bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theoretical prediction of electric field‐enhanced coalescence of spherical drops
Authors: Zhang Xiaoguang , Basaran Osman A. , Wham Robart M. 
Published: June 2004

AbstractA fundamental study of drop collision, coalescence and growth induced by combined effects of gravitational and electrostatic forces is presented. The focus is on the enhancement of rates of collision and growth of spherical, conducting drops bearing zero net charge in dilute, homogeneous dispersions by an external electric field. By completely accounting for hydrodynamic and electrostatic interactions, a trajectory analysis is used to follow the relative motion of two drops equation is then solved to predict the evolution in time of the size distribution and the average size of drops. The results show that the rates of drop collision and growth can be increased significantly by applying an electric field, in accord with fundamental experiments and patents on electrocoalescence. The enhancement of drop collision and coalescence is especially pronounced when the imposed electric field acts horizontally, that is, in a direction perpendicular to gravity.
Pressure filtration of flocculated suspensions
Authors: Landman Kerry A. , White Lee R. , Eberl Maria 
Published: June 2004

AbstractFrom the development of a compressional rheology of a flocculated suspension, a number of separation processes have been modeled. With respect to the two‐stage pressure filtration process of compact formation and then consolidation, the rheological formulation appears at first examination to eb significantly at variance with the conventional engineering approach. The present model may be reconciled to the early engineering model. Moreover, the filtration parameters extracted from experiments can be related to the more fundamental rheological parameters, r(ϕ), the hindered settling factor, which is a function of solids volume fraction ϕ — it takes into account hydrodynamic interactions between local particles, which increase the drag forces. Useful estimates of the compact bed formation resistance and the formation time are provided as a function of applied pressure. The initial time dependence of the consolidation ratio on the elapsed consolidation time is not found to be a square root behaviour as suggested by the conventional modeling.
Detection of gross erros in data reconciliation by principal component analysis
Authors: Tong Hongwei , Crowe Cameron M. 
Published: June 2004

AbstractStatistical testing provides a tool for engineers and operators to judge the valididty of process measurements and data reconciliation. Univeriate, maximum power and chisquare tests have been widely used for this purpose. Their performance, however, has not always been satisfactory. A new class of test statistics for detection and identification of gross errors is presented based on principal component analysis and is compared to the other statistics. It is shown that the new test is capable of detecting gross erros of smallmaginitudes and has substantial power to correctly identify the variables in error, when the other tests fail.
Reactions at supercritical conditions: Applications and fundamentals
Authors: Savage Phillip E. , Gopalan Sudhama , Mizan Thamid I. , Martino Christopher J. , Brock Eric E. 
Published: June 2004

AbstractSupercritical fluids posses properties that make them attractive as media for chemical reactions. Conducting chemical reactions at supercritical conditions affords opportunities to manipulate the reaction environment (solvent properties) by manipulating pressure, to enhance the solubilities of reactants and products, to eliminate interphase transport limitations on reaction rates, and to integrate reaction and separation unit operations. Supercritical conditions may be advantageous for reactions involved in fuels processing, biomass conversion, biocatalysis, homogeneous and heterogeneous catalysis, environmental control, polymerization, materials synthesis, and chemical synthesis. Moreover, supercritical fluids can be used profitably in fundamental chemical investigations of intermolecular interactions and their influence on chemical processes. Work on chemical reactions in and with supercritical fluids is reviewed. We discuss both fundamental studies and applications of reactions at supercritical conditions, with focus on work published after 1985.
Numerical study on hydrodynamics of short‐dwell paper coaters
Authors: Cao Zhenlei , Esmail M. Nabil 
Published: June 2004

AbstractThe influence of flow hydrodynamics is studied numerically on the operating parameters of short‐dwell paper coaters. The flow in and around a coater is numerically simulated using the method of finite difference, body‐fitted numerical grid generation, and a new computational technique for the solution of viscous incompressible Navier‐Stokes equations. The result reflect a simultaneous solution of the problem in and around the coating pond. The computational strategy includes the treatment of mathematical singularities at dynamic and static contact points, and the boundary conditions at free surfaces with stagnation points. A dynamic contact angle is calculated simultaneously with the solution. Results include shear rate, centrifugal force, pressure, and velocity distributions in the flow field related to the operating parameters of the coater, the quality of product, and the efficiency of operation.
A reaction network model for phenol oxidation in supercritical water
Authors: Gopalan Sudhama , Savage Philip E. 
Published: June 2004

AbstractDilute aqueous solutions of phenol were oxidized in a flow reactor at 420, 440, 460 and 480°C at 250 atm. Phenol disappearance kinetics followed the trends exhibited by previously published data obtained at T < 420°C. By merging the two sets of data, a global rate low for phenol disappearance kinetics valid between 380 and 480°C was determined to be rate = 102.34 exp( −12.4/RT) [ϕOH]0.85 [O2]0.50 [H2O]0.42. Undesired multiring products, whose formation was reported previously at the lower temperatures, continued to form in high selectivities at these higher temperatures. Reaction products were classified into three categories: dimers, gases, and a remainder that included products from ring‐opening reactions. A global reaction network that describes the transformation of phenol into these product groups was developed. Steps in the network are: parallel oxidation paths for phenol that from dimers and ring‐opening and other products, secondary decomposition of dimers of ring‐opening and other products, and oxidation of the ring‐opening and other products to carbon oxides. The experimental products yields were used to determine optimal values for the reaction orders and rate constants for each step in the network. This quantitative reaction model shows that dimerization is the dominant primary path for phenol consumption. High temperatures and long residence times reduce the concentration of dimers in the reactor effluent and maximize the gas yield. High oxygen concentrations also increase the gas yield. The quantitative reaction network model is consistent with previously published product yields for T = 380 – 420°C.
Detailed chemical kinetics model for supercritical water oxidation of C1 compounds and H2
Authors: Brock Eric E. , Savage Phillip E. 
Published: June 2004

AbstractA detailed chemical kinetics model comprising 148 reversible elementory reactions for the supercritical water oxidation (SCWO) of methane, methanol, carbon monoxide and hydrogen was developed. Rate constants were taken from previous critical evaluations. The Lindemann model, at times modified with a broadening parameter, was used to account for the effects of pressure on the kinetics of unimolecular reactions. Model predictions were compared with published experimental SCWO kinetics data for 450–650°C and 240–250 atm. The model correctly predicted global reaction orders for all four fuels to within their uncertainties. In addition, the model correctly predicted that the global reaction orders for O2 during methanol and hydrogen oxidation were essentially zero, and that the O2 concentration had the greatest effect on the methane oxidation rate. The pseudo‐first‐order rate constants predicted by the model were consistently higher than the experimental values, but the global activation energies were predicted correctly for methane oxidation and for CO and H2 oxidation at high temperatures. The model's predictions generally became worse as the temperature decreased toward the critical point of water. A sensitivity analysis revealed that fewer than 20 elementaty reactions largely controlled the oxidation kinetics for the compounds studied. Nearly half of these reactions involved HO2, which is an important free radical for SCWO. Quantitative agreement with the experimental methane conversions was obtained by adjusting the preexponential factors for three elementary reactions within their uncertainties. It could also be obtained by using the JANAF value (0.5 kcal/mol) for the standard heat of formation of HO2, but this value is lower than other recently recommended values.
Analysis of interface evolution and pattern formation during CVD
Authors: Thiart Jacob J. , Hlavacek Vladimir 
Published: June 2004

AbstractMorphological aspects of the evolution of a gas ‐ solid interface during typical CVD processes are presented, as well as a continuum model of CVD growth. A linear stability analysis used determines the effect of reactor conditions on the stability of planar growth. The main focus, however, is numerical solution of governing equations under a wide variety of conditions and with different initial interface shapes as starting point. Simplified solutions under specific deposition conditions and the numerical procedure for solving the complete system of equations are presented. The focuses are on the use of a parametrization that eliminates numerical problems encountered with steep interface gradients and the automatic generation of an adaptive mesh for the domain above the interface. Several examples illustrate the numerical solution procedure. To our knowledge, this is the first attempt to simulate interface evolution during CVD for long deposition times from various initial interface shapes. The simulation revealed several morphological phenomena observed experimentally in previous studies, including the formation of occlusions that contributes to film porosity and was clearly shown by the numerical results. Film uniformity strongly depends on the controlling mechanism of deposition. Severe nonuniformities develop under diffusional limitations, while deposition is very uniform under conditions of kinetics control. Film uniformity could be improved by choosing conditions for which a Damköhler number of deposition, Da, would have the lowest value.
Multiphase ozonolysis of organics in wastewater by a novel membrane reactor
Authors: Guha Asim K. , Shanbhag Purushottam V. , Sirkar Kamalesh K. , Vaccari David A. , Trivedi Deven H. 
Published: June 2004

AbstractConventional ozonation of recalcitrant organic compounds in wastewater suffers from low transfer rate of ozone into water. The low transfer rate can be enhanced by adding an inert fluorocarbon (FC) liquid immiscible with water but having a much higher solubility for ozone. A novel membrane reactor was studied for the destruction of organic pollutants by using PC liquid simultaneously as a reaction medium and a liquid membrane. The membrane reactor consisted of two sets of microporous and/or non‐porous hollow‐fiber membranes well‐mixed in a cylindrical shell filled with the inert FC liquid. Wastewater was allowed to flow through the lumen of one set of microporous fibers; O3‐containing gas flowed through the bore of the other set. Oxidative degradation products get partitioned back into the two mobile phases. Degradation of such pollutants as phenol, acrylonitrile, nitrobenzene, trichloroethylene, and toluene in such a reactor is presented. The kinetics of degradation of each pollutant in the two‐phase (aqueous‐ FC) system were studied using batch and semibatch experiments. Simulation results based on a first‐order model to predict the behavior of pollutant degradation in such a membrane reactor are compared with experimental data.
Wave model for longitudinal dispersion: Development of the model
Authors: Westerterp K. R. , Dil'man V. V. , Kronberg A. E. 
Published: June 2004

AbstractA new 1‐D model for longitudinal dispersion is proposed as an alternative to the Fickian‐type dispersed plug‐flow model. Accounting for significant features of longitudinal mixing gives rise to a quasilinear hyperbolic system of two first‐order equations for the average concentration. The model equations are obtained based on minor extensions of the heuristic equilibrium analysis of Taylor. A qualitative, more general derivation of the equations is given on the basis of the simple generalization of Fick's law, taking into account the finite velocity of fluid elements. For linear problems the mean concentration and the dispersion flux obey a hyperbolic equation of the second order. The proposed hyperbolic model contains three parameters that depend only on the flow conditinos, the physical properties of the fluid, and the gemetry of the system. It effectively resolves the well‐known problem of boundary conditions that, for unidirectional flow, are formulated now only at the reactor inlet. The new model eliminates the conceptual shortcomings inherent to the Fickian dispersed plug‐flow model: it predicts a finite velocity of signal propagation and does not involve backmixing in the case of unidirectional flow.
Droplet deposition and momentum transfer in annular flow
Authors: Fore Larry B. , Dukler Abraham E. 
Published: June 2004

AbstractEntrainment and deposition in gas‐liquid annular upflow are known to account for as much as 20% of the pressure gradient, through droplet acclelerations in the core refion. Momentum is transerred from the core when droplets decelerate upon impactwith the liquid film. It is usually assumed that all of this momentum is transferred to the film, essentially driving the film upwardin conjunction with interfacial friction. New data, abtained for annular gas‐liquid upflow in a 5.08‐cm‐ID tube, are used in a momentum balance analysis to determine the mechanismof momentum transfer from depositing droplets. Measurements include the liquid film thickness, wall shear stress, pressure gradient, entrained liquid fraction, droplet deposition rate, droplet centerline axial velocity, and mass‐average drop size for two gas‐liquid systems. This analysis supports the idea that large droplets displace the film locally and decelerate primarily at the wall, effectively transferring negligible momentum to the liquid film.
Catalytic oxidation of toluene and tetralin in superoritical carbon dioxide
Authors: Zhou Luho , Erkey Can , Akgcrinan Aydin 
Published: June 2004

AbstractThe catalytic total oxidation of toluene and tetrahydronaphthalene (tetralin) in super‐critical carbon dioxide over a 0.5% platinum γ ‐alumina catalyst was studied in a fixed‐bed reactor. Toluene oxidation experiments were performed at 618, 633, 648 and 663 K, and at 7.93, 9.31 and 10.7 MPa. Tetralin oxidation experiments were performed at 573, 598, 623 and 648 K and at 8.96and 10.0 MPa Inlet concentrations of toluene and tetralin were varied in the ranges 569 to 2,858 ppm (mass/mass) and 1,420 to 3,648 ppm, respectively. Reactions were run at excess oxygen with a 25:1 molar ratio of oxygen to toluene and a 15:1 molar ratio of oxygen to tetralin. A stepwise mechanism was postulated for the oxidation reaction to describe the kinetics of toluence and tetralin oxidation in supercritical carbon dioxide, and the reaction orders and activation energies were determined.
Interfacial force field characterization in a constrained vapor bubble thermosyphon
Authors: Dasgupta Sunando , Plawsky Joel L. , Wayner Peter C. 
Published: June 2004

AbstractIsothermal profiles of the extended meniscus in a quartz cuvette were measured in the earth's gravitational field using an image‐analyzing intefferometer thai is based on computaer‐enhanced video microscopy of the naturally occurring ineetference fringes. These profiles are a function of the stress field. Experimentally, the augmented Young‐Laplace equation is an excellent model for the force field at the solid‐liquid‐vapor intrfeces for heptane and pentane menisci on quartz and tetradecane on SFL6. Effects of refractive indices of the solid and liquid on the measurement techniques were demonsrrauzd. Experimentally obtained values of the disjoining pressure and dispersion constantswere compared to those predicted from the Dzyaloshiniskii‐Lifshitz‐Pitaevskii theory for an ideal surface and reasonableagreements were obtained. A parameter introduced gives a quantitative measurement of the closeness of the system to equilibrium. The nonequilibrium behavior of this parameter is also presented.
Analysis of shear‐dependent bacterial adhesion kinetics to biomaterial surfaces
Authors: Dickinson Richard B. , Cooper Stuart L. 
Published: June 2004

AbstractA 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

AbstractAn 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

AbstractA 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

AbstractConstant 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

AbstractIn 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.