界面传质中Rayleigh对流的格子Boltzmann模拟和实验验证(英文)

Concentration gradient induced Rayleigh convection can influence effectively interfacial mass transfer processes, but the convection phenomena are known as mesoscopic and complex. In order to investigate this phe-nomenon, a two-equation Lattice Boltzmann Method (LBM) is proposed to simulate the velocity and the concentra-tion distributions of Rayleigh convection generated in the CO2 absorption into ethanol liquid. The simulated results on velocity distributions are experimentally verified by PIV (particle image velocimetry technique) measurements. In order to simplify the analysis, the convection in the simulation as well as in the experiment, the Rayleigh convec-tion was manipulated into a single down flow pattern. The simulated results show that the concentration contours agree qualitatively with the schlieren images in the literature. The experimental and simulated results show that the Rayleigh convection under investigation is dominated by the flow in the downward direction and impels exchange of the liquid between the interfacial vicinity and the liquid bulk promoting the renewal of interfacial liquid, and hence enhances mass transfer. The comparison between the simulated and experimental results demonstrated that the proposed LBM is a promising alternative for simulating mass transfer induced Rayleigh convection.     

MDEA吸收CO2稳态模型的数值求解方法

The shooting method and the difference method are used for numerical simulation of CO2 absorption with aclueous solution of methyldiethanolamine (MDEA). It is demonstrated that these methods axe available for the steady-state model, which may be expressed as a set of differential algebraic equations (DAEs) with two-point boundary values. This method makes it possible not only to obtain the concentration profiles for MDEA system, but also to reveal the effect of CO2 interfacial concentration on the enhancement factor. With this numerical simulation,the mass transfer process with multicomponent diffusion and reactions can be better understood.     

A New Method to Solve Film Model for CO_2 Absorption with Aqueous Solution of AT-Methyldiethanolamine

The shooting method and the difference method are used for numerical simulation of CO2 absorption with aqueous solution of methyldiethanolamine (MDEA). It is demonstrated that these methods are available for the steady-state model, which may be expressed as a set of differential algebraic equations (DAEs) with two-point boundary values. This method makes it possible not only to obtain the concentration profiles for MDEA system, but also to reveal the effect of CO2 interfacial concentration on the enhancement factor. With this numerical simulation, the mass transfer process with multicomponent diffusion and reactions can be better understood.     

Mass transfer characteristics in a rotating packed bed with split packing

The rotating packed bed (RPB) with split packing is a novel gas–liquid contactor, which intensifies the mass transfer processes controlled by gas-side resistance. To assess its efficacy, the mass transfer characteristics with adjacent rings in counter-rotation and co-rotation modes in a split packing RPB were studied experimentally. The physical absorption system NH3–H2O was used for characterizing the gas volumetric mass transfer coeffi-cient (kyae) and the effective interfacial area (ae) was determined by chemical absorption in the CO2–NaOH sys-tem. The variation in kyae and ae with the operating conditions is also investigated. The experimental results indicated that kyae and ae for counter-rotation of the adjacent packing rings in the split packing RPB were higher than those for co-rotation, and both counter-rotation and co-rotation of the split packing RPB were superior over conventional RPBs under the similar operating conditions.     

A Reynolds mass flux model for gas separation process simulation:I. Modeling and validation

Separation process undertaken in packed columns often displays anisotropic turbulent mass diffusion. The aniso-tropic turbulent mass diffusion can be characterized rigorously by using the Reynolds mass flux (RMF) model. With the RMF model, the concentration and temperature as well as the velocity distributions can be simulated numerical y. The modeled Reynolds mass flux equation is adopted to close the turbulent mass transfer equation, while the modeled Reynolds heat flux and Reynolds stress equations are used to close the turbulent heat and mo-mentum transfer equations, so that the Boussinesq postulate and the isotropic assumption are abandoned. To val-idate the presented RMF model, simulation is carried out for CO2 absorption into aqueous NaOH solutions in a packed column (0.1 m id, packed with 12.7 mm Berl saddles up to a height of 6.55 m). The simulated results are compared with the experimental data and satisfactory agreement is found both in concentration and temper-ature distributions. The sequel Part II extends the model application to the simulation of an unsteady state ad-sorption process in a packed column.     

Entransy dissipation analysis of interfacial convection enhancing gas–liquid mass transfer process based on field synergy principle

An exploration of the gas CO2 absorbed into liquid ethanol accompanied with Rayleigh convection is performed by analyzing the mass entransy dissipation; this new statistical quantity is introduced to describe the irreversibility of mass transfer potential capacity. Based on the general advection–diffusion differential equation for an unsteady mass transfer process, the variation of the included angle between the velocity vector and concentration gradient fields is investigated to reveal the underlying mechanism of interfacial convection enhancing mass transfer. Results show some identical characteristics with the qualitative analyses of the synergy effects generated by the concentration and velocity fields after interfacial convection occurring for a boundary condition of fixed surface concentration. And the equivalent mass resistance for convective mass transfer process presents the similar variation with the reciprocal of instantaneous mass transfer coefficient. Accordingly, it is reasonable to be seen that mass transfer dissipation rate could be provided to assess the convection strength and explain fundamentally how Rayleigh convection improves mass transfer performance through establishing a close relationship between the mass transfer capacity and field synergy principle from the view of mass transfer theory.     

Three-dimensional simulation of interfacial convection in CO2-ethanol system by hybrid lattice Boltzmann method with experimental validation☆

By using a hybrid lattice-Boltzmann–finite-difference method (hybrid LBM–FDM method), three-dimensional simulations of solutal interfacial convection were conducted for the process of CO2 absorption in...     

两液层体系传质引发的Marangoni效应的数值模拟

The Marangoni effect induced by mass transfer at the interface between two immiscible liquids displays important influence on laboratory and industrial operation of solvent extraction. A systematic numerical study of the two-dimensional Marangoni effect in a two liquid layer system was conducted. The linear relationship of the inter- facial tension versus the solute concentration was incorporated into a mathematical model accounting for liquid flow and mass transfer in both phases. The typical cases analyzed by Sternling ＆ Scriven （AIChE J., 1959） using the linear instability theory were simulated bv the finite difference method and good agreement between the theory and the numerical simulation was observed. The simulation suggests that the Marangoni convection needs certain time to develop sufficiently in strength and scale to enhance the interphase mass transfer, the Marangoni effect is dynamic and transient, and remains at some stabilized level as long as the mass transfer driving force is kept con- stant. When certain level of shear is imposed at the interface as in most cases of practical significance, the Maran- goni effect is suppressed slightly but progressively as the shear is increased gradually. The present two-dimensional simulation of the Marangoni effect provides some insight into the underlying mechanism and also the basis for further theoretical study of the three-dimensional Marangoni effect in the real world and in chemical engineering applications.     

第三分散相液滴增强气体吸收的一维非稳态非均相传质模型

A model for one-dimensional unsteady heterogeneous mass transfer was developed based on Danckwerts’ surface renewal theory in order to describe the mass transfer enhancement of absorption process for a slightly soluble gas in a gas-liquid-liquid system. The model accounts for the mass transfer resistance within the dispersed phase and the effect of emulsion viscosity on mass transfer. An analytical solution for enhancement factor was obtained by Laplace domain transformation. The absorption rates of carbon dioxide in the dodecane-in-water and castor oil-in-water systems were measured in a thermostatic reactor, and the enhancement factors were calculated at different volume fractions of dispersed phase and stirrer speeds. The model predictions agree well with the experi-mental data.     

MASS TRANSFER IN MEMBRANE ABSORPTIONDESORPTION OF AMMONIA FROM AMMONIA WATER

Hydrophobic membrane can provide fast mass transfer for absorption-desorption of gasesform liquid to absorbent.The removal of ammonia from ammonia water and absorption with dilutesulphuric acid was studied in a pilot plant with polypropylene hollow fiber column,The removalrate and influences of operation temperature,flow rate and concentration on mass transferperformances were discussed mathematically.Experimental results and computer calculation show thatthe ammonia removal rate is not affected by the feed concentration for a given system.Both partialand overall mass transfer coefficients vary along the axis of the fiber,and the mass transfer for themembrane process is controlled by membrane resistance.     

鼓泡塔中低浓度表面活性剂对CO2吸收传质系数的影响（英文）

The effect of different surfactants (n-octyltrimethylammonium bromide (OTABr), sodium dodecyl benzene sulfonate (SDBS) and Tween 80) with different critical micelle concentrations (CMC) on the CO2 absorption into aqueous solutions in a bubble column is analyzed in the present work. The presence of these surfactants in-creased the gas–liquid interfacial area, and decreased the liquid phase mass transfer coefficient, but with signif-icant different extent. The results indicated that the CMC can be a key parameter affecting the mass transfer of CO2 absorption into a dilute aqueous solution of a surfactant. Sardeing's model was used to fit the experimental data successfully by re-correlating the parameters.     

Three Dimensional Simulation of Liquid Flow on Distillation Tray

The liquid flow on a single-pass sieve distillation tray is simulated with a three-dimensional computational fluid dynamics (CFD) program with the K-ε turbulence model. In the model, a source term SMi is formulated in the Navier-Stokes equations to represent the interfacial momentum transfer and another term SC is added to the mass transfer equation as the source of interfacial mass transfer. The simulation provides the detailed information of the three-dimensional distribution of liquid velocity on the tray, the circulation area and the concentration profile along the height of liquid layer.     

萃取体系滴内和两相阻力控制的单液滴传质实验和数值模拟研究

Numerical simulation of transient mass transfer to a single drop controlled by the internal resistance or by the resistance in both phases was mathematically formulated and simulated in a boundary-fitted orthogonal coordinate system. The simulated results on the transient mass transfer dominated by the internal resistance are in good agreement with the Newman and Kronig-Brink models for drops with low Reynolds number. When the drop Reynolds number is up to 200, the mass transfer coefficient from numerical simulation is very low as compared with the Handlos-Baron model. The cases with mass transfer resistance residing in both the continuous and drop phases were simulated successfully and compared with the experimental data in three extraction systems recommended by European Confederation of Chemical Engineering (EFCE). For single drops with Re ＜ 200, the numerically predicted values of the extraction fraction and overall mass transfer coefficient are in reasonable coincidence with the experimental data. It is concluded that the numerical simulation can be resorted in some cases of solvent extraction for conducting numerical experiments and parametric study. Nevertheless, for better resolution as higher Reynolds number drops are simulated, more sophisticated techniques should be developed and incorporated to deal with the large deformation and transient shape oscillation as well as possible Marangoni effect.     

A two-stage blade-packing rotating packed bed for intensification of continuous distillation

A two-stage blade-packing rotating packed bed(TSBP-RPB) was designed and developed for the intensification of continuous distillation. The mass transfer parameters of the TSBP-RPB were investigated using a chemisorption system. Continuous distillation experiments were conducted in the TSBP-RPB by the methanol–water binary system. Experimental results showed that values of the effective interfacial area and liquid-side mass transfer coefficient of the TSBP-RPB were 93–337 m~2·m~(-3) and 0.05–0.19 cm·s~(-1), respectively. The height of equivalent theoretical plate(HETP) of the TSBP-RPB ranged from 1.9 to 10 cm. Moreover, the TSBP-RPB is easy to be manufactured, which shows great potential for the application of continuous distillation.     

MASS TRANSFER IN TURBULENT PULSATING FLOWS

The effect of flow oscillation to the mass transfer between turbulent fluid and solid wall was investigatedby measuring the mass transfer rate between fluid and pipe wall with imposed oscillating flow usingelectrochemical method.The velocity and concentration field in the viscous sublayer which controls the mass trans-fer in such a process was simulated by a simple wave model of single harmonics.Experimental results confirmthat the flow oscillation has no influene on time averaged mass transfer rate,but the phase difference betweenphase averaged velocity field and concentration field shifts with the frequency of imposed oscillating flow.Numeri-cal analysis reveals that the concentration boundarylayer which is responsible for the mass transfer is muchthinner than the viscous sublayer which greatly weakens the influence of imposed oscillating flow on mass transfer.     

伴有Rayleigh对流的气液吸收过程数值模拟

Flow and concentration fields of liquid phase in a gas-liquid contacting system are simulated to show the Rayleigh convection by utilizing the finite-element method. The Schlieren images in C02-ethanol system provided direct visual verification of the present simulation, and the simulated results were well consistent with the experimental observation. The influence of the Rayleigh convection on mass transfer is analyzed qualitatively and quantitatively based on the simulated and the experimental results.     

The Numerical Analysis of the Gas-Liquid Absorption Process Accompanied by Rayleigh Convection

Flow and concentration fields of liquid phase in a gas-liquid contacting system are simulated to show the Rayleigh convection by utilizing the finite-element method. The Schlieren images in CO2-ethanol system provided direct visual verification of the present simulation, and the simulated results were well consistent with the experimental observation. The influence of the Rayleigh convection on mass transfer is analyzed qualitatively and quantitatively based on the simulated and the experimental results.     

Recovery of carbon monoxide from flue gases by reactive absorption in ionic liquid imidazolium chlorocuprate(I):Mass transfer coefficients

Recovery of carbon monoxide from flue gases by selective absorption of carbon monoxide in an imidazolium chlorocuprate(I) ionic liquid is considered in this work as an alternative to the use of molecular volatile solvents such as aromatic hydrocarbons. The present work evaluates the CO mass transfer rates from the gas phase to the ionic liquid solutions in the absence of chemical reaction. To that end, carbon dioxide was employed as an inert model gas and absorption experiments were performed to assess the influence of different process variables in a batch reactor with flat gas–liquid interface. The experimental mass transfer coefficients showed significant var-iation with temperature, (3.4–10.9) × 10-7 m·s-1 between 293 and 313 K; stirring speed, (10.2–33.1) × 10-7 m·s-1 between 100 and 300 r·min-1;and concentration of copper(I), (6.6–10.2) × 10-7 m·s-1 between 0.25 and 2 mol·L-1. In addition, the mass transfer coefficients were eventually found to follow a poten-tial proportionality of the type kL∝μ-0.5 and the dimensionless correlation that makes the estimation of the mass transfer coefficients possible in the studied range of process variables was obtained:Sh=10-2.64·Re1.07·Sc0.75. These results constitute the first step in the kinetic analysis of the reaction between CO and imidazolium chlorocuprate(I) ionic liquid that determines the design of the separation units.     

正十二烷-水乳液吸收丙烷的传质增强作用(英文)

A one-dimensional unsteady heterogeneous parallel mass transfer (ODUHPMT) model was developed for the absorption enhancement of volatile organic compounds (VOC) by the dispersed droplets. An analytical solution for enhancement factor was obtained based on surface renewal theory and the Laplace domain transformation. The absorption rate of propane into water at dif-ferent stirring speeds with the added micro dodecane droplets was investigated experimentally in a thermostatic stirred tank. The mass transfer flux across the gas-liquid interface and the enhancement factor were measured. The results showed that the dodecane has an obvious enhancement effect on propane absorption into water, the maximum enhancement factor reached 11. The enhance-ment factor increased with increasing dodecane volume fraction and decreased with increasing stirring speed. The experiment data agreed well with the model predictions and showed high prediction accuracy of ODUHPMT model.     

机械力强化作用下轻烧氧化镁碳化过程的传质与反应动力学研究

The carbonization of magnesium oxide particles by CO2 was investigated using a stirring mill reactor. The effects of the system temperature, stirring rotation speed, influx rate of CO2 and initial diameter of the magnesium oxide particles on the carbonization process were determined, The results show that the system temperature and the stirring rotation speed are the most significant influencing factors on the carbonization rate. The determi-nation of critical decomposition temperature (CDT) gives the maximum carbonization rate with other conditions fixed. A theoretical model involving mass transfer and reaction kinetics was presented for the carbonization process. The apparent activation energy was calculated to be 32.8kJ·mol-1. The carbonization process is co-controlled by diffusive mass transfer and chemical reaction. The model fits well with the experimental results.