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.     

Rate of Bitumen Film Transfer from a Quartz Surface to an Air Bubble as Observed by Optical Microscopy

The rate of bitumen transfer from a bitumen‐coated quartz plate to a gas bubble surface in aqueous alkaline solutions was recorded photographically. During bitumen spreading, a bulk layer followed the formation of thin bitumen films (precursor films). The bulk layer spread at the bubble surface with a velocity of about one order of magnitude less than the velocity of the precursor film. The energy of activation for spreading of the bulk layer varied from about 66 to 123 kJ/mol depending on the stage of bitumen spreading but remained constant at about 105 kJ/mol for the precursor film. Results are discussed with respect to fundamental issues associated with flotation recovery of heavy oils.     

Electron Attachment to 5-Fluorouracil: The Role of Hydrogen Fluoride in Dissociation Chemistry

We investigate dissociative electron attachment to 5-fluorouracil (5-FU) employing a crossed electron-molecular beam experiment and quantum chemical calculations. Upon the formation of the 5-FU⁻ anion, 12 different fragmentation products are observed, the most probable dissociation channel being H loss. The parent anion, 5-FU⁻, is not stable on the experimental timescale (~140 µs), most probably due to the low electron affinity of FU; simple HF loss and F⁻ formation are seen only with a rather weak abundance. The initial dynamics upon electron attachment seems to be governed by hydrogen atom pre-dissociation followed by either its full dissociation or roaming in the vicinity of the molecule, recombining eventually into the HF molecule. When the HF molecule is formed, the released energy might be used for various ring cleavage reactions. Our results show that higher yields of the fluorine anion are most probably prevented through both faster dissociation of an H atom and recombination of F⁻ with a proton to form HF. Resonance calculations indicate that F⁻ is formed upon shape as well as core-excited resonances.     

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.     

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.     

Adhesion of Bitumen to a Metal Surface in a Flowing Oil Sands Slurry

Bench‐scale experiments were conducted to study the behaviour of oil sands slurries. While a slurry was being stirred with a standard impeller, the mass of bitumen, M_ad, that adhered to a steel probe dipped into the slurry was measured. M_ad remained small up to a critical adhesion time, τ_ad, and then increased rapidly. τ_ad depended on ore grade, temperature, pH, and clay content. The implication for hydrotransport of oil sands is clear: τ_ad should be greater than the residence time of the slurry to avoid the problem of bitumen coating the pipe wall and the attendant increase in pumping pressure.     

Assessment of Bitumen Re c overy from the Athabasca Oil Sands Using a Laboratory Denver Flotation Cell

A methodology was developed in this study to evaluate the effect of operating parameters on the processability of oil sands using small‐scale laboratory experimental devices. By subtracting bitumen recovered to the froth by entrainment with water, the concept of “true flotation recovery” is proposed to describe bitumen recovery resulting from bitumenbubble attachment. The experimental results indicated that “true flotation recovery” is a more sensitive and meaningful marker than overall bitumen recovery to evaluate the processability of oil sands using small‐scale laboratory test units.     

Bubble size distribution in a flotation column

The bubbles that were generated in a flotation column were measured. The bubble size distributions were obtained both for air-water and air-water-coal systems. The size distribution pattern was fitted to different equations. It was found that the bubble size distribution in both the flotation and cleaning zones follows the Rosin-Rommler equation used to describe the particle size distribution in crushing. This study indicates that bubbles in the cleaning zone are always larger than those of the flotation zone and finer bubbles are generated when a mixture of frothers is used instead of individual frothers.     

模拟变形液滴和气泡运动的改进水平集算法

An improved level set approach for computing the incompressible two-phase flow with significantly deformed free interface in presented.The control volume formulation with the semi-implicit method for pressure-linked equations consistent(SIMPLEC)algorithm incroporated is used to solve the governing equations on a staggered grid.Several improvements concerning the convergence and numerical stability.The motion of a bubble or drop in a liquid with large density ratio,viscosity ratio and surface tension in numerically simulated.The computational results are in good agreement with the reported experimental data.     

由氢、氧直接合成过氧化氢研发新进展

介绍了氢、氧直接合成过氧化氢过程中催化剂、反应介质、反应器(微反应器、膜反应器等)、操作方式等方面近2～3年来的研发新进展。重点介绍了Au-Pd负载催化剂研究应用情况,涉及不同载体、不同Au与Pd质量比等对过氧化氢生成速率、选择性及浓度的影响。还较详细地介绍了无机酸和卤离子在不同条件下对合成反应结果(包括氢转化率、生成过氧化氢选择率及浓度等)的提高所起到的促进作用及其机理。     

Effect of insoluble amine on bubble surfaces on particle–bubble attachment in potash flotation

This study shows that in the potash flotation system, in which long‐chain amine collector appears in the form of colloidal particles, the hydrophobicity of sylvite surfaces critically depends on whether the amine is placed onto the solid surface or onto the surface of a bubble. The transportation of amine collector on the surface of bubbles was found to be beneficial for the bubble/KCl particle attachment.     

Application of Statistical Analysis on the Bubble Surface Area Flux in a Column Flotation Cell

Flotation is a widely used separation process with applications from mineral separation to de-inking of recycled paper, waste water treatment, and solid remediation. In flotation column, bubble surface area flux (S_b) has been reported to describe the gas dispersion properties, and it has a strong correlation with the flotation rate constant. No information is available regarding S_b for coal flotation in column cell. This paper describes the effects of hydrodynamic parameters on S_b by means of a 2³ factorial experimental design in designed flotation column using coal slurry. The results showed that S_b increased with increasing superficial gas velocity and frother concentration, but decreased with increasing solid concentration. The main and interaction effects of operating parameters on S_b were evaluated using Yates’ analysis. The statistical model was developed to predict S_b in column flotation cell using experimental data. This paper also presents the development of the statistical model and the validation using a number of additional data sets. There is a good agreement between experimental results and predicted results from the developed model.     

Mixing Time in a Short Bubble Column

Mixing time measurements have been carried out in a 0.2m I.D. short bubble column (Hc/D ? 5) with different spargers and for different clear liquid height to diameter (H_C/D) ratios. Superficial gas velocity has been varied in the range of 0.01m/s to 0.1m/s. Effect of bulk fluid viscosity on the mixing time has also been studied. The circulation cell model, with two fitted parameters viz. number of circulation cells, S and the inter‐cell exchange velocity, V_e, has been used to predict and explain the variation in mixing time and the flow pattern in the short bubble column for different types of spargers.     

Interaction between Bitumen and Fines in Oil Sands Extraction System: Implication to Bitumen Recovery

Colloidal interactions between bitumen and fines, extracted directly from oil sand ores, were investigated with zeta potential distribution measurement and surface force measurement using an atomic force microscope (AFM). Fines from good processing ores exhibit a negligible attachment to bitumen surfaces, due to hydrophilic nature of the fines. Fines from poor processing ores exhibit a stronger attachment to bitumen surfaces by an attractive hydrophobic force between bitumen and fines, due to hydrophobic nature of the fines and the presence of high concentration divalent cations in the processing water.     

焦化汽柴油加氢装置床层压降大的原因及对策

层压降对加氢装置来说是一个很重要的参数,它直接影响到装置安,稳,长的运行,压降小有利于装置的操作,压降大将直接导致装置停工,本文就反应器压降大而导致装置两次停工进行分析和处理,并采取相应的措施后,装置的床层压降问题基本解决。     

鼓泡塔中气泡群运动的实验与模拟

采用高速摄像法测量了均匀鼓泡流状态下,水以及体积分数分别为20%和40%的甘油-水体系中气泡群的浮升运动,考察了气含率、雷诺数和分布器孔径对气泡尺寸、形状、浮升速率和曳力系数的影响。构建了立方体单元胞模型,并根据雷诺数的不同选取层流和湍流模型,模拟得到气泡的浮升速率和曳力系数与实验值吻合较好。结果表明:随着气含率及液体黏度的提高,气泡群浮升阻力增大,浮升速率减少;随着雷诺数和气泡直径的增加,曳力系数减小,气泡浮升速率增大。单元胞模型能较好地反映气泡群浮升过程中各因素的影响,是处理气泡群运动的有效工具。     

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。     

Ternary Gels of a Polymer Blend and a Recycled Oil: Their Use as Bitumen Modifiers

A blend of random ethylene‐vinyl acetate copolymer (EVA) and triblock styrene‐butadiene‐styrene copolymer (SBS) was dissolved in a recycled engine oil to obtain ternary thermoreversible gels. As the temperature was increased, first a network associated with EVA disappeared, and a second one associated with SBS dominated, maintaining the elastic response of the system. The principal advantage of these ternary systems is that their mechanical properties and thermal stability are better than that of binary gels. These gels, made from waste, can be used as bitumen modifiers to obtain binders of improved properties and good stability, which are useful for road surfacing.

Temperature sweeps of elastic modulus performed at a frequency of 1 Hz.     

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     

Bubble size distribution in a bubble column with vertical tube internals: Experiments and CFD-PBM simulations

Knowledge of bubble size distribution (BSD) is critical for controlling mass transfer and reaction in bubble column reactors. Installation of internals further complicates this issue. The effects of internals on BSD were systematically investigated through experiments and computational fluid dynamics-population balance model simulations. The experiments show a bimodal distribution of the volume-based BSD except at low superficial gas velocity of 0.01 m/s. Addition of 20% internals increases the small-bubbles fraction, making the first BSD peak more evident. Correspondingly, the simulation reveals a prominent decrease of turbulent dissipation rate and turbulent kinetic energy. Moreover, while the unresolved turbulent kinetic energy dominates in the empty columns, the resolved portion becomes the major component in the presence of internals. This suggests that internals may redistribute turbulent kinetic energy in each scale, which provides more insights into the complex flow characteristics in the presence of internals and process intensification.