bluuebunny/crossref_metadata_2025_split huggingface dataset:
Principles of dynamic balancing
Authors: Almasy Gedeon A. 
Published: June 2004

AbstractThe principles of static balancing, also called measurement error reconciliation (MER), have been generalized to transient conditions. An exactly linear dynamic balance model has been stated where flow variables are assumed to be stochastic processes with independent increments. With this model the residual error of static MER due to dynamic effects can be estimated. Dynamic balancing is proposed as the estimation of flow and inventory variables by Kalman filtering applied to the balance model. The error of estimates obtained in this way is significantly less than that for the static MER estimates, even if the process is nearly in steady state. The main problem of dynamic balancing is that it requires not only the redundant observation of flow variables but also the observation of inventory variables. Compatibility of MER and dynamic balancing has been shown.
Transport of aromatic molecules in NaY Zeolite powders
Authors: Chmelka B. F. , Gillis J. V. , Petersen E. E. , Radke C. J. 
Published: June 2004

AbstractXenon‐129 NMR is used to probe macroscopic distributions of aromatic molecules adsorbed in a packed bed of 1‐μm NaY zeolite particles. Relative rates of guest transport through the intracrystalline (micro) and intercrystalline (macro) pores play a unique role in the axial distribution of sorbate molecules, such as hexamethylbenzene, in a zeolite powder. Xenon‐129 NMR spectra show that a sharp HMB adsorption front advances through a bed of dehydrated NaY crystallites at 523 K. However, at 573 K or in the presence of coadsorbed water, HMB species disperse through the bed without forming a sharp boundary between adsorption zones.When guest transport is controlled by pseudosteady‐state diffusion in the macropores, axial penetration of the bed by vapor‐phase guest species occurs in a sharp adsorption front. A shrinking‐core transport model then quantitatively estimates the intracrystalline diffusivities of HMB in dehydrated and partially hydrated NaY zeolite of 10−11 and 10−13 m2/s, respectively, at 523 K. Xenon‐129 NMR proves to be a powerful tool for probing adsorbed guest distribution in zeolites, allowing relative time scales to be established for transport of molecular guests in NaY powders.
New hypotheses for Mercury porosimetry with percolation approach
Authors: Park Churl‐Young , Ihm Son‐Ki 
Published: June 2004

AbstractNew hypotheses of no coalescence and no entrapment are proposed for mercury intrusion and extrusion. Pore structures are represented by a two‐dimensional lattice for bond percolation and the Rayleigh distribution function taken for the pore size distribution. Different modes of hysteresis are found with the new hypotheses and the effect of accessible probability on the hysteresis loop is analyzed. A bimodal size distribution with micropores and macropores is analyzed by considering the extent of overlapping and the sequence of connection between both distributions. Mercury entrapment is also predicted by considering the pressure difference between the applied and assigned pressures, as determined by the Washburn equation, as a parameter for mercury breakage. The applicability of the proposed hypotheses is demonstrated by showing that experimental data on an α‐alumina sample could be well correlated.
Optimizing the throughput of hazardous waste incinerators
Authors: Behmanesh Nasrin , Manousiouthakis Vasilios , Allen David T. 
Published: June 2004

AbstractThis work presents a linear, steady‐state model of a rotary kiln hazardous waste incinerator. Mass balance constraints, energy balance constraints, constraints typically imposed by incinerator permits, and constraints imposed by design limitations are all included in the model. The model is used to perform optimization studies, which maximize a measure of the incinerator's throughput. The sensitivity of the model to uncertainties in the chemical property values of the waste streams is also examined. For the spectrum of case studies examined, the optimal operating conditions are most sensitive to halogen content and water content of the wastes and are less sensitive to variations in heating value and nitrogen content.
Nonlinear analysis in process design
Authors: Seider Warren D. , Brengel David D. , Widagdo Soemantri 
Published: June 2004

AbstractAs steady‐state and dynamic simulators with optimal controllers have evolved, tools for nonlinear analysis have been developed by reactor and thermophysical property specialists. Designers lag behind in developing and utilizing these tools, as many design strategies assume idealized behavior even though processes contain an increasing number of nonlinear elements. This article examines the sources of the nonlinear elements, often associated with physical and chemical interactions, in designs and their control systems. Promising methods for nonlinear analysis are reviewed.In each design activity, involving simulation, economic optimization, projections of controllability and operability, emphasis is on the sources of nonlinearities and solution methods. These are examined for the equality constraints and nonlinear programs in phase and chemical equilibria, in reactors and separators, and in the simulation and optimization of flowsheets. Also examined are the impact of non‐linear predictive control in screening designs and methods to insure operability, in the face of uncertainties.
Simulation of methane partial oxidation over silica‐supported MoO3 and V2O5
Authors: Amiridis Michael D. , Rekoske James E. , Dumesic James A. , Rudd Dale F. , Spencer Nicholas D. , Pereira Carmo J. 
Published: June 2004

AbstractMicrokinetic simulations have been carried out to describe the partial oxidation of methane over silica‐supported molybdena and vanadia. The objective of this study was to formulate a physically reasonable reaction network to capture the basic aspects of the surface catalytic chemistry and to use this network to link methane oxidation kinetics with the kinetics observed for the oxidation of subsequent gaseous products, i.e., methanol, formaldehyde, and carbon monoxide. The most abundant reactive intermediates on the catalyst surface are suggested to be oxygen and hydroxyl groups. This reaction network successfully predicts the catalytic activities, selectivities, activation energies, and reaction orders observed over silica‐supported molybdena and vanadia; and the microkinetic model also semiquantitatively explains the kinetic trends for related catalyst systems and is consistent with surface bonding energetics reported in the literature over various oxide catalysts. The microkinetic reaction network properly reduces to the more simple macrokinetic model reported previously for methane partial oxidation.
Bubble size prediction for rigid and flexible spargers
Authors: Geary Nicholas W. , Rice Richard G. 
Published: June 2004

AbstractThere exists a narrow operating window in bubble columns where the motion is so gentle that the normally dominating forces of coalescence and breakup no longer define the bubble size, hence formation dynamics must control. Elementary force balances are presented to predict bubble size, which compares favorably with experimental data and is shown to be applicable to both rigid and flexible spargers. The main focus is on the prediction and performance of a small‐holed flexisparger, for which it is proved that the gas momentum term is highly significant. Also, it is shown that the intermediate drag law is more appropriate than Stokes for forming bubbles.
Effect of scale of operation on CSD dynamics in evaporative crystallizers
Authors: Jager Johan , Kramer Herman J. M. , Scarlett Brian , De Jong Esso J. , De Wolf Sjoerd 
Published: June 2004

AbstractExperimental measurements of the crystal‐size distribution (CSD) clearly indicate a pronounced difference in the dynamic behavior of a 20‐ and 970‐L continuous crystallizer that produces ammonium sulfate. The difference in their circulation time offers a probable explanation for this phenomenon. It causes different supersaturation profiles in the two crystallizers, which leads to internal fines dissolution in the large crystallizer. This contributes to the observed oscillations in the 970‐L crystallizer as opposed to the first‐order responses in the 20‐L crystallizer. To numerically study the effect of the supersaturation profile a dynamic model, from which the MSMPR (mixed suspension mixed product removal) assumption is omitted, is developed. Calculated supersaturation profiles differ considerably for the 20‐L, the 970‐L and an imaginary 50,000‐L continuous evaporative crystallizer. Coincident with changes in the supersaturation profiles, the numerical solution of the model indicates the tendency of large crystallizers to oscillate and supports this suggested explanation.
Data reconciliation in generalized linear dynamic systems
Authors: Darouach Mohamed , Zasadzinski Michel 
Published: June 2004

AbstractA generalized linear dynamic model or singular model, for which the standard state space representation and the Kalman filtering cannot be applied, is used to develop a new algorithm to solve the linear dynamic material balance problem. This algorithm is based on the method developed in the steady‐state case and leads to a recursive scheme, which is very useful in real‐time processing. It reduces the computational problem such as singularities and round‐off errors that may occur in complex systems. Convergence conditions are given and verified for the dynamic material balance case.
Experimental study of reaction in a partially wetted catalytic pellet
Authors: Funk Gregory A. , Harold Michael P. , Ng Ka M. 
Published: June 2004

AbstractA single‐pellet reactor has been used to investigate the impact of partial external wetting on catalyst performance in a multiphase reaction system. The novel design simulates the local environment within a trickle‐bed reactor, and permits the direct measurement of the degree of wetting under reaction conditions. Experimental data of the hydrogenation of α‐methylstyrene (AMS) over a Pd/Al2O3 pellet provide unequivocal evidence of effectiveness enhancement by partial wetting, a predicted single‐pellet phenomenon (e.g., Harold and Ng, 1987; Funk et al., 1988, 1989). The overall reaction rate is an increasing (decreasing) function of the degree of wetting if the overall limiting reactant is more effectively supplied through the wetted (nonwetted) part of the surface. A maximum in the reaction rate can occur at an intermediate degree of wetting, signaling a transition from an overall AMS‐limited to hydrogen‐limited reaction. The dependence of the degree of wetting on the liquid flow rate for low reaction rates is consistent with a simple rivulet flow model. At higher reaction rates the degree of wetting decreases, with all other conditions fixed. Possible mechanisms for this interesting link between the degree of wetting and reaction are discussed.
Enhanced dispersion resulting from solute exchange between phases
Authors: Grosser Karen A. , Erickson Kenneth L. , Carbonell Ruben G. 
Published: June 2004

AbstractThe enhanced dispersion resulting from solute exchange between phases was investigated experimentally for the case of a long, cylindrical capillary tube, in which a stationary absorbing phase formed a thin annular film around a flowing fluid. Solute diffusion into the stationary phase was analyzed in detail to accurately determine the coupling of film diffusion and hydrodynamic effects. The experimental results and analyses showed an increase in dispersion relative to the usual Taylor effect. The increased dispersion was a function of the relative partitioning of solute between phases and was in quantitative agreement with predictions from previously published theoretical studies.
Eddy diffusivity for distillation sieve trays
Authors: Bennett Douglas L. , Grimm Henry J. 
Published: June 2004

AbstractAn understanding of the eddy diffusivity on a distillation tray is important to accurately predict the distillation tray efficiency from the point efficiency. This article presents a new correlation to predict liquid‐phase eddy diffusivity (De) on sieve trays. This correlation has been developed by modeling backmixing as the trajectory motion of liquid droplet elements through the two‐phase layer height on the tray. The trajectory model indicates that De is a strong function of the two‐phase layer height. An expression for froth height is derived.The new De correlation offers two main improvements over existing literature correlations. First, this model is phenomenologically‐based and, therefore, not limited to air/water. Second, the new De correlation gives significantly lower average actual and relative errors and a lower standard deviation of the actual error than do other available correlations.
Molecular thermodynamics of solute‐polymer‐supercritical fluid systems
Authors: Shim Jae‐Jin , Johnston Keith P. 
Published: June 2004

AbstractThe distribution coefficients of the solutes (toluene, naphthalene, and phenanthrene) are reported at infinite dilution between silicone rubber and supercriticalfluid carbon dioxide. A new technique is described in which a thin film of polymer is coated and cross‐linked onto silica, and the distribution coefficient is measured rapidly by elution supercritical‐fluid chromatography. Because CO2 significantly enhances the solute's volatility and its diffusion coefficient in the polymer, it is possible to study solute‐polymer interactions at room temperature for nonvolatile compounds which would be difficult to study by conventional techniques such as gas chromatography. These infinite dilution data are used to determine solutepolymer interaction parameters to calculate phase diagrams over a wide concentration range. The residual, combinatorial, and cross‐link contributions to the solute activity coefficient in the polymer are discussed as a function of concentration. In addition, pronounced pressure and temperature effects are described in terms of experimentally measured solute partial molar volumes (to – 14 L/mol) and partial molar enthalpies (to – 850 kJ/mol) in the fluid phase.
Rotary kiln transport processes
Authors: Ferron John R. , Singh Dilip K. 
Published: June 2004

AbstractSlow rotation of a cylindrical kiln, partially filled with powder or granular solid, produces a planar interface between the bulk of the solid and the gas phase, tilted at the angle of repose. Particles cascade downward on this plane, moving relatively freely and randomly, providing the principal mechanism for particulate diffusion and mixing in the kiln. The plane is also the most favorable location for chemical reactions that require efficient gas–solid heat and mass transfer. Conservation equations are constructed for planar and bulk regions, coupled by the particulate exchange produced by rotation. Sample problems of mixing and heat exchange illustrate problem formulation and useful simplifications. A penetration model predicts wall‐to‐bed heat transfer coefficients, leading to better agreement with experiment than is obtained when planar processes are omitted.
Rapid carbothermal reduction of boron oxide in a graphite transport reactor
Authors: Weimer Alan W. , Roach Raymond P. , Haney Christopher N. , Moore William G. , Rafaniello William 
Published: June 2004

AbstractUniform submicron crystals of B4C, boron‐enriched boron carbide, and B4C/TiB2 composite powders have been synthesized continuously by rapid carbothermal reduction at approximately 2,200 K in a 0.14 m ID × 1.68 m long pilot‐scale graphite transport reactor. A unique reactor design allowed for continuous feeding of a meltable boron oxide containing precursor, rapid heating rates that completed the carbothermal reduction reaction in seconds, and an expanded cooling that allowed for the precipitation in space of volatile excess boron oxides. Powder morphology resembled that of powder synthesized by laser pyrolysis of gaseous reactants. Rapid heating rates and minimized reaction times at high temperatures promoted nucleation with limited crystal growth. Dense parts fabricated from these powders had fine grains and extreme hardness.
Critical velocity correlations for slurry transport with non‐Newtonian fluids
Authors: Shah Subhash N. , Lord David L. 
Published: June 2004

AbstractTransport properties of various uncross‐linked and cross‐linked non‐Newtonian slurries in horizontal pipes are studied. Flow data are gathered in three long, different diameter, transparent horizontal pipes. Investigated are the effects of the pipe size, polymer concentration, fluid rheological properties, cross‐linking effects, particle size and density, solids concentration, fluid density, and slurry rate on the critical deposition velocities and particle resuspension velocities. It is found that critical deposition and resuspension velocities for the non‐Newtonian carrier fluids tested are significantly lower than those for water. Both velocities depend greatly on pipe size and particle density. Higher critical velocities are required to minimize settling (1) in larger pipe sizes and (2) for pumping solids denser than sand. For less viscous fluids, critical deposition and resuspension velocities increase slightly with increasing solids concentration. They are, however, independent of solids concentration for more viscous fluids.
Supercritical CO2 extraction of organic contaminants from aqueous streams
Authors: Ghonasgi D. , Gupta S. , Dooley K. M. , Knopf F. C. 
Published: June 2004

AbstractSupercritical fluid extraction (SCFE) for the removal of organic toxins from water has been studied using a continuous‐flow view cell system. Distribution coefficients (ratio of mole fraction of contaminant in supercritical CO2 to mole fraction in the aqueous phase at equilibrium) have been determined for a homologous series of contaminants as individual components in pure water: benzene, phenol, p‐chlorophenol, and m‐cresol. Data were obtained at two temperatures (313 and 323 K) and over a pressure range of 9.65 to 17.23 MPa for each contaminant. The distribution coefficients of the contaminants follow a pattern that can be explained in terms of molecular interactions both with water in the aqueous phase (as quantified by the pure contaminant solubility in water) and with CO2 in the SCF phase (as quantified by the pure contaminant solubility in near‐critical CO2 and crossover phenomena in SCF CO2). These results have been accurately modeled using a hardsphere, perturbation‐theory‐based Carnahan‐Starling‐DeSantis‐Redlich‐Kwong equation of state and simple van der Waals mixing rules.
L‐serine obtained by methanol addition in batch crystallization
Authors: Charmolue Hervé , Rousseau Ronald W. 
Published: June 2004

AbstractThe solubility of L‐serine in water was measured as a function of temperature, and the solubility in methanol‐water solutions was determined as a function of temperature and methanol concentration. Solubility in aqueous solutions was found to be a linear function of temperature. Additionally, a statistical design of experiments was used to identify the kinetic variables that influence the purity of L‐serine crystals recovered by batch crystallization. Agitation and the rate at which super‐saturation was generated through cooling and methanol addition were found to influence the methanol content of the recovered crystals. The size of the recovered crystals also was found to depend on agitation and the rate at which methanol was added to the L‐serine mother liquor.
Water and ethanol sorption phenomena on starch
Authors: Lee Jay Y. , Westgate Paul J. , Ladisch Michael R. 
Published: June 2004

AbstractThe sorption behavior of water and ethanol on starch material has been investigated in relation to the adsorptive separation of water from ethanol. The adsorption isotherms of water‐starch, ethanol‐starch and water‐ethanol‐starch were measured using a Cahn electrobalance. Careful examination of the many sorption isotherm models resulted in selection of Sircar's model and the potential theory to best represent the isotherm data of water‐starch and ethanol‐starch adsorption. Experimental results showed that ethanol as well as water can adsorb on starch. The adsorption rate of ethanol, however, is much slower than that of water. This suggests that the selective removal of water from ethanol vapor in a packed‐bed adsorber is likely a rate‐dependent, not an equilibrium‐dependent, process.
Lattice relaxation in type I gas hydrates
Authors: Rodger P. M. 
Published: June 2004

AbstractComputer simulations have been used to examine the approximations upon which the van der Waals‐Platteeuw theory of hydrate stability is based, and in particular, the extent to which the water lattice relaxes about the guest molecules. It is found that the behavior of the water lattice depends significantly on both the nature and number of guest molecules present—an effect that is neglected in the van der Waals‐Platteeuw theory. The simulations also indicate an important role for the repulsive guest‐host interactions in generating the mechanical stability of gas hydrates in the bulk. On the basis of these simulations, it is conjectured that surface interactions (particularly at a water/guest interface) are fundamental to the phase behavior of gas hydrates.
Trapping of solid particles at a wall in a turbulent flow
Authors: Young James B. , Hanratty Thomas J. 
Published: June 2004

AbstractStudies of the motion of a dilute suspension of 100‐micron glass and stainless steel spheres in water flowing turbulently down a pipe revealed that they could be trapped in necklace formations that move slowly at a distance of less than one particle diameter from the wall. The tendency toward trapping increases with particle density and decreases with flow rate. The phenomenon is interpreted as occurring when the Saffman lift force toward the wall overcomes the ability of fluid turbulence to mix the particles. The location of the particles is dictated by a balance between the Saffman lift force and a wall‐induced force associated with the displacement of fluid as a particle moves parallel to the wall.
Oscillatory cross‐flow electrophoresis
Authors: Chandhok Ajay K. , Leighton David T. 
Published: June 2004

AbstractElectrophoresis is a useful analytic technique for the separation of proteins and other large molecules, but has proven resistant to scale‐up to production levels. In this article we describe a new technique that permits the use of much greater feed rates than possible in a conventional electrophoresis unit. The technique, in its simplest form similar to the cyclical field‐flow fractionation technique developed by Giddings (1986) and extended by Shmidt and Cheh (1990), relies on the application of an oscillatory electric field across the narrow gap of the electrophoretic cell. The motion of the solute species induced by this field interacts with an oscillatory cross‐flow to cause a separation based on the electrophoretic mobility of the species. This horizontal separation is combined further with a gradient in the strength of the oscillating electric field and oscillations in the vertical downflow to lead to different steady streamlines for species with different mobilities.