bluuebunny/crossref_metadata_2025_split huggingface dataset:
A numerical model of the synthesis of carbon black by benzene pyrolysis
Authors: Ivie J. J. , Forney L. J. 
Published: June 2004

AbstractA numerical model has been developed to predict the formation of carbon black particles by benzene pyrolysis. The approach, patterned after the work of Jensen, assumes that particle formation is controlled by four steps: gas phase reactions producing radical species, nucleation, growth and coagulation, and oxidation. In the present model, 15 reactions based on the work of Fujii and Asaba are used to describe the gas phase kinetics in which the phenyl radical is treated as the important intermediate in the formation of carbon black. A discrete distribution of 10 particle radii is also used to approximate the simultaneous growth and coagulation of spherical carbon particles. The results of the model show that a self‐preserving log normal distribution of carbon particles develops after an initial nucleation and growth period. The model results also compare favorably with reactor data. In particular, the numerical model predicts a mass median carbon particle diameter to within 10% of measured values.
Rigorous thermodynamic treatment of gas adsorption
Authors: Talu Orhan , Myers Alan L. 
Published: June 2004

AbstractMulticomponent adsorption equilibria are predicted from theories based on experimental data for single‐gas adsorption isotherms. Theories of multicomponent adsorption differ in the details of their results but should agree in special cases such as low surface coverage and ideal solution behavior. This paper is a summary of rules, limits, and consistency requirements that apply to adsorption of single gases and their mixtures. These rules and limits provide a basis for comparing theories with each other and with experimental data.
Kinetics of the dissolution of alumina in acidic solution in a flow system
Authors: Crawford Myles D. , Baumgart Jerry , Shoaei Mahnoosh , Ernst William R. 
Published: June 2004

AbstractThe kinetics of dissolution of alumina in aqueous solutions of H2SO4 was studied at ambient temperature under continuous‐flow conditions. The results are consistent with a model involving rapid hydration of the surface, adsorption‐desorption of H+ to form precursor sites, and rate‐determining parallel reactions of the precursor sites to form dissolved aluminum and an insoluble surface species. The model also involves renewal of a precursor site after each dissolution step.The adsorption‐desorption of H+ was represented by a Langmuir isotherm. The dissolution data were correlated by a kinetic equation that was developed by assuming the dissolution step is first order in precursor concentration, and the deactivation step is second order in precursor concentration.
Dispersion coefficient for laminar flow in curved tubes
Authors: Daskopoulos Ph. , Lenhoff A. M. 
Published: June 2004

AbstractThe axial dispersion coefficient in a fluid in laminar flow in a tube is generally smaller in a curved tube than in a straight tube, because of the enhacement of lateral transport by secondary flows. In this paper the extent of this reduction is computed using Horn's modification of Aris's method of moments. Dimensional analysis suggests that the most convenient form in which to represent the results is that obtained empirically by Trivedi and Vasudeva. The results presented here cover the whole laminar flow regime, and show the region of applicability of previously computed dispersion coefficients to be limited. The computed dispersion coefficients agree well with previously reported experimental results for small Schmidt numbers; however, discrepancies are present at large Schmidt numbers. Possible causes are discussed.
Plasma processing in microelectronics manufacturing
Authors: Graves David B. 
Published: June 2004

AbstractPlasma processing has emerged as an important technology for the deposition and etching of thin solid films in the manufacture of microelectronic devices. In fact, much of the progress achieved to date in device miniaturization would have been much more difficult without the unique characteristics of plasma processes. It is anticipated that future progress will continue to rely heavily on plasma technology. Although plasma chemical reactors are widely used, a lack of fundamental understanding has resulted in heavy reliance on empiricism in process design and control. The complexities inherent in any chemical reactor are compounded in plasma processing by the presence and active participation of the discharge in both gas phase and surface chemical processes. This has resulted in a technology that is sensitive to many design and operating parameters. A large parameter space gives process engineers flexibility in tailoring process conditions to meet objectives. However, without fundamental insight into the key physical and chemical processes, reactor design and control cannot be based on systematic, rational procedures. The purposes of this review are to introduce chemical engineers to plasma processing practice and phenomenology; to outline the progress made to date in fundamental studies of discharge physics and chemistry; to indicate areas in which chemical engineers must expand their traditional training to participate in plasma processing research; and finally to suggest how established chemical engineering methodology can be applied to plasma chemical reactors.
Product yields and kinetics from the vapor phase cracking of wood pyrolysis tars
Authors: Boroson Michael L. , Howard Jack B. , Longwell John P. , Peters William A. 
Published: June 2004

AbstractThe homogeneous vapor phase cracking of newly formed wood pyrolysis tar was studied at low molar concentrations as a function of temperature (773–1,073 K), at residence times of 0.9–2.2 s. Tar conversions ranged from about 5 to 88%. The tars were generated by low heating rate (0.2 K/s) pyrolysis of ∼2 cm deep beds of sweet gum hardwood, and then rapidly conveyed to an adjacent reactor for controlled thermal treatment. Quantitative yields and kinetics were obtained for tar cracking and resulting products formation. The major tar conversion product was carbon monoxide, which accounted for over two‐thirds of the tar lost at high severities. Corresponding ethylene and methane yields were each about 10% of the converted tar. Coke formation was negligible and weight‐average tar molecular weight declined with increasing tar conversion. A first‐order distributed activation energy model more closely correlated tar conversion kinetics over a wider range of reaction conditions than did a single‐reaction model.
Flow in packed tubes with a small tube to particle diameter ratio
Authors: Chu C. F. , Ng K. M. 
Published: June 2004

AbstractA computer‐generated slim tube randomly packed with spheres of almost uniform size is used to model single‐phase flow in a packed tube with a small tube diameter to particle diameter ratio, R. To obtan a detailed description of its morphology, the slim packed tube is first tessellated into tetrahedra in the interior, and pentahedra near the walls of the tube. Then, the pore space is represented by a network of interconnected circular and triangular sinusoidal flow channels. The size and length of each channel, as well as their interconnectivity, are exactly known. In addition, porosity and solid surface area per unit volume of the porous medium are determined as a function of distance away from a wall. These data suggest that the presence of the walls has two counteracting effects on fluid flow. A higher porosity promotes flow along the walls but a higher surface area per unit volume hinders it. To confirm this prediction, experimental permeability data are obtained for tubes with R between 2.5 and 40. For R > 25, the permeability is the same as that of a large diameter tube, k∞. Between 8 and 25, the permeability can be larger or less than k∞. The way the tube is packed determines whether the higher porosity or surface area dominates in the wall region, and thus higher or lower permeability. Below R = 8, the confining walls cause a marked increase in overall bed porosity and the permeability is always larger than k∞. Theoretical predictions of the permeability of such very slim tubes are in good agreement with experimental data.
Dynamics of Haines jumps for compressible bubbles in constricted capillaries
Authors: Gauglitz P. A. , Radke C. J. 
Published: June 2004

AbstractThe unsteady, impulsive motion of a compressible bubble expanding out of a constricted capillary is quantified with a macroscopic momentum balance. Numerical solution demonstrates the importance of the Ohnesorge number, the geometry of the constriction, the length of the initial gas bubble, and the surface tension, density, and unconstricted capillary radius, which combine to form a characteristic scaling time. Experimental data for the position of the bubble front as a function of time confirm the theoretical result when the time scale for the bubble jump is longer than that required to achieve fully developed parabolic flow. Theory also predicts the capillary number of the bubble jump which, in conjunction with previous theoretical results, determines the time to snap‐off of gas bubbles moving through constricted capillaries. Excellent agreement is found with existing experimental data for Ohnesorge numbers ranging from 5 × 10−3 to 0.3.
A state space formulation for model predictive control
Authors: Li Sifu , Lim Kian Y. , Fisher D. Grant 
Published: June 2004

AbstractModel predictive control (MPC) schemes such as MOCCA, DMC, MAC, MPHC, and IMC use discrete step (or impulse) response data rather than a parametric model. They predict the future output trajectory of the process {ŷ(k + i), i = 1, …, P}, then the controller calculates the required control action {Δu(k + i), i = 0, 1, …, M − 1} so that the difference between the predicted trajectory and user‐specified (setpoint) trajectory is minimized. This paper shows how the step (impulse) response model can be put into state space form thus reducing computation time and permitting the use of state space theorems and techniques with any of the above‐mentioned MPC schemes. A series of experimental runs on a simple pilot plant shows that a Kalman filter based on the proposed state space model gives better performance that direct use of the step response data for prediction.
Wall‐cooled fixed‐bed reactors: Parametric sensitivity as a design criterion
Authors: Borio Daniel O. , Gatica Jorge E. , Porras José A. 
Published: June 2004

AbstractMultitubular reactors of the heat exchanger type are commonly used to carry out highly exothermic reactions. Two of the main goals, when designing this type of reactor, are to guarantee a safe operation and to minimize the reactor length. Therefore, these concepts are used here as criteria for comparing the performance of the three most common cooling‐medium flow arrangements. The analysis of the parametric sensitivity behavior, as well as that of some related measures, indicates that, at least from the steady‐state standpoint, the cocurrent arrangement should be considered the most attractive alternative.
Effect of molecular association on diffusion in binary liquid mixtures
Authors: McKeigue Kevin , Gulari Erdogan 
Published: June 2004

AbstractA predictive equation for the mutual diffusion coefficient is developed for binary solutions which contain a self‐associating component. The solution is modeled as a nonideal multicomponent mixture consisting of the solvent molecules and various association complexes. The model provides for a unique mobility for each of the species present and accounts for both physical and chemical contributions to the solution thermodynamics and their effects on the diffusive fluxes. The predictions of the theory were evaluated for n‐alcohols in nonpolar solvents using data for six systems at temperatures ranging from 293 to 363 K. In each case, the predictions of this theory are found to be superior to other currently available methods.
Hydrodynamics of a three‐phase fluidized bed containing low‐density particles
Authors: Tang Wen‐Tzung , Fan Liang‐Shih 
Published: June 2004

AbstractExperiments were conducted to study the hydrodynamics of a gas‐liquid‐solid fluidized bed containing low‐density particles. The density and size of the particles employed were comparable to those ordinarily encountered in fluidized‐bed bioreactors for either wastewater treatment or fermentation. A dual resistivity probe and a conductivity probe were employed to study the axial holdup of gas and liquid phases and the bubble size distribution. The behavior of the axial holdup distribution for solid, gas, and liquid phases is reported. A mechanistic model, based on solids entrainment and deentrainment mechanisms by bubbles, is developed to describe the behavior of the axial solids holdup distribution. The model is shown to satisfactorily account for the experimental data.
Thermoflow multiplicity in a packed‐bed reactor: Conduction and cooling effects
Authors: Pita Jorge , Balakotaiah Vemuri , Luss Dan 
Published: June 2004

AbstractSteady states with different flow rates and temperature profiles may exist in different tubes of a multitube packed‐bed reactor due to the coupling among the species, energy and momentum balances, and the change of physical properties with temperature and pressure. Under typical operating conditions if no axial conduction of heat occurs thermoflow multiplicity can be found only for unrealistically high heats of reaction and/or over a very narrow range of exit pressures. However, accounting for the finite but small heat conduction in the reactor tubes leads to multiplicity for typical parameters and a reasonable range of exit pressures. Cooling tends to decrease the region of parameters for which the multiplicity occurs.
Cell transport in the millipore filter assay
Authors: Buettner Helen M. , Lauffenburger Douglas A. , Zigmond Sally H. 
Published: June 2004

AbstractDuring inflammation, leukocytes cross the blood vessel wall and migrate to the inflammatory site in response to gradients of diffusible chemical attractants produced there. This directed migration response to a chemical gradient, termed chemotaxis, can be studied experimentally in the Millipore filter assay. We have applied a mathematical model to analyze cell population migration in the assay in terms of two parameters analogous to molecular transport coefficients. The random motility coefficient, μ, reflects the cell response to uniform concentrations of chemical attractant, while the chemotaxis coefficient, χ, reflects the response to a concentration gradient. We have measured μ and χ by comparing theoretical cell density profiles to those measured in the assay. Both parameters vary as a function of the attractant concentration; μ ranges from 10−10–10−9 cm2/s and χ ranges from 10–100 cm2/s.M for the attractant tested. These values agree with ones predicted from a priori theoretical relationships for μ and χ. Quantitation of the Millipore filter assay provides a framework for the quantitation of analogous cell transport systems such as a composite assay simulating cell migration across the vessel wall.
A group contribution method for second virial coefficients
Authors: Abusleme J. A. , Vera J. H. 
Published: June 2004

AbstractA semitheoretical group contribution method for predicting pure‐compound second virial coefficients is proposed. An expression for the second virial coefficient, expressed as the product of a nonpolar and a polar contribution, is derived using statistical thermodynamic concepts and an approximate form for the radial distribution function. For polar compounds the nonpolar contribution is assumed to be given by the Tsonopoulos correlation with the nonpolar acentric factor defined by Thompson and Braun. The polar contribution is represented by an energetic term expressed in terms of group contributions. Second virial coefficient predictions for strong polar and associating systems are comparable with those obtained with the correlations of Tsonopoulos and Hayden and O'Connell. Cross‐second virial coefficients for mixtures obtained using well‐defined molecular mixing rules compare well with literature values.
Structural changes in surfactant‐modified sorbents during furnace injection
Authors: Kirchgessner David A. , Jozewicz Wojciech 
Published: June 2004

AbstractA calcium hydroxide [Ca(OH)2] sorbent modified by the addition of calcium lignosulfonate has recently been developed for use in the Environmental Protection Agency's limestone injection multistage burner process. The increased reactivity with sulfur dioxide (SO2) displayed by this modified sorbent has been shown to be caused, in part, by its decreased particle (agglomerate) size compared to conventional Ca(OH)2. Subsequent work has shown that surfactant‐modified Ca(OH)2 also undergoes significantly different structural changes during furnace injection. For a given reactor temperature and residence time, the modified sorbent calcines to a greater extent than unmodified sorbent. It also loses surface area more slowly, and retains more of its porosity, suggesting that it sinters more slowly than conventional sorbent. Therfore, in addition to reducing the particle size of Ca(OH)2 in some applications, calcium lignosulfonate also to inhibit one or more of the diffusion mechanisms responsible for the process of sintering.
Thermodynamics of high‐pressure aqueous systems containing gases and salts
Authors: Harvey Allan H. , Prausnitz John M. 
Published: June 2004

AbstractThis work provides a new method for calculating phase equilibria for systems where conventional activity‐coefficient models are not suitable. A procedure is presented for superimposing ionic effects on a conventional equation of state for nonelectrolytes. A modification of Born's equation is used to describe charging the ions; ion‐ion interactions are described with the Mean Spherical Approximation, coupled with an adjustable salt/solvent parameter that is obtained from osmotic‐coefficient data at room temperature. The equation of state is used to predict gas solubilities in aqueous salt solutions at high pressures. While this method produces qualitative agreement with the experimental solubility data, quantitative agreement requires a salt/ gas parameter obtained from Setchenow‐constant data. When Setchenow constants are used, agreement with experiment is good except at high salt concentrations, where salting‐out is usually underpredicted. Good results are obtained for phase equilibria in a natural‐gas/brine system at high pressures.
Process optimization via simulated annealing: Application to network design
Authors: Dolan W. B. , Cummings P. T. , LeVan M. D. 
Published: June 2004

AbstractSimulated annealing is a multivariable optimization technique based on the Monte Carlo method used in statistical mechanical studies of condensed systems and follows by drawing an analogy between energy minimization in physical systems and costs minimization in design applications. In this paper, simulated annealing is introduced and reviewed. The utility of the method for optimization of chemical processes is illustrated by applying it to the design of pressure relief header networks and heat exchanger networks.
Hollow‐fiber liquid chromatography
Authors: Ding Hongbing , Yang Ming‐Chien , Schisla David , Cussler E. L. 
Published: June 2004

AbstractModules containing from 120 to 27,000 parallel hollow fibers 100 μm in diameter can separate mixtures by reversed phase chromatography. The mixtures separated include aqueous solutions of ketones using alkanes as the stationary phase, and aqueous solutions of the proteins myglobin and cytochrome‐c using an octane solution of reversed micelles as the stationary phase. The dispersion observed in these separations is comparable to that predicted from the Aris‐Taylor theories. Modules of these fibers promise a lower pressure drop and a greater reproducibility than columns of spheres of equivalent surface area per volume. Such modules can facilitate scale‐up of liquid chromatography.
Holdup and interfacial area measurements using dynamic gas disengagement
Authors: Patel Snehal A. , Daly James G. , Bukur Dragomir B. 
Published: June 2004

AbstractThe dynamic gas disengagement technique is discussed comprehensively in this paper. Also outlined is the procedure for estimating holdup structures and bubble rise velocities in a bubble column, which is extended to include the methodology for estimating the Sauter mean bubble diameter and therefore the specific gas‐liquid interfacial area. The error limits for the estimated quantities are established using two extreme cases to describe the disengagement process: constant rate disengagement and interactive disengagement of bubbles. The analysis is done assuming a bimodal bubble size distribution; however, generalized equations for a multimodal bubble size distribution are also presented. Sensitivity of results to the two cases is illustrated using results obtained from experiments conducted with the air‐tap water system in two bubble columns (0.05 and 0.23 m in diameter, 3 m tall). Sauter mean bubble diameters and specific interfacial areas estimated using the two approaches provide lower and upper limits for values reported in the literature.
Simulation of microstructure/mechanism relationships in particle deposition
Authors: Tassopoulos M. , O'Brien J. A. , Rosner D. E. 
Published: June 2004

AbstractThe important connection between particulate deposit properties and deposition mechanism remains poorly understood and only scarcely studied. Accordingly, in this research, we develop a discrete stochastic model to simulate particulate deposition processes resulting from realistic combinations of deposition mechanisms. Particle motion is assumed to be determined by the superposition of a deterministic force that acts toward the collecting surface and a random force, which produces Brownian diffusion. We characterize the resulting deposit microstructure via porosity and pore size/area distribution, surface area; and we examine the evolution of these descriptors with time (number of particles deposited) for different deposition mechanisms. We also examine the effect of particle polydispersity, spatial orientation (for nonspherical particles), and mean‐free‐path on the resulting deposit structure.
Experimental data for the crossover process in a model supercritical system
Authors: Kelley F. D. , Chimowitz E. H. 
Published: June 2004

AbstractThis paper presents the experimental technique and data acquired in the evaluation of a separation process in the crossover region of a model supercritical fluid system consisting of benzoic acid, 1–10 decanediol, and carbon dioxide. The results show that by exploiting the crossover effect it is possible to obtain essentially pure benzoic acid (>99.5% purity) with a single temperature cycle. A number of other issues are also discussed including the tradeoff between yield and purity and the manner in which the process variables are specified, which involves the interplay of experiment and model calculations.
Role of porosity loss in limiting SO2 capture by calcium based sorbents
Authors: Newton Gerald H. , Chen Shih Lin , Kramlich John C. 
Published: June 2004

AbstractThe extent of high temperature (900‐1,300°C), short time (<1 s) SO2 capture was found to be limited by temperature‐dependent losses in the porosity of calcium based sorbents. At 970°C these porosity losses were caused by CO2‐activated sintering. Sulfation of the sorbents either prevented or reduced the extent of porosity losses. Differences in SO2 capture between hydroxides from different commercial sources, and significantly lower levels of capture by calcium carbonates compared to hydroxides were attributed to differences in particle size and the degree of porosity loss.