bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of shear‐dependent bacterial adhesion kinetics to biomaterial surfaces
Authors: Dickinson Richard B. , Cooper Stuart L.
Published: June 2004

A methodology and analysis is presented to quantitatively characterize bacterial attachment and detachment kinetics on biomaterial surfaces in a laminar flow field as a function of shear stress. The spatial distribution of adherent bacteria on the surface of a radial‐flow chamber is monitored via automated videomicroscopy with motorized three‐axis stage and focus control, allowing rapid automated measurement of the attached cell density as a function of time and radial position. Intrinsic rate constants for attachment and detachment are defined and estimated by fitting mathematical models to the resulting data. The model for cell attachment accounts for the global transport of cell in the chamber to estimate the cells concentration near the collector surface. The model for cell detachment accounts for heterogeneity in the adhesion energy of the attached cell population. These models yield first‐order attachment and detachment rate constants that intrinsically reflect the probabilities of bacteria attachment and detachment as a function of applied shear stress, depending on only the local interactions between the cell and the surface. The validity of each model was tested by statistical analyses of the goodness‐of‐fit to data that resulted from a study comparing adhesion of Staphylococcus aureus to three different polymeric surfaces of Varying surface properties and adhesive protein coatings.
Steady‐state modeling and experimental measurement of a baffled impeller stirred tank
Authors: Harvey Albert D. , Lee Cassian K. , Rogers Stuart E.
Published: June 2004

An approximate steady‐state method is devised for computing the flow field in a baffled, impeller‐stirred tank reactor. The flow field in a cylindrical tank with a 45° pitched‐blade impeller rotating at 100 rpm and four stationary rectangular side‐wall baffles is simulated using a new approximate steady‐state approach. The method provides an alternative to a full unsteady Navier‐Stokes simulation. The new steady‐state analysis involves accurately defining the geometry of the mixing tank using a multiblock grid technique. The flow is solved from a rotating frame of reference for a single position of the impeller relative to the side‐wall baffles. The steady‐state numerical results are then spatially averaged and compared with time‐averaged data obtained experimentally using laser Dopler velocimetry (LDV). Spatially averaged numerical predictions obtained using this approximate steady‐state method for the radial and axial velocity components agree well with the LDV data. The predicted magnitude of the tangential velocity component, however, is higher than the experimentally measured values. Closer agreement of the tangential velocities with experimental values is obtained using a finer grid and it is found that a relatively fine grid is needed for accurately predicting the tangential velocity magnitude. Use of this approximate steady‐state method allows designers of mixing vessels to obtain flow‐field results for baffled vessels much more efficiently than using full unsteady Navier‐Stokes simulations.
Numerical computation of turbulent gas‐solid particle flow in a 90° bend
Authors: Tu J. Y. , Fletcher C. A. J.
Published: June 2004

A numerical computation of the LDV results of Kliafas and Holt is reported for a turbulent gas‐solid particle flow in a square‐sectioned 90° bend. A Eulerian model with generalized Eulerian solid surface boundary conditions for the particulate‐phase momentum exchanges with solid walls are included. The turbulent closure is effected by using the gas‐phase RNG‐based k‐ϵ turbulence model, and the particulate turbulence diffusivity is related to the turbulent viscosity of the gas phase. Comparisons are made with experimental data for the mean streamwise velocities of both phases, the streamwise turbulence intensity of the gas phase, and the particulate concentration distribution in the bend. The localized high particulate concentration near the outer curve of the bend that occurs at large Stokes number is accurately predicted. Empirical computational evidence is presented for a relaxation of the minimum particle number density required to allow the use of a continuum model.
Activity coefficients in nearly athermal model polymer/solvent systems
Authors: Sheng Yu‐Jane , Panagiotopoulos Athanassios Z. , Tassios Dimitrios P.
Published: June 2004

Constant pressure Monte Carlo simulations were performed to study the activity coefficients of bead‐spring polymers dissolved in a monomeric solvent. Activity coefficients were obtained for binary mixtures of monomer and 20‐mer for compositions ranging from pure 20‐mer to pure solvent, using the chain increment method to obtain the chemical potentials of long‐chain solute and monomeric solvent. Infinite dilution activity coefficients were also calculated for polymeric solutes in monomeric solvents and monomeric solutes in polymeric solutes in monimeric solvents and monomeric solutes in polymeric solvents solutions with chain length up to 60. Such detailed information on activity coefficnets in polymer/solvent systems with large size differences had not been available previously from simulation or experiment. Several engineering models were tested for their ability to predict the activity coefficients in these nearly athermal systems. Results indicate that simple free‐folume models can provide us with qualitatively accurate predictions for both short‐chain solvent and long‐chain solutes, provided that the functional form of the free‐volume dependence is chosen appropriately.
A mathematical model for a dissolving polymer
Authors: Edwards David A. , Cohen Donald S.
Published: June 2004

In certain polymer‐penetrant systems, nonlinear viscoelastic effects dominate those of Fickian diffusion. This behavior is often embodied in a memory integral incorporating nonlocal time effects into the dynamics; this integral can be derived from an augmented chemical potential. The mathematical framework presented is a moving boundary‐value problem. The boundary separates the polymer into two distinct states: glassy and rubbery, where different physical processes dominate. The moving boundary condition that results is not solvable by similarity solutions, but can be solved by perturbation and integral equation techniques. Asymptotic solutions are obtained where sharp fronts move with constant speed. The resultant profiles are quite similar to experimental results in a dissolving polymer. It is then demonstrated that such a model has a limit on the allowable front speed and a self‐regulating mass uptake.
Maximum likelihood data rectification: Steady‐state systems
Authors: Johnston Lloyd P. M. , Kramer Mark A.
Published: June 2004

A maximum likelihood rectification (MLR) technique that poses the data‐rectification problem in a probabilistic framework and maximizes the probability of the estimated plant states given the measurements is proposed. This approach does not divide the sensors into “normal” and “gross error” classes, but uses all of the data in the rectification, each sensor being appropriately weighted according to the laws of probability. In this manner, the conventional assumption of no sensor bias is avoided, and both random errors (noise) and systematic errors (gross errors) are removed simultaneously. A novel technique is introduced that utilizes historical plant data to determine a peior probability distribution of the plant states. This type of historical plant information, which contains the physical relationships among the variables (mass balances, energy balances, thermodynamic constraints), as well as statistical correlations among the variables, has been ignored in prior data‐rectification schemes. This approach can use the historical plant information to solve a new class of data‐rectification problems in which there are no known model constraints. The MLR method is demonstrated on data from a simulated flow network and a simulated heat‐exchanger network. The MLR technique provides considerably improved performance over existing data‐reconciliation schemes in these examples.
Synthesis of separation system flowsheels
Authors: Douglas J. M.
Published: June 2004

A hierarchical decision procedure for the synthesis of separation system flowsheets for vapor–organic liquid– aqueous liquid– solid mixtures is proposed. An expanded set of synthesis rules that can be used to obtain a first design is discussed, but the final goal of the procedure is to generate a complete list of separation alternatives (by changing the decisions) that when coupled with short‐cut screening techniques, can be used to identify the best few process flowsheets. The procedure is based on a decomposition of the separation system synthesis problem by phase splitting into a vapor recovery system, a solid recovery system, and liquid separation systems. A general superstructure presented for these subsystems includes all of the common unit operations for petrochemical processes. The procedure focuses on the development of a complete flowsheet for the separation system: which separation system recycle loops (in contrast to reactor system recycle loops) are required, as well as interactions among separation subsystems and those between the separation system and remainder of the process. An example presented illustrates the procedure, and the opportunities for pollution prevention at the source are noted.
Electrochemically modulated complexation process for gas removal and concentration
Authors: Terry Patricia A. , Walis H. Jeremy , Noble Richard D. , Koval Carl A.
Published: June 2004

An electrochemically modulated complexation process was designed to extract and concentrate a gas‐phase solute. The process was based on flowthrough electrolysis cells that electrochemically modulate a liquid‐phase mass‐transfer agent between high and low solute affinity forms. The liquid phase in the high‐affinity form contacts a feed gas phase for the extraction and contacts the receiving gas phase in the low‐affinity form. The chemical system used to demonstrate the general process was a Cu(II)/Cu(I) redox couple in an acidic chloride electrolyte to both concentrate carbon monoxide against a pressure gradient and selectively separate it from a mixture with nitrogen. Experimental results and modeling of this process are reported. The kinetics of the electrolysis reactions in the flow cells are discussed within the context of rotating ring disk voltammetry experiments.
Modeling and dynamic simulation of a bleach plant
Authors: Wang R. X. , Tessier P. J.‐C. , Bennington C. P. J.
Published: June 2004

A dynamic model of five‐stage (C+D)EDED bleach plant was developed using SIMNON a dynamic simulation language developed at Lund Institute of Technology, as a platform. The model is composed of individual modules that represent each bleaching stage. Each module includes chemical addition and mixing, diffusion and reaction in a retention towel, and washing. These unit operations are coupled with chemical kinetics for each bleaching stage using appropriate models. A relationship between the (C+D)E Kappa number and the input absorption coefficient to the D1 stage was used to link the delignification and brightening partial sequences of the bleach plant. The model, verified using steady‐state data, was used to model the dynamic response of the plant to step changes in production rate, (C+D) chemical addition, and incoming Kappa number, as well as the open‐loop response of the plant to a simulated variation in incoming Kappa number. The modular structure of the program allows a variety of bleach plants to be assessed once flow parameters and chemical kinetics are known. The dynamic model can also be used to develop and compare control strategies before being implemented at the mill.
Asphalt flocculation and deposition: I. The onset of precipitation
Authors: Rassamdana Hossein , Dabir Bahram , Nematy Mehdi , Farhani Minoo , Sahimi Muhammad
Published: June 2004

Formation of asphalt aggregates and their deposition on the pore surfaces of a porous medium, which alter the structure of the medium and its effective properties, is a critical problem to catalytic and oil recovery and refinery processes. Extensive new experimental data for the amount of precipitated asphalt formed with crude oil and various solvents are presented. Results indicate that, contrary to the previous assumptions, asphalt formation is at best partially reversible. A thermodynamic model based on the Flory–Huggins theory of polymer solutions is used, together with the Soave equation of state, to predict the data. Critical evaluation of the model shows that its predictions do not agree well with our data. As an alternative, we propose a new model that employs a scaling equation, somewhat similar to those encountered in aggregation and gelation phenomena. The scaling function takes on a very simple form, and its predictions are in very good agreement with the data. It also predicts that the onset of precipitation may obey a simple universal equation.
Velocity profiles in a baffled vessel with single or double pitched‐blade turbines
Authors: Armenante Piero M. , Chou Chun‐Chiao
Published: June 2004

A laser‐Doppler velocimetry (LDV) apparatus and a computational fluid dynamic (CFD) software package (FLUENT) were used to experimentally determine and numerically predict the velocities in a baffled vessel agitated by one or two 45° pitched‐blade turbines. The flow characteristics in the impeller regions were measured by LDV and used as boundary conditions in the numerical computations. Turbulence effects were simulated using either the k‐ε model or algebraic stress model (ASM). The CFD predictions were compared to the LDV measurements in terms of average velocities in all three directions as well as turbulent kinetic energies. Predictions based on ASM were typically in closer agreement with the experimental data than those based on the k‐ε model. Flow patterns in both configurations were dominated by the axial and tangential components. The presence of the upper impeller altered the flow considerably, producing a strong vertical recirculation pattern between the impellers and significantly reducing the circulation flow below the lower impeller.
Journal review. Azeotropic distillation
Authors: Widagdo Soemantri , Seider Warren D.
Published: June 2004

Recent and ongoing research in the distillation of nonideal mixtures is reviewed focusing on advances in the methodologies for the synthesis, design, analysis and control of separation sequences involving homogeneous and heterogeneous azeotropic towers. Maps of residue curves and distillation lines are examined, as well as geometric methods for the synthesis and design of separation sequences, trends in the steady‐state and dynamic analysis of homogeneous and heterogeneous towers, the nonlinear behavior of these towers, and strategies for their control.

Emphasis is placed on the methods of computing all of the azeotropes associated with a multicomponent mixture, on the features that distinguish azeotropic distillations from their zeotropic counterparts, on the potential for steady‐state multiplicity, and on the existence of maximum and minimum reflux bounds. Important considerations in the selection of entrainers are examined. For the synthesis of separation trains, when determining the feasible product compositions, the graphical methods are clarified, especially the conditions under which distillation boundaries can be crossed and bounding strategies under finite reflux. The application of geometric theory to locate the fixed points, at minimum reflux, is reviewed in connection with homotopy‐continuation algorithms for this purpose. The use of homotopy‐continuation algorithms, especially for the steady‐state simulation of heterogeneous azeotropic distillations, is justified. Methods for phase stability analysis are reviewed in connection with the location of real bifurcation points at phase transitions, an important feature of algorithms for the dynamic simulation of heterogeneous azeotropic distillations.
Drying with internal heat generation: Theoretical aspects and application to microwave heating
Authors: Constant T. , Moyne C. , Perré P.
Published: June 2004

A model of simultaneous heat and mass transfer presented describes drying with internal heat generation. Since a liquid expulsion phase is observed, a numerical procedure was developed to account for saturated and unsaturated zones and to model the liquid expulsion. The model was validated by a drainage experiment. An experimental rig was built to conduct microwave drying experiments in well‐controlled conditions using capillary porous body (light concrete) as test material. Two types of drying (high and low power) were distinguished, depending on whether or not boiling occurred in the sample. The heat source term in the medium was determined from the experimental results. The numerical results agree with the experimental observations in terms of drying kinetics and transfer mechanisms. This allows a very accurate description of the transport phenomena and the liquid expulsion phase associated with high‐power drying.
Adsorption of carbon monoxide on activated carbon impregnated with metal halide
Authors: Tamon Hajime , Kitamura Kenji , Okazaki Morio
Published: June 2004

Activated carbon was impregnated with a metal halide, and adsorption and desorption characteristics of CO on the carbon were measured by fixed‐bed runs. It was found that the impregnation of PdCl2 or CuCl effectively increases CO absorption. PdCl2/CuCl‐impregnated carbons were characterized by N2 adsorption, SEM, EPMA, and XPS. Adsorption isotherms of CO were also measured on these carbons, and the influence of the loading of impregnant on CO adsorption was experimentally elucidated. A selection procedure of impregnant was proposed based on the frontier orbital theory. The perturbation energy for molecular orbital mixing was estimated by the HOMO – LUMO interaction. CO adsorption on impregnated carbons was qualitatively interpreted using the perturbation energy, and the energy was regarded as an index of impregnant selection.
Predictive control of quality in batch polymerization using hybrid ANN models
Authors: Tsen Andy Yen‐Di , Jang Shi Shang , Wong David Shan Hill , Joseph Babu
Published: June 2004

Two issues involving the methodology used for on‐line control of product quality in batch manufacturing processes are addressed: the generation of fast, data‐driven process models and the use of such process models for on‐line feedback control of product quality. The methodology is investigated using the example of the control of dispersity and molecular weight distribution in a batch reactor for emulsion polymerization of vinyl acetate. An artifical neural network (ANN) is used as a model to predict the quality as a function of the manipulated variables and on‐line measurements. This model is constructed using an augmented dataset that integrates experimental information and knowledge from a mathematical model. The proposed model is compared with other types such as a theoretical model whose key parameters are fitted to experimental data. The hybrid ANN is superior to the parameter‐fitting approach for this case. Experimental and simulation studies confirm the advantage of using the proposed model and the predictive control algorithm.
Radiative transfer in photocatalytic systems
Authors: Pasquali Matteo , Santarelli Francesco , Porter John F. , Yue Po‐Lock
Published: June 2004

Radiation absorption at the surface of catalytic particles is the initial step of photocatalytic oxidation reactions currently considered for their potential effectiveness in the treatment of polluted water with traces of highly toxic organics. Owing to the presence of catalyst particles within the fluid phase, the radiation field within a photocatalytic reactor results from the absorption and scattering within the participating medium. An annular reactor with a coaxial central lamp was considered, and the resulting 2‐D radiation field was analyzed using a Monte Carlo technique to solve the radiative transfer equation. Results are discussed based on the relevant optical parameters, and a heuristic is derived for the design and rating of a photocatalytic reactor. To exploit the reaction volume effectively, the order of magnitude of the optical thickness should be close to unity, and for a given value of the absorption coefficient the catalyst with the lowest albedo should be selected; however, a precise evaluation of the phase function is not crucial to a relable representation of the radiation field.
Phase equilibria and volumetric properties of aqueous CACl2 by an equation of state
Authors: Jiang Shaoyi , Pitzer Kenneth S.
Published: June 2004

A comprehensive equation of state was developed to represent the phase equilibria and volumetric properties of aqueous calcium chloride solutions at temperatures above 523 K. The equation consists of a reference part and a perturbation contribution. The reference function is developed from the statistical mechanical theory for mixtures of dipolar and quadrupolar hard spheres, which agrees well with the Monte Carlo simulation results. In this treatment, calcium chloride is described by the completely undissociated model. The empirical perturbation function is a truncated series of virial expansion terms. Thus, mixing rules are guided by those of virial coefficients, which are derived rigorously from statistical mechanics. The equation reproduces experimental saturated vapor pressures and volumetric data within experimental uncertainty for temperatures to 623 K. At higher temperatures, few and less accurate experimental data are available, but values of the saturated vapor pressures of the liquid have been reported and are represented satisfactorily.
Leveling of a film with stratified viscosity and insoluble surfactant
Authors: Joos F. Miguel
Published: June 2004

The evolution of a film with insoluble surfactant on a wavy horizontal wall differs from flow without surfactant (the way it usually is studied) in that the film passes through different stages. The first stage is as if the surfactant were absent. Once the surface tension gradient—induced by the nonuniform surfactant concentration adsorbed at the free surface—starts resisting the flow effectively, the evolution enters a transitional stage. A final stage is reached once the free surface becomes rigid due to the surface‐tension gradient (high elasticity limit) or becomes virtually leveled before the surface‐tension gradient is released (low elasticity limit). The velocity profile through the film changes with time, sol fluid is depleted or accumulated at different strata in the film as the flow evolves. The velocity profile and resulting deformations throughout the film can be influenced significantly by the viscosity distribution or stratification, which occurs, for example, when multiple layers of different viscosity are coated simultaneously. A model and applications for the leveling of such a film are presented. The evolution is described in general terms for a film of uniform viscosity and for a film of two discrete layers of different viscosity. Then the three limiting cases are established. For two of these limits, the effect on the exponential decay rate of the flow and the deformation of the different strata or layers is examined when the viscosity is changed in an infinitesimally thin layer or stratum, and in a layer of finite thickness in films of two and three discrete layers.
Absorption of chlorine into aqueous bicarbonate solutions and aqueous hydroxide solutions
Authors: Ashour Sami S. , Rinker Edward B. , Sandall Orville C.
Published: June 2004

The absorption of Cl2 into aqueous bicarbonate and aqueous hydroxide solutions was studied both experimentally and theoretically. The rate coefficient of the reaction between Cl2 and OH− was estimated over the temperature range of 293–312 K and fitted by the Arrhenius equation:

.

If Cl2 were assumed to react only with water and OH− in an aqueous bicarbonate solution, the predicted absorption rate would be much lower than that experimentally measured. This suggests that Cl2 reacts with HCO3− in an aqueous bicarbonate solution. The rate coefficient of the reaction between Cl2 and HCO3− was estimated over the temperature range of 293–313 K and fitted by the Arrhenius equation:

.

More importantly, under absorption conditions, the amount of hydroxide consumed for absorbing a specific amount of Cl2 into an aqueous hydroxide solution is almost twice the amount of bicarbonate consumed for absorbing the same amount of Cl2 into an aqueous bicarbonate solution.
Thermal frequency response method for the study of mass‐transfer kinetics in adsorbents
Authors: Bourdin V. , Grenier Ph. , Meunier F. , Sun L. M.
Published: June 2004

The frequency response method measuring the temperature and pressure of an adsorbent sample determines the mass‐ and heat‐transfer kinetics in adsorbents, especially in zeolites. The temperature of the sample (large crystals or monolayers of pellets) is measured by infrared detection. The main aspects of the in‐phase and out‐of‐phase functions as given by an analytical bidispersed model are described. They depend on characteristic times related to kinetic paprameters. Experimental results on adsorption of water on NaX zeolite (crystals or pellets) show that this method allows heat transfer to be very clearly delineated from mass‐transfer modes and the separation of different mass‐transfer modes. For a bidispersed sample, macro‐ and microporous mass‐transfer parameters may be obtained with the same sample. Results on a contaminated 5A zeolite‐propane system show the presence of mass‐transfer resistance at the pellet surface. The infrared temperature measurement associated with the frequency response appears to be powerful in determining kinetic adsorption, and gives more information than the pressure measurement.
Adsorption of associating molecules in micropores and application to water on carbon
Authors: Talu Orhan , Meunier Francis
Published: June 2004

A general theory for the adsorption of self‐associating molecules in microporous structures is developed. The approach is similar to the “chemical” interpretation of nonideality of vapor and liquid phases. The theory displays Type 5 isotherm behavior and can explain Types 1 and 5 transition. Isothermal data are represented by only three parameters: Henry's law constant, saturation capacity, and reaction constant for “cluster” formation in the micropores. When isotherms at different temperatures are available, the theory can be used with five temperature‐independent parameters to describe the entire phase behavior including the heat of adsorption. Water adsorption on activated carbon, the most common display of Type 5 behavior, is used to test the theory. Analysis of several data sets indicates that the theory can closely correlate data, provide physically meaningful parameter values in line with carbon properties, and it is highly effective in correlating temperature variation. The reaction enthalpy for water dimerization in the carbon micropores is lower than that in vapor phase. This preliminary conclusion with the theory needs to be supported with more accurate data when available.
Effects of mixing on the composition and morphology of tissue‐engineered cartilage
Authors: Vunjak‐Novakovic Gordana , Freed Lisa E. , Biron Robert J. , Langer Robert
Published: June 2004

Cartilage constructs were grown using isolated chondrocytes and biodegradable polymer scaffolds made of fibrous polyglycolic acid in the form of 1‐cm‐dia × 5‐mm‐thick discs. The scaffolds were seeded in a mixed cell suspension and cultured for up to 8 weeks under static or mixed tissue culture conditions in petri dishes and spinner flasks. Turbulent mixing significantly improved the biochemical compositions and altered morphologies of the cartilage constructs, which were the thickest ones cultured to date in vitro. Constructs from mixed cultures were more regular in shape and contained up to 70% more cells, 60% more sulfated glycosaminoglycan, and 125% more total collagen when compared to constructs from static cultures. Mixing also induced the formation of an outer capsule with multiple layers of elongated cells and collagen fibrils around the inner tissue phase, while statically grown constructs consisted of round cells embedded in cartilaginous matrix. Mixing during cell seeding and tissue culture is thus an important parameter for the cultivation of tissue‐engineered cartilage in a range of sizes, shapes and compositions for a variety of clinical applications (e.g., fibrous cartilage for reconstructive surgery or articular cartilage for joint resurfacing).
Fickian diffusion in binary mixtures that form two liquid phases
Authors: Pertler Manfred , Blass Eckhart , Stevens Geoffrey W.
Published: June 2004

New data on the variation of the diffusion coefficient with concentration in binary nonideal liquid mixtures are presented. The diffusion coefficients were measured with laser holography with an improved analysis procedure and are primarily in systems that form two liquid phases. The results show that for such systems the diffusion coefficient is constant if a chemical‐potential driving force is used. If, however, the miscibility gap is wide, the Schreiner equation (Schreiner, 1922) is shown to be more accurate than relations that consider the variation of viscosity. Cluster theories developed for diffusion behavior near critical points were found to explain the data well only in water‐organic systems on the water‐rich side.
Wall effects on the sedimentation velocity of suspensions in viscous flow
Authors: Di Felice Renzo , Parodi Enrico
Published: June 2004

The sedimentation velocity of multiparticle suspensions was investigated experimentally for cases where the column wall is likely to have a nonnegligible effect. The experiments demonstrate that the container wall diameter influeces the falling velocity only for dilute systems, which is in contrast with a widely used, established empirical relationship.
Absorption‐induced separations in oscillatory liquid chromatography
Authors: Van Lishout Yolanda M. M. , Leighton David T.
Published: June 2004

It has been shown that small‐amplitude oscillations can augment the diffusional flux across a cylindrical tube by several orders of magnitude through Taylor–Aris dispersion phenomena (Aris, 1960). This enhancement in mass transport is selective for species with different molecular diffusion coefficients. This article shows that by coupling fluid oscillations with a reversible absorption in a stationary phase, the transport of species, which have similar molecular diffusivities but different affinities for the stationary phase, can be enhanced selectively. We developed analytical and asymptotic solutions to the enhancement of mass transfer as a result of the interaction between reversible absorption and fluid oscillations in a cylindrical tube. These results were qualitatively confirmed by experiments with a model system. For purely oscillatory flow, the maximum selectivity (the ratio of the fluxes of the species to be separated) achievable is 4.4 for solute species with widely different affinities for the stationary phase. The superposition of a small‐amplitude steady backflow, however, can greatly increase the selectivity, but at the expense of throughput. Analysis shows that this technique may offer improvements relative to conventional liquid membrane separations, if the solute affinities for the stationary phase do not greatly differ or if a thick membrane is required for stability.
Statistical process monitoring and disturbance diagnosis in multivariable continuous processes
Authors: Raich Anne , Çinar Ali
Published: June 2004

Detecting out‐of‐control status and diagnosing disturbances leading to the abnormal process operation early are crucial in minimizing product quality variations. Multivariate statistical techniques are used to develop detection methodology for abnormal process behavior and diagnosis of disturbances causing poor process performance. Principal components and discriminant analysis are applied to quantitatively describe and interpret step, ramp and random‐variation disturbances. All disturbances require high‐dimensional models for accurate description and cannot be discriminated by biplots. Diagnosis of simultaneous multiple faults is addressed by building quantitative measures of overlap between models of single faults and their combinations. These measures are used to identify the existence of secondary disturbances and distinguish their components. The methodology is illustrated by monitoring the Tennessee Eastman plant simulation benchmark problem subjected to different disturbances. Most of the disturbances can be diagnosed correctly, the success rate being higher for step and ramp disturbances than random‐variation disturbances.
The kinetics of carbonyl formation in asphalt
Authors: Liu Meng , Lunsford K. M. , Davison R. R. , Glover C. J. , Bullin J. A.
Published: June 2004

The oxidation of asphalt is a major cause of pavement failure. The low‐temperature oxidation kinetics of 14 asphalts are presented. At constant temperature and oxygen presure, asphalt oxidation occurs in two stages: (1) a relatively rapid‐rate period, followed by (2) a long period of constant rate. Activation energies for the constant‐rate region vary from 64 to 109 kJ/mol, and reaction orders relative to oxygen pressure vary from 0.25 to 0.61. This variation in activation energy and reaction order leads to skepticism regarding the present practices of evaluating road‐condition asphalt‐hardening rates at a single elevated temperature and perhaps at an elevated pressure. The asphalts occur in essentially two groups, one at high values of both activation energy and reaction order and the other at low values of each. The data indicate the existence of an isokinetic temperature near 100°C. The degree of oxidation that occurs during the initial rapid‐rate region varies inversely with the oxygen reaction order of the constant‐rate region.
Stability of the ignited state in packed‐bed reactor
Authors: Viljoen H. J. , Everson R. C.
Published: June 2004

The ignited state is associated with a thin reaction zone and a steep temperature gradient ahead of the front. The stability of this front is analyzed for small radial and azimuthal perturbations. The near‐equidiffusional assumption is made, and the deviation of the Lewis number from unity is considered as the bifurcation parameter. The analysis shows that the planar front becomes unstable at Lewis numbers above unity after a Hopf bifurcation. The oscillatory front collapses into hot spots or rings which oscillate around the axial axis. For Lewis numbers less than one, a steady‐state cellular front structure is found.
Hydraulic permeability of agarose gels
Authors: Johnson Erin M. , Deen William M.
Published: June 2004

A new technique was developed to measure the hydraulic permeability of reinforced gel membranes and allows calculation of the Darcy permeability (κ) of the gel. It was applied to agarose with concentrations ranging from 2.0 to 7.3%. To create membranes that would be thin enough to yield easily measured filtration rates at modest applied pressures and yet withstand handling, gels were cast on woven polyester meshes. The resulting membranes had thicknesses of 70–100 μm and a fractional open area of 0.32. To correct for the presence of the mesh, finite‐element solutions were obtained for the pressure field in the 3‐D region occupied by the gel. For the meshes used here, the hydraulic permeability of the reinforced membrane was calculated to be 0.47–0.55 times that for a layer of pure gel, the exact value depending on the thickness of the composite membrane. The principal determinant of κ was the agarose concentration, but there was a secondary effect of applied pressure. The Darcy permeability extrapolated to zero applied pressure (κ0) varied from 616 nm2 for 2.0% agarose to 22 nm2 for 7.3% agarose. At a given gel concentration, the value for κ0 was as much as twice the value for κ measured at the maximum pressure difference of 20 kPa. This method can be adapted to a variety of other gel materials.
In‐situestimation of MOCVD growth rate via a modified Kalman filter
Authors: Woo Wilbur W. , Svoronos Spyros A. , Sankur Haluk O. , Bajaj Jagmohan , Irvine Stuart J. C.
Published: June 2004

In‐situ laser reflectance monitoring of metal‐organic chemical vapor deposition (MOCVD) is an effective way to monitor growth rate and expitaxial layer thickness of a variety of III–V and II–VI semiconductors. Materials with low optical extinction coefficients, such as ZnTe/GaAs and AlAs/GaAs for a 6328 Å HeNe laser, are ideal for such an application. An Extended Kalman filter modified to include a variable forgetting factor was applied to the MOCVD systems. The filter was able to accurately estimate thickness and growth rate while filtering out process noise and cope with sudden changes in growth rate, reflectance drift, and bias. Due to the forgetting factor, the Kalman filter was successful, even when based on very simple process models.
Convective transport about cylinder with surface reaction of arbitrary order
Authors: Nguyen Hoa D. , Paik Seungho , Douglass Rod W.
Published: June 2004

Heat and mass transfer from a circular cylinder exposed to a convective environment with a surface reaction of arbitrary order is studied based on the stream function‐vorticity formulation. A hybrid numerical scheme combining the Fourier spectral method in the angular direction and the spectral element method in the radial direction is used to solve the conservation equations along with an influence matrix technique to resolve the vorticity boundary conditions. Results showing the temporal evolution of the flow, temperature and concentration fields are presented for cases with and without vortex shedding with the latter triggered by the cylinder's rotation. A parametric study is also performed to examine the influence of the Reynolds number, Grashof number, Prandtl number, Schmidt number, Damköhler number, the reaction order, the flow alignment, the heat of reaction, the rotational velocity and the flow pulsation on the effectiveness of the reaction surface. With the exception rotation, they all exhibit strong dependence.
Electrostatic effect on the flow behavior of a dilute gas/cohesive particle flow system
Authors: Zhang Yu‐Feng , Yang Yi , Arastoopour Hamid
Published: June 2004

Cohesive (Group C) particles have been widely used in various industries. To handle and process such fine particles, a clear understanding of the flow behavior and interparticle force, is needed. To achieve that objective, a Laser Doppler Anemometer system was used to measure particle velocity, fluctuating velocity, and size and extent of agglomeration or cluster formation of particles in a dilute gas/fine oil shale particle flow system with particle density of 2,082 kg/m3, average particle volumetric concentration of 1.5%, and average particle mass flux of about 100 kg/m2·s in a controlled‐moisture environment. The flow behavior of the particles was also studied for a mixture of 99% shale particles and 1% antistatic agent (Larostat powder, a quaternary ammonium compound) to examine the role of electrostatic force in gas/cohesive particle flow behavior. The addition of Larostat powder significantly reduced the electrostatic force and, in turn, made Group C particles behave similar to Group A or in some cases to Group B particles. In addition, our experimental data showed that the Maxwellian distribution function is a reasonable assumption to describe the velocity probability density function of the shale particles with or without antistatic agents.
Statistics of multiple particle breakage
Authors: Hill Priscilla J. , Ng Ka M.
Published: June 2004

A method for generating theoretical breakage distribution functions for multiple particle breakage is presented. It starts with the joint probability function that accounts for all the child particles; it is then reduced to the marginal probability function commonly used in the breakage equation. This method is flexible enough to allow the user to choose the number of child particles and the functional form to be used. The method is demonstrated with both product and summation functions with a power‐law form. To facilitate the use of these theoretical functions for statistical analyses, a companion discretized breakage equation is developed. The new equation guarantees the conservation of mass and correct prediction of the total number of particles despite discretization. It is easy to use because it is a set of ordinary differential equations and applicable to both equal‐size and geometric‐size intervals. Simulation results show that different breakage distribution functions coupled with different breakage rates can produce almost indistinguishable particle‐size distributions, signifying the need for further work in this area.
Coagulation and fragmentation: Universal steady‐state particle‐size distribution
Authors: Spicer Patrick T. , Pratsinis Sotiris E.
Published: June 2004

A population balance model presented describes simultaneous coagulation and fragmentation during shear‐induced flocculation. Given sufficient time, a floc‐size distribution reaches steady state that reflects the balance between coagulation and fragmentation. The model agrees with experimental data for the evolution of the average floc size. Higher shear shifts the steady‐state size distribution to smaller sizes. When the steady‐state size distributions obtained at various shear rates are scaled with the average floc size, however, they collapse onto a single line. This indicates that the steady‐state floc‐size distribution is self‐preserving with respect to fluid shear. This distribution is universal for the employed coagulation and fragmentation rates provided that less than 5% (by number) of the particles remain unflocculated. This result is supported with experimental data on shear‐induced flocculation of polystyrene particles, although a detailed quantitative comparison is limited by the irregular structure of the flocs.
Modeling thermal regeneration of wall‐flow diesel particulate traps
Authors: Koltsakis Grigorios C. , Stamatelos Anastasios M.
Published: June 2004

Stricter emission control legislation for diesel use has been increasing interest in highly efficient wall‐flow particulate filters. The mathematical modeling of the filter regeneration process is indispensable in developing reliable and durable trap systems for various applications. Although modeling of wall‐flow filters has been investigated extensively, significant problems still exist in the correlation of modeling results with measurements. This article describes an improved modeling and model tuning approach. A classical zero‐dimensional regeneration model, modified to account for incomplete soot oxidation effects, is discussed, and existing and novel methods of estimating trap loading, crucial in all modeling applications, are compared. The design of a model tuning approach based on full‐scale experiments is highlighted with examples of model predictions during trap failure that show capabilities of supporting the design of trap protection techniques. Applications to regeneration rate control, filter sizing and the development of on‐board diagnostics are demonstrated with examples. Dimensional analysis is used for the concise quantitative evaluation of the parameters affecting the evolution of the regeneration process.
Two‐dimensional modeling of electroremediation
Authors: Jacobs Richard A. , Probstein Ronald F.
Published: June 2004

A mathematical model and numerical code for the simulation of contaminant removal from soils by electric fields are applied in two dimensions. The model describes the coupled transport of mass and charge, and the chemical speciation of a multicomponent system subjected to an electric field. Transport mechanisms included are electroosmosis, pressure‐driven convection, electromigration, and diffusion. The model can also describe complexation, dissolution and precipitation reactions, surface complexation and sorption processes, and electrochemical reactions. Chemical and sorption equilibria are assumed. Transport equations used are based on quantities conserved throughout chemical reactions so that only the time scales of transport processes need to be resolved. The model is used to simulate the removal of phenol from kaolin clay for which experiments are presented. The successful explanation of the experimental observations confirms the theoretical bases of the model.
Study of polymer melt flow in sequential injection molding process
Authors: Chen S. C. , Chen N. T. , Hsu K. S. , Hsu K. F.
Published: June 2004

Experimental studies of polymer melt flow in the filling and post‐filling stages of the injection molding process were performed using the sequential injection of transparent and colored polystyrene resin. Effects of fountain flow in the filling stage, geometrical factors caused by edges and corners, as well as flow through contractions and expansions, were identified. Significant polymer melt flow which increases with increased packing pressure was observed in the post‐filling process. The melt flow is more concentrated around the gate area than away from the gate. It was also found that the polymer melt flows across the gap center, resulting in partial annihilation of the weld line. Simulations based on the control‐volume/finite‐element method employed within each gapwise layer combined with the dual‐filling‐parameter technique were developed to trace the advancements in melt fronts for both skin and core materials. Numerical simulations show reasonable consistency with experimental results in both skin and core material distribution. If the edge effect is taken into account using a shape factor as a geometrical correction, the simulation accuracy is further improved.
Effect of powder bed on critical heating rates for thermolysis of ceramic injection moldings
Authors: Song Jin‐Hua , Evans Julian R. G. , Edirisinghe Mohan J. , Twizell E. H.
Published: June 2004

The mass transport during pyrolysis of the degradation product of a polymeric binder used for ceramic molding is analyzed. Two series resistances to transport are incorporated: the diffusion of the product of degradation through its parent polymer during decomposition and the permeation of vapor through a static powder bed used to support the molding. The model predicts the critical rate of heating, Zc, above which defects caused by boiling of the organic phase occur at the center of the molding. For the system modeled, the permeability of the powder bed has little effect on Zcif the moldings are small but this is not the case for large moldings where well‐packed fine powders should be avoided and the thickness of the powder bed should be kept to a minimum.
Thermodynamic micellizatin model of asphaltene precipitation from petroleum fluids
Authors: Victorov Alexey I. , Firoozabadi Abbas
Published: June 2004

A thermodynamic micellization model is proposed for the description of asphaltene precipitation from petroleum fluids. It describes the solubilization of asphaltene polar species by resin bipolar molecules in the micelles. A simple form of the standard Gibbs free energy of micellization is used. The petroleum fluid is assumed to be a dilute solution with respect to the monomeric asphaltenes, resins, and micelles. The Peng–Robinson equation of state (PR‐EOS) is applied to describe the fugacity of monomeric asphaltene in the bulk of the petroleum fluid. Intermicellar interactions as well as osmotic pressure effects are neglected. The proposed model shows promising results to describe asphaltene deposition from crude mixtures. It predicts the change in precipitation power of different alkane precipitants and the effect of pressure on asphaltene precipitation. The amount and the onset of predicted asphaltene precipitation are sensitive to the amount of resins in the crude. All these results are in line with laboratory observations and oil‐field data.