bluuebunny/crossref_metadata_2025_split huggingface dataset:
A moving horizon‐based approach for least‐squares estimation
Authors: Robertson Douglas G. , Lee Jay H. , Rawlings James B. 
Published: June 2004

AbstractA general formulation of the moving horizon estimator is presented. An algorithm with a fixed‐size estimation window and constraints on states, disturbances, and measurement noise is developed, and a probabilistic interpretation is given. The moving horizon formulation requires only one more tuning parameter (horizon size) than many well‐known approximate nonlinear filters such as extended Kalman filter (EFK), iterated EKF, Gaussian second‐order filter, and statistically linearized filter. The choice of horizon size allows the user to achieve a compromise between the better performance of the batch least‐squares solution and the reduced computational requirements of the approximate nonlinear filters. Specific issues relevant to linear and nonlinear systems are discussed with comparisons made to the Kalman filter, EKF, and other recursive and optimization‐based estimation schemes.
Optimal design of dynamic systems under uncertainty
Authors: Mohideen M. Jezri , Perkins John D. , Pistikopoulos Efstratios N. 
Published: June 2004

AbstractFundamental developments of a unified process design framework for obtaining integrated process and control systems design, which are economically optimal and can cope with parametric uncertainty and process disturbances, are described. Based on a dynamic mathematical model describing the process, including path constraints, interior and end‐point constraints, a model that describes uncertain parameters and time‐varying disturbances (for example, a probability distributions or lower/upper bounds), and a set of process design and control alternatives (together with a set of control objectives and types of controllers), the problem is posed as a mixed‐integer stochastic optimal control formulation. An iterative decomposition algorithm proposed alternates between the solution of a multiperiod “design” subproblem, determining the process structure and design together with a suitable control structure (and its design characteristics) to satisfy a set of “critical” parameters/periods (for uncertainty disturbance) over time, and a time‐varying feasibility analysis step, which identifies a new set of critical parameters for fixed design and control. Two examples are detailed, a mixing‐tank problem to show the analytical steps of the procedure, and a ternary distillation design problem (featuring a rigorous tray‐by‐tray distillation model) to demonstrate the potential of the novel approach to reach solutions with significant cost savings over sequential techniques.
Monte Carlo simulation of carbon gasification using molecular orbital theory
Authors: Kyotani Takashi , Ito Ken‐ichi , Tomita Akira , Radovic Ljubisa R. 
Published: June 2004

AbstractAn attempt was made to simulate carbon gasification with the aid of molecular orbital theory. A simple Hückel method was applied to calculate molecular orbitals of a large polynuclear aromatic molecule, which was employed as a model crystallite for carbon. A free valence at each carbon atom in model crystallites of varying size and shape was determined, and this value was taken as a measure of reaction probability for the Monte Carlo simulation. Simulation of carbon gasification was performed by removing the carbon atoms from the model crystallites according to their corresponding reaction probabilities. This simulation made it possible to visualize how the shape of carbon crystallite is changed during gasification. It was found that the specific gasification rate depends on molecular size, but is essentially independent of the geometry of the starting model crystallite.
Controlled black liquor viscosity reduction through salting‐in
Authors: Roberts Joanna E. , Khan Saad A. , Spontak Richard J. 
Published: June 2004

AbstractBlack liquor viscosity increases exponentially with solids content and therefore causes processing problems for the paper industry by being a limiting factor in the Kraft pulp process. This study investigates a new approach for achieving viscosity reduction by “salting‐in” black liquor through the addition of thiocyanate salts. These salts generally increase the solubility of the polymer constituents in black liquor, leading to a decrease in its viscosity. Several thiocyanate salts capable of reducing liquor viscosity by more than two orders of magnitude have been identified, with viscosity reduction greatest at high solids content. Salting‐in of black liquor depends on the cation paired with the thiocyanate anion, as well as on solution pH and temperature. Comparative studies reveal that GuSCN is the most effective viscosity‐reducing agent of the series examined and that lignin plays an important role in the viscosity behavior of both unmodified and salted‐in black liquor at high solids concentrations. These experimental findings are interpreted in terms of the underlying principles that describe salting‐in and how it affects aqueous solution structure.
Analysis of excess free energy based equations of state models
Authors: Orbey Hasan , Sandler Stanley I. 
Published: June 2004

AbstractA comparison is made of the capabilities of various equation of state (EOS) + excess free energy (Gex) models in representing the activity‐coefficient models they incorporate. Such EOS models need to reproduce the excess Gibbs free energy behavior of the activity‐coefficient models as closely as possible in order to represent low‐pressure vapor–liquid equilibrium behavior of complex mixtures accurately, and also to make accurate the vapor–liquid predictions at higher temperatures and pressures using only low‐pressure information. It is demonstrated that the EOS models that use the excess Helmholtz free energy instead of the excess Gibbs free energy, and that combine the EOS with activity‐coefficient models at the infinite pressure limit, are successful for calculations of the type just described.
Measurement and modeling of activities of amino acids in aqueous salt systems
Authors: Khoshkbarchi Mohammad K. , Vera Juan H. 
Published: June 2004

AbstractActivity‐coefficient data were measured for NaCl in the system water–NaCl–DL‐valine at 25°C. The activity coefficients of DL‐valine were then calculated through rigorous thermodynamic relations. The activity coefficients of the amino acids in this and other aqueous systems containing electrolytes were modeled using an expression for the excess Gibbs free energy of the solution. The model combines a contribution for long‐range interactions, given either by the Bromley equation or the K‐V equation, and a contribution of short‐range interactions represented by a ternary NRTL or Wilson expression. The model accurately correlates the activity coefficients of ten amino acids in aqueous solutions and of six amino acids in aqueous electrolyte solutions.
Flow structure of the solids in a 3‐D gas–liquid–solid fluidized bed
Authors: Larachi F. , Cassanello M. , Chaouki J. , Guy C. 
Published: June 2004

AbstractLocal and macroscopic solids flow structure and kinematics in a 3‐D gas–liquid–solid fluidized bed were studied using a noninvasive radioactive‐particle tracking (RPT) technique. Based on the multisite detection of γ radiations emitted from a single radiolabeled tracer particle freely moving in the fluidized bed, RPT permitted to obtain fast sampling of 3‐D trajectories of the tracer, whose physical properties were similar to those of the solids inventory. These trajectories showed the detailed motion sequences of the solid particles as entrained in the bubble wakes, fluctuating randomly or sinking deterministically in the liquid–solid emulsion. Based on measurements done in the vortical‐spiral flow regime, the dynamic solids flow structure inside a three‐phase fluidized bed can be viewed as a three‐zone core–annulus–annulus structure: (1) a central fast‐bubble flow region with the particles swirling upward; (2) a vortical flow region around the velocity inversion point with the particles momentarily captured in emulsion vortices; and (3) a relatively bubble‐free descending flow region where the particles spiral down between the velocity inversion point and vessel walls. Our solids flow structure of dense fluidized beds are similar to the flow structure of liquid and/or solid in lean fluidized beds (observed through laser sheeting imaging). Measured distributions of local ensemble‐averaged particle velocities and turbulence intensities were consistent with the existence of a toroidal recirculatory solids flow pattern in the bed. Measured mean circumferential ensemble‐averaged radial velocity was essentially zero throughout most of the bed. The solids flow turbulence field was nonisotropic, as radial turbulence intensities were generally lower than longitudinal turbulence intensities.
Geometry and heat loss in channel flow of a fluid with temperature‐dependent density
Authors: Bechtel Stephen E. , Cao Dongbu , Hsiao Hsien‐fu 
Published: June 2004

AbstractCao et al. previously derived a thermomechanically constrained theory for materials with temperature‐dependent density and applied it to the illustrative problem of plane Poiseuille flow between isothermal walls. Here the theory is applied to geometries and thermal boundary conditions of practical importance in polymer processing: flows through planar, circular and annular dies with heat loss through the die walls. How geometry and thermal boundary conditions combine with material properties, especially thermal expansivity, to effect velocity and temperature profiles, and mass and volume flow rates is explored. A comparison is made with predictions that follow if temperature‐dependence of density is either ignored or handled (as is the standard practice) by a posteriori insertion of a temperature‐dependent expression for density into equations derived for constant density.
Effect of condensation heat on the condensation coefficient
Authors: Chekmarev Sergei F. 
Published: June 2004

AbstractTo account for the effect of condensation heat on the condensation coefficient (α), a semiempirical model is proposed. The model contains two free parameters: a characteristic size of the “hot spot” where the heat release occurs and its lifetime. At reasonable values of the parameters, the model agrees well with experimental and computer‐simulated data for both simple and associating liquids. For nonequilibrium conditions, the model leads to the Hertz–Knudsen equation with α dependent not only on characteristics of the liquid but also on those of ambient vapor. This offers an explanation for the existing scattering of experimental data in α. Among other things, the expression for α obtained shows that for the net evaporation process α is always higher than that for the net condensation, and moreover, α = 1 for all liquids if evaporation occurs in vacuum. The model also indicates that for complex associating liquids like glycerol α may be quite sensitive to peculiarities of the liquid state under consideration.
Process modeling using stacked neural networks
Authors: Sridhar Dasaratha V. , Seagrave Richard C. , Bartlett Eric B. 
Published: June 2004

AbstractA new technique for neural‐network‐based modeling of chemical processes is proposed. Stacked neural networks allow multiple neural networks to be selected and used to model a given process. The idea is that improved predictions can be obtained using multiple networks, instead of simply selecting a single, hopefully optimal network, as is usually done. A methodology for stacking neural networks for plant‐process modeling has been developed. This method is inspired by the technique of stacked generalization proposed by Wolpert. The proposed method has been applied and evaluated for three example problems, including the dynamic modeling of a nonlinear chemical process. Results obtained demonstrate the promise of this approach for improved neural‐network‐based plant‐process modeling.
Sensor network design for maximizing reliability of bilinear processes
Authors: Ali Yaqoob , Narasimhan Shankar 
Published: June 2004

AbstractThe problem of selecting the variables to be measured in order to maximize process reliability was tackled in our previous articles (Ali and Narasimhan, 1993, 1995). In this article, this approach is extended to the optimal design of sensor networks for bilinear processes. Diverse processes, such as a mineral beneficiation plant, a separation system of a synthetic juice plant, and a crude preheat train of a refinery are used to illustrate the utility of this approach.
Microencapsulation in polyurea shell: Kinetics and film structure
Authors: Yadav S. K. , Khilar Kartic C. , Suresh A. K. 
Published: June 2004

AbstractInterfacial polycondensation is an important polymerization technique that encapsulates a variety of active principles. Mechanisms governing the reaction and interplay of physical and chemical rate processes need to be understood for both rational design of reaction equipment and the process control to produce capsules with desired characteristics. A theoretical and experimental study of the process is reported here. Kinetic data were obtained over a range of concentrations, monomer mole ratios and polymer film thicknesses, using a technique that relies on the on‐line measurement of pH as a function of time. To understand the mechanisms the reaction was slowed down by reducing the interfacial area. A minimum thickness of the polymer was observed to be necessary so that capsules preserve their integrity and do not break up. The theoretical model developed considers ionic equilibria in the aqueous phase and the resistance due to external mass transfer, diffusion through the polymer, and interfacial reaction. Under the conditions chosen, the resistance due to the chemical reaction is generally more dominant. Values of rate parameters were determined by fitting the model to the experimental data. Observed variations in the diffusivity between different experiments were rationalized through a study of the crystalline structure of polymers.
Continuous lumping model for simulation of hydrocracking
Authors: Laxminarasimhan C. S. , Verma R. P. , Ramachandran P. A. 
Published: June 2004

AbstractHydrocracking of vacuum gas oil is an important chemical process involving complex reaction mixtures. The reaction is carried out in a trickle‐bed reactor, considering reaction kinetics along with such hydrodynamic effects as mass transfer, intraparticle diffusion, and partial wetting. Since reaction kinetics is critical to modeling and simulation of a hydrocracking reactor, a modeling approach needs to capture the complex chemistry of the process, along with the elegance of the solution method. The complex chemistry of hydrocarbon is represented by an elegant continuous lumping approach to modeling. The true boiling point of the mixture is used as the characterization parameter. Since the rate constant of hydrocracking is assumed to be a monotonic function of the true boiling point, it is possible to reformulate mass‐balance equations in terms of rate constant as a continuous variable. A novel distribution function p(k, K), which determines the fractional yield distribution of species, was formulated based on data from the cracking patterns of various model compounds. Resulting integrodifferential equations are solved numerically to obtain yields of various fractions as a function of reactor residence time. Model predictions are compared with limited published data to show the utility of the model.
Transport phenomena and kinetics in an extravascular bioartificial pancreas
Authors: Buladi Bora M. , Chang Chen C. , Belovich Joanne M. , Gatica Jorge E. 
Published: June 2004

AbstractA bioartificial pancreas, consisting of immobilized islets encapsulated within hollow fibers, is investigated as an alternative treatment for insulin‐dependent diabetes. A mathematical model is developed to determine whether this configuration of the bioartificial pancreas can yield an insulin response to a glucose challenge with the appropriate dynamics in diabetic humans. The model consists of the 2‐D mass‐conservation equations for glucose and insulin within the hollow fiber and capillaries. The equations contain terms for insulin‐production kinetics by porcine islets and glucose‐consumption kinetics. The boundary conditions account for transport resistances of the fiber membrane, the tissue surrounding the implant, and a thin film within the capillaries. The equations are coupled to a pharmacokinetic model of the circulatory system. The calculations show that an optimized design with this configuration will be feasible for human use and requires a total volume of 4.6 mL to reach the target insulin concentration in the bloodstream following a glucose challenge. The parameters and processes controlling the system performance are discussed.
Sorption‐enhanced reaction process
Authors: Carvill B. T. , Hufton J. R. , Anand M. , Sircar S. 
Published: June 2004

AbstractA process for carrying out simultaneous reaction and separation of desired products in a single unit operation is described. It uses a fixed packed column of an admixture of a catalyst and a sorbent that selectively removes a reaction by‐product from the reaction zone. The sorbent is periodically regenerated by using the principles of pressure‐swing adsorption. The process steps allow direct production of the desired product at high purity and at the reaction pressure. High conversion of the reactants to products in an endothermic, equilibrium‐controlled reaction can be achieved while operating the reaction at a substantially lower temperature than would be necessary by a plug‐flow reactor packed with the catalyst alone. The equilibrium‐controlled reverse water‐gas shift reaction for the production of carbon monoxide is experimentally evaluated as a proof of the concept.
Theory for multicomponent adsorption equilibrium: Multispace adsorption model
Authors: Gusev Vladimir , O'Brien James A. , Jensen Craig R. C. , Seaton Nigel A. 
Published: June 2004

AbstractA new theory for the prediction of multicomponent adsorption equilibrium in non‐crystalline porous solids is presented: the multispace adsorption model (MSAM). This theory allows for the inherent nonuniformity of the adsorbed phase by describing separately the adsorption in “spaces” close to, and far from, the adsorbent surface. The inputs to the calculation are the pure‐species adsorption isotherms and a single parameter characteristic of the adsorbent that can be obtained from very limited mixture data. We evaluate the theory by predicting multicomponent adsorption for a range of carbon adsorbents, making use of our own experimental results and literature data. The MSAM gives quantitative predictions for all the systems studied.
Optimal pressures and temperatures for isobaric, isothermal chemical vapor infiltration
Authors: Ofori John Y. , Sotirchos Stratis V. 
Published: June 2004

AbstractThis study addresses the possibility identifying optimal pressure and temperature pairs that can be used to give the least processing time during isobaric isothermal chemical‐vapor infiltration (CVI) within a window of operating conditions. Optimal pressure—temperature pairs are determined as the solution of an optimization problem that seeks to minimize the processing time predicted by a CVI model under the constraint that the maximum density difference in the preform at the end of the densification does not exceed a preset limit. Results are presented on the dependence of the optimum processing time on the type of structure of the preform, the specifications that the final product has to conform to, and the kinetics of the chemical reaction. The results show that operation at low pressure affects adversely the processing time and that a dramatic reduction in the processing time can be achieved by operating in the vicinity of the optimal pressure.
Data reconciliation and gross‐error detection for dynamic systems
Authors: Albuquerque João S. , Biegler Lorenz T. 
Published: June 2004

AbstractGross‐error detection plays a vital role in parameter estimation and data reconciliation for dynamic and steady‐state systems. Data errors due to miscalibrated or faulty sensors or just random events nonrepresentative of the underlying statistical distribution can induce heavy biases in parameter estimates and reconciled data. Robust estimators and exploratory statistical methods for the detection of gross errors as the data reconciliation is performed are discussed. These methods have the property insensitive to departures from ideal statistical distributions and to the presence of outliers. Once the regression is done, the outliers can be detected readily by using exploratory statistical techniques. Optimization algorithm and reconciled data offer the ability to classify variables according to their observability and redundancy properties. Here an observable variable is an unmeasured quantity that can be estimated from the measured variables through the physical model, while a nonredundant variable is a measured variable that cannot be estimated other than through its measurement. Variable classification can be used to help design instrumentation schemes. An efficient method for this classification of dynamic systems is developed. Variable classification and gross‐error detection have important connections, and gross‐error detection on nonredundant variables has to be performed with caution.
Diffusion of additives during in‐situ suspension polymerization
Authors: Cunningham M. F. 
Published: June 2004

AbstractHigh value‐added specialty composite materials can now be made by in‐situ suspension polymerization of monomers with additives incorporated to impart a specific property. In these composite particles, the nature of the additive dispersion is often of critical importance in determining final product properties. During polymerization, viscosities in the droplets are sufficiently low that significant diffusion can occur, resulting in dramatic changes to the additive dispersion quality. This article examines the importance of process parameters controlling diffusion lengths of small particle additives during in‐situ polymerizations. A model was developed to provide a basis for devising polymer reactor operating strategies that minimize small‐particle diffusion. Effects of varying polymerization rate, molecular weight and initial conversion were investigated. Model results were validated by comparing to experimental data. Increasing the initial conversion is shown to be highly effective in reducing diffusion of additive particles.
Preferentially oriented submicron silicalite membranes
Authors: Lovallo Mark C. , Tsapatsis Michael 
Published: June 2004

AbstractAn oriented submicron silicalite membrane has been prepared by growing a layer of oriented silicalite crystals on a composite precursor nanocrystalline silicalite/alumina film using controlled secondary growth. The orientation of the crystals at the surface was such that both straight and sinusoidal channel networks run nearly parallel to the membrane surface. The membrane exhibits ideal selectivities for H2 over N2 as high as 60 at 150°C and O2 over N2 as high as 3.6 at 185°C. H2, N2 and O2 permeances are 2.13, 0.05 and 0.17 cm3(STP)/(cm2·min·atm) at 185°C, respectively, and the corresponding apparent activation energies are 11, 26 and 32 kJ/mol. The permeation characteristics are attributed to the preferred orientation of the molecular sieving layer.