Simulation of the hydrodynamics and mass transfer in a falling film wavy microchannel

The flow in a liquid falling film is predominantly laminar, and the liquid-side mass transfer is limited by molecular diffusion. The effective way to enhance the mass transfer is to improve the liquid film flow behavior. The falling film behaviors of water, ethanol and ethylene glycol in nine different wavy microchannels were simulated by Computational Fluid Dynamics. The simulation results show that the falling film thickness exhibits a waveform distribution resulting in a resonance phenomenon along the wavy microchannel. The fluctuation of liquid film surface increases the gas–liquid interface area, and the internal eddy flow inside the liquid film also improves the turbulence of liquid film, the gas–liquid mass transfer in falling film microchannels is intensified. Compared with flat microchannel, the CO_2 absorption efficiency in water in the wavy microchannel is improved over 41%. Prediction models of liquid film amplitude and average liquid film thickness were established respectively.     

Mass transfer performance of structured packings in a CO2 absorption tower

This paper studies the mass transfer performance of structured packings in the absorption of CO2 from air with aqueous NaOH solution. The Eight structured packings tested are sheet metal ones with corrugations of different geometry parameters. Effective mass transfer area and overall gas phase mass transfer coefficient have been measured in an absorption column of 200 mm diameter under the conditions of gas F-factor in 0.38–1.52 Pa0.5 and aqueous NaOH solution concentration of 0.10–0.15 kmol·m?3. The effects of gas/liquid phase flow rates and packing geometry parameters are also investigated. The results show that the effective mass transfer area changes not only with packing geometry parameters and liquid load, but also with gas F-factor. A new effective mass transfer area correlation on the gas F-factor and the liquid load was proposed, which is found to fit experiment data very well.     

Measurements of the effective mass transfer areas for the gas–liquid rotating packed bed

Rotating packed bed(RPB) is one of the most effective gas–liquid mass transfer enhancement reactors, its effective specific mass transfer area(ae) is critical to understand the mass transfer process. By using the NaOH–CO₂ chemical absorption method, the aevalues of three RPB reactors with different rotor sizes were measured under different operation conditions. The results showed that the high gravity factor and liquid flow rate were major affecting factors, while the gas flow rate ex...     

筛板塔气-液-液系统内相含率和传质特性研究

The gas and dispersed phase holdups and mass transfer coefficients of liquid-iquid were determined for gas-liquid-liquid three phase system in a screen plate column. The flow pattern of gas-liquid-liquid three phase system was studied under different gas velocities. The shape factors showed the geometric properties of screen plates and the corrected drop chaxacteristic velocities were introduced. The phase holdup in two phases was correlated.The research results indicated that mass transfer coefficient for liquid-liquid system in a column with screen plates and gas agitation was found to increase apparently.     

CO2 absorption performance in a rotating disk reactor using DBU-glycerol as solvent

Gas–liquid mass transfer of rotating disk reactor was studied in CO_2 absorption using 1,8-diazabicyclo-[5.4.0]-undec-7-ene(DBU)-glycerol solution as solvent. Effects of the rotating disk structure and various operation parameters on the CO_2 absorption rate and CO_2 removal efficiency were investigated. The rotating disk with optimal holes is conducive to mass transfer of CO_2 and the formation of thin liquid film at the opening increases the gas–liquid contact area. With the increase of rotating speed, the liquid flow pattern on the rotating disk surface changes from thin film flow to separated streams and creates extra liquid lines attached to the rim of the disk,which leads to a very complicated change on the CO_2 absorption rate and CO_2 removal efficiency. The overall gas-phase mass transfer coefficient increases 138% as the rotating speed increasing from 250 to 1400 r·min~(-1).Increasing temperature from 298 to 338 K can enhance the CO_2 absorption rate due to lowering the viscosity of the solvent. The rate-determined step for the absorption is focused on the gas side. The rotating disk reactor can effectively enhance the absorption of CO_2 with viscous DBU-glycerol solvents.     

在高压下规整填料中的流动实验研究

Both distillation performance and hydrodynamic study for backmixing by tracer technique were carried out in a high-pressure packed column with 0.15 m inner diameter over a wide range of operating conditions. Isobutane and n-pentane are employed as test mixture in the distillation experiment and air/water is used for the hydrodynamic study. The column is installed with Mellapak 350Y structured packing and the total packing height is 2.0 m. With the increasing operating pressure, the separation efficiency increases slightly while the F-factor corresponding to the maximum efficiency at each pressure is descending. It is noted that, at all operating pressures, with the increase of F-factor, the packing efficiency is slightly higher up to the flooding point. The application of SRP model to high-pressure distillation gives much lower values of HTUOG than those obtained experimentally. An additional term, the height of mixing unit, is introduced to correct the SRP model and improve its accuracy at high pressure. From the tracer experiments, the height of mixing unit for gas phase was found to be larger than that for the liquid phase. From this viewpoint, it is believed that the gas phase backmixing gives more unfavorable influence on the separation efficiency in comparison with liquid phase.     

翅片导流板填料应用于旋转填料床的特性

For an alcohol/water system and with fin baffle packing, continuous distillation experiments were carried out in a rotating packed bed (RPB) system at atmospheric pressure. The effects of the average high gravity factor (β), liquid reflux ratio (R) and feedstock flux (F) on the momentum transfer and mass transfer were investigated. The gas phase pressure drop of RPB increased with the average high gravity factor, liquid reflux ratio and feedstock flux, which was 13.55-64.37 Pa at β of 2.01-51.49, R of 1.0-2.5, and F of 8-24 L&;#8226;h－1 for a theoretical tray in the RPB with fin baffle packing. The investigation on the mass transfer in the RPB with different packings showed that the number of transfer units of RPB with a packing also increased with the average high gravity factor, reflux ratio and feedstock flux. It is found that the fin baffle packing (packing III) presents the best mass transfer performance and lowest pressure drop for the height equivalent to a theoretical plate (HETP), which is 6.59-9.84 mm.     

并流喷射填料塔板流体力学及传质性质性能的实验研究

The jet co-flow packing tray(JCPT) with three different types of perforation in equal opening fraction was tested in two rectangular columns with 0.12 m in width and 0.27 m in length operated with air-water system.The influences of gas phase orifice F-factor and clear liquid height He on the amount of liquid lifted, Q, were examined. The corresponding correlation between Q with F-factor and equivalent diameter of perforated holes as well as Hc was obtained. Furthermore, the non-steady state mass transfer performance of JCPT was tested by the humidification of air with water. Finally, by the analysis of data and comparison, it was found that the JCPT tray with single cap and two holes exhibited the highest mass transfer efficiency and best performance.     

一串上升气泡周围流体的湍动特性(英文)

The turbulence behavior of gas-liquid two-phase flow plays an important role in heat transfer and mass transfer in many chemical processes. In this work, a 2D particle image velocimetry (PIV) was used to investigate the turbulent characteristic of fluid induced by a chain of bubbles rising in Newtonian and non-Newtonian fluids. The instantaneous flow field, turbulent kinetic energy (TKE) and TKE dissipation rate were measured. The results demonstrated that the TKE profiles were almost symmetrical along the column center and showed higher values in the central region of the column. The TKE was enhanced with the increase of gas flow and decrease of liquid viscosity. The maximum TKE dissipation rate appeared on both sides of the bubble chain, and increased with the increase of gas flow rate or liquid viscosity. These results provide an understanding for gas-liquid mass transfer in non-Newtonian fluids.     

旋转填料床中硝酸吸收NO_x的实验研究(英文)

Absorption of NOx into nitric acid solutions was studied in the presence of ozone by using a rotating packed bed (RPB) contactor. The influences of operating parameters, such as high gravity number, amount of ozone, gas velocity, liquid spray density and inlet concentration of NOx, on the removal efficiency of NOx were investigated, among which the high gravity number and ozone amount are more important. Ozone was introduced to oxidize HNO2 to HNO3 to prevent the decomposition of HNO2 in the liquid phase. The high gravity number presents the effective external force for enhancing the mass transfer of ozone from gas phase to liquid phase. Under the experimental condition, the removal efficiency of NOx is higher than 90% and the concentration of nitric acid product exceeds 45%.     

液相流动方式对波纹规整填料性能的影响

根据液相在波纹规整填料片上呈现渗流、膜状流等不同的流动方式,选择5种不同的波纹规整填料对其流体力学和传质性能进行研究,以探究液相在波纹片上的流动方式对波纹规整填料性能的影响.研究结果表明,液相呈渗流流动的泡沫碳化硅波纹规整填料(SCFP型)有利于液体横向扩散和液膜均匀分布,当液相喷淋密度和气相F因子均较小时,其压降最低,传质效率最高;液相主要呈渗流流动、兼有膜状流动的双层错孔丝网填料(DMⅢ型)有利于波纹片两侧液体交换,强化液体在流动过程中的扰动,其压降及传质性能略逊于SCFP型填料;液相主要呈膜状流动的BX型、DMⅠ型及DMⅡ型填料波纹片表面液膜较厚,横向扩散能力差,其传质效率低于SCFP型和DMⅢ型填料.研究揭示了依靠渗流作用的波纹规整填料具有较好的应用性能,为波纹规整填料的进一步发展开拓了新思路.     

气-液-液萃取的流体力学研究

在液-液萃取过程中,提高分散相的表面更新速率可有效提高萃取的传质效率。研究发现,在萃取过程中使用气体搅拌可以增加液液之间的接触面积,促进液相内的湍动和循环。本文研究了气-液-液三相下油滴的流动形态,并对不同填料的流体力学性能进行了测定。实验结果表明,气相速度的增加可导致气含率、液含率的增加,从而提高分散相在填料萃取塔中的停留时间,在一定的速度范围内明显降低萃取的表观传质单元高度,极大地强化传质效果。通过与散装填料对比,发现规整填料更利于强化萃取效果,其液泛速度平均增加25%。     

利用CFD及结点网络相结合的方法研究规整填料传质效率

气液两相不均匀流动是造成填料塔传质效率下降的主要原因之一.采用计算流体力学方法,定量分析规整填料内气液两相流动对传质效率影响的研究尚未见文献报道.从Navier-Stokes方程出发,首先建立了考虑气液之间相互作用的CFD计算模型,定量描述了填料片内的气相流场分布.在此基础上,结合文献中提出的液相结点分布模型及一些经典的传质理论,初步提出了适用于定量计算金属板波纹填料传质效率的耦合型算法,并对规整填料内的传质效率进行了计算,模型结果与实验值吻合较好.为规整填料传质效率的定量研究提供了新的方法和思路.     

规整填料波纹结构上的二维两相流模拟方法

规整填料是由规则排列的波纹板组成的。液相是沿着波纹板壁面往下流动,而气相则是在波纹板之间形成的通道内与液相呈并流或逆流的状态。因此,气液两相的水力学特性决定着填料塔的操作弹性和质量传递效率。波纹板上的液膜流动状态因在很多应用领域都发挥作用而备受关注。本文从物理建模、自由界面处理方法、表面张力模型以及湍流模型等方面对规整填料波纹板上的二维液膜数值模拟方法作了详细的陈述,并且对该领域的研究现状作了进一步分析和总结。     

倾斜波纹板上液膜流动的CFD研究

利用VOF法建立了液膜在倾斜波纹板上的气-液两相流CFD模型,并根据液膜流动特点提出了表面张力动量源项和气液界面作用力动量源项.模拟结果与文献实验值吻合较好,表明本文提出的CFD液膜流动模型具有一定的可靠性.通过模拟不同性质的液体在不同表面结构波纹板上的流动过程发现,波纹板表面微观结构以及液体性质尤其是液体的表面张力对连续液膜的形成有重要作用,表明通过改变波纹板面微观结构以及降低液体的表面张力可以促进连续液膜的形成,对提高气液之间的传质效率有重要意义.     

规整填料气体脱碳塔模拟计算

基于实际填料高度 ,本文首次建立了高效规整填料塔DEA活化热钾碱脱碳系统传质模型沿规整填料高度上CO2 气相浓度、溶液转化度、气液相CO2 分压等模拟计算结果与工业实例吻合很好     

Direct numerical simulation of reactive absorption in gas–liquid flow on structured packing using interface capturing method

Direct numerical simulations are performed in order to study physical and reactive absorption in gas–liquid flow on structured packing. The volume of fluid method is used to capture the gas-liquid interface motion. The mass transport is computed by additional chemical species concentration transport equation with adequate modelling of solubility and chemical reaction. The numerical difficulties arise in imposing jump discontinuity for chemical concentrations at the interface due to different solubility. These difficulties are solved by an original method using a continuum mechanical modelling of two phases flow and Henry's law with constant coefficient. The present study shows how the mass transfer is affected by the complex geometry considered here and by the flow conditions. The results show firstly that the liquid side mass transfer is well predicted by the Higbie theory and the exposure time of a typical element of volume near the interface corresponds to ratio between characteristic length and velocity of the interface provided that the real velocity of the interface is used. For the considered geometry, the transfer is found to be increased compared to the transfer of a plane liquid film. Finally, for the case where the mass transfer is accompanied by second order irreversible chemical reaction in the liquid phase, the numerical results are compared to approximate solution presented by Brian et al. [1961. Penetration theory for gas absorption accompanied by a second order chemical reaction. A.I.Ch.E. J. 7, 226–231] and good agreement is observed.     

Liquid film flow on structured wires: Fluid dynamics and gas‐side mass transfer

The liquid film flow on different structured wires and chains is observed experimentally to assess the suitability of a structured packing consisting of vertical wires. The results show that liquid beads as they appear on cylindrical wires are inhibited by certain chain geometries. This increases the flooding gas load up to F = 12 Pa^0.5. As the stabilized film shows no liquid bead motion, the liquid velocity at the interface is less which results in lower gas‐side mass‐transfer coefficients. An estimation of the packing characteristics for different chain geometries with an assumed wire packing density of 40,000 wires/m² is made. The interfacial area, mass‐transfer coefficients, and consequently the separation efficiency strongly depend on the liquid load. However, the proposed gas‐side separation efficiencies are slightly lower compared to common structured packings but the advantages are higher load limits, a better liquid distribution, and lower pressure drop. © 2012 American Institute of Chemical Engineers AIChE J, 59: 295–302, 2013     

A corrugation geometry based model for efficiency of structured distillation packing

Although the structured packing is a well established gas–liquid contacting device, the understanding of its function is insufficient and often leads to poor exploitation of the available phase separating potential. This is a consequence of a rather superficial approach to modelling the packing performance through the years resulting in a lack of information on the nature and extent of interaction between counter-currently flowing gas and liquid phases and the micro and macro geometry of a rather ordered structure with a pronounced flow discontinuity at the transition among packing elements. This paper addresses the relation between the fluid-dynamics imposed by packing geometry and the mass transfer efficiency, and introduces a performance prediction method which does not require packing specific constants to describe mass transfer coefficients of phases.