bluuebunny/crossref_metadata_2025_split huggingface dataset:
A two‐dimensional model for the free‐settling regime in continuous thickening
Authors: Fitch Bryant 
Published: June 2004

AbstractAll classical models for thickening assume one‐dimensional continuity. However, the free‐settling domain in continuous thickeners is not one‐dimensional. Therefore, a two‐dimensional model is investigated. The two‐dimensional model gives the same values for thickener area demands as the one‐dimensional model, but the relationships between batch and steady‐state thickening are not the same. Free‐settling Kynch characteristics can arise in the continuous operation that do not arise in batch tests. Therefore, design procedures that rely on Kynch theory, such as that of Talmage and Fitch, are not completely valid.A method is developed, based on extrapolating the Kynch or free‐settling segment of a batch settling, curve, that yields an improved prediction for thickener area demand.
Optimum mixture compositions for measurement of cross virial coefficients
Authors: Eubank Philip T. , Hall Kenneth R. 
Published: June 2004

AbstractRandom error propagation is examined to determine cross second and third virial coefficients from binary gas density measurements by both the indirect and direct methods. Determination of the cross second virial coefficient B12 from Bm at a single composition via the indirect method is optimized when ye1 = ye2, where e1 and e2 are the pure component uncertainties. When all errors are equal, the equimolar mixture is optimum as expected.Corresponding analysis of the cross third virial coefficients, C112 and C122, show that the optimum compositions are not (frac13;, frac23;) as expected for equal error distribution, but rather (frac14;, frac34;). Equations presented allow determination of the two optimum compositions, when em varies with composition. Minimization of the combined errors in B12, C112, and C122 via mixture measurements at two compositions provides results near (frac13;, frac23;), when all errors are equal. Methods for direct measurement of B12 are reexamined. Optimal compositions are found using third virial coefficient correlations.
Multiple filter methods for detection of hazardous states in an industrial plant
Authors: King R. , Gilles E. D. 
Published: June 2004

AbstractModel‐based detection systems are presented and classified according to their complexity. The main emphasis is put on multiple Kalman filters. A two‐stage approach including Bayes formula and inhomogeneous Markovian processes is suggested to achieve a fault discrimination. Methods are presented to use the information of nondisjunctive models in this context. To show the proper working of the detection algorithms simulation studies and on‐line laboratory experiments with runaway reactions are considered first. A report on an implementation at a large‐scale industrial process unit concludes the discussion.
Chromatography theory: Application to supercritical fluid extraction
Authors: Erkey C. , Akgerman A. 
Published: June 2004

AbstractThe adsorption equilibrium constants for naphthalene on alumina have been measured in the presence of subscritical and supercritical carbon dioxide by the dynamic tracer response technique. The equilibrium constants decrease with increases in density, and the isochroic temperature dependency is very small at supercritical conditions. Through chromatography theory, an expression has been developed for the density dependency of the capacity factor, a quantity related to the adsorption equilibrium constant by the porosity and density of the particle and the porosity of the bed, in terms of the partial molar volume of the solute at infinite dilution in the fluid phase. The partial molar volumes extracted from the data agree well with the published data. Investigation of the dynamics of the bed shows that a model, including axial dispersion and effective diffusion into the pores, successfully represents the data. The effective diffusivities and the axial dispersion coefficients were also extracted from the second central moments of the response curves at each condition.
Prediction of binary, overloaded elution profiles using the simple wave effect
Authors: Katti A. M. , Ma Z. , Guiochon Georges 
Published: June 2004

AbstractThe separation of binary mixtures in overloaded elution chromatography has been investigated experimentally and theoretically using the Rouchon‐Golshan‐Shirazi implementation of the semiideal model (equilibrium‐dispersive model). A competitive Langmuir isotherm with parameters determined from single‐component data gives good prediction of the experimental data. Improved predictions, however, can be obtained by directly measuring the binary isotherm using the method of the hodograph transform.
High‐pressure vapor‐liquid equilibrium with a UNIFAC‐based equation of state
Authors: Dahl Søren , Michelsen Michael L. 
Published: June 2004

AbstractRecent procedures developed by Heidemann (1990) and by Michelsen (1990a, b) enable us to formally incorporate excess Gibbs energy model parameters into a fully consistent equation of state, cith accurate reproduction of the behavior of the excess Gibbs energy model at atmospheric pressure.This paper investigates the ability of the mixing rules proposed by Michelsen to predict high‐pressure phase equilibrium, when used in combination with the parameter table of modified UNIFAC. Considering that a group contribution method is used for the excess Gibbs energy and that model parameters are extrapolated over a 200 K temperature interval, quite satisfactory results are obtained for the mixtures investigated.
Effective Kundsen diffusivities in structures of randomly overlapping fibers
Authors: Tomadakis Manolis M. , Sotirchos Stratis V. 
Published: June 2004

AbstractEffective Knudsen diffusion coefficients are presented for fibrous structures consisting of overlapping fibers. The fibers are distributed randomly in d (d=2 or 3) directions with their axes perpendicular to one direction (d=2) or in the three‐dimensional space with no preferred orientation (d=3), or they are grouped into d (d=1, 2, or 3) mutually perpendicular bundles of parallel, randomly overlapping fibers. Effective diffusivities are computed using a Monte Carlo simulation scheme to determine the mean square displacement of molecules traveling in the interior of the porous medium for large travel times. Our results show that structures with fibers distributed randomly in d directions have diffusion coefficients identical, within the accuracy of our simulation, to those of d‐directional, parallel fiber structures. Effective Knudsen diffusivities are strongly influenced only by the directionality of the fiber structure, with tridirectional or randomly oriented fiber structures presenting lower percolation thresholds (0.04 vs. 0.11) and higher effective diffusivities than bidirectional or random structures with their axes perpendicular to one direction. The tortuosity factor is in general found to decrease with increasing porosity, approaching for each case, as the porosity goes to unity, the corresponding lower bound that is derived using variational principles.
Influence of chemical and electrostatic gradients on diffusion in microemulsions
Authors: McGreevy Robert J. , Schechter Robert S. 
Published: June 2004

AbstractNonequilibrium diffusion behavior in nonionic and ionic surfactant microemulsion systems has been studied experimentally using the open‐ended capillary method. Experimental results for these systems have been compared with a drop theory of diffusion for microemulsions under conditions where large concentration and electrostatic gradients exist. The results show good agreement in concentration profiles between theory and experiment for the microemulsion components—water, benzene, and phenol. Furthermore, under certain conditions the theory predicts that over a limited time interval phenol will diffuse from low‐concentration regions to regions of higher concentration. This phenomenon has been observed.
Nonlinear principal component analysis using autoassociative neural networks
Authors: Kramer Mark A. 
Published: June 2004

AbstractNonlinear principal component analysis is a novel technique for multivariate data analysis, similar to the well‐known method of principal component analysis. NLPCA, like PCA, is used to identify and remove correlations among problem variables as an aid to dimensionality reduction, visualization, and exploratory data analysis. While PCA identifies only linear correlations between variables, NLPCA uncovers both linear and nonlinear correlations, without restriction on the character of the nonlinearities present in the data. NLPCA operates by training a feedforward neural network to perform the identity mapping, where the network inputs are reproduced at the output layer. The network contains an internal “bottleneck” layer (containing fewer nodes than input or output layers), which forces the network to develop a compact representation of the input data, and two additional hidden layers. The NLPCA method is demonstrated using time‐dependent, simulated batch reaction data. Results show that NLPCA successfully reduces dimensionality and produces a feature space map resembling the actual distribution of the underlying system parameters.
Analysis of microwave heating of materials with temperature‐dependent properties
Authors: Ayappa K. G. , Davis H. T. , Davis E. A. , Gordon J. 
Published: June 2004

AbstractTransient temperature profiles in multilayer slabs are predicted, by simultaneously solving Maxwell's equations with the heat conduction equation, using Galerkin finite elements. It is assumed that the medium is homogeneous and has temperature‐dependent dielectric and thermal properties. The method is illustrated with applications involving the heating of food and polymers with microwaves. The temperature dependence of dielectric properties affects the heating appreciably, as is shown by comparison with a constant property model.
Modeling and simulation of NOX absorption in pilot‐scale packed columns
Authors: Suchak N. J. , Jethani K. R. , Joshi J. B. 
Published: June 2004

AbstractAbsorption of nitrogen oxides was studied in three packed columns in series. Two were 254 mm ID and 6 m tall, the third was 800 mm ID and 3 m tall. Absorption was also studied in two packed columns of 800 mm ID, 7 and 10 m tall, operated in series. Solutions of mixed nitric and sulfuric acids were used as absorbents. Specific rates of absorption were measured using a stirred cell with a flat interface.A mathematical model is developed for an adiabatic operation. The gas phase reactions and equilibria, gas phase mass transfer, interface equilibria, and liquid phase reactions are included in the model. Heterogeneous gas‐liquid equilibria are included in the model for the first time. The variation in the rates of absorption with chemical reaction (of NO2, N2O3, and N2O4) with respect to acid concentration is considered. The formation of nitric acid in the gas phase is also considered in the model. Favorable agreement is shown between the model predictions and the experimental observations.
Effect of unfavorable continuous phase density gradient on axial mixing
Authors: Holmes Timothy L. , Karr Andrew E. , Baird Malcolm H. I. 
Published: June 2004

AbstractField experience with several industrial reciprocating plate liquid‐liquid extraction columns indicated that large density gradients in the continuous phase resulted in excessive backmixing. Since there are no published data on the effect of higher density in the upper section compared to lower density in the bottom section of the column, experiments were performed with the calcium chloride brine‐water system in a 76.2 mm diameter reciprocating plate column.Axial dispersion coefficients, E, were found to be 10–20 times higher than the values in systems with uniform densities. E decreased with increasing agitation to 30% of the value with no agitation. The effect of increasing flow rate of water up the column was to increase both E and the Peclet number. E was correlated with the density difference between any point in the column and tap water. Another correlation was obtained showing the effects of buoyant and mechanical energy input on axial dispersion.
An analytic model of direct‐contact heat transfer in spray‐column evaporators
Authors: Mori Yasuhiko H. 
Published: June 2004

AbstractThe heat transfer to, and the resultant evaporation of, drops of a volatile liquid sprayed upward in an immiscible liquid flowing down in a vertical column are analyzed to enable calculation of the volumetric heat transfer coefficient in the column. For this analysis, a model is contrived that assumes no nucleation delay in initially monodispersed drops and a heat transfer to each of the drops, with simultaneous evaporation, that can be approximated by an empirical correlation for heat transfer to an isolated drop evaporating in a quiescent, sufficiently extended medium. The expression obtained for the volumetric heat transfer coefficient is used to predict its values under some particular column operating conditions, which are then compared with relevant experimental data found in the literature.
Fault diagnosis based on qualitative/quantitative process knowledge
Authors: Yu Cheng‐Ching , Lee Chyuan 
Published: June 2004

AbstractRecent advances in knowledge engineering have led to develop the qualitative (deep) model based diagnostic systems. As process knowledge accumulated, however, the diagnostic system remains strictly qualitative. This limits the usefulness of such systems. In this work, a framework is developed for integrating quantitative process knowledge into the qualitative model. Once quantitative process information, e.g., steady‐state gains, is available, it can be incorporated into the simplest qualitative process model called the signed directed graph. The quantitative process knowledge is described in terms of membership functions of fuzzy set theory. According to the measurement pattern, the truth values of a hypothesis (e.g., a fault origin) can be calculated based on the fuzzy logic. Consequently, the diagnostic resolution can be improved significantly. Furthermore, the proposed method becomes a strictly qualitative diagnostic system, if no quantitative information is available. A chemical reactor example illustrates the design and performance of the qualitative/quantitative model‐based diagnostic system. The proposed approach can also be extended to the multiple‐fault situations in a straightforward manner.
Ignition and extinction of surface and homogeneous oxidation of NH3 and CH4
Authors: Williams William R. , Zhao Jin , Schmidt Lanny D. 
Published: June 2004

AbstractIgnition, extinction and autothermal behavior of surface and homogeneous oxidation reactions of CH4, NH3, and mixed NH3/CH4 fuel systems in air over resistively heated Pt foils was studied in an atmospheric pressure flow reactor. Also examined were the effects of varying fuel concentration on the ignition, extinction, and autothermal surface temperatures. Heterogeneous ignition occurred at ∼200°C for NH3 and at ∼600°C for CH4. The mixed fuel systems exhibited two surface ignitions (∼200°C and ∼600°C), implying a sequential ignition of the two fuels. The effects of removing one of the fuels during autothermal operation gave results consistent with this hypothesis.In homogeneous ignition, two types of flames were observed: a boundary layer flame associated with NH3 systems and an independent flame observed in all systems. Homogeneous ignition of the two fuels and the mixtures occurred at surface temperatures ranging from 1,100°C to 1,600°C and appeared to be dominated by CH4 in the mixed systems. A generic behavior is proposed for homogenous‐heterogeneous combustion of single and mixed fuels.
Partial internal wetting of catalyst particles: Hysteresis effects
Authors: Jaguste D. N. , Bhatia S. K. 
Published: June 2004

AbstractCondensation‐evaporation hysteresis associated with the internal wetting of catalyst particles is examined here by the Kelvin and Cohan equations. It is shown that in the absence of information on the thermal history, it is difficult to predict the extent of internal wetting and the associated reaction rate, for states with partial internal wetting, with the actual rate lying anywhere between the limits specified by the Kelvin and Cohan equations. Hysteresis effects arising from thermal cycling are discussed, and the predictions are shown to agree with the experimental data of Kim and Kim (1981a). Experimentally observed transitions between states with markedly different extents of internal wetting and with associated sudden evaporation or condensation are also rationalized by the theory.
Pillared clays as a new class of sorbents for gas separation
Authors: Yang R. T. , Baksh M. S. A. 
Published: June 2004

AbstractHigh‐surface‐area, Zr‐pillared, layered clays are synthesized and characterized for their adsorption properties. Although large free interlayer spacings are claimed in the literature (as also found in this work, 14.3 Å), the limiting pore size is the narrow interpillar spacing. The distribution of interpillar spacing is determined by molecular probing and adsorption data along with a theoretical framework available from the literature. Interpillar spacing can be tailored by controlling the number density of pillars inserted during the ion exchange (oligomer inserting) step. The following variables in the ion exchange solution result in lowering the pillar density: higher pH, lower oligomer concentration, and introduction of competitive cations. By changing these variables, peak interpillar spacing is shifted by nearly 2 Å (from 5 to 7 Å). The versatility of pillared clays as sorbents for kinetic separation (i.e., separation based on diffusivity differences) has been demonstrated by the separations of air and xylene isomers.
Fractional extraction with hollow fibers with hydrogel‐filled walls
Authors: Ding Hongbing , Cussler E. L. 
Published: June 2004

AbstractExtractions using hollow fibers can be faster and more efficient than those in conventional equipment. These advantages, due to the large area per volume possible with fibers, can be compromised by accidental convection through the fibers' pores. When these pores are filled with gels of crosslinked polyvinyl alcohol, convection through the pores is stopped but the overall mass transfer is unaltered. The separations across these gel‐filled fiber walls provide excellent yield and purity, especially in the case of fractional extraction.
Experimental study of the tubular multiphase catalyst
Authors: Cini Philippe , Harold Michael P. 
Published: June 2004

AbstractA new type of multiphase catalyst is developed for transport‐controlled, volatile‐reactant‐limited reactions: the tubular‐supported ceramic membrane. A microporous, catalytically‐impregnated γ‐Al2O3 film (permeable membrane) coats the inside wall of a hollow, macroporous α‐Al2O3 tube. The gas containing the volatile reactant flows through the tube core, and the liquid containing the nonvolatile and dissolved volatile reactants flows on the shell side. Reaction occurs in the film. Results using the hydrogenation of α‐methylstyrene to cumene on Pd/Al2O3 reveal that the tubular catalyst compares favorably to conventional catalyst designs. The results demonstrate that the main benefit is the more efficient supply of the volatile reactant. Apparent activation energy analyses reveal that for catalyst temperatures below 40° C, the rate is kinetically‐controlled and catalyst utilization nearly complete. A reduction in the activation energy above 45°C indicates the onset of transport limitations or heat effects. A comparison between the tubular catalyst and a fully‐wetted pellet reveals rate increases by up to a factor of 20.
Gas‐solid flow in vertical tubes
Authors: Pita Jorge A. , Sundaresan Sankaran 
Published: June 2004

AbstractA computational study of fully‐developed flow of gas‐particle suspensions in vertical pipes was carried out, using the model proposed recently by Sinclair and Jackson (1989), to understand the predicted scale‐up characteristics. It was shown that the model can capture the existence of steady‐state multiplicity wherein different pressure gradients can be obtained for the same gas and solids fluxes. A pronounced and nonmonotonic variation of the pressure gradient required to achieve desired fluxes of solid and gas with tube diameter was predicted by the model, and this is explained on a physical basis. The computed results were compared with the experimental data. The model manifests an unsatisfactory degree of sensitivity to the inelasticity of the particle‐particle collisions and the damping of particle‐phase fluctuating motion by the gas.
Dynamics of carbon dioxide sorption on activated‐carbon particles
Authors: Gray Peter G. , Do Duong D. 
Published: June 2004

AbstractA theoretical model comprising the processes of micropore, macropore and surface diffusion was derived and applied to the dynamics of adsorption of CO2 on a single activated‐carbon particle. The effects of a nonlinear isotherm (Langmuir), particle nonisothermality and concentration dependence of the surface diffusivity were also incorporated. The theoretical model was fitted to a preliminary set of adsorption experimental data (two particle sizes, and various temperatures and concentrations) to determine the diffusion coefficients. The validity of the theoretical model was checked by using the model, with fitted diffusivities, to simulate dynamic adsorption curves at conditions different from those of the preliminary fitting data set. These model simulations were found to predict the experimental data in a satisfactory manner.
Zn/Br2 cell: Effects of plated zinc and complexing organic phase
Authors: Kalu Egwu E. , White Ralph E. 
Published: June 2004

AbstractA model is presented for a zinc/bromine cell that considers the effects of an increase or a decrease in the cathode channel width due to zinc removal on discharge and zinc deposition on charge, respectively. The model also includes the effect of an organic bromine complexing agent (OCA) on the cell performance. Changes in the channel width affect the catholyte velocity, cathode side pressure drop, mass transfer and potential drop in the cell, while the inclusion of the bromine complexing organic phase shows a marked effect on the available bromine in the aqueous phase.It is shown that during discharge, the release of complexed Bromine by the OCA could degrade the cell performance. A simple equation is derived and used to express the relationship between the total bromine in the organic phase and the bromine in the aqueous phase.
Melt crystallization: Process analysis and optimization
Authors: Gilbert Samuel W. 
Published: June 2004

AbstractMelt crystallization manufacturing systems are characterized mathematically and optimized. Directional solidification and sweating are modeled, and the results are correlated to plant data. A nonlinear programming algorithm is constructed to determine the optimal design and operation of a production plant. Process constraints include product purity, process yield, capital cost, phase equilibria, kinetic, and operational factors. An objective function is constructed from scaled yield and capital outlay formulae, and is optimized over a variably constrained feasible space. The dependence of the optima on the separation distribution coefficients and on the constraints is given for specific one‐stage examples for three operational regimes. The one‐stage analyses are applied for the solution of the n‐stage problem.