bluuebunny/crossref_metadata_2025_split huggingface dataset:
On‐line optimizing control of a nonadiabatic fixed bed reactor
Authors: Lee K. S. , Lee Won‐Kyoo 
Published: June 2004

AbstractA scheme of on‐line optimizing control is presented for a nonadiabatic fixed bed reactor which experiences a highly exothermic reaction. The control scheme has been devised to perform adaptive control of bed temperature and on‐line steady state optimization simultaneously.Experiments were conducted with a pilot scale fixed bed reactor where partial oxidation of n‐butane to maleic anhydride occurs. The reactor system was interfaced with a microcomputer for real‐time control and optimization. With an objective function consisting of a net profit by producing maleic anhydride plus a penalty term on high bed temperature, it was clearly shown that the reaction conditions were driven to the expected optimum region.
Simple, analytical criteria for the sequencing of distillation columns
Authors: Malone M. F. , Glinos K. , Marquez F. E. , Douglas J. M. 
Published: June 2004

AbstractA quantitative criterion for the selection of simple distillation sequences is derived for ideal mixtures. A simple cost model, along with a short‐cut solution of Underwood's equations, gives an analytical form for the total vapor rate, which is the key design variable. The results for column sequencing that are based on the analytical criterion agree well with more exact solutions, but they indicate that in numerous situations the commonly accepted heuristics are incorrect.
Solid‐solid and gas‐gas mixing properties of a new two‐impinging‐streams mixer
Authors: Tamir Abraham , Luzzatto Kfir 
Published: June 2004

AbstractA new device for solid‐solid and gas‐gas continuous mixing, based on the impingement of two streams, was developed and successfully tested. It was found that in comparison to other available solid‐solid pneumatic mixers, such as the fluidized bed, spouted bed, air mixer, and mixing silo, the new device is very convenient and easy to operate and more energy‐efficient. This is also true for gas‐gas mixing when compared with a fluidized bed. A model for the gas phase behavior in the mixing of two gases was successfully tested, which supplements the picture of the solid particles behavior predicted from a model previously derived by the authors.
Some details of developing slugs in horizontal two‐phase flow
Authors: Kordyban Eugene 
Published: June 2004

AbstractA photographic study has been carried out to uncover the details of development of slugs in horizontal two‐phase flow. Based on the observations, it is proposed that the slugs originate as a consequence of local Kelvin‐Helmholtz instability at the wave crest, rather than the instability of the whole wave. The findings are in reasonable agreement with published results on the transition to slug flow.
Thermal resistance models of packed‐bed effective heat transfer parameters
Authors: Dixon A. G. 
Published: June 2004

AbstractSimple thermal resistance models of packed‐bed heat transfer can be used to derive predictive formulas for the effective axial and radial thermal conductivities and apparent wall heat transfer coefficient. In particular, the behavior of the heat transfer parameters over the entire range of Reynolds number can be explained by considering the two asymptotic cases of low Re (solid phase dominant) and high Re (fluid phase dominant).
Density of an equimolar mixture of ethane and methyl chloride
Authors: Eubank P. T. , Kreglewski Aleksander , Hall K. R. , Holste J. C. , Mansoorian Hamazasm 
Published: June 2004

AbstractWe have measured the density of an equimolar gas mixture of C2H6–CH3Cl between 323.15 and 473.15 K at pressures to 14.0 MPa. Interaction second virial coefficients and dew‐point pressures are extracted from the measurements. Intermolecular force constants for the Lennard‐Jones and Stockmayer models are determined optimally for like and unlike pair interactions. Recent methods of prediction for second virial coefficients, both pure and interaction, are tested against experiment.
Dynamic modeling of emulsion polymerization reactors
Authors: Penlidis A. , MacGregor J. F. , Hamielec A. E. 
Published: June 2004

AbstractThis paper is a survey of recent published works on the dynamic and steady state modeling of emulsion homo‐ and copolymerization in batch, semicontinuous, and continuous latex reactors. Contributions to our understanding of diffusion‐controlled termination and propagation reactions, molecular weight, long chain branching and crosslinking development, polymer particle nucleation, and of the dynamics of continuous emulsion polymerization are critically reviewed.
The diffusivity of potassium chloride and sodium chloride in concentrated, saturated, and supersaturated aqueous solutions
Authors: Chang Y. C. , Myerson A. S. 
Published: June 2004

AbstractThe diffusion coefficients of potassium chloride and sodium chloride were measured in concentrated, saturated, and supersaturated solutions at 25°C employing Gouy interferometry. The results indicate a maximum in the diffusivity vs. concentration curve near saturation followed by a rapid decline in diffusivity toward zero with increasing concentration in the supersaturated region. This behavior supports the idea that the diffusion coefficient approaches zero at the spinodal concentration. The data were successfully correlated by modifying an empirical activity coefficient equation (Robinson and Stokes, 1955) to account for molecular cluster effects and employing the calculated activity coefficients along with a predictive equation for diffusivity in electrolytes (Robinson and Stokes, 1955).
Rapid hydropyrolysis of softening coal particles—A modeling study. Part I: Model formulation and parameter values
Authors: Schaub Georg , Peters W. A. , Howard J. B. 
Published: June 2004

AbstractA mathematical model is developed for rapid hydropyrolysis of softening coal particles. It is aimed to represent previously measured effects of pressure and particle size on product yields. The model includes a global chemical reaction scheme combined with diffusional transport of hydrogen dependent on the transient physical properties of the coal. Model predictions are compared with experimental data in a companion paper.
Catalysis and synergism in the reduction smelting of lead sulfide with carbon and lime
Authors: Rao Y. K. , El‐Rahaiby S. K. 
Published: June 2004

AbstractThe catalyzed direct reduction of lead sulfide with carbon and lime was investigated at several temperatures and under two different inert gas atmospheres. The catalyzed reduction kinetics were determined both with a nitrogen atmosphere and a helium‐rich helium‐nitrogen atmosphere. The reduction kinetics under the latter were decidedly superior to those under the former. The differences were interpreted in terms of faster diffusion rates in a helium medium and synergistic effects. The catalyst used was a ternay eutectic mixture (K, Li, Na)2CO3, which amounted to 2.5 wt. % of the PbS:4CaO:4C reaction mixture.
The role of zeolite pore structure during deactivation by coking
Authors: McLaughlin K. W. , Anthony R. G. 
Published: June 2004

AbstractResidues accumulating within the cavities of a small‐pore zeolite, isolated by extraction, are composed of a series of aromatics up to a distinct cutoff at pyrene. Similar analysis of partiall‐regenerated catalyst reveal pathways by which residue oxidation can occur and pathways by which these residues can participate during methanol decomposition.
Effects of surface viscosities on the stability of a draining plane parallel liquid film as a small bubble approaches a liquid‐gas interface
Authors: Hahn P.‐S. , Slattery J. C. 
Published: June 2004

AbstractWhen a small bubble is driven through a liquid phase to a liquid‐gas interface, a thin liquid film forms between them and drains until an instability forms and coalescence occurs. Following Lin and Slattery (1982b), Chen et al. (1984) and Hahn et al. (1985) analyzed this process, neglecting the effects of electrostatic forces and of the surface viscosities. Here we extend their theory to include the effects of the surface viscosities. We employ a modification of the development by Barber and Hartland (1976; Flumerfelt et al., 1982) for a draining film bounded by parallel planes.For a large intermediate range of the surface viscosities, the coalescence time is a strong function of these parameters. Inclusion of the surface viscosities acts to moderate or even reverse trends previously established for the dependence of the coalescence time on the bubble radius, the viscosity of the film liquid, the interfacial tension, the strength of the London‐van der Waals forces, and the density difference between the two phases.
Stochastic modeling of a fluidized‐bed reactor
Authors: Too J. R. , Fox R. O. , Fan L. T. , Nassar R. 
Published: June 2004

AbstractIn this work dispersive mixing and chemical reactions are treated simultaneously by resorting to the theory of stochastic processes. A fluidized‐bed reactor is modeled by discretizing it into ideally stirred tanks of various sizes corresponding to bubble, cloud, and emulsion phases. All parameters in the model are correlated with known or experimentally obtainable quantities. Examples using a complex chemical reaction are given to demonstrate the applicability of the approach.
Surface phenomena and mass transfer interactions in liquid‐liquid systems
Authors: Thornton J. D. , Anderson T. J. , Javed K. H. , Achwal S. K. 
Published: June 2004

AbstractThe surface dynamics of pendant aqueous droplets forming at a submerged nozzle in an immiscible organic solvent have been studied using a novel laser‐activated photochromic tracer technique. This enabled a small element of surface to be labeled so that its subsequent history could be recorded photographically.Results for aqueous droplets forming in toluene in the absence of any mass transfer indicated only a slow interfacial circulation from the front to the rear, and there was no indication of any surface renewal as a result of hydrodynamic flow even at nozzle Reynolds numbers as high as 300. By contrast, the introduction of any one of a number of organic solutes into the toluene phase led to sporadic Marangoni‐type interfacial disturbances, which in turn resulted in rapid replacement of elements of the droplet surface. It is proposed that renewal of the droplet surface is dependent on solute diffusion in the present instance and that the processes of surface renewal and mass transfer are likely to be interactive.
Continuous thermodynamics of multicomponent systems
Authors: Kehlen Horst , Rätzsch M. T. , Bergmann Joachim 
Published: June 2004

AbstractBased on a continuous distribution function instead of the mole fractions of individual components, a consistent building of continuous thermodynamics is presented. It may be favorably used in all cases where there are a large number of very similar chemical species such as in polymers, in heavy petroleum fractions, or in coal‐derived liquids.
Molecular theory of transport in fluid microstructures: Diffusion in interfaces and thin films
Authors: Adolf D. , Tirrell M. , Davis H. T. 
Published: June 2004

AbstractGradient theory of equilibrium fluid microstructures is extended to nonequilibrium isothermal processes. The theory is applied to steady diffusion across liquid‐liquid interfaces. It is shown that local equilibrium across a fluid‐fluid interface is maintained even in the presence of very high diffusion fluxes and that the concept of an interface acting as an applied potential energy for a diffusing species is of limited utility. The theory is suited for practical, semiempirical calculations of structure, stress, and isothermal transport in systems containing interfaces.
Performance studies of the measurement test for detection of gross errors in process data
Authors: Iordache C. , Mah R. S. H. , Tamhane A. C. 
Published: June 2004

AbstractThe measurement test proposed by Mah and Tamhane (1982) allows the gross error associated with a measurement to be directly identified without a separate procedure. In this paper a comprehensive evaluation of this test was carried out based on two different definitions of its power. The influence of constraints, network configuration, position of measurement, magnitudes of gross error and standard deviations, number of measurements, and other factors were summarized as rules and guidelines for the application of this test. The simulation procedure developed in this investigation may be used to design a gross error detection scheme for any specific application.
Representation of deviation from ideality in concentrated aqueous solutions of electrolytes using a mean spherical approximation molecular model
Authors: Ball Francois‐Xavier , Planche Henri , Fürst Walter , Renon Henri 
Published: June 2004

AbstractA semiempirical expression for the Helmholtz energy of mixed electrolyte solutions in solvents mixtures is obtained from the solution of the mean spherical approximation given by Planche and Renon (1981) for a nonprimitive model of interactions. A consistent set of analytical equations for the related thermodynamic properties was further derived and used to represent osmotic coefficient data of strong aqueous electrolytes at 25°C. Data correlation was performed on more than 80 systems up to a 6 M molality using generally one adjustable parameter for each single electrolyte; from these parameters the properties of mixtures can be calculated in a predictive manner without additional parameters.
Hydrodynamic simulation of periodic cycled plate columns
Authors: Thompson M. F. , Furzer I. A. 
Published: June 2004

AbstractA mathematical model of the hydrodynamic processes occurring in a periodic cycled plate column is developed and experimentally confirmed. The model is applied to the prediction of the holdup distribution and the investigation of hydrodynamic problems. An effective manifold arrangement is proposed to minimize the uneven liquid draining encountered in previous experimental studies.
Absolute rates of the carbon‐carbon dioxide reaction
Authors: Yang K. L. , Yang R. T. 
Published: June 2004

AbstractThe etch‐decoration transmission electron microscopy technique was used to measure the turnover frequencies of the C‐CO2 reaction in the temperature range 600–900°C. The absolute rate constants of the elementary rate steps were determined, and were in reasonably good agreement with statistical theories. The rates on monolayer steps of graphite were higher than those on multilayer steps by approximately four orders of magnitude at 800°C, because the CO bond in the reaction intermediate is stronger by about 9 kcal/mol on the monolayer steps. The rates of vacancy formation in the lattice were also determined. The vacancies are formed by atomic oxygen dissociated from CO2.
A theory for the most stable variable viscosity profile in graded mobility displacement processes
Authors: Gorell S. B. , Homsy G. M. 
Published: June 2004

AbstractThe stability of the displacement of a viscous fluid in a porous medium by a less viscous fluid containing an additive is considered. For the case in which the total amount of injected additive is fixed, a theory has been formulated to find the graded mobility profile which minimizes the instability due to an adverse mobility ratio. The result is a constrained nonlinear eigenvalue problem in which the mobility ratio of the fluids, α, and the total dimensionless amount of additive,N, appear as parameters. Estimates showNis typically large for practical situations. An asymptotic solution for largeNis developed which shows that the optimal mobility profile is always an exponential curve at leading order. It is shown that although the optimal mobility profile is nearly exponential, the optimal concentration profile is not necesarily so, contrary to previous suggestions in the literature. Furthermore, it is shown that, unlike the case of a mobility jump, a graded mobility process under optimal conditions has amplifications independent of displacement velocity. We also discuss a possibile stabilization mechanism due to the very long wavelength disturbances which occur under optimal conditions.
Tracer diffusion of aromatic hydrocarbons in liquid cyclohexane up to its critical temperature
Authors: Sun C. K. J. , Chen S. H. 
Published: June 2004

AbstractTracer diffusion coefficients in liquid cyclohexane of benzene, toluene, p‐xylene, mesitylene, naphthalene, and phenanthrene have been determined from 298.2 to 523.2 K (TR = 0.54 ∼ 0.95) using the Taylor dispersion method. Positive deviations from the Arrhenius relationship are observed as the critical temperature is approached, but a rough‐hard‐sphere theory is found to be adequate for describing the data across the entire temperature range. On the basis of the computer simulation results for hard‐sphere fluids, correlations involving solute and solvent critical volumes and their molecular weights have also been developed for practical applications. Tracer diffusivities in supercritical carbon dioxide are also adequately represented by the proposed correlation, as the fluid density is not far removed from that of liquid carbon dioxide.
Deterministic variability analysis for intermediate storage in noncontinuous processes: Part II: Storage sizing for serial systems
Authors: Karimi I. A. , Reklaitis G. V. 
Published: June 2004

AbstractThe allowability conditions derived in Part I of this series are applied to develop intermediate storage sizing expressions for serial systems subjected to process parameter variations. Multiple variations in either starting moments, transfer flow rates, or transfer fractions are considered first. These results are then combined using a worst‐case analysis to develop size estimates under general variations. A simple statistical basis is given for the bounds on the cumulative variations which are employed in the sizing expressions. An example serial system is discussed to illustrate the results.
Hollow fiber gas membranes
Authors: Qi Zhang , Cussler E. L. 
Published: June 2004

AbstractGas membranes can be used to rapidly remove volatile solutes like hydrogen sulfide and sulfur dioxide from dilute aqueous solutions. The gas membranes are supported by microporous hydrophobic hollow fibers. The aqueous feed containing the volatile component flows down the fiber lumen, and an aqueous stripping solution bathes the outside fiber surface. Thus the membrane consists of gas trapped in the hydrophobic pores. The fluxes across these membranes, which can be much faster than those across polymer films, are consistent with a nonlinear mechanism which includes solute ionization.
Characteristics of slugging regime and transition to turbulent regime for fluidized beds of large coarse particles
Authors: Satija Sunil , Fan Liang‐Shih 
Published: June 2004

AbstractSlugging characteristics, including slug velocity and frequency and the height of the slugging bed, for a slugging bed of four different types of coarse particles ranging from 1 to 7 mm in size are determined based on pressure fluctuation behavior of the bed. The slugging characteristics of coarse particle slugging beds are found to be much different from those of the particle slugging beds reported in the literature. The pressure fluctuation behavior in a coarse particle turbulent bed and the transition velocity from a slugging bed to a turbulent bed is also examined.
An analysis of the lyophilization process using a sorption‐sublimation model and various operational policies
Authors: Millman M. J. , Liapis A. I. , Marchello J. M. 
Published: June 2004

AbstractThe freeze‐drying process is studied under various operational policies through the use of a sorption‐sublimation model. The operational policy that provides the shortest drying times keeps the pressure at its lowest value. The upper and lower heating plates are independently controlled so that the material constraints are encountered and held throughout the free water removal phase.Under certain conditions, and for the case of samples of small thickness, the sorbed water profiles may have segments whose bound water concentrations are higher than those at the start of the free water removal phase. It is shown that the criterion used in terminating the freeze‐drying process is of extreme importance, since it may lead to an undesirable sorbed water profile which may deteriorate the quality of the dried product.
Behavior of nucleation sites in pool boiling
Authors: Sgheiza J. E. , Myers J. E. 
Published: June 2004

AbstractThe behavior of active boiling site populations was monitored for pool boiling on an electrically heated 1‐mil stainless steel sheet. The boiling sites were located using a high‐speed infrared camera focused on the underside of the boiling surface. Experiments were conducted to determine factors affecting the origin, concentration, and lifetime of active sites.
Design of cyclic fixed‐bed adsorption processes. Part I: Phenol adsorption on polymeric adsorbents
Authors: Costa Carlos , Rodrigues Alirio 
Published: June 2004

AbstractA model for the adsorption of phenol in a fixed bed of a polymeric adsorbent is developed. Model parameters (equilibrium parameters, capacity factor, axial dispersion, film mass transfer coefficient, and intraparticle effective diffusivity) are experimentally determined from independent experiments. Numerical solution of the model equations uses the method of lines with double orthogonal collocation in finite elements. The model is used for the prediction of breakthrough curves and is part of a package for the design of cyclic processes.
Knudesen diffusion in random assemblages of uniform spheres
Authors: Huizenga D. G. , Smith D. M. 
Published: June 2004

AbstractExperimental measurements have been conducted of Knudsen diffusion through a model porous medium fabricated by the pelleting of monodisperse silica spheres. Tortuosity factors for this random‐assemblage‐of‐spheres porous solid are calculated and compared with values obtained from both theory and measurements made in the bulk diffusion regime. Evidence is presented to support the use of a mean pore radius calculated as twice the ratio of pore volume to surface area, as opposed to values obtained from mercury porosimetry or sorption isotherm analysis.
Mixing/segregation in two‐ and three‐dimensional fluidized beds: Binary systems of equidensity spherical particles
Authors: Rice R. W. , Brainovich J. F. 
Published: June 2004

AbstractA comparison was made of the equilibrium mixing/segregation behavior of binary mixtures of different‐sized, equal‐density glass beads in two‐ and three‐dimensional fluidized beds. Several empirical equations for mixing index were examined, all involving a dimensionless function of excess gas velocity. This function, which appeared to largely account for the effect of aspect ratio, was found to optimally correlate the data for both types of beds. However, a much better fit was obtained for the threedimensional bed data, most probably because wall effects significantly retarded mixing in the two‐dimensional bed.
Application of percolation theory to noncatalytic gas‐solid reactions
Authors: Yortsos Y. C. , Sharma M. 
Published: June 2004

AbstractPrevious models of noncatalytic gas‐solid reactions are based primarily on parallelpore representations, thus excluding important topological effects of the porous medium. This paper utilizes network representations and percolation theory to develop expressions for pore closure time and the evolution of accessible volume, effective diffusivity, and conversion rates.