bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamic structural transformations for distillation control configurations
Authors: Yang Dae R. , Waller Kurt V. , Seborg Dale E. , Mellichamp Duncan A. 
Published: June 2004

AbstractA control structure transformation is presented that includes the effects of inventory control system dynamics and internal flow dynamics on flows and compositions. This new transformation can be used to predict column dynamic operation for any alternative control structure from the open‐loop model (inventory control only) obtained for a particular control structure (LV). New types of inverse responses are predicted using this technique and verified both by rigorous dynamic simulation and by experimental studies on a pilot‐scale distillation column. These features also can be shown theoretically using a simplified transfer function model.
Kinetics of nucleation from aqueous solution
Authors: Mohanty Rita , Bhandarkar Suhas , Estrin Joseph 
Published: June 2004

AbstractHomogeneous nucleation is achieved in aqueous systems by creating adequately high levels of supersaturations. This process can be fully described by considering depletion of supersaturation due to simultaneous growth of the nuclei. Nielsen (1964) formulated this by integrating the growth kinetics with classical nucleation theory. This paper uses his combined nucleation‐growth approach, as well as more recently developed mechanisms of adding monomers to developing nuclei (Chiang et al., 1988). The experimental data considered suggest that the systems fall into two categories: one involving the same mechanism for nucleation and growth and the other involving different mechanisms. A dimensionless parameter which evolves in the development permits the comparison of the rate of nuclei formation with that of nuclei growth. The inferences from this approach suggest further that the surface energy parameter is an indicator of the category to which a solution system belongs.
Mercury‐sensitized photochemical vapor deposition of amorphous silicon
Authors: Albright D. E. , Saxena N. , Fortmann C. M. , Rocheleau R. E. , Russell T. W. F. 
Published: June 2004

AbstractA reaction engineering model has been developed to describe the mercury‐sensitized photochemical vapor deposition of hydrogenated amorphous silicon (a‐Si:H) semiconductor thin films. Model equations governing the gas‐phase generation, transport, and surface reactions of SiH3 and H film precursor radicals are solved to predict film growth rate and bonded hydrogen content. Behavior of the model has been studied as a function of deposition conditions (pressure, temperature, feed composition, and flow rates) and has been verified by comparison with experimental results.
Analysis of liquid chromatography with nonuniform crystallite particles
Authors: Lin Y. S. , Ma Y. H. 
Published: June 2004

AbstractA mathematical analysis for the pulse responses of a liquid chromatographic column packed with crystal powders having a particle size distribution and a nonlinear adsorption isotherm is presented. The mathematical model is solved numerically by the orthogonal collocation method. Based on the parametric analysis of the model, the effects of a symmetrical and moderately asymmetric PSD on the LC responses are shown to be negligible in comparison with the effects of other parameters, such as isotherm nonlinearity, whose effects are much more profound. The simulated responses are compared with the experimental response data for an LC column packed with silicalite crystals, and a good agreement is found between the theoretical and experimental results. Using the nonlinear LC model, the simultaneous determination of nonlinear adsorption isotherms and intraparticle diffusivities from LC pulse responses is demonstrated for liquids in porous adsorbents.
Application of the group contribution lattice‐fluid EOS to polymer solutions
Authors: High Martin S. , Danner Ronald P. 
Published: June 2004

AbstractA new group contribution lattice‐fluid equation of state (GCLF‐EOS) is described that can accurately predict the activities of solvents in polymer solutions. This equation of state is a modification of the equation of state derived by Panayioutou and Vera (1982), which is based on the lattice statistics developments of Guggenheim (1952). The group contribution modification permits the prediction of solvent activity, given only the structure of the polymer and solvent involved. The GCLF‐EOS can accurately predict solvent activities in polystyrene, polyethylene, poly(ethylene oxide), poly(ethylene glycol), poly(propylene oxide), and poly(vinyl chloride). The model does not perform as well for solvent activities in polyisobutylene due to the inaccurate group contribution values for the quaternary carbon group.
NMR imaging of saturation during immiscible displacements
Authors: Mandava Shanthi S. , Watson A. Ted , Edwards Carl M. 
Published: June 2004

AbstractThe use of magnetic resonance imaging (MRI) for monitoring multiphase displacement experiments for quantitative characterization of fluid saturation is demonstrated. Displacements are conducted with one fluid phase in a porous medium being immiscibly displaced by another. Our objective is to accurately measure porosity and saturation distributions corresponding to one spatial dimension. Measures for the accuracy and resolution, with which the properties are identified, are developed.
Vector processing strategies for chemical process flowsheeting
Authors: Vegeais James A. , Stadtherr Mark A. 
Published: June 2004

AbstractThe potential for effective vectorization of the sequential‐modular, simultaneous‐modular, and equation‐based approaches to process flowsheeting is assessed. The last appears to be the most promising, but the required sparse matrix techniques currently used do not vectorize well. Different approaches to vectorizing the sparse matrix calculation are considered. With a good matrix reordering scheme, the most promising sparse matrix strategy for the vectorization of flowsheeting problems is the frontal method, a technique currently used primarily on finite‐element problems.
Diffusion‐controlled surfactant adsorption studied by pendant drop digitization
Authors: Lin Shi‐Yow , McKeigue Kevin , Maldarelli Charles 
Published: June 2004

AbstractPendant drop tensiometry enhanced by video‐image digitization is shown to be a useful tool for the experimental measurement of the relaxation in interfacial tension due to the adsorption of surfactant at a fluid interface. Using this method, profiles of the relaxation in surface tension of a diffusion‐controlled, nonionic polyethoxy surfactant were measured. A diffusion coefficient was computed by comparing these profiles with numerical solutions of the bulk surfactant diffusion equation and a Frumkin equilibrium adsorption isotherm. This comparison was made for the entire relaxation period. This method establishes a more reproducible diffusion coefficient than current techniques that utilize only the short‐ or long‐time parts of the relaxation spectrum. In addition, lower bounds on the kinetic constants for the sorption process are inferred for the polyethoxy surfactant used by comparing numerical solutions of mixed diffusion and surface kinetic transfer with the diffusion‐limited result.
CO oxidation on Pt: Variable phasing of inputs during forced composition cycling
Authors: Graham William R. C. , Lynch David T. 
Published: June 2004

AbstractA combined experimental and theoretical investigation of the effect of forced feed composition cycling for CO oxidation on platinum has been performed. A novel approach to forced composition cycling was examined, in which the phase angle between the two input streams was varied. Reaction rate enhancement is shown to occur, and by varying the phasing of the feed streams it is possible to achieve a global maximum in the time‐average reaction rate. This phenomenon can be explained quantitatively by a model based on an adsorbate‐induced phase change of the Pt surface combined with CO adsorption self‐exclusion. This mathematical model can also quantitatively describe the complex steady‐state behavior (uniqueness‐multiplicity transitions) observed for this reaction. The predictions of the model have been validated further through a detailed experimental study of the effects of feed flow rate, temperature, size of catalyst charge, and cycling frequency on the instantaneous and time‐average conversions during forced cycling of the feed composition.
Microcomputer‐automated reactor for synthesis of 13C‐labeled Monosaccharides
Authors: Stafford Ulick , Serianni Anthony S. , Varma Arvind 
Published: June 2004

AbstractFor less labor‐intensive, larger‐scale, and more efficient production of D‐[1‐13C] glucose and other labeled monosaccharides using the cyanohydrin reduction reaction, an automated reactor was designed, constructed, and tested. A suitable vessel and all ancillary and control equipment were fabricated, or otherwise obtained, and the apparatus was controlled with a microcomputer program written in BASIC. Running without manual intervention, the yields for the condensation reaction of D‐arabinose with KCN and the recovery of the excess cyanide were high (>90%), and the resultant aldononitriles were reduced to product aldoses with little reduction of the intermediate imines to amines. The reduction rate could be improved by controlling pH between 2–4 and by agitation speeds >250 rpm, while no improvement resulted from the use of high hydrogen pressures [> 129 kPa (4 psig)]. Reduction reactions conducted in the presence of formic acid (to regulate pH) suggest that formic acid acted as a coreducing agent.
Thermodynamics of Lewis acid‐base mixtures
Authors: Economou Ioannis G. , Ikonomou George D. , Vimalchand P. , Donohue Marc D. 
Published: June 2004

AbstractThe associated perturbed‐anisotropic‐chain theory (APACT) has been applied to treat multicomponent mixtures, in which components exhibit Lewis acid‐base interactions. Mixtures of amphoteric molecules (such as alcohols), acidic molecules (such as chloroform), and basic molecules (such as ketones) as well as nonassociating components (diluents) are treated. The acid‐base version of the perturbed‐anisotropic‐chain theory (ABPACT) is a closed form equation of state that takes into account explicitly dispersion interactions, polar interactions, and hydrogen bonding interactions between components that self‐associate or solvate. The equation fits binary VLE mixtures quite accurately. Calculated results also are compared with those obtained from the Peng‐Robinson equation of state, UNIFAC and the original APACT. In all cases where there are mixtures of associating components, the ABPACT gives a better fit of experimental data than these other equations.
Interrelating excess thermodynamic functions using fusion properties
Authors: Hansen Allen R. , Eckert Charles A. 
Published: June 2004

AbstractA new model that interrelates the liquid‐phase excess Gibbs energy, enthalpy and volume, called the GHV model, is developed and discussed. The model is based on the fact that most mixtures are immiscible in solid phases and, therefore, have steep solid‐phase boundaries. This single assumption allows the model to be applied potentially to all types of mixtures, including organic, metallic, electrolytic and polymeric solutions. The model, which predicts that excess properties are related to one another through various fusion properties, pure component volumes, and enthalpies of fusion in particular, has been applied to a wide variety of organic and liquid metal mixtures. The results show at least qualitative validity without adjustable parameters and more quantitative ability with “effective” fusion properties. The model is also shown to rationalize some sign, magnitude and shape phenomena.
Void wave propagation phenomena in two‐phase flow (Kern Award Lecture)
Authors: Lahey R. T. 
Published: June 2004

AbstractA detailed linear and nonlinear analysis of void wave phenomena in two‐phase flow is presented. A state‐of‐the‐art, one‐dimensional two‐fluid model was used as the basis for this analysis. It is shown that void wave dispersion is strongly influenced by phasic slip. In particular, the smaller the slip the more dispersion occurs. It has also been found that nonlinear wave forms, such as shocks and solitons, may occur. Moreover, the virtual mass force was found to be an important parameter in the modeling of void waves. It is shown that void wave analysis is an excellent means of assessing the closure assumptions used in two‐fluid models. It is also implied that carefully taken void wave data are needed for this purpose.
Kinetic invariant model of dissolution with chemical reaction of large particles
Authors: Bhaskarwar Ashok N. 
Published: June 2004

AbstractThe kinetic invariant model has been reformulated and an approximate analytical form of a kinetic function is obtained for the dissolution accompanied by a chemical reaction of large solid particles. A restriction on the analytical solution is provided in the form of a sufficient condition for the convergence of the series involved. Expressions for the concentration of unreacted, dissolved solid reactant, the time of complete conversion, and the ratio of driving forces available for the reaction and mass transfer steps are presented. Solutions for the rate‐limiting regimes are deduced as special cases of the general solution. The small‐particle solution is recovered as a special case in the limit of a vanishingly small Reynolds number. Rigorous numerical solution has been obtained to assess the accuracy of the pseudostationary‐state solution and to discern the validity of the approximations.
Effect of dispersion quality on particulate magnetic recording disk properties
Authors: Shah M. J. , Karis T. E. , Cuka G. M. 
Published: June 2004

AbstractThe production of particulate magnetic disks or tapes requires consistent and uniform magnetic characteristics over the entire disk or tape to have as few defects as possible. To achieve this goal, the magnetic particle suspension used to coat the disk must be well dispersed. This article describes the use of a rheomagnetic instrument that provides an indirect measurement of the dispersion quality prior to coating application. The instrument was designed, tested, and put on a manufacturing scale line to characterize the relationships between the measured dispersion quality and functional characteristics of the magnetic coating. The results of tests done during scaleup for production yielded a qualitative correlation between the in‐situ measurements made on the magnetic particle suspension at the coater with the surface roughness due to flocs, the on‐disk orientation ratio, and the signal to noise ratio. The current results are the first demonstration of the dispersion quality measurement in a practical manufacturing environment.
Curvature and parametric sensitivity in models for adsorption in micropores
Authors: Saito A. , Foley H. C. 
Published: June 2004

AbstractThe sensitivity of the calculated micropore size of zeolite Y in a fluidized cracking catalyst based on empirical models for argon adsorption has been tested by examining the effect of curvature and by systematically verifying the magnitude of physical constants in the model equations. With a consistent set of physical parameters the slit model provided a pore size value of 0.45 nm, while the new cylindrical models provided values of 0.69 and 0.74 nm. The latter values are found to correspond well with the known aperture size of zeolite Y, 0.74 nm. By separately varying the magnitudes of five of the physical constants in the model over a range of ±30%, it was concluded that the diameter of the oxide ion at the surface had a large effect on the calculated pore size, while the other parameters had only moderate to small effects. Preliminary application of the cylindrical pore model to isotherms of argon on other zeolites and molecular sieves leads to promising results, especially for medium to large pore zeolites. These results suggest that the cylindrical pore model is a useful means for the transformation of argon adsorption data on a zeolite into a micropore size distribution.
Prediction of the three‐dimensional turbulent flow in stirred tanks
Authors: Kresta Suzanne M. , Wood Philip E. 
Published: June 2004

AbstractEfforts to model the turbulent flow in stirred tanks require accurate boundary conditions at the tip of the impeller, not just of velocities, but of the turbulence quantities k and ε. Kolar's (1982) phenomenological, swirling radial jet model of the impeller region is extended by using a two‐equation k – ε turbulence model to obtain direct estimates of k and ε on the impeller periphery. The model is extended and clarified, so that the number of parameters required for its application is reduced to two: the rotational speed and the diameter of the impeller. Three‐dimensional simulations allow a realistic treatment of the baffles. Agreement of the modeling results with recently published experimental data is excellent. This is particularly true in the important impeller discharge zone, where details of the predicted behavior of the turbulence kinetic energy and dissipation rate are in quantitative agreement with the available data. Based on these results, average values of ε are calculated, along with the zones over which the apply. For the impeller discharge zone, the dimensionless, volume‐averaged ε is 0.19.
Methods of deterministic chaos applied to the flow of thin wavy films
Authors: Lacy C. E. , Sheintuch M. , Dukler A. E. 
Published: June 2004

AbstractThe structure of thin, wavy falling films was studied to evaluate whether the random‐appearing wave structure is a result of deterministic chaos or a purely stochastic process. The time‐varying film thickness was obtained at different spatial locations near the point of wave inception for flow rates in the range of Re=3–10. Under all conditions the wave structure was aperiodic in nature and displayed none of the known transitions to chaos. However, the power spectra followed an exponential decay law at high frequencies that is characteristic of chaotic systems. The estimated attractor dimension, used to characterize the complexity of a chaotic system, was much higher than those of known model chaotic systems. It is demonstrated that these high values could be explained due to small levels of noise present in experimental situations. Since experimental data are seldom noise free, a basic limitation in applying these methods to experimental measurements is demonstrated.
Multiple steady states in ideal two‐product distillation
Authors: Jacobsen Elling W. , Skogestad Sigurd 
Published: June 2004

AbstractSimple distillation columns with ideal vapor‐liquid equilibrium may display multiple steady‐state solutions. Two fundamentally different sources for the multiplicity are presented. Both bring about the unexpected result that increasing reflux makes separation worse in the top part of the column. It corresponds to an unstable operating point.The first type of multiplicity is found for columns with mass or volume inputs (e.g., mass reflux and molar boilup). Even for constant molar flows, the transformation from the actual input units to molar units may become singular (corresponding to a pitchfork bifurcation point), resulting in multiple steady‐state solutions. The results are highly relevant in practice, as industrial columns usually have inputs on a mass or volume basis. The second type for specifications on a molar basis (e.g., molar reflux and molar boilup) depends on the presence of an energy balance in the model. The multiplicity is caused by interactions between flows and compositions in the column.
Effects of protein aggregation in isocratic nonlinear chromatography
Authors: Whitley Roger D. , Van Cott Kevin E. , Berninger James A. , Wang N.‐H. Linda 
Published: June 2004

AbstractA versatile reaction‐separation (VERSE) model was developed to quantitatively simulate the behavior of chromatographic separations coupled with reactions. Detailed mass transfer and reaction mechanisms are considered. Aggregation data of myoglobin and β‐lactoglobulin A verified the model. The effects of concentration, equilibrium distribution, reaction rate, convection rate, particle radius, and relative affinity are shown for a dimerizing system. When the aggregation rate is relatively slow compared with convection and mass transfer rates, the individual forms behave as separate species in frontal, elution, and displacement chromatography. For rapid aggregation rates, the individual forms behave as a single component with an average affinity. The wave asymmetry and increased spreading due to aggregation depend on relative affinity differences. Serious error may result if aggregation is overlooked in parameter estimation using frontal or pulse analysis. The dimensionless group principles developed here are useful in scaling and predicting when peak or wave splitting or merging will occur in reaction chromatography systems.
Extent of reaction in open systems with multiple heterogeneous reactions
Authors: Friedly John C. 
Published: June 2004

AbstractThe familiar batch concept of extent of reaction is reexamined for systems of reactions occurring in open systems. Because species concentrations change as a result of transport processes as well as reactions in open systems, the extent of reaction has been less useful in practice in these applications. It is shown that by defining the extent of the equivalent batch reaction and a second contribution to the extent of reaction due to the transport processes, it is possible to treat the description of the dynamics of flow through porous media accompanied by many chemical reactions in a uniform, concise manner. This approach tends to isolate the reaction terms among themselves and away from the model partial differential equations, thereby enabling treatment of large problems involving both equilibrium and kinetically controlled reactions. Implications on the number of coupled partial differential equations necessary to be solved and on numerical algorithms for solving such problems are discussed. Examples provided illustrate the theory applied to solute transport in groundwater flow.
Mass transfer and axial dispersion in a Kühni extraction column
Authors: Dongaonkar Kishor R. , Pratt H. R. Clive , Stevens Geoffrey W. 
Published: June 2004

AbstractConcentration profiles were determined in both phases for the system methyl isobutyl ketone (MIBK)—water‐acetic acid in a Kühni 72.45‐mm‐dia. Extraction column of 25 stages. Mass transfer and backmixing parameters were estimated numerically from the profiles in terms of the backflow model. The results indicated that backmixing of the continuous phase was appreciable, while that of the dispersed phase was negligible. Independent values of the continuous‐phase backmixing coefficient, αc, were also determined by both unsteady‐state and continuous tracer injection, in the former case both with and without mass transfer. The results indicated that αcis increased by mass transfer, and that the tracer values, both with and without mass transfer, are greater than those obtained from the profile data.