转盘萃取塔中连续相轴向混合的研究

根据塔内流体运动规律,分别研究了转盘萃取塔单相流和两相逆流时连续相轴向混合的机理.采用光导纤维测定脉冲示踪的浓度响应,从而得到单相流轴向混合Peclet数和两相逆流时分散相对连续相轴向混合的影响(f_w-△~W)的数学表达式.这些表达式对轴向混合的计算,能从高转盘转速扩展到低转速,并能适用于较广的流速范围.为了分析连续相的轴向混合,对分散相滞留量及分散相液滴直径也作了初步研究,并得出了关联式.     

Application of Ferromagnetic Particles to Emulsion Liquid Membranes

Abstract

A study has been undertaken to develop a novel operation mode of emulsion liquid membrane by using ferromagnetic particles. Zinc extraction from aqueous solution with both magnetic oil and water-in-oil (W/O) emulsion drops containing D2EHPA was examined in a spray column under magnetic fields, including behavior of the drop motion. For the W/O drops, more flexible operation was realized by setting up permanent magnets to separate the dispersed phase from the continuous phase. The magnetic drops exhibited unique motions in rotating and alternating magnetic fields, depending on the field strength. It was found that the W/O drops are held in a strong alternating magnetic field and then form a fluid packed bed, whereby the extraction efficiency was significantly improved especially in a counterflow mode, by effective contact between the phases. This finding suggests the potential of a hybrid operation of a moving-bed and a spray column using magnetic W/O drops.     

Drop mixing in suspension polymerisation

In suspension polymerisation, monomer is suspended as liquid droplets in a continuous water phase by means of strong agitation and the presence of a suspending agent. As the suspension polymerisation proceeds, the viscosity of a monomer-polymer droplet increases with conversion. Hence, the physical behaviour of the droplet changes during the process. When new dispersible material is added to the existing suspension drops, the new material and existing drops can remain segregated for significant amounts of time. The aim of this project was to study the behaviour of drop mixing when new material is added to the existing suspension polymerisation. This study concentrated on the effect of the dispersed phase viscosity on drop mixing. The results show that viscosity affects drop size and that may then affect the rate of coalescence between drops. A critical drop size exists which determines the coalescence efficiency effect. Above the critical drop size, mixing rate increases as the drop viscosity decreases. While below the critical drop size, drop size of the dispersion determines the coalescence rate; as the drop size increases, coalescence rate also increases. The investigation of the effect of suspending agent shows that Tween 20 is more efficient in stabilising and protecting the drops, based on a weight basis, than PVA as the coalescence rate is lower with Tween 20.     

SK静态混合器中液液两相流的标准欧拉模型和拉格朗日模型

利用计算流体动力学（CFD）模拟SK静态混合器中液液两相流动。采用欧拉模型中的代数滑移混合模型（ASM）,预测通过混合元件的压降、速度场和两相的体积分数分布。拉格朗日方法被用来追踪静态混合器中离散相的运动轨迹,用粒子的运动轨迹来分析混合的停留时间。     

Compartment-model for the simulation of the separation performance of stirred liquid–liquid-extraction columns

For detailed simulation and evaluation of stirred extraction columns a CFD based compartment-model was developed. Instead of simulating all effects in a computational expensive PBE-CFD-model, the velocity field calculation of the continuous phase is decoupled from the calculation of the dispersed phase (one-way coupling). In CFD only the continuous phase is simulated and the resulting velocity profile is used in the compartment-model to simulate the drop movement, coalescence, breakage and mass transfer for a representative number of drops (Monte-Carlo Method). This decoupling has a major impact on the calculated fluid-dynamics. Thus, the velocity profile of the CFD results is modified in the model to account for phase interaction. The compartment-model is applied for the simulation of a Kühni extraction column with the system toluene/water/acetone. The simulation results, namely holdup, drop size and concentration profiles over the column height, are in good agreement with experiments for different loads and different stirrer speeds.     

Dynamic behaviour of drops in oil/water/oil dispersions

The dynamic behaviour of drops of oil/water/oil (O/W/O) and water/oil (W/O) in abnormal polymer/water/surfactant systems was investigated. The size of internal oil droplets continuously decreased with time until it reached a steady-state value. Whereas the size of multiple water drops showed a minimum. After the minimum, the size of multiple water drops either reached a steady-state value or continued enlarging until phase inversion occurred. The phase inversion occurred because inclusion of oil droplets into water drops resulted in a continuous increase in effective volume fraction of dispersed phase. The time evolution of the size of multiple drops was described in terms of a balance between (a) drop break-up and escape and (b) drop coalescence and inclusion. The inclusion events retarded the initial decrease in the size of multiple water drops with time and increased the drop size after the minimum. By reducing the surfactant concentration, the ability of the dispersed phase to entrain the continuous phase decreased so that no minimum was achieved for the size of multiple drops with time, similar to conventional systems with simple drops. The size distribution of the multiple water drops initially narrowed and then widened again, whereas the size distribution of internal oil droplets continuously narrowed with time until it reached a constant value. Generally, the size distribution of drops narrowed as the average size of drops decreased. The possible mechanisms for complex drop formation were discussed and drop deformation was suggested as the main cause for inclusion at a low dispersed phase ratio.     

Effect of system properties on the performance of Liquid—Liquid extraction columns—II: Oldshue—Rushton column

Mean drop size, fractional hold-up of dispersed phase and axial mixing characteristics have been determined in a 72 mm diameter mechanically agitated extraction column of Oldshue—Rushton type, using the two liquid—liquid mass transfer systems, toluene—acetone—water and MIBK-acetic acid—water. As for normal conditions of packed column operation described in Part I, solute presence and the direction of mass transfer has a significant effect on mean drop size, fractional hold-up and to a lesser extent, axial mixing in the dispersed phase. Probably the most dramatic effect however is the manner in which solute transfer affects dispersed phase behaviour. Highly coalescing conditions with transfer from the dispersed to the continuous phase can make the column practically unoperable. As for the packed column, axial mixing in the continuous phase is unaffected except in so far as solute presence and direction of mass transfer affect the hold-up of dispersed phase.     

Extraction of rare earth metals with a multistage mixer-settler extraction column

Extraction behavior of rare earth metals within a mixer-settler extraction column has been analyzed with the stage efficiency calculated from mass transfer coefficients and interfacial area. The mass transfer coefficient within the dispersed drops is determined from a rigid sphere model by taking into account the residence time distribution of drops, and the coefficient around the drops is calculated by Ranz-Marshall's correlation with the terminal settling velocity of a rigid sphere. The interfacial area of dispersed drops is calculated by the use of correlations for the drop diameter and the holdup of dispersed phase in the mixer-settler extraction column. The calculated results for the separation of samarium and gadolinium with a five-stage mixer-settler extraction column are compared with the experimental results at various agitation speeds and flow ratios between two phases. The extraction behavior in the multistage column is explained by a model based on the hydrodynamics and the mass transfer within the mixer. Effects of the pH value in aqueous phase, the extractant concentration in organic phase and the number of stages on the extraction behavior in the mixer-settler column are also shown.     

Drop formation mass transfer coefficients in extraction columns

Mass transfer coefficients (MTC) of single liquid drops during drop formation period, in the presence and absence of down flow of the continuous phase, were measured in an extraction column. The effects of formation time, needle size, and flow rates of the continuous and dispersed phase were evaluated experimentally. It was found that the drop size increases with increasing formation time and decreasing down flow of the continuous phase. The mass transfer coefficients are the largest in the initial stages of drop formation when convection is the most significant. Both flow rates have a significant effect on the rate of the mass transfer, and the convection caused by the dispersed phase flow is more important than the continuous phase. The mass transfer coefficient and the degree of extraction increase with increasing down flow rate of the continuous phase.     

Identical Feed Drops in a Flow Vessel May not Always Be Desirable

In this paper, the effect of feed size and daughter drop size distributions on the steady‐state drop size distribution in a continuous flow vessel is discussed. For identical sizes of feed drops, a new criterion has been proposed to ensure the complete breakage of the feed drops giving rise to smooth continuous drop size distributions. This has been predicted on the basis of two competing time scales, namely, breakage and residence times.     

THE INFLUENCE OF SPRAYING ANGLE ON AERODYNAMIC CHARACTERISTICS OF FGD SPRAY TOWERS

A model for aerodynamic characteristics predictions of flue gas desulfurization scrubber was developed. Droplets motion was considered as two-dimensional and initial droplets velocity and spraying angle were assumed as parameters. The presented model is able to predict pressure drop caused by the presence of spray, local dispersed phase concentration and droplets residence time for co- or counter-current apparatus. The results obtained for constant initial, vertical component of droplets velocity were compared to those evaluated for constant initial drops velocity (module). A range of applicability of one-dimensional model developed only for vertical drops motion is given.     

Electrostatic effects on inertial particle transport in bifurcated tubes

Most aerosols found naturally in the ambient environment or those dispersed from artificial devices such as dry powder inhalers, are electrically charged. It is known that a strong electrostatic charge on aerosols can result in transport behavior dramatically different from that of uncharged aerosols, even in the absence of an external electric field. In the present work, we study pneumatic transport of corona‐charged particles in bifurcated tubes. This is accomplished by tracking the motion of discrete particles numerically under the influence of drag, gravitational, and electrostatic forces. The model aerosol is fly ash powder, whose size and charge distributions have been determined experimentally. The electrical mobility of the charged particle cloud is modeled through coulombic interactions between discrete point charges. For the case of polydispersed particles electrically charged across a distribution, the deposition efficiency was found to be greater than what is indicated by the mean charge and size. In particular, use of negatively charged fly ash powder of mean size of 2 μm and mean charge of ?1.5 C/kg led to significant increase in deposition efficiency (～29%) compared with uncharged fly ash powder of the same size distribution (～8%). Analysis of particle residence times suggests significant interaction between electrical and drag forces. These findings could have implications for pneumatic powder conveying or pulmonary drug delivery applications. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Numerical and Experimental Performance Evaluation of the 3-Stage FROSTY Supercooled Cloud Collector

An evaluation of the collection characteristics of a new multistage cascade inertial impactor designed for size-resolved cloud drop collection has been performed. The FROSTY supercooled cloud collector is intended for the collection of supercooled cloud drops in a winter environment in three independent size fractions with stage 50% cut diameters of 15 θ m, 10 θ m, and 4 θ m. Two approaches were selected for the evaluation of the collector. Numerical simulations provided a visualization of the airflow patterns and drop trajectories through the collector while experimental laboratory calibration provided a quantitative analysis of true collection performance. For each of these methods, 50% cut diameters, efficiency curves, and wall losses for each stage of the collector were determined. Collection characteristics were determined experimentally by introducing fluorescein-tagged monodisperse drops into the collector and analyzing collection patterns by fluorescence. The experimental measurements at laboratory conditions indicated 50% cut diameters of 19.0, 11.5, and 5.0 θ m for the three stages. Adjusted for operation at collector design conditions, the 50% cut diameters were 17.0, 10.5, and 4.5 θ m. Numerical modeling of the airflow patterns and drop trajectories through the collector was performed with the commercially available Computational Fluid Dynamics (CFD) software package FLUENT. Trajectory simulations based on the average continuous phase (air) velocity field as well as trajectory simulations which included the effects of statistically derived turbulent velocity fluctuations on drop motion were performed. Comparisons between the numerical and experimental work indicated that the inclusion of turbulent fluctuation effects on drop motion provided much better agreement with experimental observations than trajectories based solely on average flow field velocities. However, the use of continuous phase velocity fluctuations also produced unrealistic losses to wall surfaces for small drop sizes. Despite this shortcoming, numerically derived 50% cut diameters and overall collection efficiency curve shapes for drop trajectories including turbulent velocity fluctuations agreed reasonably well with experimental observations.     

Kinetics Measurements in Liquid-Liquid Exchange Applied to Isotopic Separation

Abstract

A method using calibrated drops, freely falling through a stationary continuous phase, is commonly used to study the kinetics of heat or mass transfer. This technique has been applied to uranium isotopic transfer between free ions dissolved in an aqueous phase and the corresponding complexes of an organic phase.

In this report, results are presented for experiments in which an aqueous hydrochloric acid solution of U(IV) of naturally occurring isotope composition and an organophosphorous extractant, diluted in aromatics, containing a U(IV) complex at ²³⁵U atom fraction of 0.5% were used to determine isotopic mixing kinetics. The aqueous phase was fed as calibrated drops through the stationary organic phase at a velocity depending on the drop size and the physical characteristics of the contacted phases. The ²³⁵U concentration of the effluent stream was determined as a function of the drop residence time.

An isotopic transfer coefficient k_A (cm/sec) was calculated. Its variation was investigated as a function of drop diameter between 0.07 to 0.4 cm. The plot of k_A vs diameter can be divided in two regions where k_A is practically constant. In the region of small drops, the activation energy of k_A was measured. The low value, 6 kcal/mole, indicates diffusional, rather than chemical transfer resistance. In the diffusion control region the isotopic exchange kinetics are controlled by the physical characteristics of the phases. A model which was developed from this studyis shown to be useful in optimizing the operation of the process.     

A model for liquid-liquid extraction column performance — The influence of drop size distribution on extraction efficiency

A precise model for predicting liquid-liquid extraction column efficiency based upon assumed hydrodynamic, axial mixing and mass transfer behaviour has been formulated and solved numerically. The complex nature of the dispersed phase can be better described by drop-size-dependent residence time distribution (RTD). Both the variation of axial velocities due to drops of different sizes, i.e. forward mixing, and the axial dispersion for the drops of the same size have been considered in this model. The computed results reveal that the effects of both varying velocities and dispersion of drops on extraction efficiency are appreciable and cannot be neglected, and the efficiency may be overestimated if only a forward mixing model is adopted. The comparison of the experimental values of N_ODP with those predicted shows that the mass transfer data obtained in RDC agree well with the values predicted by the present model for the case of solute transfer in c→d direction, and are slightly higher than the predicted ones for the transfer in d→c direction.     

由转盘塔内连续相溶质浓度轴向分布 估算传质系数和轴向混合系数的研究

根据转盘萃取塔内连续相溶质浓度的轴向分布进行了参数估算.在估算中应用液滴尺寸分布,将带轴向混合的柱塞流模型应用于塔内连续相,将前混模型应用于分散相.参数估算结果表明:应用d_(32)所获得的连续相轴向混合系数E_c和传质系数k_c的估算值比应用液滴尺寸分布所得的E_c、k_c的估算值偏高;如果忽略液滴生成过程传质的影响,k_c的估算值略有增加,而E_c的估算值则明显偏高.     

A model for two-phase turbulent mixing in a jet bubble column

Mixing behavior of the two phase air-water turbulent flow in a jet bubble column is examined. The time evolution of the mixing behavior of a liquid tracer in a turbulent air-water flow within a jet bubble column is predicted using a model based on the fundamental governing equations of fluid motion. The predictions of the model are compared with experimental measurements. Measured residence time distributions (RTD) of the liquid tracer within the cone agree well with the predicted values given by the model. For the range of parameters considered in the study, lack of radial mixing and large axial mixing are evident within the cone of the jet bubble column. Use of fundamental mathematical models for the study of hydrodynamics in a two-phase conventional bubble column has been reported earlier (Torvik, 1990; Jakobsen et al., 1993). The present paper extends the use of such models to predict the mixing characteristics in a jet bubble column.     

Neue Erkenntnisse zum Mischverhalten von Submersreaktoren

Mixing behaviour of submersed reactors. New improved measuring techniques lead to new insights into the local mixing behaviour of submerse reactors. As exemplified by airlift tower loop reactors, it is shown that it is possible to obtain more information from gas residence time distributions if the signal-to-noise ratio of the measurement can be improved significantly. Additional information is obtained, e.g., on that part of the gas recirculated around the loop or the circulation time of the gas phase. The recirculated gas significantly influences the gas backmixing in such reactors. A more thorough investigation of the gas phase motion requires locally resolved data. For the properties of the gas phase, local measuring techniques are available, which allow for measurements of the mean bubble velocity profile even during production runs in large aerated stirred tank reactors. The results show that the gas backmixing is acutely dependent on the viscosity of the continuous liquid phase. Complementary measurements on the properties of the continuous liquid phase can be investigated by means of the heat-pulse-technique. This also is applicable in real media, e.g., during biotechnological cultivation runs. Besides the measurement of the mean liquid velocity, one can, furthermore, obtain some information on the locally dominating mixing mechanism. One significant result of such investigations is that in the airlift reactors investigated the bubble-wake mixing mechanism dominates, whereas the isotropic turbulence in terms of the statistical turbulence theory plays a secondary role. This even holds at very high energy inputs.     

Process intensification of gas–liquid downflow and upflow packed beds by a new low‐shear rotating reactor concept

In the present work, a new low‐shear rotating reactor concept was introduced for process intensification of heterogeneous catalytic reactions in cocurrent gas–liquid downflow and upflow packed‐bed reactors. To properly assess potential advantages of this new reactor concept, exhaustive hydrodynamic experiments were carried out using embedded low‐intrusive wire mesh sensors. The effect of the rotational velocity on liquid flow patterns in the bed cross‐section, liquid saturation, pressure drop, and regime transition was investigated. Furthermore, liquid residence time and Péclet number estimated by a stimulus‐response technique and a macro‐mixing model were presented and discussed with respect to the prevailing flow patterns. The results revealed that the column rotation induces different flow patterns in the cross‐section of the packed bed operating in a concurrent downflow or upflow mode. Moreover, the new reactor concept exhibits a more flexible adjustment of pressure drop, liquid saturation, liquid residence time, and back‐mixing at constant flow rates. © 2016 American Institute of Chemical Engineers AIChE J, 63: 283–294, 2017     

The effect of electric field on mass transfer from drops dispersed in a viscous liquid

Mass transfer of benzoic acid from drops dispersed into a continuous phase of mineral oil with high viscosity has been investigated both with and without an imposed non-uniform d.c. electric field. Total mass transfer efficiency was significantly enhanced in the presence of the high voltage electric field. The results indicate that the application of the electric field to the drop formation process does not change the fundamental mass transfer mechanisms and the mass transfer during drop free fall can also be described by existing mass transfer models. The results also suggest that the high viscosity of the continuous phase inhibits the drops oscillation as well as circulation when the drop sizes become smaller under the applied high voltage electric field. Therefore the significant enhancement of mass transfer efficiency in the present work is mainly due to the increased specific interfacial area.