bluuebunny/crossref_metadata_2025 huggingface dataset:
Oscillatory cross‐flow electrophoresis
Authors: Chandhok Ajay K. , Leighton David T.
Published: June 2004

Electrophoresis is a useful analytic technique for the separation of proteins and other large molecules, but has proven resistant to scale‐up to production levels. In this article we describe a new technique that permits the use of much greater feed rates than possible in a conventional electrophoresis unit. The technique, in its simplest form similar to the cyclical field‐flow fractionation technique developed by Giddings (1986) and extended by Shmidt and Cheh (1990), relies on the application of an oscillatory electric field across the narrow gap of the electrophoretic cell. The motion of the solute species induced by this field interacts with an oscillatory cross‐flow to cause a separation based on the electrophoretic mobility of the species. This horizontal separation is combined further with a gradient in the strength of the oscillating electric field and oscillations in the vertical downflow to lead to different steady streamlines for species with different mobilities.
Adaptive generic model control: Dual composition control of distillation
Authors: Rani K. Yamuna , Gangiah K.
Published: June 2004

Generic model control (GMC) takes care of parametric mismatch for underdamped, closed‐loop specification, whereas robust generic model control (RGMC) can handle parametric mismatch for any closed‐loop specification. But, neither GMC nor RGMC is capable of compensating for structural mismatch. In this study, adaptive GMC(AGMC) and adaptive RGMC (ARGMC) structures are proposed, and their effectiveness over GMC and RGMC is demonstrated with several examples. AGMC exhibits better performance over ARGMC, GMC, and RGMC in all the cases of no process/model mismatch, parametric mismatch as well as structural mismatch.

Distillation adaptive generic model control (DAGMC) structure is also proposed for dual composition control of distillation. Since embedding of distillation state‐space model in the basic GMC law is practically impossible, linear and nonlinear models are proposed with adaptation using distillation process data, and DAGMC is applied to two typical nontrivial distillation units. Nonlinear DAGMC exhibited better performance over linear DAGMC.
Explicit runaway criterion for catalytic reactors with transport limitations
Authors: Balakotaiah Vemuri , Luss Dan
Published: June 2004

Most existing criteria for predicting parametric sensitivity or runaway in a catalytic reactor are based on a single‐phase model that does not account for interparticle heat and mass transfer resistances and intraparticle diffusion. Accounting for these effects, the simple criterion

defines the boundary of operating conditions, in which a catalytic reactor is insensitive to small perturbations. Here, r(Tf,Cf) is the intrinsic reaction rate at inlet conditions, dt(dp) and U(h) are the diameter of reactor tube (catalyst particle) and heat transfer coefficient between the fluid and tube wall (catalyst particle), respectively. The function f(ϕ0), where ϕ0 is the normalized Thiele modulus at inlet conditions, accounts for the effects of intraparticle diffusion. For the common case of equal coolant and feed temperatures, f(ϕ0) = 1 for ϕ0 < 0.5 and f(ϕ0) = 2 ϕ0 for ϕ0>0.5. The conservatism associated with the above criterion is comparable to the uncertainty involved in determining the parameters of the packed bed.
Effect of electrode surface area on chaotic attractor dimensions
Authors: Wang Ying , Hudson John L.
Published: June 2004

An experimental study of the dynamics of electrodissolution of iron in sulfuric acid is reported. The experiments were done under potentiostatic conditions with a rotating disk electrode as a function of two parameters, potential and electrode diameter. The dynamic behavior depends strongly on the latter parameter; with increasing electrode size we observe transitions from periodic oscillations to low‐order chaos to higher‐order chaos. The attractor dimension increases with increasing electrode size. In addition, for the large electrodes at more positive potentials, a secondary higher frequency oscillation also arises.
Comparing two neural networks for pattern based adaptive process control
Authors: Cooper Douglas J. , Megan Lawrence , Hinde Ralph F.
Published: June 2004

An adaptation strategy based on an analysis of patterns exhibited in the recent controller error history is presented. The strategy is a two parameter adaptation, where the gain and time constant of the controller's internal model are adjusted to make the closed loop error response match a target pattern. Both a back‐propagation network and a vector quantizer network (VQN) are compared as pattern analysis tools. This strategy is established for a number of model based controllers and is demonstrated here using the Generalized Predictive Control algorithm. Details of this set point tracking strategy are presented along with demonstrations on both simulated and real single loop processes that experience significant changes in process gain and time constant. Results show both networks to be equally capable at pattern recognition with the VQN's ease of training and implicit ability to assess the accuracy of the pattern match as deciding factors in network selection.
Automatic verification of sequential control systems using temporal logic
Authors: Moon Il , Powers Gary J. , Burch Jerry R. , Clarke Edmund M.
Published: June 2004

Clarke et al. (1986) have developed a model‐based verification method and have applied it to validation of VLSI circuits. We have used the method to test automatically the safety and operability of discrete chemical process control systems. The technique involves: (1) a “system model” describing the process and its software; (2) “assertions” in temporal logic expressing user‐supplied questions about the system behavior with respect to safety and operability; and (3) a “model checker” that determines if the system model satisfies each of the assertions and provides a counterexample to locate the error if one exists. Temporal logic is used for reasoning about occurrence of events over time. To reveal discrete event errors, we have applied the verification method to a simple combustion system and an alarm acknowledge system.
Adequacy of lumped parameter models for SCR reactors with monolith structure
Authors: Tronconi Enrico , Forzatti Pio
Published: June 2004

Two‐and one‐dimensional steady‐state isothermal mathematical models of monolith reactors for selective catalytic reduction (SCR) of NOx by NH3 are compared for circular, square and triangular geometry, as well as for linear and Rideal kinetics. Solutions for the two‐dimensional model demonstrate that, as the reaction rate decreases from infinity to zero, the Sherwood number varies from the values of the Nusselt number characteristic of the Graetz‐Nusselt problem with constant wall temperature to those with constant wall heat flux but with peripherally varying temperature. A lumped‐parameter treatment, based on similarity with the constant wall temperature heat transfer problem, agrees satisfactorily with the solutions for a far more expensive two‐dimensional model. The agreement is excellent for square channels, but the NH3 slip tends to be underestimated in the triangular geometry. The one‐dimensional model reproduces successfully experimental effects of the NH3/NO feed ratio, and of the area velocity and the size of monolith channels.
Parallel finite element computations on a network using NCS
Authors: Bertrand F. H. , Tanguy P. A.
Published: June 2004

Research has been carried out on the use of NCS (Network Computing System) to distribute the processing of a finite element application to multiple computers at once. Coarse‐grained parallelism of specific routines on loosely coupled CPUs has been implemented and tested. In a step‐by‐step fashion, the method of using NCS to convert finite element software POLY2D is explained for its application in parallel computing resources throughout a network. For the modeling of a simple conductive heat transfer problem, the distributed version of POLY2D on a homogeneous token ring network of nine Apollo workstations is used. Some timings given are compared to those obtained from a standard nondistributed simulation.
Semibatch reaction crystallization of benzoic acid
Authors: Slund Bengt L. Å , Rasmuson Å Ke C.
Published: June 2004

An experimental study of a semibatch reaction crystallization is presented. Dilute hydrochloric acid is fed to a stirred solution of sodium benzoate to crystallize benzoic acid. The weight mean size of the product crystals increases with increasing stirring rate, reaches a maximum, and then decreases again. Larger crystals may be produced if the reactant feed point is positioned close to the outlet stream of the impeller. At equal power input the influence of stirrer type is negligible. Decreasing reactant concentrations or feed rate increases the crystal size significantly. Experimental results are explained qualitatively focusing on nucleation and growth conditions and on feed point mixing. The feed point micromixing brings reactants together to generate supersaturation and allow for nucleation. Continued mixing, however, may partially dilute supersaturation before nucleation takes place or may restrict nuclei growth, thus promoting more efficient Ostwald ripening in the bulk. This may result in high bulk supersaturations which in turn hampers the dilution effects.
Agglomeration in a continuous MSMPR crystallizer
Authors: Tavare Narayan S. , Patwardhan V.
Published: June 2004

Experimental responses from crystallization of copper sulfate pentahydrate, nickel ammonium sulfate, and soy protein in continuous MSMPR crystallizers were used to determine simultaneously crystal growth and nucleation rates and agglomeration kernels. Measured product crystal size distributions at steady state for all these systems were transformed into crystal volume coordinates to use two methods: moments analysis and optimization procedure for parameter characterization. An iterative nonlinear parameter estimation by optimization procedure was used to deduce the kinetic rate parameters in the solution of the agglomeration model in crystal volume coordinates, extended from the analysis by Liao and Hulburt (1976), from the translated data set for the product crystals. The kinetic results obtained for the copper sulfate pentahydrate system were correlated in terms of power law kinetic expressions depicting the effect of significant observable variables.
Alkaline hydrolysis of n‐butyl acetate with phase transfer catalyst aliquat 336
Authors: Asai Satoru , Nakamura Hidemi , Furuichi Yousuke
Published: June 2004

A reasonable analytical procedure of the overall reaction rate for the phase transfer catalysis with mass transfer is discussed. Alkaline hydrolysis of n‐butyl acetate with a phase transfer catalyst Aliquat 336 (tricaprylmethylammonium chloride, Q+Cl−) was chosen as a model system and carried out in an agitated vessel with a flat interface. Overall reaction rates observed were proportional to the interfacial concentration of the actual reactant Q+OH− (the ion pair consisting of quaternary ammonium cation Q+ and OH−) for the hydrolysis in the organic phase. The interfacial concentration of Q+OH− was a unique function of bulk concentrations of the catalyst and NaOH, and the ionic strength of the aqueous solution. This behavior of the overall reaction rates was explained by the proposed model solution. The reaction rate constant, evaluated by fitting the rate data to the model prediction, was 47 m3/kmol·s at 298 K. It was 70 or more times greater than that of conventional alkaline hydrolysis in the aqueous phase.
Fraction of Pt surface covered with coke following hydrogenolysis of hexane
Authors: Rivera‐Latas F. J. , Betta R. A. Dalla , Boudart M.
Published: June 2004

Following hydrogenolysis of n‐hexane on an alumina‐supported platinum catalyst, the surface of the metal is covered partially with carbonaceous residues or coke. The fraction of surface platinum not covered with coke has been found to be about one half by four independent techniques: titration of preadsorbed oxygen by dihydrogen, chemisorption of carbon monoxide, infrared spectroscopy of chemisorbed carbon monoxide, and hydrogenation rate of ethylene. The first of these techniques suggests itself as the simplest one for further studies of deactivation by coking of platinum catalysts.
Growth processes in bioreactors with external sources of biomass: Application of structured, continuum models
Authors: Fredrickson A. G.
Published: June 2004

Batch, fed‐batch, and single‐stage CSTR bioreactors operate without external sources of biomass after they have been inoculated. However, other kinds of bioreactors, such as the second and subsequent reactors in a cascade of CSTRs, operate with continuous introduction of biomass from one or more external sources. The biomass in a bioreactor with an external source is not homogeneous with respect to past history of environmental conditions, and growth of this biomass is not balanced (steady‐state) growth even when the bioreactor operates in steady state. So‐called unstructured models of growth, which assume biomass to lack any internal structure or to have an invariant internal state, can give only a first approximation to the growth rate behavior of the biomass in a bioreactor with an external source of biomass. Structured models, which endow biomass with a changeable internal structure, are required to obtain more accurate predictions of growth rate behavior in such reactors. Introduction of structure is not sufficient for improved accuracy, however, and the fact that biomasses from different sources are remain segregated from one another must also be accounted for by any structured growth model used. This article presents, among others, the systems of different equations that result from application of the notions to the reactors of a cascade of CSTRs.
High‐temperature membrane reactor for catalytic gas‐solid reactions
Authors: Sloot H. J. , Smolders C. A. , Van Swaaij W. P. M. , Versteeg G. F.
Published: June 2004

A mathematical model, based on the dusty‐gas model extended with surface diffusion, is presented that describes mass transport owing to molecular diffusion and viscous flow, as well as an instantaneous reversible reaction inside a membrane reactor. The reactants are fed to opposite sides of the membrane, considering masstransfer resistances in the gas phase outside the membrane. The Claus reaction is chosen as a model reaction to study this membrane reactor.

The model is used to validate a previously presented simplified model. The simplified model predicts correct molar fluxes when it is very dilute and can therefore be considered a pseudo‐binary system. Occurrence of a maximum or a minimum in the pressure profile inside the membrane, in the absence of an overall pressure difference over the membrane, depends not only on the stoichiometry of the reaction but on mobilities of the different species.

The Claus reaction is used to verify experimentally the transport model for a nonpermselective membrane reactor with a mean pore diameter of 350 nm. At 493 K and 542 K, molar fluxes experimentally determined are 10 to 20% lower than those predicted by the transport model. Conversions measured at pressures of 220 kPa and 500 kPa demonstrate that surface diffusion occurs as a transport mechanism despite the large pore diameter of the membrane. In the presence of a pressure difference over the membrane, there is a reasonable agreement between experimentally determined molar fluxes and those calculated by the transport model.
Analysis and design of melt and solution polycondensation processes
Authors: Jacobsen Lance L. , Ray W. Harmon
Published: June 2004

Polycondensation processes include up to three distinct process stages: prepolymerization, polymerization, and finishing. One or more of these stages often have serious reaction rate limitations due to chemical equilibrium and the need to remove a condensate product. The problems arising in each process stage and the methods of designing each stage are unique. This article discusses many of the problems inherent to each process stage and basic design tools useful in designing each process stage. Two process design tools discussed are the mass‐transfer potential and pressure‐chain length plots. The application of these tools is illustrated through two design examples: nylon‐6,6 and poly (ethylene terephthalate) production.
Modeling of supercritical oxidation of aqueous wastes in a deep‐well reactor
Authors: Kodra Dusan , Balakotaiah Vemuri
Published: June 2004

A mathematical model is developed for deep‐well oxidation of wastes in supercritical water. The model accounts for the variation of thermodynamic and transport properties with temperature and pressure. It is used to examine the steady‐state behavior of the supercritical‐water deep‐well oxidation reactors. The effects of inlet flow rate, heat losses from the reactor, inlet concentration of organics, oxygen injection depth, reactor length, inlet pressure, and inlet temperature on the exit conversion and the bottom temperature are examined. The simulations show that under practical conditions the capacity of the reactor is dictated by hydrodynamic considerations rather than the oxidation kinetics, and that obtaining temperatures of 10 to 50 K above critical temperature at the bottom of the reactor requires longer tubes and/or high inlet pressures. Heat losses to the earth can be modeled accurately by treating the earth as an infinite reservoir by properly choosing the effective heat‐transfer coefficient.
Two‐mode boiling on a horizontal heating wire
Authors: Lee D. J. , Lu S. M.
Published: June 2004

Two‐mode boiling on a horizontal heated wire immersed in a pool of liquid under atmospheric pressure has been investigated. Methanol, acetone, isopropanol, and isobutanol were boiled using wires made of tungsten (0.15, 0.50, 0.82, 1.01, and 1.55 mm dia.), tantalum (0.30 and 0.82 mm dia.), molybdenum (0.125 and 1.01 mm dia.) and titanium (1.01 and 1.55 mm dia.). Two‐mode boiling may be steady or unsteady. In steady two‐mode boiling, both modes of boiling are stationary on the wire. The applied current in this case is referred to as the equilibrium current. In this article a method devised to calculate this current is discussed. The calculated results agreed well with the experimental results. In unsteady two‐mode boiling, one of the two modes automatically takes over the other and boiling changes into a one‐mode boiling. A method to calculate this transition velocity is presented. The calculated results correlated well with the experimental work.
Modeling of the sulfidation of zinc‐titanium oxide sorbents with hydrogen sulfide
Authors: Lew Susan , Sarofim Adel F. , Flytzani‐Stephanopoulos Maria
Published: June 2004

The overlapping grain model was used to describe the sulfidation of zinc oxide and zinc‐titanium oxide powders at temperatures between 400–700°C in H2S‐H2‐N2 gas mixtures. Experimental data were collected under conditions free of mass‐transfer and pore diffusion limitations. Thus, the only resistances to reaction were due to intrinsic sulfidation kinetics (surface reaction) and diffusion through the product layer. The product layer diffusion coefficient was used as a fitting parameter in the model. As the relative amount of titanium in the sorbent was increased, the product layer diffusion coefficient decreased. Similar activation energies (26.6 kcal/mol) were obtained for the product layer diffusion coefficient of ZnO and Zn‐Ti‐O sulfidation. From the similarity in activation energies, it is proposed that for both types of sorbents diffusion occurs primarily through ZnS.
The modular multivariable controller: I: Steady‐state properties
Authors: Meadowcroft T. A. , Stephanopoulos G. , Brosilow C.
Published: June 2004

The modular multivariable controller (MMC) represents a multivariable controller design methodology which is based on the solution of multiobjective optimization problems using the strategy of lexicographic goal programming; priority‐driven, sequential satisfaction of objectives. This article formally introduces the concept of the MMC, analyzes its static characterstics, and proposes a specific methodology for the design of steady‐state MMCs. It is shown that the framework of MMC can explicitly handle all types of control objectives (for example, equality or inequality specifications on controlled outputs), and constraints on manipulations. Its priority‐driven, sequential satisfaction of control objectives leads to a modular, hierarchical structure of controllers with specific objectives. The modular character of MMC allows the explicit maintenance, tuning, and reconfiguration of multivariable control systems, while its hierarchical structure explicitly expresses engineering decisions and trade‐offs. Its static design incorporates uncertainty in process gains and automatic reconfiguration to account for failure in sensors and/or actuators. The design of an MMC for a heavy oil fractionator is presented to illustrate the controller's character and the proposed methodology for the design of static MMCs.
Nonlinear control of a batch polymerization reactor: An experimental study
Authors: Soroush Masoud , Kravaris Costas
Published: June 2004

This work studies the experimental application of the globally linearizing control (GLC) method to a batch polymerization reactor. The nonlinear controller is implemented on a microcomputer to start up the reactor and then track a precalculated optimal temperature profile. The reactor temperature is controlled by manipulating two coordinated inputs: power to an electrical heat and cooling water flow rate. A reduced‐order observer is used to estimate the concentration of initiator and monomer. Systematic tuning guidelines are proposed for the nonlinear control method. The experimental results show the excellent servo and regulatory performance of the nonlinear controller in the presence of modeling and observer initialization errors and active manipulated input constraints. Furthermore, in comparison to a conventional PID controller, the performance of the nonlinear controller is significantly superior, and its tuning is much easier.
Separation regions and processes of zeotropic and azeotropic ternary distillation
Authors: Stichlmair Johann G. , Herguijuela Juan‐Ramon
Published: June 2004

The rigorous calculation of top and bottom fractions of a multicomponent distillation is very time consuming and involved as it can only be done iteratively, and convergence problems are often encountered, especially in azeotropic systems. This article presents a method for the easy determination of possible top and bottom fractions of a ternary distillation. This method, which works for zeotropic as well as for azeotropic mixtures, is especially useful in the first steps of process synthesis and design since impossible separations can be determined and thus excluded from further analysis so that work can be concentrated on feasible processes. A very important application of the method developed in this article is to the design and analysis of processes for complete separation of binary azeotropic mixtures by use of an entrainer (for example, Azeotropic Distillation and Extractive Distillation). Knowledge of the separation regions in the distillation diagram allows for the development of a generalized process and the formulation of criteria for entrainer selection. The effectiveness of the method is demonstrated on a number of industrial important processes.
Real‐time qualitative analysis of the temporal shapes of (bio) process variables
Authors: Konstantinov Konstantin B. , Yoshida Toshiomi
Published: June 2004

One of the limitations of today's knowledge‐based (KB) systems for diagnostics and supervision is a lack of adequate temporal reasoning mechanisms. Most of these systems are designed primarily to operate with the current values of the process variables and, sometimes, with their derivatives. Such simple capabilities, however, are not always sufficient to identify some complex dynamic phenomena, which in many cases leave their own unique “stamp” on the process behavior, expressed in the form of characteristic temporal shapes of the related variables. To detect and diagnose adequately the events of interest, the KB system should be able to reason about the temporal shapes of the process variables. Although during manual supervision process operators rely heavily on such characteristic shapes as reliable symptoms of underlying phenomena, their exploitation has not been considered seriously by the designers of KB control systems. We propose a generic methodology for qualitative analysis of the temporal shapes of continuous process variables designed to be embedded into a real‐time KB environment. It is applicable to bioprocesses, as well as to other complex dynamic systems.
Falling film absorption on a cylindrical tube
Authors: Conlisk A. T.
Published: June 2004

The falling liquid film has become a popular means of transferring heat and mass from a vapor to a binary liquid film; applications include heat pump systems, desalination, and gas‐liquid contactors. In the heat pump application, in particular, the length of the liquid film is a crucial factor because of size and weight limitations. Consequently, it is desirable to be able to predict the amount of mass absorbed in a given length of tube. In this work the absorption of water vapor into a Lithium‐Bromide Water mixture is considered. It is shown that mass transfer takes place in a thin layer of fluid near the liquid‐vapor interface which is indicative of a very high level of liquid‐side mass‐transfer resistance. Closed form solutions for the velocity field may be used to derive a simple closed form solution for the mass fraction. For very thin films the temperature distribution may be obtained analytically in Laplace transform space; however, due to the complexity of the solution, numerical techniques are employed to obtain quantitative results. For thicker films a closed form solution for the temperature may be obtained as well. The principal objective of this work is to develop a design procedure not requiring a significant amount of numerical work whereby the absorption capacity of a given tube may be predicted as a function of the governing geometrical and physical parameters. The analytical/numerical results are presented for parameters corresponding to those of recent experiments and the agreement between theory and experiment is good.
Mass/heat‐exchange network representation of distillation networks
Authors: Bagajewicz Miguel J. , Manousiouthakis Vasilios
Published: June 2004

This article introduces the “state space” conceptual framework to process synthesis, which is used to provide a novel representation of a distillation network as a composite heat‐ and mass‐exchange network. This representation suggests that distillation network synthesis may best be viewed as an interacting heat‐ and mass‐exchange network synthesis problem. In that regard, familiar tools (such as pinch diagrams) from both heat‐exchange network (HEN) and mass‐exchange network (MEN) synthesis are shown to be of use in arriving at energy‐efficient distillation network designs. Examples of propylene‐propane and solvent‐water separations are used to illustrate the proposed conceptual framework.
Steric mass‐action ion exchange: Displacement profiles and induced salt gradients
Authors: Brooks Clayton A. , Cramer Steven M.
Published: June 2004

The study of nonlinear competitive equilibrium is of fundamental importance in understanding the behavior of proteins in preparative ion‐exchange chromatographic separations. In this work we present a steric mass‐action (SMA) ion‐exchange equilibrium formalism, which explicitly accounts for the steric hindrance of salt counterions upon protein binding in multicomponent equilibria. An analytical solution has been derived for the calculation of isotachic effluent profiles of displaced proteins and induced salt gradients under ideal chromatographic conditions. A stability analysis has been employed to establish the order of the feed components in the displacement train. Theoretical predictions are compared to experimental results for the separation of proteins by cation‐exchange displacement chromatography. These results demonstrate the efficacy of the SMA formalism in predicting complex behavior present in ion‐exchange displacement systems. Furthermore, the analytical solution of ideal isotachic displacement profiles with the SMA formalism enables rapid methods development and optimization of ion‐exchange displacement separations.
Depostition of submicron aerosol particles in turbulent and transitional flow
Authors: Shimada Manabu , Okuyama Kikuo , Asai Masahito
Published: June 2004

Brownian and turbulent diffusive deposition of submicron aerosol particles from pipe flow is studied experimentally and theoretically. A theoretical model for evaluating the turbulent diffusive deposition is presented in which a turbulent flow in a circular pipe is numerically calculated based on the k‐ϵ turbulent flow model and deposition velocities are derived by solving the convection‐diffusion equation. Deposition velocities of monodisperse aerosol particles, 0.01–0.04 μm in diameter, are obtained experimentally by measuring the decrease in the particle number concentration of an aerosol at two cross‐sections of a circular test pipe through which the aerosol is flowing. The deposition velocities obtained when Re is larger than about 3,000 agree well with those predicted by the present analysis which are proportional to the 0.92nd power of Reynolds number and the 0.33rd power of Schmidt number. The particle deposition rates are measured when 1, 000 ≲ Re ≲ 2,000 suggest a transitional state for particle deposition which cannot be explained by the present analysis nor by the laminar pipe flow deposition theory.
Wave‐net: a multiresolution, hierarchical neural network with localized learning
Authors: Bakshi Bhavik R. , Stephanopoulos George
Published: June 2004

A Wave‐Net is an artificial neural network with one hidden layer of nodes, whose basis functions are drawn from a family of orthonormal wavelets. The good localization characteristics of the basis functions, both in the input and frequency domains, allow hierarchical, multiresolution learning of input‐output maps from experimental data. Furthermore, Wave‐Nets allow explicit estimation for global and local prediction error‐bounds, and thus lend themselves to a rigorous and explicit design of the network. This article presents the mathematical framework for the development of Wave‐Nets and discusses the various aspects of their practical implementation. Computational complexity arguments prove that the training and adaptation efficiency of Wave‐Nets is at least an order of magnitude better than other networks. In addition, it presents two examples on the application of Wave‐Nets; (a) the prediction of a chaotic time‐series, representing population dynamics, and (b) the classification of experimental data for process fault diagnosis.
Model identification of a spatiotemporally varying catalytic reaction
Authors: Krischer K. , Rico‐Martínez R. , Kevrekidis I. G. , Rotermund H. H. , Ertl G. , Hudson J. L.
Published: June 2004

The occurrence of instabilities in chemically reacting systems, resulting in unsteady and spatially inhomogeneous reaction rates, is a widespread phenomenon. In this article, we use nonlinear signal processing techniques to extract a simple, but accurate, dynamic model from experimental data of a system with spatiotemporal variations. The approach consists of a combination of two steps. The proper orthogonal decomposition [POD or Karhunen‐Loève (KL) expansion] allows us to determine active degrees of freedom (important spatial structures) of the system. Projection onto these “modes” reduces the data to a small number of time series. Processing these time series through an artificial neural network (ANN) results in a low‐dimensional, nonlinear dynamic model with almost quantitative predictive capabilities.

This approach is demonstrated using spatiotemporal data from CO oxidation on a Pt (110) crystal surface. In this special case, the dynamics of the two‐dimensional reaction profile can be successfully described by four modes; the ANN‐based model not only correctly predicts the spatiotemporal short‐term behavior, but also accurately captures the long‐term dynamics (the attractor). While this approach does not substitute for fundamental modeling, it provides a systematic framework for processing experimental data from a wide variety of spatiotemporally varying reaction engineering processes.
Experimental validation of a mathematical model for fixed‐bed desulfurization
Authors: Efthimiadis Evangelos A. , Sotirchos Stratis V.
Published: June 2004

Porous particles of two commercially available ZnO sorbents differing in porosity, surface area, and pore‐size distribution were reacted with H2S at 500 and 600°C in a fixed‐bed reactor. Concentration breakthrough curves were determined by analyzing the effluent of the reactor using a gas chromotograph equipped with thermal conductivity and flame photometric detectors. The pore structure of samples collected from different positions in the reactor was analyzed by mercury porosimetry and gas adsorption to determine the variation of the average structural properties of the sorbent with the length of the reactor. The obtained experimental data were used to validate a fixed‐bed desulfurization model, which employs detailed submodels for diffusion, reaction, and structure evolution in the porous sorbent particles. With the various parameters appearing in the submodels determined from independent thermogravimetric reactivity evolution experiments, the fixed‐bed desulfurization model was found to be capable of providing an excellent description of the behavior of the desulfurization sorbents in a fixed‐bed reactor.
A kinetic model for olefin polymerization in high‐pressure autoclave reactors
Authors: Chan Wai‐Man , Gloor Paul E. , Hamielec Archie E.
Published: June 2004

Free radical copolymerization in high‐pressure autoclave reactors is studied by developing a mathematical model. Kinetic mechanisms to describe the polymerization rate, molecular weight averages, branching frequencies, as well as copolymer composition are presented. Two phase kinetics due to polymer‐monomer solubilities in the reaction mixture are taken into account. Gel formation from cross‐linking reactions is also analyzed. A mixing model is developed to represent the stirring effect inside the reactor. The mathematical model is implemented as a computer program to simulate commercial autoclave reactors. PID control equations are used to maintain operation at the unstable steady state. A sensitivity study is performed on the mixing model parameters and on some of the kinetic parameters and the model is compared to rate data from commercial reactors.
Fibroblast‐populated collagen microsphere assay of cell traction force: Part 1. Continuum model
Authors: Moon Alice G. , Tranquillo Robert T.
Published: June 2004

The most popular in vitro assay currently used to characterize cell traction forces exerted on extracellular matrix (ECM) fibers is the fibroblast‐populated collagen lattice (FPCL) assay. The compaction of a disk of cell‐populated collagen gel, in terms of rate or extent of diameter reduction, is typically reported as the measure of cell traction. This measure, however, depends on assay properties incidental to the intrinsic traction, such as the initial cell concentration, the initial collagen concentration, and the geometry of the gel. Thus, there is a clear need to identify and measure an objective index of cell traction. Here, we propose as such an index a traction parameter (reflective of the cell‐fiber mechanical interaction) defined in a continuum theory in which the interactive processes of cell motility and ECM deformation are modeled by expressions for cell and ECM conservation coupled to the mechanical force balance for the cell‐ECM composite. The equations are formulated and solved for our adaptation of the FPCL assay in which cells are initially dispersed in a collagen gel microsphere, conferring several experimental and theoretical advantages over the popular disk geometry. The solution of the nonlinear system of partial differential equations (parameterized on the traction parameter) is then compared to compaction data for the fibroblast‐populated collagen microspheres (FPCM). We show that the model predictions are consistent with the data when the initial cell concentration and the initial FPCM diameter are varied. In Part 2, we show how these results, along with the determination of the growth parameters of the cells and the viscoelastic parameters of the gel, have allowed us to estimate the magnitude of the traction parameter, which is a direct measure of the traction exerted by fibroblasts in a physiologically relevant collagen gel.
Rheological properties of Hydroxypropyl Guar (HPG) slurries
Authors: Shah Subhash N.
Published: June 2004

Rheological behavior of moderately concentrated (up to 35 vol. %) suspensions or slurries prepared with non‐Newtonian carrier fluids is investigated. Extensive experimental data on the Poiseuille slit flow of suspensions of sand in Hydroxypropyl Guar (HPG) solutions are presented. Flow data are gathered by pumping various non‐Newtonian slurries into a unique, 8 ft (2.4 m) tall vertical apparatus, with great care taken to calibrate the instrument and to avoid settling difficulties. Investigated are the effects of polymer concentration, solids concentration, test temperature, and shear rate on the rheological properties of slurries. The rheological behavior of HPG solutions and HPG suspensions is characterized by a pseudoplastic power law non‐Newtonian fluid model over a shear rate range of 30 to 500 s−1. The correlations for predicting the relative slurry viscosity for HPG fluids are presented. Substantial increase in viscosity of these non‐Newtonian fluids is observed, and they are found to be a strong function of polymer concentration, shear rate, test temperature, and particle concentration. Results of this investigation are also compared with those available for Newtonian and non‐Newtonian suspensions.
Dynamics of shell‐and‐tube heat exchangers to arbitrary temperature and step flow variations
Authors: Xuan Y. , Roetzel W.
Published: June 2004

A versatile and efficient method is developed for predicting dynamic performances of parallel and counterflow heat exchangers subject to arbitrary temperature variations and step flow disturbances, including the effect of flow maldistribution and the influence of heat capacities of both fluids, shell wall and tube bank as well as nonzero initial temperatures. Two algorithms of numerical inversion of the Laplace transform are introduced to determine the final temperature profiles in the realtime domain and some examples are calculated with nonuniform initial conditions. The accuracy of the proposed method is demonstrated with the calculated results at new steady states. Experiments are carried out on a labor‐sized heat exchanger to further examine the feasibility of this method and the comparison between calculated and measured temperature profiles is illustrated and discussed.
Control of nonlinear systems using polynomial ARMA models
Authors: Hernández Evelio , Arkun Yaman
Published: June 2004

Most of the advanced nonlinear control algorithms require a model of the system to be controlled. Unfortunately, most of the processes in the chemical industry are nonlinear, and fundamental models describing them are lacking. Thus there is a need for the identification and control of nonlinear systems through available inputoutput data. In this article, we briefly introduce the input‐output model used (polynomial ARMA models), and analyze its stability and invertibility. This paves the way to the development of a nonlinear‐model‐predictive controller. Implementation issues such as modeling of disturbance, state and parameter estimation are discussed. The theory presented is illustrated through examples.
Kinetics of carbothermal reduction synthesis of beta silicon carbide
Authors: Weimer Alan W. , Nilsen Kevin J. , Cochran Gene A. , Roach Raymond P.
Published: June 2004

Carbothermal reduction kinetics to synthesize SiC is studied under conditions of high carbon/silica precursor heating rates (105 K/s) and minimized reaction times (s) over a wide temperature range (1,848⩽T⩽2,273 K). The reaction mechanism includes rapid formation of a gaseous SiO intermediate. Further carbon reduction of the SiO to SiC is reaction‐rate‐controlling. Carbon crystallite diameter, d, has a substantial influence on the rate of reaction and the size of synthesized SiC. Fractional oxide conversion, X, can be described by a contracting volume shrinking core model:

where k0 = 27.4 m/s and E = 382±34 kJ/mol.
Developing flow of a gas‐particle mixture in a vertical riser
Authors: Pita Jorge A. , Sundaresan Sankaran
Published: June 2004

A computational study of steady, developing flow of gas‐particle suspensions in a vertical riser has been carried out, using a model based on kinetic theory of granular materials, to understand the role of inlet configuration on the pattern of flow development. Three inlet configurations—uniform inlet, core‐annulus flow at the inlet and circumferential injection of secondary gas—were examined. It is found that the inlet configuration can have a profound impact on the rate of segregation of particles to the wall and the internal recirculation. Circumferential injection of gas has a favorable effect on the flow in the sense that it can decrease the extent of internal recirculation.
Application of flexible recipes for model building, batch process optimization and control
Authors: Keesman Karel J.
Published: June 2004

Unlike the traditionally fixed recipes in batch process operation, flexible recipes allow the adjustment of some of its relevant recipe items. These adjustments can either be predefined in cases of planned experimentation, or suggested by a formal process optimization or control algorithm on the basis of actual information. In both the response surface methodology and the simplex evolutionary operation (EVOP), some well‐known methods for empirical model building and process optimization, flexible recipes are involved. Another application of flexible recipes arises in a feedforward quality control strategy of batch processes when variations in market or process conditions are known a priori. The experimental results of these strategies are presented for the batchwise production of benzylalcohol on a pilotplant scale. Experiments have been performed to obtain a reliable model of the yield. On the basis of this model, better process conditions have been suggested, which substantially deviate from the final simplex resulted from experiments within simplex EVOP. Finally, an adaptive feedforward control strategy has been applied for a priori known disturbances in the process inputs.
Nonlinear predictive control of periodically forced chemical reactors
Authors: Özgülşen Fatih , Kendra Scott J. , Çinar Ali
Published: June 2004

A nonlinear model‐predictive control strategy is developed to maintain the superior‐to‐steady‐state performance of a periodically forced chemical reactor. The performance of the predictive controller is investigated in the presence of measurement disturbances and parametric uncertainty. It is also shown that statistically inferred input‐output models can be a substitute whenever detailed fundamental models are not available. A nonlinear autoregressive polynomial model based on observed plant data is built and incorporated into the control scheme. The catalytic oxidation of ethylene in a periodically‐forced, continuous stirred‐tank reactor is considered as the test case.
Membrane elasticity effects on permeability measurements in vesicles
Authors: Chiruvolu Shivkumar , Zasadzinski Joseph A. N.
Published: June 2004

Typical experiments to measure permeability in biologically relevant cell membranes utilize vesicles, single bilayer membrane capsules, as idealized cells. The permeation of solute through the vesicle membrane is analyzed with the assumption that the vesicle volume and membrane area are fixed during the experiment. In response to the excess solute concentration internal to the vesicle, however, an osmotic stress is set up that acts to stretch the vesicle membrane, resulting in an initial dilution of the vesicle contents, followed by a continued elastic response of the vesicle membrane as the experiment proceeds and the internal and external concentrations equilibrate. We derive a simple analytic theory of this process that couples the mass‐transfer process with the area elasticity of the vesicle membrane. If dilution of the exterior solution is used to initiate the permeation, significant effects on measured permeabilities are predicted for membranes with a low elastic modulus, when large concentration differences are imposed or vesicles are greater than 0.1 micron in diameter. In practice, this leads to an underestimate of the permeability of membranes composed of polyunsaturated lipids or lipids in contact with alcohols or alkanes. It could also lead to the erroneous conclusion that the permeability is concentration‐dependent. The effects of elasticity, however, are minor, if dialysis is used to continually remove any exterior solute or if saturated phospholipid membranes with a large elastic modulus or vesicles of less than 0.1 micron diameter are used.
Visualization of flow characteristics in a 2‐D bubble column and three‐phase fluidized bed
Authors: Tzeng J.‐W. , Chen R. C. , Fan L.‐S.
Published: June 2004

Macroscopic flow structures of gas‐liquid and gas‐liquid‐solid fluidization systems are studied through flow visualization using a two‐dimensional column under various operating conditions. The gas distributor in the column comprises multiple injectors which are individually regulated to generate desired gas flow rates, bubble injection frequencies, and bubble sizes. Colored bed particles and neutrally buoyant particles as solid and liquid tracers, respectively, are used for flow visualization through video photography. In a gas‐liquid system operated under liquid‐batch conditions, bubble streams injected near both sidewalls are observed to migrate toward bed vertical axis, and vortices appear along the sidewalls when gas velocity exceeds 4–6 mm/s. A considerable amount of liquid descends along the sidewalls in a vortical flow pattern. The gross circulation pattern occurring at high gas velocities is associated closely with induced liquid or liquid‐solid flows resulting from rising bubbles and bubble wakes. When the gross circulation occurs, four flow regions can be distinguished. The formation of and mechanism for gross circulations can be interpreted in part based on two simplified flow conditions involving single bubbles rising in a stationary liquid and single chains of bubbles injected in a batch liquid. The effects of particle size, inlet liquid velocity and gas flow distribution on the macroscopic flow structure are also examined.
A simple model and experiments for adsorption‐desorption hysteresis: Water vapor on silica gel
Authors: Rajniak Pavol , Yang Ralph T.
Published: June 2004

A simple model is proposed for the evaluation of the primary and secondary adsorption and desorption processes for hysteresis‐dependent sorption systems. The model is based on the use of pore blocking interpretation of hysteresis in an interconnected network of pores. The model is simple to use and requires only the primary adsorption and primary desorption isotherms to predict all secondary desorption and adsorption isotherms. A complete set of equilibrium adsorption‐desorption curves covering the hysteresis loop (appearing in the range of relative pressure 0.3–0.7) was measured for water vapor on silica gel at 25° C. The usefulness of the model is supported by its agreement with experimental data.