bluuebunny/crossref_metadata_2025_split huggingface dataset:
Vacuum membrane distillation: Experiments and modeling
Authors: Bandini Serena , Saavedra Aldo , Sarti Giulio Cesare 
Published: June 2004

AbstractVacuum membrane distillation is a membrane‐based separation process considered here to remove volatile organic compounds from aqueous streams. Microporous hydrophobic membranes are used to separate the aqueous stream from a gas phase kept under vacuum. The evaporation of the liquid stream takes place on one side of the membrane, and mass transfer occurs through the vapor phase inside the membrane. The role of operative conditions on the process performance is widely investigated in the case of dilute binary aqueous mixtures containing acetone, ethanol, isopropanol, ethylacetate, methylacetate, or methylterbutyl ether. Temperature, composition, flow rate of the liquid feed, and pressure downstream the membrane are the main operative variables. Among these, the vacuum‐side pressure is the major design factor since it greatly affects the separation efficiency. A mathematical model description of the process is developed, and the results are compared with the experiments. The model is finally used to predict the best operative conditions in which the process can work for the case of benzene removal from waste waters.
Thermodynamic consistency of vapor‐liquid equilibrium data at high pressure
Authors: Bertucco Alberto , Barolo Massimiliano , Elvassore Nicola 
Published: June 2004

AbstractA method for testing the thermodynamic consistency of binary and isothermal vapor‐liquid equilibrium data at moderate and high pressures is proposed, using a ϕ‐ϕ approach. The Redlich‐Kwong‐Soave equation of state with Huron‐Vidal mixing rules at infinite pressure is used in the data‐reduction procedure, and a Margules equation is used to calculate the activity coefficients at infinite pressure. This model is shown to be thermodynamically consistent. The proposed method allows us to check consistency of vapor‐liquid equilibrium data in the presence of components at the gaseous and supercritical states.
Unsteady heat and mass transfer from a spheroid
Authors: Feng Zhi‐Gang , Michaelides Efstathios E. 
Published: June 2004

AbstractThe unsteady heat‐transfer processes from oblate or prolate spheroids, at the limit of very small Peclet numbers is examined. A perturbation technique for the temperature and the geometry of the particle is used to obtain the rates of heat and mass transfer, first in the Laplace and then in the time domain. A solution to the problem is obtained, including the ϵ2 contribution (ϵ is the eccentricity). The solution reveals the existence of several history terms, which are analogous to the history terms of the creeping flow equation of motion. One of these terms is solely due to the eccentricity of the spheroid. This is an indication that the shape of the particle is a factor of the existence and from of history terms. In addition, an exact expression for the steady‐state heat transfer from a spheroid is obtained using a convenient transformation of the heat‐transfer integral.
Resonant microwave power absorption in slabs and cylinders
Authors: Ayappa K. G. , Davis H. T. , Barringer S. A. , Davis E. A. 
Published: June 2004

AbstractResonant power absorption is an important phenomenon during microwave heating. The resonances that occur when plane electromagnetic waves are incident on infinitely long cylinders and slabs are investigated as a function of sample dimensions. For cylinders two kinds of incident waves are studied: TMz when the electric field is oriented along the axis of the cylinder and TEz when the magnetic field is oriented along the axis. At a resonant condition the overage power absorbed by the sample is a local maximum. Due to attenuation within the sample the resonances decrease in intensity as the sample size increases. Using the dielectric properties of water, resonances are found to be a function of the ratio of the sample dimension to the wavelength of radiation, λs, in the sample. For slabs of thickness L and integer values of n, resonances occurred at L/λs = 0.5n; for cylinders of diameter D, resonances occurred at D/λs = 0.5n – 0.257. The generality of these relations to predict resonances in other food samples are shown using existing dielectric data. Resonances in cylinders for both polarizations occurred at similar radii. However, the radius at which the first resonance occurred for the TMz case was absent in the TEz case.
Transient behavior of pulsed particulate fluidized beds
Authors: van der Wielen L. A. M. , Fa A. W. K. G. Sjauw Koen , Potters J. J. M. , Luyben K. Ch. A. M. 
Published: June 2004

AbstractTransient phenomena in solid–liquid fluidized‐bed systems are important in designing pulsed, countercurrent (multistage) fluidized‐bed contactors of the Cloete‐Streat type at high‐solids flow rate. Of particular interest are the residence times or corresponding velocities of porosity gradients in the bed and the excess or overshoot height of the bed after refluidization. Theory assuming local equilibrium between holdup and velocity of the phases (local‐equilibrium model) for stepwise perturbations in the liquid flow is readily available. It is investigated whether the local‐equilibrium theory can be used for more complex perturbations and whether inertia effects, such as are encountered in countercurrent multistage fluidized‐bed systems, can be ignored. Therefore, the detailed particle‐bed model of Foscolo and Gibilaro, which incorporates inertia effects, was applied to investigate the transient behavior of fluidized‐bed systems. Transient fluidization experiments were performed with a broad range of water‐fluidized particles in a laboratory‐scale multistage fluidized‐bed contactor. The operating conditions corresponded to those for countercurrent contact.Numerical simulations with the particle‐bed model predict satisfactory experimental results. The “overshoot” heights of the fluidized bed were estimated correctly by the particle‐bed model, whereas the local‐equilibrium model only provides a conservative estimate. However, the local‐equilibrium model allows an analytical solution that is more interesting for design, as it avoids tedious calculations. The residence time of the last perturbation before the fluidized bed relaxes to steady state was estimated with similar accuracy by both models.
Identification of full profile disturbance models for sheet forming processes
Authors: Rigopoulos Apostolos , Arkun Yaman , Kayihan Ferhan 
Published: June 2004

AbstractIn this article we present a method for the on‐line identification and modeling of full profile disturbance models for sheet forming processes. A particular principal components analysis technique called the Karhunen‐Loève expansion is used to adaptively identify the significant features of the profile. In addition, we show how the temporal modes of the reconstructed profile can be modeled using low‐order linear autoregressive (AR) processes. By simulation examples, the effect of the order of the AR model is studied, as well as the window size of the data used in the on‐line application of the KL expansion, the effect of data weighting, the importance of the correct selection of the number of modes, and the frequency of updating the parameters of the AR models. Identified disturbance models can be easily incorporated into model‐predictive control algorithms.
Effects of particle‐phase turbulence in gas‐solid flows
Authors: Hrenya Christine M. , Sinclair Jennifer L. 
Published: June 2004

AbstractNumerous experimental investigations on the vertical transport of dense gas–solid suspensions indicate that particles tend to segregate toward the tube wall. Although models based on the kinetic theory analogy can predict such patterns for perfectly elastic particle‐particle collisions, the predictive ability of these models breaks down for inelastic collisions. In the present effort, a mathematical model is developed that incorporates two mechanisms that give rise to the lateral segregation of solids: interactions associated with individual particles based on a kinetic theory treatment and interactions associated with collections of particles based on an analogy with single‐phase turbulent flows. Although these two mechanisms have been treated independently by previous workers, their combined contributions to the overall flow behavior have not been thoroughly investigated. The effect of such a treatment on the sensitivity of the model predictions to the inelasticity of particle–particle collisions is explored. A key element in eliminating the undue sensitivity appears to be a consideration of the effects associated with the collective motion of particles on the kinetic theory expressions. The resulting model can predict the expected segregation patterns for systems characterized by inelastic collisions, as well as many of the other salient features of vertical gas–solid flows.
Simulated moving bed under linear conditions: Experimental vs. calculated results
Authors: Yun Tong , Zhong Guoming , Guiochon Georges 
Published: June 2004

AbstractA simulated moving bed (SMB) was operated for the separation of mixtures of 2‐phenyl ethanol and 3‐phenyl‐1‐propanol on columns packed with Zorbax C18 bonded silica, using a 60:40 (v/v) solution of methanol and water as the mobile phase. Series of four or eight columns were used. The experiments were carried out with low concentration mixtures, that is, under linear conditions. Band profiles of both compounds eluted from one of the columns during successive periods after steady state had been reached were recorded, as were the concentration histories at the extract and raffinate ports. These experimental results are compared to those predicted by two models: the linear ideal and the linear equilibrium‐dispersive models of chromatography, applied to the SMB separator. These two models give excellent agreement between the experimental profiles and those calculated with the model. As expected, the profiles predicted by the ideal and the equilibrium‐dispersive models differ only by the lack of dispersion in the profiles given by the former. The latter model is demonstrated to be a solid, reliable tool for further studies of the SMB design and optimization.
Pulsed electrophoretic filter‐cake release in dead‐end membrane processes
Authors: Bowen W. Richard , Ahmad A. Latif 
Published: June 2004

AbstractThe application of electric fields can be a very effective means of removing deposits from membrane surfaces. Such a means of process improvement has usually been applied to cross‐flow filtration, allowing efficient operation at low cross‐flow velocities. In the limiting case of dead‐end filtration (zero crossflow) it is possible to use electric‐field pulses to release the filter cake for collection. Experimental data are presented for the dead‐end ultrafiltration of silica colloids and the protein bovine serum albumin and for the dead‐end microfiltration of titania dispersions taking as variables the magnitude of the applied field, the pulse interval, the pulse duration, and the feed conditions (pH, ionic strength, concentration). The data identify the conditions when pulsed electric fields can be used as an efficient means of releasing filter cakes for collection. A force balance model is developed to predict the filtration rate at the end of the release process, taking into account electrophoretic, electroosmotic, and hydrodynamic forces. The model shows excellent agreement with the experimental data for ultrafiltration and reasonable agreement with the experimental data for microfiltration. The use of pulsed electric fields to release filter cakes in dead‐end membrane processes is a promising technique that is most likely to find application in the clarification of process feeds containing low dispersed solutes.
Inference in dynamic error‐in‐variable‐measurement problems
Authors: Albuquerque JoãO S. , Biegler Lorenz T. , Kass Robert E. 
Published: June 2004

AbstractEfficient algorithms were developed for estimating model parameters from measured data, even in the presence of gross errors. In addition to point estimates of parameters, however, assessments of uncertainty are needed. Linear approximations provide standard errors, but they can be misleading when applied to models that are substantially nonlinear. To overcome this difficulty, profiling methods were developed for the case in which the regressor variables are error free. These methods provide accurate nonlinear confidence regions, but become expensive for a large number of parameters. These profiling methods are modified to error‐in‐variable‐measurement models with many incidental parameters. Laplace's method is used to integrate out the incidental parameters associated with the measurement errors, and then profiling methods are applied to obtain approximate confidence contours for the parameters. This approach is computationally efficient, requires few function evaluations, and can be applied to large‐scale problems. It is useful when certain measurement errors (such as input variables) are relatively small, but not so small that they can be ignored.
Integrated flexibility and controllability analysis in design of chemical processes
Authors: Bahri Parisa A. , Bandoni Jose A. , Romagnoli Jose A. 
Published: June 2004

AbstractA systematic approach for the synthesis of flexible and controllable plants is presented. It provides a new quantitative measure of the flexibility and controllability of a design and allows the designer to systematically evaluate different process structures and/or control systems. An integrated approach based on the dynamic mixed‐integer nonlinear‐programming problem is introduced that consists of two stages in each iteration of the algorithm. In this way, the effect of disturbances on the process design and operation, as well as its ideal performance, under a variety of control schemes can be estimated. The method is illustrated using a mini‐integrated plant as a case study.
LP methods in MPC of large‐scale systems: Application to paper‐machine CD control
Authors: Dave Prashant , Willing Dennis A. , Kudva Gautham K. , Pekny Joseph F. , Doyle Francis J. 
Published: June 2004

AbstractAn application of a linear‐programming based model‐predictive control strategy to the paper‐machine cross‐direction (CD) control problem is presented. The objective of CD control is to maintain flat profiles of variables of interest by minimizing worst‐case deviations from setpoints (defects). These control problems can have as many as 200 actuatiors (inputs) and 400 sensor measurements (outputs). This large size coupled with the stringent real‐time requiremnt of computing a control move in a few seconds poses a very challenging control problem. The LP‐based strategy is particularly well suited for solving such classes of control problems. This strategy has demonstrated its ability to solve large‐scale control problems (over 100 inputs and 100 outputs) in real time and exhibits robustness to model uncertainty.
Design procedure for stable operations of first‐order reaction systems in a CSTR
Authors: Heiszwolf Johan J. , Fortuin Jan M. H. 
Published: June 2004

AbstractAn application‐oriented design procedure is presented for unique and point‐stable operations of first‐order reaction systems in a continuous stirred‐tank reactor (CSTR). For a given set of values of kinetic constants, reaction enthalpy, feed conditions, residence time, and relevant physical properties, two boundary values of the heat‐transfer capacity (St1, St3) and two of the modified coolant temperature (θmc, 2, θmc, 3) are analytically derived after a linearization of the unsteady mass and energy balances. With these boundary values, two separate design conditions are formulated; one for the heat‐transfer capacity (HTC, characterized by St) and one for the modified coolant temperature (MCT, characterized by θmc). Each of these conditions is sufficient to guarantee unique and point‐stable steady‐state operations for a range of St or θmc values. Predicted behaviors of reacting systems are compared with experimental results obtained from five different systems reacting in four bench‐scale and two commercial reactors.
Estimation of nonlinear systems using linear multiple models
Authors: Banerjee A. , Arkun Y. , Ogunnaike B. , Pearson R. 
Published: June 2004

AbstractThis article addresses the problem of estimating the states of a nonlinear plant that operates in multiple regimes and makes transitions between them. It is often difficult to obtain a single nonlinear model that accurately describes the plant in all regimes. Even if a global model is available, it sometimes cannot be used conveniently in an estimator. An alternative approach is presented where local linear models are identified at each different operating point, and estimation is performed by tracking the transitions from one regime to another. This is done by first estimating the validity of the local models on‐line and then constructing a time‐varying global model by interpolating between the local linear models. State and parameter estimation is then performed using this global model in a moving horizon estimator. To demonstrate the effectiveness of this method, it is applied to three test systems: a simple numerical example, a CSTR, and a copolymerization reactor.
Optimal molecular design under property prediction uncertainty
Authors: Maranas Costas D. 
Published: June 2004

AbstractA systematic method that quantitatively assesses property prediction uncertainty (imprecision) on optimal molecular design problems is introduced. Propety–structure relations are described with specific nonlinear functionalities based on group contribution methods. Property prediction uncertainty is explicitly quantified by using multivariate probability density distributions to model the likelihood of different realizations of the group contribution parameters. Assuming stability of these probability distributions, a novel approach is introduced for transforming the original nonlinear stochastic formulation into a deterministic MINLP problem with linear binary and convex continuour parts with separability. The resulting convex MINLP formulation is solved to global optimality for molecular design problems involving many uncertain group contribution parameters. Results indicate the computtional tractability of the method and the profound effect that property prediction uncertainty may have in optimal molecular design. Specifically, trade‐off curves between performance objectives, probabilities of meeting the objectives, and chances of satisfying design specifications offer a concise and systematic way to guide optimal molecular design in the face of property prediction uncertainty.
Modeling of imperfect mixing and its effects on polymer properties
Authors: Zhang Simon X. , Ray W. Harmon 
Published: June 2004

AbstractA compartmental model is used to study imperfect mixing and its effects on polymer properties. Examples of imperfect feed mixing caused by a rapidly decomposing initiator are shown for styrene polymerization, high‐pressure ethylene polymerization, and vinyl acetate/methyl methacrylate solution copolymerization. Continuation analysis indicates mixing can change reactor steady states and stability. A composite approach is proposed to construct full molecular weight distribution (MWD) under imperfect mixing. In linear polymerization imperfect mixing broadens MWD; however, in nonlinear polymerization mixing can cause either broader or narrower MWD. By changing the dominant chaintermination mechanism to chain transfer, the influence of imperfect mixing on the MWD can be reduced. Depending on reactivity ratio and monomer composition, mixing also affects copolymer composition and chain sequence length.
Mechanisms of initiation of incrustation
Authors: Vendel Martin , Rasmuson Åke C. 
Published: June 2004

AbstractInitiaton of incrustation by crystallization mechanisms is studied. An experimental technique was developed by which nucleation of a crystalline phase on a solid surface is investigated at controlled local supersaturation without the interference of particle deposition. Experiments were carried out with different substances and surface materials. The results show that the solid surface may catalyze primary nucleation and hence promote the initiation of incrustation, but this was recorded only at quite high supersaturation. Collision of crystals with the solid surface in a supersaturated solution may initiate incrustation at a reasonably low supersaturation and can be of substantial industrial importance.
Parameterization of pressure‐ and temperature‐dependent kinetics in multiple well reactions
Authors: Venkatesh Prasana K. , Chang Albert Y. , Dean Anthony M. , Cohen Morrel H. , Carr Robert W. 
Published: June 2004

AbstractIt is now well confirmed that the influence of temperature on the fall‐off behavior of dissociation, recombination and chemically‐activated reactions can be dramatic. For single‐well, single‐product dissociation reactions, it is customary to approximate these fall‐off surfaces using extensions of Lindemann's empirical expression. We consider here chemical‐activation and dissociation reactions possessing multiple wells and multiple products. We show that direct approximation of the rate coefficients via Chebyshev expansions yields reliable and accurate representations of their pressure and temperature dependences, which are superior to those from a Lidemann approach to fit the form factor representing the fall‐off surface. The superiority of the method is demonstrated in a study of seven channels corresponding to four different reactions important in combustion chemistry over the ranges 300–3,000 K and 0.02–200 atm.
Crystallization process optimization via a revised machine learning methodology
Authors: Sheikh Ahmad Y. , Jones Alan G. 
Published: June 2004

AbstractA revised machine learing methodology is applied to a simulated crystallization process flowsheet for continual imporvement of its performance by generating and analyzing process data. The aim is to identify bands of crucial decision variables leading to zones of best average process performance. The methodology comprises two components: symbolic induction and case‐based reasoning. It uses an incremental algorithm to update performance classification rules, which not only improves the efficiency of the symbolic induction of the classification rules by eliminating the need for their periodic reinduction, but also simplifies the case‐based reasoning step. The new concepts and procedures are illustrated by application to a potassium nitrate crystallization process comprising a mixed‐suspension, mixed‐product‐removal crystallizer, a hydrocyclone, and a fines dissolver, By identifying and establishing ranges for the most crucial decision variables, namely, feed concentration, flow rate, and cooling stream temperature, three zones leading to an improvement of nearly 12% on nominal average performance are detected within two generations of the classification rules.
Prototype for intergated hazard analysis
Authors: Kuo Dong‐Hsiung , Hsu Ding‐Shang , Chang Chuei‐Tin , Chen Dong‐Han 
Published: June 2004

AbstractThe prototype of an integrated hazard‐analysis system (IHAS) was developed. Essentially any process can be analyzed with this software if the system topology is correctly supplied by the user. Since all altorithms adopted are digraph‐based, the system digraph must be constructed first with IHAS. The embedded feedforward and feedback loops are then identified and classified. On the basis of this information, three widely accepted hazard‐assessment procedures—FTA, ETA, and HAZOP—can be performed automatically. From the results obtained in practical applications, one can see that the quality. From the results obtained in practical applications, one can see that the quality of hazard analysis is indeed improved if IHAS can be used as an aid to the human experts.