bluuebunny/crossref_metadata_2025 huggingface dataset:
An efficient, general method for computation of countercurrent separation processes with axial dispersion
Authors: Ricker N. L. , Nakashio Fumiyuki , King C. J.
Published: June 2004

A calculational method is proposed for the simulation of steady‐state, multisolute, countercurrent extraction with axial dispersion. The method provides for complex chemical‐equilibrium and phase‐equilibrium relationships, and accounts for the individual resistances of the liquid phases in the calculation of mass‐transfer rates. The solution procedure follows that developed by Newman (1967, 1968) for systems of simultaneous, second‐order difference equations.

Three example problems are solved to demonstrate the efficiency and flexibility of the method. These include (1) an example from McSwain and Durbin (1966), (2) calculation of axial‐dispersion and mass‐transfer parameters from experimental data for the extraction of acetic acid from water by a tertiary amine in an RDC extractor, and (3) simultaneous extraction of solutes that interact in an acid‐base complexing reaction at the liquid‐liquid interface. The examples all assume that extraction is governed by interphase mass‐transfer rates and cell‐wise backmixing; however, the method is also applicable to equilibrium‐stage separators, separators described by the diffusional model of axial dispersion, and other countercurrent separation processes.
Forces on immersed tubes in fluidized beds
Authors: Kennedy T. C. , Donovan J. E. , Trigas Athanasios
Published: June 2004

The external forces imparted by the bed material on tubes in a fluidized bed contribute to failure of the tubes and their support systems. The objective of this investigation was to provide data on tube forces to be used in structural design. Forces on tubes of various lengths were measured in fluidized beds operating at room temperature. The parameters varied in the experiments were superficial gas velocity and tube array height above the gas distributor. The force‐time histories consisted of a series of pulses, whose magnitudes were approximately linearly proportional to tube length. Spectral analyses of the time series indicated that the primary frequency composition of the load was below 25 Hz.
Local hold‐up and liquid velocity in air‐lift reactors
Authors: Merchuk Jose C. , Stein Yehuda
Published: June 2004

Measurements of local hold‐up and liquid recirculation rate in an air‐lift reactor were performed with two types of gas spargers using a manometric technique. A simple exponential function correlated properly the liquid velocity measured to the gas flow rate. The local hold‐up varied appreciably along the column and showed a maximum in most of the cases. A simple linear relationship correlated the local gas velocity with the total flow rate of the mixture.
A perturbed hard‐sphere, corresponding states model for liquid metal solutions
Authors: Paulaitis M. E. , Eckert C. A.
Published: June 2004

Molecular thermodynamics is used to develop a new model for the prediction of the thermodynamic properties of liquid metal mixtures. It combines corresponding states theory with a perturbed hard sphere model to predict successfully, without adjustable parameters, a variety of mixture properties from pure component properties for simple eutectic mixtures.
Studies in reaction path synthesis
Authors: Govind Rakesh , Powers G. J.
Published: June 2004

The development of processes requires the consideration of a wide variety of reactions which are required to transform raw materials into desired products, solve separation problems, and heat or cool process streams. These reactions have to be evaluated on the basis of raw material costs, kinetics, potential separation difficulties, catalyst costs, safety and reliability, as well as other factors that would arise in their industrial implementation. In this paper, the current status of research in reaction path synthesis has been reviewed. Details have been presented on the REACT program that has been developed for the synthesis of reaction paths for industrial organic chemicals.
Computation of phase and chemical equilibrium, part IV: Approach to chemical equilibrium
Authors: White Charles W. , Seider Warren D.
Published: June 2004

The Rand algorithm for calculation of compositions in phase and chemical equilibrium is extended to permit specifications of extents of reactions that cannot be taken at equilibrium. Pseudo‐Gibbs free energies of formation are introduced to permit specification of temperature approaches. The extended algorithm is demonstrated for methane reforming.
Intermixing over cell boundary between taylor vortices
Authors: Kataoka Kunio , Takigawa Takahiro
Published: June 2004

The rate of exchange of fluid elements between Taylor vortices was experimentally determined for low axial flow rates. A model was formulated defining the exchange coefficient appropriate for this flow system. In the laminar vortex flow region, the measured exchange coefficient increases with Re but is almost independent of Ta.
Steady flow through porous media
Authors: Greenkorn R. A.
Published: June 2004

The increasing demands for oil, water, and food produced in an environmentally sound manner have placed emphasis on the manner of their production, a major part of which is concerned with flow through porous media.

The movement of materials through porous media is of interest in many disciplines: in chemical engineering—adsorption, chromatography, filtration, flow in packed columns, ion exchange, reactor‐engineering; in petroleum engineering—displacement of oil with gas, water and miscible solvents including surface‐active agent solutions and description of reservoirs; in hydrology—movement of trace pollutants in water systems, recovery of water for drinking and irrigation, salt water encorachment into fresh water reservoirs; in soil physics—movement of water, nutrients, and pollutants into plants; in biophysics—life processes such as flow in the lung and the kidney.

This paper reviews the fundamentals of steady flow through porous media: it discusses the pseudotransport coefficients permeability, capillary pressure, and dispersion and relates these coefficients to the geometry of porous media. It also discusses single‐fluid flow, multifluid immiscible flow, and multifluid miscible flow including the effects of heterogeneity, nonuniformity, and anisotropy of media.
Evolutionary synthesis of separation processes
Authors: Nath R. , Motard R. L.
Published: June 2004

This paper deals with the problem of finding, among many alternatives, the sequence of separation units that will isolate desired products from given feed at the minimum cost. Multicomponent products can be specified. An evolutionary procedure is presented. This method consists of two phases. In the first phase, a good initial structure is created by heuristic methods. In the second phase, the initial structure is successively modified by making evolutionary structural changes. This logic has been programmed on a digital computer and has been tested on several problems.
Solubility extrema in solid‐fluid equilibria
Authors: Kurnik R. T. , Reid R. C.
Published: June 2004

Experimental data and theory both support the contention that there is a maximum solubility in solid‐fluid equilibria. An example system, naphthalene‐ethylene, at temperatures between the upper and lower critical end points and at pressures from 1 to 1000 bar is considered. There is also a solubility minimum in this system.
Distillation models for two partially immiscible liquids
Authors: Ferraris Guido Buzzi , Morbidelli Massimo
Published: June 2004

We hereby submit three different numerical methods for the solution of the multicomponent distillation model for two partially immiscible liquids. A procedure to define the real number of phases present on each stage has been developed. The proposed Newton‐Raphson method allows efficient solution of problems with a large selection of the unknowns and the specification equations.
Modeling the flow of viscoelastic fluids through porous media
Authors: Deiber J. A. , Schowalter W. R.
Published: June 2004

A tube with sinusoidal axial variations in diameter has been used as a first step toward modeling the flow channels of a porous medium in such a way that appreciable Lagrangian unsteadiness is present. Experiments with dilute aqueous solutions of a polyacrylamide (Dow Separan AP‐30) show that the Lagrangian unsteadiness gives rise to an increase in resistance to flow through the sinusoidal channel relative to that predicted for a purely viscous fluid. The increase in pressure drop can occur as a consequence of fluid elasticity, without any observable secondary flow. At sufficiently high flow rates, secondary flow appears.
Progressive freezing of composites analyzed by isotherm migration methods
Authors: Talmon Yeshayahu , Davis H. T. , Scriven L. E.
Published: June 2004

The Isotherm Migration Method of numerically analyzing conduction with phase change is modified to handle surface and external resistances, appearance, and propagation of successive fronts into slabs of composite material of one or more constituents finely dispersed in a matrix, different components transforming at different temperatures. Procedures are developed for selecting temperature intervals between isotherms, initially locating isotherms by means of analytical approximations to the earliest stages, and thereafter inserting and removing isotherms as appropriate, particularly when each component gives rise to a separate front.
Numerical solution of nonequilibrium multicomponent mass transfer operations
Authors: Billingsley D. S. , Chirachavala Arun
Published: June 2004

An improved model and solution procedure for nonequilibrium, multicomponent, two‐phase, steady‐state mass transfer problems are developed. Processes as diverse as packed column operation and the drying of porous solids are included. Ideas such as “HETP,” “HTU” or “mass transfer section” are avoided. “Stiff” systems appear to be handled well.
Electrokinetic phenomena in the filtration of colloidal particles suspended in nonaqueous media
Authors: Chowdiah P. , Wasan D. T. , Gidaspow D.
Published: June 2004

Filtration of carbon black particles from tetralin through a bed of sand with simultaneous measurement of bed streaming potential shows that the charge on the filter and its neutralization by depositing colloidal particles plays an important role in filter performance. Filter capacities up to the point of charge neutralization, calculated from knowledge of the colloid and filter zeta potentials using a semitheoretical model for variation of filter surface charge characteristics, are found to be in good agreement with experimental values.
Analysis of particulate removal in venturi scrubbers—effect of operating variables on performance
Authors: Placek T. D. , Peters L. K.
Published: June 2004

A theoretical model of venturi scrubber performance consisting of the governing differential equations for momentum, material, and energy exchange is solved using a Milne fourth‐order predictor—Hamming corrector numerical integration procedure. The model provides for specification of the operating variables, including scrubber geometry, throat gas velocity, liquid to gas loading ratio, and collector droplet and particle‐size distributions. Liquid loading ratio and gas velocity are shown to be the two most important operating variables, while the dispersity of the droplet size distribution only slightly affects collection efficiency over the operating range normally encountered. Location of the liquid injection site and length of the throat are also important design considerations. While particle collection in venturi scrubbers has typically been assumed to occur in the potential flow regime, the present results show that collection can also occur under conditions corresponding to viscous flow about the collecting droplets. The transition Reynolds number used to change from the potential to viscous flow equations affects the predicted performance.
Adsorption‐desorption barrier, diffusional exchanges and surface instabilities of longitudinal waves for aperiodic regimes
Authors: Hennenberg M. , Sanfeld A. , Bisch P. M.
Published: June 2004

Our purpose is to give the physical conditions under which transfer of a surfactant through a fluid interface between two immiscible liquids may induce aperiodic convective motion.

Adsorption‐desorption rates are considered together with diffusional exchanges. New kinds of surface instabilities are then predicted.
Reduction of thermodynamic data by means of the multiresponse maximum likelihood principle
Authors: Kemeny S. , Manczinger J. , Skjold‐Jørgensen S. , Toth K.
Published: June 2004

The statistical behavior of some common parameter estimation methods is investigated by simulation. The methods based on the maximum likelihood principle give the best estimates of parameters in a given model. An analysis of the possibilities for detecting systematic errors by means of the maximum likelihood method showed that this method gives at best the same information as other well known tests.
Solute condensation in adsorption beds during thermal regeneration
Authors: Friday David K. , Levan M. Douglas
Published: June 2004

This theoretical study shows that a liquid phase can be developed in and passed through a fixed‐bed adsorber during thermal regeneration. The liquid results from passing hot gas from the inlet end of the bed, where the adsorbate is desorbed, towards the cool outlet end, where condensation of the solute occurs. The stage model of an adsorption bed is applied to two examples, the regeneration of an activated carbon bed with adsorbed benzene using hot nitrogen and the regeneration of a 4A molecular sieve bed with adsorbed water using hot methane.
Carbon dioxide concentration for manned spacecraft using a molten carbonate electrochemical cell
Authors: Winnick J. , Toghiani H. , Quattrone P. D.
Published: June 2004

A high‐temperature molten carbonate electrochemical cell has been tested for use as a carbon dioxide concentrator in a manned spacecraft. Carbon dioxide is removed from a stream of cabin air supplied to the cathode of the bench scale cell. It is then concentrated through the molten carbonate electrolyte to the anode. The anode is fed either hydrogen (energy producer) or nitrogen (substance producer). Performance variation with gas flow rate, cell temperature, carbon dioxide partial pressure, and current are presented and analyzed.
The rheological characterization of coal liquefaction preheater slurries
Authors: Thurgood J. R. , Hanks R. W. , Oswald G. E. , Youngblood E. L.
Published: June 2004

Rheological characterizations were made for a coal liquefaction preheater slurry; measurements were made in line at high temperature and high pressure. Above 400°K, the coal‐solvent slurry (35 wt. % coal) was pseudoplastic and was adequately modeled by a power‐law equation. Experimental data over a temperature range of 400 to 700°K were correlated, and critical slurry velocities for transition from laminar flow were calculated for flow in several pipe diameters.
A study of the volumetric and phase behavior of binary systems. Part I. Critical properties of propane‐perfluorocyclobutane mixtures
Authors: Barber J. R. , Kay W. B. , Teja A. S.
Published: June 2004

The volumetric and phase behavior of propane‐perfluorocyclobutane mixtures has been determined in the critical region. This system exhibits a minimum temperature point in its critical locus curve and forms a positive critical azeotrope. The measured critical points in this system and their correlation using an extended corresponding states principle are reported in this paper.
A study of the volumetric and phase behavior of binary systems. Part III. P‐V‐T‐x data and second virial coefficients of propane‐perfluorocyclobutane mixtures
Authors: Barber J. R. , Kay W. B. , Teja A. S.
Published: June 2004

P‐V‐T‐x data for the propane‐perfluorocyclobutane system are reported in this paper. The data cover a temperature range from 329.4 to 397.7°K and a pressure range from 60 to 6920 kPa. The low pressure compressibility measurements were used to determine second virial coefficients of pure propane and pure perfluorocyclobutane and for seven of their mixtures. The prediction of second virial coefficients using an extended corresponding states principle is also reported. Excellent predictions of the second virial coefficients of both pure components and mixtures have been obtained using, in the case of mixtures, a binary interaction coefficient obtained from a study of the critical states of the system.
A dynamic method for liquid‐particle mass transfer in trickle beds
Authors: Tan C. S. , Smith J. M.
Published: June 2004

Previous investigations of liquid‐to‐particle mass transfer in trickle beds have used non‐porous particles. However, the applications of trickle beds have been for reactions or adsorption employing porous catalysts as adsorbents. In this study a method of dynamic adsorption with porous particles is developed. The procedure is to extrapolate the response to a step‐function input of non‐volatile adsorbate to a short time where intraparticle diffusion and adsorption do not affect the overall process.

The method is applied to the adsorption of benzaldehyde from aqueous solutions in a bed of granular, activated carbon particles. Measurements were made for three particle sizes, in adsorbers of two diameters, at 298K and 1 atm. The gas flow rate had no discernible effect on the mass transfer coefficients, kLsaLs, over a superficial velocity range of 1.47 to 8.0 × 10−2 m/s, but kLsaLs increased with liquid rate. The results, correlated as Sherwood vs. Reynolds number, agree well with the nonporous particle data of Van Krevelen and Krekels (1948), but suggest larger Sherwood numbers than similar data from later investigations.

The wide range of mass transfer results for either liquid‐to‐particle or liquid‐to‐gas in trickle beds seems to be due in large measure to the difficulty in reproducing the rivulent flow pattern of liquid from bed to bed.
Dynamics of a creeping Newtonian jet with gravity and surface tension: A finite difference technique for solving steady free‐surface flows using orthogonal curvilinear coordinates
Authors: Dutta Anit , Ryan M. E.
Published: June 2004

A finite difference technique capable of simulating steady, incompressible, viscous, free‐surface flows has been successfully applied to the motion of a creeping Newtonian jet, including both surface tension and gravitational forces. In accordance with experimental results, the numerical solutions predict either a 12 or 16% increase in the jet dimensions depending on whether the jet emerges from a circular or a slit die. Both gravity and surface tension inhibit the swelling behavior.
A chemical theory for the thermodynamics of highly‐solvated liquid metal mixtures
Authors: Eckert C. A. , Smith J. S. , Irwin R. B. , Cox K. R.
Published: June 2004

Chemical solution theory has been shown to be particularly well‐suited for certain classes of liquid metal mixtures. A generalized formulation of this approach is presented and it eliminates the need for mechanistic information. The results are in good agreement with many data, and could lead to a variety of industrial applications of liquid metal solvents.
Hydrogenation of nitrobenzoic acid
Authors: Andersson Bengt
Published: June 2004

Aqueous solutions of p‐nitrobenzoic acid were hydrogenated in the presence of Pt/C and Pd/C catalysts in a slurry reactor. External as well as internal mass transport steps were studied using a membrane H2‐electrode and a metal probe electrode. After the influence of the mass transport effects was corrected for, it was possible to obtain corrected values of the kinetic characteristics of the overall chemical reaction. The mechanism was studied using potential and polarization methods.
Further work on multicomponent liquid phase adsorption in fixed beds
Authors: Wang Shu‐Chieh , Tien Chi
Published: June 2004

The problem of multicomponent liquid phase adsorption in fixed beds was studied further. In contrast to the earlier work (Hsieh et al., 1977), the method developed in this work is more efficient and also has a greater scope of applicability as it incorporates the use of the IAS (Ideal Adsorbed Solution Theory) method for the estimation of multicomponent adsorption equilibrium data. It was shown that the use of the more complex IAS method for the prediction of the isotherm data does not present insurmountable obstacles as once feared (DiGiano, 1978) but provides much better prediction of carbon adsorption. An extension of the method to batch adsorption was shown to be straightforward and presented no special difficulty.
Nitrogen pollutant formation in a pulverized coal combustor: Effect of secondary stream swirl
Authors: Harding N. S. , Smoot L. D. , Hedman P. O.
Published: June 2004

Concentrations of NO, NH3, and HCN, together with coal particle burnout and gas composition, were measured during combustion of a bituminous coal. Control of incoming secondary gas swirl level and overall stoichiometric ratio led to significant reductions in nitrogen oxide pollutant concentration. In‐situ measurements showed that coal particles were confined near the reactor center during rapid particle reaction. This took place in a locally fuel‐rich environment, producing near‐quantitative conversion of fuel‐nitrogen to NH3 and HCN, with some NO. Subsequent gas phase reactions of these nitrogen species were identified as important in establishing the ultimate NO concentration.
Optical fiber probe transit anemometer for particle velocity measurements in fluidized beds
Authors: Patrose B. , Caram H. S.
Published: June 2004

A compact optical fiber probe to measure the velocity of solid particles in two‐phase flows was constructed. The probe has been used to measure particle velocities and obtain flow trajectories of solids in the distributor grid region of a two‐dimensional fluidized bed. Air was used as the fluidizing medium in a bed of glass beads of size ranging form 0.2 to 0.7 mm.

Particle velocities were measured at corresponding points within a jet in the two‐dimensional bed, using the optical fiber probe and a Laser Doppler Velocimeter (LDV). The probe measurements compare well with the LDV results in the main jet region. Particle velocities were also measured with the probe in the dense phase region of the fluidized bed where measurements were not possible using LDV. The resulting flow maps clearly indicate solids circulation patterns around jets and identify dead zones formed on the distributor plate.
Approximate solutions to explosion kinetics
Authors: Aiken R. C.
Published: June 2004

Stiffness in combustion models is quite different from that in more conventional kinetic descriptions. The steady‐state approximation, so useful in other contexts, cannot be applied in the usual ad hoc manner but can be applied with attention to its origins in singular perturbation analysis. The magnitude and time scaling on the equations representing the isothermal kinetics of hydrogen combustion reveal distinct regions of the transient to which this approximation may naturally and successfully be made to reduce computation time. The steady‐state approximation is found to apply to some free radicals, but not all, and these can change between regions. An analytical solution to an important section of the transient is found and illustrates dramatically the power of the approach. The analysis may be applied a priori and leads to a stagewise efficient numerical solution.
Viscoelastic flow from a tube into a radial slit
Authors: Co Albert , Stewart W. E.
Published: June 2004

The viscoelastic flow from a tube into a radial slit between two parallel disks is investigated numerically by orthogonal collocation. A modified ZFD model and a generalized Newtonian fluid, with identical viscosity functions, are investigated. Results for these models indicate that fluid elasticity alters the velocity profiles significantly, but has little effect on the pressure profile in the radial flow region.
Analysis of evaporation of cadmium sulfide for manufacture of solar cells
Authors: Rocheleau R. E. , Baron B. N. , Russell T. W. F.
Published: June 2004

Vacuum sublimation of cadmium sulfide for manufacture of thin film solar cells was analyzed. The sublimation unit consisted of a two chamber cylindrical source bottle having a rate control orifice and exit nozzle. Coupled heat and mass balance equations were solved using appropriate rate equations for flow in the free molecular‐to‐viscous transition regime. The model equations predicted that heat transfer has a significant effect on sublimation rate. Experiments were carried out over a range of temperatures with several rate control orifices and exit nozzles. Quantitative agreement between measured rates and those calculated from the model equations was obtained.
An improved correlation for densities of compressed liquids and liquid mixtures
Authors: Thomson G. H. , Brobst K. R. , Hankinson R. W.
Published: June 2004

The Tait equation has been extended and generalized to permit the calculation of densities of compressed liquids and their mixtures to a pressure of 68,950 kPa (10,000 psia) using only critical temperature, critical pressure, Soave‐Redlich‐Kwong acentric factor, saturation pressure, and saturated volume for a pure liquid or the corresponding mixture parameters for a liquid mixture. This correlation, together with the correlation developed by Hankinson and Thomson (1979) for saturated liquid densities, comprise COSTALD (COrresponding STAtes Liquid Density), an integrated method for estimating densities of nonpolar and slightly polar liquids and mixtures. The new correlation gave 0.446 average absolute percent error for 6,338 data points for nonpolar liquids, 2.57% error for 1352 data points for polar and quantum liquids, 0.369% error for 319 data points for LNG/LPG mixtures, and 1.61% error for all mixtures tested.
Decomposition strategy for designing flexible chemical plants
Authors: Grossmann I. E. , Halemane K. P.
Published: June 2004

One of the main computational problems faced in the optimal design of flexible chemical plants with multi‐period operation is the large number of decision variables that are involved in the corresponding nonlinear programming formulation. To overcome this difficulty, a decomposition technique based on a projection‐restriction strategy is suggested to exploit the block‐diagonal structure in the constraints. Successful application of this strategy requires an efficient method to find an initial feasible point, and the extension of current equation ordering algorithms for adding systematically inequality constraints that become active. General trends in the performance of the proposed decomposition technique are presented through an example.
Parametric sensitivity and runaway in tubular reactors
Authors: Morbidelli Massimo , Varma Arvind
Published: June 2004

Parametric sensitivity of tubular reactors is analyzed to provide critical values of the heat of reaction and heat transfer parameters defining runaway and stable operations for all positive‐order exothermic reactions with finite activation energies, and for all reactor inlet temperatures. Evaluation of the critical values does not involve any trial and error.
Distribution for maximum activity of a composite catalyst
Authors: Dadyburjor D. B.
Published: June 2004

For a catalyst composed of a more active component embedded in a less active (but not inert) and more diffuse matrix, an optimum distribution of the active component in the catalyst pellet may lead to significantly higher reaction rates per unit volume of pellet, compared with reaction rates using pellets with a uniformly distributed active component or with an active component concentrated on the outside or the inside of the pellet. The optimum distribution changes qualitatively with the physical parameters of the pellet and with changes in the rate constants and diffusion coefficients of the catalytic compoenents. This is relevant to the performance of coking zeolite/silica‐alumina catalysts in hydrocarbon cracking reactions.
Solution of recycle problems in a sequential modular approach
Authors: Pierucci S. J. , Ranzi E. M. , Biardi G. E.
Published: June 2004

Recycle problems in a sequential modular approach are solved by adopting evolutionary models. When describing a process scheme by means of evolutionary models, a nonlinear algebraic system of equations is obtained. The resulting solution is utilized for updating the values of torn variables in the iterative solution of the scheme.
Experimental measurement of the thermal stability criteria for the low pressure methanol synthesis
Authors: Berty J. M. , Lenczyk J. P. , Shah S. M.
Published: June 2004

The mathematical basis was derived for the experimental measurement of the “Slope Condition” and of the “Dynamic Condition” of the thermal stability criteria in a laboratory‐scale internal recycle reactor. This work also resulted in clearer interpretations and simpler expressions for the two stability criteria. The method was experimentally demonstrated on the example of the low pressure methanol synthesis. Only seven experiments were needed to evaluate the stability criteria of this reaction for which the kinetics is unknown.
Time dependence of pressure in a bubbler tube
Authors: Gaigalas A. K. , Robertson Baldwin
Published: June 2004

An experimental and theoretical study is presented of the time dependence of air pressure in a bubbler tube used to measure the liquid level in a tank. The observed time dependence of the air pressure is a superposition of two components. The first component is a repeated slow rise and sudden fall in the air pressure that is associated with bubble growth and breakoff. It is the sudden breakoff that generates the second component consisting of damped oscillations associated with sound waves in the air interacting with an oscillating flow of the liquid. The air pressure during bubble growth is described theoretically. This result is combined with the gas law to predict the functional form of the slow pressure rise; this prediction agrees with experiment. An equation for the oscillation frequencies is derived, solved, and compared with experiment; agreement is within the measurement accuracy of 5%.
Photo‐assisted heterogeneous catalysis with optical fibers. Part III: Photoelectrodes
Authors: Marinangeli R. E. , Ollis D. F.
Published: June 2004

The concept of using optical fibers to distribute light within heterogeneous photo‐assisted catalysts is extended to photo‐electrochemical cells. The potential drop in a semiconductor photo‐electrode is predicted for various types of ohmic electrical contacts, and the optimum contact location is determined. The variation of electrical conductivity with temperature in non‐isothermal bundles of semiconductor‐coated optical fibers is considered.
Mass transfer between a turbulent fluid and a solid boundary: Linear theory
Authors: Campbell J. A. , Hanratt T. J.
Published: June 2004

A linear form of the mass balance equation is used to determine how turbulent transport of mass to a solid wall is related to the fluctuating velocity field. It is found that at high Schmidt numbers the Reynolds transport is controlled by fluctuations of much lower frequency than the most energetic velocity fluctuations. The characteristic of the velocity field that emerges as being most important is the small frequency limiting value of the spectral function of the velocity fluctuations normal to the wall. However, the linear theory that is explored does not predict the correct dependency of the average and the mean‐squared deviation of the mass transfer coefficient on Schmidt number. A nonlinear analysis must be performed to examine fully the mechanism of turbulent mass transfer to a solid surface.
Kinetics of absorption of carbon dioxide into aqueous sodium sulfite solutions
Authors: Hikita Haruo , Asai Satoru , Yano Akinori , Nose Haruji
Published: June 2004

The rates of absorption of pure carbon dioxide into aqueous sodium sulfite solutions containing or not containing sodium sulfate were measured at 15, 25, 35 and 45°C and at atmospheric pressure using a liquid‐jet column, a wetted‐wall column, and a quiescent‐liquid absorber. The experimental results were analyzed by the chemical absorption theory based on the penetration model. The second‐order forward rate constants for the reaction between carbon dioxide and sulfite ion in aqueous solutions were calculated and correlated as a function of temperature and ionic strength of the solution. The chemical equilibrium constants for the reaction were also determined from the measurements of the total solubility of carbon dioxide in aqueous sodium sulfite solutions.
Carbon attrition during the fluidized combustion of a coal
Authors: Arena U. , D'Amore M. , Massimilla L.
Published: June 2004

The generation of carbon fines by attrition during the fluidized combustion of a bituminous coal has been studied by means of a 140mm ID fluidized‐bed combustor under variable excess air factor, bed temperature, fluidizing velocity and size of bed sand and coal. Results indicate that rates of attrited fines are roughly proportional to excess of gas velocity above the minimum for fluidization and bed carbon exposed surface. Attrition rate constant is affected by size of sand and, to a less extent, and particularly with finer coal, by bed temperature.
Absorption of sulfur dioxide into aqueous double slurries containing limestone and magnesium hydroxide
Authors: Sada E. , Kumazawa H. , Nishimura H.
Published: June 2004

The absorption of dilute SO2 into aqueous double slurries containing CaCO3 and Mg(OH)2 was carried out using a stirred tank with a plane gas‐liquid interface. The absorption rate increased and finally reached that under the completely gas‐film controlled conditions as the absorption process proceeded. The desulfurization process using the double slurry was formulated by a two‐reaction‐plane model in which there are no particles suspended in‐between the interface and the primary reaction plane. It was suggested from comparison of the experimental absorption rates with the theoretical predictions that 40 to 60% of the absorbed sulfur dioxide may be present as an effective magnesium sulfite ion pair.
Multivariable control of a wet‐grinding circuit
Authors: Hulbert D. G. , Woodburn E. T.
Published: June 2004

The dynamic behavior of a pilot‐plant grinding circuit was modelled by relating three output variables that were representative of the conditions within the mill and the classifier to three input variables, namely feed rates of the solids, mill water, and sump water.

A multivariable controller was designed, by the use of Inverse Nyquist Array techniques, for feedback control of the outputs by the inputs, and applied to the plant by a process‐control computer with the use of direct digital control.
Experimental measurements of the effect of viscosity on drag for liquid drops
Authors: Gillaspy P. H. , Hoffer T. E.
Published: June 2004

The drag coefficients of drops of various liquids falling in air were measured experimentally. The drag coefficient was linearly related to the viscosity in the Reynolds number and viscosity range measured. Measurements also suggested there is no difference between Newtonian and non‐Newtonian liquids.
Fault diagnosis in nonlinear chemical processes. Part II. Application to a chemical reactor
Authors: Watanabe K. , Himmelblau D. M.
Published: June 2004

A two‐level strategy for fault detection and diagnosis developed in Part I is applied to a chemical reactor in which heptane is converted to toluene. Simulation of various faults demonstrates that the proposed strategy is valid, and that it also represents an improvement over fault diagnosis via an extended Kalman filter.
Reduced‐order steady‐state and dynamic models for separation processes. Part II. Application to nonlinear multicomponent systems
Authors: Cho Y. S. , Joseph B.
Published: June 2004

In Part I, a novel method for reducing the order of models for countercurrent staged separation systems was presented. In this paper, the method is applied to the modeling and simulation of nonlinear multicomponent distillation systems. Some additional properties of the model reduction procedure are derived. The accuracy of the approximation is established by comparison of the steady‐state profiles and transient responses to that of rigorous dynamic models. The results indicate that the proposed technique is an effective way of reducing the number of equations needed to model stagewise multicomponent separation systems.
Interfacial area, bubble coalescence and mass transfer in bubble column reactors
Authors: Miller D. N.
Published: June 2004

Relationships are developed for determining interfacial areas as a function of bubble coalescence and for predicting liquid‐film‐controlled mass transfer in deep seal bubble column reactors. Interfacial area is inversely dependent on mean bubble size; the mass transfer constant is directly dependent on bubble size. A correction for enhancement due to liquid‐phase reaction must be applied, and enhancement is shown to decrease with increasing bubble size.

Experimental measurements on the catalyzed rate of oxygen absorption from air in aqueous sodium sulfite solutions were made in a 0.299 m diameter × 9.14 m high glass column. Water and aqueous solutions of a surfactant and corn syrup were used to simulate ranges of surface tensions, densities, and viscosities. Perforated plates with 0.00635‐m holes and 2.85% open area were inserted at 1.524‐m spacing on half of the experimental runs to show the effects of gas redispersion. Two‐phase flow velocities were adjusted to cover ranges of interest in full‐scale, commercial bubble column reactor design.
Four environment model of mixing and chemical reaction. Part I. Model development
Authors: Mehta R. V. , Tarbell J. M.
Published: June 2004

A new mathematical model (the four environment model) to describe turbulent flow chemical reactors with complex reactions and separate reactant feed streams is developed. The feed stream residence time distributions, the batch chemical kinetics, and a single turbulent micromixing parameter, which may be estimated from direct turbulence theory, are required as input information to the model. The model is computationally efficient as it involves only ordinary differential equations.
PVT analysis of a new cubic‐perturbed, hard‐sphere equation of state
Authors: Martin J. J.
Published: June 2004

The cubic‐perturbed, hard‐sphere equation of state proposed in 1980 by Ishikawa, Chung and Lu, has been analyzed by PVT criteria, as contrasted to the single component and multicomponent vapor‐liquid equilibria to which it was applied. The analysis compares its representation of the PVT behavior of substances with that of a simpler equation.
Modelling of rapidly‐mixed fast‐crosslinking exothermic polymerizations. Part I: Adiabatic temperature rise
Authors: Chella R. , Ottino J. M.
Published: June 2004

A lamellar mixing approach has been applied to the modelling of an imperfectly mixed, fast, crosslinking, exothermic polymerization. The model involves the solution of coupled nonlinear partial differential equations representing mass and energy transfer in locally structured lamellar domains with diffusion and reaction occurring between initially segregated lamellae.

Several seemingly unusual features of experimental results can be explained qualitatively in terms of this simplified model. The phenomena investigated include: effect of variations in mixing, catalyst concentration (intrinsic reaction rate), and initial temperature for equal mixing conditions.
Distributed pore‐size model for sulfation of limestone
Authors: Christman P. G. , Edgar T. F.
Published: June 2004

A model is proposed to study the reaction between a porous solid and a reactant gas resulting in solid and gaseous products. The model describes the reacting solid as a sphere made up of a distribution of randomly oriented open pores. The evolution of the pore‐size distribution is followed by use of a population balance, using a combination of the independent variables of time and location first presented by Dudukovic (1976). The macroscopic properties of the solid are obtained by integrating over the pore size distribution. The results of the population balance are used with a mass balance on the reacting gas to obtain rate and conversion data.

The results of the model are compared to experimental data obtained for the sulfation of limestone (Ulerich et al., 1977). Both rate vs. conversion as well as conversion vs. time plots are presented, which serve as a more strenuous test of the model than either type of plot alone.
Effect of pressure fluctuation on coal combustion in large‐particle fluidized beds
Authors: Bywater R. J. , Chung P. M.
Published: June 2004

Atmospheric fluidized‐bed combustors (AFBC) operate in the large‐particle (>1 mm) fluidization regime. Characteristics of this regime, combined with the fact that as much as 50% of the coal combustibles are volatiles, result in localization of the devolatilization and combustion of the volatilized gases to the neighborhood of the coal‐particle and volatile gas plumes arising from the injector region. The volatile gas plume resulting from the large‐particle fluidization dynamics wanders due to pressure fluctuations induced by bubble passage.

The purpose of the present work is to determine the impact of these characteristics on the design of AFBC's. This has been accomplished by a linearized analysis of the governing equations to describe the periodic wandering of the volatiles plume diffusion flame and the corresponding fluctuation of the combustion rate. The flame oscillation increases the overall combustion rate above the steady‐state value. This increase diminishes with increasing fluctuation frequency until the flame becomes insensitive to the fluctuation in the high frequency limit.
Optimal control policy for substrate inhibited kinetics with enzyme deactivation in an isothermal CSTR
Authors: San Ka‐Yiu , Stephanopoulos Gregory
Published: June 2004

A slow enzyme deactivation process taking place in parallel with the main enzymatic reaction in a continuous stirred‐tank reactor can cause a departure from the optimal operating conditions, or, even a reactor failure. One way of minimizing productivity losses and maintaining optimal reactor conditions is by properly manipulating the flow rate of the reactor. The optimal flow‐control policy for typical enzyme kinetics with parallel enzyme deactivation is derived. Both the complete and an approximate analytical solution are presented. The approximate solution, which is actually a quasisteady‐state solution, is a very good approximation when the deactivation process is slow compared to the main enzymatic reaction and can be easily implemented as a feedback control based on the current state of the reactor. If the deactivation kinetics is the same as that of the main reaction and the cost of the reactant is negligible compared to that of the product, the quasisteady‐state solution is indeed the exact solution.
Optimal process design under uncertainty
Authors: Halemane K. P. , Grossmann I. E.
Published: June 2004

A rigorous mathematical formulation is presented for the problem of optimal design under uncertainty. This formulation involves a nonlinear infinite programming problem in which an optimization is performed on the set of design and control variables, such that the inequality constraints of the chemical plant are satisfied for every parameter value that belongs to a specified polyhedral region. To circumvent the problem of infinite dimensionality in the constraints, an equivalence for the feasibility condition is established which leads to a max‐min‐max constraint. It is shown that if the inequalities are convex, only the vertices in the polyhedron need to be considered to satisfy this constraint. Based on this feature, an algorithm is proposed which uses only a small subset of the vertices in an iterative multiperiod design formulation. Examples are presented to illustrate the application to flexible design problems.
Tube‐wall catalytic reactor cooled by an annular heat pipe
Authors: Parent Y. O. , Caram H. S. , Coughlin R. W.
Published: June 2004

Cooling a tube‐wall reactor using an annular heat pipe (AHP) is more temperature‐stable, more flexible and more productive than cooling by conventional means. Tube‐wall reactors cooled by an annular heat pipe arrangement exhibit flatter temperature profiles and uniform redistribution of the imposed heat load. The combination of tube‐wall reactor and annular heat pipe is subject to the usual capacity limitations of the heat pipe: sonic flow, boiling heat transfer, liquid entrainment, and capillary flow of the working fluid.
Combustion of carbon residue from oil shale retorting
Authors: Hiskakis Miltiadis , Hanratty T. J.
Published: June 2004

The combustion of a bed of particles impregnated with carbon is considered. An analysis is developed for the combustion wave after it has progressed some distance into the bed. It is shown that the calculations are considerably simplified by choosing a coordinate system that moves with the combustion wave and by neglecting dispersion of heat or mass.
Multiplicity criteria for multireaction networks
Authors: Balakotaiah Vemuri , Luss Dan
Published: June 2004

A general method is developed for a systematic determination of criteria predicting steady‐state multiplicity in lumped‐parameter systems in which many irreversible reactions occur simultaneously. The method enables use of criteria derived for simple reaction networks to predict the behavior of more complex networks. The available multiplicity criteria for the single‐ and two‐reaction networks can always be used to write down sufficient multiplicity criteria for any multireaction system. Several examples illustrate the power of the proposed technique.
Diffusion of gases in porous solids: Monte Carlo simulations in the Knudsen and ordinary diffusion regimes
Authors: Abbasi M. H. , Evans J. W. , Abramson I. S.
Published: June 2004

Porous solids have been simulated in the computer as assemblages of spheres. When such assemblages contain spheres distributed in size and randomly arranged in space, the structure of the resulting solid resembles that of a real porous solid. Monte Carlo calculations of gas molecule trajectories through the assemblages were carried out for both the Knudsen and ordinary diffusion régimes. Tortuosities calculated from the simulated diffusion “data” fell in the range obtained experimentally by other investigators. Correlations were obtained that enable the prediction of diffusion rates from measurement of the porosity, mean pore size, and standard deviation of the pore size.
Tracer diffusion in methanol, 1‐butanol and 1‐octanol from 298 to 433 K
Authors: Chen S.‐H. , Evans D. F. , Davis H. T.
Published: June 2004

Diffusion coefficients of argon, krypton, xenon, methane, carbon tetrachloride and the tetraalkyltins (methyl through butyl) were measured in methanol, 1‐butanol and 1‐octanol over the temperature range 298 to 433 K. With temperature‐dependent solvent diameters fitted from the tracer diffusivity of one of the solutes, a rough‐hard‐sphere theory predicts well the observed tracer diffusivity over the solvent density range in which hard‐sphere computer simulations are available. The Wilke‐Chang correlation predicts diffusion coefficients in the higher alcohols with an average error of 80% and a maximum error of 200%. A correlation of the form Dμp/T = A where p and A depend on solute and solvent size is more successful giving an average error of 7% and a maximum error of 24%.