bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nonlinear wave theory for dynamics of binary distillation columns
Authors: Hwang Yng‐Long 
Published: June 2004

AbstractA major difficulty in control of distillation columns stems from their nonlinear behavior, especially of columns producing high‐purity products. Based on a previous development that adapted fixed‐bed theories to simple countercurrent processes, this study has established a nonlinear wave theory for the nonlinear and distributed dynamics of binary distillation columns by including the effects of reflux, reboil, and combination of sections. This theory clearly elucidates the intriguing dynamic behavior of distillation columns such as high steady‐state gains, large response lags, strong dependence of dynamics on the magnitudes and directions of disturbances, and asymmetric dynamics of the transitions between two steady states. It also underlines the inadequacy of conventional linearized models for high‐purity columns. With fairly simple mathematics, this nonlinear wave approach may be useful for model development, control system design, dual‐composition control, and feedforward control.
Slit devolatilization of polymers
Authors: Maffettone Pier Luca , Astarita Gianni , Cori Laura , Carnelli Lino , Balestri Franco 
Published: June 2004

AbstractA model of the process of polymer devolatilization in a heated slit is presented. Momentum, heat, and mass transfer in the slit are taken into consideration, and only one adjustable parameter is used. The model predicts pressure and temperature profiles, and residual volatile contents at the exit which are in good agreement with those measured in a single instrumented slit.
Flow characteristics of waxy crude oils: Application to pipeline design
Authors: Wardhaugh L. T. , Boger D. V. 
Published: June 2004

AbstractWaxy crude oils are highly non‐Newtonian materials known to cause handling and pipelining difficulties and whose flow properties are time‐ and history‐dependent. Experimental techniques are described that enable reproducible steady‐state flow property data to be obtained from rotational viscometers. The flow properties are shown to depend strongly on the shear rate applied during cooling (shear history effect). This leads to a definable minimum operating point below which flow in a waxy crude oil pipeline would cease. Modified pipeline design techniques are presented for both laminar and turbulent flow at temperatures below the pour point, and it is shown that existing techniques overestimate the flow rate in laminar flow by the order of 100%. The modified design techniques can be used to quantitatively assess the performance of flow improver (pour point depressant) additives under steady‐state conditions.
Schedule optimization with simultaneous lot sizing in chemical process plants
Authors: Musier Reiner F. H. , Evans Lawrence B. 
Published: June 2004

AbstractOperational problems are of increasing importance as the process industries turn to the batch manufacture of high‐value specialty products. A method is presented to minimize stockout for multiunit plants where customer orders may constitute nonintegral batch multiples. Product‐ and unit‐dependent processing times and batch sizes, sequence‐dependent changeover times, and product‐to‐unit assignment constraints are modeled for nonidentical parallel processes. Arbitrary initial conditions are also modeled. The algorithm determines the number of production runs of each product, run length (lot sizing), the assignment of run to units, and run sequence on each unit.Scheduling with simultaneous lot sizing has not previously been addressed in the literature. The evolutionary method presented here obtains near‐optimal (and often globally optimal) solutions on industrial‐sized test problems. These results are significant since near‐optimal scheduling of many industrial process plants now becomes possible, although problems of this complexity are intractable using exact methods.
A Monte Carlo analysis of acid hydrolysis of glycosidic bonds in polysaccharides
Authors: Pinto José‐Henrique Q. , Kaliaguine Serge 
Published: June 2004

AbstractKinetic experiments for the hydrolytic depolymerization of cellobiose and amylose were performed in acidic medium. In the case of amylose, only the production rate of glucose was monitored. Then, a Monte Carlo procedure was developed to simulate long‐chain saccharide acid hydrolysis using the kinetic information obtained from the model compound, cellobiose. This stochastic procedure, which is applicable to the homogeneous acid hydrolysis of highly amorphous polysaccharides of sufficient degree of polymerization, provides estimated curves for the time evolution of all intermediate products. Literature data on the hydrolysis of oligoxylans were also compared to the results obtained from the Monte Carlo procedure. The depolymerization of linear polysaccharides, which should normally be viewed as a nonhomogeneous Markov chain, could be considered as a homogeneous Markov chain, provided that the chain is visited at specifically determined time intervals.
Model for spherical cavity radii and potential functions of sorbates in zeolites
Authors: Baksh M. S. A. , Yang R. T. 
Published: June 2004

AbstractA spherical pore model for calculating the zeolite cavity radius and the potential energy of interactions of noble gases (Ar, Kr, Xe) is presented. The model utilizes the gas adsorption isotherm and equates the free energy change upon adsorption to the potential energy of interaction of the gas molecules with the zeolite cavity. The results obtained for the cavity radius using Ar, Kr, and Xe adsorption isotherms are in excellent agreement with those of the cavity radius for 5A, 13X, and Y zeolites obtained from crystallographic data. Also, the average potential energies of interaction of these gases with the surface atoms of the zeolite cavities, calculated from the isotherms and the spherical pore model, compare reasonably well with the internal energies determined from the experimental heats of adsorption.
Comparative analysis of qualitative models when the model changes
Authors: Grantham S. D. , Ungar L. H. 
Published: June 2004

AbstractAn important application of the recently developed techniques in qualitative mathematical modeling is to qualitatively predict how changes in the operation of chemical units affect their behavior. Weld (1987, 1988a,b) has developed a series of comparative techniques that analyze the effect of perturbations to the parameters of a given qualitative unit model. In this article we demonstrate a system, based on the qualitative process theory of Forbus (1984), which extends comparative analysis in two ways. First, it predicts the effects of changes in the qualitative equations and in parameter values. Secondly, it compares physical descriptions, rather than comparing models directly, and builds and compares the associated models automatically.
Periodic forcing of the CSTR: An Application of the generalized II‐criterion
Authors: Sterman Leah E. , Ydstie B. Erik 
Published: June 2004

AbstractNonlinearities give the opportunity to influence the time average performance of a system by periodic forcing of external parameters. In this article, this concept is applied to the following reactions occurring in a continuous stirred tank reactor: A → B, A → C; A ⇋ B; A → B → C; and A → B, A + B → C. It is shown, using a generalized II‐criterion, that if the activation energies satisfy the constraint E1 > E2, then the yield of B is improved using high‐frequency periodic perturbations in the temperature regardless of reaction order and operating conditions. Conversely, if E1 > E2, then high‐frequency forcing always leads to a deterioration of the yield. There exist regions of parameter space where low‐frequency forcing may lead to an improvement. Results valid for low and intermediate frequencies are developed and can be used to predict additional areas of parameter space of interest for periodic operation.
Axial mixing in a reciprocating plate column with very small density gradients
Authors: Baird Malcolm H. I. , Rao N. V. Rama 
Published: June 2004

AbstractAxial dispersion coefficients have been measured in single‐phase flow conditions in a 5.08‐cm‐dia. reciprocating plate extraction column. The measurements were done under steady‐state conditions by analyzing temperature profiles (for hot and cold water mixing) and concentration profiles (for mixing of water and salt solutions). The results confirm previous published data of Holmes et al. (1991) in showing that axial dispersion is increased strongly in the unstable situation, where liquid density increases with height. The earlier work is extended to the condition where buoyant energy dissipation is exceeded by mechanical energy dissipation by four orders of magnitude. Even in this case, axial mixing is increased significantly by density gradient‐induced instability. Results have been correlated by a simple equation based on a mixing length model.
Knudsen diffusivities and properties of structures of unidirectional fibers
Authors: Tomadakis Manolis M. , Sotirchos Stratis V. 
Published: June 2004

AbstractEffective Knudsen diffusion coefficients are presented for fibrous structures consisting of parallel, nonoverlapping or partially overlapping fibers. They are computed by means of a Monte Carlo simulation scheme which is employed to determine the mean square displacement of molecules travelling in the interior of the porous medium for large travel times. The results show that structures of paralle, non‐overlapping fibers have smaller effective diffusion coefficients parallel to the fibers than structures of parallel, randomly overlapping fibers of the same porosity and fiber radius, but larger in directions perpendicular to the fibers. Partially overlapping fiber structures are found to exhibit behavior intermediate to those of the two extreme cases. Molecular trajectory computations are also used to obtain results for the structural properties of partially overlapping fiber structures (e.g., porosity and internal surface area, accessible porosity and internal surface area, and percolation threshold), which are compared with some results of the literature for the equivalent problem of partially overlapping disks on a plane.
Transient deformation of freely‐suspended liquid droplets in electrostatic fields
Authors: Haywood R. J. , Renksizbulut M. , Raithby G. D. 
Published: June 2004

AbstractThe problem of freely‐suspended liquid droplets deforming due to an applied electrostatic field is examined. Developed is a numerical model capable of predicting the complete transient histories of droplets in systems with a wide range of dispersedand continuous‐phase densities, viscosities, relative permittivities, and electric field strengths. For liquid/gas systems, the predictions of the numerical model demonstrated that the critical field strength and critical permittivity ratio during actual transient breakup are not necessarily the same as those predicted by steady‐state theories. An approximate analytical model of transient droplet deformation is also developed, which is able to predict the deformation time histories for large Ohnesorge number, small‐deformation liquid/liquid systems. The approximate analytical model agreed well with the results of the complete numerical model.
Multicomponent adsorption and chromatography with uneven saturation capacities
Authors: Gu Tingyue , Tsai Gow‐Jen , Tsao George T. 
Published: June 2004

AbstractIn chromatographic separations involving elutes with large differences in the molecular size, the adsorption saturation capacities of the elutes may differ because of the differences in the degree of size exclusion. With uneven saturation capacities, isotherm crossovers may occur, which often results in selectivity reversal. In this work, a new multicomponent isotherm has been developed for this kind of system. The isotherm is an extension of the common multicomponent Langmuir isotherm and introduces no or a very limited number of new parameters for its construction. The isotherm crossover conditions have also been derived. Simulations based on a general rate model using the new isotherm have successfully demonstrated the phenomena of peak reversal and crossover of breakthrough curves.
A series solution for mass transfer in laminar flow with surface reaction
Authors: Bašić Andjelko , Duduković Milorad P. 
Published: June 2004

AbstractWe present an explicit analytical solution for the Lévêque's problem with the boundary condition of the third kind. This solution is applicable to problems of mass (heat) transfer with surface reaction (surface resistance) in the entry region of fully developed flow fields of power law fluids, and to the developing boundary layer flows that admit Falkner‐Skan solutions, provided that the Schmidt (Prandtl) number is large. The series form of the solution developed by inversion of the Laplace transform has excellent convergence properties within the concentration (temperature) boundary layer in contrast to the integral forms that are usually reported for problems of this type. An efficient computational algorithm for evaluation of the surface concentration is presented, as well as accurate approximate formulas in the form of simple algebraic expressions for the local and average mass (heat) transfer coefficients and the surface concentration (temperature).
Modeling and simulation of a honeycomb reactor for high‐severity thermal cracking
Authors: Heynderickx G. J. , Froment G. F. , Broutin P. S. , Busson C. R. , Weill J. E. 
Published: June 2004

AbstractA new steam cracking technology has been developed that uses honeycomb‐type ceramic reactors with high surface to volume ratios and is heated by flue gas. “Rectangular” process gas temperature profiles are possible with such a reactor. An optimal combination of temperature profile and residence time leads to a very significant increase in olefins yield with respect to conventional cracking units. Benchscale results are compared with predictions based on a reactor model, which accounts in great detail for the geometry of the structure and the associated heat transfer, combined with a rigorous kinetic model based on radical reaction mechanisms.
Equation of state for pure fluids and mixtures based on a truncated virial expansion
Authors: Anderko Andrzej , Pitzer Kenneth S. 
Published: June 2004

AbstractAn accurate, yet simple, equation of state was developed for pure fluids ranging from nonpolar to H2O and their mixtures. The equation consists of a virial expansion truncated after the fourth virial coefficient and a closed‐form term approximating higher coefficients. For nonpolar or weakly polar compounds, the equation is generalized using critical temperature, critical pressure, and acentric factor. Despite its simplicity, the equation represents the P‐V‐T and saturation properties of pure fluids with a very good accuracy, which is comparable to that of multiparameter, generalized BWR‐type equations. For mixture calculations, mixing rules were formulated based on the rigorously known composition dependence of virial coefficients. The equation represents vapor‐liquid, gas‐gas and liquid‐liquid equilibria, as well as volumetric properties of mixtures containing nonpolar components and/or water. Binary parameters can be generalized for series of mixtures containing a common component.
Baffle effects on performance of catalytic circulating fluidized bed reactor
Authors: Jiang Peijun , Bi Hsiaotao , Jean Rong‐Her , Fan Liang‐Shih 
Published: June 2004

AbstractBaffle effects on the performance of a catalytic circulating fluidized bed reactor were examined experimentally. The circulating fluidized bed reactor or riser was 102 mm in diameter and 6.32 m in height. Reaction was the catalytic decomposition of ozone using FCC particles with a mean diameter of 89 μm, impregnated with ferric oxide as catalysts. Four ring‐type baffles, mounted horizontally around the riser wall, were used in this study. Ozone concentrations were measured in both axial and radial directions under various operating conditions in a riser with and without baffles. Experimental results showed that in a riser with baffles, the ozone concentration in the radial direction was more uniform and the ozone conversion was higher than that in a riser without baffles except at the lowest gas velocity used. A mathematical model developed accounted for the gas‐phase ozone conversion under various operating conditions. The gas‐solid contact efficiency in the riser was discussed in light of the model.
Molecular thermodynamics of solubilities in gas antisolvent crystallization
Authors: Dixon David J. , Johnston Keith P. 
Published: June 2004

AbstractAn expanded liquid molecular thermodynamic model is developed to predict the solubilities of pure solids in a liquid expanded with a gaseous antisolvent. Experimental data are presented for systems containing naphthalene, phenanthrene, and a mixture of both in toluene expanded with a gas antisolvent, CO2. The pressure range is 1 to 64 bar and the temperature is 25°C. The data are predicted accurately with regular solution theory up to moderate pressures, but not at the higher pressures where the liquid phase is nearly pure CO2. In contrast, the new expanded liquid equation of state model describes the wide range of behavior from the nearly ideal liquid solution at ambient pressure to the highly nonideal compressible fluid at elevated pressures. As a result, it predicts solubilities accurately over three orders of magnitude by using only binary interaction parameters. The implications of the phase behavior on fractional crystallization with a gas antisolvent are discussed.
Nonisothermal photochlorination of methyl chloride in the liquid phase
Authors: Cabrera María I. , Alfano Orlando M. , Cassano Alberto E. 
Published: June 2004

AbstractA model for the photochlorination of methyl chloride in the liquid phase was developed, with numerical solution and experimental verification. The reaction was carried out under pressure, using carbon tetrachloride as a solvent with polychromatic radiation in a nonisothermal tubular reactor. Momentum, thermal energy, mass and photon balances were established rigorously and solved numerically. Reaction constants were taken from the known reaction mechanistic kinetics in the gas phase. Theoretical results agreed well with bench‐scale experiments performed inside an elliptical reflector in the prediction of both reactant conversion and product selectivities. The validated model was used to show the existence of significant temperature and concentration gradients inside the reactor, both in the radial and in the axial directions.
Model of particle‐vapor codeposition with application to ceramic materials synthesis
Authors: Hurt Robert H. , Allendorf Mark D. 
Published: June 2004

AbstractThe simultaneous deposition of particles and material from the vapor phase gives rise to surface deposits having characteristic structure. A mathematical model of the particle‐vapor codeposition process is developed that predicts the structure and properties of these deposits as well as their growth rate over a wide range of conditions. A random sphere formulation is developed that provides the framework for a unified treatment of both subprocesses: ballistic particle deposition and porous media densification through vapor deposition. The model is applied to particleenhanced chemical vapor deposition (PECVD) processes for the production of ceramic materials. In PECVD, particles are introduced into a CVD process, either in the form of an aerosol created in situ by a controlled amount of gas‐to‐particle conversion or in the form of independently charged powder. The model identifies PECVD conditions that produce deposition rates substantially higher than those achievable by conventional CVD.
Stability of SISO quadratic dynamic matrix control with hard output constraints
Authors: Zafiriou Evanghelos , Marchal André L. 
Published: June 2004

AbstractThe inclusion of output constraints in the on‐line optimization problem solved by quadratic dynamic matrix control (QDMC) can result in a unstable, closed‐loop system, even when the corresponding unconstrained algorithm is stable. The presence of constraints in the optimization problem produces a nonlinear, closed‐loop system, although the plant and model dynamics are assumed linear. This article quantifies the effect of output constraints on both nominal and robust stability for single‐input/single‐output processes. Stability conditions provided can be used to select the QDMC parameters and constraint window. Examples demonstrate that these conditions can capture the nonlinear effect of the constraints and that tuning rules developed for the unconstrained case should not be used with output constraints. An example with dead time error illustrates the use of this framework to guarantee the robustness of constrained QDMC with respect to modeling error.
An efficient design method for binary, azeotropic, batch distillation columns
Authors: Diwekar Urmila M. 
Published: June 2004

AbstractUsing rigorous models to simulate batch distillation involves the solution of many stiff differential equations. The dimensionality of the problem also increases with an increase in the number of plates and components, which imposes limitations on the use of rigorous models. Furthermore, problems in design, optimization, synthesis, and control involve iterative procedures, and considerable computational efforts would be required to solve them rigorously. As an alternative, the short‐cut method (Diwekar and Madhavan, 1991a) provided reasonably accurate solutions without much computational effort. This method in the present form, however, cannot be applied to azeotropic systems because of the impassable barrier of the azeotropic point and needs to be modified. The azeotropic approximation proposed by Anderson and Doherty (1984) was used to modify the short‐cut method for binary azeotropic systems. The modified algorithm presented here was tested extensively with a number of binary azeotropic systems for both constant reflux and variable reflux modes of operation, and the results were shown to compare well with the rigorous models. The method requires significantly less computational efforts and is very useful in analyzing feasible region of operation.
Linear oscillations of a drop in uniform alternating electric fields
Authors: Yang Wenrui , Carleson Thomas E. 
Published: June 2004

AbstractOscillations of a conducting drop immersed in a dielectric fluid in an alternating electric field were modeled to understand the enhancement of transport processes by the electric field. Numerical solutions for oscillation amplitude, velocity distribution, resonant frequency and streamlines were obtained. The effects of viscosity and density on the resonant frequency and the velocity distribution were investigated. It was found that the resonant frequency of viscous fluids was always smaller than the free oscillation frequency of the same droplet. The predicted scanning frequency response curve and the streamlines agree well with the experimental observations.
Diffusion in ion‐exchanged clinoptilolites
Authors: Ackley Mark W. , Yang Ralph T. 
Published: June 2004

AbstractThe two‐dimensional channel structure of clinoptilolite has been altered systematically by ion exchange to study the effects of cation type, size, location, and distribution on the diffusion of N2 and CH4 probe molecules. Concentration‐dependent diffusion time constants (D/L2) were determined from gravimetric uptake measurements for fully‐exchanged K+, Na+, and H+ clinoptilolites, and highly‐exchanged Ca2+ (89%) and Mg2+ (72%) clinoptilolites. Both plane sheet and parallel channel diffusion models were developed from the one‐dimensional plane sheet diffusion equation and fit to the uptake data. Resulting values of D/L2 varied by a factor of more than 1,000 for both N2 and CH4, while kinetic selectivity spanned nearly two orders of magnitude for this group of modified clinoptilolites. Achieving this range in performance for the difficult N2/CH4 separation demonstrates the excellent potential for tailoring clinoptilolite by cation manipulation for the kinetic separation of other gas mixtures.