bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spatiotemporal temperature patterns during hydrogen oxidation on a nickel disk
Authors: Lane Samuel L. , Graham Michael D. , Luss Dan 
Published: June 2004

AbstractSpatiotemporal temperature patterns on a polycrystalline nickel disk were recorded using infrared video imaging during atmospheric hydrogen oxidation and characterized by the proper orthogonal decomposition pattern analysis technique. The system was studied at two different residence times, 3.2 s and 6.4 s. At moderate feed temperatures, steady‐state multiplicity and rate oscillations were found. Oscillations at a residence time of 6.4 s were periodic and essentially spatially uniform. At a residence time of 3.2 s, however, the surface temperature became nonuniform, and rate oscillations occurred via traveling temperature waves which emanated from “pacemakers” (locally active regions) on the edge of the catalyst. During periodic oscillations, the waves were emitted synchronously from the pacemakers, while during chaotic oscillations, the pacemakers were desynchronized and emitted waves independently of each other. Nonlocal gas‐phase coupling between distance surface elements caused spatial desynchronization during rate oscillations.
Transport of gases in miscible polymer blends above and below the glass transition region
Authors: Li R. J. , Hsu W. P. , Kwei T. K. , Myerson A. S. 
Published: June 2004

AbstractThe study of diffusion and permeation of methane, nitrogen, and helium in miscible blends of poly(styrene‐stat‐acrylonitrile) (PSAN) and poly (methyl methacrylate) (PMMA) at 35–140°C shows that permeation coefficients (P) of helium followed the linear logarithmic mixing rule. Positive deviations from the linear logarithmic mixing rule were observed for permeation and diffusion coefficients (D) of methane and nitrogen below the glass transition temperature (Tg). The deviations decreased with increasing temperature and disappeared above Tg. The experimental results were analyzed by free volume and activated state theories. The Arrnenius plots of log D or log P vs. the reciprocal of temperature exhibited discontinuities in the glass transition region for all gases and blend compositions. The discontinuities are caused by large thermal expansion coefficient differences between the rubbery and glassy states of PSAN and PMMA. The sorption of methane in 50/50 PSAN/PMMA has dual‐mode characteristics below Tg.
Use of lagrangian statistics to describe slurry transport
Authors: Binder J. L. , Hanratty T. J. 
Published: June 2004

AbstractLagrangian statistics are explored as a means of describing the transport of solids in a turbulently flowing liquid. The essential feature of the approach is to represent the concentration field as resulting from a distribution of sources of particles. It is argued that this provides a better framework to understand the physics than the Eulerian analysis currently being used. Fully developed concentration fields are calculated, using the assumptions of homogeneous turbulence and plug flow. It is found that the configuration of solids and the suspended load depend primarily on the ratio of the settling velocity to the friction velocity, which is a measure of the relative importance of turbulence and of settling in depositing particles. The analysis emphasizes the need for a better understanding of the mechanism and the rate of entrainment of particles into a turbulently flowing liquid.
Effect of chemical reactions on turbulent diffusivities
Authors: Toor H. L. 
Published: June 2004

AbstractA mixing length model describes the recently observed (Bilger et al., 1991) effect of chemical reactions on turbulent diffusivities. From this viewpoint, the coupling between microscale reactions and macroscale mixing occurs because the reaction rate is a quasitransferable property which causes more reaction in fluctuating fluid lumps leaving regions of high rate than low rate. The net effect, which raises or lowers reactant diffusivities, depends on a characteristic macromixing time and the rate at which the mean reaction rate changes with mean concentration:

The model shows correct qualitative behavior and appears to agree quantitatively with much of the existing data. It adds an apparent flux, ετM(drA/dy), to the convective diffusion equations which can enhance or hinder the normal turbulent fluxes, but is likely to have little effect on the mean concentration field.
A combined heat‐transfer analysis of a single‐fiber CVD reactor
Authors: Kassemi M. , Gokoglu S. A. , Panzarella C. H. , Veitch L. C. 
Published: June 2004

AbstractA combined‐conjugated heat‐transfer and fluid‐flow analysis is presented for coating fibers by CVD in a vertical cylindrical quartz reactor. The numerical model focuses on radiation and natural convection. Three case studies are performed, and the wall temperature predictions are compared to experimental measurements. In the first case, the flowing gas is hydrogen, and conduction is more important than both radiation and convection, in which case measured and predicted wall temperatures agree excellently. In the second, hydrogen is replaced by argon, thus making radiation heat transfer more important than the previous situation. Three radiation models with increasing degrees of sophistication are compared: an approximate nongray model (no wavelength dependence of emissivity), an approximate semigray model, and a rigorous semigray model with view factor calculations. Comparison with experiments suggest that a semigray radiative analysis is needed for correct determination of wall temperatures. The third involves argon at a lower flow rate, where natural convection effects are more pronounced. Checking the validity of the Boussinesq approximation by incorporating the explicit dependence of density on temperature in the model shows a slight difference between the velocity fields predicted using the Boussinesq approximation and those obtained using the explicit dependence of density on temperature. However, there is negligible difference between the temperature fields predicted in the two cases.
Self‐similar collapse of stationary bulk foams
Authors: Patzek Tad W. 
Published: June 2004

AbstractIn bulk foams, the dependence of bubble size on time can be deduced from a hypothesis of statistical self‐similarity and the scaling characteristic of the volume change rate of a foam bubble. If this rate, \documentclass{article}\pagestyle{empty}\begin{document}$ {\dot v} $\end{document}, scales as the mean bubble volume v to the power α, the total surface area of the foam decreases as an inverse of time to the power 1/[3 (1 − α)]. Coarsening of polyhedral foam scales with α = 5/6, when molecular diffusion limits gas transport across lamellae and liquid drainage through Plateau borders limits lamella thinning. Excess liquid is released by disappearing small bubbles and flows into the lamellae and Plateau borders of growing large bubbles. If none of this liquid accumulates in the foam, coarsening is exponential and α = 1. When resistance to mass transfer at the lamella surfaces is the rate‐limiting step, polyhedral foam coarsens with α = 1/3. Coarsening of slowly draining, spherical‐bubble foam scales with α = 0. The theory is compared with nine measurements of the total surface area of polyhedral and spherical‐bubble foams pregenerated from aqueous solutions of sodium lauryl sulfate, hexadecyltrimethylammonium bromide, alpha‐olefin sulfonate with alkyl chain lengths from C14 to C16, and two shaving creams. The theory also proves that the collapse of a two‐dimensional, polygonal foam is self‐similar and scales with α = l. In all cases, our theory agrees well with experiment and numerical calculations.
Electrochemical measurements of mass transfer at surfaces with discrete reactive areas
Authors: Juhasz Nikola M. , Deen William M. 
Published: June 2004

AbstractThe limiting current technique was used to measure area‐averaged mass‐transfer coefficients for surfaces containing many small reactive areas arranged in various patterns. Partially masked platinum electrodes were fabricated using photolithography, and mass‐transfer measurements were performed with a rotating disk apparatus. The average mass‐transfer coefficient was sensitive to the fraction of the electrode area exposed (ε), declining from values near that for a fully exposed surface for ε = 0.5 to less than 1% of the fully exposed value for ε = 0.001. For any given ε, the mass‐transfer coefficient declined with increased spacing between reactive sites. The results were relatively insensitive to details of the site distribution, such as whether the sites were arranged in regular arrays (square or hexagonal lattices) or distributed randomly over the surface. For all conditions studied, the mass‐transfer coefficient greatly exceeded that predicted by conventional models which apply the stagnant film approximation to the fluid surrounding a representative active site. This finding is qualitatively consistent with recent computational results, which suggest that convective transport enhances mass transfer at partially active surfaces to an extent not accounted for by adjustments in the effective film thickness.
Initiation of slugs in horizontal gas‐liquid flows
Authors: Fan Z. , Lusseyran F. , Hanratty T. J. 
Published: June 2004

AbstractExperiments were conducted with air‐water flow in a horizontal 0.095‐m pipeline at atmospheric pressure to examine the mechanism by which slugs form in a stratified flow. A specially designed entrance box was used to avoid disturbances. In these experiments, at superficial gas velocities less than 3 m/s, the slugs are found to evolve from waves, with a length of about 0.085 m, that are generated by a Jeffreys mechanism. These waves grow in height and eventually double in wavelength by a nonlinear resonance mechanism. Depending on the height of the liquid, the growth can lead to a breaking wave or to a wave that fills the whole pipe cross section. At superficial gas velocities equal to or greater than 4 m/s capillary‐gravity waves with a wide range of lengths are generated by a linear Kelvin‐Helmholtz mechanism. These rapidly evolve into long waves outside the range of linear instability. If the liquid height is large enough, these waves can form slugs through a nonlinear Kelvin‐Helmholtz instability that is aided by wave coalescence.
Adsorption characteristics of octadecylsilyl‐silica gel in gaseous systems
Authors: Miyabe Kanji , Suzuki Motoyuki 
Published: June 2004

AbstractAdsorption rates and thermodynamic parameters were determined for the gasphase adsorption of n‐alkanes and benzene derivatives on octadecylsilyl‐silica gel (ODS) by chromatographic measurement and moment analysis. Thermodynamic characteristics of adsorption phenomena on ODS were similar to those on the surface. The contribution of intraparticle diffusion to mass‐transport resistance was dominant in the ODS column, and the role of surface diffusion was significant for the intraparticle diffusion. The values of the surface diffusion coefficient were of the order of 10−5 cm2/s and could be estimated by assuming that the surface migration on ODS is a tracer diffusion of an adsorbate molecule in n‐octadecane.
Thermophoretic and evaporational losses of ultrafine particles in heated flow
Authors: Shimada Manabu , Seto Takafumi , Okuyama Kikuo 
Published: June 2004

AbstractThe transport, wall deposition and evaporation of nanometer‐sized aerosol particles are studied using a nonisothermal laminar flow in a pipe. The test aerosol particles, monodisperse Ag and NaCl particles of 7–40 nm dia., are introduced into a vertical circular pipe with wall temperature distribution in the axial direction. The measured particle loss during transport through the pipe increased with the wall temperature difference. The enhancement of particle loss due to diffusive and thermophoretic deposition is examined by the gas flow, temperature, and particle concentration distribution equations. Predicted particle losses agreed with the experimental results when the local variation of gas properties, particle Brownian diffusion, and thermophoretic migration are considered. Sudden increases in the particle loss due to particle evaporation were also observed at very high temperatures (about 700°C for Ag particles and 400°C for NaCl particles). The measured reductions of particle diameter due to evaporation showed good agreement with calculation based on aerosol evaporation theory for free‐molecule regime.
Parametric study on the bulk hydraircooling of spherical food products
Authors: Rao K. V. Narasimha , Narasimham C. S. V. L. , Murthy M. V. Krishna 
Published: June 2004

AbstractA numerical study of the bulk hydraircooling of spherical food products is performed using the technique of spraying chilled water to form a thin film over the food products while blowing cold unsaturated air in the countercurrent or cocurrent direction. This precooling process is found to combine the advantages of hydro‐and air cooling.Governing equations describing the simultaneous heat and mass transfer occurring in the hydraircooling process for both counterflow and parallel‐flow arrangements are solved using finite‐difference numerical methods. A parametric study is performed to determine the effect of important processing parameters on the process time. It is generally observed that higher quantities of spray water, air‐mass flow rate and product thermal conductivity, as well as lower values of water temperature will result in faster rates of cooling. For the same operating conditions, parallel‐flow arrangement leads to higher plant capacities.
Procedure for regulatory control structure selection with application to the FCC process
Authors: Hovd M. , Skogestad S. 
Published: June 2004

AbstractControl structure (strategy) selection consists of the selection and pairing of manipulated and measured variables. This article outlines a procedure that uses such tools as the existence of right half plane (RHP) transmission zeros, the relative gain array, the performance relative gain array, and the closed‐loop disturbance gain. The regulatory control system for the fluid catalytic cracking process is used as an example. Several authors found the Kurihara control structure to be preferable to the conventional control structure. The reason is that RHP transmission zeros limit the achievable bandwidth for the conventional control structure. Two other control structures, however, have better controllability characteristics than both the conventional and the Kurihara control structures. The sensitivity of the measurement selection and variable pairing with respect to changes in the operating point and parametric uncertainty is examined, as well as the general objectives of the regulatory control level and its interaction with the higher levels in the control hierarchy.
Upper and lower limits of human skin electrical resistance in lontophoresis
Authors: Dinh Steven M. , Luo Ching‐Wang , Berner Bret 
Published: June 2004

AbstractThe time‐dependent electrical resistance of human cadaver skin was shown to be bound by an upper limit at equilibrium and a lower limit at steady state. The time to reach steady state from any initial condition by applying a current was much shorter than the recovery to equilibrium, due to different driving forces. The ratio of the equilibrium to the solution resistances increased with the salt concentration in free solution. This equilibrium relative resistance was sensitive to skin variability, primarily due to its dependence on porosity and pore geometry. A model was developed relating the equilibrium relative resistance to the structural properties of skin. The estimated pore radius of 25 × 10−10 m from the equilibrium resistance data is consistent with the average pore radius of human skin reported in the literature. In contrast, the steady‐state resistance could be several orders of magnitude lower than the equilibrium resistance and depended on current density and salt concentration but not on the history of prior exposures of a skin sample to a current. This difference can greatly reduce the power requirement for iontophoresis and can make this technology more practical. A linear relationship was found between the logarithm of the steady‐state relative resistance (skin/solution resistances) and the logarithm of the current density divided by the salt concentration. The slope of −0.65 was in excellent agreement with the theoretical slope of −2/3 that was derived for the convective transport of ions in a charged pore under a constant current.
Activated carbon adsorption and desorption of toluene in the aqueous phase
Authors: Chatzopoulos Dimitrios , Varma Arvind , Irvine Robert L. 
Published: June 2004

AbstractThe equilibrium and dynamics of toluene adsorption and desorption in singlecomponent aqueous solutions were investigated. Adsorption rates in a batch reactor under a variety of operating conditions were fitted successfully with the homogeneous surface diffusion model and a surface diffusion coefficient that increases exponentially with surface concentration. The dependence of the external mass‐transfer coefficient on the hydrodynamic conditions in the liquid phase was taken into account. Desorption studies in the aqueous phase and solvent regeneration of tolueneloaded activated carbon suggest that only a small fraction of toluene adsorbs irreversibly. Moreover, irreversible adsorption occurs only on virgin activated carbon, while adsorption on solvent‐regenerated activated carbon is fully reversible. After accounting for irreversible adsorption, the model successfully predicted toluene desorption rates in the aqueous phase under various operating conditions using toluene transport parameters determined from the adsorption studies.
Dynamic scaling of the cluster‐size distribul nucleation: Precoalescence stages
Authors: Shi Frank G. , Seinfeld John H. 
Published: June 2004

AbstractThe dynamic evolution of the cluster‐size distribution (CSD) in the precoalescence stages of nucleation and growth for sizes within and beyond the nucleation barrier layer (NBL) has been obtained. The existence of several universal kinetic laws of nucleation is predicted. In the precoalescence stages of nucleation, the CSD for sizes within and beyond the NBL obeys dynamic scaling relations. In a range of sizes beyond the NBL, the CSD exhibits a universal power law behavior, the exponent of which depends only on the interphase monomer transfer mechanism. Based on the results for the CSD, a general foundation is developed for nucleation kinetic measurements including the determination of the nucleation barrier and the inter‐facial monomer transport rate by measuring the CSD. A preliminary comparison with an experimental study confirms the predicted dynamic scaling and the power law behavior of the CSD in the early stages of nucleation and growth.
Modeling bubble and drop formation in flowing liquids in microgravity
Authors: Kim Ieehwan , Kamotani Yasuhiro , Ostrach Simon 
Published: June 2004

AbstractA theoretical model for the process of bubble and drop formation in flowing liquids, applicable for both terrestrial and microgravity environments, has been developed by using a force balance. The contact angle variation at the nozzle due to the bubble motion and the added mass coefficient of the bubble moving through a pipe have been theoretically analyzed, considering bubble motions during its expansion and detachment stages. Predictions of bubble size of the model show satisfactory agreement with available experimental results in the case of normal gravity. The effects of the nondimensional variables on bubble and drop size are evaluated in microgravity conditions. In microgravity, the bubble is detached from the nozzle only by the liquid flow drag, and in the region of low liquid velocity the bubble size becomes much larger than that in normal gravity.
Breakthrough of lysozyme through an affinity membrane of cellulose‐cibacron blue
Authors: Liu Hsien‐Chang , Fried J. R. 
Published: June 2004

AbstractThe dynamic affinity adsorption oflysozyme through stacked flat‐sheet cellulose membranes with immobilized cibacron blue 3GA was studied and compared to three affinity‐membrane models: diffusion model to explore the importance of axial and radial diffusion; variation model to study the effects of pore‐size distribution or thickness variation; and stack model to investigate the effects of stacking flat‐sheet membranes. For the diffusion model, when Per > 0.1, radial diffusional resistance is significant, but when Pez < 25, axial dispersion must be considered. For the variation model, increasing pore‐size distribution or nonuniform membrane thickness greatly broadens the breakthrough curve. The stack model shows that the stacking of membranes significantly sharpens the breakthrough curves by averaging out the flow dispersion due to pore‐size distribution or thickness variation.
Nonlinear inferential control of pulp digesters
Authors: Lee Jay H. , Datta A. K. 
Published: June 2004

AbstractMonitoring and control of batch pulp digesters, which convert wood chips to pulp by Kraft process are discussed. The Kappa number, which represents the extent of delignification, is the key controlled variable, which cannot be measured on‐line and must be estimated through secondary liquor measurements. Given a fixed batch time, the final Kappa number should be as close to the target Kappa number as possible, despite errors in the initial state estimates and input disturbances. To fulfill this objective, a state‐observer‐based model‐predictive controller is designed using a detailed nonlinear dynamic model of the digester. The extended Kalman filter (EKF) using on‐line measurements of various liquor characteristics is capable of recovering from significant errors in the initial state estimates. In addition, the EKF is shown to be robust to the errors in the covariance matrices and most model parameters, but quite sensitive to some model parameter errors. Coupled with the EKF, a finite‐horizon model predictive controller (MFC) based on successive linearization of the nonlinear pulping model, is found to work efficiently for controlling the Kappa number and batch time.
Tubular reactors for emulsion polymerization: I. Experimental investigation
Authors: Paquet D. A. , Ray W. H. 
Published: June 2004

AbstractExperimental results using a pulsed tubular reactor are presented. The use of a pulsation source eliminates the reactor fouling and plugging issue that has occurred in previous investigations. Startup data and steady‐state profiles are presented. Comparisons in monomer conversion and particle‐size distribution for batch, CSTR and tubular reactor are made. The influence of pulsation on the particle‐size dis‐tribution is discussed. It is shown that high‐conversion latex with a narrow particle size distribution can be produced continuously in the pulsed tubular reactor.