bluuebunny/crossref_metadata_2025 huggingface dataset:
Gas absorption with zero‐order chemical reaction
Authors: Riazi Mohammed , Faghri Amir
Published: June 2004

The governing differential equation for gas absorption in laminar falling film with zero‐order homogeneous reaction is solved analytically by the method of separation of variables, and subsequent solution with confluent hypergeometric function. The result for concentration profile was obtained in the forms of a sum of a polynomial and an infinite series of hypergeometric functions.

An enhancement factor, E, is defined as the ratio of the calculated absorption rates and the absorption rates found from a simple penetration model. When the Hatta number, is greater than 2, the enhancement factor is given by a simplified form with an error of less than 2%.
Pressure swing adsorption. Part III: Numerical simulation of a kinetically controlled bulk gas separation
Authors: Raghavan N. S. , Ruthven D. M.
Published: June 2004

A numerical simulation has been developed for a simple two‐bed PSA system in which kinetic effects and changes in flow rate due to adsorption are significant. The model is therefore more general than most previous models for the PSA cycle. The model equations are solved by the method of double collocation. When applied to air separation on a carbon molecular sieve, using independently measured kinetic and equilibrium parameters, the predicted performance appears consistent with available performance data for a commercial unit.
Nonlinear parameter estimation: A case study comparison
Authors: Biegler L. T. , Damiano J. J. , Blau G. E.
Published: June 2004

The literature abounds with the application of optimization methods for estimating model parameters in equation systems. The utility of these methods is frequently demonstrated on pathological examples using simulated data generated from a known model with a random error component and a known statistical distribution. Unfortunately, parameter estimation problems encountered in practice do not have this advantage. The true model is frequently not known. In fact, one is faced with choosing among various candidate models, all of which may be wrong. Moreover, the error structure is generally unknown and must be estimated from the data. Finally, a great deal of mathematical expertise is required to transform the model and select meaningful starting guesses before parameter estimation can be successful.

In order to demonstrate the difficulties of parameter estimation in the industrial environment and the limitations of existing methods, a parameter estimation problem formulated by the Dow Chemical Company is presented and solved. This test problem consists of a stiff differential/algebraic (DAE) model that describes complex kinetics and requires the estimation of nine parameters from batch reactor data. Here the model was inadequate to describe the data, the error structure was not specified and the starting guesses led to a nontrivial optimization problem.

The Dow parameter estimation problem was distributed in 1981 to 165 researchers as a followup to the 1980 FOCAPD conference. Of those researchers, eleven agreed to apply their methodologies and expertise to this problem. However, only five acceptable solutions were finally submitted. Here we present and compare these results. Each solution was obtained using different strategies. In most cases the form of the model was also changed to accommodate the algorithms used and to ease the solution procedure. Therefore, while this case study does not present a direct numerical comparison of algorithms, it does offer guidelines and insight towards the solution of difficult parameter estimation problems.
A general design equation for air lift pumps operating in slug flow
Authors: Clark N. N. , Dabolt R. J.
Published: June 2004

Air lift pumps are finding increasing use where pump reliability and low maintenance are required, and where corrosive, abrasive, or radioactive fluids must be handled. Although air lifts are used in nuclear fuel reprocessing plants, no general, theoretically sound equation has been proposed in the literature for tall air lift design. Such an equation is developed from two‐phase flow theory to predict the height to which an air lift pump operating in the slug flow regime can lift a given volumetric flow rate of liquid, given the air flow rate and pressure at the point of gas introduction. The widely used drift‐flux model for the prediction of holdup is combined with an approximate relationship to predict pressure loss, and is substituted into the total pressure differential. Integration of the resulting equation provides an explicit formula for the calculation of lift. Experimental work using a variety of liquids in a 38 mm dia. air lift test installation supports the new design equation and demonstrates its flexibility.
A statistical mechanical model for adsorption and flow of pure and mixed gases in porous media with homogeneous surfaces. Part I: Theoretical development
Authors: Lee C. S. , O'Connell J. P.
Published: June 2004

A unified statistical mechanical treatment is developed for adsorption and surface diffusion on homogeneous surfaces. Using molecular parameters, the model accounts for all physical effects of adsorbent‐adsorbate, adsorbate‐adsorbate, and adsorbate‐gas interactions at submonolayer coverages.
A statistical mechanical model for adsorption and flow of pure and mixed gases in porous media with homogeneous surfaces. Part II: Applications
Authors: Lee C. S. , O'Connell J. P.
Published: June 2004

Application of the model of Part I is made to several systems with various graphitized carbon blacks over wide ranges of temperatures and submonolayer coverage. Agreement with all data for equilibrium and transport is probably within experimental error.
Simultaneous optimization and heat integration of chemical processes
Authors: Duran M. A. , Grossmann I. E.
Published: June 2004

A procedure is proposed for simultaneously handling the problem of optimal heat integration while performing the optimization of process flow sheets. The method is based on including a set of constraints into the nonlinear process optimization problem so as to insure that the minimum utility target for heat recovery networks is featured. These heat integration constraints, which do not require temperature intervals for their definition, are based on a proposed representation for locating pinch points that can vary according to every set of process stream conditions (flow rates and temperatures) selected in the optimization path. The underlying mathematical formulations correspond to nondifferentiable optimization problems, and an efficient smooth approximation method is proposed for their solution. An example problem on a chemical process is presented to illustrate the economic savings that can be obtained with the proposed simultaneous approach. The method reduces to simple models for the case of fixed flow rates and temperatures.
Comparison of linear distributed‐parameter filters to lumped approximants
Authors: Cooper D. J. , Ramirez W. F. , Clough D. E.
Published: June 2004

Optimal distributed‐parameter filters are commonly implemented using approximating lumped Kalman filtering theory. The effect of such an approximation is investigated. A theoretical development shows that there is a loss in the spatial noise correlation for the lumped approximants. Two numerical examples of engineering significance illustrate that one result of this loss is slower filter convergence for the lumped approximants relative to the full distributed‐parameter filters.
Theory of electrophoretic separations. Part I: Formulation of a mathematical model
Authors: Saville D. A. , Palusinski O. A.
Published: June 2004

A general model is developed for the electrophoresis of soluble materials. The model describes the evolution of concentration fields for a set of compounds which undergo transport by flow, diffusion, and migration in an electric field and simultaneously participate in rapid dissociation‐association reactions. Modes of electrophoresis requiring special treatment can now be studied in a unified context. As an example of its utility, the model is used analytically to study a process known as isotachophoresis. In Part II two electrophoretic separation processes are simulated numerically, demonstrating the model's versatility.
Effect of catalyst pore and pellet sizes on deactivation in SRC oil hydrotreatment
Authors: Chang Hong Ju , Crynes B. L.
Published: June 2004

A reaction‐deactivation model based on experimental observations was used to predict catalyst life for hydrotreating a solvent‐refined coal oil. The model coordinates catalyst pore and pellet sizes to the quantity of carbonaceous material deposited. The results show that for a parallel fouling mechanism, a larger pore size and/or smaller pellet size catalyst tends to have a longer life as well as higher activity. The model also shows that deactivation due to coke deposition approaches a limit.
Effect of specific surface area on the reactivity of CaO with SO2
Authors: Borgwardt R. H. , Bruce K. R.
Published: June 2004

The rate of reaction of calcined limestone with SO2 and O2 was measured at conditions that eliminate all resistances not associated with the CaO grain surface. Reactivity increased with the square of the BET surface area when grain size was varied as an experimental parameter. The observed effects of surface area and temperature account for the SO2 capture reported for boiler tests of the limestone injection process.
The hydrodynamics of trickling flow in packed beds. Part I: Conduit models
Authors: Sáez A. E. , Carbonell R. G. , Levec J.
Published: June 2004

The hydrodynamics of trickling flow in packed beds is modeled by representing the porous medium as an array of parallel conduits of circular cross section.

First, a straight tube model is developed and analytical solutions are obtained for the relative permeabilities of the gas and liquid phases. Then a periodically constricted tube model is proposed and the equations of motion are solved numerically to determine the effect that surface tension forces have on the relative permeabilities. The constricted tube model predicts that the relative permeabilities of the phases are appreciably sensitive to surface tension forces, a prediction that seems at odds with experimental observations. This discrepancy may be caused by the assumption of fully wetted surface area of particles employed in the model.

The straight tube model confirms experimental results indicating that the liquid phase relative permeability is, for practical purposes, insensitive to the gas flow rate and to the gas‐to‐liquid density and viscosity ratios. Both conduit models show that the gas phase relative permeability curves are strong functions of the gas phase Reynolds number when this parameter is small. For large gas Reynolds numbers, a single curve for the relative permeability as a function of saturation is obtained. These trends are observed in previous experimental studies.
Capillary condensation of water vapor within a particulate bed
Authors: Shukla P. N. , Wilkinson B. W.
Published: June 2004

For situations in which capillary condensation of water occurs (e.g., within porous media), the thermodynamics can usually be studied by means of the Laplace and Young equations and a compressibility equation. We show here that the compressibility equation for the liquid does not reflect the criteria of equal gas and liquid phase potential changes at equilibrium, for departures from a specified reference state.

Carman (1953) concluded that the capillary condensate can exist in a state of tension for large vapor‐liquid pressure differentials and may exhibit physical properties that differ substantially from normal values. The familiar Kelvin equation is used to calculate the capillary curvature and is derived from the general Laplace and Young relationship. Melrose (1966) has obtained this relationship by matching the coefficients of the internal free energy and hydrostatic balances of the system shown in Figure 1.
Path‐following approaches to the solution of multicomponent, multistage separation process problems
Authors: Vickery D. J. , Taylor Ross
Published: June 2004

In solving the nonlinear algebraic equations that are normally used to model multicomponent separation processes, one is not guaranteed that Newton's method or any of its relatives will converge to the solution. This paper describes two homotopies and their use in the solution of difficult equilibrium stage separation process problems. The first, the Newton homotopy, is able to solve more problems than a standard implementation of Newton's method but is not the most reliable homotopy. Since the equations being solved no longer model a separation process unit, the Newton homotopy sometimes suffers from intermediate solutions that are physically meaningless. The second, the thermodynamic homotopy, is strongly based on the thermodynamic properties of the systems involved. This new homotopy is able to handle not only the more traditional distillation problems (hydrocarbon systems and mildly nonideal systems), but is also extremely effective at solving azeotropic and extractive distillation problems. The implementation of these methods requires only minor modifications to existing software.
Fluid flow patterns and velocity distribution on commercial‐scale sieve trays
Authors: Solari R. B. , Bell R. L.
Published: June 2004

A fluorimetric technique was used to determine detailed residence time and velocity distribution on commercial sieve trays installed in a five‐tray, 1.22 m dia. air/water simulator. Results show a strong effect of the gas rate on the residence time distribution. At low air rates, isochron lines of high residence time are found at the column wall, and the variance distributions suggest the existence of zones of different degrees of mixing. The velocity profiles at Fs (vapor velocity load) factors less than 0.65 show severe flow nonuniformities characterized by a high velocity at the centerline and stagnant zone close to the wall. At higher Fs factors the velocity maldistribution seems to be relatively mild. Correlations are presented to estimate the velocity distribution on the tray as a function of the gas rate.
Drop breakup in turbulent stirred‐tank contactors. Part I: Effect of dispersed‐phase viscosity
Authors: Calabrese R. V. , Chang T. P. K. , Dang P. T.
Published: June 2004

The extent to which dispersed‐phase viscosity influences equilibrium mean drop size and drop size distribution at constant interfacial tension is determined for dilute suspensions by dispersing silicone oils of various viscosity grades in water. A mechanistic model for mean drop size is developed which predicts the moderate‐viscosity data and whose parameters correlate the high‐viscosity results. Trends in the mean size data coincide with those for the drop size distribution, which broadens considerably as viscosity increases and suggests a dependency on breakage mechanism.
Mixing in continuous crystallizers
Authors: Tavare N. S.
Published: June 2004

The review is concerned primarily with some aspects of mixing in continuous crystallizers and recognizes the central importance of the interplay between the mixing and crystallization (or precipitation) processes in the design and performance evaluation of industrial crystallizers. The paper adopts a unifying treatment from a chemical reaction engineering viewpoint in which the Lagrangian approach to mixing in crystallizer systems is emphasized. The concepts of macro and micromixing applied to crystallization configurations have been introduced with due emphasis on the modeling efforts. The present state of knowledge in various related areas of continuous mixing is assessed to help direct future trends in research.
Interactions of precipitation/dissolution waves and ion exchange in flow through permeable media
Authors: Bryant S. L. , Schechter R. S. , Lake L. W.
Published: June 2004

This paper describes reactive flow in permeable media based on a numerical model that assumes local thermodynamic equilibrium. The model simulates single‐phase, one‐dimensional flow with greater generality than any model in the current literature. The mathematical foundation for the formulation is discussed in some detail. Results for hypothetical examples demonstrate that ion exchange and precipitation/dissolution of solids can interact to produce wave behavior not possible with either phenomenon alone. An important application involving both ion exchange and precipitation/dissolution is alkaline flooding. Model predictions for several laboratory alkaline floods indicate that the assumption of equilibrium is justified for these experiments. Simple calculations based on the equilibrium theory provide estimates of pH loss and hydroxide penetration distance.
Dyanmic compartmental models for separation processes
Authors: Benallou A. , Seborg D. E. , Mellichamp D. A.
Published: June 2004

A low‐order modeling technique for separation processes is developed by considering a staged column as a compartment system in which a number of stage are lumped to form an equivalent stage. This method leads to low‐order models of separation processes directly and without linearization. Moreover, the resulting models have state variables and parameters that are physically significant. In contrast to alternative model reduction methods, compartmental analysis guarantees preservation of both material balances and steady states for arbitrary changes in the input variables.

A comparison of compartmental analysis to a recently proposed technique based on orthogonal collocation, both methods incorporating an equimolal overflow assumption, shows the efficiency and robustness of the compartmental method.
Treatment of gas‐solid adsorption data by the error‐in‐variables method
Authors: High M. S. , Danner R. P.
Published: June 2004

A recently developed error‐in‐variables method of calculating regression parameters was applied to the modeling of gas‐solid adsorption equilibria. The method accounts for error in all experimental variables in the regression calculations. Regression coefficients from pure component data calculated by the new method were used to predict multicomponent equilibria. The multicomponent predictions using pure component parameters calculated by the error‐in‐variables method were more accurae than predictions using parameters calculated by conventional least‐squares regression.
Water sorption from air by celite‐supported CaCl2: Mathematical model/experimental studies
Authors: Heiti R. V. , Thodos George
Published: June 2004

A feasible means for the long‐term storage of thermal energy considers the hydration of CaCl2. Differential and integral beds of Celite pellets impregnated with CaCl2 were employed to dehydrate humid air. Experimental studies were used in modeling the behavior of this system, which involved the solution of four partial differential equations. The simultaneous solution of these equations, using a modified Gear's method, yielded information about the temperature and composition distribution of both the air stream and the impregnated pellets. The mathematical solution predicts the time‐dependent moving front characterized by a maximum temperature. Predicted and experimental measurements were found to be in good agreement.
Mechanisms and kinetic modeling of calcium oxalate crystal aggregation in a urinelike liquor. Part II: Kinetic modeling
Authors: Hartel R. W. , Randolph A. D.
Published: June 2004

A general form of the population balance equation, including aggregation and rupture terms, was solved numerically to model the experimental calcium oxalate distributions generated in Part I of this series. Semiempirical formulations for the aggregation and disruption functions were found that resulted in excellent matches between experimental and predicted distributions. Both the aggregation and the disruption rates were found to vary with oxalate concentration and inner cylinder rpm of the aggregator.
Use of adaptive methods in premixed combustion
Authors: Smooke M. D.
Published: June 2004

This paper investigates the application of spatially adaptive numerical methods in the solution of one‐dimensional premixed combustion problems. The selection of grid points by equidistribution of positive weight functions across consecutive mesh intervals is considered. The method is applied in the solution of a steady premixed laminar flame problem and a time‐dependent freely propagating flame problem. The adaptive numerical results are compared with corresponding equispaced calculations.
Distillation with intermediate heat pumps and optimal sidestream return
Authors: Lynd L. R. , Grethlein H. E.
Published: June 2004

The technique of distillation with intermediate heat pumps and optimal sidestream return—IHOSR distillation—is presented. IHOSR distillation allows heat to be moved between points in a distillation column with greater efficiency than several other methods of using heat pumps for distillation.
Steady state analysis of a continuous clarifier‐thickener system
Authors: Lev O. , Rubin E. , Sheintuch M.
Published: June 2004

Kynch's theory of sedimentation is adopted to solve for the attainable steady state concentration in a vertical continuous sedimentation basin incorporating a thickener and a clarifier. The limiting flux solution corresponding to the local minimum at the flux concentration curve is proved to have a limited range of validity and is shown to apply only to the intermediate range of feed concentrations. This limit is replaced by a five‐region diagram; the solution is determined by the feed coordinates in the flux concentration plane, with respect to the flux concentration curve. Each section exhibits different characteristic solutions for both the clarifier and the thickener.

The analysis, which combines dispersion, dynamics, and stability considerations, reveals new possible ranges of operating conditions where the flux exceeds the limiting flux and solids are not entrained. The results, contradicting previous published work, are verified by a finite‐difference dynamic simulator.
Pore structure and kinetics of the thermal decomposition of Al(OH)3
Authors: Candela Lawrence , Perlmutter D. D.
Published: June 2004

The isothermal decomposition of gibbsite (aluminum hydroxide) was studied under controlled, pure water vapor pressures from 50 to 3,000 Pa over the temperature range from 458 to 508 K; the effect of sample particle size was also investigated. The partial conversion to boehmite (AlOOH) and the subsequent formation of a ρ‐transition alumina product phase were followed with respect to the reactor operating conditions. Nitrogen and water vapor adsorption measurements were used to evaluate the chemical kinetics of the formation of ρ‐alumina in terms of an interface velocity, and to interpret the observed dependencies on temperature and water vapor pressure. An adsorption/decomposition model is presented for these kinetics. The interpretation is consistent with the observation that decomposition rate is inversely proportional to the square of the water vapor pressure. The apparent activation energy of 342 ± 15 kJ/mol includes a water adsorption energy, as well as the chemical decomposition contribution of 260 ± 20 kJ/mol.
A theoretical analysis of Smith and analytical predictors
Authors: Wong S. K. P. , Seborg D. E.
Published: June 2004

A theoretical analysis has been performed to elucidate the relationship between two popular time delay compensation techniques, the Smith predictor and the analytical predictor. In general, use of these two techniques results in different closed‐loop responses. It is only for the special case where the process model is perfect and set point changes occur, that the two techniques are equivalent. A modification of the analytical predictor has been proposed that allows the technique to be used with any feedback controller, instead of the special PI controller employed by Moore et al. (1970).
Aerosol collection in the jet region of fluidized filters
Authors: Ushiki K. , Tien Chi
Published: June 2004

A method is proposed for calculating aerosol collection in the jet region of fluidized filters with sieve plate distributors. With the use of the model proposed earlier by Lefroy and Davidson and a new correlation for the single‐collector efficiency, which was established as part of this study, a compartment‐to‐compartment procedure was developed for estimating aerosol collection. The results were compared with experimental data for model validation.
Analytic solution for adsorber breakthrough curves with bidisperse sorbents (zeolites)
Authors: Cen P. L. , Yang R. T.
Published: June 2004

A time‐domain solution in the form of infinite series for the break‐through curves is derived for zeolite adsorbers. Three diffusion steps are accounted for in the solution: external film, macropore, and micropore. The solution is based on the assumption that the concentration profiles in micropores and macropores are both parabolic.

Based on the analytic solution, a simple criterion is given for the relative importance of the three individual mass transfer resistances. The adsorber behavior is determined by four independent dimensionless parameters. For the commercial zeolite sorbents, the bed behavior is dominated by two parameters: Henry's law constant (K) and the parameter M2, which is the product of the stoichiometric time (L/v) and the time constant for macropore diffusion (Dp/Ro2).

The analytic solution is in good agreement with experimental data for the breakthrough curves of nitrogen and methane carried in helium in 5A zeolite beds. When reduced to monodisperse pores, the solution is also in good agreement with Rosen's exact solution.
Thermodynamic representation of phase equilibria of mixed‐solvent electrolyte systems
Authors: Mock Bill , Evans L. B. , Chen Chau‐Chyun
Published: June 2004

The electrolyte nonrandom two‐liquid model proposed by Chen and Evans provides a thermodynamically consistent framework for representation of the phase equilibria of mixed‐solvent electrolyte systems. Using only binary adjustable parameters, the model satisfactorily correlates the vapor‐liquid equilibrium and liquid‐liquid equilibrium of mixed‐solvent electrolyte systems over the entire range of temperature and concentrations.
Process synthesis concepts for supercritical gas extraction in the crossover region
Authors: Chimowitz E. H. , Pennisi K. J.
Published: June 2004

A procedure is presented for designing supercritical gas extraction processes using a pure solvent fluid to effect the separation. The necessary conditions for the procedure to be applicable are the existence of crossover behavior and separable crossover pressures in the fluid phase mixture. Data are presented to support the existence of such phenomena in ternary systems, and an actual separation process has been designed and operated based upon the data. For systems exhibiting this behavior, process synthesis principles are developed to illustrate the evolution of a process flowsheet for the separation of a mixture into its pure components.
Cocurrent downflow of air and water in a two‐dimensional packed column
Authors: Christensen G. , McGovern S. J. , Sundaresan S.
Published: June 2004

Multiple hydrodynamic states were observed during cocurrent down‐flow of air and water under trickling flow conditions in a packed bed of rectangular cross section. Although the multiplicity was exhibited by both pressure gradient and liquid holdup, the pressure gradient showed the largest variations at identical conditions. The multiplicity is interpreted as being due to the liquid flowing in two different modes, namely, film flow and rivulet flow.

The characteristics of pulsing flow in a packed bed of rectangular cross section were found to be appreciably different from those reported in the literature for flow in small‐diameter cylindrical columns. The most significant observation in the packed bed of rectangular cross section was that the pulses did not always span the column cross section, unlike the case in small‐diameter columns. The lower pressure drop and pulse velocity in the packed bed of rectangular cross section are believed to result from the bypassing of gas around the edge of the pulses. The location of the pulses was found to depend on the quality of gas and liquid distribution at the top of the column, and the shape of the top surface of the packing. A distributor configuration in which the gas was injected directly into the bed was found to be the most desirable, and is recommended in industrial practice.
A collocation approach to distillation column design
Authors: Swartz C. L. E. , Stewart W. E.
Published: June 2004

A reduced‐order collocation method is applied to the optimal design of distillation columns. The resulting number of equations is determined by the user and is independent of the numbers of stages in the column sections. The collocation method furthermore permits these stage numbers to be treated as continuous variables, thus extending the discrete solution set. This greatly facilitates the optimization. Several demonstration problems are worked out.
Scaling‐up distillation efficiencies
Authors: Dribika M. M. , Biddulph M. W.
Published: June 2004

This paper describes a study of the possibility of using point efficiencies, measured in a small laboratory column, in the scale‐up of distillation efficiencies. The conditions on a large rectangular tray were closely duplicated in a small glass Oldershaw column with one sieve tray having similar hole size and percent free area. Point efficiencies on the large rectangular sieve tray were deduced from the composition profiles and compared with the point efficiencies measured in the small column. A simple relationship between the two columns was found in terms of the froth heights and liquid holdups. The results demonstrate that the slightly lower point efficiencies measured in the Oldershaw column could be used in conjunction with a mathematical mass transfer model based on the eddy diffusion concept, to relate the point efficiencies to the tray efficiences, resulting in a conservative design provided either that allowance is made for other factors, such as nonuniform flow patterns and stagnant zones, or that these are eliminated. A wide range of composition was covered using the two systems MeOH‐nPrOH and EtOH‐nPrOH operating in the froth region.
Vapor‐liquid equilibria from perturbation gas chromatography. Part II: Application to the polybutadiene/benzene/cyclohexane ternary system
Authors: Ruff W. A. , Glover C. J. , Watson A. T. , Lau W. R. , Holste J. C.
Published: June 2004

This work brings together recent gas chromatography experiments and theory involving multiple sorbing species at finite concentration, and theories for multicomponent polymer solutions by means of the parameter estimation procedure of Part 1. Results quantitatively describe the wide variation in peak retention times that are caused by phase equilibrium and chromatographic interference, the best solution models doing so to within or near experimental error. The chromatographic method is capable of detecting differences and peculiarities in the various polymer solution models in both the accuracy of the calculated retention times and the sensitivities of the calculations to the model parameters. Perturbation chromatography offers some unique capabilities for multicomponent vapor‐liquid equilibrium determinations.
Down‐flow shell‐side forced convective boiling
Authors: Bennett D. L. , Hertzler B. L. , Kalb C. E.
Published: June 2004

One hundred sets of R‐11 two‐phase pressure drop and boiling heat transfer data are reported for cocurrent down‐flow over an in‐line tube bundle. The pressure drop data agree with predicitions using the Diehl correlation. A new heat transfer correlation is reported, accounting for the observed convective and nucleate mechanisms.
Activity coefficients of aroma compounds in model food systems
Authors: Sorrentino F. , Voilley A. , Richon D.
Published: June 2004

Infinite dilution activity coefficients of aroma compounds from various chemical series were measured in model food systems (water/carbohydrates, water/polyethylene‐glycols) at concentrations of various solutes. These measurements were made with a specially designed equilibrium cell. Experimental results were used to determine the parameters of group contribution thermodynamic models. The predictive capacities of the equations obtained were shown to be quite precise (8% mean deviation).
Continuous thermodynamics of phase equilibria using a multivariate distribution function and an equation of state
Authors: Willman B. T. , Teja A. S.
Published: June 2004

The dew points of 40 multicomponent fluid mixtures including gas condensates, absorber oils, crude oils, synthetic aromatic heavy oils, and coal liquids were calculated using the method of continuous thermodynamics and the Patel‐Teja cubic equation of state. These multicomponent mixtures were characterized by a log normal distribution function in two variables: the boiling point and specific gravity in this work. Comparisons were made with the case when a single variable distribution function is employed and also with the method of Cotterman et al. In general, the new method leads to excellent predictions of both phase equilibria and liquid densities.
Batch extraction of amines using emulsion liquid membranes: Importance of reaction reversibility
Authors: Baird R. S. , Bunge A. L. , Noble R. D.
Published: June 2004

Experimental results for the batch extraction of amines using emulsion liquid membranes with an internal aqueous HCI solution are presented. Four amines and mixtures of one binary pair were studied. Reversibility of the acid‐amine reaction within the internal droplets affected extraction rates. The reversible reaction model presented earlier satisfactorily predicts these experimental results.
Malfunction diagnosis using quantitative models with non‐boolean reasoning in expert systems
Authors: Kramer M. A.
Published: June 2004

An approach to chemical plant fault diagnosis is presented that utilizes patterns of violation and satisfaction of the quantitative constraints governing the process. Process knowledge consists of a list of the operational constraints on the plant together with sufficient conditions for violation of each constraint. Interpretation of the pattern of constraint violations is treated by Boolean and non‐Boolean techniques. It is shown that non‐Boolean reasoning techniques increase the stability and sensitivity of the diagnosis in the presence of noise. The techniques introduced in this paper are easily implemented in rule‐based expert systems using certainty factors.
The kinetic rate of SO2 sorption by CaO
Authors: Simons G. A. , Garman A. R. , Boni A. A.
Published: June 2004

The intrinsic rate constant for the rate of reaction of SO2 with porous CaO in an excess of O2 to form CaSO4 has been determined from SO2 sorption data on a wide range of particle diameters (1 μm‐ 1mm), SO2 partial pressures (60 Pa to 5 kPa), and temperatures (973‐ 1,478 K). An intrinsic SO2 reaction order of unity has been validated through current fixed‐bed experiments in the 60 to 300 Pa SO2 partial pressure range, while fluidized‐bed data were used to validate the reaction order from 500 Pa to 5 kPa SO2 partial pressure. The absolute value of the rate constant and the activation energy was derived from data on small (1 μm) particles, which approach the limit of kinetic control. While analysis of this data base does minimize the role of intraparticle diffusion through the porous sorbent particle, the filling of the small pores by the product deposits and the associated loss of internal surface area is critical to the data reduction. It is believed that the intrinsic rate constant is known to the accuracy to which the reactivity and the BET surface area may be measured.
A reduced hessian strategy for sensitivity analysis of optimal flowsheets
Authors: Ganesh N. , Biegler L. T.
Published: June 2004

An efficient and rigorous strategy is presented for evaluating the first‐order sensitivity of the optimal solution to changes in process parameters or process models. An algorithm that constructs a reduced Hessian in the null space of the equality constraints is used to solve the sensitivity equations; the resulting effort to solve these equations depends only on the space of the decision (independent) variables. Consequently, large computational savings can be realized because the solution procedure eliminates the need for obtaining second partial derivatives with respect to tear (dependent) variables explicitly. The method is applied to several flowsheeting examples in order to determine efficiently the sensitivity of the optimal solution to parametric and physical property model changes.
Finite‐element simulation of stratified multiphase flows
Authors: Mavridis H. , Hrymak A. N. , Vlachopoulos J.
Published: June 2004

The analysis of stratified multiphase flow fields is difficult because the position of the interface is unknown a priori and there is a discontinuity in the normal viscous stress and/or pressure at the interface. A finite‐element technique that uses double nodes along the interface has been implemented. The immiscible liquid displacement in a capillary tube was examined in detail. Fountain flow in the advancing fluid, reverse fountain flow in the receding fluid, and a recirculating flow region in the less viscous fluid were determined. In Newtonian flat film coextrusion the entry region, where the two immiscible fluids form an interface, and the characteristic swelling and bending of the extrudate at the die exit were studied. The computational results compare favorably with available experimental observations.
Multicomponent diffusion in concentrated electrolyte solutions: Effect of solvation
Authors: Pinto N. G. , Graham E. E.
Published: June 2004

A method is presented to estimate the diffusivities of electrolytes in concentrated multicomponent systems. The method is based on the Stefan‐Maxwell flux equations. Explicit expressions have been developed for the phenomenological transport coefficients. These expressions incorporate the effects of solvation, viscosity, and ionic interactions. It has been shown that multicomponent diffusion behavior can be related to corresponding single‐electrolyte and tracer diffusion cases. Thus, solvation effects are estimated from single‐electrolyte data, and ion‐ion interaction effects are obtained from tracer diffusion studies. The method has been tested for the ternary system NaCl‐KCl, at concentrations of up to 3.0 M, and for corresponding single‐electrolyte and tracer diffusion cases at concentrations of up to 4.0 M. In general, the method predicts phenomenological coefficient values within 1.5% of the experimental values for univalent systems.
Design of commercial‐scale gas‐liquid contactors
Authors: Otero Keil Z. , Russell T. W. F.
Published: June 2004

A systematic design procedure using a liquid circulation unit for gas‐liquid systems containing low‐viscosity liquids is developed. The procedure can be used to predict and optimize the fluid mechanics and mass transfer in gas‐liquid contactors for a specified performance. Batch liquid mass transfer data obtained from a commercial‐scale aeration basin (12.2 m × 12.2 m × 6.7 m; gas flow rate range, 0.0023–0.01 m3/s) are used to verify the model predictions and to test the design procedure.
Separation synthesis of multicomponent feed streams into multicomponent product streams
Authors: Floudas C. A.
Published: June 2004

The synthesis problem of separation sequences that separate several multicomponent feed streams into several desired multicomponent product streams is addressed. A superstructure is proposed for this separation problem that has embedded all the alternative separation configurations of interest. This superstructure, which has as separator units the separation tasks that are defined for each separation breakpoint, involves options for series and/or parallel sequences, as well as stream splitting, mixing, and bypassing. Formulating and solving this superstructure as a nonlinear programming problem that has as unknowns the stream interconnections, results in an optimal separation sequence. This sequence, which may involve fewer separator units than those included in the superstructure, is shown to be a realistic and practical one. The synthesis approach is illustrated with four example problems.
Nonlinear state feedback synthesis by global input/output linearization
Authors: Kravaris Costas , Chung Chang‐Bock
Published: June 2004

This paper studies the design of feedback controllers for trajectory tracking in single‐input/ single‐output nonlinear systems x = f(x) + g(x) u, y = h(x). A nonlinear transformation of the form v = k(x) + λ(x) u that transforms this nonlinear input/output system into a linear system is first constructed. On the basis of this transformation, an approach for designing control laws for trajectory tracking is presented. The control law is robust in the sense that small changes in it do not produce large steady state errors or loss of stability. The theory provides a unified framework for treating control problems arising in nonlinear chemical processes; this is illustrated by a batch reactor control example.
Fluidized‐Bed reactor model verification on a reactor of industrial scale
Authors: Johnsson J. E. , Grace J. R. , Graham J. J.
Published: June 2004

Previous published comparisons between fluidized‐bed reactor models and experimental data have almost exclusively been in laboratory and pilot‐plant scale equipment. This paper compares data obtained in an industrial phthalic anhydride reactor of 2. 13 m dia. using naphthalene as the feedstock with three models, the Kato and Wen bubble‐assemblage model, the Kunii and Levenspiel three‐phase bubbling‐bed model, and Grace's two‐phase bubbling‐bed model. For the conditions of operation (U = 0.43 m/s, d̄p = 53 μm, H = 7.9 m, T = 636 K), all three models give similar predictions and each gives a good overall prediction of the conversion and selectivity if the reaction kinetics are based on the early study of DeMaria et al. (1961). Hydrodynamic parameters needed for the models are calculated from equations available in the literature. Grid and freeboard effects appear to play relatively minor roles in determining the overall conversion and yields for the reactor in question.
Minimum energy requirements of thermally coupled distillation systems
Authors: Fidkowski Zbigniew , Królikowski LechosłW
Published: June 2004

Energy requirements of four different thermally coupled distillation systems were minimized for an assumed ideal ternary solution being separated. Minimum vapor flows and values of decision variables have been found in the form of analytical expressions. This enables making a quick and simple comparison of these systems. The solution method can be used for synthesis of separation systems or for screening calculations.
Pressure swing adsorption: A theoretical study of diffusion‐induced separations
Authors: Shin Heung‐Soo , Knaebel K. S.
Published: June 2004

This report examines gas separation by a pressure swing adsorption (PSA) process that exploits differences in intraparticle rates of diffusion, rather than differences in adsorption isotherms. Film and intraparticle diffusion resistances are taken into account, but only the latter is examined closely. Each step of a four‐step cycle is incorporated, and concentration profiles within the particles and along the column axis are predicted. Several critical PSA operating conditions, including step times, velocities, and pressures are studied in the context of separation of nitrogen from air with zeolite 4A.
A chemical reaction model for physical vapor deposition of compound semiconductor films
Authors: Jackson S. C. , Baron B. N. , Rocheleau R. E. , Russell T. W. F.
Published: June 2004

A model for the physical vapor deposition of compound semiconductor films that describes film growth from component molecular beams is presented. Constitutive relationships are used in the model to account for incomplete adsorption from the incident molecular beams, emission of adsorbed components into vacuum, and surface reactions of the elemental species. The model predicts film composition and growth rate as a function of incident fluxes and substrate temperature. It is applicable for important binary and ternary alloy semiconductors including the II‐VI and III‐V compounds over the range of deposition conditions yielding both stoichiometric and two‐phase films. In this paper the model equations and the behavior predicted by the model are described for a number of material systems including (CdHg)Te, (CdZn)S, and CuInSe2.
Fundamentals of a centrifugal fluidized bed
Authors: Chen Ye‐Mon
Published: June 2004

A fundamental theory based on the local momentum balances is proposed to explore the fluidizing phenomena of a centrifugal particle bed. Unlike the conventional vertical bed, a centrifugal bed is predicted to be fluidized layer by layer from the inner free surface outward, in a range of aeration rates. The span of this range increases with the depth of the particle bed. The pressure drop is predicted to exhibit a plateau, which agrees very well with the observations of many investigators, but disagrees with the investigations of Takahashi et al. and Fan et al., in which the pressure drop exhibited a maximum. Predictions of the critical fluidizing velocity and the corresponding pressure drop agree well with the data of Fan et al.
CO oxidation on Pt: Model discrimination using experimental bifurcation behavior
Authors: Graham W. R. C. , Lynch D. T.
Published: June 2004

An experimental determination of the steady state behavior for the supported platinum catalyzed oxidation of carbon monoxide in a recycle reactor was performed. Steady state multiplicity was observed. The effects of the size of catalyst charge, feed flow rate, feed composition, and reactor temperature on the location of the boundaries of the steady state multiplicity region were determined. The sensitivity of these bifurcation points to variations in reactor parameters was used to discriminate among five reaction mechanisms. Only an elementary step model incorporating carbon monoxide self‐exclusion from the catalyst surface could quantitatively describe all observed steady state data. An explicit rate function based on this model is presented.
Computing multiple solutions to systems of interlinked separation columns
Authors: Lin Wen‐Jing , Seader J. D. , Wayburn T. L.
Published: June 2004

Globally convergent homotopy continuation methods have been used successfully to find multiple solutions to systems of nonlinear equations used to model multicomponent, multistage separation processes. However, the solutions were achieved by using a multitude of different starting points. This paper describes a procedure for finding all or some solutions of the nonlinear equation system from just one starting point. A reliable algorithm, which utilizes a deflated decomposition technique to overcome the turning‐point problem, an efficient procedure to estimate step sizes, and variable mapping functions to prevent failure when computing physical properties, is developed to follow the homotopy path. The Jacobian matrix is retained as a special structure in all calculation steps. The algorithm has found, from one starting point, all the real roots of the interlinked separation system studied by Chavez et al. (1986). Two additional examples, including one optimization problem and one constrained nonlinear equation system, are presented to illustrate other applications of the algorithm.
Heat and power integration of chemical processes
Authors: Colmenares T. R. , Seider W. D.
Published: June 2004

An efficient nonlinear programming strategy is presented for integration of heat engines and heat pumps with chemical processes. The strategy utilizes the temperature interval method and shows how to use negative heat deficits to obtain lower cost designs. Two important situations are presented in which the resulting designs are less costly when the heat engines and heat pumps are integrated with temperature intervals having negative heat deficits.