bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fixed‐bed multisolute adsorption characteristics of nonwet adsorbents
Authors: Rixey William G. , King C. Judson 
Published: June 2004

AbstractCertain nonfunctional macroreticular polymeric adsorbents are nonwet by suffciently dilute aqueous solutions and enable separations not achievable with adsorbents in the prewet state. Fixed‐bed adsorption data were obtained for a multisolute aqueous solution containing acetic acid, 1,3‐butanediol, and succinic acid, with Porapak Q and Amberlite XAD‐4 as adsorbents in both the prewet and nonwet states. The prewet breakthrough data agree with a model allowing for axial dispersion and a linear rate law, using independently estimated parameters. Break‐through curves for the nonwet case depend strongly upon solute volatility since mass transport within the particles appears to occur by Knudsen diffusion, and is rate limiting. Data for Porapak Q reflect an effective particle diffusivity about ten times lower than for Amberlite XAD‐4.
Methane steam reforming: II. Diffusional limitations and reactor simulation
Authors: Xu Jianguo , Froment Gilbert F. 
Published: June 2004

AbstractGiven the intrinsic kinetics, the tortuosity factor of a Ni/MgAl2O4 catalyst was determined under reaction conditions by minimizing the sum of squares of residuals of the experimental and the simulated conversions. The parallel cross‐linked pore model with uncorrelated pore size distribution and orientation was used in the calculation of the effective diffusivities. A modified collocation method was used to obtain the partial pressure profiles of the reacting components in the catalyst pellet. The simulation of the experimental reactor during the optimization of the tortuosity factor also yielded the effectiveness factors of the reactions. The results of the simulation of an industrial steam reformer are also discussed.
Experimental study of particle to gas heat transfer in fixed‐bed reactors
Authors: Pathangey Balachanderrao , Kovenklioglu Suphan 
Published: June 2004

AbstractParticle to gas heat transfer studies were carried out for the exothermic benzene hydrogenation and endothermic cyclohexane dehydrogenation reactions on the same catalyst bed. A recirculation type reactor and eggshell type commercial platinum on alumina catalyst were used. When the thermodynamic value for the heat of reaction is used for both reactions in the steady‐state energy balance, local JH factors for the exothermic reaction were found to be, in general, higher than those for the endothermic reaction. This was attributed to product molecules leaving the catalyst surface with excess vibrational energy, which implies that the actual heat of reaction would be different than the thermodynamic value used in the JHfactor calculations. The study also indicated significant variations in the local JH factors; these were attributed to variations in the linear velocity in the radial direction.
CO hydrogenation over alumina‐supported sulfide cluster catalysts
Authors: Thompson Levi T. , Schwank Johannes , Curtis M. David 
Published: June 2004

AbstractBimetallic Mo‐Fe and Mo‐Co sulfide clusters were anchored on Al2O3 and used for CO hydrogenation. In addition to methane, significant amounts of dimethyl ether were produced. The reaction orders obtained from power rate laws for methanation indicated that the surfaces of the catalytic ensembles were not completely saturated by CO, in contrast to the observations for most conventional CO hydrogenation catalysts. A kinetic analysis and parameter estimation was performed to identify the rate‐determining step for methanation. A catalytic cycle was postulated that could account not only for the formation of methane and higher hydrocarbons, but also for dimethyl ether as a primary product.
Insights into the hydrodynamics of free falling wavy films
Authors: Wasden Frederic K. , Dukler A. E. 
Published: June 2004

AbstractThree isolated waves of differing amplitude and shape were selected from experimental measurements of a falling liquid film at Re = 880 for study using an algorithm developed for solution of the Navier‐Stokes equations. The method computes the velocity and pressure fields as well as the velocity of the wave. The results show that large streamwise accelerations exist along with regions of recirculating flow in a moving coordinate system. These features can explain the enhanced rates of heat and mass transfer observed in wavy film flow. Computed wave velocities and wall shear stress were in reasonably good agreement with measurements. Wave velocity is shown to be sensitive to small variations in the wave shape and explains the apparent random variation of wave velocity with amplitude that has been observed experimentally. This numerical experiment points to the shortcomings of the many methods used to model large waves on falling films that have been based on parabolic velocity profiles.
Particle motion in axisymmetric stagnation flow toward an interface
Authors: Stoos J. A. , Leal L. G. 
Published: June 2004

AbstractNumerical solutions for the creeping motion of a spherical particle in a linear axisymmetric straining flow normal to a deformable interface are presented for a range of viscosity ratios, capillary numbers, and Bond numbers. The parameter ranges investigated have applications in areas of flotation (small interface deformation) and material processing (large interface deformation). The accuracy of previous solutions for flotation problems which neglect interface deformation is considered, along with the magnitude and form of interface deformation “defects” which may appear in material processing applications involving fluids containing bubbles or small particles.
Control of processes with noise and time delays
Authors: Walgama Kirthi S. , Fisher D. Grant , Shah Sirish L. 
Published: June 2004

AbstractA stable Kalman filter predictor (KFP) is developed which generates minimum variance estimates of the future outputs {y(t + i | t), i = 1, … d} of stochastic, single‐input/single‐output processes with time delay, d. The predicted outputs are used for time delay compensation and in the design of a predictive feedback controller. An innovation model analysis is used to convert the state space formulation to transfer function form and to show the relationship between the KFP, the Smith predictor, and the internal model controller. A modified KFP includes a disturbance model, and eliminates offset due to deterministic disturbances (e.g., steps) and modeling errors. Simulation results show that the modified KFP also predicts the disturbances and gives significantly better performance than the Smith predictor, particularly in the presence of process and measurement noise.
A study of Cr(III)‐polyacrylamide reaction kinetics by equilibrium dialysis
Authors: Hunt James A. , Young Teng‐Shau , Green Don W. , Willhite G. Paul 
Published: June 2004

AbstractA kinetic model was developed to describe the rate of reaction between chromium(III) and polyacrylamide (PAAm) that leads to the crosslinking or gelation of the polymer. Cr(III) was added directly to solutions of polyacrylamide which had a degree of hydrolysis of approximately 4%. The unreacted Cr(III) was separated from that which had reacted with the polymer by equilibrium dialysis and measured by atomic absorption.The rate of the reaction was described by an empirical model based on the assumption of invariant polymer group concentration during the reaction. The order of reaction was determined to be 1.32 for Cr(III), 0.8 for the polymer group, and −1.0 for hydrogen ion. Modifications were made to the model to allow for variation during reaction of the concentration of the polyacrylamide reactive group. The modified model accurately described the reaction rate for Cr(III) concentration ranging from 0.19 to 1.2 mM, polyacrylamide concentrations from 6.9 to 69 mM, and pH values from 4.0 to 5.5.
Extension of Chen's (1982) theory to correlate densities of aqueous electrolytes
Authors: Humffray Alan A. 
Published: June 2004

AbstractThe model proposed by Chen et al. for treating nonideality in concentrated electrolyte solutions has been extended to the correlation of the densities of solutions of single electrolytes (1:1, 2:1, 1:2, and 2:2) in terms of Chen's energy interaction parameters τca,m and τm,ca. At any single temperature, only three adjustable parameters, V (the partial molar volume of the solute at infinite dilution), and the pressure derivatives (δτca,m/δp)T and (δτm,ca/δp)T are required for correlating the density as effectively as the conventional treatment employing a power series in (molality)1/2. For some electrolytes, only the latter two parameters are required, as tabulated V values also lead to satisfactory correlations. The treatment can be extended to cover the temperature range 0–100°C, using either τca,m and τm,ca values derived from activity or osmotic coefficients, or constant τm,ca and τca,m values, but the irregular variation with temperature of the pressure derivatives precludes their representation by simple analytical functions, and individual values of the pressure derivatives at each temperature are necessary.
Flow of noncolloidal slurries in pipelines
Authors: Hsu Feng‐Lung , Turian Raffi M. , Ma Tzu‐Wang 
Published: June 2004

AbstractA multiphase model for the flow of dense, noncolloidal, settling slurries through horizontal pipelines, and an associated Galerkin‐finite element numerical scheme to carry out computer simulations based on the model, were developed. The principal elements of the model are: equations for estimation of the velocity distributions for each component; and those for the concentration distributions. In the former, which are derived from the local volume‐averaged, time‐smoothed conservation of mass and momentum equations, the total stress is comprised of components to account for interparticle and particle‐boundary as well as viscous and turbulent interactions. The governing equations for the concentration distributions are derived similarly from the convective diffusion equation, with the eddy diffusivity modified to account for the presence of the solid particles. Numerical simulations and detailed comparisons with experiment for the flow of gypsum, coal, crushed glass, sand and gravel, covering particle sizes from 38.3 μm to 13,000 μm, and pipe diameters from 4 cm to 49.5 cm, were carried out. The agreement between model prediction and experiment is excellent.
The birefringence problem in optical disk substrates: A modeling approach
Authors: Greener Jehuda , Kesel Raymond , Contestable Beverly A. 
Published: June 2004

AbstractAn analytical model has been constructed to predict the birefringence level in an injuection‐molded disk with direct application to optical disk substrates. The model incorporates simplified analyses for the flow in a center‐gated cavity during the filling stage, the heat transfer during the cooling stage, and the stress relaxation following the cessation of flow at the end of the filling stage of the injection‐molding cycle. The stress relaxation process is analyzed with the integral constitutive equation of Wagner and the residual stresses are converted to retardation via the stress‐optical law. Predictions of normal retardation profiles are in line with experimental data and the general effects of melt temperature, mold temperature, and injection speed are closely captured by the model. By contrast, the observed transverse retardation is not in accord with the predicted response. This discrepancy is attributed to the fact that the transverse retardation is induced by cooling stresses and thus cannot be explained in terms of a flow stress mechanism employed in the present analysis.
Numerical calculation of particle‐laden gas flows past tubes
Authors: Schuh M. J. , Schuler C. A. , Humphrey J. A. C. 
Published: June 2004

AbstractA numerical study has been conducted for the flow of a dilute particleladen gas moving past one or more tubes undergoing erosion. A nonor‐thogonal body‐fitted coordinate system was used to calculate three tube configurations for laminar and turbulent flow regimes. The assumption of one‐way coupling allows the calculation of individual particle velocities from the fluid flow field. The significant effects of turbulent velocity fluctuations are taken into account by means of the stochastic separated flow model. The particle flow field information is then used to predict circumferential distributions of particle flux and erosion. Predictions of trajectories for the case of two in‐line tubes show that particles with inertia numbers λ > 1 will strike many tubes in a tube bank due to particle rebounding from tube surfaces. By contrast, particles with λ < 1 are entrained in the bulk flow between tubes. In general, the effect of increasing the particle‐gas suspension temperature is to couple the particle‐fluid motion more closely through viscous drag and, thus, to decrease erosion.
A model for unsteady analysis of preform drawing
Authors: Myers Matthew R. 
Published: June 2004

AbstractA model is introduced for analyzing diameter variations occurring in glass fibers drawn from preforms. The heat transfer is shown to be radiation‐dominated, and approximate expressions for radiative exchange are developed. The expressions are used in the one‐dimensional governing equations for extensional flows to derive a set of linearized disturbance equation as an eigenvalue problem. The sensitivity to an oscillatory take‐up rate is also studied as a boundary‐value problem. Calculated amplitudes of final diameter perturbations are found to agree well with experimental values.
The continuous countercurrent moving‐bed separator
Authors: Fish Barry B. , Carr Robert W. , Aris R. 
Published: June 2004

AbstractAn investigation of the continuous chromatographic separation of an equimolar mixture of 1,3,5‐trimethylcyclohexane and 1,3,5‐trimethylbenzene with a 2.4 m × 1.37 cm ID vertical countercurrent moving bed is reported. The solid adsorbent was 30 mesh Al2O3, and the separation was carried out at 200°C. Steady‐state axial concentration profiles of each species were determined by withdrawing vapor samples for analysis by gas chromatography. The binary mixture was continuously fed through a port located at approximately the midpoint of the column. The relative solids and carrier gas flow rates could be adjusted so that the more strongly adsorbed trimethylbenzene was transported downward, and less strongly adsorbed trimethylcyclohexane moved upward. For low feed rates, high‐purity product streams of each were obtained at the bottom and top of the separator. For sufficiently high feed rates, trimethylbenzene was transported upward as well as downward, and top product purity deteriorated. This behavior is in qualitative accord with the predictions of a dispersionless, one‐dimensional flow, adsorption equilibrium model incorporating a Langmuir isotherm.
Dynamics of packed‐bed reactors loaded with oxide catalysts
Authors: Arnold Ernest W. , Sundaresan Sankaran 
Published: June 2004

AbstractThe lattice of an oxide catalyst can act as a reservoir for oxygen, storing and releasing it for oxidation reactions at the catalyst surface under appropriate transient conditions. The implication of this oxygen storage property on the dynamic response characteristics of packed‐bed reactors loaded with oxide catalysts has been investigated through an experimental study of 2‐butene oxidation over vanadium oxide. Temperature profiles in a wall‐cooled packed‐bed reactor have been measured at steady state and following step changes in the feed butene concentration and in the feed gas flow rate. Thermal reactor runaway was observed experimentally for large step increases in the feed butene concentration following certain catalyst pretreatments. Gas flow rate step increases and less severe butene step increases resulted in the reactor temperature overshooting its final steady‐state profile. These response characteristics are a direct consequence of the oxygen storage property of the vandaium oxide catalyst.
Electrosorption of n‐alcohols on graphite particles
Authors: Zabasajja J. , Savinell R. F. 
Published: June 2004

AbstractThe loading of organic molecules adsorbed on high surface area carbon materials can be influenced by the potential of the surface. This phenomenon can form the basis for carbon regeneration and for separation processes. A theoretical treatment demonstrates that adsorption loading becomes more sensitive to potential change when the double layer capacitance of the interface and the size of the organic species are increased. An experimental method was developed to estimate isotherm parameters. The technique was demonstrated on model adsorbates, pentanol and heptanol. The values of the measured isotherm parameters (B = 3.4–9.1 V−2: Emax = 0.36‐0.5 V vs. Hg/Hg2 SO4) are in the range of expected values based on literature values for similar systems. Although only 5% of activated carbon surface area was shown to be electrochemically accessible, it still has ten times the area available for electrosorption as compared to the graphite, thus making it attractive for industrial application.
An internally staged hollow‐fiber permeator for gas separation
Authors: Sidhoum M. , Majumdar S. , Sirkar K. K. 
Published: June 2004

AbstractConventional membrane permeation of gases employ a non‐step process between the feed and the product on two sides of a membrane. By applying the overall driving force change through a two‐step process using two membranes in one device, we illustrate theoretically the possibility of achieving a much higher enrichment without any extra energy consumption. Such an internally staged permeation is experimentally carried out in a hollow‐fiber permeator with two sets of asymmetric cellulose acetate hollow fibers for the systems of O2N2 (air) and CO2N2. The superior enriching performance of the internally staged permeator over the same permeator operated in the conventional mode is demonstrated experimentally. A cocurrent flow pattern is found to be superior to a countercurrent flow pattern for the conditions employed. The simulation model incorporating fiber lumen pressure drop predicts the experimental performance quite well. A further improvement in performance can be achieved by recycling the intermediate pressure shell reject stream to the feed stream. The energy requirement in an internally staged permeator without recycle is less than that of a conventional permeator with permeate recycle.
Controller design for integrating and runaway processes involving time delay
Authors: Quinn Stanley B. , Sanathanan C. K. 
Published: June 2004

AbstractThis paper presents an efficient method for the design of controllers for integrating and runaway processes. The method is based on model matching in the frequency domain. The presence of open‐loop instability as well as pure time delay in the process models make the design task challenging for these classes of processes.The goal is to achieve low‐order, easily implementable cascade controllers in a unity‐output‐feedback configuration. It is shown that the central problem is in the selection of appropriate reference models. Several key constraints are developed which relate a given process model to a class of reference models for achieving total stability. Typical design examples are presented to clearly illustrate the various mathematical techniques.
Absorbed solution theory models for multicomponent adsorption equilibria
Authors: Gamba Giuseppe , Rota Renato , Storti Giuseppe , Carra Sergio , Morbidelli Massimo 
Published: June 2004

AbstractA new approach is developed for applying ideal and real adsorbed solution theory models to the description of multicomponent adsorption equilibria at fixed pressure. This allows ignoring single‐component behavior in the Henry's law region, P → O, but introduces new parameters that must be evaluated from binary equilibrium data. Comparisons with various sets of experimental data show that the new approach gives results as good as the classical one, but without requiring knowledge of the single component behavior in the Henry's law region; more over, it removes the sensitivity to the type of model adopted in fitting single‐component equilibrium data.
Laser‐induced ignition in solid‐state combustion
Authors: Dimitriou P. , Hlavacek V. , Valone Steven M. , Behrens Robert G. , Hansen G. P. , Margrave J. L. 
Published: June 2004

AbstractThe ignition process of condensed‐phase combustion by a laser is studied experimentally as well as numerically. Numerical simulations are performed in one, two and three spatial dimensions, and are compared with the experimental observations. The effects of energy‐dissipative mechanisms, such as melting and ablation due to laser irradiation and the effects of laser power output fluctuations, are also studied. We find that the ignition process depends mainly on the energy deposited in the system. The time leading up to ignition is longer for higher light fluxes keeping the average laser power constant, since a larger fraction of the energy is reradiated from the heated surface or consumed during the process of material removal.
Pellet‐model effects on simulation models for fixed‐bed desulfurization reactors
Authors: Sotirchos Stratis V. , Zarkanitis Solon 
Published: June 2004

AbstractDetailed mathematical models, pore or grain based, describing diffusion, reaction, and pore structure evolution in pellets of porous solids are used to simulate, along with a macroscopic reactor design model, the transient phenomena that take place during desulfurization of coal gas in fixed‐bed reactors of pellets of metal oxide sorbents. Our computer simulation results show that the form of the pore‐ or grain‐size distribution strongly influences the predictions of the overall reactor design model.
Numerical simulation of theories for gas absorption with chemical reaction
Authors: Glasscock David A. , Rochelle Gary T. 
Published: June 2004

AbstractSteady‐ and unsteady‐state theories for interfacial mass transfer are used to model gas absorption with second‐order, reversible reaction and the absorption of CO2 into aqueous MDEA (methyldiethanolamine). The latter case represents a system of industrial interest, having both finite rate and equilibrium reactions. Steady‐state theories studied are film theory, simplified eddy diffusivity theory, and an approximation to surface renewal theory. Higbie's penetration and Danckwert's surface renewal theories are the unsteady‐state theories reviewed. The Nernst‐Planck equations for diffusion and reaction in ionic systems are solved numerically using orthogonal collocation on finite elements. Comparisons are made between the absorption enhancement factor obtained for all theories. The applicability of approximate methods of solution for absorption with chemical reaction is also discussed.
Laser‐doppler velocimeter measurements in simulated entrained gasifier flows
Authors: Lindsay Jeffrey D. , Hedman Paul O. , Smith Philip J. 
Published: June 2004

AbstractA laser‐Doppler velocimeter (LDV) was used in a cold‐flow study of a simulated entrained‐flow coal gasifier. The study was designed to provide fundamental information about the flows in such a gasifier and to provide data for the validation of a turbulence submodel used in modeling combustion processes. Measurements in 20 swirling and nonswirling flow cases were made with several levels of replication. This study emphasized the effects of inlet conditions on flow properties within the simulated reactor.Unsteady flow phenomena with time scales on the order of seconds to minutes were sometimes observed. The unsteadiness was apparently associated with relaminarization‐type flow transitions.Comparisons were made with model predictions from PCGC‐2, a model for combustion processes based on the k, — ϵ turbulence model. Several areas of weakness in the model results were observed, but the unusual flow regimes measured in this study may be beyond the abilities of practical computer models.