bluuebunny/crossref_metadata_2025_split huggingface dataset:
Precipitation of microsize organic particles from supercritical fluids
Authors: Chang C. J. , Randolph A. D. 
Published: June 2004

AbstractThe precipitation of organic particles from supercritical fluids (SF) by expansion (SFX) has become an interesting alternative to milling without thermal decomposition. Through the rapid expansion process, a dramatic change of the solute supersaturation ratio is created causing subsequent precipitation with a narrow particle‐size distribution. It was found that β‐carotene precipitates from SF ethylene and ethane have the feed material crystallinity. However, SF CO2 reacted with β‐carotene and did not give characteristic β‐carotene X‐ray spectra. The mean particle sizes of these precipitates were in the submicron range (ca 0.3 μm). Increased solubility was obtained by addition of toluene as cosolvent in SF ethylene. It was found that the mean size of β‐carotene particles, generally remained unchanged if the toluene concentration was less than 11/2 mol %. The SFX process appears to be in a single fluid phase when up to 11/2 mol % toluene cosolvent is used.
Multicomponent diffusion and convection in capillary structures
Authors: Sotirchos Stratis V. 
Published: June 2004

AbstractA previously developed method (Sotirchos and Burganos, 1988) for studying isobaric multicomponent diffusion in a class of capillary networks is extended for application to the problem of convection and diffusion of gaseous mixtures in porous media. The method is used to develop flux models for nonisobaric transport in capillary structures, which are then compared with corresponding “three‐parameter” dustygas models. Results for discrete and continuous pore size distributions show that the predictions of the developed flux models depend strongly, both qualitatively, and quantitatively, on the procedure used to average the dusty‐gas model equations for a single pore over the pore‐size distribution.
Capillary experiments of flow induced crystallization of HDPE
Authors: Titomanlio G. , Marrucci G. 
Published: June 2004

AbstractFlow‐induced crystallization experiments are made in a capillary apparatus modified with a downstream reservoir under pressure. Capillary length, diameter, and entrance angle are changed, as well as flow rate. The results show that the crystallization temperature is influenced both by the elongational flow at the capillary entrance and by the shear flow along the capillary. The independent effect of the pressure equals that obtained under static conditions. The effect of shear is correlated in terms of shearing work.
Oxygen transport in biofilm electrodes for screening of toxic chemicals
Authors: Goldblum David K. , Holodnick Steven E. , Mancy Khalil H. , Briggs Dale E. 
Published: June 2004

AbstractA biosensor electrode system with unique configuration and a thin layer of immobilized yeast cells, set on the surface of an amperometric oxygen membrane electrode, was developed for rapid screening of toxic chemicals in a variety of pollution and process control applications. Measurement is based on the instantaneous detection of changes in oxygen respiratory activity of biofilm of yeast cells upon exposure to toxic chemicals.The design of this electrode system, referred to as biofilm electrodes, was based on a mathematical model of oxygen transport in the biofilm and the electrochemical current response. The biofilm, which consists of three sublayers—boundary layer, filter pad, and yeast cell layer—was modeled as a one composite diffusion layer, or three separate layers in series. While the three layer model is more theoretically complete, the one layer model was more reliable and simpler to use.
A model for volatiles release into a bubbling fluidized‐bed combustor
Authors: Stubington John F. , Chan Shu W. , Clough Stephen J. 
Published: June 2004

AbstractA volatiles release model has been developed to predict the location and quantity of coal volatiles that are released into a bubbling fluidized‐bed combustor, using overbed, in‐bed or underbed feed systems. This model not only considers time resolution of the simultaneous processes of coal devolatilization and coal particle movement after injection, but also takes account of the stochastic nature of this particle movement. Volatiles release is nonuniform, occurring throughout an industrial‐scale bed, but only in restricted parts of a laboratory‐scale bed. For the industrial‐scale bed, 32% of volatiles are released directly into the freeboard while the particle is devolatilizing at the surface, whereas 24% are released there for the laboratory scale bed. The model predicts the formation of numerous discrete volatiles regions within the bed, in agreement with a new interpretation of experimental measurements from an in‐bed oxygen probe. The model is shown to be consistent with other experimental in‐bed measurements obtained during combustion of “simulated” volatiles.
Consequence of flow nonuniformity on the measurement of effective diffusivity
Authors: Cui L. C. , Schweich D. , Villermaux J. 
Published: June 2004

AbstractMeasurements of effective diffusivity by the chromatographic method are shown to be biased by nonuniformity of the external porosity in a cross‐section of the column. A very simple model is proposed to interpret experimental results. A modified Van Deemter method is given to extract the axial dispersion and effective diffusion coefficients from chromatographic peaks. This method allows one to ignore the external porosity distribution. Experiments show that even though axial dispersion obeys classical correlations, the internal mass transfer parameters may be strongly affected by the external porosity distribution.
Bubble‐size distribution in Fischer‐Tropsch‐derived waxes in a bubble column
Authors: Patel Snehal A. , Daly James G. , Bukur Dragomir B. 
Published: June 2004

AbstractBubble sizes were measured for molten wax‐nitrogen systems using photography and dynamic gas disengagement. The effects of operating conditions, system geometry and wax type were studied in 0.05‐ and 0.23‐m‐diameter by 3‐m‐tall bubble columns. Both techniques were used with FT‐300 wax, while only the dynamic gas disengagement technique could be used with reactor waxes due to their dark color. For FT‐300 wax, Sauter mean diameters obtained from photographs taken near the column wall were significantly lower than those obtained from photographs taken near the center. The ds values obtained from dynamic gas disengagement and photographic (near the column center) methods, for this noncoalescing medium, were in the range 0.5–1.6 mm in the large‐diameter column. For reactor waxes, ds values were significantly higher (1–2 mm for Sasol and 1–5.5 mm for Mobil's reactor wax) and are in agreement with results reported in earlier studies with similar waxes (ds = 2–4 mm), where different experimental techniques (light transmission or hot wire anemometry) were employed.
A discretized population balance for continuous systems at steady state
Authors: Hounslow Michael J. 
Published: June 2004

AbstractThis paper is concerned with the solution of the population balance for continuous systems at steady state, in which the active mechanisms are nucleation, growth and aggregation. A discretized population balance, initially proposed by Hounslow et al. (1988a) for batch systems, is adapted for use with continuous systems at steady state. It is shown that simultaneous nucleation and growth can be described very effectively by the discrete equations. Criteria are developed for the selection of the optimal size domain. A simple modification to the original discrete equations describing growth, permits the modelling of size‐dependent growth effects. Both size‐independent and size‐dependent aggregation are described by the discrete equations with three significant‐figure accuracy. The complete set of discrete equations is used to simulate the nucleation, growth and aggregation of Nickel Ammonium Sulphate. It is shown that analysis by the approximate model must lead to underestimation of the nucleation and growth rates.
Ultrapurification of SiCl4 by photochlorination in a bubble column reactor
Authors: Mixon David A. , Bohrer Michael P. , O'Hara Patricia A. 
Published: June 2004

AbstractThe development and performance of a bubble column photoreactor for ultrapurification of SiCl4 is described. Trichlorosilane (SiHCl3), the principle contaminant in SiCl4 commercially available for use in optical fiber manufacture, is converted to SiCl4 and HCl by UV‐initiated photochlorination. Studies of the homogeneous photochlorination kinetics and of Cl2 gas absorption in a bubble column were undertaken. In addition, an extensive set of data was collected from continuous‐flow bubble column reactor (BCR) runs. The rate of photochlorination in the BCR was found to be mass‐transfer‐limited. A simple model of BCR performance, incorporating the effect of Cl2 mass transfer rate enhancement by chemical reaction, was tested that agrees well with the experimental data. The BCR was found to be operable over a wide range of SiHCl3 concentrations and SiCl4 feed rates, and capable of lowering the concentration of SiHCl3 in product to below measurable levels (<1 ppm).
Unifying indicator and instantaneous reaction methods of measuring micromixing
Authors: Shenoy U. V. , Toor H. L. 
Published: June 2004

AbstractInstantaneous chemical reactions, either themselves or together with chemical indicators, have previously been used as probes of turbulent micromixing. Both methods obtain statistics of the micromixing from measurement of time mean quantities. The mean reactant concentration, which is the quantity measured in the instantaneous reaction method, is shown here to be the integral with respect to feed concentration ratio of the mean color density, which is the quantity measured in the chemical indicator method. Differentiation of the mean color density gives the scalar probability density while integration gives the mean reactant concentration. Measurements of the color density of bromothymol blue at the centerline of a turbulent jet of base mixing with acid are used as an example.
Restricted diffusion through granular materials
Authors: Limbach Kirk W. , Wei James 
Published: June 2004

AbstractThe restricted diffusion of nickel etioporphyrin is experimentally measured in six granular catalyst support materials. These materials include five γ‐aluminas and one small‐pore silica‐alumina. Pore size distribution is narrow for three of the supports and roughly bimodal for the remaining three. Diffusivities are determined by a transient uptake technique utilizing a Freundlich equilibria adsorption isotherm.Experimentally determined diffusivities agree well with restricted diffusion theory based on a circular pore model when the appropriate characteristic length scales are used to describe the molecule and pore size. For the restricted diffusion of dilute solute molecules in neutral pores, the appropriate measure of granular pore size is the hydraulic pore radius. Molecule size, in this case, is best described by a mean projected molecule radius for partitioning and a Stokes‐Einstein radius for hydrodynamic aspects of restricted diffusion.
Synthesis of multivariable nonlinear controllers by input/output linearization
Authors: Kravaris Costas , Soroush Masoud 
Published: June 2004

AbstractThis work concerns the synthesis of nonlinear controllers for multivariable nonlinear processes that make the closed‐loop system linear in an input/output sense. Necessary and sufficient conditions for input/output linearizability via static state feedback are derived as well as formulas for the feedback law. Once such a static state feedback is applied to the process, an external multivariable linear controller with integral action can control it to set point. The proposed control methodology is tested through simulations in a semibatch copolymerization reactor example.
Experimental study and parameterization of interfacial gas absorption
Authors: Caussade B. , George J. , Masbernat L. 
Published: June 2004

AbstractExperiments of simultaneous absorption of carbon dioxide and helium, in transient absorption regimes, have been carried out in a gas‐liquid flume for stratified‐type cocurrent flows. There was a need to improve a method of chromatographic analysis for helium and CO2 titrations in the gaseous phase and the liquid phase; this led us to study simultaneous absorption of CO2 and He independent of dynamic conditions. In addition the dominant wave characteristics were studied and the interfacial friction velocity was measured. It was confirmed that, for two gases presenting a large contrast in diffusivities, gas absorption rates are related directly to the physical properties of the gases. The mass transfer coefficient varies with the − 1/2 exponent of the Schmidt number for a large interfacial stress and a clean interface whereas it varies with the − 2/3 exponent for weaker winds.
Spatial instabilities in the regeneration of diesel‐particulate filters
Authors: Saunders James H. 
Published: June 2004

AbstractAn instability is proposed that can lead to channel formation during the regeneration of monolithic diesel‐particulate filters. This instability, which occurs during the transport‐controlled combustion of the soot bed, is compared to a kinetically driven instability by using a numerical model for channel growth. Both mechanisms are shown to be important and may lead to higher thermal stresses in the filter wall. It is suggested that both mechanisms can be controlled by the ratio of the filter‐plate to soot‐bed flow resistance, lateral heat transfer, and other design parameters.
Computer simulation of isothermal fluidization in large‐scale laboratory rigs
Authors: Richner D. W. , Minoura T. , Pritchett J. W. , Blake T. R. 
Published: June 2004

AbstractFinite‐difference computer models have been used by several investigators to predict hydrodynamic mixing in fluidized beds. In the present study the finite‐difference model CHEMFLUB is used to simulate cold, isothermal mixing in axisymmetric fluidized beds. The bed geometries and the operating conditions are based upon those of two large‐scale laboratory cold flow rigs. The finite‐difference model is an iterative, implicit formulation to solve continuum equations describing the gas and particle dynamics of fluidization. Comparisons with experimental data are presented. It is shown that the model provides a good prediction of jet penetration height, bubble frequency, and bubble velocity.
Microencapsulation in polyurea shell by interfacial polycondensation
Authors: Yadav S. K. , Suresh A. K. , Khilar Kartic C. 
Published: June 2004

AbstractA model and a simple measurement technique for time of encapsulation have been developed to study the microencapsulation of butachlor in polyurea shell by means of interfacial polymerization. The model is based on diffusion of the hydrophilic monomer through the polymeric shell with an interfacial reaction at the inner surface while the measurement technique is based on the indirect determination of the concentration of the hydrophilic monomer in the continuous phase by monitoring the pH. Measurements show that capsule sizes ranging from 1 to 20 μm can be produced, and the surface to volume mean size varies only from 2 to 6 μm for a large variation in rpm of the agitator. Time of encapsulation is found to be approximately proportional to the microcapsule size, and it varies from 150 to 300 s. Both the data and the model were used to discern that the process is kinetically‐controlled by and large. It is also shown that time of encapsulation varies with the square of the capsule size in a diffusion‐controlled regime.
Ceramic processing: An overview
Authors: Rice Roy W. 
Published: June 2004

AbstractProcessing of ceramics is reviewed from a broad perspective, with emphasis on the predominant powder‐based methods, but with considerable attention to other methods. Major stages of the powder process, from preparation, modification, and handling, to sintering or pressure densification (or postdensification) are discussed. Nonpowder‐based methods, such as chemical vapor deposition, melt, and polymer pyrolysis processing, are also presented. Processing of ceramic composites is reviewed, noting the shifts in processing technology this entails. Practical aspects, such as part size, shape, volume, and the costs of various processes are also addressed.
Magnetic resonance imaging and modeling of flow in hollow‐fiber bioreactors
Authors: Heath C. A. , Belfort G. , Hammer B. E. , Mirer S. D. , Pimbley J. M. 
Published: June 2004

AbstractNuclear magnetic resonance flow imaging (MRFI) was used to measure fluid flow noninvasively in the extracapillary space (ECS) of a hollow‐fiber bioreactor without cells. Agreement between these axial flow measurements in a single hollow‐fiber module and predicted axial velocity contour plots at various image planes along the path length was good.Flow in a solid‐wall tube (phantom) was first used to calibrate pixel intensities with axial velocities. Flow images at several locations along the permeable hollow fiber length were then obtained in order to observe the well‐known leakage or Starling flow in the ECS. These quantitative spatially dependent velocity measurements were then compared to theoretically derived velocities obtained from a solution of Poisson's equation with a constant pressure gradient and no slip at the solid surfaces. A mathematical transformation was used to simplify the numerical methods. Leakage flow through the ECS of a multifiber bioreactor (40 fibers) was also measured by MRFI, illustrating the applicability of this method for optimizing operational procedures and design of membrane bioreactors and filtration devices.
Pitch‐to‐diameter effect on two‐phase flow across an in‐line tube bundle
Authors: Dowlati Ramin , Kawaji Masahiro , Chan Albert M. C. 
Published: June 2004

AbstractVoid fraction and friction pressure drop measurements were made for an adiabatic, vertical two‐phase flow of air‐water across two horizontal, in‐line, 5 × 20 rod bundles, one with a pitch‐to‐diameter ratio, P/D, of 1.3, the other 1.75. For both bundles the average void fraction showed a strong mass velocity effect and values were significantly less than those predicted by a homogeneous flow model. All void fraction data were found to be well correlated, with no P/D effect, using the dimensionless gas velocity, j*g. The two‐phase friction multiplier data exhibited a strong effect of P/D and mass velocity, however, the data for both bundles could be well correlated with the Martinelli parameter for G > 200 kg/m2s. The correlations developed for void fraction and two‐phase friction multiplier were successfully tested in predicting the total pressure drop in boiling freon experiments.
Conical moving‐bed shale retort model
Authors: Anderson David H. , Sapre Ajit V. , Kennedy Clinton R. , Krambeck Frederick J. 
Published: June 2004

AbstractThis two‐dimensional model of a moving‐bed shale oil retort accounts for the major physical interactions of convective heating and kerogen decomposition coupled with the shale and gas flow distributions. Data in a small‐sale apparatus support a solids flow model of potential flow, although the exiting boundary conditions are uncertain. The calculations show that efficient retorting will only occur if the upper shale surface is shaped so that the shale particle velocity is perpendicular to this surface, and parallel to the entering retort gas flow. Even in the ideal flow case, performance is quite sensitive to gas/solids flow ratio. This model could be used with measured temperature distributions to optimize the surface profile.
Gas phase and catalytic ignition of methane and ethane in air over platinum
Authors: Griffin Timothy A. , Pfefferle Lisa D. 
Published: June 2004

AbstractThe ignition of gas phase combustion by a heated catalytically active surface involves dynamic coupling of transport processes and chemical kinetics. Researchers have observed that surfaces with high catalytic activity require higher surface temperatures to ignite gas phase combustion, compared to nonactive surfaces, and that this difference is greatest for a stoichiometric mixture. In this work an analysis of the ignition of surface‐catalyzed oxidation is developed along with an experimental technique for independently monitoring both surface and gas phase ignition such that the dynamics of these two events can be decoupled. Experiments suggest that the sharp maximum in surface temperature required for gas phase ignition observed in previous work is an artifact caused by transient heating of the surface as ignition occurs. Analysis of surface ignition was also used to investigate the kinetics of methane and ethane oxidation on platinum.
Effects of osmotic pressure and adsorption on ultrafiltration of ovalbumin
Authors: Nabetani Hiroshi , Nakajima Mitsutoshi , Watanabe Atsuo , Nakao Shin‐Ichi , Kimura Shoji 
Published: June 2004

AbstractThe influence of osmotic pressure and solute adsorption on permeate flux during ultrafiltration of a solute that forms a gel‐like layer on membrane surfaces was investigated. Ovalbumin solutions were ultrafiltrated using three different kinds of membranes, polyolefine, polysullfone, and polyacrylonitrile. Flux data were analyzed by three conventional models: gel polarization, osmotic pressure, and resistance in series.The experimental data were in conflict with all conventional models. Data analysis suggested that the main factors which influence permeate flux decline were osmotic pressure increase at the membrane surface and resistance caused by solute adsorption.A new model, which takes into account both osmotic pressure and resistance due to solute adsorption, is proposed. Permeate flux declines observed in the experiments fit this model quite precisely. The gel layer that forms on the membrane surface has little influence on permeate flux and can be neglected.
Electrokinetic dispersion in capillary electrophoresis
Authors: Datta Ravindra , Kotamarthi Veerabhadra R. 
Published: June 2004

AbstractA “Taylor” dispersion‐type model is developed for the electrokinetic dispersion coefficient of a solute in capillary electrophoresis that accounts for the effects of Poiseuille and/or electro‐osmotic flow of the elutant for the case of low ζ potential. The expression obtained for the height equivalent of a theoretical plate is compared with experimental results reported in the literature for the case of neutral, nonretained solutes propelled by electro‐osmotic flow. The results further reveal some interesting and somewhat unexpected interactions of the electro‐osmotic and Poiseuille components of the elutant flow. Superposition of Poiseuille flow on the natural electro‐osmotic flow allows greater freedom in the choice of elutant velocity, without necessarily increasing the dispersion. In fact, it results in lower dispersion under some conditions. Optimum flow conditions are obtained for minimizing the plate height or, equivalently, for maximizing the Peclet number.
Thermal integration of homogeneous azeotropic distillation sequences
Authors: Knapp Jeffrey P. , Doherty Michael F. 
Published: June 2004

AbstractExisting methods for synthesizing thermally‐integrated distillation sequences fail frequently when applied to nonideal and azeotropic systems, because increasing the column pressures often introduces new azeotropes and distillation boundaries into the mixture, which make some separation tasks infeasible. A new thermal integration procedure is presented that combines a bifurcation and residue‐curve map analysis with the methods of Andrecovich and Westerberg. The procedure is demonstrated with two commercially important separations: ethanol‐water‐ethylene glycol and methanol‐acetone‐water. Energy savings of 65% and 40%, respectively, over the optimized nonintegrated sequences are possible.