bluuebunny/crossref_metadata_2025_split huggingface dataset:
Efficient implementation of VLE procedures in equation‐oriented simulators
Authors: Macchietto S. , Maduabueke G. I. , Szczepanski R. 
Published: June 2004

AbstractModern equation‐oriented simulators solve systems of equations and procedures using Newton's method or its variants. Partial derivatives of the output variables of procedures with respect to their input variables are required and are usually approximated by perturbation or quasi‐Newton methods. Here it is shown how this partial derivative information can be computed exactly for procedures in general, with particular applications to flash and multicomponent distillation procedures. Results indicate that 1. physical property procedures should provide analytical derivatives of properties in addition to point values; 2. commonly used procedures for vapor‐liquid equilibria calculation can easily be modified, and should be, to also return output/input gradients; and 3. the use of exact derivatives at all levels results in significant improvements in efficiency over present methods.
Scaling rules for isocratic elution chromatography
Authors: Wankat Phillip C. , Koo Yoon‐Mo 
Published: June 2004

AbstractScaling rules for both linear and nonlinear elution chromatography with independent solutes are discussed. The scaling method utilizes smaller diameter particles with high mass transfer rates. The column length, diameter, and cycle time are then scaled so that pressure drop, separation, and throughput are the same or better than in the old design. The new design uses much less packing and cycles more rapidly than the old design. Mathematical derivation shows that the scaling rules for systems with linear and nonlinear isotherms are the same in certain circumstances. Gaussian solutions are used for studying linear systems. Mass transfer zone and diffusive wave analyses are used for constant and proportional patterns, respectively, to describe elution when plateaus form at the feed concentration. Numerical examination of the constant‐pattern elution curve using the Thomas solution shows that the scaling rules are applicable to short columns, which means that there is a negligible entrance effect on the scaling rules. The Thomas solution also shows that the mass transfer resistance has little effect on the scaling rules for the proportional‐pattern wave of a nonlinear solute. Shock and diffusive wave analyses based on the local equilibrium model are employed to describe the separation when the elution curves do not have plateaus. The calculated results show that the scaling rules are followed exactly when pore diffusion controls. Separation of two noninteracting nonlinear components and of a linear and a nonlinear component remains constant when these scaling rules are followed. Several example calculations are used to demonstrate the method.
Electrophoresis in a dilute dispersion of colloidal spheres
Authors: Chen Shing B. , Keh Huan J. 
Published: June 2004

AbstractAn analytical study of the electrophoretic motion of two freely‐suspended, nonconducting spheres with thin electrical double layers is presented using a method of reflections. The particles may differ in radius and/or in zeta potential at the surface, and they are oriented arbitrarily relative to the direction of applied electric field. Corrections to Smoluchowski's equation due to particle interactions are determined in a power series of 1/r12 up to 0(r), where r12 is the center‐to‐center distance between the particles. It is found that the electrophoretic particles do not interact with one another when they have equal zeta potentials. For the specific case of spheres with identical radii, our results agree well with the exact calculations using bipolar coordinates. Based on a microscopic model, the results for two particles are used to find the effect of volume fractions of particles of each type on the mean particle velocities in a bounded dispersion. Of particular interest is the electrophoresis of a suspension of particles with arbitrary size distribution but with identical zeta potentials, in which the sole factor influencing the mean particle velocity is the volume fraction of all particles. In general, the effect of particle interactions on electrophoresis is much weaker than that on sedimentation.
Evaluation and control of particle properties in aerosol reactors
Authors: Wu Jin Jwang , Nguyen Hung V. , Flagan Richard C. , Okuyama Kikuo , Kousaka Yasuo 
Published: June 2004

AbstractThe production of powders by aerosol routes spans a wide range of operating temperatures depending on the type of aerosol reactors used. The dominant mechanism of particle growth and evolution depends highly on the rate at which the reactions producing the condensible species are carried out. Numerical solutions of the discrete‐sectional aerosol general dynamic equation that accounts for the interactions of the discrete clusters were obtained for conditions representative of the different types of aerosol reactors used for powder production today. Simplified reaction and coagulation equations that give fast and useful prediction of the evolution of aerosols associated with chemical reactions were derived, and a simple reaction‐coagulation model was developed. The effects of reaction rate, initial vapor concentration, residence time, seed particles, and temperature profile on the properties of tine particles produced by gas‐phase chemical reactions were evaluated using both models. Results show good agreement between the two.
Hydrodynamics and mass transfer on three‐phase distillation trays
Authors: Herron Charles C. , Kruelskie Bradley K. , Fair James R. 
Published: June 2004

AbstractSeveral oil‐water mixtures were contacted by air in a sieve tray distillation column simulator. The oil was mineral spirits with 183–206°C boiling range and 51.8° API gravity. Two sieve tray designs were used, and both hydraulic and mass transfer measurements were made, the latter utilizing acetone as the transferring solute. It was found that gas agitation caused the mixtures to behave as a homogeneous liquid that followed general correlations for pressure drop, liquid holdup, froth height, downcomer liquid level, and fractional entrainment. No unusual problems with foaming or entrainment were observed. Mass transfer efficiency was influenced by oil‐water ratio, with mild minima occurring at about 50 vol % mixtures. It was concluded that, when the immiscible liquids are both present in significant proportions, designers need not avoid formation of a second liquid phase for fear of unusual hydraulic or mass transfer behavior.
Generalized likelihood ratios for gross error identification in dynamic processes
Authors: Narasimhan Shankar , Mah Richard S. H. 
Published: June 2004

AbstractGross error identification in dynamic processes is important in ensuring proper process control. This paper describes the application of a generalized likelihood ratio (GLR) method for identifying gross errors caused by biases in measuring instruments and controllers, process leaks, and failure of controllers. As shown in the application to steady state processes (Narasimhan and Mah, 1987), this method provides a general framework for identifying different types of gross errors whose effect on the process can be modeled. An important feature of the work is the treatment of closed‐loop dynamic processes. The formulation of the hypotheses of the GLR method proposed by Willsky and Jones (1974) is extended for this purpose. For estimating the time of occurrence of the gross error, a simple chi‐square test on the innovations (measurement residuals) is used, which is computationally more efficient than the method used by Willsky and Jones. Through simulation studies of a level control process the appropriate selection of parameters of the GLR method is investigated.
Pressure swing adsorption: An experimental study of diffusion‐induced separation
Authors: Shin H.‐S. , Knaebel K. S. 
Published: June 2004

AbstractGas separation based on differences in intraparticle diffusion rates was achieved by four‐step pressure swing adsorption (PSA) process. The application studied was the separation of nitrogen from air using molecular sieve type RS‐10. Systematic PSA experiments were conducted in bench‐scale equipment to study several variables, including duration of steps of the cycle, flow rates, pressure ratio, subatmospheric blowdown and purge, and column geometry.The test results were compared with predictions of a mathematical model (Shin and Knaebel, 1987). In all cases, the trends of product purity and net recovery of both theory and experiment were in close agreement. Since the theory accurately portrays the overall behavior of the process, the transport mechanisms embodied in the theory may provide insight into diffusion‐induced separation by PSA. In addition, by reviewing the results of the parametric studies of the variables, it has been possible to gain an intuitive understanding of the relations between factors that affect each step, and hence overall performance.
Dispersion in laminar tube flow at low Peclet numbers or short times
Authors: Vrentas J. S. , Vrentas C. M. 
Published: June 2004

AbstractA new asymptotic solution is developed for the dispersion of a passive solute in a Newtonian fluid in fully‐developed laminar flow through a straight circular tube. A perturbation solution to the convective dispersion problem is constructed by utilizing the pure diffusion solution as an initial approximation in an iterative successive approximation procedure. The derived perturbation solution is shown to be valid at both short and long times for sufficiently low values of the Peclet number and is also valid at any value of the Peclet number for sufficiently small values of time.
Mathematical modeling of boron diffusion from boron oxide glass film sources
Authors: Yeckel Andrew , Middleman Stanley 
Published: June 2004

AbstractMathematical models are developed to examine two alternative means of boron doping from boron‐rich glass films. For the planar source diffusion system, in which boron diffusion and glass film growth occur simultaneously at high temperature (900–1,200°C), glass film growth rates and the degree of doping achieved are predicted. In most cases, the solubility limit of boron in silicon is attained at the silicon surface. It is found that depletion of the boron source wafers used in this process may be slowed considerably by their removal from the reactor after a short time. Model predictions for an alternative method, in which the glass film is pregrown at low temperature (300°C) and the diffusion subsequently performed at high temperature, demonstrate a strong dependence of the boron surface concentration on the initial boron content in the pregrown glass film, for concentrations of boron near the solubility limit. The conditions for which a masking film of SiO2 is insufficient to prevent boron diffusion into silicon, known as mask failure, are also predicted by the models.
Pressure swing adsorption: Effects of incomplete purge
Authors: Matz Michael J. , Knaebel Kent S. 
Published: June 2004

AbstractTheoretical and experimental studies of pressure swing adsorption (PSA) cycles for various extents of purging have been conducted. In both the theoretical and experimental portions, pressurization was accomplished with product rather than with feed. A simple, local equilibrium model was employed, and the results were analyzed by the method of characteristics. It was found that for difficult separations (i.e., closely spaced isotherms and/or heavily contaminated feeds), incomplete purging, e.g., as little as 50% complete, yielded recoveries attainable only at much higher pressure ratios with complete purge. Conversely, for easy separations (i.e., widely spaced isotherms and dilutely contaminated feeds), incomplete purging was less attractive, yielding only slight improvement over complete purge.Splitting oxygen from air with zeolite 5A is moderately difficult due to the proximity of the isotherms and due to the predominance of the more strongly adsorbed nitrogen in the feed. This case was also modeled and was studied experimentally. The experiments yielded nearly double the recovery of oxygen for minimal purge compared with that available with complete purge. The productivity of oxygen was relatively high, e.g., 0.0378 m3(O2 at STP)/kg (adsorbent) · h. Those experiments validated the trends predicted theoretically.
Mass transfer from dispersed bubbles to electrolyte solution in packed beds
Authors: Takahashi Ken M. , Alkire Richard C. 
Published: June 2004

AbstractThe measurement of gas‐liquid interfacial areas and mass transfer coefficients in concurrent upward bubbly flow (uG from 0.02 to 0.16 m/s, uL from 0.0051 to 0.056 m/s) over a packed bed consisting of 1.2 mm glassy carbon particles is described. Specific surface areas were measured by chemical absorption of O2 into Na2SO3 solutions; volumetric mass transfer coefficients were measured by physical desorption of O2 into N2 bubbles. Surface areas were obtained in the range of 4 × 103 to 2 × 105 m−1, much higher than have been previously reported. High areas are related to the use of electrolytes and small packing particles. Bubble size was found to depend primarily on liquid velocity. Volumetric mass transfer coefficients kLaG are also high (0.1 < kLaG < 2.3 s−1), primarily as a result of high gas‐liquid interfacial areas. Mass transfer coefficients kL are small, however. For the smaller bubble dispersions, mass transport is controlled by diffusion rather than by convection.
Thermodynamics of liquid‐liquid equilibria including the critical region
Authors: De Pablo Juan José , Prausnitz John M. 
Published: June 2004

AbstractTo obtain good representation in the liquid‐liquid critical region, a semitheoretical correction is added to a conventional expression (e.g., van Laar or NRTL) for the excess Gibbs energy of a binary or ternary system along the coexistence curve. This correction is an exponential function of a suitable distance from the critical point; it is significant in the critical region but not elsewhere. In the correction function, the preexponential factor is determined from stability considerations. In the exponential argument, two parameters are determined from theoretical power laws. While the coordinates of the critical point must be known (or estimated), no phase‐equilibrium data in the critical region are required to determine parameters. The correction presented here provides an excellent approximation for phase equilibria along the coexistence curve close to and remote from critical conditions. Further, the correction facilitates simultaneous representation of isothermal vapor‐liquid and liquid‐liquid equilibria including the liquid‐liquid critical region.
Hydrogen transfer in slurries of carbon supported catalyst (HPO process)
Authors: Lindner D. , Werner M. , Schumpe A. 
Published: June 2004

AbstractThe effect of suspended activated carbon on gas/liquid mass transfer is studied for the Pd/C‐catalyzed hydrogenation of nitrate to hydroxylamine (HPO process). In a bubble column and in a stirred autoclave, physical mass transfer (kLa) in the concentrated salt solution is improved by more than a factor of three by the catalyst. Chemical absorption enhancement by the zero‐order catalytic reaction is insignificant at the employed catalyst diameter (40 μm), but hydroxylamine selectivity depends on the absorption regime.
A network model for deep bed filtration of solid particles and emulsion drops
Authors: Rege S. D. , Fogler H. S. 
Published: June 2004

AbstractA network model has been developed to simulate the flow of emulsions and solid particles through porous media. Particle deposition due to direct interception, as well pore plugging by straining are accounted for in the model. The effects of two important factors—the ratio of particle size to pore size, and the fluid velocity—on particle deposition are also investigated. The strength of the model lies in its ability to predict accurately effluent concentration profiles, permeability changes occurring during deep bed filtration, and the evolution of the filter coefficient with time. Model predictions for different particle and pore size distributions of both solid and emulsion particles are in agreement with experimental data.
Flocculation of colloids suspended in a viscoelastic fluid undergoing shear
Authors: Mifflin R. T. , Schowalter W. R. 
Published: June 2004

AbstractThe effect of viscoelasticity on the kinetics of the shear‐induced flocculation of colloids has been investigated theoretically and experimentally. A numerical technique for such three‐dimensional problems called global residual minimization (GRM) has been developed as an alternative to finite element and finite difference methods. In the GRM method, minimization of the residual of the momentum balance is used as the selection criterion for the velocity‐field solution. Trajectory simulations were carried out for spheres in a corotational Jeffreys fluid at a variety of Weissenberg numbers, We. For We ≤ 0.01, the effect of viscoelasticity is found to be negligible. For We = 1.0, flocculation rates are enhanced. For We = 10.0, a possibly large reduction in flocculation rate is indicated.Experiments were conducted using 600 nm radius polystyrene spheres in hydroxyethyl cellulose solutions. At shear rates corresponding roughly to We = 10.5 and 15.3, the flocculation rates were found to be at least an order of magnitude less than the rate expected in a Newtonian fluid. It is postulated that this reduction in flocculation rate is caused by the viscoelasticity of the suspending fluid.
A gas‐solid reaction with nonuniform distribution of solid reactant
Authors: Dassori C. G. , Tierney J. W. , Shah Y. T. 
Published: June 2004

AbstractA pore‐pellet model is used to analyze experimental data for SO2 removal using CuO impregnated on alumina as a sorbent. The effect of structural changes in the active solid (CuO) is included in the analysis and found to be important. The changes are characterized by three parameters: the ratio of solid product (CuSO4) molal volume to solid reactant (CuO) molal volume, the weight fraction of active solid, and the radial distribution of the active solid within the pellet.The calculated kinetic constants are independent of CuO weight fraction and can be used for pellets with different CuO weight fractions. For the data set used in this work, it is shown that some degree of nonuniformity in the CuO distribution within the alumina matrix is needed in order to obtain a good fit of the data by the model.
Transient free‐surface flows: Fluid advancing through a bed of cylinders
Authors: Behrens R. A. , Crochet M. J. , Denson C. D. , Metzner A. B. 
Published: June 2004

AbstractThe flow of a viscous liquid into a bed filled with a regular array of cylinders was observed experimentally and simulated numerically. Viscous forces were always dominant, as is expected to be the case in many actual resin transfer molding operations.Excellent agreement on the shape of the free surface was found between experiment and simulation over the full experimental range. The work accordingly validates a very simple algorithm for representing the surface motion of a fluid at its contact line with a solid surface, and extends its use to surfaces with smaller radii of curvature than considered previously. Consequently, this algorithm is expected to be valid for fluid flow into any irregularly shaped empty domain and to be useful in molding operations in inferring the presence of voiding, and of molecular orientations and conformations adjacent to fibers or other solids.
Characterization of fuel cell electrode processes by AC impedance
Authors: Yuh C. Y. , Selman J. R. 
Published: June 2004

AbstractAlternating current impedance measurements can be used as an in situ method for characterizing rate‐limiting processes in fuel cell electrodes. Theoretical models have been derived and solved analytically. Theoretical analysis indicates that kinetic information can be extracted from the effect of temperature and gas composition on the size of the kinetic loop. The relative importance of kinetics and mass transfer can be inferred from AC impedance analysis. Several examples are given for the case of molten carbonate fuel cell (MCFC) electrodes. Such electrodes are not accessible to classical kinetic investigation techniques due to the high operating temperature and corrosive environment. Relevant kinetic information about MCFC electrodes has been obtained successfully using this in situ technique.
Calculation of the temperature field in injection molding
Authors: Dupret F. , Vanderschuren L. 
Published: June 2004

AbstractThe numerical simulation of nonisothermal effects during the filling stage of injection molding is investigated here. Generalized Newtonian fluid flows are simulated within thin cavities of arbitrary shape. The numerical scheme is based on a hybrid spatial discretization: classical low‐order Lagrangian interpolants are used in the midsurface directions, while full polynomials constitute the approximation in the gapwise direction. Discrete equations are obtained by use of the Galerkin finite element method combined with a collocation procedure. Special attention is devoted to the influence of the fountain flow (occurring at the front) on the temperature field. A correct writing of the front thermal boundary condition is derived in agreement with the Hele‐Shaw simplified form of the equations. Some illustrative results are presented.
Mass‐transfer effects of bubble streams rising near vertical electrodes
Authors: Whitney Gina M. , Tobias Charles W. 
Published: June 2004

AbstractMass‐transfer enhancement by a stream of bubbles rising near a planar, vertical surface is resolved spatially and temporally using a micromosaic electrode. A stream of gas bubbles is generated electrolytically, either at a segment directly below and in the plane of the monitoring electrodes, or at a wire tip that can be positioned inside or outside the mass‐transfer boundary layer. The mass‐transfer enhancement resulting from bubbles rising within the mass‐transfer boundary layer is found to be strong and localized, in agreement with trends predicted by a surface‐renewal model. Mass transfer resulting from bubbles rising outside the boundary layer is found to receive a steady, laminar enhancement, correlating well with predictions from an idealization of the bubble stream entraining a cylinder of liquid.
Discrete structural models and their application to gas‐solid reacting systems
Authors: Zygourakis Kyriacos , Sandmann Charles W. 
Published: June 2004

AbstractDiscrete models are developed to simulate the reaction of solids with complex pore structures in the kinetic‐ and diffusion‐controlled regimes. Simulations employ two‐ and three‐dimensional computational grids, and model parameters are directly obtainable from measurable physical properties of the unreacted solid. Model predictions can be displayed pictorially, allowing for direct visualization of the simulated process, while image processing of the computational grids can provide detailed structural information not easily obtainable from other analytical models. The effects of various pore structural parameters on the predicted reactivity patterns are investigated. Several examples are presented to illustrate the use of the models and demonstrate the significance of the pore structure in determining the reactivity of coal‐derived chars.