Prediction of mass transfer coefficients in an asymmetric rotating disk contactor using effective diffusivity

Mass transfer characteristics have been investigated in a 113 mm diameter asymmetric rotating disk contactor of the pilot plant scale for two different liquid–liquid systems. The effects of operating parameters including rotor speed and continuous and dispersed phase velocities on the volumetric overall mass transfer coefficients are investigated. The results show that the mass transfer performance is strongly dependent on agitation rate and interfacial tension, but only slightly dependent on phase flow rates. In this study, effective diffusivity is used instead of molecular diffusivity in the Grober equation for estimation of dispersed phase overall mass transfer coefficient.The enhancement factor is determined experimentally and there from an empirical expression is derived for prediction of the enhancement factor as a function of Reynolds number. The predicted results compared to the experimental data show that the proposed correlation can efficiently predict the overall mass transfer coefficients in asymmetric rotating disk contactors.

Use of axial dispersion model for determination of Sherwood number and mass transfer coefficients in a perforated rotating disc contactor

The mass transfer process in a perforated rotating disk contactor(PRDC) using a toluene-acetone-water system was investigated.The volumetric overall mass transfer coefficients are calculated in a PRDC column.Both mass transfer directions are considered in experiments.The influences of operating variables containing agitation rate,dispersed and continuous phase flow rates and mass transfer in the extraction column are studied.According to obtained results,mass transfer is significantly dependent on agitation rate,while the dispersed and continuous phase flow rates have a minor effect on mass transfer in the extraction column.Furthermore,a novel empirical correlation is developed for prediction of overall continuous phase Sherwood number based on dispersed phase holdup,Reynolds number and mass transfer direction.There has been great agreement between experimental data and predicted values using a proposed correlation for all operating conditions.

A convenient method for measuring gas-liquid volumetric mass transfer coefficient in micro reactors

The research on gas-liquid multiphase reactions using micro reactors is becoming increasingly widespread, given their excellent mass transfer performance. Establishing an accurate and reliable method to measure the gas-liquid mass transfer performance of micro reactors is crucial for evaluating and optimizing the design of micro reactor structure. In this paper, the physical absorption method of aqueous solution-CO_(2) and the chemical absorption method of sodium carbonate solution-CO_(2) were proposed. By analyzing the chemical reaction equilibrium during the absorption process, the relationship between the mass transfer of CO_(2) and the solubility of hydroxide ions in the solution was established, and the total gas-liquid mass transfer coefficient was immediately obtained by measuring the p H value. The corresponding testing platform and process have been established based on the characteristics of the proposed method to ensure fast and accurate measurement. In addition, the chemical absorption method takes into account temperature factors that were not previously considered. The volumetric mass transfer coefficient measured by these two methods is in the same range as those measured by other methods using the same microchannel structure in previous literature. The methods have the advantages of low equipment cost, faster measurement speed, and simpler procedures, which can facilitate its wide application to the evaluation of the mass transfer performance and hence can guide the structure optimization of microchannel reactors.

FLOW BEHAVIOR AND MASS TRANSFER IN THREE-PHASE EXTERNAL-LOOP AIRLIFT REACTORS WITH LARGE PARTICLES

The flow behavior and mass transfer in a three-phase external-loop airlift reactor can be improved by adding large particles. The mass transfer and liquid dispersion behavior for a three-phase external-loop reactor with large particles are studied in terms of the effect of the diameter and loading of the large particles on the liquid dispersion coefficient and mass transfer coefficient, The results showed that increasing the diameter or loading of the large particles tend to decrease dispersion and intensify mass transfer, and that an increase in the diameter of the large particles remarkably decreases the particle loop rate, while the effect of fine particles is much less notable.

Mass transfer between bubbles and the dense phasein gas fluidized beds

Mass transfer between a bubble and the dense phase in gas fluidized beds of Group A and Group B particles was proposed based on previous experimental results and literature data. The mass transfer coefficient between bubbles and the dense phase was determined by kbe = 0.21 db. A theoretical analysis of the mass transfer coefficient between a bubble and the dense phase using diffusion equations showed that the mass transfer coefficient between a bubble and the dense phase is kbe α εmf√ub/db in both three- and two-dimensional fiuidized beds. An effective diffusion coefficient in gas fluidized beds was introduced and correlated with bubble size as De = 13.3db2.7 for Group A and Group B particles. The mass transfer coefficient kbe can then be expressed as kbe = 0.492εmf√ubdb1.7 for bubbles in a three-dimensional bed and kbe = 0.576εm√ubdb1.7 for bubbles in a two-dimensional bed.

金属板波纹规整填料在CO_2吸收塔中的传质性能

开发高效规整填料,有利于降低CO2捕集过程的能耗和成本。文章在直径200 mm的填料塔中,使用氢氧化钠水溶液吸收空气中微量CO2的方法研究了金属板波纹规整填料的传质性能,测定了具有不同几何参数的规整填料的有效传质面积。实验结果表明:随着气液相流量的增加,有效传质面积逐渐增大,且气相流量的影响相对较大。当气液流量达到一定值时,有效传质面积会超过填料的比表面积。而填料几何参数对有效传质面积也有较大的影响。当波纹倾角α=30°,波纹齿顶角β=75°时,有效传质面积较大。而且α对有效传质面积的影响较β大。在同时考虑气液相流速的影响的基础上,文章提出了新的有效传质面积的关联式,计算值与实验值吻合较好。

三相下喷式环流反应器的传质性能

在三相非牛顿型流体体系中，对下喷式环流反应器传质特性进行了实验研究。讨论了表观气速、能量耗散速率、导流筒直径与反应器直径比、喷嘴直径、导流筒下端距反应器底部的距离、固体装填量、羧甲基纤维素钠（ＣＭＣ）溶液浓度及其流变特性对它的影响。实验结果表明，容积传质系数随表观气速和能量耗散速率的增加有所增加，在实验条件下，发现最优的导流筒直径与反应器直径比在０．４～０．４５这一范围、固体装填量大约为３％（体积百分比）、导流筒下端距反应器底部的距离为０．０８ｍ左右。同时提出了容积传质系数的经验关联式。

第二液相对气液二相体系传质的影响

以CO2气体-K2CO3/KHCO3水溶液吸收过程为研究体系,用酸解法测量气体被吸收的速率,通过对比试验考察了加入第2液相(有机相)对体系传质速率的影响。经过试验研究证明,第2液相的加入对气液传质过程的影响程度与加入的物质有关,在试验条件下甲苯对体系强化作用高于异辛醇和庚烷对体系的强化作用。当第2液相加入量较小时,随加入量的增加,其对气液传质过程的促进作用增强,但当第2液相加入量较大时,这种作用则不明显。同时第2液相对传质作用的影响与流动场有关,增加流动场的搅动有助于强化气液传质作用。

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.

气液界面传质过程Rayleigh对流模拟的格子Boltzmann方法

浓度梯度导致的Rayleigh对流是一种通常在传质过程中观察到的界面现象.为了模拟乙醇吸收CO2气液传质过程中界面传质引发的Rayleigh对流现象,提出了描述界面扰动的随机扰动模型,并建立了带有双分布模型的二维格子Boltzmann方法(LBM).模拟二维液相Rayleigh对流过程中,假设界面上CO2浓度为常数.通过模拟研究,确定了随机扰动模型的2个参数:局部扰动概率P和浓度扰动大小ρD.模拟结果表明,当0<ρD≤10-9,kg/m3、10-6≤P≤10-1时,平均液相传质系数存在一个稳定值:(1.09±0.02)×10-5,m/s.通过考察浓度分布结构,分析了Rayleigh对流的时空演化过程.根据模拟结果定义并计算了传质增强因子,其证明了Rayleigh对流能够有效地强化界面传质.

气液固三相循环流化床气液传质行为

气液固三相流化床反应器在石油化工、湿法冶金、环境工程和煤的液化等工业领域得到了广泛应用,其基础研究也取得了很大进展.但是。

三相逆流湍动床气液传质性能的研究

由空气-水（清水/废水）-中空玻璃珠构成三相体系，在表观气速0．53～10mm·s^-1、固含率为0～0．3、表观液速0～0．2mm·s^-1的条件下，采用溶氧仪研究了三相逆流湍动床的气液传质性能，考察了操作参数和液体性质对液相容积传质系数kLa的影响。结果表明，在所试条件下，kLa为0．0456～1．414min^-1。kLa随着表观气速和表观液速的增加而增加，随着固含率的增加先增加后减小，0．05～0．08为反应器传质的最优固含率条件。液体性质对kLa有重大影响，高浓度模拟废水和工业废水中的kLa比清水中的kLa分别减小39．0％和50．9％。研究结果可为后续逆流湍动床废水生物处理过程分析与模拟提供传质基础数据。

用填料萃取塔时青霉素 G 钠盐在双水相系统中的传质性能

以填料塔为萃取设备，对青霉素Ｇ钠盐在ＰＥＧ－（ＮＨ４）２ＳＯ４双水相系统中的传质性能进行了探索性的研究，测定了分散相含率εＤ和分散相体积传质系数ｋＤａ随分散相流率ＶＤ的变化规律．并用修正的Ｈａｎｄｌｏｓ－Ｂａｒｏｎ模型对实验数据进行关联．

大型液相色谱分离过程参数辨识新方法

本文提出大型液相色谱分离过程流体轴向扩散系数、吸附相平衡常数和总传质系数参数辨识模型,用惰性物为示踪剂扰动应答实验技术和色谱测量技术测定参数。结果表明:在轴向扩散中,涡流扩散占主导地位;轴向扩散系数随流体流速以及装填密度的增大而增大;相平衡常数比总传质系数有较高灵敏度;葡萄糖果糖的相平衡常数随温度的升高而降低,而总传质系数随流体流速和温度的增大而增大;得到理论流出曲线与实验流出曲线一致的结果。

自吸式反应器的数值模拟及在酵母发酵中的应用

采用计算流体力学(CFD)模拟和酵母发酵实验相结合的方法,研究自吸式反应器内的气液两相流动及传质。基于对自吸式反应器内流体流动、气液相际传质的研究,采用加置气体分布器的方法强化自吸式反应器内流体力学传递性能,并将数值模拟结果应用于酵母发酵。结果表明:在相同的培养条件下,加装气体分布器的自吸式反应器培养酵母比无气体分布器的自吸式反应器产率平均提高23.64%。

填料塔中牛血清清蛋白在聚乙二醇-硫酸铵双水相系统中的传质特性

研究了填料塔中牛血清清蛋白在聚乙二醇－硫酸铵双水相系统中的传质特性，测定了分散相含率和传质系数，用修正的Ｈａｎｄｌｏｌｓ－Ｂａｒｏｎ模型对实验数据进行关联，得到了相应的关联式，关联值与实验值相比，偏差小于５％。

并流降膜塔液相传质系数实验研究

水吸收含１０％ＣＯ２的混合气为体系，测定了并流降膜塔中液相传质系数与气液相流量的关系。液相传质系数与液相流量基本呈线性关系。在较低气相流量情况下，液相传质系数ｋＬ随气相流量的增加而增大，但当气相流量超过某一定值时，随着气相流量的增加反而减小。

浸没式膜生物反应器内膜面传质特性实验

应用粒子图像测速(PIV)技术测试膜面附近的气液两相流动力学特性,在6种不同曝气强度条件下,测试得到膜面附近的液相流场数据,并计算得到膜面传质系数、浓差极化边界层厚度以及膜面切向应力等膜面传质特性参数。结果表明,曝气强度和液相速度对膜面传质特性的影响较大,在一定范围内增加曝气强度可以使得膜面传质特性加强。本文的研究结果为膜生物反应器系统的优化设计提供了研究经验和实验数据。

三相连续环流反应器中氧的液相传质过程

在空气-水-玻璃珠三相连续操作环流反应器中,利用动态溶氧方法研究了表观气速(Ug=0.01～0.13m/s)、进料浆速(USL=0.001～0.011m/s)、浆相质量固含率(εs=0～30%,ω)和固相颗粒大小(dp=59,200μm)对环流反应器内氧的液相传质性能的影响.结果表明,在考察范围内,环流反应器传质系数随表观气速增大而增大,受进料浆速变化的影响较小,随浆相固含率增大呈现先增大后减小的趋势,但在高固含率下(εs≥10%,ω)的影响不显著;随固相颗粒粒径增大而减小.同时得到了液相体积传质系数的经验关联式.

火炮装药床中气—固相间对流换热系数的实验研究

本文采用萘升华质/热比拟法,对填充床内气体与颗粒之间的对流换热系数进行了实验研究。试样模仿炮用发射药粒,直径d=7、10、13mm,长径比约为l/d=2.0。以颗粒当量直径d_p计算的雷诺数Re_(?)=3 500～88 200,空隙率ε=0.450～0.457。床径D=100mm,床高H=70、100mm。对4种床层81个试验点进行了拟合,得到努塞尔特数的拟合式(4.7)。针对火炮膛内工况进行实验研究,本文尚属首例。