气相中乙醇对水吸收CO_2过程界面对流的影响

考察了在气相中加入少量乙醇对水吸收CO2过程中液相界面对流的影响。采用粒子成像测速仪(PIV)测定了这一气体吸收过程中液体瞬时流场。通过对液体流场信息进行处理,得到了不同条件下速度和湍动能的数据及其分布;根据流场内速度和湍动能及其分布结构,定量分析了气相中加入乙醇对气液传质过程界面对流的影响,发现气相中乙醇的加入导致了局部Marangoni效应,很大程度上增大了界面附近的对流,为促进气液传质提供了依据。     

气液界面对流传质的观测与定量分析

采用光学纹影系统对乙醇和水双组分解吸传质过程的对流结构的界面湍动进行了定性观察和定量分析。建立了一套水平非稳态气液传质设备,试验观测了乙醇和水体系中液相组分向气相传质过程的Marangoni界面对流结构。还通过对传统纹影方法的改进,对乙醇解吸传质过程的浓度(本文用质量分数表示)梯度场进行了定量测量。定量分析表明乙醇和水系统解吸过程中,引发界面湍动的原因是局部较大的表面张力梯度。定量分析的结果很好的解释了伴随Marangoni效应的传质过程的混乱的对流结构,为进一步对界面湍动现象的分析提供了帮助。     

Numerical simulation of the Marangoni effect on transient mass transfer from single moving deformable drops

A level set approach was adopted in numerical simulation of interphase mass transfer from a deformable drop moving in a continuous immiscible liquid, and the simulation results on Marangoni effect were presented with respect to three experimental runs in the methyl isobutyl ketone–acetic acid–water system. Experiments showed that when the solute concentration was sufficiently high, the Marangoni effect would occur with the interphase mass transfer enhanced. Numerical results indicated that the mass‐transfer coefficient with Marangoni effect was larger than that without Marangoni effect and stronger Marangoni effect made the drop deform more easily. The predictions were qualitatively in accord with the experimental data. Numerical simulation revealed well the transient flow structure of Marangoni effect. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

CO2在纳米流体解吸过程中的微对流现象

建立了一套水平气液界面传质模拟装置,利用粒子成像测速仪（PIV）对CO2从乙醇和乙醇纳米流体中解吸过程液相流场进行了观测和分析。传质发生时,在近界面处均观察到了由Marangoni效应造成的湍动。通过对平均速度的分析,发现在乙醇纳米流体中发生的湍动强度和湍动范围较乙醇溶液中大。纳米流体中的Marangoni效应加剧了纳米粒子的布朗运动,引发了纳米流体中的微对流,从而将界面处的湍动传递至液相主体中,导致液相主体的漩涡增多、流体混合加剧,促进了气液传质。     

Influence of the Marangoni Effect on the Efficiency of Plate Columns for Binary Distillation

The main feature of a distillation process is its efficiency. The gas‐liquid bubbling layer formed on the trays and the ongoing mass‐exchange process during distillation is influenced by the change of the surface tension gradient during this mass‐exchange procedure. Binary mixtures with respect to the change of the surface tension effect can be divided into positive, negative, and neutral ones. In order to assess the effect of surface tension on mass transfer, the stabilization index quantity is applied, representing the product of the liquid phase process momentum and the surface tension gradient in the mixture of the liquid phase. One possibility to express the Marangoni efficiency enhancement ratio by experimental distillation data obtained under identical hydrodynamic conditions in two binary systems, i.e., a positive (methanol‐water) and a neutral one (methanol‐ethanol), is presented.     

伴有Marangoni效应的传质动力学

结合Marangoni对流的流体动力学条件，通过建立的半经验模型研究了伴有Marangoni效应的传质动力学，阐述了Marangoni效应增强传质的机理，得到了传质Sherwood数与Marangoni数之间的连续指数关联，从而得以解释不同实验过程中得到的不同Sherwood数与Marangoni数之间的关系.研究表明，由Marangoni效应而增强的传质系数与界面Marangoni湍动的表现形式有关.     

Visualization of Mass Transfer during Droplet Formation

The impact of mass transfer in liquid‐liquid extraction during droplet formation in a quiescent continuous phase was investigated. The impact of droplet size, concentration, and formation rate on a hanging droplet was analyzed via laser induced fluorescence (LIF) using rhodamine 6G as tracer in the system of toluene and acetone in water. The droplet formation rate has a major impact on mass transfer and the mixing pattern inside the droplet. Very fast mass transfer induced by Marangoni convection was visualized at a high local resolution independently of concentration and formation rate.     

Experimental investigation and numerical simulation of Marangoni effect induced by mass transfer during drop formation

Marangoni effect induced by interphase mass transfer plays an important role in liquid–liquid extraction and reaction processes. The interaction of Marangoni effect and interphase mass transfer during drop formation at different injection rates and different initial solute concentrations was investigated by experimental and numerical simulation. The extraction fraction was measured and the corresponding correlation was proposed. The level‐set method coupled with mass‐transfer equation is for the first time used to simulate the mass‐transfer induced Marangoni effect during drop formation. The simulated drop volume, shape, and extraction fraction are in good accordance with experimental data. Through the numerical simulation, it is found that the mass transfer in the first mass‐transfer period is the most efficient during drop formation when Marangoni convection occurs. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4424–4439, 2013     

相间传质对气泡聚并过程影响的实验研究

设计了一套双气泡聚并实验系统,考察了相间传质对气泡聚并过程的影响,气相采用非相变的N2,液相为挥发性的丙酮和乙醇水溶液. 利用该系统测定了25~50℃温度下,不同组分浓度、鼓泡频率和气泡直径时气泡的聚并特性. 结果表明,相间传质诱导的Marangoni效应使聚并时间随温度升高呈先减小后增大的趋势,聚并时间的分散性在较高温度下显著增大,采用聚并效率描述气泡聚并特性更合适;聚并效率在温度升高到一定程度后开始降低并趋于最小值,该值随溶液浓度增加而减小,稳定因子可定量描述Marangoni效应;鼓泡速率和气泡直径增加1倍,最小聚并效率分别减小50%和67%.     

Marangoni对流的纹影实验分析

通过纹影系统对乙醇溶液解吸CO₂的过程进行了实验研究,液层自由界面的俯视纹影图记录了对流结构的演化过程,并捕捉到了Marangoni对流结构的初始形态。相应的胞型结构因发展空间的限制,由初始的近圆形逐渐变成了多边形结构。利用纹影图片的灰度分布信息,对单个胞型结构的出现、发展及分裂阶段进行了定性分析,发现界面非均匀传质所引发的界面对流在其胞型发展的过程中将会导致界面的变形。湍动的后期,液层表面将布满多边形结构,且胞型结构基本保持不变。相应纹影图片的颜色差异随解吸的进行逐渐减小,即随着传质推动力的减小,湍动强度也将减弱。     

Transient rise velocity and mass transfer of a single drop with interfacial instabilities—Numerical investigations

Full 3D-simulations of transient interfacial mass transfer accompanied by Marangoni convection at a single spherical droplet in a quiescent liquid were performed in a moving reference coordinate system. The flow and concentration field are solved simultaneously, coupled via the additional Marangoni stress generated by concentration gradients at the interface. Fluid dynamics and mass transfer are investigated in the Marangoni convection dominated toluene/acetone/water system. The numerical results are qualitatively and quantitatively compared with own experimental results. The simulation results reveal that mass transfer is always enhanced—compared to calculations where no Marangoni convection appears—independently from the initial solute concentration. The enhancement factor of mass transfer ranges between 2 and 3.     

Numerical Simulation of the Solute‐Induced Marangoni Effect with the Semi‐Lagrangian Advection Scheme

The level set method is combined with the concentration transformation method to solve the interphase mass transfer process. However, the artificial diffusion generated in the mass transfer convection term across the interface is inevitable, especially when large shape deformation is encountered at high Reynolds numbers. A semi‐Lagrangian advection scheme is introduced to overcome this disadvantage. The methyl isobutyl ketone (MIBK)‐acetic acid‐water system is adopted to study the unsteady mass transport process accompanied with the Marangoni effect of a single deformable drop ascending in the infinite continuous phase. The predicted overall mass transfer coefficients agree with experimental data very well. The configuration of Marangoni convection is revealed and its effect on the interphase mass transfer process is investigated.     

Marangoni效应对填料塔精馏传质过程的影响

通过 4种正体系、 5种负体系的精馏实验 ,考察了Marangoni效应对填料塔中传质过程的影响。结果表明 :正体系的气相体积总传质系数KGa与组成无关 ,仅受气相流量 qG 的影响 ,可用关联式KGa =AqGB,和B =0 .94± 0 .0 4表示 ;而对负体系 ,由于Marangoni效应的存在 ,顺着液相流动方向 ,KGa逐渐减小。其关联式为KGa =AqGBMsC,B =1.0 5± 0 .0 4,C =0 .3± 0 .0 5 ,该式的平均误差约为 6%。     

Marangoni效应与汽液传质过程

介绍Marangoni效应对液体混合物流型的影响,同时指出其影响传质过程的机理。在概述国内外这一领域的研究动态和进展的基础上,提出了在Marangoni效应作用下传质过程的控制与操作以及设计和开发新传质元件的思路与策略。     

伴随传质的液液体系微分散流型图的实验研究(英文)

This paper presents the experimental results of liquid-liquid microflows in a coaxial microfluidic device with mass transfer.Three working systems were n-butanol + phosphoric acid(PA) + water,methyl isobutyl ketone(MIBK) + PA + water,30% kerosene in tri-n-butylphosphate(TBP) + PA + water.The direction and intensity of mass transfer were adjusted by adding PA in one of two phases mutual saturated in advance.When PA transferred from the organic phase to the aqueous phase,tiny aqueous droplets may generate inside the organic phase by mass transfer inducement to form a new W/O/W flow pattern directly on some special cases.Once the PA concentration was very high,violent Marangoni effect could be observed to throw part of organic phase out of droplets as tail.The interphase transfer of PA could expand the jetting flow region,in particular for systems with low or medium inter-facial tension and when the mass transfer direction was from the aqueous phase to the organic phase.     

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。     

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.     

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.     

Investigation of the mass transfer across the interface of two concurrent laminal flowing liquids in a horizontal cylindrical channel—I Experimental results

The concentrations of the solute (pyridine) were measured by means of modified liquid scintillation techniques to within 0.66,μm of the interface as well as in the bulk of the organic (toluene) phase during the solute transfer from the toluene to the water phase at different temperatures, flow rates and solute concentrations. These measurements allow the comparison of the mass transfer resistance of the diffusive transfers with the interfacial resistance. In extremely pure systems the interfacial resistance is negligible in comparison with the resistances of the diffusive transfers. In the presence of surface active agents the interfacial resistance strongly increases and exceeds those of the diffusive transfers. The solute transfer from the water to the toluene phase because of the Marangoni instabilities could only be considered qualitatively.The concentrations of the solute (pyridine) to within 0.66 μm of the interface and in the bulk of the organic phase (toluene) during the solute transfer from the organic to water phase in a horizontal cylindrical flow channel with concurrent flow of the phases at different temperatures, flow rates and solute concentrations were measured by means of a modified liquid scintillation technique. These measurements allow the comparison of the mass transfer resistances of the diffusive transfers to and from the interface with the interfacial resistance. In extremely pure systems, the solute concentration at the interface quickly drops to very low values with increasing distance from the channel entrance, which indicates that the mass transfer resistance of the interface is negligible in comparison with the resistances of the diffusive transfers in the laminar flow region. In the presence of surface active agents (LPC) the solute concentration to within 0.66 μm of the interface dramatically increases and exceeds the solute concentration in the bulk of the toluene phase. This indicates a strong increase of the mass transfer interfacial resistance. The high solute concentration at the interface, exceeding its bulk concentration, is caused by the enrichment of the solute in the interface, which was measured by the interfacial tension depression in the presence of the solute. Because the solute transfer from the water to the toluene phase causes interfacial (Marangoni) instabilities, which increase the geometrical interfacial area due to uncontrolled eruptions and formations of microemulsions, the solute concentration could not be measured to within 0.66 μm of the interface in the toluene phase during the water to toluene solute transfer. Only qualitative statements could be made with regard to the area of the interface. Further measurements are necessary in order to determine quantitative relationships with regard to the mass transfer interfacial resistance as a function of different process parameters     

周期性机械激励液液体系相界面层的传质特性

在改装的恒界面池中采用微分传质系数研究了无机酸和金属盐液液萃取 (反萃 )体系动态相界面的传质速度对可控界面机械激励的响应 .作用于液液体系相界面区域的机械激励不仅显著影响相间区域的扩散渗透性 ,而且明显稳定了液液体系相间区域的传质条件 ,减小了实验误差 .微多相层的形成和发展决定相间动量与物质的传输特性 .用微多相层的概念解释了对相界面区域的激励有助于引发Marangoni表面对流及其他实验现象 .