Effect of aqueous phase pH on liquid–liquid extraction with impinging-jets contacting technique

The influence of aqueous phase pH on the rate of liquid–liquid extraction was investigated using a two impinging-jets contacting device with a high velocity of jet flows. The recommended chemical system of toluene–acetone–water was employed. Applying pH values from its natural value of 5.6–8, a range in which most industrial waters are lain, for the jets colliding force within 70.3–214.6 mN, leads a reduction in extraction efficiency and overall volumetric mass transfer coefficient up to about 18.9% and 35.2% respectively. A significant high variation is observed when the aqueous phase pH exceeds the water neutral value toward alkali conditions. These variations can be attributed to the adsorption of hydroxyl ions and lowering interfacial tension. A comparison between the results in this work and those for drop dispersion extraction indicates a high sensitivity in the impinging technique. As expected, increasing jets force improves the performance of the contacting device; however, simultaneously, the retarding effect of pH would be intensified. The variation of interfacial tension with pH was obtained and with the aid of dimensionless numbers, an empirical correlation was developed for the prediction of overall volumetric mass transfer coefficient.     

Mass transfer at the confining wall of helically coiled circular tubes with gas–liquid flow and fluidized beds

Experiments were conducted to investigate the effect of various dynamic and geometric parameters on mass transfer coefficients in two-phase helically coiled flow systems. Computation of mass transfer coefficients was facilitated by the measurement of limiting current at the electrodes fixed flush with the inner surface of the tube wall. Two flow systems were chosen: a two-phase liquid solid fluidized bed and a two-phase gas–liquid up flow. An equimolar potassium ferrocyanide and potassium ferricyanide solution in the presence of sodium hydroxide was used as the liquid phase. In the fluidized bed, glass spheres and sand of different sizes were employed as fluidizing solids. In two-phase flow system nitrogen was employed as inert gas. The pressure drop in the presence of fluidizing solids in helical coils was found to increase with increase in the pitch of the coil and was maximum for straight tube. The mass transfer coefficients were found to increase with increase in liquid velocity. The mass transfer coefficients in case of gas–liquid flow were found to be independent of liquid velocity and the pitch of the coil, and were largely influenced by gas velocity only. The data were correlated using j_D factor, Helical number, Froude number and Stanton number.     

Mixing times in single and multi-orifice-impinging transverse (MOIT) jet mixers with crossflow

We study the macromixing behavior of single and multi-orifice-impinging transverse (MOIT) jet mixers with crossflow, in particular, the overall mixing time and the back-splash mixing time of the injected flow with the crossflow, using the PLIF technique. It is found that for a given mixer configuration, there is a critical jet-tocrossflow velocity ratio r_c at which the back-splash begins to occur. Further increase in the velocity ratio r leads to sharp increase in the back-splash mixing time, which can offset the intensification of the downstream mixing. The dimensionless overall mixing time decreases as r increases to reach either a plateau or a local minimum, and the corresponding r value represents the optimal velocity ratio r_opt for the macromixing. The momentumratio of the two liquid streams is a key factor determining r_c and r_opt. For a larger scale mixer, a higher momentum ratio is required to achieve the optimal macromixing with the minimum dimensionless overall mixing time.     

低速横流作用下液体射流初次破碎实验

基于专门搭建的射流破碎雾化实验平台,利用高速摄像可视化研究低速横流作用下不同气液量纲为1参数对液体射流初次破碎模式特征和射流穿透轨迹特征的影响规律。实验结果表明,低速横流作用下液体射流破碎存在柱状破碎和袋式破碎两种模式,其中柱状破碎又可以分为鼓包破碎和拱形破碎。从实验得到的液气动量通量比q和液体韦伯数We_j射流破碎模式图可以看出,液气动量通量比q和液体韦伯数We_j共同决定低速横流条件下射流破碎模式,不同破碎模式之间存在明显的过渡边界。结合液气动量通量比q、液体韦伯数We_j、液体雷诺数Re_j等量纲为1参数,拟合得到了射流穿透轨迹曲线对数形式公式,该公式能够很好地预测低速横流作用下液体射流穿透轨迹,其中液气动量通量比q是影响射流穿透轨迹的主要量纲为1参数。     

Numerical Simulation of a Two-Phase Gas-Particle Jet in a Crossflow

A computational model using Lagrangian approach has been proposed to analyze momentum and heat transfers of a gas-particle jet in a crossflow. The effect of the free stream velocity gradient on the two-phase crossjet trajectories and the heat transfer mechanism was investigated in this study. Estimate of average temperature of a particle-laden gas jet was obtained by accounting for thermal energy losses of the gas jet flow due to forced convection and to entrainment of free stream fluid into the jet and for thermal energy transferred from the particles to the gas jet. According to the computational results of the heated two-phase temperature of a gas-particle jet in a crossflow. crossjet, the mean temperature of the carrier gas phase near the jet exit is dependent upon the forced convection and entrainment of the free stream, while far downstream, it is mainly affected by the quantity of thermal energy transferred from the solid particles to the carrier gas phase. When the ratio of the gas jet momentum flux to the momentum flux of the cross free-stream at the jet exit and the free stream conditions are constant, the trajectories of the particle-laden gas and particle phases and the normalized mean temperature difference between both phases are not significantly affected by the change of injection gas     

Measurements and modeling of heat generation in a trickling biofilter for biodegradation of a low concentration volatile organic compound (VOC)

The experimental and theoretical heat generation behavior of a trickling biofilter treating toluene is discussed. The experimental results show that the temperature of the packed bed has a significant effect on the purification performance of the trickling biofilter and that an optimal operation temperature exists between 30 and 40 °C. During the gas–liquid co-current flow, the temperature in the packed bed gradually rises along the direction of the gas and liquid flow due to the exothermic biodegradation of toluene. The temperature rise between the inlet and outlet of the trickling biofilter increases with an increase in the gas flow rate and inlet toluene concentration. In addition, a larger liquid flow rate leads to a smaller temperature rise. The heat generation process occurring in the trickling biofilter is modeled by representing the packed bed as an equivalent set of parallel capillary tubes covered by the biofilm. The temperature profile in the packed bed during the liquid–gas co-current flow is analyzed by simultaneously solving the problem of gas–liquid two-phase flow and heat and mass transfer through the liquid film and biofilm. It is shown that the model agrees well with the experimental data, predicting the variations of the temperature rise between the inlet and outlet of trickling biofilter with the increasing gas and liquid flow rates.     

Dynamics of Unsteady-State Evaporation of Binary Mixtures in Closed Systems

The rate of unsteady-state evaporation of a stagnant layer of methanol–water, formic acid–water, ethanol–isopropanol, methanol–ethanol, and methanol–isopropanol binary solutions into an inert gas (helium or argon) is studied in a closed system. The ratio between the molecular weights of the components in a gas–liquid system is shown to have a substantial effect on the process kinetics. For the first time, a synergetic interaction between the components during unsteady-state mass transfer is observed. The experimental data satisfactorily agree with the calculated results.     

动量比对气液射入压载水管路混溶过程的影响

船舶排放的压载水是造成地理性隔离水体间有害生物传播的最主要途径,至今还没有一种环境友好的阻断方法。在压载水输运管路中,利用高级氧化技术可以有效致死水中携带的大量海洋微小生物,是目前实现在船在线治理远洋船舶压载水最可行的方法。但由于压载水排放量大、流速高,其与高级氧化剂溶液的混溶过程直接影响海洋微小生物的致死效果。针对这一问题,利用Eulerian-Eulerian 双流体模型数值模拟了含有羟基自由基的气液垂直射入压载水输运管路的混溶过程。气体体积分数示踪结果显示,在约束横流环境中,冲击射流在上游壁面形成的scarf涡是形成下游反向涡旋对的主要原因,也是冲击射流与横流混合的源动力。同时也发现在下游壁面射流内存在气体集中的问题。     

Liquid mixing intensification by adding swirling flow in the transverse jet mixer

In this study, effect of swirling addition on the liquid mixing behavior of multiorifice-impinging transverse jet mixer has been investigated by planar laser-induced fluorescence as well as large eddy simulation (LES). In the case of swirling addition into the jet flow, there exists an optimized swirling jet angle or optimized jet-to-cross velocity ratio for the fixed mixer configuration. A larger swirling jet angle will make the flow dominated by the swirling, resulting in a slower mixing process. Interaction of swirling crossflow with no-swirling-injected streams, or with swirling-injected streams in the opposite direction is beneficial for the mixing. LES predictions show that many small vortices are produced homogenously due to intensified impingement in the case of opposite swirling directions, leading to a relative fast mixing process in few milliseconds. Whereas the mixing is restrained when the swirling directions of two flows are the same.     

平面激光诱导荧光技术用于快速液-液混合过程温度场测量

利用平面激光诱导荧光技术(Planar Laser Induced Fluorescence,PLIF)研究了毫米尺度流道内,两股不同温度液膜的错流混合过程. 根据激光诱导作用下荧光强度的温度依赖特性,可视化地揭示了液-液错流混合区的二维温度场分布. 采用温度离析度(Intensity of Segregation,IOS)的概念定量描述了液-液混合的发展过程,分析了不同射流动量比对混合过程的影响. 计算了该过程混合区水的总传热系数,与纯湍流作用的总传热系数比较发现,两液膜撞击射流对传热有强化作用,射流动量比是影响其总传热系数的重要因素.     

Quantum study of hydrogen–oxygen–graphite interactions

Density functional calculations are used to study the reactions of hydrogen and oxygen atoms on the basal plane of graphite. Oxygen atoms can strongly bond to the graphite surface forming an epoxide-like structure. Hydrogen atoms can react with the adsorbed oxygen and form hydroxyl (OH) radicals. The low-energy OH radicals can be retained on the graphite surface and then they can undergo recombination with hydrogen to form water molecules which leave the surface. Both the formation of hydroxyl radicals and water molecules can occur through Eley–Rideal or Langmuir–Hinshelwood mechanisms. The Eley–Rideal mechanism is kinetically favored. The study on formation of OH radicals was completed with quantum molecular dynamics calculations (Verlet algorithm).     

Modeling of Hydrodynamics and Mass Transfer in Countercurrent Polydisperse Gas–Liquid Flow

A one-dimensional model is suggested for a countercurrent polydisperse gas–liquid flow in a vertical column in which the liquid drops both coagulate and break. A method is developed for calculating the intensity of wet purification of a gas in a scrubber. The calculated volumetric mass transfer coefficient is in satisfactory agreement with observed data.     

Influence of surface texture and acid–base properties on ozone decomposition catalyzed by aluminum (hydroxyl) oxides

The decomposition of aqueous ozone in the presence of three aluminum (hydroxyl) oxides was studied, respectively. It was hypothesized that surface hydroxyl groups and acid–base properties of aluminum (hydroxyl) oxides play an important role in catalyzed ozone decomposition. The variables investigated were oxide dose, aqueous pH, presence of inorganic anions (sulfate and nitrate), the effect of tert-butyl alcohol (TBA) and surface hydroxyl groups density of the three aluminum (hydroxyl) oxides. All three aluminum (hydroxyl) oxides tested, i.e. γ-AlOOH (HAO), γ-Al₂O₃ (RAO) and α-Al₂O₃ (AAO), enhanced the rate of ozone decomposition. The net surface charge of the aluminum (hydroxyl) oxides favored in catalyzed ozone decomposition. The greatest effect on catalyzed ozone decomposition was observed when the solution pH was close to the point of zero charge of the aluminum (hydroxyl) oxide. Sulfate and nitrate were substituted for the surface hydroxyl groups of the aluminum (hydroxyl) oxides, which then complexed with Al³⁺ in a ligand exchange reaction. Therefore, inorganic anions may be able to inhibit catalyzed ozone decomposition. It was confirmed that surface hydroxyl groups were important for ozone decomposition with aluminum (hydroxyl) oxides as catalysts. TBA inhibited ozone decomposition in the presence of HAO, RAO and AAO. It was also tested whether aluminum (hydroxyl) oxides catalyzed ozone-transformed hydroxyl radicals. The relationship between surface hydroxyl groups and the ratio of hydroxyl radical concentration to ozone concentration (R_ct) was investigated quantitatively. Higher density of surface hydroxyl groups of the aluminum oxide tested was favorable for the decay of ozone into hydroxyl radicals.     

Electrochemical degradation of anionic surfactants

This study was performed to investigate the electrochemical oxidation of anionic surfactants. In particular, a synthetic solution of sodium dodecyl benzene sulfonate and a real car wash wastewater were treated by galvanostatic electrolysis using a Ti–Ru–Sn ternary oxide and a boron-doped diamond (BDD) anode. Measurements of the Chemical Oxygen Demand (COD) and the concentration of the anionic surfactants were used to follow the oxidation. Using the Ti–Ru–Sn ternary oxide anode, the complete removal of COD and sodium dodecyl benzene sulfonate was obtained only in the presence of chloride ions that act as inorganic mediators. The oxidation rate was almost independent of current density and electrolyte flow rate. In the case of BDD the mineralisation of the sodium dodecyl benzene sulfonate was achieved in all experimental conditions due to reaction with hydroxyl radicals electrogenerated on the diamond surface during electrolysis. The COD removal rate increased with increase in electrolyte flow rate, indicating that the oxidation was mass-transfer controlled. Comparison of the results of the two electrodes showed that chlorine mediated oxidation at the Ti–Ru–Sn ternary oxide anode allowed a faster COD removal of both the synthetic solution and real car wash wastewater.     

Turbulent gas jets and diesel-like sprays in a crossflow: A study on axis deflection and air entrainment

The interaction between a turbulent gas jet/diesel spray and a crossflow has been analysed. This phenomenon is a simplification of a more complex one that takes place in the combustion chamber of small direct injection diesel engines, and its study will help to better understand this more complex case. The two main aspects analysed here are axis deflection and air entrainment. It was found that both aspects are related to each other, and that the air/jet (or air/spray) momentum flux ratio is very relevant in the phenomenon. Scaling laws for the axis deflection of a jet/spray were obtained, and an original method to obtain fuel concentration along the axis of a jet/spray in a crossflow has been established. Gas jets and diesel sprays are found to be very similar even when they interact with a crossflow.     

Transmission of Bubble Detonation through a Layer of an Inert Liquid

The possibility of detonation transmission through a water plug from one column of a chemically active bubbly medium to another is experimentally verified. The critical length of the liquid plug is determined. The experiments are performed in a shock tube with bubbles of a stoichiometric acetylene–oxygen mixture in water. The character of peakpressure decay after detonationwave departure from the bubbly medium to the liquid is established. It is shown that the pressure profile retains similarity as the compression wave propagates over a discrete gas–iquid medium.     

THE DEVELOPMENT OF HIGH INTENSITY GAS-LIQUID JET REACTORS

A novel type of gas-liquid contactor was researched and developed to enhance phase mixing. These high velocity impinging stream reactors are characterised by small reactor volumes supplied with nozzles, which are directed towards each other. The gas and liquid feed streams are jetted through the nozzles into the reactor volume, resulting in a highly turbulent mixture of the phases. Under these enhanced mixing conditions, mass transfer rates are increased dramatically. A mechanism for bubble formation and breakup in gas —liquid jet reactors. operated in the bubble mode, is proposed and a design philosophy of such reactors is also formulated.     

Experimental study of reactive mixing in a mini-scale mixer by laser-induced fluorescence technique

The liquid–liquid mixing process coupled with chemical reactions in a mini-scale jet mixer was visualized by reactive laser-induced fluorescence (reactive-LIF) technique for a deep understanding of the interplay between the mixing and the simultaneous reactions. A novel approach for implementing the reactive-LIF measurements was advanced in this work, where the principle was based on the quenching of the fluorescence signal emitted from the Rhodamine-B dye using the mechanism of Fenton reaction. The purely physical mixing and the reactive mixing processes were investigated extensively by comparing the concentration fields under different operating conditions, i.e. the different momentum ratios between the jet and the bulk flows, and the different Reynolds numbers in the mixing channel of a mini-scale mixer. The results revealed that the transient dynamics in the reactive mixing process cannot be precisely understood based on the time-averaged concentration fields from either the physical or the reactive mixing measurements. The coupled mixing and the reaction processes occurred simultaneously, unless the rapid mixing was achieved by tuning the operating conditions so that the processes can be decoupled into two isolated ones.     

横向射流中心轨迹和扩展宽度

引言 工业中广泛存在着横向射流(jet in crossflow,JICF)问题,如火力发电厂的燃煤锅炉中,为降低SOx和NOx等污染物的排放,目前广泛采用的技术是在燃尽区增加一层或数层横向射流,喷入尿素、天然气、焦炉煤气或携带超细煤粉的三次风等营造还原气氛以实现燃煤锅炉的低污染排放[1-2].     

Momentum correction coefficient for two jet flows mixing in a tee junction

Momentum correction coefficient (K) is an important parameter for the mixing process of two jet flows. In this paper, momentum correction coefficient for two jet flows mixing in a tee junction was investigated with systems of air–air, water–water and air–water in a wide region of mass ratio of flow rate. The pressure drop was analyzed, where the total pressure drop was mainly attributed to momentum exchange and friction. Based on the experimental data, pressure drop due to momentum exchange was obtained by extrapolation methods, and then the momentum correction coefficient was fitted. It turned out that the momentum correction coefficient was mainly dependent on the momentum flux ratio (M) of the two jets and almost independent with the physical properties of jet flows. The relationship between K and M was correlated as the following equation:

K=1+0.256M^0.223