bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modeling multicomponent gas separation using hollow‐fiber membrane contactors
Authors: Coker D. T. , Freeman B. D. , Fleming G. K. 
Published: April 2004

AbstractA model developed for multicomponent gas separation using hollow‐fiber contactors permits simulation of cocurrent, countercurrent, and crossflow contacting patterns with permeate purging (or sweep). The numerical approach proposed permits simulation to much higher stage cuts than previously published work and provides rapid and stable solutions for cases with many components, with widely varying permeability coefficients. This new approach also permits the rational and straightforward incorporation of effects such as permeate sweep, pressure‐dependent permeability coefficients, and bore side pressure gradients. Simulation results are presented for separation of commercially significant multicomponent gas mixtures using polymer permeation properties similar to those of polysulfone. The effect of permeate purging on separation performance is explored for air separation. The influence of pressure ratio on hydrogen separation performance for a refinery stream is presented. Air is modeled as a four‐component mixture of O2, N2, CO2, and H2O and the refinery stream contains five components: H2, CH4, C2H4, C2H6, and C3H8. In air separation, permeate purging with a small fraction of the residue stream provides a very effective method for improving module efficiency for drying but is not efficient for improving nitrogen purity or recovery. In multicomponent mixtures, maxima in the compositions of components of intermediate permeability may be observed as a function of distance along the hollow fiber. This result suggests the use of membrane staging to capture these components at their maximum concentration.
Efficient use of an intermediate reboiler or condenser in a binary distillation
Authors: Agrawal Rakesh , Herron D. Michael 
Published: April 2004

AbstractThe impact of an intermediate reboiler or condenser on the distillation of ideal binary mixtures into pure product streams is studied using a simplified model. The advantage of heuristics derived from this study is that they can quickly tell a process engineer if an intermediate reboiler or condenser is going to be effective in improving the efficiency and, of the two options, which one would be more effective. The heuristics simply states that if the actual fraction of liquid in a given feed is less than that with the maximum thermodynamic efficiency for distillation with no intermediate reboiler or condenser, then an intermediate condenser not only substantially improves the thermodynamic efficiency but is also more effective than an intermediate reboiler. An analogous heuristics exists for the intermediate reboiler when the fraction of liquid in the feed is greater than the optimum. Quick identification of cases that can achieve a substantial improvement in efficiency provides an incentive to search for the proper utilities needed for the intermediate reboiler or condenser. When relatively pure feed streams (concentration of either component greater than 90%) are distilled, the extremely low efficiencies of distillation can be remarkably improved by using an intermediate reboiler or condenser.
Adsorption dynamics of a layered bed PSA for H2recovery from coke oven gas
Authors: Yang Jaeyoung , Lee Chang‐Ha 
Published: April 2004

AbstractThe adsorption dynamics of a layered bed packed with activated carbon and zeolite 5A were studied experimentally and theoretically through breakthrough experiments and two‐bed pressure swing adsorption (PSA) processes by using coke oven gas (56.4 vol. % H2; 26.6 vol. % CH4; 8.4 vol. % CO; 5.5 vol. % N2; and 3.1 vol. % CO2). The results of breakthrough curves of a layered bed showed an intermediate behavior of those of zeolite‐5A bed and activated carbon bed, because each concentration front propagates with its own wavefront velocity in each layer by a different adsorption equilibrium. Since a fast and dispersed mass‐transfer zone of CO in the zeolite layer of a layered bed leads to a long leading front of the N2wavefront, controlling the leading wavefront of the N2plays a very important role in obtaining a high‐purity product and in determining the optimum carbon ratio of a PSA process for H2recovery from cokeoven gas. The layered bed PSA process was simulated in a simplified form of two single‐adsorbent beds linked in series. The dynamic model incorporating mass, energy, and momentum balances agreed well with the experimental data. Concentration profiles inside the adsorption bed were also investigated.
Permeation dynamics of small molecules through silica membranes: Molecular dynamics study
Authors: Takaba Hiromitsu , Mizukami Koichi , Kubo Momoji , Fahmi Adil , Miyamoto Akira 
Published: April 2004

AbstractThe permeation of He, CO2, and N2 through a thin silica membrane was investigated using molecular dynamics. The permeance of He follows Knudsen flow. The permeation of CO2 is higher than the estimated value from Knudsen theory. Inside the pore, CO2, tends to be parallel to the pore wall. This orientation is suitable for diffusion. In contrast, N2, shows lower permeance compared to the value from Knudsen theory. The molecules present perpendicular orientations inside the pore wall, which reduces their diffusion. In mixed CO2/N2, gas simulation, the selective permeation of CO2 relative to N2 was observed.
Sorption and diffusion of chlorinated methanes in moist clay
Authors: Cabbar H. Canan , Varol Nesrin , McCoy Benjamin J. 
Published: April 2004

AbstractThe dynamic behavior of chlorinated methanes in clays exposed to relative humidities (RH) from 0 to 80% was investigated with the single‐pellet pulse‐response moment technique. Values of effective diffusion coefficients obtained from zeroth moment analysis differed only slightly for dry and moist clay pellets. When the clay pellet was dry, equilibrium adsorption constants of dichloromethane (D), trichloromethane (T), and carbon tetrachloride (C) at the gas‐mineral interface were determined from first moments to be 118, 92, and 90, respectively. Dryness factors (dry fraction of surface area) for clays with RH of 5, 20, 40, and 60% were also calculated from first moments as 0.5, 0.1, 0.04, and 0.01, respectively. When the pore surfaces were covered with the water film (dryness factor was 0 for the pellet at RH 80%), overall equilibrium adsorption constants for the same tracers (D, T, C) at the gas‐water and water‐mineral interfaces were determined to be 7.5, 7.2, and 3.6, respectively.
Simplification techniques for EKF computations in fault diagnosis: Model decomposition
Authors: Chang Chuei‐Tin , Hwang Jung‐Ing 
Published: April 2004

AbstractThe extended Kalman filter (EKF) is one of the most popular model‐based techniques for fault detection and diagnosis. In this study, the suboptimal EKF technique is utilized to enhance computation efficiency without sacrificing diagnostic accuracy. In particular, three simple strategies are proposed to decompose the filter model according to the precedence order of the state/parameter estimation process. The computation load needed in fault identification can be reduced significantly by implementing all or part of these decomposed EKFs on‐line. Extensive simulation results are also presented to demonstrate the effectiveness of these proposed techniques.
Discrimination and goodness of fit of multiresponse mechanistic models
Authors: Stewart W. E. , Shon Y. , Box G. E. P. 
Published: April 2004

AbstractCriteria are derived for objective choice among rival models of multiresponse processes. Formulas are given for the relative posterior probabilities of candidate models and for their goodness of fit as tested on a common data set with Normally distributed errors. The formulas are demonstrated with examples from chemical kinetics and catalysis.
Hydrodynamic model for gas‐lift reactors
Authors: Sáez A. Eduardo , Márquez Marco A. , Roberts George W. , Carbonell Ruben G. 
Published: April 2004

AbstractThe hydrodynamic model of Young et al. (1991) for external‐loop gas‐lift reactors was modified to account for buoyancy forces in the gas phase. The revised model is based on macroscopic balances for the gas‐liquid separator and external downcomer and spatially‐averaged, 1‐D mass and momentum balances in the riser. Using only the physical properties of the gas and liquid phases, the reactor dimensions, and the gas superficial velocity, the model predicts gas holdup profiles, gas and liquid velocity profiles, and pressure profiles in the riser for bubbly flow. Empirical correlations are used to represent frictional and drag effects, but there are no adjustable parameters in the model. The system of equations that must be solved to predict hydrodynamic behavior is simpler than that of Young et al. The sensitivity of the model to choice of drag coefficient correlation is analyzed. The model predictions match experimental data of previous works.
Kinetics of 2‐hexanol and 3‐hexanol oxidation reaction over TS‐1 catalysts
Authors: Gallot J. E. , Kapoor M. P. , Kaliaguine S. 
Published: April 2004

AbstractA kinetic investigation of the catalytic oxidation of 2‐(3‐) hexanols to 2‐(3‐) hexanones over a series of titanium silicalites [TS‐1] is reported. This study considers the biphasic character of the reaction medium and uses the mathematical theory of linear graphs to derive rate equations for both hexanols' oxidation and hydrogen peroxide's decomposition. The 2‐hexanols' oxidation is usually considered as the secondary reaction in the n‐hexane oxyfunctionalization process. Comparing the kinetic constants obtained in this study and those generated by the analysis of previously published n‐hexane oxyfunctionalization rate data allows one to conclude that in the latter case, hexanones are also produced by a direct primary oxidation of n‐hexane.
Thermodynamics of fluid mixtures near to and far from the critical region
Authors: Lue Leo , Prausnitz John M. 
Published: April 2004

AbstractA theory for an equation of state for simple fluid mixtures valid both near to and far from critical points is presented. The base equation of state obtained from integral‐equation theory using the mean‐spherical approximation is used to compute the contribution of short‐wavelength fluctuations to the free energy of the fluid mixture. Wilson's phase space cell approximation, as extended by White, is used to compute the contribution of long‐wavelength fluctuations. The resulting theory possesses nonclassic critical exponents similar to those observed experimentally. Far from the critical region, where long‐wavelength fluctuations are not important, the theory reduces to that corresponding to the base equation of state. The complete theory is used to represent the thermodynamic properties and phase behavior of binary mixtures of methane, carbon dioxide, and n‐butane. In the critical region, agreement with experiment is dramatically improved upon, adding to the base equation of state corrections from long‐wavelength fluctuations.
Model of stress‐induced defect formation in drying polymer films
Authors: Christodoulou K. N. , Lightfoot E. J. , Powell R. W. 
Published: April 2004

AbstractPhotographic films are multilayer polymer structures coated from solution onto a relatively rigid substrate, chilled into a solid gel, and then dried into a permanent coating. This model predicts stress growth and defect formation during drying of such films that remain above their glass transition temperature, so that Fickian difision persists. The stress in the drying gel is taken from mixture theory; the polymer network is a nonlinear elastic or hypoelastic solid, whereas the solvent is an ideal fluid. Conservation laws and constitutive equations are formulated in terms of the polymer network velocity and discretized by the mixed method of Guenette and Fortin on an elliptically genereted, independently evolving finite‐element mesh. Results include evolution of polymer velocity, free surfaces, solvent concentration, and residual stress. Various model problems are solved for drying of uniformly coated films, suspended films (as in tenter‐frame ovens) and around rigid particle inclusions in suspended films and in multilayer photographic coatings causing particle migration and drying defects.
Bubble formation in a coflow configuration in normal and reduced gravity
Authors: Bhunia Avijit , Pais Salvatore C. , Kamotani Yasuhiro , Kim Iee‐Hwan 
Published: April 2004

AbstractA study of bubble generation for constant gas‐flux condition by single‐nozzle injection in a coflowing liquid is reported. Focusing on single‐bubble generation in the dynamic and bubbly flow regime, the onset condition for bubble coalescence is investigated. The role of various forces involved in the bubble formation process is studied, and an overall force balance describing bubble dynamics is developed. Gas‐momentum flux and buoyancy in normal gravity enhance, while the surface‐tension force at the nozzle rim inhibits bubble detachment. On the other hand, liquid drag and inertia can act both as attaching or detaching forces, depending on the relative velocity of the bubble with respect to the surrounding liquid. Predictions of the theoretical model compare well with the present reduced‐gravity experiment and available normal‐gravity experiments. Effects of the fluid properties, injection geometry, and flow conditions on bubble size are investigated.
Screening procedure for synthesizing isothermal multiphase reactors
Authors: Kelkar Vaibhav V. , Ng Ka M. 
Published: April 2004

AbstractA procedure is developed to identify a multiphase reactor for carrying out a given reaction at the early stage of process development. There are three elements to this screening approach: a generic reactor model, an accompanying sensitivity model, and a knowledge base consisting of heuristics, plus correlations on hydrodynamics, heat, and mass transport. In synthesizing a generic reactor model, the conuentional multiphase reactors are decomposed into common attributes and constituent parts, and reaggregated for the reaction under consideration. Thus, in addition to choosing one among conventional reactor types, the procedure prouides insights for the creation of novel reactors. The sensitivity model quantifies the relative impact of the model parameters on the reactor performance. The knowledge base provides heuristics, estimates, and reality checks in the decision‐making process. While this article focuses on isothermal systems with a single reaction, the framework is applicable for general multiphase reactions.
Multiscale PCA with application to multivariate statistical process monitoring
Authors: Bakshi Bhavik R. 
Published: April 2004

AbstractMultiscale principal‐component analysis (MSPCA) combines the ability of PCA to decorrelate the variables by extracting a linear relationship with that of wavelet analysis to extract deterministic features and approximately decorrelate autocorrelated measurements. MSPCA computes the PCA of wavelet coefficients at each scale and then combines the results at relevant scales. Due to its multiscale nature, MSPCA is appropriate for the modeling of data containing contributions from events whose behavior changes over time and frequency. Process monitoring by MSPCA involves combining only those scales where significant events are detected, and is equivalent to adaptively filtering the scores and residuals, and adjusting the detection limits for easiest detection of deterministic changes in the measurements. Approximate decorrelation of wavelet coefficients also makes MSPCA effective for monitoring autocorrelated measurements without matrix augmentation or time‐series modeling. In addition to improving the ability to detect deterministic changes, monitoring by MSPCA also simultaneously extracts those features that represent abnormal operation. The superior performance of MSPCA for process monitoring is illustrated by several examples.
Molecular‐weight distribution control in emulsion polymerization
Authors: Echevarría Antonio , Leiza José R. , De La Cal José C. , Asua José M. 
Published: April 2004

AbstractEmulsion polymers with well‐defined molecular‐weight distributions (MWD) were obtained by using a control strategy based on on‐line measurements of both unreacted monomer and chain‐transfer agent (CTA). The control strategy includes a nonlinear model‐based controller that calculates the feed rates of monomer and CTA needed to obtain the desired MWD. This requires a mathematical model for the MWD that was developed based on independent measurements. The control strategy was assessed by computer simulation and experimentally verified by producing polymers with widely different MWDs in the styrene emulsion polymerization using CCl4, as CTA.
Solution viscosity increase in fusion synthesis of Ca/Mg‐resinates
Authors: Sundqvist S. , Paatero E. , Klemola A. , Tenhola H. 
Published: April 2004

AbstractThe effect of Ca/Mg‐resinate concentration on solution viscosity was studied in toluene. The viscosity was observed to increase drastically above a specific concentration value. The change in viscosity dependence on concentration implies a transition from a dilute to a concentrated regime, where viscous dissipation is governed by resinate molecular interactions and excluded volume effects. The concept of critical resinate concentration, ccrit, was applied and used to explain the nonlinear solution‐viscosity increase during the resinate synthesis. Ca/Mg‐resinates were synthesized by the fusion method at 265°C in a laboratory‐scale batch reactor. During the syntheses the increase in 50 wt. % toluene solution viscosity of the resinate turned almost exponential at a specific reaction time, denoted by t50. Based on the apparent reaction kinetics, a semiempirical model with two estimated parameters was derived for the solution viscosity to be used for the prediction of the t50, time of resinate syntheses.
Modeling and optimization of drug release from laminated polymer matrix devices
Authors: Lu Sanxiu , Fred Ramirez W. , Anseth Kristi S. 
Published: April 2004

AbstractThe design and modeling of drug delivery devices using laminated layers to produce spatially nonuniform matrix devices leading to desired release rates were investigated with the focus on their optimal laminated hydrogel matrices for the diffusion‐controlled release of dissolved drugs. The model consists of polymer layers laminated together through a photopolymerization process to form matrices with a spatially nonuniform initial drug distribution and/or nonuniform drug diffusivities. The model solution establishes that the drug diffusion behavior, especially the early time release behavior, can be manipulated by altering spatially nonuniform initial drug distributions and drug diffusivities in the assembly. Furthermore, optimal control theory and calculus of variation were used to determine a set of initial drug concentrations in the layers to attain a system that exhibits a drug release profile as close to required profile as possible for all time.
Enhanced photon‐migration methods for particle sizing in concentrated suspensions
Authors: Jiang Huabei 
Published: April 2004

AbstractThis article presents a new method for determining particle size distribution in undiluted suspensions from spectral measurement of transport‐scattering coefficients using continuous‐wave photon migration techniques. Particle size distribution (PSD) for concentrated suspensions is determined by a regularized inverse algorithm, which makes it possible to incorporate a synthesized scheme of Marquardt and Tikhonov regularizations. Spectral measurements of dense TiO2, suspensions with three different particle concentrations were used to recover the suspensions' size distributions. Our results are in excellent agreement with the size distribution measured with X‐ray sedimentation. These reconstructions of PSDs are obtained both with and without a priori distribution function assumptions.
Molecular simulation of adsorption of short linear alkanes and their mixtures in silicalite
Authors: Du Zhimei , Manos George , Vlugt Thijs J. H. , Smit Berend 
Published: April 2004

AbstractConfigurational‐bias Monte Carlo simulations in the grand‐canonical ensemble are employed to compute adsorption isotherms of methane, ethane, propane, butane and binary mixtures of methane–ethane, methane–propane, ethane–propane, and methane–butane in the zeolite silicalite. Comparison of the simulation results with the limited expetiniental data available shows good agreement. For ethane at room temperature, a small inflection point in the isotherm was observed due to a surprising ordering of the ethane molecules in the zeolite. For the simulation of a methane–ethane mixture, at low pressure ethane is preferentially adsorbed, while at high pressures methane replaces ethane due to entropic effects.
Diffusion and reaction in whole wheat grains during boiling
Authors: Stapley A. G. F. , Fryer P. J. , Gladden L. F. 
Published: April 2004

AbstractThe boiling of whole wheat grains was studied using magnetic resonance imaging (MRI) and pulsed‐gradient‐spin‐echo nuclear magnetic resonance (NMR) (PGSE NMR). MRI was used to image moisture distributions across a central section of grains boiled for different times at either 100 or 120°C. A moisture front gradually moved into the grain, although some moisture did penetrate ahead of the front. PGSE NMR, which measures self‐diffusion, indicated that two pools of water with differing diffusion characteristics may exist within the grain. Diffusion models suggested from the PGSE results were incorporated into finite‐element simulations along with the Thomas‐Windle model for diffusion/relaxation in polymers. Simulation results were compared to the MRI data, and the best fit was achieved using the Thomas‐Windle model with a step‐change in diffusivity above a critical moisture content. This behavior is similar to that of diffusion in polymers undergoing a glass transition, a phenomenon widely accepted to occur when starch gelatinizes.
Diafiltration by nanofiltration: Prediction and optimization
Authors: Richard Bowen W. , Wahab Mohammad A. 
Published: April 2004

AbstractA predictive model for the performance of a nanofiltration membrane in separating the components of a dye/salt solution was developed. It is based on the extended Nernst‐Planck equation with incorporation of concentration polarization for mixtures of charged ions. Excellent agreement between predicted and experimental rejections of anions and cations was obtained for batch nanofiltration at different ratios of dye/salt assuming that the membrane charge density (Xd) depends on the total concentration of negative charges in the solutions. Prediction for diafiltration experiments was also excellent by allowing for variation in Xd as the salt concentration in the solution changed as a function of time. The model was used to investigate optimization of the processing conditions. The overall diafiltration process operated best in a two‐phase mode, in which the dye solution was preconcentrated to the final required dye concentration before diafiltration.