bluuebunny/crossref_metadata_2025_split huggingface dataset:
Deposition rates from polydispersed particle populations of arbitrary spread
Authors: Rosner Daniel E. , Tassopoulos Menelaos 
Published: June 2004

AbstractFor particle deposition from log‐normal polydispersed aerosol streams by one or more of several mechanisms described by piecewise‐power‐law mass transfer coefficients, we derive useful relations between actual total mass deposition rates and the ‘reference’ rate one would calculate by imagining that all particles in the mainstream population had the average particle volume v(=ϕp/Np). Included here are diffusion or inertial mechanisms for laminar‐ or turbulent‐boundary layers, free‐molecular or continuum diffusion at high Peclet numbers of dense spherical particles, or fractal agglomerates. The mainstream particle volume distribution is considered to be log‐normal with arbitrary ‘spread’ parameter, thereby generalizing earlier results for “coagulation‐aged” (self‐preserving) distributions. Further generalizations include transitions between important particle transport mechanisms, opening the way to efficient, finite‐analytic methods for predicting mass deposition rates for arbitrary, size‐dependent particle capture efficiencies.
Synthesis of feedforward/state feedback controllers for nonlinear processes
Authors: Daoutidis Prodromos , Kravaris Costas 
Published: June 2004

AbstractA systematic method for synthesizing feedforward/state feedback controllers for a broad class of SISO nonlinear systems with measurable disturbances is presented. Depending on the structural characteristics of the system, the control law can be static or dynamic. The closed‐loop system is independent of the measurable disturbances and linear with respect to set point changes. The performance of the proposed control scheme is illustrated through an example of composition control in a system of three CSTR's in series.
Manipulating solids CSD in a supercritical fluid crystallizer: CO2‐benzoic acid
Authors: Tavana A. , Randolph A. D. 
Published: June 2004

AbstractThe final properties and end use of many organic solids often depends on their crystal‐size distribution (CSD), e.g., bioavailability for pharmaceutical solids. The objective of this study was to develop an alternate technology for crystallizing and manipulating size distribution of organic solids by crystallization from supercritical fluids. Such a technology might be superior to conventional‐size manipulation techniques, such as milling and recrystallization from organic solvents, which might contaminate the products and affect their physical‐chemical stability. Supercritical carbon dioxide was used as solvent to dissolve and then crystallize benzoic acid. A batch crystallizer was constructed and operated in the supercritical region. Seeded and unseeded crystallization experiments were performed. Different depressurization vs. time profiles for the supercritical fluid were used to produce crystals of various sizes.
Parametric analysis of thermal swing cycles for multicomponent adsorption
Authors: Huang Chen‐Chia , Fair James R. 
Published: June 2004

AbstractA study was made of the effect of design and operating parameters on the regeneration of a fixed bed of activated carbon. Two adsorbed species were removed by a hot gas purge, making the study relevant to thermal swing cycles used commercially. The analysis utilized direct experimental results as well as simulated results using a model described earlier by the authors (Huang and Fair, 1988).Regeneration parameters studied were: type of purge gas, purge gas contact time and velocity, regeneration temperature, initial bed loading, and bed pressure. These were related to certain parameters influencing the adsorption step: type of carrier gas, feed concentration, contact time and velocity, pressure, and initial bed temperature. The results are summarized in the form of guidelines for optimal regeneration cycle specification.
Turbulent micromixing parameters from reactive mixing measurements
Authors: Shenoy U. V. , Toor H. L. 
Published: June 2004

AbstractPreviously published conversion data for turbulent diffusion‐controlled acid‐base reactions in two different multijet reactors are used to extract the mixing parameters, tracer probability density function, and variance. The PDF is obtained with this instantaneous reaction method by differentiating twice the reactive mixing plot of mean reactant concentrations. The limiting behavior for the cases of complete segregation and complete mixing is derived and turns out to be piecewise linear on the reactive mixing plot. The variance is shown to be twice the area between the actual reactive mixing curve and the limiting curve for complete mixing; it can be computed by numerical integration without any foreknowledge of the PDF shape. The method, in principle, allows detection of Dirac delta functions (which represent unmixed virgin fluid) and indeed shows significant amounts of virgin fluid close to the inlet of one of the reactors.
Profile equations for film flows at moderate Reynolds numbers
Authors: Kheshgi Haroon S. 
Published: June 2004

AbstractAn approximate equation for the evolution of finite‐amplitude, long disturbances to Newtonian liquid films is found to be accurate over a wide range of Reynolds numbers. A long‐wave expansion leads to a film profile equation asymptotically correct when wave number and Reynolds number are small. Solutions of the film profile equation are compared to exact and other approximate solutions of the Navier‐Stokes system. An alternative form of the film profile equation results in remarkably accurate solutions, when Reynolds numbers are moderate, in the cases of standing or monotonically decaying waves in horizonatal films, rising film flow, final acceleration of a moving film, and film flow emerging from a slot coater.
Effective diffusivity by pulse gas chromatography at elevated pressures
Authors: Sarmah S. K. , Haynes H. W. 
Published: June 2004

AbstractPulse gas chromatography experiments at ambient pressure are often limited by an overwhelming contribution of axial dispersion to the observed variance and the inability to obtain a quantitative correction for this factor. Theoretically, the axial dispersion contribution can be reduced and at the same time the contribution due to particle diffusion can be enhanced by operating at elevated pressures. Our experiments on methane/helium diffusion in 0.32‐cm‐diameter commercial catalyst particles confirm this, and a new means of accounting for axial dispersion is demonstrated.
Trickle‐bed reactors: An experimental study of partial wetting effect
Authors: Ring Zbigniew E. , Missen Ronald W. 
Published: June 2004

AbstractThe effect of partial external wetting of catalyst particles on conversion for hydrodesulfurization of dibenzothiophene in a white oil was studied in a 25‐mm trickle‐bed reactor at 10 MPa and 330–370°C with Mo/SiO2 catalyst. The superficial liquid velocity (Lm) was varied from 0.092 to 0.557 kg · m−2 · s−1. Measurements of conversion were augmented by tracer, kinetics and solubility experiments. The objectives were to determine the parameters of a reactor model based on the multizone external wetting (MZEW) model for the overall effectiveness factor, ηo, and to compare the measured and predicted values of ηo. As the wetting efficiency, f, increases, ηo also increases, but, even at the highest Lm, catalyst wetting was not complete and consequently ηo was lower than the value corresponding to f = 1. The MZEW model describes the experimental data better than the simpler two‐zone model, based on a particular interpretation of f. The difference between the two models can be as high as 200%.
The critical properties of n‐alkanes using a low‐residence time flow apparatus
Authors: Rosenthal Daniel J. , Teja Amyn S. 
Published: June 2004

AbstractA low residence time flow method for the measurement of the critical temperatures and pressures of thermally‐unstable fluids was developed in this work. The low residence time at elevated temperatures minimizes decomposition and other reactions, making it possible to measure the critical properties of many unstable fluids. An extrapolation procedure was developed to obtain the critical properties of rapidly reacting substances, based on the linear behavior of the apparent critical property with residence time. The measured critical properties of 14 n‐alkanes (pentane through octadecane) using this method are reported in this paper. The results extend the available data on the critical properties of the higher alkanes and reveal a possible error in the literature value for the critical pressure of tetradecane.
An extended horizon feedback/feedforward self‐tuning controller
Authors: Kershenbaum Lester S. , Pérez‐Correa J. Ricardo 
Published: June 2004

AbstractA feedforward/feedback version of a single input/single output self‐tuning controller has been developed and tested both via simulation studies and experiments on a section of an absorption/desorption pilot plant. The algorithm is based on the recursive least squares estimation of parameters for the linear models relating the output to the controlled input and to the disturbances; adaptation is achieved using a variable forgetting factor. The control input at each time interval is calculated using one of several single‐step extended‐horizon control strategies.The results show that the performance of the algorithm is insensitive to the choice of initial parameters, all of which have a readily identifiable intuitive basis. The algorithm is especially robust against deterministic disturbances (measurable and unmeasurable) and unknown and varying time delays. Computational load beyond that of a feedback‐only version is minimal.
Lumping nonlinear kinetics in a CSTR
Authors: Astarita Gianni , Nigam Abhash 
Published: June 2004

AbstractThe model of uniform nonlinear kinetics recently developed for the continuous description of a multicomponent mixture reacting in a batch or plug flow reactor (Astarita, 1989) is applied to the analysis of a continuous stirred tank reactor (CSTR). It is shown that most of the equations can be solved in general, independently of the specific kinetic mechanism. Some specific mechanisms are discussed. The difference between the behavior in a plug flow reactor (PFR) and a CSTR turns out to be quite dissimilar from what one would expect by considering the single‐component case.
Dynamics of heterogeneous azeotropic distillation columns
Authors: Rovaglio Maurizio , Doherty Michael F. 
Published: June 2004

AbstractA new dynamic model has been developed for heterogeneous azeotropic distillation columns, which is capable of automatically detecting and accounting for multiple liquid phases on trays at each instant of time. Extensive dynamic simulations have been carried out for the heterogeneous distillation of ethanol, water and benzene. Our results are in general agreement with prior work, which shows that this class of separations can be expected to exhibit multiple steady states, complex dynamic behavior, and parametric sensitivity. One of the most unexpected results was that these systems exhibit parametric sensitivity with respect to small changes in column pressure. For systems vented to the atmosphere, small increases in the barometric pressure lead to loss of interface in the decanter over a 24‐hour period. If small pressure variations of this sort are left uncontrolled long enough, the entire separation will fail. Small decreases in the barometric pressure do not have such a disastrous effect.
A mathematical model of pulse plating on a rotating disk electrode
Authors: Yin Ken‐Ming , White Ralph E. 
Published: June 2004

AbstractA galvanostatic pulse plating model is presented for the electrodeposition of an alloy on a rotating disk electrode. This model is used to simulate the electrodeposition of nickel/chrome alloys. The mass transport equations used in the model include the effects of diffusion, migration and convection; and the electrode kinetics are described by the Butler‐Volmer equation. It is predicted that the effect of ionic migration is significant and therefore should be included in models of pulse plating.
Viscoplastic‐elastic modeling of tubular blown film processing
Authors: Cao Bangshu , Campbell Gregory A. 
Published: June 2004

AbstractThe blown film process has been modeled through the transition from liquidlike to solidlike behavior at the freeze line. A new constitutive equation has been developed that, when incorporated into the the kinematic and dynamic equations that describe the process, for the first time yields qualitatively correct predictions of all process variables. It is suggested that the demarcation between liquidlike behavior and solidlike behavior be altered from the conventional, kinematically based constraint, dr/dz = O, to a rheologically based constraint, the plastic‐elastic transition (PET). The results are qualitive in nature since the material is modeled as an elastic solid above the PET instead of as a viscoelastic material. The model is tested using the polystyrene data of Gupta (1981).
Catalytic hydroprocessing of chlorobenzene and 1,2‐dichlorobenzene
Authors: Hagh Bijan F. , Allen David T. 
Published: June 2004

AbstractThe hydrodechlorination reactions of chlorobenzene and 1,2‐dichlorobenzene on a NiMo/γAl2O3 catalyst were examined in a differential microflow reactor. The NiMo catalyst had high activity and selectivity for dechlorination; no hydrogenation of the aromatic ring was detected. The dechlorination reactions were examined at temperatures ranging from 275 to 375°C. In this temperature range the rates of adsorption and surface reaction are comparable and neither controls the overall reaction rate. A kinetic model, incorporating adsorption, desorption and surface reaction rates, has been used to model the data.
Prediction of differential sorption kinetics near Tg for benzene in polystyrene
Authors: Mehdizadeh S. , Durning C. J. 
Published: June 2004

AbstractA recent first principles theory for “anomalous” diffusion, which accounts for the effect of a protracted macromolecular response to a perturbation, is used to quantitatively predict the results from successive differential sorption experiments in the benzene/atactic polystyrene system. The physical constants in the theory are evaluated for the conditions of the experiment without reference to any non‐Fickian diffusion data. The theoretical predictions are in reasonable agreement with the experimental observations.
Critical properties of dilute multicomponent mixtures
Authors: Anselme M. J. , Teja A. S. 
Published: June 2004

AbstractEquations for the critical properties of dilute multicomponent mixtures have been derived using the Soave‐Redlich‐Kwong equation of state. The utility and limitations of the approach are described using data on 47 mixtures from the literature. New data on three dilute multicomponent mixtures have also been measured in this work and are compared with the predictions of our method. In general, it is possible to predict all three critical properties of dilute multicomponent systems with a satisfactory degree of accuracy. Predictions are as good as those obtained from conventional equation of state methods, which employ a rigorous solution of the Gibbs criteria for the critical point, but offer the advantage that no iterations are required in the calculations.
Diffusion from spheres in a continuous‐flow stirred tank
Authors: Liekhus Kevin J. , Hanley Thomas R. 
Published: June 2004

AbstractSolvent diffusion from spheres at constant mass‐transfer Fourier number, FoM, in a single continuous‐flow stirred tank (CFST) and in a series of CFSTs is simulated. A transfer efficiency is defined and transfer efficiency curves are constructed as a function of FoM and the residence time distribution of the spheres in the system. The fraction of solvent removed from the spheres in a series of CFSTs can be approximated using the transfer efficiency curves and knowledge of the operating conditions in each tank. The usefulness of the curves to predict solvent removal from polymer spheres under pilot‐plant conditions is examined.
A modified smith predictor with an approximate inverse of dead time
Authors: Huang Hsiao‐Ping , Chen Cheng‐Liang , Chao Yung‐Cheng , Chen Pei‐Lin 
Published: June 2004

AbstractA compensator that approximates the inverse of dead time at low frequencies in a modified Smith predictor (MSP) control system is proposed, and the design of an MSP control system for it is given. The performance of the MSP with compensator, using a first‐order element as a low‐pass filter, is described. Analysis and simulation results show that the compensator improves performance in the disturbance rejection of the original Smith predictor.
Adaptive‐predictive control of kamyr digester chip level
Authors: Allison Bruce J. , Dumont Guy A. , Novak Lloyd H. , Cheetham William J. 
Published: June 2004

AbstractKamyr digester chip level poses a difficult control problem, because the chip column dynamics are complex and it is difficult to measure the chip‐liquor interface. Control of the chip level is required to smooth digester operation and to stabilize the residence time. Conventional methods rely largely on fixed parameter controllers which are unable to compensate for changes in the process dynamics. Manual controller returning is often required.An adaptive chip level controller based on Generalized Predictive Control (GPC) is presented. Closed‐loop time series identification methods were used to develop the process model and to design the controller. A significant reduction in chip level and P‐number variability has been observed since commissioning the controller on an industrial digester in September 1988. The adaptive controller has eliminated the need for manual returning, reduced the need for operator intervention, and demonstrated the potential to predict hang‐ups.
Control structures for disturbance rejection and decoupling of distillation
Authors: Häggblom Kurt E. , Waller Kurt V. 
Published: June 2004

AbstractThe process gains for different distillation control structures can be calculated through transformations from known gains of one arbitrary structure.In this paper the transformation is utilized for calculation of a two‐point distillation control structure which, in the steady state, simultaneously rejects disturbances in the feed composition and in the feed flow rate and results in implicit decoupling between the two product control loops. This disturbance rejecting and decoupling (DRD) structure is tested on a model of a 15‐plate pilot‐plant distillation column. It compares favorably with standard structures for dual composition control. Experimental results agree with the simulation results.
Modeling of additive effects on the electroplating of a through‐hole
Authors: Hazlebeck David A. , Talbot Jan B. 
Published: June 2004

AbstractA mathematical model of copper plating of a through‐hole is developed which relates uniformity of deposition to bulk electrolyte composition, applied potential difference, aspect ratio, through‐hole diameter, and deposition kinetics. The electrochemical transport equations governing plating in a through‐hole are solved assuming that the fluid within the through‐hole is stagnant. Conditions for uniform plating are determined both for Butler‐Volmer kinetics considering the effects of dissociation of bisulfate ions in the electrolytic solution and for kinetics limited by complexation of cupric ions with an adsorbed neutral additive species.
Effective kinetic modeling of multistep homogeneous reactions
Authors: Chern Jia‐Ming , Helfferich Friedrich G. 
Published: June 2004

AbstractThe Bodenstein approximation for trace‐level intermediates is used to reduce multistep reaction‐kinetic networks of arbitrary topology and size to simpler forms with only pseudosingle steps between nodes and to derive explicit equations for formation or consumption rates of end members. Networks with nontrace intermediates or steps of higher orders in intermediates must be broken at the respective steps into portions to which the procedure can then be applied separately. A recipe is provided with which rate and yield‐ratio equations are readily compiled for networks of arbitrary configuration and complexity. The method is illustrated with an example of a reaction of industrial interest.
Estimation of surface diffusion through porous media
Authors: Sircar S. , Rao M. B. 
Published: June 2004

AbstractA mathematical model is developed to describe steady‐state nonequilibrium surface diffusion of an adsorbing gas through an energetically homogeneous porous medium by assuming that the adsorption isotherm is linear and that the gas‐surface mass transfer can be described by the linear driving force model. Analytical solutions for the model are reported. It is found that the conventional assumption of local thermodynamic equilibrium between the gas and surface phases within the porous medium can seriously underestimate the surface diffusivity when the mass transfer rate is finite. Also, the length of the porous medium becomes a critical variable in that case.Meaningful estimation of surface diffusivity also requires that the gas phase diffusivity through the porous medium be accurately known. The estimated surface diffusivity is model dependent when local thermodynamic equilibrium is not established instantaneously. Modeling surface diffusion can be very complex when the surface is energetically heterogeneous.
Stirring characteristics in bioreactors
Authors: Vanags J. J. , Rikmanis M. A. , Ushkans E. J. , Viesturs U. E. 
Published: June 2004

AbstractDistribution data of local values of specific kinetic energy of medium flow in the bioreactor volume made it possible to determine some integral criteria. The relationship of these criteria, microorganism growth and biosynthesis characteristics was studied in 5–5,000‐L bioreactors. Energy‐efficient stirring systems that ensure a minimum damage of cells have been also studied.
A numerical study of mass transfer in free falling wavy films
Authors: Wasden Frederic K. , Dukler A. E. 
Published: June 2004

AbstractNumerical simulations of mass transfer into falling liquid films, both through the wavy interface and from the wall, have been performed for experimentally measured large waves within which the flow fields have been computed. Experiments have shown that the occurrence of waves on free falling films causes dramatic increases in mass transfer into the film, even under laminar flow conditions. Wave effects have been modeled in several ways, none of which predicts the observed rate of enhancement. The present numerical procedure includes solving the convective‐diffusion equation for wavy films by extending a technique developed for hydrodynamic simulation. The presence of waves is shown to cause significant velocities normal to each interface. In conjunction with recirculation within the large waves, these flow patterns produce transfer rates for large waves that are several times larger than predicted for quasiparallel velocity fields. Experimental wave structure data were used to define the dimensions and frequency of an average large wave and surrounding substrate. Computed transfer rates at both the gas‐liquid interface and the wall for a film composed of a periodic sequence of average waves agree well with published data. These simulations confirm the inadequacy of parabolic, or Kapitza‐type velocity profiles in formulating transport models.