bluuebunny/crossref_metadata_2025_split huggingface dataset:
Model for Sr‐Cs‐Ca‐Mg‐Na ion‐exchange equilibria on chabazite
Authors: Perona Joseph J. 
Published: June 2004

AbstractChabazite zeolites are used at Oak Ridge National Laboratory to decontaminate wastewaters containing 90Sr and 137Cs. Treatability studies show that chabazite can remove trace amounts of these nuclides from wastewaters containing much higher concentrations of calcium and magnesium. The design of ion‐exchange columns for multicomponent systems requires a method for predicting multicomponent equilibria from binary, ternary and quaternary experiments, since the number of experiments required for an empirical equilibrium model is not generally feasible. Binary interaction parameters for the Wilson equation are used to predict solid‐phase activity coefficients for the five‐component system. The sum of squares of deviations between experimental and predicted solution concentrations for the data points available is calculated. The average deviation per data point for the five‐component system is lower than for some of the ternary‐and four‐component data sets containing calcium or magnesium.
Prediction of polydispersed fluidized bed system properties: A new approach
Authors: Ganguly U. P. 
Published: June 2004

AbstractA new approach for estimating the system properties of polydispersed liquid‐solid fluidized bed systems, based on the concept of departure from monodispersed systems, is discussed. The proposed generalized correlation based on experimental data on particulate fluidization can predict minimum fluidization velocity, minimum elutriation velocity, onset of semifluidization velocity, and free‐settling velocity with an accuracy of ±25.7%. The correlation is valid for heterogeneous systems comprising solids of various sizes and/or densities.
Shape and extent of the void formed by a horizontal jet in a fluidized bed
Authors: Chen Libin , Weinstein Herbert 
Published: June 2004

AbstractThe introduction of reactant gas into a fluidized‐bed chemical reactor as a jet is a common design practice. However, the shape and extent of the void formed by a jet into a fluidized bed and the manner in which the void breaks up into bubbles have still not been described well.An experimental study of a horizontal jet into a 15 cm by 38 cm cross‐section fluidized bed was carried out using an X‐ray system. Instantaneous solid fraction averaged along 15‐cm chords across the bed were measured. The mean value and the fluctuating component of solid fraction were determined for two initial jet diameters, 0.64 and 1.27 cm, and three initial jet velocities, 23, 46 and 69 m/s. Maps of the mean solid fraction and of statistical properties of the fluctuating component show that there are three discernible regions in the jet‐influenced area of the bed. These are a coherent void, bubble trains, and a surrounding compaction zone.
Multivariable nonlinear control of a continuous polymerization reactor: An experimental study
Authors: Soroush Masoud , Kravaris Costas 
Published: June 2004

AbstractThis experimental work concerns the multivariable nonlinear control of a continuous stirred‐tank polymerization reactor. The globally linearizing control (GLC) method is implemented to control conversion and temperature in the reactor in which the solution polymerization of methyl methacrylate takes place. Control of conversion and temperature is achieved by manipulating the flow rate of an inlet initiator stream and two coordinated heat input variables. Conversion is inferred from on‐line measurements of density and temperature. A reduced‐order state observer is utilized to estimate the concentrations of monomer, initiator and solvent in the reactor. The concentration estimates are used in the control law. This study demonstrates the considerable computational efficiency of the nonlinear controller, which is implemented on a microcomputer. The experimental results show the excellent performance of the controller in the presence of active state and input constraints. A systematic approach is also given for the synthesis of output feedback controllers within the GLC framework for processes with secondary outputs.
Gravity‐Driven reactive coating flow down an inclined plane
Authors: Qi Quan , Johnson Robert E. 
Published: June 2004

AbstractThe coating flow of a reactive fluid on an inclined plane is studied. The fluid viscosity steadily increases due to a sustained cross‐linking reaction. Using well‐known long wave approximations and a simple kinetic relation, we find that the linear stability of a uniform coating is affected not only by the inclination angle but also by the reaction order. In the weakly nonlinear limit, a generalized Kuramoto‐Sivashinsky (K‐S) equation is derived. Two interesting cases are identified in the limit of creeping flow. One is when surface tension is moderate and a generalized Burger's equation results, and the other is when the surface tension is large and the traditional K‐S equation is recovered when the inclination angle is greater than 90°. The solution in this case represents a shock‐like traveling wave down the incline and it appears to be unique for reacting coating flows.
Excitable waves and spatiotemporal patterns in a fixed‐bed reactor
Authors: Barto Martin , Sheintuch Moshe 
Published: June 2004

AbstractSpatiotemporal patterns existing in a one‐dimensional fixed‐bed reactor with oscillatory or excitable kinetics are analyzed to develop the methodology of motion identification and classification. The reactor model accounts for a local (solid‐phase) oscillator and a global (gas‐phase) convective interaction. The local oscillator incorporates a fast and diffusing surface temperature and a localized activity as its dynamic variables. Such kinetics admit a traveling pulse solution or homogeneous oscillations in a uniform medium. In a fixed‐bed reactor, the local conditions in the bed (the phase plane character) vary along the system. The response of an excitable bed to local perturbations depends on its location (at inlet or outlet) and the nature of the initial steady state ( ignite or extinguished). The main spatiotemporal‐sustained patterns in the bed are: almost homogeneous oscillations that appear as parallel bands in the time‐space contour map; oscillatory fronts that emerge from the reactor exit, and aperiodic motion that appears as split‐bands. Pattern selection is determined by the phase planes spanned by the reactor and the ratio of the two slowest time scales: front residence time and period of oscillations.
Protein polarization in isotropic membrane hollow‐fiber bioreactors
Authors: Taylor D. G. , Piret J. M. , Bowen B. D. 
Published: June 2004

AbstractA mathematical model has been developed to predict the coupled hydrodynamics and high‐molecular‐weight protein transport in mammalian‐cell hollow‐fiber bioreactors (HFBRs). The analysis applies to reactors with isotropic ultrafiltration membranes under startup conditions when the extracapillary space (ECS) is essentially unobstructed by cells. The model confirms the experimental finding that secondary ECS flows, engendered by the primary flow in the fiber lumens, can cause significant downstream polarization of ECS proteins at typical mammalian‐cell HFBR operating conditions. It also reveals that the osmotic activity of the proteins, by curtailing transmembrane fluid fluxes, can influence strongly the outcome of the polarization process. In fact, at order‐of‐magnitude higher protein concentrations and/or lower recycle flow rates, the secondary flow velocities can be reduced by as much as six orders‐of‐magnitude throughout the ECS, thereby virtually eliminating the polarization problem. This result has important implications for improved reactor startup procedures.
Random motility of swimming bacteria: Single cells compared to cell populations
Authors: Phillips Bret R. , Quinn John A. , Goldfine Howard 
Published: June 2004

AbstractThe motility of a population of swimming bacteria can be characterized by a random motility coefficient, μ, the operational equivalent of a diffusion coefficient at the macroscopic level and in the absence of interacting chemical gradients. At the microscopic level, random motility is related to the single‐cell parameters: speed, tumbling probability, and index of directional persistence (related to the angle a cell's path assumes following a change in direction). Various mathematical models have been proposed for relating the macroscopic random motility coefficient to these microscopic single‐cell parameters. In separate experiments, we have measured motility at both the cell‐population and single‐cell levels for Escherichia coli. The agreement of these results shows that the macroscopic transport behavior of a population of motile bacteria can be predicted from straightforward microscopic observations on single cells.
Protein precipitation: Effects of mixing on protein solubility
Authors: Iyer Harish V. , Przybycien Todd M. 
Published: June 2004

AbstractMixing effects in protein precipitation processes are very poorly understood. They impact apparent protein solubility, protein structure in precipitates, particle size, morphology and recoverable activity. In this work, a model is proposed to describe the impact of mixing on protein solubility in precipitation processes. A series of semibatch‐mode precipitation experiments were performed using bovine liver catalase and ammonium sulfate to test model predictions. The process variables studied include initial protein supersaturation, agitation rate, and rate of addition of salt solution to the initial protein solution. The mixing model parameters were estimated independently with the aid of a series‐parallel dye reaction. The results showed good agreement between model and experiment. The initial protein supersaturation was the most important variable at the 1‐L scale. The influence of mixing on recoverable activity was also examined. Scale‐up guidelines are suggested based on model simulations and experimental results.
Stokes flow through a thin screen with patterned holes
Authors: Wang C. Y. 
Published: June 2004

AbstractThree‐dimensional Stokes flow through a thin screen which has a regular array of holes with two orthogonal axes of symmetry has been studied. The governing equation is simplified by the Roscoe potential and solved by an efficient eigenfunction expansion and collocation method. The resistance is found for circular and square holes in square arrays, and circular and hexagonal holes in triangular arrays.
Kinetics of H2S absorption into aqueous ferric solutions of edta and hedta
Authors: Wubs Harm J. , Beenackers Antonie A. C. M. 
Published: June 2004

AbstractKinetics of the reaction of hydrogen sulfide with ferric chelates of ethylenediaminetetraacetic acid (EDTA) at 22°C and with ferric chelates of hydroxyethyle‐thylenediaminetriacetic acid (HEDTA) from 21°C to 60°C were studied in a stirred cell reactor under industrial conditions. Concentration of the ferric chelates ranged from 40 to 150 mol/m3 and the pH was varied from 4 to 10. Only the hydroxy forms of the ferric chelates appear to react with hydrogen sulfide. Under the conditions applied, the reaction appeared to be first‐order in hydrogen sulfide and first‐order in hydroxy ferric chelate. At 22°C the rate constant for the EDTA complex is 14–21 m3/mol·s. Uncertainty in this constant is due to the characteristics of the EDTA complex at pH values above 7. For the HEDTA complex, the activation energy of the reaction of hydrogen sulfide with the monohydroxy ferric chelate is (26.4 ± 0.6) kJ/mol with k = 1.8 m3/mol·s at 25°C. The rate constant for the reaction with the dihydroxy ferric chelate is (300 ± 150) m3/mol·s in the temperature range investigated.
Synthesis of discrete‐time nonlinear feedforward/feedback controllers
Authors: Soroush Masoud , Kravaris Costas 
Published: June 2004

AbstractThis work concerns the synthesis of discrete‐time feedforward/feedback control systems for general nonlinear processes with stable zero dynamics. Depending on the process under consideration, the derived feedforward/feedback controllers can completely eliminate the effect of measurable disturbances and produce a prespecified linear response with respect to a reference input, or provide integral‐square error optimal response to step changes in the disturbances and a prespecified linear response with respect to a reference input. In either case, the developed feedforward/feedback controllers allow for the asymptotic rejection of unmeasurable disturbances. These controllers are derived within the globally linearizing control frame‐work, first under full state information and then in the absence of state measurements. The internal stability of the closed‐loop system is addressed. The derived controllers are interpreted from a model‐predictive point of view, and their connections with the feedforward internal model control and the model algorithmic control are established. The theoretical results are illustrated through a continuous stirred‐tank reactor example.
Thermal dehydration of magnesium hydroxide and sintering of nascent magnesium oxide
Authors: Hartman M. , Trnka O. , Veselý V. 
Published: June 2004

AbstractIncreasing and constant temperature gravimetric methods were used to measure the thermal decomposition rates of Mg(OH)2 particles. An Arrhenius‐type kinetic equation was proposed and tested. Temperature, exposure time on surface area of the calcined particles and other effects of variables were explored. A fractional‐order sintering rate expression was developed on the basis of collected experimental data. An integrated model is also presented that considers the surface area generation by calcination and the simultaneous surface reduction caused by sintering of the nascent oxide. Obtained results enable specifying the operating conditions needed for the production of the high surface, reactive magnesium oxide.
Foam‐enhanced devolatilization of polystyrene melt in a vented extruder
Authors: Tukachinsky Alexander , Talmon Yeshayahu , Tadmor Zehev 
Published: June 2004

AbstractVented extruder devolatilization (DV) of PS melt containing 6,000 ppm styrene was studied by scanning electron microscopy (SEM) and video photography. Vacuum DV of a polymer is accompanied by foaming, which starts instantaneously upon supersaturation of the stretched melt and is enhanced at higher speeds of the vented extruder screw. As the volatiles are removed from the melt, foaming gradually ceases, starting with the pushing flight of the screw. The experimental installation design allowed us to quench the polymer melt in the DV zone at various stages of the process. Samples taken from four areas of the channel width were investigated by SEM. Bubble nucleation in the melt appears to take place mainly in the border area adjoining the gas phase. In the shear field caused by screw rotation, large bubbles become noticeably elongated. Their surface, as well as the free surface of the melt, is covered with blisters, 1–100 μm in size. Microblisters are often concentrated in areas subjected to stretching. Calculations of cooling due to volatile evaporation and of heating due to viscous dissipation near a growing bubble shows that the process of foam‐enhanced DV of a PS/styrene system can be regarded isothermal if the initial volatile concentration does not exceed approximately 1%.
Analysis of bacterial migration: I. Numerical solution of balance equation
Authors: Frymier Paul D. , Ford Roseanne M. , Cummings Peter T. 
Published: June 2004

AbstractChemotaxis describes the ability of motile bacteria to bias their motion in the direction of increasing gradients of chemicals, usually energy sources, known as attractants. In experimental studies of the migration of chemotactic bacteria, 1‐D phenomenological cell balance equations (Rivero et al., 1989) have been used to quantitatively analyze experimental observations (Ford et al., 1991; Ford and Lauffenburger, 1991). While attractive for their simplicity and the ease of solution, they are limited in the strict mathematical sense to the situation in which individual bacteria are confined to motion in one dimension and respond to attractant gradients in one dimension only. Recently, Ford and Cummings (1992) reduced the general 3‐D cell balance equation of Alt (1980) to obtain an equation describing the migration of a bacterial population in response to a 1‐D attractant gradient. Solutions of this equation for single gradients of attractants are compared to those of 1‐D balance equations, results from cellular dynamics simulations (Frymier et al., 1993), and experimental data from our laboratory for E. coli responding to α‐methylaspartate. We also investigate two aspects of the experimentally derived expression for the tumbling probability: the effect of different models for the down‐gradient swimming behavior of the bacteria and the validity of ignoring the temporal derivative of the attractant concentration.
Heat‐transfer characteristics in viscous gas‐liquid and gas‐liquid‐solid systems
Authors: Kumar Samir , Fan L.‐S. 
Published: June 2004

AbstractLocal heat‐transfer measurements are performed using a special heat‐transfer probe in gas‐liquid and gas‐liquid‐solid systems with viscous Newtonian liquids as the continuous phase. Effects of viscosity on bubble‐liquid and bubble‐liquid‐solid interactions affecting local heat transfer are studied through heat‐transfer experiments with simultaneous flow visualization in a simplified system involving single bubbles or a chain of gas bubbles moving in viscous liquids and liquid‐solid systems. Effects of viscosity on bubble wake and local heat transfer are examined with reference to heat transfer in freely‐bubbling beds (bubble columns and three‐phase fluidized beds). The kinematic viscosity of the fluid greatly influences the nature of flow in the wake which affects local heat transfer in the bed. The local heat transfer decreases with the viscosity due to the rapid decay in the circulation strength of the bubble wake caused by increased viscous dissipation of vorticity. Local heat transfer due to cyclic/periodic injection of bubbles is significantly enhanced due to increased bubble‐wake interactions which rapidly accelerate bubbles and increase average bubble rise velocity. Heat transfer in simplified liquid and liquid‐solid systems with single‐ and chain‐bubble injections characterizes the local heat‐transfer performance of freely‐bubbling beds (bubble columns and three‐phase fluidized beds). A mechanistic model developed accounts for the heat‐transfer behavior in bubble columns and three‐phase fluidized beds with viscous liquids.
Modeling of supercritical extraction of organics from solid matrices
Authors: Madras Giridhar , Thibaud Catherine , Erkey Can , Akgerman Aydin 
Published: June 2004

AbstractThe desorption profiles of various organics from soil and activated carbon using dense liquid and supercritical carbon dioxide were modeled. The model accounts for effective diffusion of the organics in the solid pores, axial dispersion in the fluid phase, and external mass transfer to the fluid phase from the particle surface. This model, involving partial differential equations, is solved using the orthogonal collocation on finite elements. The model is able to predict the experimental data quite well without any adjustable parameters. The importance of each parameter depended on the system, although adsorption equilibrium and the effective pore diffusion of the organic were the most significant parameters in all the systems investigated.
Optimization of distillation units using collocation models
Authors: Seferlis P. , Hrymak A. N. 
Published: June 2004

AbstractReduced‐order models are developed based on orthogonal collocation on finite elements for the steady‐state optimization of multicomponent distillation units. The formulation divides the column sections into subdomains (finite elements) to track irregularities in the column profiles accurately and requies that plates with discontinuities in the flows introduced by feedstreams or sidestreams should be treated as discrete equilibrium stages. Application of the model formulation to a number of examples show that reduced‐order models converge to the same optimal solution as the full‐order, tray‐by‐tray model. Optimization results show that computational time can be reduced significantly using the more compact model formulation, and it is possible to converge to the optimal solution from a larger region for the initial set of variable values.
Food sterilization by electrical heating: Sensitivity to process parameters
Authors: Zhang L. , Fryer P. J. 
Published: June 2004

AbstractThe design of efficient continuous sterilization equipment for flowing solid‐liquid food mixtures requires that temperature and velocity distributions within the fluid are known. In electrical (ohmic) heating, electric current is passed through a two‐sterilize it. This allows rapid sterilization of solid‐liquid mixtures which minimizes quality loss. A computational process model simulates the effect of realistic physical property changes. The effect of variations in physical properties can have a significant effect on the temperature of the product and thus on its sterility. Realistic designs will have to cope with temperature differences between phases. Experimental data for velocities in a food flow have been incorporated into an enthalpy balance model for heat transfer in solid‐liquid mixtures. The effect of inlet temperature on the length of hold tube required to give the necessary process sterility calculated shows the variation in output conditions that might results in real systems.
Optimal fed‐batch control of induced foreign protein production by recombinant bacteria
Authors: Lee Jongdae , Ramirez W. Fred 
Published: June 2004

AbstractOptimal control strategies for maximizing the production of induced foreign protein by recombinant bacteria were sought by the optimal control theory. Nutrient and inducer feeding rates were selected as key control variables. Since the problem is linear in the control variables, the optimal control is bang‐bang or singular. Singular solutions are shown to exist. The optimal control theory showed that the specific growth rate with respect to nutrient concentration must be kept in its maximum phase and that there exist both a cell growth period and a protein production periods. The optimal control theory calculates exactly the growth and production periods. The glucose concentration is controlled along a singular are to give a maximum specific growth rate. The inducer level is controlled along a separate singular arc.
Equilibrium and kinetics of adsorption of Freon‐12 at infinite dilution
Authors: Golden T. C. , Sircar S. 
Published: June 2004

AbstractEquilibrium and kinetic data for adsorption of trace CF2Cl2 (Freon‐12) from various carrier gases on BPL activated carbon are reported. Coadsorption of the bulk carrier gas can severely reduce the equilibrium adsorption capacity and adsorptive mass‐transfer coefficient of strongly adsorbed CF2Cl2. The difference in size between CF2Cl2 and the bulk carrier gas molecules plays a major role in establishing the binary or multicomponent equilibrium adsorption properties. The multisite (single and multicomponent) Langmuir model, which accounts for differences in adsorbate sizes, provides a reasonable framework for describing the size effects. The adsorptive mass transfer of CF2Cl2 under the experimental conditions investigated is dominated by surface diffusion into the pores of the activated carbon. The surface diffusivity is a strong function of the extent of coverage and strength of adsorption of the bulk components.