旋转填充床内高黏介质脱挥过程的传质模型(英文)

A mass transfer model for devolatilization process of highly viscous media in rotating packed bed(RPB) was developed based on penetration theory and mass conservation.Before establishing the model,some mass transfer experiments of thin film were conducted in a designed diffusion cell including vacuum and feeding system. In this study,acetone was used as the volatile organic compound(VOC) and syrup as the highly viscous media.The thickness of thin film was changed by using different liquid distributor.It was found that bubbling played an important role in the devolatilization.The correlation of diffusion coefficient of acetone in highly viscous dilute solution was proposed.The relative error between predicted and experimental data was within the range of ± 30% for diffusion coefficient of acetone in syrup.A comparison of experimental data of RPB with model indicated that the relative error was within ± 30% for efficiency of acetone removal.     

从超音速蒸汽喷嘴到过冷水直接接触冷凝的数值模拟(英文)

The phenomenon of direct-contact condensation,used in steam driven jet injectors,nuclear reactor emergency core cooling systems and direct-contact heat exchangers,was investigated computationally by introducing a thermal equilibrium model for direct-contact condensation of steam in subcooled water.The condensation model presented was a two resistance model which takes care of the heat transfer process on both sides of the interface and uses a variable steam bubble diameter.The injection of supersonic steam jet in subcooled water tank was simulated using the Euler-Euler multiphase flow model of Fluent 6.3 code with the condensation model incorporated. The findings of the computational fluid dynamics(CFD) simulations were compared with the published experimental data and fairly good agreement was observed between the two,thus validating the condensation model.The results of CFD simulations for dimensionless penetration length of steam plume varies from 2.73-7.33,while the condensation heat transfer coefficient varies from 0.75-0.917 MW·(m 2 ·K) -1 for water temperature in the range of 293-343 K.     

基于GAMs和Bootstrap的生化过程建模和故障监控(英文)

Fault monitoring of bioprocess is important to ensure safety of a reactor and maintain high quality of products. It is difficult to build an accurate mechanistic model for a bioprocess, so fault monitoring based on rich historical or online database is an effective way. A group of data based on bootstrap method could be resampling stochastically, improving generalization capability of model. In this paper, online fault monitoring of generalized additive models (GAMs) combining with bootstrap is proposed for glutamate fermentation process. GAMs and bootstrap are first used to decide confidence interval based on the online and off-line normal sampled data from glutamate fermentation experiments. Then GAMs are used to online fault monitoring for time, dissolved oxygen, oxygen uptake rate, and carbon dioxide evolution rate. The method can provide accurate fault alarm online and is helpful to provide useful information for removing fault and abnormal phenomena in the fermentation.     

基于符号有向图与定性趋势分析的化工过程故障诊断方法(英文)

In the past 30 years, signed directed graph (SDG), one of the qualitative simulation technologies, has been widely applied for chemical fault diagnosis. However, SDG based fault diagnosis, as any other qualitative method, has poor diagnostic resolution. In this paper, a new method that combines SDG with qualitative trend analysis (QTA) is presented to improve the resolution. In the method, a bidirectional inference algorithm based on assumption and verification is used to find all the possible fault causes and their corresponding consistent paths in the SDG model. Then an improved QTA algorithm is used to extract and analyze the trends of nodes on the consistent paths found in the previous step. New consistency rules based on qualitative trends are used to find the real causes from the candidate causes. The resolution can be improved. This method combines the completeness feature of SDG with the good diagnostic resolution feature of QTA. The implementation of SDG-QTA based fault diagnosis is done using the integrated SDG modeling, inference and post-processing software platform. Its application is illustrated on an atmospheric distillation tower unit of a simulation platform. The result shows its good applicability and efficiency.     

旋转填充床中沉淀过程的模型及实验验证(英文)

A mixing-precipitation model based on the modified coalescence-redispersion model was presented to describe the flow, mixing, nucleation and growth in a rotating packed bed (RPB). The model was coupled with population balance, mass balance and crystallization kinetics. It predicted well the influence of coalescence probability, which represents the mixing intensity among drop-lets, on the particle number density, supersaturation and mean particle size of the produced precipitates. The effects of the radial thickness of packing, liquid flow rate and rotating speed on the product particle size were also investigated. The results indicate that the needed radial length of packing is short for sparingly soluble substance precipitation (about 40-50 mm in this work), and the mean particle size of precipitates decreases with the increase of rotating speed and liquid flow rate, respectively. The validity of this model was verified by experiment on BaSO4 precipitation in RPB.     

非牛顿流体中气泡上升及聚并过程中液相侧浓度场的数值模拟(英文)

On the basis of Navier-Stockes equation and convection-diffusion equation, combined with surface ten-sion and penetration models, the equations of moment and mass transfer between bubble and the ambient non-Newtonian liquid were established. The formation of a single bubble from a submersed nozzle of 1.0 mm di-ameter and the mass transfer from an artificially fixed bubble into the ambient liquid were simulated by the volume- of-fluid (VOF) method. Good agreement between simulation results and experimental data confirmed the validity of the numerical method. Furthermore, the concentration distribution around rising bubbles in shear thinning non-Newtonian fluid was simulated. When the process of a single ellipsoidal bubble with the bubble deformation rate below 2.0 rises, the concentration distribution is a single-tail in the bubble’s wake, but it is fractal when the bubble deformation rate is greater than 2.0. For the overtaking of two in-line rising bubbles, the concentration dis-tribution area between two bubbles broadens gradually and then coalescence occurs. The bifurcation of concentra-tion distribution appears in the rear of the resultant bubble.     

基于时段过渡分析的多时段间歇过程质量预测(英文)

Batch processes are usually involved with multiple phases in the time domain and many researches on process monitoring as well as quality prediction have been done using phase information. However, few of them consider phase transitions, though they exit widely in batch processes and have non-ignorable impacts on product qualities. In the present work, a phase-based partial least squares (PLS) method utilizing transition information is proposed to give both online and offline quality predictions. First, batch processes are divided into several phases using regression parameters other than prior process knowledge. Then both steady phases and transitions which have great influences on qualities are identified as critical-to-quality phases using statistical methods. Finally, based on the analysis of different characteristics of transitions and steady phases, an integrated algorithm is developed for quality prediction. The application to an injection molding process shows the effectiveness of the proposed algorithm in comparison with the traditional MPLS method and the phase-based PLS method.     

有限元方法求解化学气相淀积反应器模型(Ⅱ)——热壁反应器模型及反应器中流动及传递过程的分析

分析了热壁化学气相淀积反应器在流型、温度和浓度分布以及淀积速率等方面与冷壁反应器的异同,探讨了流动特性、传递过程和反应器几何尺寸对淀积过程的影响,为淀积不同薄膜时反应器的选型及设计提供了方法和依据.     

Efficiency-based nonequilibrium modeling of industrial-scale multicomponent distillation columns

An efficiency-based nonequilibrium model is proposed to simulate two industrial distillation columns. In this model, the behavior of trays is studied by considering the mass transfer at interphase. The interphase mass transfer is simply evaluated by the simultaneous solution of the vapor material balance equation and the definition of the Murphree efficiency. A MATLAB code is developed to implement the simulation procedure. For verification, the product compositions and plate temperatures are compared with the reported experimental data. The discrepancy of the experimental and simulation results is about 0.5% and 20% for the temperature and the product compositions for both columns, respectively.     

萃取精馏的计算传质学模拟与实验验证

提出了萃取精馏过程模拟的计算传质学方法,并针对以N-甲基吡咯烷酮(NMP)为溶剂分离苯和噻吩的萃取精馏过程进行了模拟计算。在散堆填料实验塔内进行了相同的萃取精馏实验,得到了萃取精馏塔内浓度分布。将模拟计算结果与实验结果进行比较表明,提出的计算传质学方法能够有效预测萃取精馏塔内浓度和速度分布,为萃取精馏过程设计提供依据。     

外场作用下多组分质量传递Maxwell-Stefan方程及其应用：电场作用下球形颗粒中的扩散

Fick扩散定律只能用于没有外场作用下的二组分扩散过程,Maxwell-Stefan（MS）方程适用于外场作用下多组分系统中的质量传递过程。阐述了MS方程的物理意义,并由此将外场作用下普遍化MS方程的表达式改写为清晰且易于使用的形式。给出了在MS方程中常用的外场作用力的数学形式。Fick扩散定律是MS方程在没有外场作用下对二元理想流体扩散的应用;MS方程对离心分离和电解质扩散等过程的描述比传统的描述方法更全面。利用MS方程导出了欧姆定律,利用该结论可以通过测量电导率计算带电粒子的扩散系数。利用MS方程研究了电场作用下球形颗粒中的扩散过程,结果表明,该方程可以对电场强化质量传递过程给出有效描述。MS方程为外场作用下的质量传递过程提供了一种有效的理论研究方法。     

气液传质理论研究进展

文内对气液传质的理论研究进行了评述，并预测了未来的发展方向     

Modeling the axial distribution of mass transfer coefficient in an agitated-pulsed extraction column

The dispersed phase holdup and drop size in solvent extraction columns vary along the column height and this affects the mass transfer coefficient and interfacial area. In this article, mass transfer study was performed experimentally using a 25 mm diameter agitated pulsed column. The axial distribution of mass transfer coefficient was determined by coupling population balance equation and axial dispersion model by taking the longitudinal variation in hydrodynamic performance into consideration. Feasibility of different mass transfer models in predicting concentration profiles was evaluated and a novel correlation based on effective diffusivity was developed. The results showed that both overall and volumetric mass transfer coefficients have significant change along the column height and greatly depends on the agitation speed and pulsation intensity. Increasing dispersed phase velocity also augments the overall mass transfer coefficient. The maximum number of transfer unit was measured to be 10 m⁻¹ at agitation speed of 1000 rpm.     

多溢流大型塔板的计算传质学

利用计算传质学方法研究了直径12.6 m的四溢流大型塔板上液相流动结构对塔板效率的影响,建立了描述多溢流塔板上液相流动和传质状况的理论化计算模型。应用该模型,研究了传统等鼓泡面积设计方法条件下单块塔板的速度场和浓度场。结果表明,所模拟四溢流塔板的左侧翼塔板出现返流区,而右侧翼塔板流动结构相对均匀未出现返流区。为进一步优化塔板结构,提高传质效率,对左侧翼塔板提出了加设导流板的改进结构。计算结果表明,改进的塔板结构在一定程度上改善了塔板上液相的流动结构,使得塔板效率较传统设计方法提升了4.53%～9.22%（当Q₁/Q₂=［0.5,1.5］时）。     

气液液三相体系中的气液传质特征

选取CO2-K2CO3/KHCO3为吸收体系,次氯酸钠为催化剂,甲苯、异戊醇为第2液相,应用Danckwerts图来同时确定液侧传质系数KL和界面面积a,通过实验研究了分散第2液相的加入对气液传质的影响。实验结果表明,随着分散相体积分数φ(1%—10%)的增大,或分散相形成的液滴直径的减小,以及传质组分在分散相和连续相中溶解度的比值m(即传质组分在实验体系的分配系数)增加,或在二相间的相对扩散系数增加时,可显著增强气液传质,为气液液三相体系的系统化研究提供了实验依据。     

规整填料塔多元蒸馏过程混合型模型的模拟

填料塔精馏过程的模拟设计大多采用平衡级模型,但由于单一板效率值的难以确定,很多场合模拟很不成功;而新提出的非平衡级模型认为塔内传质传热均处于非平衡状态,由于方程数和经验性参数多,模型求解非常困难。文章针对规整填料的特点,建立了规整填料塔蒸馏过程的一种混合型模型,模型的主要特征是认为气液二相传质处于不平衡状态,而传热处于平衡状态。模型建立在实际填料基础上,既舍去传统的平衡级模型不确定性,又省略了非平衡级模型中复杂的经验性传热系数和液相传质系数的计算。模型计算值和实验值符合较好,也证实混合型模型既反映实际,又使模型求解变得相对容易。     

Dynamics of droplets and mass transfer in a rotating packed bed

To do further research on the mass‐transfer mechanism in rotating packed bed (RPB), dynamics of droplets in a RPB are studied by an analytical approach combined with a series of laboratory measurements. Based on the results of the fluid dynamics, mathematical models of mass‐transfer coefficient and mass‐transfer process in RPB are proposed, respectively. Mass‐transfer experiments in RPB are also carried out using ethanol–water solution. By comparison, the results of simulation agree well with that of the experiment, which demonstrate that both hydrodynamic model and mass‐transfer models can better describe the real conditions of RPB. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2705–2723, 2014     

A new model for mass transfer in direct contact membrane distillation

The mass transfer process in direct contact membrane distillation (DCMD) for three kinds of membranes was measured. Water fluxes at different temperatures and the membrane distillation coefficients (MDC) for each membrane were obtained directly from experimental data. The fact that the MDC values of membranes with larger pore size increase with temperature indicates that Poiseuille flow plays an important role in the process of mass transfer through the membrane. Based on this conclusion, a three-parameter model, named the Knudsen diffusion-molecular diffusion-Poiseuille flow transition (KMPT) model, was developed to predict MDC and water flux for membrane distillation. The parameters of the KMPT model for each membrane employed in this study, by which MDC at various temperatures can be determined, were evaluated by a nonlinear regression. The values of MDC and water fluxes for each membrane predicted by KMPT model agree well with that obtained directly from the experiment results. A large contribution of Poiseuille flow to mass transfer was observed and can be attributed to the distribution of large pores in the membranes. The KMPT model also provides a method for estimation of the effect pore size using the ratio of the MDCs; the ratio of the Poiseuille flow to molecular diffusion MDC provides the best estimation.