填料塔中氨水吸收二氧化碳的传质性能

在填料塔中对氨水吸收二氧化碳的传质性能进行了实验研究,测定了填料塔单位体积的有效传质面积aV,气相传质系数kG和体积总传质系数KGaV等,实验结果表明,随着气体流量增加,aV值略有上升,kGaV和kG值明显增大;体积总传质系数KGaV值也随着气体流量和氨水浓度的升高而增大。在总传质阻力中,气膜阻力所占比例相对较小,氨水吸收二氧化碳的过程主要受液膜阻力的控制。     

基于微吸收器的CO2吸收过程研究进展

微化工技术在流体流动、过程强化、传质与反应过程等领域备受关注,本文归纳整理了3种不同类型的微吸收器（微降膜吸收器、微通道吸收器和微网格吸收器）捕集CO₂过程中的水力学性质和传质过程及其机理研究进展,并对3种微吸收器吸收CO₂过程中存在的问题进行分析总结,同时对微吸收器能快速工业化提出展望。其中重点介绍了微通道泰勒流吸收器的水力学流动特性,包括泰勒流气泡的生成机制、气泡和液弹的长度、气泡的输运和运动速度、气泡截面形状及液膜厚度和气液两相流压降;归纳了微通道泰勒流吸收过程的传质过程机理和传质系数的模型以及不同影响因素（通道截面尺寸,通道长度,主通道结构及入口形状,气、液相组成及其流速,吸收剂和系统压力）作用下CO₂吸收效率和传质系数的研究进展。     

方肋微通道内流动沸腾的气泡动态与传热特性分析

为揭示方肋微通道热沉内流动沸腾的传热传质机理,本文基于耦合VOF方法与“饱和界面”相变模型对微通道内单个气泡绕流加热方肋的传热传质过程进行了数值研究。通过分析该过程中气泡增长速率与方肋壁面传热系数的变化,重点讨论了初始气泡体积和入口雷诺数Re对相变传热效率和流动结构的影响。结果表明：在气泡流经加热方肋过程中,气泡与方肋表面之间形成一层薄液膜,该薄液膜的相变蒸发极大强化方肋表面的换热效果,换热系数较相同条件下的单相流动提升6倍以上。此外液膜厚度随Re增大而变厚,液膜热阻相应增大,液膜蒸发对换热的促进作用随Re增大而降低。最后考察了气泡体积对方肋壁面换热的影响,结果表明：初始体积大的气泡具有更薄的液膜厚度及更大的蒸发面积,表现出更高的相变传热效率;而小气泡对壁面温度影响较小。     

Effects of gas concentration on hydrodynamics of gas absorption in a microchannel

In this article, the effects of gas concentration on hydrodynamics of gas–liquid two-phase flow with mass transfer during gas absorption in a microchannel are investigated, by using 2-amino-2-methyl-1-propanol (AMP) solution to absorb mixtures of CO₂ and N₂ with various volume fractions. The concentration of CO₂ not only affects the driving force of gas–liquid mass transfer, but also affects the pressure drop of gas–liquid two-phase flow. The average linear velocity of the liquid phase is estimated by introducing the void fraction, which accurately characterizes the difference in the bubble velocity versus the liquid velocity. On this basis, the pressure drop model of gas–liquid two-phase flow with mass transfer in a microchannel is established. Through the pressure drop model, the influence mechanism of CO₂ concentration on the pressure drop during gas absorption in a microchannel is revealed.     

Gas-liquid mass transfer in bubble columns with a T-junction nozzle for gas dispersion

Bubble break-up, gas holdup, and the gas-liquid volumetric mass transfer coefficient are studied in a bubble column reactor with simultaneous injection of a gas and liquid through a T-junction nozzle. The theoretical dependence of bubble break-up and the volumetric mass transfer coefficient on liquid velocity in the nozzle is developed on the basis of isotropic turbulence theory. It is shown that correlations which are developed based on liquid jet kinetic power per nozzle volume explain average gas holdup and the volumetric mass transfer coefficient within an error of 15% for all gas and liquid flow rates and nozzle diameters used. Experiments with a larger scale column, height 4.64 m and diameter 0.98 m, show a transition from homogeneous to heterogeneous flow at a certain liquid flow rate through the nozzle. Liquid composition was found to have a significant effect on gas-liquid mass transfer. A phenol concentration of 10–30 mg/l in water increases the volumetric mass transfer coefficient of oxygen by 100%. This phenomenon may have significance in the chemical oxidation of wastewater.     

Experimental analysis of bubble mode in a plate-type absorber

An experimental analysis of ammonia-water absorption was performed in a plate-type absorber. The flow of water and ammonia gas was performed in the bubble mode. The experiments were made to examine the effects of solution flow rate and gas flow rate on the performance of the absorber. It was found that the increase of solution flow rate rarely affected the mass transfer, but improved the heat transfer. As the gas flow rate increased, slugging occurred in the bubble mode and influenced the thermal boundary layer. Finally, the results were converted into dimensionless numbers to elucidate physical phenomena and plotted as Sherwood number versus Reynolds number for mass transfer performance and Nusselt number versus Reynolds number for heat transfer performance.     

Experimental investigation on dynamic behaviour of bubbles emerging from micro-capillary orifice in a flow channel

The flow phenomenon of liquid with bubbles is widespread in various industrial fields, which determines the mass transfer characteristics of the equipment. In this work, the dynamic behaviour of bubbles emerging from micro-capillary orifice in a flow channel was studied by a visualization experiment, while the effects of gas flow rate and liquid flow rate on these processes of bubble growth, departure, and inrush were explored. The experimental results showed that one bubble formation cycle can be divided into three stages: Waiting, departure, and inrush, as well as the dynamic behaviour of bubble emerging from micro-capillary orifice in a flow channel, were significantly affected by gas flow rate and liquid flow rate. At a higher gas flow rate, the growth time and the departure time were shorter, as well as the departure volume of the leading bubble and the inrush volume of the trailing bubble were smaller, while the transverse longitudinal ratio fluctuated more violently, and the swing amplitude of the bubble centroid was greater. With an increasing liquid flow rate, the growth time, the departure time, and the inrush time shortened, while the departure volume of the leading bubble decreased and the fluctuation of the bubble centroid weakened. These findings are conducive to improving the performance of the equipment by optimizing the design of the aerator to regulate the dynamic behaviour of bubbles.     

Bubble formation in cocurrently upward flowing liquid

The effects of liquid velocity, nozzle diameter, gas chamber volume and gas flow rate on volumes, shapes and growth curves of bubbles formed at a nozzle submerged in a cocurrently upward flowing liquid in a bubble column were experimentally investigated. The bubble volume decreases with increasing liquid flow velocity. The effect of liquid flow velocity on the volume of bubble increases with an increase in the gas flow rate. To simulate bubble formation at a nozzle submerged in cocurrently upward flowing liquid, a revised non-spherical bubble formation model was proposed. Bubble volumes, bubble growth curves and shapes experimentally obtained in this study, as well as in previous experimental studies, are well predicted by the present model.     

Numerical simulation of the mass transfer process of CO2 absorption by different solutions in a microchannel

The flow and mass transfer characteristics of CO₂ absorption in different liquid phases in a microchannel were studied by numerical simulation. The mixture gas phase contained 5 vol% CO₂ and 95 vol% N₂ , and the different liquid phases were water, ethanol solution, 0.2 M monoethanolamine solution, and 0.2 M NaOH solution, respectively. Based on the permeation theory, the distribution of velocity and concentration in the slug flow was obtained by local simulation of flow and mass transfer coupling and was described in depth. The influence of contact time and bubble velocity on the mass transfer of the whole bubble was highlighted. The volumetric mass transfer coefficient on the bubble cap and liquid film, CO₂ absorption rate, and enhancement factor were calculated and analyzed. The results showed that the volumetric mass transfer coefficients of chemical absorption were ~3 to 10 times that of physical absorption and the CO₂ was absorbed more completely in chemical absorption. The new empirical correlations for predicting the mass transfer coefficient of the liquid phase were proposed respectively in physical absorption and chemical absorption, which were compared with the empirical formulas in the literature. The volumetric mass transfer coefficients obtained by predictive correlations are in good agreement with those obtained by simulation in this paper. This work made a basic prediction for CO₂ absorption in microchannel and provides a foundation for later experimental research.     

Methanation in a fluidized bed reactor with high initial CO partial pressure: Part II— Modeling and sensitivity study

A model of a bench-scale methanation reactor was set-up by modifying the classical two-phase model approach and introducing an additional bulk flow from bubble to dense phase to consider the volume contraction of the methanation reaction. The model uses experimentally determined kinetics and hydrodynamic correlations from literature. It was satisfyingly validated by comparing the calculated gas concentration profiles with the experimental data, especially with respect to initial reaction rates and reactor exit concentrations.A sensitivity study with respect to different bubble size correlations, mass transfer rates and considering or neglecting the bulk flow (influence of volume contraction caused by the methanation reaction) was carried out. It showed that the bubble size correlation by Werther and the resulting gas concentration profiles fit the measured data better than the computed gas concentration profiles using the bubble size correlation by Rowe.Neither a variation of the mass transfer coefficient nor neglecting the bulk flow in the fluidized bed model did yield further improvement of the calculated concentration profiles.     

液体通流微小槽道内气泡动力学行为模拟

采用VOF方法,对液体通流微小通道内壁面逸出气泡的形成、生长及脱离运动进行了数值模拟,并讨论了壁面浸润性、液体流速、气体流速对气泡动力学行为的影响.结果表明:气泡生长壁面亲水性增强有利于其从壁面脱离;气泡生长壁面气相覆盖率随壁面接触角的增大而增大;流动阻力因子随壁面接触角的增大而减小.较高的液体流速会导致气泡的脱离时间...     

Influence of Chitosan and Chitosan Derivatives on Hydrodynamics and Mass Transfer in a Bubble Contactor

The behavior of chitosan and two kinds of chitosan derivatives in carbon dioxide absorption in a bubble column contactor is analyzed. The effects of absorption type (physical or chemical), polymer type, concentration, and liquid‐phase physical properties on hydrodynamics (bubble size, gas holdup, and specific interfacial area) and mass transfer (absorption rate and mass transfer coefficient) are evaluated.     

CONVECTIVE HEAT TRANSFER CHARACTERISTICS OF GAS IMPINGEMENT ON SMALL HEATED DEVICE IN LIQUID COOLANT BATH

Heat transfer characteristics of a small heated device have been investigated in a liquid bath with gas jetimpingement as function of gas flow rate,coolant temperature,liquid phsicochemical properties,heat flux,heat source size,ambient pressure and the distance between jet and heated wall.The experimental results show that the agitation of liquid caused by gas jet bubbles increases greatly therate of heat transfer,and the evaporation of coolant near the wall,which was due to the concentration differencebetween gas-liquid interface and bulk gas phase,gives additional enhancement of heat transfer.The rate ofevaporation related to the bubble growth was mathematically formulated.By using the simultaneous heat and mass transfer model,the convective heat transfer coefficient and masstransfer coefficient can be deduced from the experimental results.In addition,the local heat transfer coefficient and the distribution of evaporation heat flux on the smallheated surface are investigated mathematically and experimentally.     

降膜微反应器中CO_2化学吸收过程传质行为

Gas phase mass transfer in falling film microreactors (FFMRs) with the absorption of CO₂ into aqueous solutions of NaOH was investigated. The overall gas-phase mass transfer coefficient increases with NaOH concentration, but decreases as the concentration of CO₂ increases. There exists an entrance effect, hindering the mass transfer, which is caused by the dead volume for gas-phase flow in the gas chamber in FFMRs. The entrance effect has a larger impact in a shorter FFMR owing to the relatively large dead volume with respect to that of gas chamber. A decrease in the depth of gas chamber facilitates the mass transfer process. Therefore, the gas-phase entrance or geometry of the gas chamber should be designed appropriately to reduce the entrance effect and improve the mass transfer.     

装配水平筛板的气升式反应器中气液传质特性的数值模拟

利用Turbulent–Lehr组合模型对装配水平筛板的气升式反应器进行了计算流体力学(CFD)模拟,研究水平筛板对气含率、气泡直径、体积传质系数(kLa)和气液流速的影响。结果表明,筛板对气相的囤积作用和对液相的阻碍作用增加了反应器的整体气含率。筛板对气相的二次均布作用减弱了筛板和液面之间区域的气泡聚并过程,筛板筛孔对气泡的破碎作用产生了大量小于初始直径的气泡,增加了气泡比表面积(a);筛板对液相的阻碍作用提高了筛板附近的气–液相流动速度差,从而提高了该区域的液膜传质系数(kL),强化了反应器内的气液传质效果。     

微通道中气-液-液三相流流型及传质研究

使用双T型微通道,以体积分数为30%的磷酸三丁酯（TBP）的环己烷溶液-乙酸水溶液为萃取体系,研究了不同油水两相流量比及油水两相总流量条件下,气相的引入及气相流量分率α对流型及传质的影响,并获得总体积传质系数k_La与油水两相流量比q、气相雷诺数Re_g、液相平均雷诺数Re_M的关系式。研究结果表明,第1个T型接口处气相的引入所带来的气相剪切作用能促进第2个T型接口处分散相液滴的形成,可使液-液并行流转化为气-液-液三相弹状流;同时,由于气-液-液弹状流具有较高的相接触面积及内循环作用,传质系数k_La得到显著提高。     

Gas holdup and mass transfer in solid suspended bubble columns in presence of structured packings

Electrochemical gas absorption or biotechnical purification processes using structured packing as electrode or as biological support, respectively, may operate in bubble columns in presence of suspended solids. In both systems the knowledge of mass transfer rates from the liquid to the packing is important for the design of equipment. In the present investigation, the fluid dynamic behavior of a simple bubble column and a bubble column containing small size particles, both in presence of structured packing, was studied. Furthermore, mass transfer coefficients between the liquid and the structured packing were obtained by the electrochemical method. The influence of physical properties of the liquid phase, gas flow rate, kind and concentration of the suspended particles on both gas holdup and mass transfer was investigated. Correlations of the experimental data of mass transfer using dimensionless groups were derived and compared to previous correlations. Similarity with a heat transfer expression already used in two-phase systems was found.     

Mass transfer performance of a rotating packed bed equipped with blade packings in removing methanol and 1-butanol from gaseous streams

The removal of methanol and 1-butanol from gaseous streams by absorption with water was investigated in the RPB equipped with blade packings. The overall volumetric gas-phase mass transfer coefficient (K_Ga) for methanol and 1-butanol absorption was observed to increase with the rotational speed, the gas flow rate, and the liquid flow rate. Also, the local volumetric gas-phase mass transfer coefficient (k_Ga) was estimated, and then the portion of the total resistance to mass transfer in gas phase was determined. The result indicated that more than 90% of the total resistance to mass transfer in methanol and 1-butanol absorption was found to be due to the gas phase. Comparison with the conventional packed tower demonstrated that mass transfer efficiency in the RPB equipped with blade packing was higher than that in the conventional packed tower. Consequently, the RPB equipped with blade packings would be an excellent absorber for the removal of alkanols from the exhausted gases.     

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.     

新型气液逆流撞击洗涤喷嘴的优化

针对一种新型气液逆流撞击式洗涤喷嘴,通过冷模实验,采用溶氧法考察了不同结构喷嘴的气液两相传质性能。结合解析率及流型变化,考察了喷嘴出口直径、切向进液口倾角、旋流室收敛段锥角、切向进液口直径、喷口长度5个参数对传质的影响,确定了优选喷嘴的结构尺寸,分析了该优选喷嘴在不同操作条件下(气速、表观液气比和轴切比)的传质效果。结果表明,优选喷嘴在轴切比为0.4~0.6且气速较高时传质效果较好。