bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling of permeators with two different types of polymer membranes
Authors: Perrin J. E. , Stern S. A.
Published: June 2004

Mathematical models have been developed for the separation of binary gas mixtures in permeator modules housing two different types of membranes simultaneously. The membranes are selected so as to exhibit reverse selectivities toward the components of a mixture, i.e., so that one membrane is more permeable to one of the components while the second membrane is more permeable to the other component. The mathematical models describe the membrane separation process for three kinds of flow patterns of the permeated (low pressure) and unpermeated (high pressure) gas streams in the permeator, namely, “perfect mixing,” counter‐current flow, and cocurrent flow. Numerical solutions of the models indicate that the extent of separation achievable in a two‐membrane permeator can be much higher than in a conventional single‐membrane permeator. Also, for given product compositions, the membrane area requirements of the former permeator can be lower than those of the latter. Countercurrent flow is generally the most efficient flow pattern in a two‐membrane permeator, and “perfect mixing” is the least efficient one, but the opposite is true under special operating conditions.
The role of porosity in filtration. Part X: Deposition of compressible cakes on external radial surfaces
Authors: Tiller F. M. , Yeh C. S.
Published: June 2004

The theory of deposition of compressible, particulate beds on cyclindrical surfaces is developed for both constant‐pressure and constant‐rate filtration. Radial flow is encountered in tubular filters and in both filtering and sedimenting centrifuges. It differs mathematically from filtration on planar surfaces in the manner in which the frictional drag balance on the particle structure is coupled with Darcy's equation.
Fully developed temperature waves in a bed of processed shale
Authors: Hiskakis Miltiadis , Hanratty T. J.
Published: June 2004

The combustion of processed shale is analyzed. By using a coordinate system moving with the same velocity as the combustion zone a model is obtained for the fully developed temperature wave. Of particular interest is the interpretation of this wave in terms of the kinetics and thermal effects of the reactions that are involved.
Heat and mass transfer in water‐laden sandstone: Convective heating
Authors: Wei Chen Kou , Davis H. T. , Davis E. A. , Gordon Joan
Published: June 2004

A theoretical model was developed to predict the heat and mass transfer phenomena in porous materials. A water‐filled sandstone was heated in a convective oven and its water loss rates and temperature profiles were compared with theoretical results. In addition to local temperatures, moisture content, gas densities and pressure, this model also predicts the fluid flow pattern in the heated sample.
Dynamics of deep‐bed filtration. Part I: Analysis of two limiting situations
Authors: Chiang Hsu‐Wen , Tien Chi
Published: June 2004

The dynamic behavior of deep‐bed filtration was studied by considering two limiting situations. In the first case it was assumed that deposition leads to the presence of a reasonably smooth deposite layer over filter grains. In the second case particle aggregates, once formed, were assumed to remain rigid and the deposited particles to act as additional collectors. The effect on filter performance of the media change resulting from the presence of these two types of deposits was examined quantiatively.
Mass transfer in AC electrolysis. Part III: Study of triangular and square‐wave current on rotating electrodes
Authors: Cheng C. Y. , Chin D.‐T.
Published: June 2004

A theoretical and experimental investigation is presented for mass transfer to a rotating hemispherical electrode when direct current (DC) superimposed with symmetrical triangular‐ or square‐wave alternating current (AC) is used for electrolysis. A film model is used for the analysis of AC concentration components. The limiting AC current density corresponding to a zero instantaneous surface concentration and the phase shift between the applied AC and the periodic potential changes are calculated and compared to the experimental studies. The experimental data agreed with the theoretical prediction to within ±8% in the regime of a dimensionless AC frequency K = (ω/Ω)Sc1/3 greater than 1 and less than 180. The mass transfer behavior with the triangular and square waves is further compared to that of the sinusoidal current. It is found that for a given AC frequency and rotational speed, the limiting AC current density on the electrode decreases in the order of traingular‐wave AC > sinusoidal AC > square‐wave AC.
Thermodynamically consistent quasi‐Newton formulae
Authors: Lucia Angelo , Miller D. C. , Kumar Ashwani
Published: June 2004

Newton and quasi‐Newton methods have been used in chemical process design and optimization calculations for quite some time. They continue to be used today, both in the traditional sense and as part of the more recent hybrid method. While Newton‐based fixed‐point methods have been used to solve many different kinds of chemical process design and optimization problems, perhaps the point of single largest application has been that of multicomponent separation problems, especially equilibrium stage distillation.

Quite aside from this, classical thermodynamics provides us with certain fundamental mathematical and physical relationships governing the behavior of nonideal solutions, those being the homogeneity of partial molar excess properties and their derivatives and the Gibbs‐Duhem equation.

In this work, we draw a connection between the class of Newton‐based fixed‐point methods and classical nonideal thermodynamics. That is, it is shown that, with the exception of Newton's method, none of the conventional Newton‐like methods gives matrix approximations that are thermodynamically consistent. In other words, all existing nonsymmetric and symmetric quasi‐Newton formulae generate matrix approximations that do not satisfy, for either the zerodegree homogeneity or Gibbs‐Duhem equations.

In light of this, a new class of quasi‐Newton formulae is presented for use in chemical process problems whose models include chemical and/or phase equilibrium. In particular, several new quasi‐Newton formulae are presented that give Jacobian or Hessian approximations that satisfy the zero‐degree homogeneity and/or Gibbs‐Duhem equations, in addition to the usual secant and perhaps symmetry and sparsity condition. This new class of formulae is called thermodynamically consistent quasi‐Newton formulae. Some numerical results are presented that show that these thermodynamically consistent quasi‐Newton formulae can provide improvements in reliability and computational efficiency when compared to existing Newton‐like methods.
Formation of gas bubbles in supersaturated solutions of gases in water
Authors: Finkelstein Yehuda , Tamir Abraham
Published: June 2004

The objective of this study is to develop a model and correlate it with experimental measurements for predicting the tolerable degree of supersaturation of gas‐water solutions. This model is also capable of predicting quite accurately the cavitation phenomenon in water.
Kinetics of CO oxidation over Co3O4/γ‐Al2O3. Part III: Mechanism
Authors: Perti Deepak , Kabel R. L. , McCarthy G. J.
Published: June 2004

Interpretations of a variety of transient experiments are combined with information from the literature to reveal the roles played by the Co3O4 catalyst surface and adsorbed species. The reaction path depends on the oxidation state of the catalyst. A rather coherent picture of oxidation‐reduction catalysis by a metal oxide is obtained.
The application of drop size distribution and discrete drop mass transfer models to assess the performance of a rotating disc contactor
Authors: Al‐Aswad K. K. , Mumford C. J. , Jeffreys G. V.
Published: June 2004

A method has been developed to calculate the overall mass transfer coefficient in an agitated liquid extraction column containing a wide range of drop sizes. The method applied the drop size distribution diagram to estimate the volume percentage of stagnant, circulating, and oscillating drops in the drop population. Individual mass transfer coefficients were then evaluated for the corresponding drop state, using the different single‐drop mass transfer models, after which the overall coefficient Kcal was calculated as the fractional sum of the individual coefficients and their proportion in the drop population. These estimated mass transfer coefficients have been compared with results obtained from a large rotating disc extractor 0.45 m in diameter and 6.75 m high, extracting acetone between water and Clairsol (a parafinic hydrocarbon, principally decane). Good agreement was obtained in the majority of the experiments when the Rose‐Kintner correlation was applied to evaluate the dispersed phase mass transfer coefficient of the oscillating drops. In all experiments agreement between the calculated and experimental overall mass transfer coefficients was improved by evaluating the concentration driving force by applying Simpson's rule, thereby introducing corrections for the variation in flowrate along the column and for possible backmixing.
Kinetics of free radical polymerizations in reactive polymer processing
Authors: Huang Y. J. , Lee L. J.
Published: June 2004

A kinetic model has been developed for radical chain growth type of reactive polymer processing operations. This model incorporates considerations of the molecular diffusion that is described by a free volume theory and the basic reaction mechanism of the free‐radical chain polymerization. Experimental results from the bulk styrene polymerization and a reaction of sheet molding compound (SMC) showed good agreement with the model.
The dependence of viscoelastic flow functions on polymer structure for linear and branched polystyrene and polybutadiene
Authors: Ramachandran S. , Christiansen E. B.
Published: June 2004

Experimentally determined viscosities, first and second normal stress differences, and compliances for concentrated solutions of linear and four‐arm star‐branched polystyrenes and polybutadienes depend on the shear rate and the molecular weight, in agreement with theory and previously reported experimental results. The ratios of the second to first normal stress difference are ‐0.29 and ‐0.214 for the linear and branched polymers, respectively, independent of molecular weight, molecular weight distribution, concentration, and shear rate.
Influence of site energy distribution on catalytic rates with multicomponent chemisorption
Authors: Bhat Y. S. , Prasad S. D. , Doraiswamy L. K.
Published: June 2004

Without using the assumption of constancy of mole fractions in adsorption space, dual‐component adsorption accompanied by catalytic reaction on a heterogeneous surface is modeled. A simple parallel reaction scheme which is supposed to idelalize key steps in cracking and disproportionation reactions is studied. Quantities of interest in catalytic kinetics such as mean surface coverage, mean squared surface coverage, and others are calculated as statistical averages over the bivariate analogs of four well‐known monovariate distributions, with the assumption of relaistic heats of adsorption. Using a variant of the Mellin transform method proposed earlier, explicit expressions for the rates are given as functions of partial pressure ratio and the parameters characterizing the site energy distribution. Methods are proposed to determine the characteristic ratio of partial pressures at which a desired selectivity pattern is realized. Lastly, two reaction schemes which outline key steps in platforming and reforming reactions and which occur on bifunctional catalysts are analyzed and methods for determining the characteristic pressure ratio are suggested.
Liquid‐liquid interfacial areas formed by turbine impellers in baffled, cylindrical mixing tanks
Authors: Eckert R. E. , McLaughlin C. M. , Rushton J. H.
Published: June 2004

An extensive experimental study on the formation of liquid‐liquid interfacial areas was conducted using flat‐blade turbine impellers in standard mixing tank geometry. The interfacial areas were measured with a light probe for different combinations of volume fraction, continuous and dispersed phase physical properties, and mechanical mixing conditions.
Size‐dependent crystal growth—A manifestation of growth rate dispersion in the potassium alum‐water system
Authors: Girolami M. W. , Rousseau R. W.
Published: June 2004

Growth of potassium alum crystals was characterized by the advance rates of crystals on the leading edge of population distributions and by the advance rates of the modes of these distributions. Growth rates of crystals on the leading edge appeared to follow size‐dependent kinetics, but the observed spread of the distribution about the average size was much greater than would be expected from size‐dependent growth alone. The spread of the distribution was correlated with the extent of growth determined from the net advance of the average crystal size. These quantitative and qualitative results show that what has often been referred to as size‐dependent growth is in fact a manifestation of growth rate dispersion.
A simultaneous‐modular approach to process flowsheeting and optimization. Part I: Theory and implementation
Authors: Chen Hern‐Shann , Stadtherr M. A.
Published: June 2004

There basic problem formulations for the simultaneous‐modular approach are discussed, as are three alternative methods for computing the flowsheet‐level Jacobian. A new algorithm for partitioning and tearing when using the simultaneous‐modular approach is also presented. SIMMOD, our implementation of the simultaneous‐modular approach is then outlined. In subsequent papers in this series we use SIMMOD to study the performance of the simultaneous‐modular approach on process simulation and optimization problems, as well as to perform experiments on different numerical strategies for implementing the simultaneous‐modular approach.
Annular flow pressure drop model for pease–anthony‐type venturi scrubbers
Authors: Viswanathan S. , Gnyp A. W. , St. Pierre C. C.
Published: June 2004

An annular flow pressure drop model has been developed and compared with experimental data obtained on a pilot‐plant‐size Pease‐Anthony‐type venturi scrubber. Droplet and film accelerations as well as wall friction, based on the two‐phase Lockhart‐Martinelli correlation, are considered. Excellent agreement with experimental data is demonstrated for a wide range of throat gas velocities, liquid to gas ratios, and film flow rates for a single scrubber geometry.
Prediction of adsorption and desorption of protein on dextran based ion‐exchange resin
Authors: Tsou Hai‐Shung , Graham E. E.
Published: June 2004

The equilibrium and kinetic adsorption and desorption of bovine serum albumin (BSA), fraction V, on Sephadex A‐50 has been studied. The equilibrium data have been presented by a Langmuir isotherm for both adsorption and desorption conditions. The kinetics of adsorption in a batch system may be represented by a simple diffusional model. The kinetics of desorption of BSA in a batch system show a very fast initial rate due to the rapid shrinkage of the resin with changes in salt concentration. This has been modeled by including a protein exclusion term in the kinetics for desorption. The above information has been used to predict the breakthrough of BSA in a column operation. Under the pressure exerted in a column flow system the Sephadex A‐50 is severely compressed. The effect this has on the breakthrough rate of BSA has been demonstrated.
Role of rhenium in Pt‐Re‐Al2O3 reforming catalysis—An integrated study
Authors: Jothimurugesan K. , Nayak A. K. , Mehta G. K. , Rai K. N. , Bhatia S. , Srivastava R. D.
Published: June 2004

The inclusion of Re in Pt‐Re‐Al2O3 reforming catalysts to improve the lifetime is known, but how rhenium functions and how it is disposed in the catalyst remain unclear. These fundamental questions have been attempted in this study by the use of proton‐induced X‐ray emission and Rutherford backscattering spectrometry (together with electron microscopy and chemisorption studies) to characterize a commercial like catalyst for dehydrogenation of methylcyclohexane.
The determination of equilibrium exchange rates in catalytic reactions: Application to methanol synthesis on Cu‐Zn‐oxide
Authors: Willcox Dave , Garland Marc , Liu George , Kung H. H.
Published: June 2004

A method is described to obtain reaction rates of chemical reactions in a network in which there are more independent reactions thatn independent chemical species. The method makes use of the linear theory of nonequilibrium thermodynamics to obtain the equilibrium exchange rates of the reactions, which are calculated from the relaxation data as the system approaches chemical equilibrium. A method which follows very closely that of Wei and Prater (1962) can be used to treat the relaxation data. As an example, the method was applied to the methanol synthesis reaction from CO, CO2, and H2 over a Cu‐Zn oxide catalyst. It was concluded that successful application of the method is limited to systems in which all the processes contributing to the observed relaxation are known, in addition to the common limitations due to noise in experimental measurements.
Vacuum sorption pumping studies with pure gases on molecular sieves
Authors: Crabb K. S. , Perona J. J. , Byers C. H. , Watson J. S.
Published: June 2004

Low‐pressure, low‐temperature adsorption of N2 and CO2 were studied in beds of 4A molecular sieves. System parameters were estimated by a comparison of experimental results and a molecular‐flow theoretical model. Nitrogen data followed theoretical prediction. Theory adequately represented pressure above the bed for CO2, while pressure drops deviated deviated significantly from the model.
Effect of drag‐reducing polymers on mass transfer fluctuations
Authors: Vassiliadou Eleni , McConaghy G. A. , Hanratty T. J.
Published: June 2004

Electrochemical techniques are used to show that drag‐reducing polymers decrease the magnitude and the frequency of mass transfer fluctuations. Measurements of the frequency spectrum of the mass transfer fluctuations allow calculation of the normal component of velocity fluctuations in the immediate vicinity of the wall. This information is used to interpret the observed effect of drag‐reducing polymers on the rate of mass transfer.
Optimal, real‐time monitoring of particle size distribution in a fluidized bed
Authors: Cooper D. J. , Clough D. E.
Published: June 2004

A novel method for tracking particle size distribution dynamics in a fluidized bed yields on‐line, real‐time measurements of particle size distribution that are representative of actual conditions. These measurements are somewhat corrupted with noise (random error), however, and are available to the computer only at discrete time intervals. An optimal filtering algorithm combines the measurements with predictions from an idealized dynamic model to yield particle size distribution estimates that are not only on‐line and real‐time, but also virtually continuous and well‐behaved.
Modified sedimentation‐dispersion model for solids in a three‐phase slurry column
Authors: Smith D. N. , Ruether J. A. , Shah Y. T. , Badgujar M. N.
Published: June 2004

Solids distribution data for a three‐phase, batch‐fluidized slurry bubble column (SBC) are presented, using air as the gas phase, pure liquids and solutions as the liquid phase, and glass beads and carborundum catalyst powder as the solid phase. Solids distribution data for the three‐phase SBC operated in a continuous mode of operation are also presented, using nitrogen as the gas phase, water as the liquid phase, and glass beads as the solid phase. A new model to provide a reasonable approach to predict solids concentration distributions for systems containing polydispersed solids is presented. The model is a modification of standard sedimentation‐dispersion model published earlier. Empirical correlations for prediction of hindered settling velocity and solids dispersion coefficient for systems containing polydispersed solids are presented.

A new method of evaluating critical gas velocity (CGV) from concentrations of the sample withdrawn at the same port of the SBC is presented. Also presented is a new mapping for CGV which separates the two regimes in the SBC, namely, incomplete fluidization and complete fluidization.
Effects of surfactants on mass transfer during spray drying
Authors: Frey D. D. , King C. J.
Published: June 2004

A study was conducted to investigate the effects of added surfactants on mass transfer during spray drying. Measurements were made of retention of volatile components and amount of water evaporation at various points near the atomizer inside a spray dryer of pilot plant scale. Experimental data indicate that surfactants can have a substantial effect on transport processes when certain types of liquid solutions are spray dried. Experimental results are interpreted in terms of transport mechanisms and are compared with relevant previous studies on non‐spray systems.
The finite‐element solution of laminar combined convection from two horizontal cylinders in tandem arrangement
Authors: Wong King‐Leung , Chen Cha'o‐Kuang
Published: June 2004

A finite‐element method is used to solve the full Navier‐Stokes and energy equations for the problem of laminar combined convection from two horizontal cylinders in tandem arrangement. From comparisons with the previous theoretical and experimental results of a single‐cylinder situation, it is found that the behaviors flow and heat transfer in the upstream cylinder are close to those in a single‐cylinder, but this is not the case for the downstream cylinder.
Characteristic adsorption isotherm for adsorption of vapors on heterogeneous adsorbents
Authors: Sircar S. , Myers A. L.
Published: June 2004

The dimensionless group [(mRT/ΔG) ln(P/P°)] is a universal function of θ (fractional filling of micropores) for different vapors adsorbed on a heterogeneous adsorbent. Adsorptive parameters are the saturation capacity (m) and the free energy of immersion of the solid in bulk liquid adsorbate (ΔG). The heat of immersion of the adsorbent determines the temperature dependence of ΔG according to the Gibbs‐Helmholtz equation ΔH = ∂(ΔG/T)/∂(1/T).
Gross error detection and data reconciliation in steam‐metering systems
Authors: Serth R. W. , Heenan W. A.
Published: June 2004

Several new algorithms for the detection of gross errors in process data are presented and applied to an industrial steam‐metering system by means of computer simulation. A number of algorithms that have appeared in the literature are also applied to the steam‐metering system, and the performances of the various algorithms are compared.
Single‐Pellet, moment method for analysis of gas‐solid reactions
Authors: Doǧu Timur , Keskin Aliye , Doǧu GÜLsen , Smith J. M.
Published: June 2004

A single‐pellet, moment technique is presented for evaluating reaction rate constants, effective diffusivities, and adsorption equilibrium constants for gas‐solid noncatalytic reactions. Experimental pulse‐response data for the reaction of SO2 with activated soda at 473 K were obtained to illustrate the method. The results show that intraparticle diffusion is the controlling mechanism for this reaction. The value of the Thiele modulus for axial transport was found to be 8.6 for a cylindrical pellet of porosity 0.56, tortuosity 2.3, and length 3 × 10−2 m.
Lagrangian dispersion in turbulent flow from laser transit anemometry
Authors: Berman N. S.
Published: June 2004

The Lagrangian dispersion function in turbulent flow can be determined from measurements of the probability that a particle which is observed in a small volume is not observed in a similar size volume downstream. In this work a single‐detector method is proposed to detect the particle arrivals in a multiple series of scattering volumes; the probability can be determined from the digital record over a long time compared to the turbulent integral time scale. The method is tested at locations downstream of a water spray nozzle and a submerged jet of dilute polymer solutions.
On the stability of falling films—periodic, finite‐amplitude waves
Authors: Barrdahl Runo
Published: June 2004

An analytical, theoretical investigation regarding periodic finiteamplitude (nonlinear) waves in a Newtonian, isothermal liquid film flowing along a vertical wall is presented. The periodic solution found provides full information regarding stability, wavelength, wave velocity, and wave amplitude as expressed exclusively in terms of physical constants and flow rate.
Adaptive control strategies for process control: A survey
Authors: Seborg D. E. , Edgar T. F. , Shah S. L.
Published: June 2004

In recent years there has been extensive interest in feedback control systems that automatically adjust their controller settings to compensate for changes in the process or the environment. Such systems are referred to as adaptive controllers. This survey paper reviews the current state of the art in adaptive control from a process control perspective and describes leading design techniques. Potential operating problems associated with adaptive control schemes are considered. A survey of experimental applications of adaptive control systems to process control problems is also included.
High‐Performance multivariable control strategies for systems having time delays
Authors: Jerome N. F. , Ray W. H.
Published: June 2004

A new high‐performance multivariable time delay compensator is presented that contains the Ogunnaike‐Ray compensator as a special case, reduces to the Smith predictor for a single delay, and approaches the realizable part of the process inverse as a limit. The straightforward design procedure is illustrated with several distillation control examples.
Vapor‐liquid equilibrium of formaldehyde‐and water‐containing multicomponent mixtures
Authors: Maurer G.
Published: June 2004

The vapor‐liquid equilibria in the binary mixtures water‐formaldehyde and methanol‐formaldehyde are precisely correlated by introducing a physicochemical model that takes into account physical forces of interactions as well as chemical reactions. The most valuable feature of the model is its simple extension to multicomponent mixtures. From binary data alone the model is capable of accurately predicting vapor‐liqid equilibria in complex mixtures such as formaldehyde‐water‐trioxane and formaldehyde‐water‐methanol. This is demonstrated by comparing calculated data with experimental results taken from the literature or measured in this work, at temperatures between about 310 and 400 K at pressures up to 500 kPa, and formaldehyde concentrations in the liquid phase of up to about 70 mol %.
A study of separation efficiency in thermal diffusion columns with a permeable vertical barrier
Authors: Yeh Ho‐Ming , Tsai Shau‐Wei , Lin Cheng‐Shiung
Published: June 2004

A separation theory in thermal diffusion columns with a permeable vertical barrier has been derived by making use of the orthogonal expansion method. It is shown that the undesirable remixing effect can be effectively reduced and controlled by introducing a permeable vertical barrier. Considerable improvement in separation was obtained when the position of the barrier was carefully chosen.
Gas‐liquid reaction systems: A heuristic model and its steady solutions
Authors: White Daniel , Johns L. E.
Published: June 2004

To identify conditions under which gas‐liquid reaction systems exhibit natural oscillations, a model is formulated in which the time scales of the elementary processes play a leading role. The steady solutions of the model problem are investigated, with the finding that at most one solution may lie in each of five temperature ranges, each range corresponding to a dominant physicochemical process.
Pole‐placement self‐tuning control of a fixed‐bed autothermal reactor. Part I: Single variable control
Authors: McDermott P. E. , Mellichamp D. A. , Rinker R. G.
Published: June 2004

A pole‐placement self‐tuning controller has been used to control a fixed‐bed autothermal reactor conducting the water‐gas shift reaction at both an upper stable state and a middle unstable state. Excellent set‐point tracking and disturbance rejection characteristics were obtained using a single manipulated variable, the heat input at the entrance to the catalyst bed, to control a single bed temperature. Excellent set‐point tracking during the transition from the upper state to the middle state was obtained by using a technique that tuned the closed‐loop poles on‐line so as to give an optimal response.
Pole‐placement self‐tuning control of a fixed‐bed autothermal reactor. Part II: Multivariable control
Authors: McDermott P. E. , Mellichamp D. A. , Rinker R. G.
Published: June 2004

The multiinput/multioutput pole‐placement self‐tuning controller (MIMO PPSTC) previously developed by McDermott and Mellichamp is used to control a fixed‐bed autothermal reactor with internal countercurrent heat exchange. The performance of the controller is demonstrated using step changes in the set points and in the primary disturbance variables. It is shown that the complete temperature profile can be maintained by controlling two temperatures in the catalyst bed: one just before the hot spot and the other at the exit of the bed. Simulated results using a 36th‐order nonlinear reactor model operating at both an open‐loop upper stable steady state and an open‐loop unstable steady state are presented. Experimental results for a fixed‐bed autothermal reactor operating at an upper stable state are presented.
Mechanisms and kinetic modeling of calcium oxalate crystal aggregation in a urinelike liquor. Part I: Mechanisms
Authors: Hartel R. W. , Gottung B. E. , Randolph A. D. , Drach G. W.
Published: June 2004

The tendency for aggregation and disruption of aggregates of calcium oxalate dihydrate (CaOx) crystals in urinelike mother liquor was quantitatively studied in a two‐stage mixed‐suspension, mixed‐productremoval crystallizer/Couette‐flow aggregator operated in series. The degree of aggregation was obtained by comparing measured numbersize and volume‐size crystal distributions in the crystallizer and aggregator outlets. Aggregation was a strong function of CaOx supersaturation and may have changed slightly with rotation speed in the Couette‐flow aggregator. Rupture of the aggregates increased as the spindle rotation in the aggregator increased (presumably increasing turbulence). Average shear rates in these experiments were appreciably above estimated physiological levels.
Modeling of coal liquefaction kinetics based on reactions in continuous mixtures. Part II: Comparison with experiments on catalyzed and uncatalyzed liquefaction of coals of different rank
Authors: Prasad G. N. , Agnew J. B. , Sridhar T.
Published: June 2004

Experimental kinetic data for three Australian coals are compared with predictions from the mathematical model developed in Part I. For these coals, as well as data reported for North American coals, the model is found to show good agreement, using the characteristic molecular weight as the only parameter. The effects of reaction time and temperature are coupled via a severity index that arises in the model as a dimensionless reaction time. The model is also shown to be applicable when catalysts are present. The product distribution for a particular coal seems to be a function only of the conversion even in the presence of catalysts, as long as the chemical reaction controls the rate of liquefaction.
Tracer diffusion in dense ethanol: A generalized correlation for nonpolar and hydrogen‐bonded solvents
Authors: Sun C. K. J. , Chen S. H.
Published: June 2004

Tracer diffusion coefficients were measured for benzene, toluene, mesitylene, naphthalene, and phenanthrene in dense ethanol at 0.56 ≤ TR ≤ 1.07 and ρR ≥ 1.44. The results were used to examine the temperature dependence of the degree of association between ethanol molecules across the entire range of temperature. The hard‐sphere tracer diffusion equation and the Stokes‐Einstein equation were used to develop two engineering correlations. The former approach was found to be adequate for solvents of relatively compact molecules, and the latter to be more general in its applications. The absolute deviation of prediction from observed values of tracer diffusivities is 4%, with a maximum error of 13%.
A unified approach for prediction of thermodynamic properties of aqueous mixed‐electrolyte solutions. Part I: Vapor pressure and heat of vaporization
Authors: Patwardhan V. S. , Kumar Anil
Published: June 2004

The overall nonideality of an aqueous mixed electrolyte solution is characterized in terms of a newly defined parameter Γ*, called the overall reduced ionic activity coefficient. It is shown that Γ* for the mixed solution is simply related to the properties of single‐electrolyte solutions. Γ* is related to the vapor pressure of a mixed‐electrolyte solution through well‐known thermodynamic equations. This leads to a predictive equation for the vapor pressure of a mixed‐electrolyte solution in terms of the vapor pressures of single‐electrolyte solutions of the components. This equation is valid over the entire concentration range encountered in practice, without any empirical constants, and has a predictive accuracy of 2%. A predictive equation for the latent heat of vaporization is also developed and tested against experimental data.
A unified approach for prediction of thermodynamic properties of aqueous mixed‐electrolyte solutions. Part II: Volume, thermal, and other properties
Authors: Patwardhan V. S. , Kumar Anil
Published: June 2004

The overall reduced ionic activity coefficient Γ* is useful in characterizing the overall nonideality of an aqueous mixed‐electrolyte solution. It has been shown in Part I that Γ* can be simply related to Γ of single‐electrolyte solutions containing the component electrolytes without using empirical constants. This basic relationship is used in this paper for deriving predictive equations for several properties in terms of corresponding properties of single‐electrolyte solutions containing the component electrolytes. The predictive equations need no empirical constants. The properties covered include volume properties such as density and adiabatic compressibility, thermal properties such as enthalpy and specific heats, and others such as free energy, expansibility, and depression in freezing point. Comparison with experimental data shows that the predictive equations have an accuracy varying from 0.03% for density to 2% for freezing point depression, and are valid for the entire range of concentrations encountered in practice.
A new criterion for the pairing of control and manipulated variables
Authors: Mijares Gerardo , Cole J. D. , Naugle N. W. , Preisig H. A. , Holland C. D.
Published: June 2004

A criterion is developed for the selection of the best pairing of the control and manipulated variables of a multiloop control system. This criterion is based on the difficulty caused by the interaction terms (the off‐diagonal elements) in finding the inverse of the steady state gain matrix. From an analysis based on the proposition that the most desired or best pairing is that one for which the system most closely resembles a set of independent single‐loop systems, a quantitative measure of the best pairing is obtained. Although the development of the pairing criterion is based on purely algebraic principles, the validity of the pairing criterion is evident from analogous developments obtained within the control framework. Furthermore, it is shown that the pairing criterion may be used to determine the stability of a multiloop control system, thus enhancing the value of the criterion presented.
Mass transfer in eddies close to air‐water interface
Authors: Luk Sydney , Lee Y. H.
Published: June 2004

Deterministic analyses applied to both velocity and concentration fluctuation data obtained in a region extremely close to air‐water interface in a free‐surface, unbaffled stirred tank allow estimation of the length and the velocity scales of individual eddies taking part in gas absorption. The mass transfer prediction by this method is superior to that by a statistical method using an integral length scale in the low‐turbulence flow employed in this work. Eddy velocities are generally lower in the diffusion boundary layer zone compared with the bulk zone. Small eddies are generally associated with low velocity scales whereas large eddies occur at high velocity scales. Local mass transfer coefficients are high in regions where small eddies are dominant.
Air‐lift reactor analysis: Interrelationships between riser, downcomer, and gas‐liquid separator behavior, including gas recirculation effects
Authors: Siegel M. H. , Merchuk J. C. , Schugerl K.
Published: June 2004

An approach to air‐lift reactor analysis is presented that examines the three parts of the air‐lift—the riser, downcomer, and gas‐liquid separator—as three interconnected and interrelated elements. Downcomer flow configurations are described and characterized by either straight or oscillating bubble flow patterns. The downcomer gas flow rate is determined using a two‐sparger system, and a correlation is presented relating the downcomer superficial gas velocity to the downcomer gas holdup. Gas recirculation is calculated and related to the geometric and operating conditions of the gas‐liquid separator. It is shown that an increase in residence time in the gas‐liquid separator decreases the gas recirculation rate. Correlations are presented relating gas holdup and liquid velocities to superficial gas velocity.

A sparger was added near the entrance of the downcomer, in addition to the conventional placement near the entrance of the riser. Results of such a two‐sparger system are discussed in relation to reactor stability and liquid velocities.
Instantaneous concentration fluctuations in point‐source plumes
Authors: Georgopoulos P. G. , Seinfeld J. H.
Published: June 2004

A model for the variance σ of instantaneous plume concentrations, at a level corresponding to that of the Gaussian formulas for the mean field, is developed and tested against available data. Starting from the Eulerian species transport equation, theoretical and empirical information is used to estimate parameters and simplify the form of the transport equation for σ in a meandering frame of reference. Then, introduction of a localized production of fluctuations (LPF) scheme allows construction of analytical expressions for σ that provide a direct means for calculating the concentration variance inside the instantaneous boundaries of plumes resulting from continuous point emissions in turbulent flows with uniform mean velocity.
Detection and location of a leak in a gas‐transport pipeline by a new acoustic method
Authors: Watanabe Kajiro , Himmelblau D. M.
Published: June 2004

A new method is described for detecting and locating a leak in a gas transport pipeline lying between two pump stations by an indirect acoustic method. The basic concept is to treat the pipeline as an acoustic tube (similar to a wind instrument), and to estimate the impulse response of the acoustic wave in the pipeline solely from the acoustic signal detected at two terminal sites in the pipeline. The test signal introduced at the input site is only acoustic noise; pipeline operation need not be interrupted. If a leak occurs in the pipeline, the impulse response of the acoustic wave in the pipeline has a sharp pulse or a step at a certain time that can be directly related to the site of the leak. Using the mathematical model of the pipeline acoustics, i.e., the wave equation, a theoretical basis is developed to explain how and why the leak can be detected and located. Experiments carried out in the laboratory under conditions comparable to realistic field conditions demonstrate the validity of the proposed detection method.
The role of conduction/valence bands and redox potential in accelerated mineral dissolution
Authors: Leblanc S. E. , Fogler H. S.
Published: June 2004

The dissolution kinetics of a number of manganese oxides in acidic solutions were studied. Using a slurry reactor, rate laws were determined for each of the manganese oxides in the hydrohalogen acids. Significant variations in the reaction rates (up to five orders of magnitude over the HCl base rate) were obtained with different acids. The addition of anions as neutral salts to acidic solutions is shown to produce the same rate‐accelerating effect as acids containing that anion. The effect of the different acids on the oxide dissolution rates is explained using semiconductor band theory and energy diagrams.
Gas‐liquid mass transfer and pressure drop in pulp bed with flexible fibers as solid supports
Authors: Hsu C. L. , Hsieh J. S.
Published: June 2004

The volumetric mass transfer coefficients between oxygen and water in a pulp bed have been determined by the gas‐liquid reaction method with an enhancement factor approximately equal to one. The coefficients ranged from 0.08 s−1 at 13% to 0.34 s−1 at 19% solids content in the pulp bed, values that are close to those for comparable trickle beds. No liquid flow over the pulp bed (13–19% solids content) occurred under the operating conditions. The results showed that gas‐liquid mass transfer was affected only by the solids content of the pulp bed rather than by the oxygen superficial velocity (0.4 to 1.2 cm/s). The gas pressure drop across the pulp bed was also predicted by Ergun's equation using an estimated effective diameter for the fiber flocs.
An improved adsorption process for the production of high‐fructose syrup
Authors: Ching C. B. , Ho C. , Ruthven D. M.
Published: June 2004

By applying a temperature profile to the system, the concentration of the extract product in a countercurrent adsorption separation process may be increased relative to the maximum concentration attainable under isothermal conditions. To achieve the required temperature profile in a simulated countercurrent system it is necessary to heat and cool the columns in sequence as the feed and product draw‐off points are switched through the bed. The practical feasibility of operating the system in this way has been demonstrated experimentally for the separation of glucose‐fructose mixtures. By maintaining a temperature difference of 30–35°C across the bed an extract product containing 28% fructose and about 1% glucose was obtained, at steady state, from a feed containing 25 wt. % of each sugar.
Separation of a helium‐methane mixture in permeators with two types of polymer membranes
Authors: Perrin J. E. , Stern S. A.
Published: June 2004

The separation of a HeCH4 mixture containing 9.95 mol% He in permeator modules that incorporate two different types of polymer membranes was studied theoretically and experimentally. The membranes were symmetric dense capillaries of silicone rubber and asymmetric hollow fibers of cellulose triacetate. These membranes exhibit reverse selectivities for He and CH4, silicone rubber being more permeable to CH4, and cellulose triacetate more permeable to He. The simultaneous use of these two types of membranes in a permeator enhances the enrichment and recovery of He compared to the levels obtained with a single‐membrane permeator utilizing either membrane alone. The experimental results were found to confirm the theoretical predictions, the agreement being better at the lower stage cuts.
Measuring diffusion coefficients by Taylor's method of hydrodynamic stability
Authors: Quinn J. A. , Lin C. H. , Anderson J. L.
Published: June 2004

Diffusion coefficients for liquid solutions can be measured using a hydrodynamic stability criterion first derived by G. I. Taylor. This method is used in the present work to determine diffusion coefficients for a range of solutes from small molecules to colloidal particles, at infinite dilution and at finite concentrations. The method is simple and accurate and seems to have wide applicability. Taylor's stability criterion can also be used to establish known, linear concentration gradients of several different solutes in one column of fluid, and one solute can be used to create a desired gradient of a second solute.
Dynamic studies of catalyst poisoning: Effect on adsorption and surface reaction rates for hydrogenation of α‐methyl styrene by Pd/Al2O3
Authors: Chen Song‐Ying , McCoy B. J. , Smith J. M.
Published: June 2004

Pulse‐response data for the hydrogenation of α‐methyl styrene were obtained as a function of poisoning of the Pd/Al2O3 catalyst. The reaction is a first‐order, reversible adsorption of hydrogen followed by a first‐order, irreversible surface reaction. The experiments, at 298 to 323 K and atmospheric pressure, were carried out in a three‐phase slurry reactor for which mass transport effects could be accurately accounted.

Independent adsorption equilibrium data in cumene slurries showed that adsorption occurred to the same extent on both poisoned and unpoisoned sites with a heat of adsorption, ΔHc = −16.3 kJ/mol. Converted to styrene as the slurry liquid, ΔHs = −20.9 kJ/mol.

The zero and first moments of the response curves indicated that the rate constant for the surface reaction was independent of the extent of poisoning. The analysis required developing a new theory for interpreting dynamic data where reactant adsorption occurred on both poisoned and unpoisoned sites. The rate constant (per unit mass of catalyst) for adsorption decreased continuously to zero as the extent of poisoning increased.

The results are consistent with the concept that poisoning reduced the number of sites active for reaction, but that the activity per site for the surface reaction was constant. However, the activity per site for adsorption, while constant at poison levels up to 40%, appeared to decrease sharply at higher levels.
Unsteady heat convection over circular cylinders
Authors: Kim B. K. , Vandenbrink D. J. , Cramer M. S. , Telionis D. P.
Published: June 2004

Numerical calculations of the velocity and temperature fields were conducted for unsteady flows over a single circular cylinder and a bundle of cylinders. Periodic disturbances, natural or externally imposed, were considered. Periodic and averaged heat transfer rates were examined. Results compare favorably with experimental data. Calculations were carried out to predict heat transfer rates in regimes of unsteady flows that have not been tested experimentally.
Modeling and analysis of biospecific adsorption in a finite bath
Authors: Arve B. H. , Liapis A. I.
Published: June 2004

A general model is presented and used to predict the dynamic behavior of the adsorption and wash stages of biospecific adsorption (affinity chromatography) in a finite bath. The model accounts for film and diffusional mass transfer resistances as well as for the rates of interaction between adsorbates and ligands. The model is applicable to single and multicomponent biospecific as well as nonspecific adsorption, and the adsorbates may be monovalent or multivalent. The predictions of the model are compared with the experimental data of the adsorption of β‐galactosidase onto immobilized anti‐β‐galactosidase.

The results of biospecific adsorption of bivalent adsorbates indicate that a competition for ligands occurs between molecules forming one‐site interaction and two‐site interaction complexes. This competition can lead to the displacement of the adsorbate from the adsorbate‐ligand complex whose formation is least favored.