bluuebunny/crossref_metadata_2025_split huggingface dataset:
Continuous production of polystyrene in a tubular reactor: Part II
Authors: Wallis J. P. A. , Ritter R. A. , Andre H. 
Published: June 2004

AbstractAn analysis of the bulk polymerization of styrene by azobisisobutyronitrile in a tubular reactor was made. Rigorous models were developed and verified. A diffusion model gave predictions of molecular weights and conversions that were 2% higher on the average than the experimental values. Another model, a plug flow contraction of the diffusion model, predicted molecular weights and conversions that were 6% higher on the average than the experimental values.The diffusion model showed that optimal conversions could be obtained by proper reactor operation. Tentative studies for optimal conversion with minimal molecular weight dispersion indicated the reactor should be operated at a wall temperature 5° to 10°C below that required for optimal conversion.
Interphase mass and heat transfer in pulsatile flow
Authors: McMichael W. J. , Hellums J. D. 
Published: June 2004

AbstractA study on the effects of flow pulsations on interphase mass or heat transfer has been made. The situation corresponds to fully developed flow in a long conduit with a periodic pressure gradient at amplitudes which cause flow pulsations without flow reversal. It is shown that the basic three‐parameter formulation can be reduced to a one‐parameter problem in the boundary layer formulation. Solutions are developed over wide ranges of the parameters in both the basic and the boundary layer formulations.The boundary approach gives accurate results over wide ranges of the parameters. Pulsations cause increases in the time‐averaged interphase flux at intermediate values of a composite frequency‐space variable. However, at small values of this variable the pulsations cause a decrease in the flux such that the overall space‐averaged flux is always decreased.
Kinetics of solid phase reactions
Authors: Ruckenstein E. , Vavanellos T. 
Published: June 2004

AbstractThe kinetics of isothermal transformations or decompositions of solids proceeding through nucleation and subsequent growth is treated in the spirit of Avrami, eliminating, however, some of the internal contradictions of his treatment. Universal solutions of the dimensionless integral equation are computed. The theory is extended to nonisothermal systems and the resulting integral equations are solved numerically for the adiabatic case. It is shown that two kinds of catastrophic behavior can occur: one is characterized by slopes approaching infinity in the conversion vs. time curve following a long period of quiescent behavior; the other is characterized by a very short time for total conversion and by milder slopes in the conversion vs. time curve throughout the course of reaction. In the first kind the nucleation is mainly responsible for the catastrophic behavior, while in the second kind the rate of growth is responsible.
Oxygen reduction at an anodically activated platinum rotating disk electrode
Authors: Forbes Melvin , Lynn Scott 
Published: June 2004

AbstractThe reduction of oxygen in neutral saline solution and in seawater was studied using the rotating disk electrode (RDE). The objective was to test the applicability of the RDE as a primary reference standard for the measurement of oxygen concentrations below 0.1 ppm in seawater. Limited success was achieved with an activated platinum electrode. A gold electrode was less effective. If one postulates that the 2‐electron reduction of oxygen at an activated RDE is rapid, it appears that little or no 4‐electron reduction occurs and that the subsequent 2‐electron reduction or catalytic decomposition of hydrogen peroxide is relatively slow. The anodic activation procedure developed appears to impart a transient catalytic activity to the electrode surface for the peroxide reaction(s).
Flow maldistribution in packed beds: A comparison of measurements with predictions
Authors: Szekely J. , Poveromo J. J. 
Published: June 2004

AbstractExperimental measurements are reported on flow maldistribution in packed beds containing side streams and deliberately created spatially nonuniform resistance to flow. The actual experimental technique involved the determination of the velocity field of the gas stream exiting the column through the use of a hot wire anemometer. The experimental measurements were compared with predictions based on the numerical solution of the differential vectorial form of the Ergun equation and reasonable agreement was obtained. Both the measurements and the analysis confirmed the existence of preferential flow in the vicinity of the walls even for uniformly packed beds.
Catalytic activity and selectivity on heterogeneous surfaces with mass transfer
Authors: Loffler Daniel G. , Schmidt Lanny D. 
Published: June 2004

AbstractEffective reaction rates and selectivities on surfaces having active and inactive regions are calculated for systems in which diffusion of reactants and products through a boundary layer is significant. With a single reaction it is shown that rates are larger than those calculated assuming area weighted averages. The selectivity of production of an intermediate in a series of reactions on a heterogeneous surface is higher than on a homogeneous surface, and with parallel reactions selectivities may be lower or higher depending on the kinetics of the competing reaction.Numerical examples from NH3 oxidation on a Pt gauze and CO oxidation in the automotive converter indicate that these effects may be important in determining selectivities and conversions in some industrial reactors.
Real‐time time‐optimal control of a stirred‐tank reactor using Kalman Filtering for state estimation
Authors: Lynch Edmond B. , Ramirez W. Fred 
Published: June 2004

AbstractThis paper presents the development and real‐time implementation of a time‐optimal control algorithm for a continuous stirred‐tank reactor. A multivariable time‐optimal control law is derived and an Extended Kalman Filter formuated for on‐line estimation and filtering. The work demonstrates the powerful capability of real‐time computation and decision‐making in optimal control and optimal estimation of process states.
Pseudoplastic falling films with concurrent gas streams
Authors: Skelland A. H. P. , Popadic V. O. 
Published: June 2004

AbstractAn experimental and theoretical study on gas and pseudoplastic liquid films in vertical downward flow is reported. Good agreement was obtained between predicted and measured values of the film thickness as a function of liquid shear properties and interfacial shear except in the case of the most dilute solution. Measured pressure drops in the gas in two‐phase flow depend strongly on liquid shear properties and are up to five times higher than when gas flows alone.Aqueous Carbopol solutions were used as pseudoplastic liquids.
Modeling of heterogeneous systems in a plasma jet reactor
Authors: Bhattacharyya D. , Gauvin W. H. 
Published: June 2004

AbstractA theoretical model of the behavior of a plasma jet reactor (5 000 K to 12 000 K) considering a three‐dimensional, nonisothermal, turbulent, compressible, swirling, confined flow is developed. Single particle trajectories are predicted by solving the equations of motion for the axial, radial, and tangential directions. Calculations are carried out for both argon and nitrogen gases. The model is then extended to a multiparticle system on the basis of a feed particle size distribution, concentration distribution, and loading ratio.The calculations are applied to a study of the decomposition of molybdenum disulfide particles into molybdenum metal and elemental sulfur. Results are presented in terms of the effects on the particle history (trajectory, temperature, and conversion) of the following variables: particle size, nozzle exit temperature and velocity, injection velocity, location and angle of injection, swirl velocity, and ambient temperature conditions.
Oxygen transfer in fermentation
Authors: Tsao George T. , Lee Douglas D. 
Published: June 2004

AbstractThe rate of biological processes in aerobic fermentation and waste water treatment is often limited by the rate of dissolution of oxygen from air bubbles into the liquid. A clear understanding of interfacial resistance to oxygen transfer is thus of importance. An oxygen sensing microprobe was used to detect a stagnant film and a penetrable zone near an air‐water interface contaminated with surfactants. The technique, when used in clean water, can also measure the frequency of surface renewal. A linear relationship was found between the square root of the renewal rate S0.5 and the interfacial mass transfer coefficient kL, which is predicted by the Danckwerts theory.
Prediction of dynamic temperature distributions in the human body
Authors: Huckaba Charles E. , Tam Hak‐Shing , Darling Robert C. , Downey John A. 
Published: June 2004

AbstractA detailed procedure is presented for the calculation of unsteady state temperature distributions throughout the human body. The adequacy of the proposed computation procedure is demonstrated by comparison of calculated and experimental results for studies conducted on subjects exposed to decreasing ambient temperatures. Core temperatures were predicted within ±0.2°C, and average deviations for individual skin temperatures generally were within ±0.5°C.
Membrane ultrafiltration of a nonionic surfactant and inorganic salts from complex aqueous suspensions: Design for water reuse
Authors: Bhattacharyya Dibakar , Garrison K. A. , Jumawan Jr. A. B. , Grieves R. B. 
Published: June 2004

AbstractComplex aqueous suspensions containing a nonionic surfactant, phosphates, silicate, hypochlorite, oil, and kaolinite particulates are subjected to continuous flow membrane ultrafiltration with noncellulosic membranes. The ultrafiltrate water flux and the rejections by the Millipore PSAL membrane of total organic carbon, surfactant, and total phosphate are related by stepwise, multiple linear regression analysis (logarithmic model) to transmembrane pressure difference, thin channel velocity, membrane resistance, and feed solution concentration. The variables are adjusted to eliminate gel polarization and to minimize concentration polarization.The data are extended, by the development and use of a computer simulation scale‐up procedure, to a 1 000 cm3/s (23 000 gal/day) laundry waste treatment and water recovery unit. The procedure considers banks of modules in series, banks in parallel, and a parallel‐series‐tapered arrangement. Membrane area requirements per unit ultrafiltrate water flux and solute rejections are predicted for water recoveries up to 95% of the inlet flow rate.
A thermodynamic method of predicting the transport of steroids in polymer matrices
Authors: Michaels A. S. , Wong P. S. L. , Prather R. , Gale R. M. 
Published: June 2004

AbstractApplication of Hildebrand's theory of the solubility of microsolutes in ordinary solvents, and of the Flory‐Huggins theory to the solubility of steroids in polymers, has permitted the derivation of a predictive correlation between polymer permeability and steroid crystalline melting temperature, other correlating parameters being the entropy of fusion of the steroid and the (computed) solubility parameters of steroid and polymer. The correlation permits prediction of the permeability of any steroid in any polymer with reasonable accuracy.
Interaction of activated carbon with dissolved oxygen
Authors: Prober Richard , Pyeha John J. , Kidon William E. 
Published: June 2004

AbstractThe sorption of dissolved oxygen on activated carbon was characterized with manometric and packed column apparatus. All carbons tested, granular and powdered, virgin and reactivated, sorbed 150 to 600 μmole of oxygen/g after run times up to 1 700 hr., but sitll not at equilibrium. The rate data generally conform to a model of sorption limited by intraparticle diffusion. Carboxylic acid groups increase by about 200 μeq/g as a result of dissolved oxygen sorption, which can account for at least 10 to 50% of the oxygen sorbed. Also, about 5% of the sorbed oxygen can be eluted into deoxygenated water.
Advanced control practice in the chemical process industry: A view from industry
Authors: Lee Wooyoung , Weekman Vern W. 
Published: June 2004

AbstractThis paper presents a commentary on the status of application of modern control theories to industrial chemical processes. The difficulties encountered in the implementation of advanced control to chemical reactors are critically examined in order to determine the reasons for its limited success to date. Chemical processes, very often poorly understood because of the physicochemical complexities, are nonlinear, highly interacting, spacially dependent, and continuously disturbed by many uncharacterized noises. It is time‐consuming and expensive to develop advanced control methods for these systems because few of the available theories can be applied directly. Thus, we often find it difficult to economically justify advanced control projects.
The selection of design variables in systems of algebraic equations
Authors: Book Neil L. , Ramirez W. Fred 
Published: June 2004

AbstractPresent algorithms for the selection of design variables produce a single combination of design variables which results in a solution sequence of minimum difficulty. A new theory entitled solution mapping results in information about all optimal combinations of design variables. This theory gives detailed information about the structure of all underspecified systems of algebraic equations which do not contain persistent iteration.
Nucleation effects in the dropwise condensation of steam on electroplated gold surfaces
Authors: Detz Clifford M. , Vermesh Robert J. 
Published: June 2004

AbstractDropwise condensation heat transfer coefficients were measured for stream on gold surfaces electroplated on copper and nickel substrates. The effect on the heat transfer of the activation of very small nucleation sites present on the gold plated copper surface was observed. In addition, the heat transfer coefficient of the gold plated nickel surface was lower than that of the gold plated copper surface.
Oxidation of acetic acid solutions in a trickle‐bed reactor
Authors: Levec Janez , Smith J. M. 
Published: June 2004

AbstractRates of oxidation of dilute, aqueous solutions of acetic acid were measured at 252° to 286°C and 67 atm in liquid full and trickle‐bed reactors packed with ferric oxide catalyst particles. Predicted global rates and conversions indicated that localized vaporization and liquid channeling could affect trickle‐bed performance.
A theory of isothermal melt spinning and draw resonance
Authors: Fisher Robert J. , Denn Morton M. 
Published: June 2004

AbstractThe mechanics of isothermal melt spinning are studied for a viscoelastic liquid with a power law viscosity and a constant shear modulus. Steady state velocities and stresses are in agreement with experiment. The onset of the draw resonance instability, the magnitude of diameter fluctuations in the unstable region, and a second stable region at high draw ratio are predicted accurately.
A theoretical study of pressure drop for non‐Newtonian creeping flow past an assemblage of spheres
Authors: Mohan V. , Raghuraman J. 
Published: June 2004

AbstractA combination of Happel's free surface model and variational principles is used to obtain bounds on the drag offered by the creeping flow of a power law fluid past an assemblage of solid spheres. The theoretical predictions of the product of the Fanning friction factor ƒ and Reynolds number Rep are in close agreement with available experimental data on non‐Newtonian flow through porous media. The product (ƒ Rep) reduces for the Newtonian case to that of Happel and Brenner.
Separation of nonlinearly sorbing solutes by parametric pumping
Authors: Camero Arthur A. , Sweed Norman H. 
Published: June 2004

AbstractA rigorous mathematical analysis shows that parametric pumps can separate, concentrate, and recover in pure form all components of a multi‐solute mixture. The obtained separation cannot be predicted by existing linear models. Criteria for determining steady periodic separations of binary mixtures are discussed in detail for batch and continuous systems.
Some performance characteristics of liquid phase spray columns
Authors: Laddha G. S. , Krishnan T. R. , Viswanathan S. , Vedaiyan S. , Degaleesan T. E. , Hoelscher H. E. 
Published: June 2004

AbstractNew data on residence time distribution (RTD), axial mixing, and Peclet numbers for both phases in liquid spray columns are presented.Drop size distribution is of major interest. Continuous phase velocities affect RTD variance at high flow without appreciable effect on dispersed phase RTD variance. New correlating equations are presented.
Computer model for tubular high‐pressure polyethylene reactors
Authors: Chen C. H. , Vermeychuk J. G. , Howell J. A. , Ehrlich Paul 
Published: June 2004

AbstractA computer model was developed for tubular high‐pressure polyethylene reactors. Plug flow and absence of axial mixing were assumed. Emphasis was placed on realistic modeling of the reaction kinetics and the variation of physical properties along the reaction coordinate. A good simulation of axial temperature profiles, conversion, molecular weights, molecular weight distribution, and transport properties along the reaction coordinate is believed to have been achieved. The model can be extended readily to cases where radial diffusion is significant.
Studies in chemical process design and synthesis II. Optimal synthesis of dynamic process systems with uncertainty
Authors: Nishida N. , Liu Y. A. , Ichikawa A. 
Published: June 2004

AbstractThe concept of the optimal synthesis of dynamic process systems with uncertain parameters is introduced. A structure parameter approach is used to theoretically derive the necessary condition for the optimal performance system structure, and an effective algorithm for implementing the synthesis method is presented. The results are applied to the optimal synthesis of a reactor‐separator system for the dynamic start‐up of two reaction systems.
Multiple minima in a fluidized reactor—heater system
Authors: Chen Herbert T. , Fan L. T. 
Published: June 2004

AbstractA minimum cost design problem for a single‐reaction fluidized‐bed reactor system is analyzed in this paper. The problem's mathematical interest stems from Wilde's statements (1974) that there can be only two types of design to this nonlinear, nonconvex, multimodal problem. It is shown by a direct search procedure that, in fact, there are at least four types of optimal design. Furthermore, the type 3, rather than the type 1 design, is the global solution to the numerical example considered in Wilde's work, if the required auxiliary cooler cost is excluded.
Improving efficiency of electrostatic precipitation by physicochemical modification of the electrical resistivity of flyash
Authors: Ditl Pavel , Coughlin Robert W. 
Published: June 2004

AbstractTheory and experiment show that lowered resistivity of fly ash, frequently caused by adding conditioning agents to flue gas to improve efficiency of electrostatic precipitation, is caused by capillary condensation of liquid at the contact points of ash particles, thereby providing additional pathways for flow of electrical current.
Correlation of liquid heat capacities with a four‐parameter corresponding states method
Authors: Lyman Thomas J. , Danner Ronald P. 
Published: June 2004

AbstractA four‐parameter corresponding states method with the critical temperature, the critical pressure, the radius of gyration, and a fourth parameter developed from the Frost‐Kalkwarf vapor pressure equation has been applied to the correlation of liquid heat capacities. An equation has been developed to predict the temperature dependence of the saturated liquid heat capacities of both normal and polar fluids over the liquid range from a reduced temperature of 0.35 to 0.96. The accuracy of the predictions obtained is superior to that of the presently available generalized correlation for polar liquids. The new correlation may be easily adopted for computer use.
Electropolarization chromatography
Authors: Reis Joaquim F. G. , Lightfoot E. N. 
Published: June 2004

AbstractThe utility of electropolarization chromatography for fractionation of native protein mixtures is examined both mathematically and experimentally.Mathematical prediction based on a simplified but basically realistic model of this process suggests it to be very promising for both analytical and preparative purposes.This expectation is borne out by tests with well‐defined proteins in single ultrafiltration fibers. The major observed departure from model prediction is an unexpectedly sharp increase in retardation at a critical voltage specific to the protein and composition of the carrier electrolyte. This permits sharper separations than previously expected and is thus favorable.
Design of an lonic lattice for optimum cation diffusion
Authors: Ruckenstein Eli , Dadyburjor Dady B. 
Published: June 2004

AbstractVarying the species and/or distance parameters of a lattice changes the activation energy of a particular species diffusing through it, thus allowing transport properties to be optimized. As an example, the activation energy of silver ions in α‐silver iodidelike structures was calculated as lattice properties were changed.
An analysis of slow reactions in a porous particle
Authors: Wen C. Y. , Wu Nancy Tsai 
Published: June 2004

AbstractA one‐parameter volume reaction model is developed by a simplified analytical approach to describe reaction of a gas and a consumble solid in a porous particle. In this model, a modified Thiele modulus M is introduced to take into account the effect of solid reactant depletion during the reaction.Experimental results of an isothermal carbon‐carbon dioxide reaction in the temperature range from 1 130° to 1 365°K under atmospheric pressure were analyzed by the working diagrams derived from this model. A satisfactory agreement between the experimental results and those predicted by the model indicated the applicability of this model.
The effect of flow maldistribution on conversion in a catalytic packed‐bed reactor. Part II. Experimental studies
Authors: Choudhary Manoj , Weller Sol W. , Szekely Julian 
Published: June 2004

AbstractThe modeling equations formulated for a catalytic packed‐bed reactor with distributed resistance to flow have been applied to the alumina catalyzed isomerization of 1‐butene to cis‐ and trans‐2‐butene. Flow maldistribution was deliberately created in a 5.25 cm I.D. reactor by packing different radial sections with alumina particles of different size. Effluent gas composition, monitored by gas chromatography, was found to vary with radial position in a manner consistent with the modeling equations and with the reaction rate constant previously established in a microreactor.
Melting, freezing, and channeling phenomena in ice counterwashers
Authors: Grossman Gershon 
Published: June 2004

AbstractThermal phenomena are associated with the operation of ice counter‐washers, a major component for the separation of ice and brine in freeze crystallization processes. Melting, freezing, and channeling in the upper leg of the counterwasher occur because of the temperature difference between the wash water and the ice and have important effects on the operation of the device. In the present study, these phenomena are modeled and analyzed and their scaling laws derived. Ice and wash water temperature distributions as well as variations in porosity and wash water flow rate due to melting and freezing in the ice plug are computed and plotted. The effect of channeling on counterwasher operation is studied and formulated in terms of the channel dimensions and ice plug properties. Growth rates of channels due to melting by the wash water are calculated. Results indicate that warm wash water and slow motion of the ice plug cause rapid channel growth and may be deleterious to counterwasher operation. Best conditions for recovery from channeling are obtained with wash water temperature close to freezing and high plug velocity.