液固萃取塔中尼龙6中己内酰胺的外部传质系数

采用固定床半间歇萃取装置在工业生产温度与流速下研究了尼龙6颗粒中己内酰胺(CL)的液固传质过程,基于萃取过程中CL浓度在颗粒中呈现抛物线分布的假设,建立了液固传质过程的外部传质系数模型. 结果表明,温度65~95℃和液相流速0.27~2.71 mm/s时,提高温度与流速均能显著加快CL的液固萃取. 外部传质系数模型适用于描述无因次时间大于0.15的实验数据. 将CL外部传质系数进行无因次量纲化,建立了舍伍德数(Sh)、施密特数(Sc)和雷诺数(Re)间的相互关系,可用于预测尼龙6工业萃取塔中的CL外部传质系数.     

SD型静态混合器压力降的特性分析

借助计算流体力学软件FLUENT5/6,对含有3个流道的螺旋式静态混合器在不同的长宽比和雷诺数下的流动特性进行了数值模拟。模拟结果表明,当螺旋片长宽比为4∶1时该混合器压力降与雷诺数的1.715次方成正比;当雷诺数一定时,压力降与混合元件单元数在双对数坐标下成线性分布规律;压力降随着螺旋叶片长宽比的减小而增大;该混合器的压力降与对应结构的SK型静态混合器基本相同,大约是相同直径和管长的光滑空管压力降的10倍。     

微通道内离子液体萃取硫酸铵水溶液中丁酮肟的研究

酮胺法生产丁酮肟过程中会副产含有丁酮肟的硫酸铵水溶液,需采用合适的方式来萃取回收其中的丁酮肟,而传统萃取方式存在效率低、设备体积大等缺陷,具有过程强化、体积小、易于集成与放大等优点的微化工技术能有效解决此问题。因此,今在微通道内用离子液体进行了硫酸铵水溶液中丁酮肟的萃取研究,系统考察了总流速、水相流速、离子液体相流速、流量比、丁酮肟浓度、硫酸铵浓度、微通道内径等因素对萃取过程的影响。实验测得总体积传质系数介于0.008~1.5 s~(-1),对所测得的总体积传质系数进行关联,发现总体积传质系数在数值上与流量比的1.14次方成正比,与雷诺数的0.19次方成正比,与微通道内径的1.26次方成反比。研究结果为工业上利用微通道萃取硫酸铵水溶液中的丁酮肟提供了相关的工程基础数据。     

矩形微通道内两相流摩擦压降特性及计算方法

使用表面张力不同的纯水和乙醇作为液体,用氮气作为气体,在水平矩形微通道(d_h=0.29 mm)中开展两相流摩擦压降的实验研究,对通道进出口的压力进行了测量。结合流型说明了表面张力对摩擦压降产生的影响,并将实验压降值与均相流模型和分相流模型的预测值进行了对比,结果表明:在低压降区域,均相流模型预测值与实验值符合较好。针对于微小通道提出的分相流模型中,Zhang关系式预测结果与实验值符合稍好,但预测值整体大于实验值。根据实验分析中Chisholm系数C和L-M系数X之间存在的规律,同时考虑分液相雷诺数(Re_L)、邦德数(Bo),对Chisholm关系式进行修正,修正计算式能很好预测实验结果。     

稀土浸出过程溶质传递的格子Boltzmann模拟

采用耦合传质的格子Boltzmann方法模拟风化壳淋积型稀土矿中稀土浸出的溶质传递过程,在验证模型有效性的前提下,获得了稀土矿填充孔隙中流体流动的速度分布和伴随流动过程的溶质浓度分布. 通过考察浸取流速对溶质传递过程的影响,得到最佳浸取流速,约为0.25~0.35 mm/s,使溶质传递效率最高. 浸取流速小于0.2 mm/s导致浸取周期过长、浸取剂消耗量大;浸取流速大于0.4 mm/s引起沟流,导致稀土不能有效地浸出. 此外,模拟所得传质舍伍德数Sh随雷诺数Re的变化关系与经验关系式吻合,表明提出的模型可用于预测稀土浸出过程的溶质传递规律.     

新型旋转填料床强化气膜控制传质过程

转子结构为相互嵌套填料环的新型旋转填料床是基于强化气膜控制传质过程的新型高效传质设备,可适用于受气膜控制的吸收、精馏和低浓度工业气体的净化等过程。分别以化学吸收体系CO2-NaOH和物理吸收体系NH3-H2O测定了不同气量、液气比和超重力因子条件下的有效比表面积a和气相体积传质系数kya,并由此得到气相传质系数ky,对其传质性能进行研究。实验结果表明：a、kya和ky均随着气量、液气比和超重力因子的增大而增大。通过对比可知,新型旋转填料床的气相体积传质系数在相近操作条件下是文献逆流旋转填料床的2倍。并对实验数据进行了回归,拟合出了a、kya和ky分别与气相雷诺数ReG、液相韦伯数WeL和伽利略数Ga之间的关联式。     

滴流床气液界面液相传质系数的研究

在气液并流向下的滴流床中,应用二氧化碳-空气-水系统和氢-空气-水系统进行了滴流床气、液界面液相容积传质系数k_La的研究.在内径为0.042m的床层中分别充填有直径d_p=0.0065、0.00475和0.00154m的玻璃球.气相流速为u_G=0.12-0.56m/s,液相流速u_L=0.003-0.04m/s.容积传质系数k_La与液相物性(Sc数)、填料直径和气液流动情况有关.根据传质情况,可以划分三个流区,它们与按流动情况划分的流区一致.用回归分析方法可以得到下述关联式:滴流区k_Lad_(p~2)/D_A=0.0904Re_(L~0.82)Re_(G~0.55)Sc~0.53(d_p/T)~(0.07)脉动流区 k_Lad_(p~2)/D_A=0.0211Re_(L~0.93)Re_(G~0.76)Sc~0.57(d_p/T)~(-0.12)     

液相介质对水平气液间歇流动的压降影响

研究了水平管内不同液相介质(水、油和不同浓度的CMC溶液)对气液两相间歇流动压降的影响. 实验管道为内径50 mm的透明有机玻璃管,从入口到分离器长约30 m,实验段由2个长3 m的水平管组成. 共记录了320组不同表观流速下的压降信号：油相0.17~1.85 m/s,水相0.17~2.48 m/s,CMC溶液0.17~1.42 m/s,气相0.06~3.40 m/s. 结果表明,液相为牛顿流体(油或水)的气液流动,随着表观气相流速的增大,压降呈增加趋势;非牛顿幂率流体(不同浓度的CMC溶液)的管道流动,当流动指数低于一定值时,压降随气相流量的增加呈降低趋势,并且低于单液相流动的压降. Lockhart-Martinelli模型过高地预测了气-非牛顿幂率流体两相的压降.     

新型旋流传质元件的流体力学性能实验优化

针对一种新型旋流传质元件的溢流管高度和壳体上液相出口位置、面积及数量进行了流体力学性能优化实验研究。在直径500 mm的有机玻璃塔内,以空气-水为实验物系对具有不同壳体结构的传质元件进行了流体力学性能实验。在相同的液相负荷时,实验测定了不同气相负荷条件下传质元件的湿板压降、漏液率及雾沫夹带率。实验结果揭示了元件壳体上不同的液相出口位置和出口面积等参数以及不同的溢流管高度对湿板压降、漏液和雾沫夹带的影响规律。结果表明:当传质元件的溢流管底端距离盲板50 mm,壳体上液相出口位置距离叶片30 mm,液相出口数量为2、总面积为1. 88×10~4mm~2时的传质元件性能最优。     

中空纤维膜无泡曝气试验

对中空纤维膜无泡曝气进行了试验研究,考察了中空纤维膜的高效曝气性能,探讨了水力条件与无泡曝气泡点的关系,以及水力条件和曝气压强对曝气效果的影响。试验表明,无泡曝气泡点的大小与循环流量的大小呈负相关关系;给出了在曝气压强为0.025 MPa时雷诺数对舍伍德数的影响的估计公式;在泡点以下,液相流速一定时,氧的传质系数随曝气压强的增大而增大。     

Gas-phase mass-transfer measurements in a falling-film microreactor

The industrial-scale performance of gas–liquid reactors is difficult to control when very rapid or highly exothermic reactions are involved. Microstructured reactors offer new opportunities for these reactions by enabling precise heat management and accurate control of operating conditions.The present study examines experimentally the gas-phase mass-transfer characteristics of a reactor tool for the characterization of gas–liquid reactions: a falling-film microreactor. A well-known chemical test system, the absorption of sulfur dioxide SO₂ by sodium hydroxide NaOH is employed to determine the characteristics. The measurements of inlet and outlet concentrations in the gas phase enable the mass-transfer coefficient to be determined.The mass-transfer characteristics, in terms of dimensionless Sherwood number Sh_G, are then related to the hydrodynamic characteristics of the gas phase, through the Reynolds number Re_G, and the physico-chemical properties of the reactional system, through the Schmidt number Sc_G. A strong dependence of dimensionless Sherwood number on gas-phase Reynolds number is observed, probably resulting from the specific features of the geometry of the gas-phase inlet.     

Mass transfer coefficient in the eductor liquid-liquid extraction column

In this research gasoil desalting was investigated from mass transfer point of view in an eductor liquid–liquid extraction column (eductor-LLE device). Mass transfer characteristics of the eductor-LLE device were evaluated and an empirical correlation was obtained by dimensional analysis of the dispersed phase Sherwood number. The Results showed that the overall mass transfer coefficient of the dispersed phase and extraction efficiency have been increased by increasing Sauter mean diameter (SMD) and decreasing the nozzle diameter from 2 to 1 mm, respectively. The effects of Reynolds number (Re), projection ratio (ratio of the distance between venturi throat and nozzle tip to venturi throat diameter, R_pr), venturi throat area to nozzle area ratio (R_th-n) and two phases flow rates ratio (R_Q) on the mass transfer coefficient (K) were determined. According to the results, K increase with increasing Re and R_Q and also with decreasing R_pr and R_th-n. Semi-empirical models of drop formation, rising and coalescence were compared with our proposed empirical model. It was revealed that the present model provided a relatively good fitting for the mass transfer model of drop coalescence. Moreover, experimental data were in better agreement with calculated data with AARE value of 0.085.     

Effect of Superimposed Pulsating Flow on Liquid‐Solid Mass Transfer in Fixed Beds

The liquid‐solid mass transfer behaviour of a fixed bed of cylinders has been studied using the dissolution of copper in acidified dichromate solution under pulsating flow conditions. The bed diameter was 100 mm. The depth of the working section was 95 mm and the length and diameter of the cylinders were 19.1 mm. Variables studied were steady flow superficial liquid velocity, and oscillation amplitude and frequency. Data have been correlated as the Sherwood number in terms of Schmidt number and the cylinder Reynolds numbers for steady and oscillatory flow. The form of the correlation permits comparison with literature data for the limiting cases where either of these Reynolds numbers is zero.     

Multiphase mass transport in mini/micro-channels microreactor

This paper describes a computational study of two-phase gas/liquid flow in mini/micro-scale reaction channels at low Reynolds numbers. The direct fluorination of toluene is used as a sample process. We consider two different configurations, a falling film and membrane microreactor. The detailed mathematical model of the processes in these configurations is based on mass and momentum conservation equations, which are solved numerically using the finite element method.

Gas-phase mass transport in both reactor configurations is analysed by means of the mathematical model. For fully developed gas flow a correlation for the gas-phase mass transport is developed in terms of the Sherwood and the relative Reynolds number. It is shown that the flow pattern in this regime and entrance effects strongly influence mass transport from the bulk flow to the reaction plane. The velocity profile for the falling film reactor yields higher Sherwood numbers compared to the membrane reactor. The latter has the advantage over the falling film reactor that the gas and liquid phases are decoupled and operating conditions and channel design can be freely chosen.     

A Simple Approach to Measuring the Gas Phase Heat and Mass Transfer Coefficients in a Bubble Column

A simple experimental approach was developed to measure the gas phase volumetric heat and mass transfer coefficients in a bubble column and a slurry bubble column employing a single gas nozzle. The experimental technique was based on a transfer model that simulates humidification and direct contact evaporation models in the case of a gas bubble rising in a liquid of uniform temperature. The temperature and relative humidity of the inlet and outlet gas in the column are the only measurements required in this technique. Experiments were carried out in a 0.15 m inner diameter column using water as the liquid phase, air as the gas phase, and cation resins of 0.1 mm diameter and a specific gravity of 1.2, as the solid phase. The results showed that, when using solid concentrations in the range of 7–10 wt %, both the volumetric gas‐phase heat and mass transfer coefficients increased with an increase in the gas superficial velocity and were further enhanced by increasing the solid load after a certain minimum superficial velocity had been reached in the column (0.044 m/s in the system used). Increasing the solid load beyond 10 wt %, did not contribute to a further increase in these coefficients. Furthermore, the gas holdup in the column increased with the superficial gas velocity and was further enhanced when the solid‐phase load was in the range of 7–10 wt %. These observations agree well with previously reported findings by other investigators.     

TWO DROP MASS TRANSFER WITH CHEMICAL REACTION-ASYMPTOTIC CASE STUDIES

Mass transfer at very low and moderately high Peclet numbers has been analyzed for two interacting solid spheres and for drops in tandem. In the first case study, where the Peclet and Reynolds numbers approach zero, interactions between two drops with liquid phase chemical reaction affect the mass flux more drastically for gas resistance controlling cases than for liquid resistance controlling cases. The effects of drop size, spacing, and reaction rate on the Sherwood numbers have been considered and the various regimes of gas and liquid side control have been numerically established. The asymptotic value of the average Sherwood number as the interdrop distance approaches infinity is lower for the case of two drops than for two solid spheres, i.e. it was found that ¯Sh² _drops = ¯0.5Sh² _solidspheres, as (dAB/a)→∞

For the case of mass transfer at moderately high Peclet numbers potential flow, i.e. Re→∞, was assumed. This limited analysis indicates that there is no significant difference between the single drop and the two drop cases.     

Heat and mass transfer characteristics in a gas-slurry-solid fluidized bed

The gas-slurry-solid fluidized bed is a unique operation where the upward flow of a liquid-solid suspension contacts with the concurrent up-flow of a gas, supporting a bed of coarser particles in a fluidized state. In the present study we measured the gas holdup, the coarse particle holdup, the cylinder-to-slurry heat transfer coefficient, and the cylinder-to-liquid mass transfer coefficient at controlled slurry concentrations. The slurry particles were sieved glass beads of 0.1 mm average diameter and their volumetric fraction was varied at 0, 0.01, 0.05 or 0.1. The slurry and the gas velocities were varied up to about 12 and 15 cm/s, respectively. The coarse particles fluidized were sieved glass beads of average diameters of 3.6 and 5.2 mm. The individual phase-holdup values were measured and served for use in correlating the heat and mass transfer coefficients. The heat and mass transfer coefficients in the slurry flow, gas-slurry transport bed, slurry-solid fluidized bed and gas-slurry-solid fluidized bed operations can be correlated well by dimensionless equations of a unified formula in terms of the Nusselt (Sherwood) number, the Prandtl (Schmidt) number and the specific power group including the energy dissipation rate per unit mass of slurry, with different numerical constants and exponent values, respectively, to the heat and mass transfer coefficients. The presence of an analogy between the heat and mass transfer from the vertically immersed cylinder in these slurry flow, gas-slurry transport bed and gas-slurry-solid fluidized bed systems is suggested.     

Design and operation of gas–liquid slug flow in miniaturized channels for rapid mass transfer

The influences of operating parameters such as channel size, flow rate, and void fraction on the mass transfer rate in the gas–liquid slug flow are investigated to establish a design method to determine the parameters for rapid mass transfer. From the experimental results, the turnover index, including the slug linear velocity, its length, and the channel size that represents the turnover frequency of the internal circulation flow, is proposed. For PTFE tube in which no liquid film exists in slug flow, a master curve is derived from the relationship between the mass transfer coefficient and the turnover index. For each channel material, the Sherwood number is also roughly correlated with the Peclet number. These correlations make it possible to arbitrarily determine a set of operating parameters to achieve the desired mass transfer rate. However, the turnover index and the Peclet number include the slug length, which cannot be controlled directly. The relationship between the slug length and the operating parameters is also investigated. The slug volume mainly depends on the inner diameter (i.d.) of a union tee. At a fixed union tee i.d., the slug length is controlled through the exit i.d. of the channel connected to the union tee and the void fraction. Thus, the final slug length depends on the union tee and exit channel inner diameters. At low flow rates, the gas and liquid collision angle is significant in determining the slug length.     

射流鼓泡反应器中液相体积传质系数的测定

羰基合成反应一般采用射流鼓泡反应器,该类反应器气液混合的方式采用射流而非机械搅拌,其主要优点是结构简单、制作简便、维护费用低。研究该类型反应器的传质系数对于其设计、优化及放大操作均具有重要意义。本研究采用缩颈式圆形喷嘴,以动态溶氧法对射流鼓泡反应器内的液相体积传质系数进行测定,考察了表观气速、射流雷诺数对液相体积传质系数的影响。研究发现,随气速增大液相体积传质系数的变化规律为先增大而后保持不变。维持表观气速不变,随雷诺数增加液相体积传质系数增大,但当表观气速小于0.0012 m/s时,雷诺数对传质改善较小。建立了液相体积传质系数的经验关联式,当气体输入功率占总功率56%时,液相体积传质系数最大,气体鼓泡和液体射流的协同作用最强。     

Effect of the viscosity ratio on mass transfer from a fluid sphere at low to very high Peclet numbers

The effect of the viscosity ratio on mass transfer from a fluid sphere is examined in this paper. Numerical solutions of the Navier-Stokes equations off motion and the equations of mass transfer have been obtained for the unsteady state transfer from a fluid sphere moving in an unbounded fluid medium of different viscosity. The effects of the viscosity ratio and the flow on the concentration profiles were investigated for Reynolds number, viscosity ratio and Péclet number ranges of 0?Re?400, 0?κ?1000 and , respectively. The local and average Sherwood numbers are also presented graphically. The steady state results show that the average Sherwood number is increasing as Peclet number increases for a fixed viscosity ratio. However, for a fixed Peclet number, the average Sherwood number is decreasing as the viscosity ratio increases and reaches a limit value corresponding to the average Sherwood number for a solid spherical particle. From the numerical results, a predictive equation for the Sherwood number in terms of the Peclet number, the Reynolds number and the viscosity ratio is derived.