubbling regime was not the same whereas it was the same for the period‐1 bubbling regime. The influence of grid resolution on the transition from period‐1 to period‐2 with pairing and coalescence bubbling regimes was investigated. It was observed that the transition is extremely sensitive to the grid size. The transition of period‐1 and period‐2 with pairing and coalescence is shown on a Weber–Bond numbers map. The critical value of Weber number signalling the transition from period‐1 to period‐2 with pairing and coalescence decreases with Bond number as , which is shown to be consistent with the scaling arguments. Furthermore, comparisons of the dynamics of bubble formation and bubble coalescence in LBE and water systems are discussed. It was found that in a high Reynolds number bubble formation regime, a difference exists in the transition from period‐1 to period‐2 with pairing and coalescence between the bubbles formed in water and the bubbles formed in LBE. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3996–4012, 2015     

Enhanced gas migration through permeable bubble networks within consolidated soft sediments

Many consolidated sediments experience in situ gas generation from methanogenesis, corrosion, or radiolysis reactions and can retain bubbles for long periods. Particular interest is motivated by the retention and acute release of flammable hydrogen from nuclear legacy waste sludge. X‐ray computed tomography was employed to observe 0.07–10 mm bubble populations within 30–1112 Pa yield strength Mg(OH)₂ sediments. High rates of partial coalescence were observed among sub‐millimeter microvoids, forming extensive bubble networks which spanned the 32 mm field of view. Lattice Boltzmann and Monte Carlo modeling demonstrated these networks to be highly pervious to gas, with effective diffusivities for hydrogen of 3.7–12.5 × 10^?5 m² s^?1. Continuous vessel‐spanning bubble networks, dynamic connectivity between ganglia of coalesced bubbles, Haines jumps, and composite diffusion through the gas and aqueous phase can account for enhanced gas migration over length‐scales of several meters, thus enabling chronic gas release from low‐intermediate strength sediments ( kPa) too strong for buoyant bubble ebullition and too weak for vertical channel formation. © 2018 The Authors. AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers. AIChE J, 64: 4131–4147, 2018     

Role of Frothers in Bubble Generation and Coalescence in a Mechanical Flotation Cell

Two frothers covering a very broad range from weak and selective (DF‐200) to powerful (DF‐1012) flotation performance were chosen to test the effect of frothers on bubble generation and bubble coalescence in a laboratory scale flotation cell. In two‐phase, gas‐liquid systems, the experiments showed that the frothers affect both the bubble breaking process and the coalescence of bubbles. While the DF‐200 frother, characterized by much larger critical coalescence concentration (CCC) values than DF‐1012, has the ability to produce finer bubbles at concentrations exceeding the CCC value, the bubbles generated in the DF‐1012 solutions at concentrations exceeding CCC are much larger.     

大孔径高气速单孔气泡形成

在内径为190mm的鼓泡塔内,研究了空气-去离子水系统在大孔径高气速条件下的单孔气泡形成。考察了五个不同的孔径,分别为4、8、10、15及21mm,孔口气速范围为0.8~154.8m·s^-1。以CCD摄像记录气泡的形状及尺寸,根据气泡长径比的变化,得到气泡初始形态转变时的临界孔口气速：当孔口气速低于20m·s^-1时,孔口气泡近似于球形,长径比小于1.1;当孔口气速大于50m·s^-1时,气泡呈现椭球形,长径比大于1.5。并对气泡尺寸与孔径及孔口气速进行关联,所得关联式对孔径大于3mm、孔口气速在10~80m·s^-1范围内所形成的气泡尺寸预测效果较好。     

Effect of polymer additives on hydrodynamics and oxygen transfer in a bubble column bioreactor

The influence of polymer additives (polyethylene oxide and polyacrylamide) on the hydrodynamics and oxygen transfer in a bubble column bioreactor was examined. The addition of small amounts of these polymers has been known to cause significant drag reduction in turbulent flow circumstances. The gas hold-up was slightly decreased and the liquid-phase mixing was somewhat enhanced due to the addition of the polymers. The addition of polymer additives brought about a reduction of the volumetric oxygen transfer coefficient by about 40%. In dilute polymer solutions, large bubbles formed by bubble coalescence moved with high rise velocities in the presence of many small bubbles and the bubble size distributions were less uniform compared with those in water. The complicated changes in bubble hydrodynamic characteristics were examined to give possible explanations for oxygen transfer reduction.     

Bubble coverage and bubble resistance using cells with horizontal electrode

The resistivity ratio due to gas bubbles underneath horizontal anodes in electrolytic cells was measured and compared with that in an air–water model of identical geometry. It was found that at equal current density or equivalent gas generation rate, the difference in the bubble resistivity ratio between these two situations can be up to 20%. Consequently, the results obtained from an air–water model cannot be directly applied to an electrolytic cell. Results also showed that within the range of experimental conditions covered, the bubble resistivity ratios obtained for a given anode–cathode distance in both cells are linearly related to the bubble coverage ratio, based on bubbles greater than a certain size as limited by the measurement method.     

Breakup dynamics of slender bubbles in non‐newtonian fluids in microfluidic flow‐focusing devices

This study aims to investigate the breakup of slender bubbles in non‐Newtonian fluids in microfluidic flow‐focusing devices using a high‐speed camera and a microparticle image velocimetry (micro‐PIV) system. Experiments were conducted in 400‐ and 600‐μm square microchannels. The variation of the minimum width of gaseous thread with the remaining time before pinch‐off could be scaled as a power‐law relationship with an exponent less than 1/3, obtained for the pinch‐off of bubbles in Newtonian fluids. The velocity field and spatial viscosity distribution in the liquid phase around the gaseous thread were determined by micro‐PIV to understand the bubble breakup mechanism. A scaling law was proposed to describe the size of bubbles generated in these non‐Newtonian fluids at microscale. The results revealed that the rheological properties of the continuous phase affect significantly the bubble breakup in such microdevices. © 2012 American Institute of Chemical Engineers AIChE J,, 2012     

Studies on Liquid—Gas and Three‐Phase Fluidized Beds with Pulsating Air Flows

The effects of air‐flow pulsation and water and air flowrates on the hydrodynamics of liquid—gas and three‐phase fluidized beds containing 3‐mm glass beads have been studied in a 90‐mm i.d. column. Under steady‐flow conditions, both types of bed contained a relatively large number of small bubbles. With a pulsing air flow, however, a smaller number of much larger bubbles or slugs were formed. This was attributed to different mechanisms of bubble formation at the distributor. Variations in phase holdup were explained in terms of the effects of the operating parameters on the bubble characteristics.     

Bubble Motion Pattern and Rise Velocity in Two‐dimensional Horizontal and Vertical Vibro‐fluidized Beds

The motion pattern of a bubble was examined and the bubble rise velocity was measured in horizontally and vertically sinusoidal vibro‐fluidized beds. Experimental results showed that the motion pattern of a bubble depends on the vibration direction. Compared with the case of no vibration, it seems that the flow pattern of bubbles is not affected significantly by vertical vibrations, while bubbles rise in the form of a tower for horizontal vibrations. For vertical vibrations, all the local average bubble rise velocities were larger than those in the case of no vibration, but they were hardly influenced by horizontal vibrations at the lower bed height and were larger than those in the case of no vibration at the higher bed height.     

A unified theoretical model for breakup of bubbles and droplets in turbulent flows

Pressure has a significant effect on bubble breakup, and bubbles and droplets have very different breakup behaviors. This work aimed to propose a unified breakup model for both bubbles and droplets including the effect of pressure. A mechanism analysis was made on the internal flow through the bubble/droplet neck in the breakup process, and a mathematical model was obtained based on the Young–Laplace and Bernoulli equations. The internal flow behavior strongly depended on the pressure or gas density, and based on this mechanism, a unified breakup model was proposed for both bubbles and droplets. For the first time, this unified breakup model gave good predictions of both the effect of pressure or gas density on the bubble breakup rate and the different daughter size distributions of bubbles and droplets. The effect of the mother bubble/droplet diameter, turbulent energy dissipation rate and surface tension on the breakup rate, and daughter bubble/droplet size distribution was discussed. This bubble breakup model can be further used in a population balance model (PBM) to study the effect of pressure on the bubble size distribution and in a computational fluid dynamics‐population balance model (CFD‐PBM) coupled model to study the hydrodynamic behaviors of a bubble column at elevated pressures. © 2014 American Institute of Chemical Engineers AIChE J, 61: 1391–1403, 2015     

Hydrodynamic feedback on bubble breakup at a T‐junction within an asymmetric loop

Bubble breakup at a microfluidic T‐junction by taking into consideration the hydrodynamic feedback at the downstream channels is presented. Experiments are conducted in square microchannels with 400 μm in width. The splitting ratio of the bubble size in the bifurcations varies nonmonotonically with the flow rate ratio of gas/liquid phases, and it is also affected by the liquid viscosity. A critical size of the mother bubble determines the variation trend of the splitting ratio of bubble size with flow rates of both phases and the liquid viscosity, which is related to the different breakup mechanisms for long and short bubbles at the junction and the different additional resistances induced by long and short bubbles in downstream channels. A theoretical model is proposed to predict the tailoring size of bubbles at the T‐junction by taking into account of the additional resistance in the presence of bubbles in downstream channels. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1920–1929, 2014     

一种新型曝气设备及其气液传质研究

开发了一种叶片开孔曝气的新型搅拌设备,并以清水实验条件为基础,研究了该设备中气泡运动规律,选择传质理论中的溶质渗透模型,从单个气泡的产生到上升至液面这一过程入手,建立传质速率方程,进而分析了容器中气泡整体的分布状况,得出总的理论瞬时氧传质速率方程,用来分析和研究该类设备的气液传质效率,为设计高效的曝气设备提供理论基础。     

Study of Air‐Liquid Flow Patterns in Hydrocyclone Enhanced by Air Bubbles

In order to improve the oil‐water separation efficiency of a hydrocyclone, a new process utilizing air bubbles has been developed to enhance separation performance. Using the two‐component phase Doppler particle analyzer (PDPA) technique, the velocities of two phases, air and liquid, and air bubble diameter were measured in a hydrocyclone. The air‐liquid mixing pump can produce 15 to 60 μm‐diameter air bubbles in water. There is an optimum air‐liquid ratio for oil‐water separation of a hydrocyclone enhanced by air bubbles. An air core occurs in the hydrocyclone when the air‐liquid ratio is more than 1 %. The velocities of air bubbles have a similar flow pattern to the water phase. The axial and tangential velocity differences of the air bubbles at different air‐liquid ratio are greater near the wall and near the core of the hydrocyclone. The measured results show that the size distribution of the air bubbles produced by the air‐liquid mixing pump is beneficial to the process where air bubbles capture oil droplets in the hydrocyclone. These studies are helpful to understand the separation mechanism of a hydrocyclone enhanced by air bubbles.