bluuebunny/crossref_metadata_2025_split huggingface dataset:
Prediction of axial concentration profiles in catalytic fluidized reactors
Authors: van der Vaart D. R. 
Published: June 2004

AbstractA previous study by Fryer and Potter (1976) of the catalytic decomposition of ozone in a bubbling fluidized‐bed reactor is considered in the light of a recently developed reactor model. It is shown that since in‐bed sampling leads to an averaged concentration that is biased toward the emulsion‐phase gas composition, an increase in the ozone concentration in the sampled gas is predicted as the probe is raised above the bubbling bed. The analysis, which does not have to assume gas backmixing, shows that the minima in the ozone concentration profiles associated with this transition occurs between Hmf and H, the expanded bed height, and may even occur at lower points in the bed at higher excess fluidizing velocities. The model also correctly predicts the overall conversion of ozone as a function of the reaction rate constant and gas velocity without resorting to the fitting of any parameters.
Dynamic analysis of heterogeneous azeotropic distillation
Authors: Widagdo Soemantri , Seider Warren D. , Sebastian Donald H. 
Published: June 2004

AbstractA model and algorithm are presented for the separation of mixtures where the phase distribution on the trays is extremely uncertain, as it occurs when the mixtures have two partially‐miscible binary pairs and a minimum‐boiling ternary azeotrope. Included are an algorithm for the consistent initialization of index‐I differential/algebric equations, a novel algorithm for branch switching when the phase distribution changes at a real bifurcation point, and a reliable algorithm for phase stability analysis. Open‐loop responses are presented for the dehydration of secbutanol with disecbutylether in single‐stage, 12‐tray, and 33‐tray separators. These simulation results for the 33‐tray tower are in qualitative agreement with experimental measurements for the ARCO SBA‐II tower.
Identification and application of partial chemical equilibria in reactor modeling
Authors: Norval Graeme W. , Phillips M. Jane , Missen Ronald W. , Smith William R. 
Published: June 2004

AbstractA method is presented for identifying a subset of species (from a set of reacting species) that are within a specified numerical tolerance of equilibrium, as implied by a given experimental composition. The method also determines a linearly independent set of reactions involving these species and the number of stoichoimetric restrictions inherent in the set. This is an aid in reactor modeling, for example, in the computation of concentration profiles, in examining kinetic schemes or reaction mechanisms, and in identifying rate‐controlling processes. An example involving the methanol‐to‐gasoline synthesis is given to illustrate the method.
The curious behavior of homogeneous azeotropic distillation—implications for entrainer selection
Authors: Laroche L. , Bekiaris N. , Andersen H. W. , Morari M. 
Published: June 2004

AbstractWe examine the simplest homogeneous azeotropic distillation sequence of industrial relevance, where an entrainer is added to a binary azeotrope to recover both azeotropic constituents as pure products. Despite its apparent simplicity, such distillation columns can exhibit an unusual behavior not observed in zeotropic distillation:

For some mixtures, separation as a function of reflux goes through a maximum. At infinite reflux, no separation is achieved.

In some cases, achieving the same specifications with a larger number of trays requires a larger reflux.

Sometimes the only feasible separation yields the intermediate component as a pure distillate, while the bottom product contains the light and heavy components.

Sometimes the only feasible separation yields the intermediate component as a pure bottom product while the distillate contains the light and heavy components.

While these unusual features can be regarded as curiosities, they are essential for proper entrainer selection and design. For a minimum boiling azeotrope, the existing and conflicting entrainer selection rules state that one should use a component that introduces no distillation boundary between the azeotropic constituents (Doherty and Caldarola, 1985), and either a low or high boiling component that introduces no additional azeotrope or a component which introduces new minimum boiling azeotropes (Stichlmair et al., 1989). By taking advantage of the curious aforementioned features, as well as our experience involving more than 400 mixtures, we have been able to analyze the assumptions behind these criteria, show when those assumptions break down, and therefore understand the limitations of the criteria.
Parallel processing strategies for chemical process flowsheeting
Authors: Vegeais James A. , Stadtherr Mark A. 
Published: June 2004

AbstractThe potential for using the sequential‐modular, simultaneous‐modular, and equation‐based approaches to process flowsheeting on multiprocessing (parallel processing) computer architectures is assessed. The simultaneous‐modular and equation‐based problem formulations appear to be the most promising, but the sparse matrix techniques currently used, especially for the latter, do not perform well on parallel machines. We consider two different decomposition schemes for parallelizing the sparse matrix problems that must be solved. These are the bordered‐diagonal form and the bordered‐block‐diagonal form. The latter takes advantage of the inherent block structure of the flowsheeting matrix and represents a promising strategy for solving flowsheeting problems on parallel machines, especially for large problems.
A kinetic model for the fungal pellet lifecycle
Authors: Michel Frederick C. , Grulke Eric A. , Reddy C. Adinarayana 
Published: June 2004

AbstractMany industrially significant microbial products are produced during secondary metabolism by fungal pellets. Most models of mycelial pellet growth, however, consider only the primary growth phase. During secondary metabolism, the whiterot fungus Phanerochaete chrysosporium produces extra‐cellular lignin peroxidases and manganese‐dependent peroxidases which have been implicated in the degradation of lignin and various xenobiotics. This unstructured kinetic model for mycelial pellet cultures of P. chrysosporium describes the culture dry weight, respiration, glucose consumption, nutrient nitrogen uptake, pellet size and oxygen effectiveness factor during the lag, primary growth, secondary metabolic, and death phases. During secondary metabolism, the intraparticle diffusion of oxygen limits metabolism. Parameters for respiration during secondary metabolism are validated using three separate measurements: 1. by measuring oxygen concentration profiles in mycelial pellets using oxygen microelectrodes; 2. by measuring the depletion of oxygen from the culture fluid using a respirometer; and 3. by measuring the daily evolution of carbon dioxide. The physiological state of the mycelial pellets is predicted for various culture conditions and is related to the production of LIP and MNP during secondary metabolism.
Unified approach to solving optimal design‐control problems in batch distillation
Authors: Diwekar Urmila M. 
Published: June 2004

AbstractThis article presents a unified approach to simultaneous solution of optimization and optimal control problems in batch distillation, operating under different modes of operation: variable, constant, or optimal reflux. The simplified, computationally efficient short‐cut method and a novel algorithm to solve the optimal control problems in batch distillation is the basis of this unified approach. The short‐cut method identifies the feasible region of operation essential for optimization and optimal control problems, and provides analytical partial derivatives of the model parameters crucial to the solution.The new algorithm for the solution of optimal combination of the maximum principle and NLP optimization techniques. It circumvents the problems associated with the maximum principle approach (iterative solution of a two‐point boundary value problem, undounded control variables, and inability to handle the simultaneous optimization and optimal control problem), and the coupled ODE discretization‐NLP optimization scheme for nonlinear models (higher system nonlinearities, multiplicity of solutions, sensitivity of convergence to initial guesses). This algorithm reduces the dimensionality of the problem, and the nature of the algorithm allows a common platform to optimal solutions of different operating conditions. This article also shows that different categories of the optimal control problems in batch distillation essentially involve the solution of the maximum distillate problem.
Chemometric methods for process monitoring and high‐performance controller design
Authors: Kaspar Michael H. , Ray W. Harmon 
Published: June 2004

AbstractA huge amount of data is collected by computer monitoring systems in the chemical process industry. Such tools as principal component analysis and partial least squares have been shown to be very effective in compressing this large volume of noisy correlated data into a subspace of much lower dimension than the original data set. Because most of what is eliminated is the collinearity of the original variables and the noise, the bulk of the information contained in the original data set is retained. The resulting low dimensional representation of the data set has been shown to be of great utility for process analysis and monitoring, as well as in selecting variables for control. These types of models can also be used directly in control system design. One way of approaching this is to use the loading matrices as compensators on the plant. Some advantages of using this approach as part of the overall control system design include automatic decoupling and efficient loop pairing, as well as natural handling of nonsquare systems and poorly conditioned systems.
Enthalpy change on vaporization of aqueous and methanolic formaldehyde solutions
Authors: Liu Y.‐Q. , Hasse H. , Maurer G. 
Published: June 2004

AbstractA physicochemical model for vapor‐liquid equilibrium in multicomponent formaldehyde‐containing mixtures (Maurer, 1986; Hasse et al., 1990; Hasse and Maurer, 1991a). is extended to describe enthalpy changes upon vaporization. Predicted enthalpy changes are compared with new experimental results. The measurements were carried out with a thin‐film evaporator flow‐calorimeter (Liu and Maurer, 1991). More than 80 experimental data points for mixtures of formaldehyde + water and formaldehyde + methanol + (small amounts of water) are reported. The data cover the temperature range from 323 to 363 K (formaldehyde + water) and 312 to 347 K (formaldehyde + methanol) at liquid phase formaldehyde mole fractions up to about 0.3 (formaldehyde + water) and 0.6 (formaldehyde + methanol). Comparisons between predicted and experimental results for the enthalpy change reveal deviations of only a few percent. Further improvements are achieved by fitting some model parameters, which originally were estimated from noncalorimetric data.
Estimation of multiple specific growth rates: Experimental validation
Authors: Pomerleau Yves , Perrier Michel 
Published: June 2004

AbstractThe experimental validation of on‐line estimation of multiple specific growth rates for the bakers' yeast fed‐batch process is presented. Pole placement based parameter estimation combined with an asymptotic biomass observer constitute the basic algorithm. The full process model being ill‐conditioned for estimation using the available measured state variables, the use of two partial models related to two different states of the process is suggested. An alternating procedure between two sets of estimation algorithms designed from the partial models is proposed. The performance of the alternating procedure is validated both with simulated and experimental data. The accuracy of the estimates of the three specific growth rates involved in this process is verified according to two criteria based on the respiratory quotient and on the evaluation of the ethanol production/consumption rate.
Multidimensional modeling of turbulent two‐phase flows in stirred vessels
Authors: Gosman A. D. , Lekakou C. , Politis S. , Issa R. I. , Looney M. K. 
Published: June 2004

AbstractThis article outlines a computational procedure for the prediction of dispersed two‐phase, solid‐liquid and gas‐liquid, turbulent flows in baffled, impeller‐stirred vessels common in the chemical industries. A two‐flow Eulerian model is employed, based on the main assumption of interpenetrating coexisting continua. Mean momentum and mass conservation equations are solved for each phase and turbulent closure is effected by extending the single phase k‐ε turbulence model to two‐phase flows. The resulting set of highly coupled equations is solved by a two‐phase implicit algorithm, PISO‐2P, which allows calculation for a wide range of phase fraction, particle size and phase density rations. Predictions are presented for solid‐liquid and gas‐liquid (bubbly) flows. Comparisons are made with experimental data for the mean phase velocities and volume fraction, mean slip velocity and turbulence quantities.
Lumping nonlinear kinetics in porous catalysts: Diffusion‐reaction lumping strategy
Authors: Ocone Raffaella , Astarita Gianni 
Published: June 2004

AbstractNonlinear kinetics in multicomponent mixtures are best described in terms of continuous distribution functions. The quasilinearization procedure that we introduced in 1988 for “uniform” kinetics does not carry over to problems where second‐order derivatives appear, as in all cases where diffusion phenomena are of importance. We analyze a simple diffusion‐reaction problem in a porous catalyst, by making use of a perturbation technique. The general conclusions reached from this specific problem can be generalized to a wider class of diffusion‐reaction problems in complex mixtures.
An axial dispersion model of competing ion etching and mixing of binary solids
Authors: Elias Raul J. , Barteau Mark A. 
Published: June 2004

AbstractIon bombardment of solid surfaces produces a number of changes in the nearsurface region. The surface is etched by ejection of material by momentum exchange. The surface concentrations of the components of a multicomponent solid, such as an alloy, are altered by preferential sputtering. Finally, the incident ions penetrate a distance into the solid, producing a damaged region referred to as the “altered layer” in which diffusion is enhanced relative to that in the unaltered bulk. Previous models have not explicitly accounted for the ion penetration depth and the discontinuity of solid diffusivities at this boundary. We demonstrate that this problem is directly analogous to that of a plug‐flow reactor with axial dispersion, and solve for steady‐state and transient concentration profiles in a binary solid, taking into account the different values of the “Peclet number” appropriate for the two regions, the altered layer and the unaltered bulk of the solid.
Pressure drop, liquid holdup, and flow regime transition in trickle flow
Authors: Holub R. A. , Duduković M. P. , Ramachandran P. A. 
Published: June 2004

AbstractA phenomenological, pore‐scale, hydrodynamic model is developed for representation of the uniform, cocurrent, two‐phase flow in the low interaction regime in trickle bed reactors. Comparison of model predictions with numerous pressure drop and liquid holdup data reveals that phase interaction terms are negligible which results in a simplified model with no adjustable parameters. This model yields improved pressure drop and liquid holdup estimates for the low interaction regime. In addition, a criterion for the prediction of the trickle to pulsing flow regime transition is developed based on Kapitza's (1945) work on laminar film stability. This criterion compares favorably to data and to some other existing models for prediction of the trickle to pulsing flow regime transition.
Representation of excess properties of electrolyte solutions using a new equation of state
Authors: Fürst W. , Renon H. 
Published: June 2004

AbstractA new equation of state for electrolyte solutions has been developed from an expression of the Helmholtz free energy containing a nonelectrolyte part and a part relative to ions. The nonelectrolyte part is taken from the equations of state (EOS) of Schwartzentruber et al. (1989). The ionic part is composed of an MSA long‐range term to account for electrostatic interactions and a short‐range interaction term specific to ions. Using correlations between parameters and experimental ionic diameters, the model reduce to a one‐parameter model. It has been applied to numerous strong electrolyte systems and extended to ternary systems to test its predictability without mixing parameters for ions. Its results compare well to the results reported for other one‐parameter models (electrolyte EOS). Furthermore, it was found that the cation‐anion interaction parameter could also be correlated to experimental ionic diameters. Then, the osmotic coefficients of 28 alkaline and alkaline‐earth halide systems may be represented with a root mean square relative deviation of 2.9% using only six correlation parameters. This result has been extended to other systems, with the conclusion that the model with all parameters correlated may also be applied to systems other than halide solutions. The resulting model is predictive. The quality of the prediction was tested by determining osmotic coefficients relative to six systems without any parameter adjustment. The deviations of the predicted values range from 2.0 to 5.4%. The quality of the representation of mixed salts systems without mixing parameters was evaluated using experimental osmotic coefficients of 30 ternary systems.
Ordinary and transition regime diffusion in random fiber structures
Authors: Tomadakis Manolis M. , Sotirchos Stratis V. 
Published: June 2004

AbstractThe problem of bulk, transition and Knudsen regime diffusion in structures of freely overlapping fibers of various orientation distributions was numerically investigated, and the interrelation of the resulting effective diffusivities was examined. Fibers were randomly positioned and oriented in d = 1, 2, or 3 directions. A Monte Carlo simulation scheme was employed to determine the effective diffusivities from the mean‐square displacement of random walkers traveling in the interior of the porous structure. The effective diffusivity was found to depend strongly on the orientational distribution of the fibers, porosity of the fibrous structures, and Knudsen number. The tortuosity factor decreased in general with increasing porosity, approaching at the limit of dilute beds the lower bound derived for each direction of diffusion from variational principles. The simulation results agreed well with experimental values of the bulk tortuosity of fibrous beds from the literature. It was also found that the reciprocal additivity or harmonic average effective diffusivity expression (Bosanquet formula), commonly used to estimate transition regime diffusivities from the values at the ordinary and Knudsen diffusion limits, provides an excellent approximation for the effective diffusivity of fibrous beds, except for that parallel to the fibers of a unidirectional structure.
An experimental study of bubble deformation in viscous liquids in simple shear flow
Authors: Canedo Eduardo L. , Favelukis Moshe , Tadmor Zehev , Talmon Yeshayahu 
Published: June 2004

AbstractAn experimental study of the deformation of gas bubbles in viscous Newtonian liquids subjected to simple shear flow has been undertaken as a first step toward understanding bubble dynamics in polymer processing. Measurements of the shape, interfacial area, and volume of air bubbles suspended in the gap between two coaxial, counterrotating cylinders are presented and discussed as function of capillary number. At high capillary numbers (high deformations), the experiments confirm the theoretical model of Hinch and Acrivos.
Settling behaviors of iron oxide suspensions
Authors: Glasrud G. G. , Navarrete R. C. , Scriven L. E. , Macosko C. W. 
Published: June 2004

AbstractThis article shows the settling behaviors of flocculated, magnetic and nonmagnetic iron oxide suspensions. It is unique, since in the literature on settling of model submicron flocculated particulate suspensions there is no direct visualization of the structures and how they change during settling. Channeling, cracking, and a novel collapse phenomenon were detected during settling. Causes were investigated using lapse videorecording for side and top views. The effect of air bubbles was shown to contribute to the accelerated settling of the suspension by creating channels that conduct oil to the settling front. Settling heights were recorded for long periods of time (up to a year) for iron oxide suspensions of different concentrations. Decreasing tube diameters delayed settling, and magnetic interparticle forces produced smaller final settling heights. The effect of magnetic forces was interpreted in terms of a floc model. The model finds magnetic flocs 1.3 to 1.4 times denser than their nonmagnetic analogs. Finally, a mechanism is put forth to interpret the settling behavior observed.
Improving hydraulics and efficiencies with the T‐By sieve tray
Authors: Tedder D. William , Bravo Jose L. , Parker Byron M. , Parker Trent J. 
Published: June 2004

AbstractA modified sieve (that is, T‐By) tray uses a system of weirs and risers to approximate liquid plug flow over a cross‐flow, circular‐section tray. Vapor‐liquid contact is improved using a system of curtain‐pattern vapor holes and intermediate weirs to form cells across the tray that promote liquid mixing into discrete, wellmixed pools and stabilize froth. A theoretical model is used to analyze experimental data, guide tray design, and suggest new strategies for improving performance. These results indicate that tray efficiencies and stabilities can be increased without capacity losses. Pressure drop can also be manipulated to enhance performance.
Acceleration of chemical reaction in boiling polymer solutions
Authors: Chen L. , Hu G. H. , Lindt J. T. 
Published: June 2004

AbstractThis article discusses the effect of boiling inert hydrocarbon solvent on the model second‐order transesterification reaction of ethylene/vinyl acetate copolymer with 3‐phenyl 1‐propanol. In the presence of boiling, the overall reaction rate increases substantially due to mass‐transfer effects in the proximity of the vapor‐liquid interface. The present experiments and theory indicate that during the lifetime of a bubble in the boiling medium, the concentrations of reactants and the catalyst increase significantly near the bubble surface due to the rapid diffusion of the inert solvent. After the bubble rupture, the concentration differences persist and continue affecting the chemical reaction rate. The combination of these effects is responsible for the apparent increase in the overall reactivity.