Studies on the liquid-liquid interfacial mass transfer process using holographic interferometry

This paper aims at the interfacial phenomena of liquid-liquid mass transfer and its characteristic. By using the real-time holographic technique, the concentration distributions on the aqueous side were obtained according to holographic diagrams of mass transfer of ethanol through the interface of oil and water at different initial concentrations. Furthermore, the concentrations near the interface and the mass transfer coefficients were attained. A correlation of concentration near the interface to the concentration of the solute in the oil side was proposed. An approach of interfacial energy with solute concentration was established, and the calculated results are at good agreement with the experimental data. It is indicated that the liquid-liquid mass transfer process is approximately in accordance with two-film theory, the interfacial performance may be changed by the addition of the solute, and the interface of liquid-liquid is nonequilibrium thermodynamically during the mass transfer process. __________ Translated from Chemical Engineering (China), 2007, 35(6): 1–3 [译自: 化学工程]     

液液界面传质过程的激光干涉法研究

为了研究液液传质过程的界面现象及传质特征,采用实时激光全息干涉技术,根据不同初始浓度时乙醇通过油水界面传质过程的全息干涉图,得到了传质过程水相侧的浓度分布,据此求出了近界面浓度和基于浓度的传质系数,并关联了近界面浓度与主体相溶质浓度的关系。建立了界面能随溶质浓度改变的函数关系,计算结果与实验值吻合良好。研究结果表明,液液静止界面传质过程基本符合双膜理论,溶质的加入能改变界面性能,传质过程界面处于非平衡状态。     

Effect of interfacial velocity and interfacial tension gradient on momentum,heat and mass transfer

The effect of interfacial velocity and interfacial tension gradient on momentum, heat and mass transfer was studied theoretically. After reviewing current knowledge regarding interfacial velocity effects, the interfacial tension gradient effect is discussed as a numerical solution of the laminar boundary layer equations. The enhancement and suppression of interfacial mobility, and the rates of interphase momentum, heat and mass transfer were related to the Marangoni number. A diagram showing the effect of interfacial tension gradient on momentum, heat and mass transfer is presented.     

Two-dimensional numerical simulations of Marangoni-Bénard instabilities during liquid-liquid mass transfer in a vertical gap

Two-dimensional (2D) simulations of isothermal liquid-liquid mass transfer subject to surface tension- and buoyancy-driven hydrodynamic instabilities have been carried out. Simulation is based on the numerical solution of 2D equations of momentum and mass transport, using a combination of finite difference and finite volume methods. Two different cases have been considered: (1) buoyancy stable mass transfer, only surface tension-driven convection occurs; (2) surface tension-driven instability superseeded by buoyant convection. The faster attenuation of mass transfer coefficients in buoyancy stable situations is attributed to the merging of convection cells leading to a reduction in the number of renewal zones along the interface. Concentration profiles next to the interface reveal the diffusional nature of the mass transfer in the immediate interfacial neighbourhood.     

Transient rise velocity and mass transfer of a single drop with interfacial instabilities - experimental investigations

An experimental study of transient drop rise velocities and mass transfer rates was carried out in the system toluene/acetone/water which is known to show interfacial instabilities. The rise velocity of toluene drops was studied without added solute (acetone) in the diameter range 1-3 mm and with added solute for 2 mm drops. The initial concentration of the transferred solute was varied from 0 to 30 g/L. The transient drop rise velocities were used to quantify the Marangoni effect since the drag coefficient depends on the strength of the Marangoni convection patterns caused by interfacial tension gradients. In addition, mass transfer measurements were carried out in order to determine the modification of the mass transfer rate due to Marangoni convection. Velocity and mass transfer measurements were then correlated via the contact time. Results reveal the existence of a range in which a critical value for the solute concentration can be defined for Marangoni convection.     

A novel Hele-Shaw cell design for the analysis of hydrodynamic instabilities in liquid-liquid systems

A novel Hele-Shaw cell design for accurate experiments in liquid-liquid systems with and without chemical reactions is hereby presented. It allows the formation of a stably pinned, plane liquid-liquid interface in less than one second with a minimum shear flow. The underlying working principle and the performance for different solvent systems and gap widths are discussed.     

界面湍动对气液传质的影响

气液传质过程中经常伴有界面湍动。界面湍动由传质的不均匀性引起,反过来又极大地促进传质。介绍了界面湍动的产生机理和形成条件,对4种不同Ra和Ma准数的情况分别进行了分析。讨论了界面湍动强度对气液传质系数的影响关系。传质系数与Man成正比,其中n随着Marangoni对流胞类型的不同而在1/3和1之间变化。在气液系统中,液相与气相阻力比越大,由界面湍动引起的传质的增强效应越显著。     

Co-current flow liquid-liquid binary mass transfer in ejectors

Liquid-liquid binary mass transfer involving simultaneous transfer of an organic phase component to the aqueous phase and an aqueous phase component to the organic phase in water-n butanol and water-methyl ethyl ketone systems has been studied in a vertical ejector system. Correlations have been developed to predict both dispersed and continuous phase film capacity coefficients as function of various physical and dynamic variables of the system.     

Monte carlo simulation of mass transfer in liquid-liquid dispersions

A simulation technique is developed to predict the performance of a two phase liquid-liquid continuous flow stirred tank reactor as an extractor. The dynamics of the dispersed phase droplet interactions and the microscopic interphase mass transfer in the turbulent flow field are digitally simulated using the interval of quiescence method. The use of realistic breakage and coalescence functions together with the natural evolution of the interactive drop population has made it possible to predict the dispersed phase drop size distribution and mass transfer efficiency in a rational manner from the known physicochemical properties of the dispersion and the operating conditions of the extractor.     

折流式旋转床的流体力学与传质性能研究

开发了一种新型的旋转设备——折流式旋转床,其转子由动部件和静部件组合而成.与传统的旋转填料床相比,折流式旋转床易于实现连续精馏过程的中间进料,同时可方便地将多个转子同轴安装在-个壳体内,成倍提高单台设备的分离能力.对折流旋转床的流体力学和传质性能进行了实验研究,结果表明折流式旋转床具有良好的流体力学和传质性能.目前折流式旋转床已经成功应用于化学工业中的气液接触过程,尤其是连续精馏过程中.     

Effect of interfacial mass transfer on the dispersion in segmented flow in straight capillaries

The effect of interfacial mass transfer on the extent of dispersion in liquid‐liquid segmented flow in straight capillaries is studied. In the absence of interfacial mass transfer, dispersion coefficient was seen to go through a minimum with increasing flow rates. In the presence of mass transfer, physicochemical properties of both the phases and slug lengths were seen to vary along the capillary length. The extent of dispersion was always higher in the presence of interfacial mass transfer. The predictions using axial dispersion model deviated noticeably for larger capillaries as the model does not account for varying buoyancy, dynamic contacting, and Marangoni convection. Simulations of a first‐order interfacial reaction considering varying slug lengths showed a significant change in optimum operating parameters than the conventional approach. A special case of “drop‐on‐demand” type of controlled two‐phase flow in capillaries was also studied. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4294–4308, 2015     

Surface-tension-induced interfacial convection and its effect on rates of mass transfer

Surface-tension-induced interfacial convection (Marangoni phenomena) can appear as a result of mass and heat transfer, compression and dilatation of surface films or their non-Newtonian behaviour and owing to presence in the interface of electrostatic charges. In process engineering problems the mass transfer effect is usually predominant and, depending on the geometry of the system, leads to surface renewal or changes in interfacial area. The surface renewal phenomena can appear as instabilities or disturbances and their effect on mass transfer is presented for transfer to and from drops as well as across flat interfaces in stirred and laminar flow contactors. Mass transfer coefficients and drag coefficients of drops are compared under conditions of undisturbed (diffusional) transfer, cellular convection and interfacial turbulence for stable and unstable direction of transfer. The importance of gravitational instability is indicated.     

Effect of transfer on droplet size in liquid-liquid dispersions

Mean droplet diameter of the dispersed phase in pulsed plate extraction columns was measured for binary and ternary systems. A change in the droplet size in the presence of solute, dependent on such factors as the direction of mass transfer, droplet size in the binary system, radio of diffusion coefficients, viscosity of the continuous phase, interfacial tension and driving force for extraction was observed. Two new empirical correlations of mean droplet sizes in mass transfer conditions are proposed. These correlations have been successfully applied to other extraction columns.     

Effect of bubble interaction on interphase mass transfer in gas fluidized beds

A non-interfering technique has been used to measure the concentration of ozone in pairs of bubbles injected into a bed of inactive 390 μm glass beads fluidized by ozone-free air. The transfer of the ozone tracer from the bubble phase to the dense phase is enhanced when compared to the transfer from isolated bubbles in the same particles and the same column. Bubble growth is also greater for the case where pairs of bubbles are introduced than when bubbles are present in isolation. Enhancement of interphase mass transfer for interacting bubbles in the present work and in previous studies incr with particle size and can be explained in terms of enhancement of the throughflow (or convective) component of transfer while the diffusive component unaltered. This mechanism leads to new equations for estimating interphase mass transfer in freely bubbling fluidized beds.     

Single drop mass transfer augmented by interfacial instability

A photographic technique was used to determine mass transfer rates from single drops immediately following formation. Measurements were made on a system expected to exhibit interfacial tension driven convection and comparisons are drawn to predictions for stable systems and to measurements in the presence of surfactant. Unusually high mass transfer coefficients are reported.     

气液反应体系相界面传质强化研究

气液反应界面传质的强化是当今高效和节能反应器研究的重要课题,弄清反应器内的气液传质机理是对气液反应器进行数学描述的关键。反应过程的能效和物效与体系中的传质系数k_G,k_L,k_S以及相界面面积a等参数直接相关,这些参数受气泡尺寸、分布、表观气速和气含率等因素的制约。就确定的体系和反应条件而言,这些因素会因反应器的结构尤其是搅拌和混合方式的变化而异。文章从理论上分析了影响气液界面传质的各因素,建立了较为详细的理论模型。理论计算结果表明:气泡大小是影响气液界面传质和最终反应速率的重要流体力学参数,微米级气泡对反应过程的强化作用明显。能量耗散率是决定体系气泡大小的深层原因,强化气液反应器设计时应重点考虑。     

气体折流塔板流体力学和传质实验研究

对气体折流塔板的流体力学和传质进行了实验,找出了气液流动对塔板压降和传质的影响规律,通过气体折流塔板与传统筛板在流体力学与传质等方面的比较,找到了气体折流塔板的适用范围及相对于传统筛板的优点,为以后此塔板的应用提供了有效数据。     

导向梯形浮阀的升程对其塔板性能影响

为使导向梯形浮阀在工业应用时,选取浮阀升程有可靠的参考数据,针对导向梯形浮阀的升程这一结构参数进行试验研究。采用空气-水系统,在500 mm×500 mm的方形塔内,对不同浮阀的升程对导向梯形浮阀塔板的流体力学进行了实验研究,测定了塔板压降、泄漏和雾沫夹带。并应用空气-水-CO2系统,在不同的升程下测定了斜孔梯形浮阀塔板的传质效率。实验结果表明,导向梯形浮阀塔板的升程对其流体力学和传质性能有显著的影响,并在确定的条件下有最佳值。     

On the action of surface active agents on mass transfer in liquid-liquid extraction

The effect of the surface active agents sodium hexadecanyl sulphate and sodium undecanyl sulphate on the rate of mass transfer, droplet oscillation and terminal velocity has been studied during extraction of o-nitrophenol and iodine from aqueous solutions by single drops of carbon tetrachloride. The effect is caused by the pure surface active agents and does not depend on the presence of impurities. The hydrodynamic character of the effect has been confirmed. A comparison with solid spheres shows that the surface active agents can make the rates of mass transfer and the terminal velocities equal to those for solid bodies, internal circulation, oscillation and the zig-zag path being completely eliminated. Evidence is presented indicating that the high rates of mass transfer obtained in the absence of surface active agents, about three times that for solid spheres, are not caused by the droplet oscillation, and that, at the most, they can be accounted for only partly by internal circulation. It is suggested that the explanation must be sought in the micro structure of the flow pattern.     

Selection of mass transfer correlations for rate based liquid-liquid extraction model

A rate-based model formass transfer in liquid-liquid extraction (LLX) has been developed usingthree distinct stages of drop formation, drop fall or rise and drop coalescence. Binary diffusivities in infinite dilution as well as for concentrated multicomponent mixtures were used to estimate the Maxwell-Stefan binary mass transfer coefficients for both the phases. The mass transfer resistances associated with these coefficients have been categorized in four configurations. Because of the very large number of computations associated with repeated calculations of mass transfer coefficients, alocal model has been incorporated. Acomparative study between rate-based and non-equilibrium simulator and our bench scale experiments (LLX of toluene-acetone-water system) has been done. The stage-wise composition profiles of acetone in water and toluene phase of the experimental and simulation runs have been compared by using the relative error square analysis. Based on this analysis, best mass transfer combination and mass transfer resistance model has been selected.