Modeling of Adsorptive Drying of N-Propanol

On the basis of experimental work connected with mathematical modeling, a parameter analysis was conducted on the adsorptive drying of water-miscible organic liquids. The experimental work involved dehydration of n-propanol using two desiccants, 3A and 4A zeolite molecular sieves. The equilibrium relationship and fixed bed breakthrough curves were determined experimentally. The parameters required by the model are the equilibrium constants, liquid film mass transfer coefficient, intraparticle diffusion coefficient, and axial diffusivity. A linear driving force (LDF) relation was applied to represent the mass transfer rate in the particle liquid film and inside the adsorbent particle. The fit of the model to experimental breakthrough data was quite good.     

An experimental study of mass transfer with chemical reaction from single gast bubbles

Rates of forced convection mass transfer from single bubbles of carbon dioxide reacting in aqueous ethanolamine solutions have been determined experimentally for intermediate babble Reynolds numbers. A water tunnel apparatus, and technique for measuring mass transfer rates are described. The results of the experimental study are compared with a mathematical model describing mass transfer with an accompanying second order reaction; the hydrodynamic condition of the model is described using Kawaguti type velocity profiles. The experimental data appear to confirm the model satisfactorily.     

Hydrodynamic analogy approach for modelling of reactive stripping with structured catalyst supports

Modelling of gas/vapour–liquid separation processes usually requires experimentally determined parameters, e.g., mass transfer coefficients. This results in expensive experimental work, especially for new types of column internals. A novel modelling approach based on hydrodynamic analogies (HA) has recently been developed for distillation units equipped with structured corrugated sheet packings. The HA model takes the packing geometry directly into account whereas the experimental determination of mass transfer coefficients is not required.In this work, the HA approach is extended to cover heterogeneously catalysed reactive stripping processes. Experimental investigations are performed with a test system, esterification of hexanoic acid and 1-octanol, using different types of catalytically coated supports as column internals (one corrugated sheet packing and three film-flow monoliths with different channel geometries). Simulation results obtained with the extended HA model are in a good agreement with experimental values.     

STUDY OF DOWNFLOW LIQUID JET LOOP REACTOR

1 INTRODUCTIONLiquid jet loop reactor(JLR)may be upflow(U-JLR)or downflow reactors(D-JLR)in design.The major differences between the two are the location of the nozzle andthe direction of the fluid flow.A large number of investigations on U-JLR havebeen published,but D-JLR with nozzles positioned on the top portion of the reac-tor was not much studied until recently.Up to now,only a few experimentalstudies on the hydrodynamics and mass transfer of D-JLR have been carried out[1-4].     

预还原球团在铁碳熔体中熔融还原传质规律的研究

本文对不同预还原度的铁矿球团在铁碳熔体中熔融还原的规律进行了实验和理论研究．针时熔融还原反应特点，提出了表观FeO浓度概念．根据传质理论和球团矿熔融还原的特性，建立了反映球团矿在铁碳熔体中熔融还原反应规律的双相传质模型．实验和理论计算结果表明，球团预还原度和熔化速率等因素对熔融速率影响较大.     

Methane hydrates bearing synthetic sediments—Experimental and numerical approaches of the dissociation

The production of methane gas from methane hydrate bearing sediments may reach an industrial scale in the next decades owing to the huge energy reserve it represents.However the dissociation of methane hydrate in a porous medium is still poorly understood and controlled: the melting of methane hydrate involves fluids flows and heat transfer through a porous medium whose properties evolve as the hydrate phase disappears, and is replaced (or not) by an ice phase. Mass and heat transfers can be coupled in a complex way, firstly because of the permeability changes, and secondly due to material conduction changes. In our work, mass and heat transfers have been studied both experimentally and numerically.A 2D numerical model is proposed where heat and mass transfers govern the dissociation of methane hydrate. This model has been used to design an experimental device. Experiments have been obtained and finally the model has been validated.The experimental set-up consists of five cylindrical sand packs having the same diameter but different lengths. Each experiment starts by crystallizing a hydrate phase in a porous medium. Then the hydrate is dissociated by controlling the pressure at one boundary. The kinetic of dissociation is monitored by collecting gases in ballast. Simulations and experiments demonstrate that the dissociation limiting step switches from thermal transfer to mass transfer depending on the initial permeability and conductivity of the porous medium.     

Identification of models for control of wet granulation

The modeling work in this paper provides insight on improved control and design (including measurement selection) of a granulation process. Two different control strategies (MPC and PID) are evaluated on an experimentally validated granulation model. This model is based on earlier work done at The University of Sheffield, UK and Organon, The Netherlands [C.F.W. Sanders, W. Oostra, A.D. Salman, M.J. Hounslow, Development of a predictive high-shear granulation model; experimental and modeling results, 7th World Congress of Chemical Engineering, Glasgow (2005), C11-002]. The granulation kinetics were measured in a 10 liter batch granulator with an experimental design that included four process variables. The aggregation rates were extracted with a Discretized Population Balance (DPB) model. Knowledge of the process kinetics was used to model a continuous (well mixed) granulator. The controller model for the Model Predictive Controller is a linearized state space model, derived from the nonlinear DPB model. It has the four process variables from the experimental design and a feed ratio as input variables. Since the DPB model describes the whole Granule Size Distribution (GSD), candidate sets of lumped output variables were evaluated. When measuring controller performance based on the full granule size distribution, it is shown that a PID controller can actually produce results that fluctuate more than the open-loop response. An MPC controller improves stability on both process outputs and the full granule size distribution. The work shows that measuring and controlling specific number based lumped outputs result in a more stable process than when mass based lumped outputs are used. The paper describes a general strategy of using lab scale batch experiments to design and control (small or large scale) continuous granulators. The continuous experiments in this paper are based on simulation, therefore future experimental validation will elucidate further the link between batch and continuous granulation.     

External and internal mass transfer effect on photocatalytic degradation

A rational approach is proposed in determining the effect of internal and external mass transfer, and catalyst layer thickness during photocatalytic degradation. The reaction occurs at the liquid–catalyst interface and therefore, when the catalyst is immobilized, both external and internal mass transfer plays significant roles in overall photocatalytic processes. Several model parameters, namely, external mass transfer coefficient, dynamic adsorption equilibrium constant, adsorption rate constant, internal mass transfer coefficient, and effective diffusivity were determined either experimentally or by fitting realistic models to experimental results using benzoic acid as a model component. The effect of the internal mass transfer on the photocatalytic degradation rate over different catalyst layer thickness under two different illuminating configurations was analyzed theoretically and later experimentally verified. It was observed that an optimal catalyst layer thickness exists for SC (substrate-to-catalyst) illumination.     

Coupling between electrolysis and liquid-liquid extraction in an undivided electrochemical reactor applied to the oxidation of Ce3+ to Ce4+ in an emulsion Part II. Cell modelling

A model is presented which is able to predict the transient behaviour of a batch undivided electrochemical reactor with simultaneousin situ extraction of the product by an organic phase. The model is based on electrochemical and physical kinetic laws including mass transfer limitations for both anodic and cathodic processes and for the extraction step, mass balance equations in the aqueous and organic phases for the different species involved and a charge balance equation. With the specific example of the Ce³⁺/Ce⁴⁺ system, which was investigated experimentally in Part I of this work, the validity of this model is proved by comparison between the calculated time-variations of different parameters (cerium concentrations, anodic current density, partition coefficient of Ce⁴⁺ between the two phases) and the experimental results obtained under potentiostatic control.This paper is dedicated to Professor Dr Fritz Beck on the occasion of his 60th birthday.     

ANALYSIS OF TRANSPORT PHENOMENA DURING THE CONVECTIVE DRYING IN SUPERHEATED STEAM

This work focused on high-temperature convective drying (superheated steam drying). The process has been investigated both experimentally and numerically. The experimental analysis was carried out in an aerodynamic return-flow wind-tunnel, with very small cylinders of cellular concrete. For the local analysis, the samples were fitted with thermocouples and pressure sensors. The mean moisture content of the cylinders was measured by simple weighing while the temperature and pressure readings were being taken. Global and. local analysis of heat and mass transfer in small cylinders in superheated steam were carried out. The systematical study for several sizes and aerothermal conditions show a similar behavior for moisture content, pressure and temperature values. A numerical model for high temperature drying, using the finite elements method, in a 2-D configuration, was implemented and validated.     

Rates and equilibria of ester hydrolysis: Combination of slow and rapid reactions

The kinetics and thermodynamics of ester hydrolysis were studied experimentally in a laboratory-scale batch reactor by using ethyl formate as the model molecule. The effects of the reaction conditions, such as temperature, excess water, complexing agent and initial acid charge upon the ester hydrolysis process were investigated and a kinetic model was developed for the system. Autocatalytic kinetics was observed experimentally, which was due to the carboxylic acid formed during the reaction. The reaction rate was further enhanced and the equilibrium was shifted to the product side by adding a complexing agent into the reaction mixture. A mathematical model comprising the mass balances and rate equations were developed for the system by assuming quasi-equilibrium hypothesis for the reaction involving the complexing agent. A robust calculation scheme was developed for the estimation of the kinetic and thermodynamic parameters from experimental data. The proposed model was able to predict the experimental results satisfactorily.     

Experimental and Numerical Study of the Effect of an Electric Field on a Bunsen-type Flame

The effect of an electric field on the behavior of premixed methane-air flames has been studied. A candle-type flame has been observed experimentally and analyzed for its geometrical proportions under an electric field. A numerical model has been developed to explain some of the experimental observations. The model employs a two-dimensional cylindrical coordinate system and assumes axial symmetry. The mass, momentum, species, and energy conservation equations are solved by an integrated version of the PHOENICS and CHEMKIN computer codes. It is concluded that the effect of the electric field on the flame behavior is mainly due to ionic wind effects.     

Diffusion During the Supercritical Drying of Silica Gels

Drying is the most critical elaboration step of large monolithic and crack-free silica aerogel plates. In the present work, we are studying the supercritical CO₂ drying and more precisely the first step, here called the supercritical washing step. This phase consists of replacing the liquid phase contained in the nanopores with supercritical CO₂. Within this study, this step is governed by molecular diffusion through the gels. These phenomena were investigated experimentally in order to estimate the duration of the washing step. The experimental results were then fitted with an analytical mass transfer model to identify the effective diffusion coefficient.     

ANALYSIS OF TRANSPORT PHENOMENA DURING THE CONVECTIVE DRYING IN SUPERHEATED STEAM

Abstract

This work focused on high-temperature convective drying (superheated steam drying). The process has been investigated both experimentally and numerically. The experimental analysis was carried out in an aerodynamic return-flow wind-tunnel, with very small cylinders of cellular concrete. For the local analysis, the samples were fitted with thermocouples and pressure sensors. The mean moisture content of the cylinders was measured by simple weighing while the temperature and pressure readings were being taken. Global and. local analysis of heat and mass transfer in small cylinders in superheated steam were carried out. The systematical study for several sizes and aerothermal conditions show a similar behavior for moisture content, pressure and temperature values. A numerical model for high temperature drying, using the finite elements method, in a 2-D configuration, was implemented and validated.     

Absorption of carbon dioxide into aqueous blends of 2-amino-2-methyl-1-propanol and monoethanolamine

This work presents an investigation of CO₂ absorption into aqueous blends of 2-amino-2-methyl-1-propanol (AMP) and monoethanolamine (MEA). The acid gas mass transfer has been modeled using equilibrium-mass transfer-kinetics-based combined model to describe CO₂ absorption into the amine blends according to Higbie's penetration theory. The effect of contact time and relative amine concentration on the rate of absorption and enhancement factor were studied by absorption experiment in a wetted wall column at atmospheric pressure. The model was used to estimate the rate coefficient of the reaction between CO₂ and monoethanolamine at 313 K from experimentally measured absorption rates. A rigorous parametric sensitivity test has been done to identify the key systems’ parameters and quantify their effects on the mass transfer using the mathematical model developed in this work. The model predictions have been found to be in good agreement with the experimental rates of absorption of CO₂ into (AMP+MEA+H₂O).     

Critical heat flux of nanofluids inside a single microchannel: Experiments and correlations

This study investigated experimentally the CHF phenomena of aqueous-based alumina nanofluids in single microchannels, and assessed the validity of a number of microchannel based CHF correlations using experimental nanofluids data. While usual approaches for CHF enhancement are through the modification of different tube surfaces or employing different inserts, this work showed that CHF in microchannels could be enhanced significantly by the inclusion of small concentrations of nanoparticles. The CHF value was found to increase with increase of mass flux, initial subcooling and alumina nanoparticle concentrations. The maximum subcooled CHF enhancement occurred at the lowest mass flux and highest alumina concentration within the experimental range. In addition, the Lee and Mudawar correlation was modified to predict the critical heat flux of water and nanofluids. The new model was examined by experimental data and 24% and 30% mean absolute error were observed for water and alumina nanofluid respectively.     

A MODEL FOR THE SOLID CIRCULATION RATE IN A RECIRCULATING FLUIDIZED BED

The present work is an experimental study on the solid circulation rate in a recirculating fluidized bed and mathematical modeling of the same based on the experimental results and existing literature. The effects of particle size, spacing between the draft tube bottom and distribution plate, inventory of solids, and superficial gas velocity on the solid circulation rate are studied experimentally on a semicircular cold model recirculating fluidized bed. A mathematical model is developed for the solid circulation rate incorporating the effect of the various operating and design parameters. The model is based on the present experimental work and data available in the literature for the same kind of reactors. Dimensional analysis and nonlinear regression models are used to develop the model. The final model equation is a non linear relationship between the different operating and design variables. The model equation gives good results for the same kind of systems and can be used with reasonable accuracy for a wide range of operating parameters.     

A MODEL FOR THE SOLID CIRCULATION RATE IN A RECIRCULATING FLUIDIZED BED

The present work is an experimental study on the solid circulation rate in a recirculating fluidized bed and mathematical modeling of the same based on the experimental results and existing literature. The effects of particle size, spacing between the draft tube bottom and distribution plate, inventory of solids, and superficial gas velocity on the solid circulation rate are studied experimentally on a semicircular cold model recirculating fluidized bed. A mathematical model is developed for the solid circulation rate incorporating the effect of the various operating and design parameters. The model is based on the present experimental work and data available in the literature for the same kind of reactors. Dimensional analysis and nonlinear regression models are used to develop the model. The final model equation is a non linear relationship between the different operating and design variables. The model equation gives good results for the same kind of systems and can be used with reasonable accuracy for a wide range of operating parameters.     

Internal Mass Transfer during Isothermal Drying of a Porous Solid Containing Multicomponent Liquid Mixtures

Abstract

Internal mass transfer in a porous solid partially saturated with multicomponent liquids has been experimentally and theoretically studied. Isothermal drying experiments were performed using a jacketed wind tunnel where the transient composition profiles and total liquid content of a cylindrical sample were determined. Sand samples wetted with the ternary liquid mixtures water-methanol-ethanol and 2-propanol-methanol-ethanol were dried at two different initial compositions and temperatures. A mathematical model including mass transfer by capillary movement of the liquid and interactive diffusion in both gas and liquid phase was developed. To simulate the capillary movement of liquid mixtures, parameters experimentally determined for single liquids where weighed according to liquid composition. A fairly good agreement between theoretical and experimental liquid composition profiles was obtained provided that axial dispersion is included in the model.     

Solvent extraction of vegetable oils: Numerical and experimental study

A process for the extraction of vegetable oils from soybean seeds with a solvent was developed experimentally. The extraction was carried out in a continuous, fixed-bed extractor. A non-dimensional transient model was applied to simulate the mass transfer process which occurs during the extraction in a packed bed column. The governing dimensionless differential equations were numerically solved using the method of finite volumes. The numerical results were compared with data obtained from the experimental extraction, presenting good agreement. The values obtained numerically for the total oil mass extracted in the fluid phase presented a maximum error of 20%, when compared to the experimental data. The greatest discrepancy was observed at the end of the extraction. This maximum error can be considered small due to the use of a simple numerical model.