bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modeling the spontaneous ignition of coal stockpiles
Authors: Salinger Andrew G. , Aris Rutherford , Derby Jeffrey J. 
Published: June 2004

AbstractThe spontaneous ignition of coal stockpiles is a serious economic and safety problem. This phenomenon is analyzed using the approach of modern reaction engineering, which is made challenging by the nonlinear interactions of chemical reaction, heat transfer, and buoyancy‐driven flows within and around the stockpile. A model developed represents reaction and transport within a realistically‐shaped stockpile and transport and flow in the surrounding air. A new methodology based on the Galerkin finite‐element method (Salinger, 1993b) allows for efficient solution of flows in both porous and open domains. Bifurcation analysis is used to track steady‐state model solutions of relevant parameters, such as the Damköhler number (dimensionless reaction rate), Rayleigh number (dimensionless driving force for buoyant flow), and dimensionless permeability of the stockpile. The solutions provide an understanding of the roles of various transport mechanisms on the ignition behavior and nonlinear coupling between these mechanisms. Results clearly demonstrate the need for incorporating realistic descriptions of flow and transport in the surrounding air into the model.
Products in methane combustion near surfaces
Authors: Vlachos D. G. , Schmidt L. D. , Aris R. 
Published: June 2004

AbstractEmission of carbon monoxide (CO), formaldehyde (CH2O), and unburned methane (CH4) are calculated for premixed methane/air mixtures impinging on a flat surface as functions of surface temperature, equivalence ratio, and strain rate with detailed chemistry involving 46 reversible reactions and 16 species using numerical bifurcation theory. Multiple solutions with different selectivities to stable products are found. On the extinguished branch unburned CH4, molecular hydrogen (H2), CO, and CH2O dominate, whereas on the ignited branch carbon dioxide (CO2) predominates near the surface. Cold walls can promote the selectivity to CO and CH2O near extinction, and high flow rates can increase considerably the formation of CO, CH2O, and unburned CH4. For example, an ignited stoichiometric methane/air mixture (9.5% CH4 in air) impinging on a surface of 1,000 K is calculated to produce 2% CO, 150 ppm CH2O, and 3% unburned CH4 for a strain rate of 500 s−1. Maximum efficiency of CH4 and minimum selectivity to CH2O occur near the stoichiometric ratio, whereas minimum selectivity to CO occurs for fuel lean mixtures. Comparison of combustion near surfaces with freely propagating flames is also shown.
Electrostatic droplet generation: Mechanism of polymer droplet formation
Authors: Bugarski Branko , Li Qiangliang , Goosen Mattheus F. A. , Poncelet Denis , Neufeld Ronald J. , Vunjak Gordana 
Published: June 2004

AbstractThe mechanism of alginate droplet formation and experimental parameters for producing very small polymer microbeads (less than 100 μm dia.) using an electrostatic droplet generator studied showed that the microbead size was a function of needle diameter, charge arrangement (electrode geometry and spacing) and strength of electric field. Perfectly spherical and uniform polymer beads, 170 μm dia., for example, were obtained at a potential difference of 6 kV with a 26‐gauge needle and an electrode distance of 2.5 cm. Increasing the electric field, and thus the surface charge in the vicinity of the needle, by increasing the applied potential, resulted in needle oscillation, giving a bimodal bead size distribution with a large fraction (30–40%) of microbeads with a mean diameter of 50 μm. The process of alginate droplet formation under the influence of electrostatic forces assessed with an image analysis/video system revealed distinct stages. After a voltage was applied, the liquid meniscus at the needle tip was distorted from a spherical shape into an inverted cone‐like shape. Consequently, alginate solution flowed into this cone at an increasing rate causing formation of a neck‐like filament. When this filament broke away, producing small droplets, the meniscus relaxed back to a spherical shape until flow of the polymer caused the process to start again. A large‐scale multineedle device with a processing capacity of 0.7 L/h was also designed and produced uniform 400 ± 150 μm microbeads.
Conversion of radiant light energy in photobioreactors
Authors: Cornet J. F. , Dussap C. G. , Gros J. B. 
Published: June 2004

AbstractThe conversion of radiant light energy into chemical affinity by microorganisms in photobioreactors is examined. The kinetics of entropy production in the system is theoretically established from entropy and energy balances for the material and photonic phases in the reactor. A negative chemical affinity term compensated for by a radiant energy term at a higher level of energy characterizes photosynthetic organisms. The local volumetric rate of radiant light energy absorbed, which appears in the dissipation function as an irreversible term, is calculated for monodimensional approximations providing analytical solutions and for general tridimensional equations requiring the solution of a new numerical algorithm. Solutions for the bluegreen alga Spirulina platensis cultivated in photoreactors with different geometries and light energy inputs are compared. Thermodynambic efficiency of the photosynthesis is calculated. The highest value of 15% found for low radiant energy absorption rates corresponds to a maximum quantum yield in the reactor.
Kinetics of p‐xylene liquid‐phase catalytic oxidation
Authors: Cao Giacomo , Servida Alberto , Pisu Massimo , Morbidelli Massimo 
Published: June 2004

AbstractA Semibatch gas‐liquid reactor model based on a lumped kinetic schem for the liquid‐phase oxidation of p‐xylene to p‐toluic acid catalyzed by cobalt naphtenate is developed. The model accounts for the complex nature of the involved reaction network, as well as for the interphase and intraphase mass transport processes of both reactants and products. The model reliability is tested by comparison with suitable experimental data obtained in a semibatch oxidation reactor, where the role of the composition of both the gaseous and the liquid feed has been investigated. It is shown that the model describes the reactor behavior in any of the regimes which may prevail depending upon the operating conditions and the depletion of liquid reactants in time.
Prediction and correlation of accessible area of large multiparticle aggregates
Authors: Rosner Daniel E. , Tandon Pushkar 
Published: June 2004

AbstractAggregates (composed of large numbers of primary particles) are produced in many engineering environments. One convenient characterization is the fractal dimension, the exponent describing how the number of primary particles in each aggregate scales with radial distance from its center of mass. We describe a finite‐analytic pseudo‐continuum prediction of the normalized accessible surface area of an isothermal quasi‐spherical fractal aggregate containing N (≫ 1) primary particles, on the surfaces of which a first‐order chemical process occurs. Results are displayed for specific fractal dimensions (2.5, 2.18, and 1.8) frequently observed in aggregating systems. An effective Thiele modulus is used to develop an efficient and accurate scheme for predicting/correlating the effectiveness factor for an aggregate containing N primary particles in terms of aggregate fractal dimension, reaction probability, and Knudsen number. Our methods now allow calculations of the accessible surface area of populations of aggregates, provided pdf \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--} \rlap{--} ($\end{document}N, Df, …\documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--})$\end{document} is known for the populations of interest.
Determining fluid saturations during multiphase flow experiments by NMR imaging techniques
Authors: Chen Songhua , Qin Fangfang , Watson A. Ted 
Published: June 2004

AbstractThe quantitative determination of porosity and saturation distributions in porous media using unclear magnetic resonance imaging techniques is addresed. A method based on multiple image acquisitions with extrapolation within a model of transverse relaxation was investigated for new experimental situations. The determination of saturation was validated with limestone and sandstone samples. Experimental evidence for dependencies of transverse relaxation and linewidth on saturation is discussed, as well as their impact on image resolution and quantitation. An automatic production measurement device for independent verification of average saturations during dynamic experiments is investigated.
Local velocity and porosity measurements inside Casper sandstone using MRI
Authors: Merrill Melissa Robinson 
Published: June 2004

AbstractMagnetic resonance imaging is used to make nondestructive experimental measurements of fluid flow velocity and rock porosity inside a brine‐filled Casper sand‐stone sample during brine injection. Two‐dimensional images of these values are obtained in arbitrary cross sections, with pixel sizes on the order of 1 mm2. The data are then statistically analyzed to find the variation of the average interstitial velocity as a function of porosity, as well as frequency distributions for both the velocity and porosity. The results show that as local porosity increases, the local flow velocity increases, according to the empirical relationship, V = 0.0669 ϕ + 0.0055. Thus, higher porosity regions of the core are better contacted by the displacement fluid. Results also imply bypassing of fluid around the perimeter of the core, indicating the need for a coreholder capable of sustaining higher overburden pressures on the order of 225 psi (1.55 MPa).
Model identification and control strategies for batch cooling crystallizers
Authors: Miller Stephen M. , Rawlings James B. 
Published: June 2004

AbstractThe open‐loop optimal control strategy to regulate the crystal‐size distribution of batch cooling crystallizers handles input, output, and final‐time constraints, and is applicable to crystallization with size‐dependent growth rate, growth dispersion, and fines dissolution. The objective function can be formulated to consider solid‐liquid separation in subsequent processing steps.A model‐based control algorithm requires a model that accurately predicts system behavior. Uncertainty bounds on model parameter estimates are not reported in most crystallization model identification studies. This obscures the fact that resulting models are often based on experiments that do not provide sufficient information and are therefore unreliable. A method for assessing parameter uncertainty and its use in experimental design are presented. Measurements of solute concentration in the continuous phase and the transmittance of light through a slurry sample allow reliable parameter estimation. Uncertainty in the parameter estimates is decreased by data from experiments that achieve a wide range of supersaturation. The sensitivity of the control policy to parameter uncertainty, which connects the model identification and control problems, is assessed. The model identification and control strategies were experimentally verified on a bench‐scale KNO3‐H2O system. Compared to natural cooling, increases in the weight mean size of up to 48% were achieved through implementation of optimal cooling policies.
Automated synthesis of distillation sequences using fuzzy logic and simulation
Authors: Flowers Thomas L. , Harrison B. Keith , Niccolai Marino J. 
Published: June 2004

AbstractAn automated distillation sequencing system (DSEQSYS) is presented, which consists of three components: a control program, a fuzzy heuristic synthesis program, and a process simulator. DSEQSYS, when applied to problems previously reported in the literature, overcomes some of the disadvantages of using heuristics or mathematical programming alone. DSEQSYS can address problems involving nonsharp separations, nonideal chemical behavior, and conflicting heuristics. A simple approach for converting the traditional separation heuristics into corresponding fuzzy heuristics is also demonstrated.
Synthesis of nonequilibrium reactive distillation processes by MINLP optimization
Authors: Ciric Amy R. , Gu Deyao 
Published: June 2004

AbstractA mixed integer nonlinear programming (MINLP) model is presented for synthesizing reactive distillation columns when chemical reaction equilibrium cannot be assured. The MINLP minimizes the total annual cost subject to a rigorous tray‐by‐tray model. The solution of this MINLP yields the optimal number of trays, the optimal feed rates, and the optimal feed tray locations. The liquid holdup per tray, the reflux ratio, and the temperature and composition profiles within the column are optimized as well. The MINLP is solved using generalized Benders decomposition, and the technique is illustrated with ethylene glycol synthesis.
Dynamic optimization of nonlinear processes by combining neural net model with UDMC
Authors: Chen Qi , Weigand William A. 
Published: June 2004

AbstractA new dynamic optimization technique presented combines a neural network model with a universal dynamic matrix control (UDMC) algorithm. This technique utilizes a nonlinear‐model‐predictive control technique for on‐line optimization and feedback control by using a dynamic neural net model. This approach offers two important advantages over conventional UDMC. One is that a dynamic neural net model can be developed from process data and used for optimization calculations, thus achieving optimization without a first principle model. This neural‐network‐based optimization approach also produces good performance even with processmodel mismatch. The other is that our neural‐net‐model‐based UDMC algorithm greatly reduces the computation time required for the nonlinear dynamic matrix used for the successive quadratic programming algorithm. The development of this technique also involved an analysis of the effect of network structure on dynamic optimization. A state‐space‐based neural network model which utilizes a priori process knowledge is best suited for optimization calculations. Advantages of this technique are illustrated by simulation for two chemical processes.
Kinetics and mechanism of isobutene formation from T‐butanol in hot liquid water
Authors: Xu Xiaodong , Antal Michael J. 
Published: June 2004

AbstractIsobutene is the only product of the uncatalyzed and acid‐catalyzed dehydration of tert‐butanol in compressed liquid water at 250°C. The uncatalyzed dehydration reaction is fast: equilibrium is established after about 30 s. Only one of many chemically‐motivated kinetic models is able to fit all the experimental data. This model presumes a heterolytic dehydration mechanism that involves protonated alcohol, carbocation, di‐tert‐butyl ether, and protonated ether as intermediates. The model permits tert‐butanol to dissociate as both an Arrhenius acid and a Bronsted acid while catalyzing its dehydration to isobutene. The pKa of tert‐butanol at 250°C is predicted to be about 9, whereas its value at normal temperature and pressure is 18. This 109 increase in the Ka value of tert‐butanol hints of the promising new world of reaction chemistry in near‐ and supercritical water.
Liquid‐phase capillary condensation and adsorption isothern
Authors: Miyahara Minoru , Kato Masahito , Okazaki Morio 
Published: June 2004

AbstractA “capillary condensation” in liquid phase was analyzed theoretically and experimentally, in which a solute in solvent could be separated out as a liquid into small pores by capillary effect. The “liquid‐phase capillary condensation” is defined as capillary phase separation. The separated phase is counted as “adsorbed” amount on porous materials. The relation between the concentration and a critical radius of the phase separation was derived. A new method to estimate liquid‐phase adsorption isotherms of adsorbates with limited solubility from pore‐size distribution of solids is based on this concept. The amount absorbed consists of the separated phase and adsorption on surface expressed with a single parameter. While the surface adsorption alone could not explain measured isotherms, this model showed good agreements between experimental and estimated isotherms for adsorption of four kinds of aromatic compounds from aqueous solution onto three categories of porous solids to demonstrate the significance of the capillary phase separation. The applicability of the method to solid solutes is also discussed.
Random and systematic errors in thermophysical property measurements
Authors: Eubank Philip T. , Van Peursem David , Chao Yun‐Peng , Gupta Deepak 
Published: June 2004

AbstractGeneral procedures are outlined for the simulation and propagation of random and systematic errors in thermophysical property experiments. Density second virial coefficients B(T) from sonic velocity and Joule‐Thomson (J‐T) experiments are examined for error propagation where the connecting thermodynamic identity is a differential equation with missing boundary conditions. A recent controversy is addressed concerning B(T) at subcritical temperatures for pure hydrocarbon gases from direct density measurements vs. new sonic velocity data. Sonic velocity results are more likely correct with adsorption errors causing the problem in the density measurements.Two new model consistency tests are developed for checking assumed temperature models in the reduction of sonic velocity and J‐T data to B(T). Excellent values of B(T) are then obtained from either type of data when the original experiments are free of errors. Random errors propagate systematically when the connecting equation is a differential equation. Sonic data must be of high precision (± 10 ppm) to generate B(T) to ±1 cm3/mol due to complications in data reduction arising from the temperature model/random error interaction. Except perhaps for adsorption errors, systematic errors in the sonic velocities are unimportant to B(T). J‐T data provide propagation factors near unity with errors in B(T) higher at higher temperature, unlike sonic velocities.
Influence of large‐amplitude oscillations on turbulent drag
Authors: Mao Zhuoxiong , Hanratty Thomas J. 
Published: June 2004

AbstractThe effect of imposed large‐amplitude oscillations on turbulent drag is studied. The system consists of water flow through a straight 5.08‐cm pipe. The velocity gradient at the wall is measured with flush‐mounted electrochemical mass‐transfer probes. Newly developed numerical algorithms are used to analyze the probe performance in the presence of unsteady flows. Sinusoidal oscillations are at large enough frequencies, ω+ = 0.0138–0.0506, that a pseudo‐steady‐state approximation cannot be made. The ratio of the time‐averaged velocity gradient at the wall, with and without oscillations, S̄, varies between 1.00 and 1.03, provided flow reversal does not occur. However, two experiments in which reversed flows existed at the wall for an appreciable period of time show drag reductions of 7 and 13%.Imposed nonsinusoidal oscillations are also studied for a period of favorable pressure gradient, about twice longer than that of unfavorable, and two sudden changes in the pressure gradient. Experiments at Re = 9,700 with T0 of 2.00, 2.45, and 3.46 s, and at Re = 19,200 with T0 = 3.46 give values of S̄ = 1.04–1.08. At Re = 19,200 and T0 = 2.00, 1.50, 1.00 s, drag reductions are 10–15%. This phenomenon could be associated with the speed with which a flow adjusts to sudden changes in the pressure gradient.
Physical absorption of CO2 and propene into toluene/water emulsions
Authors: Littel R. J. , Versteeg G. F. , Van Swaaij W. P. M. 
Published: June 2004

AbstractThe physical absorption of CO2 and propene into toluene/water emulsions is studied in a stirred cell and laminar film absorber. Experimentally observed masstransfer rates are compared to an absorption model, based on Higbie's penetration theory describing physical gas absorption into an emulsion. For all absorption experiments in a stirred cell absorber (toluene fractions and stirring rates), experimentally observed mass‐transfer rates are considerably higher than the rates predicted by the absorption model. Moreover, the absorption rate decreases with increasing stirring rate, whereas no influence of the stirring rate is predicted by the absorption model. In contradiction to the absorption experiments in a stirred cell absorber, the observed mass‐transfer rates in the laminar film absorber agree with the model simulations. Probable existence of a very thin toluene layer is observed on top of the emulsion for the stirred cell experiments, likely due to minor phase separation. Since in the laminar film absorber gas‐liquid interface and the gravity force are parallel, this phenomenon does not probably occur significantly for absorption experiments in this absorber. The observed mass‐transfer phenomena can be explained, at least qualitatively, from the occurrence of a thin toluene layer.
Automatic synthesis of batch plant procedures: Process‐oriented approach
Authors: Rotstein G. E. , Lavie R. , Lewin D. R. 
Published: June 2004

AbstractA strategy for the automatic synthesis of plant operating procedures, through the integration of artificial intelligence and mathematical modeling tools is discussed. This “predicative/numerical” modeling paradigm integrates qualitative and quantitative aspects of the problem in a same framework. It uses a “process‐centered” qualitative modeling approach together with MILP optimization techniques to automatically generate operating strategies. The operation procedures network (OP‐Net), formulated in terms of processes from a generic library, describes abstract (hardware‐independent) processing paths leading to the desired operational goals. In this approach, the model assumptions, conservation expressions and data are described at the same level of abstraction, using the same formal representation. This permits the direct, automatic generation and modification of operation procedures in situations involving changes in basic assumptions and initial scenarios. Thus, flexibility, an essential feature of batch processing, is safeguarded.
Fouling of tube surfaces: Modeling of removal kinetics
Authors: Yiantsios S. G. , Karabelas A. J. 
Published: June 2004

AbstractFouling of tube surfaces from flowing solutions or suspensions is examined. A new approach to the removal aspects of this process is presented linking removal to the morphological and mechanical characteristics of deposit microstructure. A simplified description of deposit microstructure is employed, involving a collection of geometrically similar roughness elements. A dynamic situation is envisioned whereby these elements grow due to deposition and suffer breakage under the action of hydrodynamic forces. A mathematical model for the macroscopic fouling behavior based on the techniques of population balances is obtained and numerically analyzed. The behavior found is in agreement with experimental evidence.
On‐line terpolymer composition control in semicontinuous emulsion polymerization
Authors: Urretabizkaia Agustín , Leiza José R. , Asua José M. 
Published: June 2004

AbstractA closed‐loop strategy for terpolymer composition control in semicontinuous emulsion polymerization of high solids content systems is presented. This strategy is based on a nonlinear adaptive controller that calculates the flow rate of the more reactive monomers to be added into the reactor to produce a terpolymer of a given composition. The nonlinear adaptive controller is based on a simplified mathematical model of the process that includes the on‐line estimation of an adjustable parameter. The addition of a conventional feedback proportional‐integral (PI) controller to the prediction of the nonlinear controller was studied by simulation. It is shown that the contribution of the PI controller is negligible. The controller was checked by computer simulation and also experimentally verified during the semicontinuous emulsion terpolymerization of high solids content (55 wt. %) of vinyl acetate, methyl methacrylate and butyl acrylate.