bluuebunny/crossref_metadata_2025_split huggingface dataset:
Absorption‐induced separations in oscillatory liquid chromatography
Authors: Van Lishout Yolanda M. M. , Leighton David T. 
Published: June 2004

AbstractIt 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

AbstractDetecting 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

AbstractThe 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

AbstractThe 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

AbstractA 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

AbstractIn‐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

AbstractHeat 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

AbstractCohesive (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

AbstractA 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

AbstractA 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

AbstractStricter 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

AbstractA 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

AbstractExperimental 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

AbstractThe 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

AbstractA 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.
Micromixing effects in a two‐impinging‐jets precipitator
Authors: Mahajan Amarjit J. , Kirwan Donald J. 
Published: June 2004

AbstractTo carry out rapid precipitation on a practical scale, the use of a two‐impinging‐jets (TIJ) mixer was explored in terms of its ability to deliver rapid micromixing. The two‐step Bourne reaction scheme between 1‐naphthol and diazosulfanilic acid was used to characterize micromixing in the TIJ mixer as a function of hydrodynamics and mixer geometry. The characteristic time for micromixing in this device was at least as small as 65 ms. The larger the jet diameter, the higher the jet Reynolds number required to achieve the same micromixing quality. The micromixing time in the TIJ mixer correlated well as a function of a Damkohler number that led to a scale‐up criterion giving an inverse relationship between the micromixing time constant and the 1.5 power of the jet velocity. Finally, the precipitation of Lovastatin was carried out in the TIJ mixer under well and poorly micromixed conditions. The level of micromixing in the precipitator affected the crystal size distribution of the precipitated product only when the time constant for micromixing was comparable to or larger than the induction time for nucleation of the solute.
Temperature polarization in mass transport through hydrophobic porous membranes
Authors: Martínez‐Díez L. , Vázquez‐Gonzàlez M. I. 
Published: June 2004

AbstractMembrane distillation is a membrane process in which two liquid phases at different temperatures are separated by a microporous hydrophobic membrane. The membrane plays the role of physical support for the vapor‐liquid interface. Pure water transport through PTFE and PVDF flat membranes was studied, as well as the dependence of the phenomena on average temperature and recirculation rate at membrane sides. The influence of these operating conditions on mass transfer is also discussed, taking into account mass and heat transfer within the membrane and adjoining liquid phases. The concept of temperature polarization introduced into the transport equations shows its importance in experimental results.
Effect of pH and concentration on column dynamics of weak electrolyte ion exchange
Authors: Jansen Marcel L. , Hofland Gerard W. , Houwers Joop , Straathof Adrie J. J. , van der Wielen Luuk A. M. , Luyben Karel Ch. A. M. , van den Tweel Will J. J. 
Published: June 2004

AbstractThe column dynamics of simple ion‐exchange processes involving acetic acid and N‐acetylmethionine were studied using a strong‐base anion exchange resin to reveal the complex relation between pH, concentration, equilibrium isotherms, and chromatographic separation in ion‐exchange chromatography of weak electrolytes. Changing either the influent pH or the concentration, while keeping the other variable constant, led to considerable effluent concentration and pH fluctuations, respectively. This behavior is caused mainly by the uptake of undissociated acids. To describe these phenomena quantitatively, a rigorous thermodynamics‐based equilibrium model for ion exchange, including Donnan potential and reaction equilibria, was incorporated into a fixed‐bed model. Experimental results can be described well by this dynamic model, which is superior to conventional models due to its explicit incorporation of coions and partitioning of neutral species. It has great potential for optimizing chromatographic separations of weak electrolyte solutions.
Improved thermodynamic parameters for prediction of structure H hydrate equilibria
Authors: Mehta Ajay P. , Sloan E. Dendy 
Published: June 2004

AbstractAn improved set of all the thermodynamic and molecular properties required for the prediction of the existing 20 systems of Structure H (sH) hydrate phase equilibrium data is presented. The statistical thermodynamics model was based on the van der Waals and Platteeuw theory, and the spherical core Kihara potential was used for guest‐water interactions. Optimized Kihara parameters and reference thermodynamic properties were derived from experimental data of over 20 sH hydrate forming systems. The model could fit all the existing sH hydrate data within an accuracy of ± 6%. Inhibitor predictions were also shown to fit recent data with no adjustable parameters. The feasibility of using hydrate cage occupancies to derive refined Kihara parameters of the guest molecules was investigated. Possible existence of sH hydrates at cryogenic temperatures was also established based on the model.
Boundary effects on the sedimentation and hindered diffusion of charged particles
Authors: Pujar Narahari S. , Zydney Andrew L. 
Published: June 2004

AbstractA general formalism is developed to examine the sedimentation of a charged particle in a bounded system at small Peclet numbers and small particle‐surface potentials. The excess viscous force is evaluated using a generalized form of the Lorentz reciprocal theorem, eliminating the need to calculate the detailed fluid flow around the charged particle. Specific calculations are provided for the sedimentation of a charged sphere in a concentric (uncharged) spherical cavity. Boundary interactions increase the magnitude of the excess force at small Debye lengths, with the opposite effect seen at very large Debye lengths. A general solution is presented for the sedimentation velocity for an arbitrary particle in both unbounded and bounded systems in the limit of very thin double layers. The excess force under these conditions is proportional to the square of the Debye length, with the proportionality constant being a function of the detailed system geometry. These results provide important insights into the transport of charged particles in porous membranes and chromatographic materials.