bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of boundary layer and solute transport in osmotic evaporation
Authors: Romero J. , Rios G. M. , Sanchez J. , Saavedra A. 
Published: April 2004

AbstractThe osmotic evaporation process (OE) is based on the transfer of solvent from a dilute solution to be concentrated to an extraction medium (for example, a highly concentrated brine) separated by a macroporous hydrophobic membrane. Mass transfer takes place in the gas phase through the membrane pores under the influence of the water activity gradient. The OE process has been analyzed before in experiments by Courel et al. in 2000 and models by Romero et al. in 2001. These previous studies take into account the effect of structural membrane parameters and working conditions of water flux performance. An algorithm has been developed to solve the system constituted of the mass‐ and heat‐transfer equations. In order to validate it more easily, the simulation was conducted for the results of pure water evaporation. This provides a lot of interesting information on transfer resistances, temperature, and concentration profiles, as well as the prediction of water flows. A work that is the logical continuation of these previous studies is proposed. First, it aims at explaining the influence of the concentration polarization that develops at the solution–membrane interface when the concentration is applied to a sucrose solution. The transfer of very dilute volatile compounds from the sweetened solution is also analyzed with a view to understanding the mechanism that controls the loss of aroma compounds during the concentration of fruit juices.
Fluid dynamic simulation of O3 decomposition in a bubbling fluidized bed
Authors: Syamlal Madhava , O'Brien Thomas J. 
Published: April 2004

AbstractRecent advances in dense, multiphase, computational fluid dynamics (CFD) have allowed accurate simulation of the gas and particle motion in bubbling and circulating fluidized beds. Since fluidized‐bed reactors are used for many chemical processes, a simulation must also be able to accurately couple chemical reactions to bed hydrodynamics. The catalytic decomposition of ozone (O3) often has been used to study experimentally the contacting behavior of catalytic reactors. Simulations of laboratory‐scale experiments of premixed O3 decomposition in a bubbling fluidized bed using the multiphase CFD code MFIX were conducted. The grid‐independent results are in very good agreement with reported experimental data on total conversion over a range of fluidization velocities and initial bed heights. This confirms the ability of multiphase hydrodynamic models to capture quantitatively the effect of hydrodynamics on chemical reactions in a bubbling fluidized bed.
Observations and process parameter sensitivities in fluid‐bed granulation
Authors: Cryer S. A. , Scherer P. N. 
Published: April 2004

AbstractA numerical approach using mechanistic modeling (population balance) for fluid‐bed agglomeration is documented elsewhere. Here important factors for a pilot‐scale fluid‐bed granulater as determined by a 1/2 fraction factorial statistical design of experiment (DOE), Monte Carlo analysis of the mechanistic model, and comparison of experimental observations to model predictions, are summarized. DOE results indicate sensitive primary process parameters affecting granule size include the bed bowl charge, binder spray rate, air flow rate, and input air temperature. Sensitivity analysis of model results suggest the binder spray rate accounts for approximately 65% of the predicted variance, with the next most sensitive parameter the binder droplet diameter (∼11%). Population balance modeling specifically for fluid beds, coupled with a DOE can be combined so the behavior of agglomeration of wettable powders within a fluid bed can be understood and predicted. Good agreement between experiment and simulation results is found for particles grown to sizes of industrial importance.
Scaling and intensification procedures for simulated moving‐bed systems
Authors: Kim Jeung Kun , Wankat Phillip C. 
Published: April 2004

AbstractScaling rules and intensification procedures developed for single adsorption or chromatographic columns are extended for both linear and nonlinear isotherms to simulated moving‐bed (SMB) systems. The effects of particle diameter, column length, column diameter, switching time, flow rates, mass transfer, axial dispersion, and dead volume are studied in order to design a new SMB. Changes in the pressure drop, separation, and throughput can be changed as desired. Once an original design has been developed, the scaling procedure requires only algebraic manipulation. Simulations done by Aspen Chromatography showed that the new designs were remarkably good at producing the same product purities and pressure drops as the original design. Intensification is predicted when particle diameter is decreased. The limitations of the technique are that the number of columns per zone cannot be changed, the relative velocities in each zone are fixed, and for nonlinear systems the results apply only for the same feed concentration.
Graphical and stage‐to‐stage methods for reactive distillation column design
Authors: Daza Oscar Sánchez , Pérez‐Cisneros Eduardo S. , Bek‐Pedersen Erik , Gani Rafiqul 
Published: April 2004

AbstractBased on the element mass‐balance concept, three graphical methods and one stage‐to‐stage computation method for design of reactive distillation columns have been developed. The element‐based approach allows the design of reactive distillation columns by using simple tools similar to those that are typically employed for nonreactive systems. For example, simple design methods employing reactive McCabe‐Thiele‐ and reactive Ponchon‐Savarit‐type diagrams for design of reactive distillation of binary‐element systems—which may be ternary or higher in terms of mixture compounds—are presented. Also, the driving‐force approach has been extended to employ the element concept for reactive systems. For multielement systems, the design is performed by employing a stage‐to‐stage computation method. For combined reactive distillation columns, comprising both reactive and nonreactive stages, a simple design strategy is proposed, based on the stage‐to‐stage computation method considering reactive and nonreactive bubble‐point calculations. This strategy tracks the conversion or generation and temperature between the feed and the end stages of the column, and indicates when and where nonreactive stages should be added to a reactive distillation column in order to achieve the desired separation. Illustrative examples highlight the application of the design methods, as well as the verification of such designs through rigorous simulation.
Thermodynamically equivalent configurations for thermally coupled distillation
Authors: Caballero José A. , Grossmann Ignacio E. 
Published: April 2004

AbstractIn this work a systematic way of generating all the thermodynamically equivalent structures for a given sequence of separation task in N‐1 distillation columns (N is the number of components to be separated) is presented first. The problem is represented through a set of symbolic relations that can be written as propositional logic expressions. Alternatives from fully thermally coupled systems (only one reboiler and one condenser) to conventional columns (each column with a reboiler and a condenser), plus all the intermediate possibilities, are considered. Then all the thermodynamically equivalent structures that do not have control problems associated with the flow transfer among columns are generated. Again the problem is formulated as a set of symbolic relations written as propositional logic expressions. A formula with a detailed derivation to calculate the number of alternatives for a given sequence of tasks is also presented. Logic expressions in propositional logic form or translated into algebraic expressions in terms of binary variables can be integrated in the framework of Disjunctive Programming to extract the best solution for a given objective function. Several results are presented with systems involving mixtures of 4 and 5 components.
Integrated approach to optimization of an ultrasonic processor
Authors: Moholkar Vijayanand S. , Warmoeskerken Marijn M. C. G. 
Published: April 2004

AbstractIn an ultrasonic processor, the input electrical energy undergoes many transformations before getting converted into the cavitation energy, which is dissipated in the medium to bring out the physical/chemical change. An investigation of the influence of free and dissolved gas content of the system on the efficiency of this energy transformation chain is attempted. The results of the experiments reveal that the cavitation intensity produced in the medium varies significantly with the gas content of the system. A unified physical model, which combines basic theories of acoustics and bubble dynamics, has been used to explain the experimental results. An attempt has been made to establish the mechanism of the steps in the energy transformation chain, the involved physical parameters, and interrelations between them. It has been found that the influence of free and dissolved gas content of the medium on the overall energy transformation occurs through a complex inter‐dependence of several parameters. Thus, simultaneous optimization of individual steps in the energy transformation chain, with an integrated approach, is necessary for the optimization of an ultrasonic processor. The present study puts forth a simple methodology, with the gas content of the system as manipulation parameter, for this purpose.
Glucose hydrogenation in a membrane trickle‐bed reactor
Authors: Diakov Victor , Varma Arvind 
Published: April 2004

AbstractThe concept of membrane distributed feed to a packed‐bed reactor is applied to multiphase catalytic reaction systems. The expected benefits of this approach include enhanced reactant conversion. The concept may be applied to a wide variety of reactions conducted over trickle‐beds and is supported experimentally for the reaction of glucose hydrogenation to sorbitol.
Regular solution model for asphaltene precipitation from bitumens and solvents
Authors: Alboudwarej Hussein , Akbarzadeh Kamran , Beck James , Svrcek William Y. , Yarranton Harvey W. 
Published: April 2004

AbstractA regular solution theory liquid‐liquid equilibrium model was developed to predict asphaltene precipitation from Western Canadian bitumens. The input parameters for the model are the mole fraction, molar volume, and solubility parameters for each component. Bitumens were divided into four main pseudo‐components corresponding to SARA fractions: saturates, aromatics, resins, and asphaltenes. Asphaltenes were divided into fractions of different associated molar mass based on a Schultz‐Zimm molar mass distribution. Asphaltene self‐association was accounted for through the average molar mass of the distribution. The molar volumes and solubility parameters of the pseudo‐components were calculated using solubility, density, and molar mass measurements. The model successfully predicted the effect of solvent type and associated molar mass on asphaltene precipitation for model oil and n‐alkane systems. The model also predicted the onset and amount of asphaltene precipitation from bitumens.
Gas and liquid distribution in the monolith film flow reactor
Authors: Heibel Achim K. , Vergeldt Frank J. , van As Henk , Kapteijn Freek , Moulijn Jacob , Boger Thorsten 
Published: April 2004

AbstractThe gas‐liquid distribution in a monolith film flow reactor is investigated in the scope of this work. Magnetic resonance imaging (MRI) and a customized liquid collection method have been successfully applied to determine the liquid distribution over the monolith cross‐section. Using a well‐positioned spray nozzle liquid distributor, very uniform distributions are found which address the needs for applications that require high single‐pass conversions. Due to the lack of radial convective flow in monoliths, the initial distribution propagates through the reactor. With a correct positioned spray nozzle distributor, a far more uniform distribution than the “natural” one for trickle beds is obtained. MRI, applied to study the local gas‐liquid distribution in a monolith channel, clearly shows the accumulation of the liquid in the corners of the individual channel with an arc‐shaped gas‐liquid interface. Differences in local liquid holdup over the channel corners were found, which is described as channel scale nonuniformities. The experimental results are in good agreement with a fundamental hydrodynamic model based on the Navier‐Stokes equations. The average liquid saturation is conveniently described with an engineering correlation βL = 6.6·(Fr/ReLs)0.46, as a function of the liquid phase Reynolds and Froude number.
Convective heat and mass transfer to a cylinder sheathed by a porous layer
Authors: Sobera Michal P. , Kleijn Chris R. , Van den Akker Harry E. A. , Brasser Paul 
Published: April 2004

AbstractA systematic study of the flow, heat, and mass transfer around a cylinder sheathed by a second, porous cylinder and placed in a perpendicular turbulent air flow has been performed. The focus of the study was on applications in heat and mass transfer to a clothed human limb in outdoor conditions. Both numerical and experimental investigations have been carried out for the fluid flow. Dimensionless scaling rules have been presented for flow, heat and mass transfer as a function of the free stream Reynolds number, the Darcy number, the dimensionless air resistance of the porous layer, and the dimensionless distance between the outer and inner cylinder. The results have been compared to available data in the literature and to the present experiment. An empirical correlation, which concludes the most important results, has been proposed. The largest reduction of heat and mass transfer due to the sheath layer, compared to that for an uncovered cylinder, was found for intermediate values of the Reynolds number, the flow resistance of the sheath layer, and the thickness of the air gap between solid and sheath cylinder.
Three dimensional model of oxygen transport in a porous diffuser of a PEM fuel cell
Authors: Zhukovsky K. V. 
Published: April 2004

AbstractBinary molecular diffusion and pressure‐driven fluxes of gas in porous media are studied. A 2‐dimensional model of gas transport in porous media is developed in the field of nonzero gradients of pressure and concentration. Spatial distributions of oxygen concentration and fluxes in a porous diffuser are analyzed for geometric and physical parameters of the electrode. A three‐dimensional generalization of the model is performed. Application to oxygen‐flow modeling in electrodes of polymer electrolyte fuel cells (PEFC) is discussed for two simple configurations of gas supply channels: serpentine and interdigitated. Comparison of the results obtained for the two configurations is carried out. Oxygen flux through the catalytic membrane plane is investigated for physical characteristics of gases and the diffuser, geometry of the gas supply channels, and gas pressure in them. Recommendations for an optimal pressure regime for the specific geometry of the system and its physical characteristics are given.
Effects of fractal trajectory on gas diffusion in porous media
Authors: Zhang Baoquan , Liu Xiufeng 
Published: April 2004

AbstractA mathematical model was developed to represent the effect of tortuous trajectory and irregular step length on gas diffusion in porous media, and then it was conformed by analyzing the experimentally determined flux with respect to 19 groups of binary gas mixtures in a porous catalyst pellet. Based on the analysis of actual diffusing distance within porous media, the diffusing trajectory of gas molecules was characterized into fractal curves, leading to a novel flux equation of binary gas mixtures. The established model represented the tortuous structure by the only model parameter the fractal dimension of diffusion trajectories dF. A yardstick was devised to account for the influence of pore size, diffusing species, temperature and pressure on the trajectory length of gas diffusion. The size of the yardstick δ could be found after diffusing species, temperature and pressure were specified for a given porous medium. The fitting between the experimentally determined flux and the model equation resulted in a fractal dimension of 1.102. It was evident that the model prediction was in fairly good agreement between the experimental results in the literature and those of the study, and the irregular degree of diffusing trajectory is much less than that of the pore surface. Detailed comparison with the traditional treatment by the tortuosity factor demonstrated that the methodology established here would be especially significant for very tortuous pore systems.
Particle‐size distribution effects in batch adsorption
Authors: Carta Giorgio , Ubiera Antonio 
Published: April 2004

AbstractMathematical models for pore‐diffusion‐controlled batch adsorption that take an arbitrary distribution of particle sizes into account are developed and solved for two extreme cases: the linear isotherm case and the irreversible isotherm case. Numerical calculations based on these solutions show that the effects of the particle‐size distribution (PSD) are significant, even for relatively narrow and symmetrical PSDs. The uptake rate is faster initially and slower as equilibrium is approached than is predicted using the volume‐average particle radius. These results are confirmed by comparing model predictions with experimental results obtained for the batch uptake of the protein α‐chymotrypsinogen on SP‐Sepharose‐FF. Although the PSD of this commonly used commercial medium for preparative protein chromatography is fairly narrow, significant effects are observed in both shallow‐bed and stirred batch‐uptake experiments. As a result, the PSD needs to be taken into account when precise predictions are desired, such as when batch‐uptake experiments are used for diffusivity measurements. The PSD also affects the shape of the breakthrough curve in packed beds. The effects are somewhat less pronounced, but still quite significant for the irreversible isotherm case.
Optimal solvent design for batch separation based on economic performance
Authors: Giovanoglou Apostolos , Barlatier Julie , Adjiman Claire S. , Pistikopoulos Efstratios N. , Cordiner Joan L. 
Published: April 2004

AbstractA mixed‐integer dynamic optimization (MIDO) framework for solvent design in batch processes is presented. Performance measures reflecting process economics and computed on the basis of process dynamics are used to validate candidate solvent structures built from the UNIFAC molecular groups. These define the discrete space in the overall material formulation and are combined according to molecular design feasibility rules to guarantee realistic molecular representations. The algorithm is based on the decomposition of the MIDO primal subproblem into several steps that are solved successively. This allows unsuitable solvents to be detected and discarded quickly and without significant computational cost. Emphasis is placed on problem formulation in order to match accuracy of process model and physical property predictions. The algorithm is applied successfully to an industrial case study dealing with a three‐phase dehydration column and a decantation unit for solvent recovery. The proposed algorithm can be regarded as a promising initial step toward an integrated and simultaneous methodology for material process design in batch separation systems.
Steady‐state process optimization with guaranteed robust stability and feasibility
Authors: Mönnigmann M. , Marquardt W. 
Published: April 2004

AbstractA new approach is presented to the optimization based design of continuous processes in the presence of parametric uncertainty. In contrast to previous works focusing on process feasibility, it allows to consider both feasibility and stability of the process in the presence of parametric uncertainty. The new approach, therefore, permits an integrated treatment of steady‐state flexibility and robust stability in the optimization of continuous processes. The process optimization problem is extended by constraints that ensure a lower bound on the distance of the nominal point of operation to stability and feasibility boundaries in the space of the uncertain parameters. While previous approaches are based on evaluating constraint violation in the range space of the constraints, the measure for flexibility and robustness used here is given in the domain space of the uncertain parameters. The method is discussed in the context of existing approaches to flexibility in process optimization and is illustrated with a continuous polymerization which is known to have a nontrivial stability boundary resulting from multiple steady states and sustained oscillations.
Hybrid approach to modeling an industrial polyethylene process
Authors: Hinchliffe Mark , Montague Gary , Willis Mark , Burke Annette 
Published: April 2004

AbstractA hybrid model of a polyethylene production process is developed. The mechanistic model utilizes fundamental material and energy balances to predict important process conditions, such as the reactor temperatures, conversions, and the molecular‐weight distribution (MWD) of the polymer. Using plant data, it is shown that accurate MWD predictions are not obtained from the mechanistic model alone, despite efforts to accurately model the system and improve the accuracy of the input data. Because an accurate prediction of the MWD is required to predict end‐use properties, a hybrid model was developed by adding an empirical layer to the mechanistic model. The empirical layer was developed by using an optimization algorithm to adjust the predicted MWD by manipulating multipliers of the key descriptors (states or functions of states) of the distribution. These multipliers were then predicted from plant data using feedforward artificial neural networks (FANNs). They are then combined with the mechanistic model to allow accurate MWD prediction.
Design and optimization of free‐fall electrostatic separators for plastics recycling
Authors: Wei Jing , Realff Matthew J. 
Published: April 2004

AbstractElectrostatic separation is a promising technique for separating a mix of plastics, which can acquire different sign charges through triboelectrification. A particular application of growing importance is the separation of plastics with overlapping densities from a waste stream of electronic products. Particle charging, which plays an important role in separation efficiency, has been the topic of much research. However, no systematic method has been proposed for design and optimization of the separation process itself, a gap that this research seeks to fill. The aim is to compare several design options for free‐fall electrostatic separators, taking into account the distribution of the particle charge and initial position. Particle trajectory and recovery models are derived under a set of simplifying assumptions that are carefully analyzed. Optimization models are developed that trade off the strength of the electric field with the size and number of stages of the free‐fall separator. Several different configurations are optimized and compared under various conditions (mean value and standard deviation of particle charges, feed rate, and product prices). Finally, a general guide is proposed for selecting an appropriate design.