Modeling of a process for removal of metal ions by electromigration and electrodeposition

A mathematical model for the removal of impurities of the metal ions of Fe, Ni, and Cu from hard chromium plating solution by electromigration and subsequent electrodeposition has been developed and presented. Experimental data for the metal removal at 45°C and constant cell voltage using o‐phosphoric acid as the catholyte are presented. Up to 36% iron and 29% nickel removal is obtained over about 25 h. The copper removal rate is observed to be approximately four times greater than the rate of nickel removal. The experimental data were found to closely match results predicted from the model developed. The inherent model parameters such as mobility, diffusivity, mass transfer coefficient and metal deposition rate constants were estimated. The calculated values of these parameters are found to be in good agreement with the published data.     

盘式连续干燥器的传质传热模型

建立了盘式连续干燥器内加热盘面物料的传质模型,给出了干燥器内料环高度、盘面积料量及干燥时间的计算方法.应用颗粒传热理论和扩散理论,导出了每道料环的传热计算公式,由该迭代公式可逐步计算出每道料环的出料温度、出料湿含量及干燥速率.扩散理论中的惟一经验参数——搅拌参数N_mix,在本模型中可由不同进料工况下的多组实验数据加以确定.最后给出了应用该模型进行计算的实例,结果表明,理论计算值与实测值吻合较好,误差一般在20%以内.     

Velocity of elastic waves in porous ceramic materials: influence of pore structure

Abstract

A review has been undertaken of recently published data on ultrasonic velocity-porosity for a variety of porous ceramic materials, including information on pore structure. These experimental data have been compared with data calculated using a spheroidal pore model incorporating information on pore volume fraction, shape, and orientation. Good agreement is obtained between experimental and calculated values, especially when fractional porosity is less than about 0·25, even when a single 'effective' pore shape is employed in the calculation. The agreement improves if a different pore shape for each porosity level (point by point analysis) is used. The predictive ability of the spheroidal pore model is thus demonstrated.     

An investigation into a carbon burnout kinetic model for oxy-coal combustion

This paper investigates coal char burnout kinetics in the oxygen-enriched environments of oxy-coal combustion. The Carbon Burnout Kinetic model (CBK) developed by Hurt et al. was used as the basic model for air-coal combustion and a modified version for oxy-coal combustion. In order to assess the performance of the original CBK model published experimental data from standard char combustion studies at near-atmosphere and elevated pressures were used. The results of the evaluation suggested that the modified model can be utilized for oxy-coal applications. The modifications include the integration of Langmuir-Hinshelwood kinetic rate mechanisms for C-CO₂ and C-H₂O reactions and the effects of CO and H₂ concentration on these reactions. The modified code is validated using published experimental data. It is shown that using this modified code, the burnout prediction in both N₂ and CO₂ environments has improved significantly. Computed results of Loss on Ignition (LOI) in a 1 MW_th pilot scale combustion test facility are compared with experimental data.     

CFD Modeling of a Spouted-Bed Dryer Hydrodynamics

Abstract

A hydrodynamic model based on continuity and conservation equations was used to predict flow behavior in a spouted-bed dryer with a draft tube. The Eulerian-Eulerian multi-fluid modeling approach was applied to predict a gas–solid flow behavior. The model was qualitatively validated and the results of simulations were compared with the experimental data published by various researchers. The model predicts flow behavior well with fluctuations, circulations of phases, and cluster formations in the loading region, as was observed in experiments. The predicted solids circulation rate and the fraction of gas bypassing were close to experimental values published for various systems. The coarse 2D axisymmetric grid, used in simulations, can handle the main process dependencies with a sufficient accuracy for engineering calculations.     

Method of calculating the bed combustion of a solid fuel coke residue

An approximate method of solving the steady-state problem of the bed combustion of a solid fuel coke residue is proposed. The method is based on splitting the initial problem into thermal and chemical problems. The former represents the problem on the hydrodynamics and heat transfer in a blown heat-generating granular bed. The latter is the problem on the chemical conversion of a mixture of reactants in a specified temperature field. These auxiliary problems are combined into an iteration cycle to match their solutions. The model problem on the combustion of a milled peat coke residue was calculated for the cocurrent and countercurrent process schemes. The bed combustion of coke is calculated for the experimental conditions published in the literature. The calculated results are compared with the experimental data obtained under these conditions.     

Theoretical Drying Model of Single Droplets Containing Insoluble or Dissolved Solids

A literature survey of published single-droplet drying models has exposed their various shortcomings. An advanced theoretical model of drying of single droplets, containing either insoluble or dissolved solids, has been developed and numerically solved. The validation of the developed model has been accomplished by comparison of the predicted temperature and mass histories with published experimental data for slurries of silica and skim milk solution under different conditions. The results of simulations showed a good agreement between the calculated curves and experimental points in all case studies.     

CFD study of solids concentration in a fluidised-bed coater with variation of atomisation air pressure

The solids volume fraction inside a tapered fluidised bed coater was simulated with the use of an Eulerian computational fluid dynamics (CFD) model with atomisation nozzle sub-model. The drag force, describing momentum transfer between the gas and solid phases was calculated using the drag model proposed by [1]. In order to account for the particle size distribution of the fluidised solid materials, a 4-phase Eulerian model was used. The model-predicted results for different atomisation air pressures were verified using published experimental data [2]. It was shown that the model proved to be highly sensitive to changes in the fluidisation air flow rate with regard to the model-predicted solids volume distribution.     

Mathematical model for growth process of a recombinant yeast having saccharification and fermentation activities

A mathematical model for direct alcohol fermentation from starch was proposed using an amylase‐producing recombinant yeast, Saccharomyces cerevisiae SR93. This model consisted of the reaction rate equations for glucoamylase synthesis in the recombinant yeast, starch degradation by a glucoamylase, cell growth, production of glucose, and production of ethanol. The rate of glucoamylase synthesis was expressed on the basis of the diauxic growth model that represents catabolite repression and enzyme induction. The rate of starch degradation was expressed on the basis of the enzymatic hydrolysis model representing the change of structure resulting from starch degradation. The calculated values were in satisfactory agreement with the experimental data in a batch culture of direct alcohol fermentation from starch using S cerevisiae SR93. Furthermore, the calculated values obtained by changing only one parameter concerning the synthesis rate of glucoamylase were in satisfactory agreement with the experimental data using another recombinant yeast, S cerevisiae SR96. Copyright © 2003 Society of Chemical Industry     

THE TWO-THIRDS POWER MODEL FOR PREDICTING DIFFUSION COEFFICIENTS IN LIQUIDS

Most of the models found in the literature for predicting diffusion coefficients in liquids take the viscosity of the solution as inversely proportional to the diffusivity. A model (previously derived for sucrose-water system)which considers the viscosity raised to the two-third power, is evaluated here using published data for the Benzene—Cylohexane, Ethanol-Water and Acetone-Chloroform systems. These results, and results for the sucrose-water system are compared with the experimental values, and with those obtained using the Hartley—Crank equation. Better agreement with the experimental values at low and in the middle of the concentration range was found when diffusivities were calculated using the model proposed than when using the Hartley-Crank equation.     

Two layer heat transfer model for supercritical fluid flow in a vertical tube

Experimental heat transfer data in a supercritical vertical upward CO₂ flow were analyzed, based on the relationship between the wall heat flux and mass flux, buoyancy and flow acceleration effects, and specific heat variation across the turbulent boundary layer. These analyses indicated that the flow acceleration and significant specific heat variation in the boundary layer greatly influenced the heat transfer phenomena under the tested experimental conditions. A two layer heat-transfer model that sufficiently reflects both the effects of flow acceleration and specific heat variation was proposed to quantify the heat-transfer characteristics of supercritical fluids. This model was based on the thermal resistance behavior in the viscous sub-layer and the buffer layer. In our assessment of this model, the Nusselt number calculated from various experiments agreed with our data within a margin of error of ±30%. Also, the location of the peak inner wall temperature from experimental data almost coincided with the peak maximum thermal resistance in the viscous sub-layer, calculated using the proposed model.     

Molecular diffusion in the laminar sub-layer during turbulent flow in a smooth tube

A model is proposed that can predict the fully developed mass transfer coefficient for a turbulent flowing fluid in a smooth tube. Model results are compared to experimental data over a range of Reynolds number from 7750 to 50,200 and for Schmidt numbers of 850, 900, and 2400. Also, the model prediction is compared to an existing correlation that was derived from experimental data. In all cases the model prediction is in excellent agreement with the published experimental data and is an improvement over the existing correlation.     

Modeling of biomass devolatilization in a fluidized bed reactor

A simple model that simulates a single biomass particle devolatilization is described. The model takes into account the main physical and chemical factors influencing the phenomenon at high temperatures (>700 K), where the production of gaseous components far outweighs that of liquids. The predictions of the model are shown to be in good agreement with published data. The model is then applied to the devolatilization of biomass in a fluidized bed, in which attention is focused on heat transfer, particle mixing and elutriation, and gas production. Predictions on the overall devolatilization time for a biomass particle are compared with experimental results obtained in a fluidized bed reactor in which the process was monitored by continuous measurement of the bed pressure. Good correspondence of predicted with calculated values was obtained, supporting the validity of the many approximations made in the derivation of the governing relationships for the pyrolysis process.     

Calculation of infinite dilution activity coefficients by the NRTL and UNIQUAC models

Infinite dilution activity coefficients have been calculated for 42 binary systems using the NRTL and UNIQUAC models. Temperature dependent parameters of the models are used in the calculations. These parameters have been estimated by using excess Gibbs free energy and enthalpy of mixing data simultaneously. The calculated values are compared with experimental infinite dilution activity coefficients obtained by extrapolation of vapor-liquid equilibrium (VLE) data published in the literature. The agreement between the calculated and experimental values is poor for highly nonideal system. The selection of the best model is difficult and may be system dependent.     

气液两相垂直管流中弹状流型数学模型

本文对气液两相垂直管流的弹状流型的流动机理进行了分析,建立了数学模型。模型的特点是采用了以弹状气泡速度运动的相对座标系,在弹状气泡周围下落液膜流动、液体段空隙率计算和压降计算等方面部提出了新的观点。在两种管径中用空气-水系统进行了实验以验证模型,与一些其他作者的实验数据和理论模型也进行了比较,结果都表明这个机理模型计算的弹状流型的各种流体力学参数值与实验值吻合良好,也优于其他作者提出的模型。     

Modeling of industrial nylon‐6,6 polymerization process in a twin‐screw extruder reactor. II. Neural networks and hybrid models

This article describes the application of neural networks and hybrid models to the finishing stage of nylon‐6,6 polycondensation in a twin‐screw extruder reactor. A planned experiment in the industrial and in the pilot plant was employed to build the neural network and the hybrid model. The hybrid model combines information calculated from the phenomenological model with the neural network model. The comparison of experimental with calculated data shows good agreement. During two years, industrial data were collected. The comparisons of the models' prediction with these data were performed and reasonable results are achieved from the industrial point of view. These models help an increase of industrial production of about 20%. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 905–912, 1999     

Experimental studies and model validation for the optimization of electrodes configuration in a molten salt electrorefiner

Molten salt electrorefining is a high-temperature electrochemical process for treating the spent metallic fuel from fast reactors and is aimed at the separation of U and Pu from fission products. Potential and current distribution analysis was carried out by experimental studies as well as modelling using COMSOL Multiphysics for various electrode configurations. A 2D/2D axisymmetric geometry model was used to evaluate the potential and current distributions. The effect of the following parameters was evaluated: (1) configuration having two pairs of electrodes in parallel/staggered arrangement; (2) centre-to-centre distance between the electrodes; (3) solid cathode with and without insulation at the bottom; (4) Cd cathode and (5) cathode surface area. The resistance of the electrorefiner was calculated using COMSOL model for various electrode configurations and compared with that obtained experimentally. There was very good agreement between the experimental values and the simulation results. The computed cell resistance was also validated with published data. A sensitivity analysis was also performed to determine the parameter that more significantly influences the cell resistance. The two parameters that were varied were the electrolyte conductivity and the cell voltage. It is observed that of the two parameters the cell resistance is most sensitive to the electrolyte conductivity and there is no change in cell resistance with cell voltage.     

Estimation of stereospecific fatty acid distribution in vegetable oils from liquid chromatography data

The fatty acid distribution in triacylglycerols (TG), the major components of vegetable oils, affects the physical properties of oils and their physiological effects as components of the human diet. A computational scheme is proposed for estimating the stereospecific distribution of fatty acids in TG on the basis of the data from HPLC analysis, using a model for TG synthesis. A new model for the synthesis is proposed which, in contrast to the widely used model published independently by Vander Wal and Coleman, enables us to simulate the asymmetrical fatty acid distribution at the sn‐1 and sn‐3 stereochemical positions. The computational scheme combined with either literature models or the new model was validated by its application to several TG profiles and comparison of the resulting fatty acid distribution at stereochemical positions with experimental data from the literature. The stereospecific composition of TG was calculated using the new model for nine vegetable oils.     

CFD Modeling of a Spouted-Bed Dryer Hydrodynamics

A hydrodynamic model based on continuity and conservation equations was used to predict flow behavior in a spouted-bed dryer with a draft tube. The Eulerian-Eulerian multi-fluid modeling approach was applied to predict a gas-solid flow behavior. The model was qualitatively validated and the results of simulations were compared with the experimental data published by various researchers. The model predicts flow behavior well with fluctuations, circulations of phases, and cluster formations in the loading region, as was observed in experiments. The predicted solids circulation rate and the fraction of gas bypassing were close to experimental values published for various systems. The coarse 2D axisymmetric grid, used in simulations, can handle the main process dependencies with a sufficient accuracy for engineering calculations.     

新近理想气体热容数据与温度的关联

根据1968年至1978年期间新近发表的C_p~o数据,最小二乘法由电子计算机计算,确定了435种物质的理想气体热容C_p~o与温度的四项关联式C_p~o=A+BT+CT~2+DT~3中的常数A、B、C、D。计算的C_p~o值与实验值的平均百分误差为0.160。这些物质是按它们在基本化学工业中的相对重要性选择的。它们或是还没有C_p~o的温度关联式,或是虽然已有这种关联式,但并不是基于新近发表的C_p~o数据。