bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractA 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

AbstractApplication 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

AbstractA 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

AbstractOptimal 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

AbstractA 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractFor 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

AbstractIn 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractThis 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

AbstractA 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

AbstractA 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

AbstractA 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

AbstractA 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

AbstractThis 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

AbstractThe 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

AbstractKynch'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

AbstractThe 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

AbstractA 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

AbstractA 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

AbstractA 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

AbstractThe 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

AbstractA 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

AbstractMultiple 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.