bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical model of the boundary condition at a fluid‐porous interface
Authors: Ross S. M.
Published: June 2004

An equation for the volume average fluid velocity in a boundary layer region between a fluid and a porous medium is derived. The result is valid for a general anisotropic porous medium subject to the restrictions imposed by the assumptions made in the analysis. The basic equations of motion for an incompressible Newtonian fluid with negligible inertia are used and a linear map Mij from the volume average velocity 〈v〉 into the point velocity v is assumed to exist. Using scaling arguments, an equation for 〈v〉 is found which reduces to the Darcy equation for a point entirely within the porous medium below the boundary region and to the usual Navier‐Stokes equation for a point entirely within the fluid above the boundary region. The form of the equation contains two of the terms that were originally hypothesized and tested experimentally by Beavers and Joseph (1967). In particular, the following equation is obtained:

where the tensors Kij, Ljmk and Njm are mathematically defined in terms of the map Mij.
Laser doppler measurements of flow in freeboard of a fluidized bed
Authors: Levy Y. , Lockwood F. C.
Published: June 2004

One of the factors which reduces combustion efficiency in a fluidized‐bed combustor is the elutriation of fine coal particles from the freeboard above the bed surface. To our knowledge, data about the real local flow behavior of the two‐phase flow in the freeboard are lacking in the literature. This paper concerns the measurement of the gas and the elutriated particle velocities in the freeboard of a cold fluidized bed using Laser Doppler Anemometry. A special electronic system has been devised to record simultaneously the gas and particle velocities and to indicate the size of the particles. In this paper the apparatus and some preliminary measurements are reported. The most significant observation is that the gas velocity profiles exhibit minima near the bed center and maxima near the walls.
Variable‐volume hollow‐fiber enzyme reactor with pulsatile flow
Authors: Kim In Ho , Chang Ho Nam
Published: June 2004

Hollow‐fiber device has been used to investigate the effect of ultrafiltration swing on the performance of membrane‐enzyme reactor. Experiments with β‐galactosidase and ONPG have shown that bidirectional ultrafiltration induced by pulsatile flow gives rise to an increase in conversion relative to that obtained at steady operation without ultrafiltration swing. This increase apparently comes from the enhanced mass transfer due to ultrafiltration.
Separating efficiency of a water elutriator
Authors: Biddulph M. W.
Published: June 2004

This paper investigates the separating efficiency of a vertical water elutriator operating on particle mixtures. In particular, comparisons are made with a previously developed mathematical model based on an eddy diffusion mechanism of mixing. Standard mixtures of glass spheres, of uniform size and shape, are used to study the equipment characteristics. It is found that the separating efficiency follows the same trend as predicted by the model and that “wall flow” of particles occurs. This affects the required water velocity, resulting in the equipment producing a top product generally purer than the bottom product.
Separation of benzene and toluene from close boiling nonaromatics by extractive distillation
Authors: Berg Lloyd
Published: June 2004

Benzene and toluene are virtually impossible to separate from close boiling nonaromatic hydrocarbons by rectification. Benzene and toluene can be readily separated from similar boiling nonaromatics by using extractive distillation in which the extractive distillation agent is a proper mixture of organic compounds boiling higher than benzene or toluene. A typical extractive distillation agent for benzene is a mixture of phthalic anhydride, maleic anhydride, and adiponitrile; for toluene, phthalic anhydride, maleic anhydride, and glycerol triacetate.
Kinetics of pyrolysis of some fire retardants and treated fabrics
Authors: Gadalla A. M. , Abadir M. F. , Kasem M. Y. , Salem F. T.
Published: June 2004

Intermediate phases and reactions occurring on decomposing diammonium hydrogen phosphate, ammonium para molybdate, sodium tungstate dihydrate and ammonium meta vanadate were established by thermal analysis and X‐ray examination.

These salts promote fabric degradation at low temperatures but are effective at high temperatures. Diammonium hydrogen phosphate produced maximum amount of gases, absorbed the highest amount of heat and gave the highest fire retardation above 350°C.
Selective adsorption of organic homologues onto activated carbon from dilute aqueous solutions: Solvophobic interaction approach: Part IV. Effect of simple structural modifications with aliphatics
Authors: Belfort Georges , Altshuler G. L. , Thallam K. K. , Feerick Jr C. P. , Woodfield K. L.
Published: June 2004

Preferential adsorption of organic compounds onto activated carbon from dilute aqueous solutions is studied to develop a comprehensive theoretical basis for predicting the adsorption of structurally different isomers for different homologous series. The fundamental multidimensional approachof the solvophobic (cϕ) thermodynamic theory is further refined and used to correlate the extent of adsorption for the comprehensive theory with the overall standard net free energy change (ΔGnet/RT) for the association‐adsorption reaction in solution, and for the simplified theory with the cavity surface area of the solute (TSA).

Experimental adsorption isotherms of two homologous series (12 aliphatic alcohols and 21 aliphatic ketones) were measured and used to test and compare the cϕ theory with seven independent parameters characterizing the sorbates. Several experimental innovations for measuring equilibrium adsorption isotherms are introduced to reduce the possible loss of sorbate during the procedure and to provide reproducible and reliable results.

Comparing the coefficients of linear correlation (r), the results for 12 aliphatic alcohols give greater than 99% confidence that the r‐values are different for ΔGnet/RT and molecular weight (MW). For the 15 aliphatic ketones, greater than 90% confidence interval is obtained for different r‐values for TSA and MW.

These results support the contention that simple structural modifications of aliphatic homologous compounds can be used to predict the effect of solute‐solvent‐sorbent interactions on adsorption. The cϕ theory can thus be used to rank‐order adsorption intensity of these compounds from the aqueous phase onto activated carbon.
Experimental and mathematical modeling of three‐dimensional natural convection in an enclosure
Authors: Curlet N. W. E. , Won K. J. , Clomburg L. A. , Sarofim A. F.
Published: June 2004

Three‐dimensional natural convection patterns in an enclosure under conditions simulating flow in glass‐making furnaces have been calculated using an approximate method in which solutions for the temperature and velocity fields in orthogonal two‐dimensional planes are superposed. The computational method was tested by comparison with measurements of the temperatures and velocities in an enclosure heated and cooled from above and with a controlled heat loss from the sides. Good agreement was found between measurements and computations under conditions of interest in glass‐making furnaces, wherein the motion in one of the two orthogonal planes is dominant.
Experimental study of deep bed filtration: A stochastic treatment
Authors: Hsu E. H. , Fan L. T.
Published: June 2004

A stochastic pure birth process, which describes pore blockage in a filtration process, has been coupled with the Carman‐Kozeny equation to simulate the pressure buildup in deep bed filtration. It has been shown that the resultant one parameter model equation fits adequately the experimental data obtained under the straining dominated condition, and that available data obtained under the adhesion dominated condition can also be described by the model.
Kinetics of short contact time coal liquefaction. Part II: Effect of nature of coal and solvent
Authors: Abichandani J. S. , Wieland J. H. , Shah Y. T. , Cronauer D. C.
Published: June 2004

A bituminous coal (Powhatan No. 5) and a subbituminous coal (Belle Ayr) were liquefied in the presence of hydrogen donor solvents. Statistical analyses of the data showed that for contact times up to 10 min, the coal conversion, measured in terms of tetrahydrofuran solubles, was not significantly different for the two coals. However, the subbituminous coal gave more asphaltenes than the bituminous coal.

The hydrogen‐donating capacity of the solvent was varied by the addition of hydrogenated phenanthrene to SRC‐II recycle solvent. The results indicated that there are two routes for the formation of oils from coal. One is by adduct formation giving asphaltenes and preasphaltenes, which in turn gives oils, and the other is direct oil formation from coal. The preferred route depends on the hydrogen‐donating capacity of the solvent. The kinetic model, proposed in Part I of this paper, is extended to account for the change in the donor capacity of the solvent.
Coupled boundary layer transport involving particles
Authors: Shaeiwitz J. A.
Published: June 2004

Particle deposition by diffusiophoresis and thermophoresis is described using the linearized Fickian multicomponent diffusion equations. For these cases, the diagonal component of the diffusivity matrix for the particle is expected to be much smaller than the other diagonal components. Intuitive arguments, dimensional analyses and the standard interfacial transport theories in multicomponent form suggest that the larger boundary layer due to the larger diffusivity component describes the transition between bulk and surface values for both components.
Anomalous convective diffusion in films of polymeric solutions
Authors: Mashelkar R. A.
Published: June 2004

The process of gas absorption in freely falling films of dilute polymer solutions under different kinematic conditions shows some hitherto unreported and dramatic differences. The absorption rates are reduced when films are generated under rapid stretch conditions over axisymmetric bodies of revolution, whereas they are enhanced when films are generated in a long, wetted wall column. Absorption rates are enhanced on polymer addition in freely falling turbulent films. Possible mechanistic explanations have been offered for these phenomena.
Dynamics and control of an activated sludge process as a mixed culture system
Authors: Takamatsu Takeichiro , Shioya Suteaki , Kurome Hirokazu
Published: June 2004

One of the difficulties encountered in the operation of an activated sludge process is the phenomenon of bulking sludge.

In an activated sludge process which is composed of a completely mixed aeration tank and a sedimentation vessel, the dynamic behavior of the system can be analyzed using a mathematical model. The model developed here is based on the kinetics and settleability of the combination of floc‐forming sludge and bulking sludge. The operating conditions that cause the bulking phenomenon are clarified on the phase plane. It is also shown that a type of nonlinear state feedback regulator makes the system stable.
Prediction of the effect of weeping on distillation tray efficiency
Authors: Lockett M. J. , Rahman M. A. , Dhulesia H. A.
Published: June 2004

The reduction in distillation tray efficiency caused by uniform weeping of liquid from the tray has been calculated. Numerical results are presented for all three Lewis cases over the range of variables of interest to tray designers. Analytical equations are given for Lewis' cases 2 and 3 for plug flow of liquid on the tray.
The VIM theory of molecular thermodynamics: Part II: Analytic equation of state of polar fluids
Authors: Alem A. H. , Mansoori G. A.
Published: June 2004

Variational inequality minimization (VIM) theory of statistical mechanics is used to derive analytic equations of state for polar fluids. For the pair‐intermolecular potential energy function in the formulation of this theory, the Lennard‐Jones, dipolar, quarupolar, and dipolar‐quadrupolar interactions are used. For the three‐body potential Axilrod‐Teller function is used. The VIM theory has made it possible to derive algebraically analytic expressions for the thermodynamic functions of polar fluids. Thermodynamic properties of carbon dioxide, methyl chloride, ethane, hexane, iso‐butane, and sulfur dioxide in the liquid and vapor phases are predicted with the use of the VIM equation of state. The results of the predictions are shown to be in very good agreement with the experimental data for majority of the fluids which are studied.
Effect of the interfacial viscosities upon displacement
Authors: Stoodt T. J. , Slattery J. C.
Published: June 2004

A capillary rise technique was developed for measuring the effect of the surface viscosities upon the displacement of air by liquids in glass capillaries. Measurements were made in two tubes with optically measured radii of 37.5 and 48.6 μm.

No surface viscous effects were observed with doubly distilled water or with octane, in good agreement with the Washburn equation. The behavior of a dilute aqueous solution of dodecyl sodium sulfate was easily distinguished from that corresponding to zero surface viscosities. The surface dilatational viscosity was found to be two orders of magnitude greater than the surface shear viscosity. Previous qualitative (Slattery, 1974, 1979) and quantitative (Giordano and Slattery, 1983) theories for the effect of the interfacial viscosities upon displacement are fully supported by this experimental study.
Noncatalytic coal char gasification
Authors: Lee Sunggyu , Angus J. C. , Edwards R. V. , Gardner N. C.
Published: June 2004

A simple particle model is used to interpret differential thermogravimetric data taken on the gasification of coal/char with CO2, H2 and H2O. The model takes into account the major physical factors which influence the gasification rate, viz., the changing magnitudes of surface area, porosity, activation energy and effective diffusivity during gasification. Specific reaction rate constants based on surface area and activation energies are extracted from the data. Practical criteria for regimes of reaction rate and diffusion control and for particle isothermality are developed. For isothermal particles at low classical Thiele moduli, the data can be correlated with only one parameter, which has a simple physical interpretation.
A new two‐impinging‐streams heterogeneous reactor
Authors: Luzzatto Kfir , Tamir Abraham , Elperin Isaak
Published: June 2004

The characteristics of a new heterogeneous reactor of the “two impinging streams” type, suitable for gas‐solid heat and mass‐transfer operations, were investigated.

The operating limits of the reactor, with respect to gas and solid particles mass flow rate and pressure drop, were determined; scale‐up criteria with respect to the hydrodynamics of the reactor were also established. It has been found that, under certain conditions, the introduction of solid particles into the gas stream lowers the pressure drop on the reactor. In addition, the maximal pumping energy per kg of solids transported through the reactor by the air is much lower than in a fluidized‐bed‐type reactor.

A stochastic model based on Markov processes was developed which closely describes the behavior of the solid particles in the reactor. A technique based on this model was employed for determining the residence time distribution of the particles in the reactor.
Estimation of parameters where dependent observations are related by equality constraints
Authors: Solomon B. O. , Oner M. D. , Erickson L. E. , Yang S. S.
Published: June 2004

Pirt's model for microbial growth and product formation are reparameterized to obtain multiresponse models with common parameters. The dependent variables in the models are related through the available electron and carbon balance constraints. Covariance adjustment is used to reduce the growth model to a unit variate linear model with covariates. Therefore, standard multiple regression programs can be used to obtain combined point and interval estimates of true biomass energetic yield, true product yield and maintenance coefficient. This approach may yield “better” estimates than the maximum likelihood approach when an appropriately selected subset of covariates is used. Nonlinear estimation procedures are also considered; these procedures are efficient with few responses; however, as the number of responses per observation increase, they may require a lot of computing time. For illustration several data from the biochemical engineering literature are analyzed by the proposed methods.
Mass transfer in AC electrolysis part II: Experimental study on sinusoidal current
Authors: Cheng C. Y. , Chin D‐T.
Published: June 2004

An experimental study has been made for laminar mass transfer to a rotating disk and a rotating hemispherical electrode when sinusoidal alternating current (AC) together with direct current (DC) are flowing across the electrode/electrolyte interface. A resistor‐capacitor circuit was used to measure the phase shift between the applied AC and the resulting periodical concentration overpotential. The limiting AC current density corresponding to a zero instantaneous surface concentration was determined as a function of AC frequency and DC current density. The experimental data agreed with the theoretical calculations in a regime of a dimensionless AC frequency K = (ω/Ω)Sc1/3 greater than 1 and less than 200.
Gas entry effects in fluidized bed reactors
Authors: Yates J. G. , Rowe P. N. , Cheesman D. J.
Published: June 2004

Experimental results from an X‐ray study of gas bubbles entering a fluidized bed of two differently sized powders are presented and their significance for chemical reactions taking place in the distributor region of a fluidized bed reactor are examined using a simple two‐phase model.
Distribution of bubble properties in a gas‐liquid‐solid fluidized bed
Authors: Matsuura Akinori , Fan Liang‐Shih
Published: June 2004

The behavior of bubbles in a cocurrent gas‐liquid‐solid fluidized bed was investigated in a column of 76.2 mm ID in this study. The particles used were glass beads of 3 and 6 mm and a binary mixture of these particles. A novel dual electrical resistivity probe system was developed and utilized to obtain bubble properties including bubble size and rise velocity. The distributions of the bubble properties in the gas‐liquid‐solid fluidized bed were evaluated for three flow regimes: the dispersed bubble flow regime; the coalesced bubble flow regime; and the slug flow regime.
Theory and operational characteristics of the magnetic valve for solids Part II: Collar design
Authors: Zhang Guo‐Tai , Jaraiz‐M. Eladio , Wang Yang , Levenspiel Octave
Published: June 2004

This paper reports on the operating characteristics of the collar type MVS which uses either orifice plates or screens as supports for the solids.

The optimum placement for the support (screens or orifice plates), the current needed to operate the valve as a function of vessel size (up to 0.55 m) and screen or orifice opening, and the response characteristics of the valve were all determined. These findings were then compared with theory.

Finally, the operational characteristics of the MVS (magnetic valve for solids) when handling a mixture of magnetic and nonmagnetic solids were briefly examined.
Correlation of critical properties and acentric factor of hydrocarbons and derivatives
Authors: Lin Ho‐Mu , Chao Kwang‐Chu
Published: June 2004

The critical constants and acentric factor are generally required in thermodynamic calculations based on the principle of corresponding states. In this work, these properties of hydrocarbons and derivatives are correlated with the molecular weight, specific gravity, and normal boiling point. Properties of n‐alkanes are correlated with the molecular weight. Properties of other hydrocarbons and derivatives are expressed as perturbations from those of the n‐alkanes, and the perturbations are corrlated in terms of specific gravity and normal boiling point.
Growth rate dispersion in MSMPR crystallizers
Authors: Larson M. A. , White E. T. , Ramanarayanan K. A. , Berglund K. A.
Published: June 2004

A model is presented which relates the crystal size distribution (CSD) from a mixed–suspension, mixed‐product‐removal (MSMPR) crystallizer to the distribution of growth rates. This model is based on the assumption that individual contact nuclei have some inherent growth rate which remains constant, but the growth rate may vary from crystal to crystal. The crystal size distribution can be calculated from prior knowledge of the growth rate distribution. Even a limited knowledge of only the coefficient of variation and the mean growth rate permits an approximation of the expected crystal size distribution. Conversely, estimates of the mean and variance of the growth rate distribution can be determined from the moments of the CSD from an MSMPR crystallizer.
Separation of helium‐methane mixtures by pressure swing adsorption
Authors: Cheng H. C. , Hill F. B.
Published: June 2004

The separation of mixtures of helium and methane using a single column of activated carbon in a pressure swing adsorption process was studied experimentally. Process performace was predicted with an average error of 10% or less by a local‐equilibrium well‐stirred cell model in which dead volumes at the feed and product ends of the column were accounted for. Systematic differences between experiment and model were ascribed to omission from the model of flow resistance and heat release.
Taylor‐aris dispersion arising from flow in a sinusoidal tube
Authors: Hoagland D. A. , Prud'Homme R. K.
Published: June 2004

An analysis of dispersion arising from creeping flow through a periodically constricted tube is developed with the goal of evaluating the effect of converging and diverging pore structure on dispersion in porous media. The theory is based on rigorous long‐time solutions of the convective‐diffusion equation. The calculations are done numerically over a range of Peclet numbers and tube geometries; for the geometrical parameters which correlate permeability data in packed beds, the results of the present work agree well with literature data for dispersion in such beds.
A generalized model for predicting equilibrium conditions for gas hydrates
Authors: John V. T. , Papadopoulos K. D. , Holder G. D.
Published: June 2004

A modification of van der Waals and Platteeuw's (1959) hydrate equilibrium model which incorporates the effect of spherical asymmetry is developed. A corresponding states correlation is used to predict the deviation of Langmuir constants from ideal values. In this model the Kihara parameters obtained from hydrate equilibrium data agree well with those obtained from virial coefficient data.
Surfactant chromatographic movement: An experimental study
Authors: Harwell J. H. , Schechter R. S. , Wade W. H.
Published: June 2004

Previous papers (Trogus et al., 1979a; Harwell et al., 1982) have developed a theory of surfactant chromatographic movement on the assumption that micelles may be treated as a separate thermodynamic phase in predicting surfactant adsorption. The work examined here demonstrates that, even with incorporation of the complex surface interactions between surfactant molecules that are present in real systems, conclusions and observations made in the previous studies hold true. Additionally, theoretical predictions are compared to experimental results to demonstrate that for the system studied the phase separation model of micelle formation (Shinoda, 1963) and the plateau adsorption model (Trogus et al., 1979a) are powerful and useful simplifications for predicting surfactant chromatographic behavior.
A nonequilibrium stage model of multicomponent separation processes. Part II: Comparison with experiment
Authors: Krishnamurthy R. , Taylor R.
Published: June 2004

A nonequilibrium stage model of countercurrent separation processes is used to predict composition and temperature profiles during binary and multicomponent distillation in wetted‐wall and bubble‐cap‐tray columns. The profiles predicted by the model are compared with experimental data for the binary systems benzene‐toluene, ethanol‐water, and acetone‐chloroform and for the ternary systems benzene‐toluene‐ethylbenzene, acetone‐methanol‐water, methanol‐isopropanol‐water, acetone‐methanol‐ethanol, and benzene‐toluene‐m‐xylene. The model does a very commendable job of predicting the composition profiles measured for these systems; average absolute differences between predicted and measured mole fractions are seldom greater than 4 mole percent and are often very much less.
The unusual behavior of extractive distillation—Reversing the volatility of the acetone–isopropyl ether system
Authors: Berg Lloyd , Yeh An‐I
Published: June 2004

Extractive distillation can not only negate azeotropes to produce pure compounds by rectification but in some cases will reverse the volatility and bring out the less volatile component before the more volatile component. As an example, isopropyl ether, b.p. = 68.5°C, was distilled off as the overhead from mixtures with acetone, b.p. = 56.2°C, leaving the acetone in the stillpot and column until all the isopropyl ether was removed. This reversal phenomenon does not occur in the isopropyl ether‐methyl ethyl ketone system, although the azeotrope is negated.
Longitudinal and lateral thermal dispersion in packed beds. Part I: Theory
Authors: Levec J. , Carbonell R. G.
Published: June 2004

A new model is developed for the transient thermal response of a packed bed, using the method of spatial averaging. Equations for the average temperature of the fluid and the solid phase are derived from the point equations for thermal energy in each phase. The new model exhibits some unusual convective and dispersive coupling between the equations for the average fluid and solid temperatures. The response of the model equations to a pulse disturbance is analyzed. It is found that after a sufficiently long time has elapsed, the temperature pulses for the fluid and solid phases will be separated by a constant distance and will spread or disperse about their centroids at an equal rate. The pulse separation predicted by the new model equations is larger than that predicted using more conventional analyses of heat transfer in packed beds. Effective thermal conductivities measured under steady state conditions can differ significantly from those observed in transient experiments due to the spread in temperature pulses caused by heat exchange between phases. Estimates are made of the magnitude of the more important terms affecting longitudinal and lateral effective thermal conductivities under flow conditions, in order to make possible a direct comparison between theory and experiment in a companion paper.
Prediction of steady state dispersion height from batch settling data
Authors: Jeelani S. A. K. , Hartland Stanley
Published: June 2004

In order to design continuous industrial settlers, it has in the past been necessary to obtain extensive pilot plant data, the interpretation of which required considerable experience before it could be used for scale‐up purposes. The idea of using batch settling tests has always seemed attractive, but the difficulty of reconciling unsteady‐ and steady‐state experiments has so far proved physically and mathematically insurmountable.

In this study the variation in steady state height with dispersion throughput in a continuous settler is predicted from unsteady state data obtained in a small‐scale batch settler. Models are presented which relate the drop sedimentation and coalescence in batch and continuous dispersions, thus enabling the steady state settler behavior to be predicted from parameters obtained from the batch data. These models are verified with available experimental data and should greatly simplify the future design and scale‐up of continuous settlers.
Development of a catalytic two‐stage combustion system
Authors: Sadakata M. , Shigehisa T. , Kunii D.
Published: June 2004

A new NOx‐free combustion system using a new catalyst produced from stainless steel by special treatment was proposed and studied. A series of experiments verified that this new system could produce a high reduction rate of NO under the hostile flue gas conditions of a practical combustion process.
Hydrodynamics and mass transfer characteristics of a scheibel extractor. Part I: Drop size distribution, holdup, and flooding
Authors: Bonnet J. C. , Jeffreys G. V.
Published: June 2004

The hydrodrynamic behavior of a 1.0 × 10−1 m dia. Scheibel column packed with a material preferentially wetted by the dispersed phase has been investigated with and without mass transfer. Drop size and size distribution and dispersed phase holdup were measured as a function of flow rates, agitator speed, packing pad height, and mass transfer direction in a 24 factorial design. Flooding rates were measured and found to be dependent on the impeller position.
Activity coefficients for binary and multicomponent liquid mixtures from unary property model for Wilson parameters
Authors: Ash S. N. , Ray P. , Dutta B. K.
Published: June 2004

A model has been developed for prediction of Wilson parameters from single component properties. Activity coefficients and VLE data for miscible binary or multicomponent systems can be calculated from the standard form of the Wilson equation using these properties. The major advantage of this model is that experimental determinations of binary data are not required. Relevant properties for a fairly large number of chemical species have been provided. This method has been compared with UNIFAC, which is generally used for prediction of activity coefficients and has been found to give comparable results with considerably less computational effort.
Solids mixing in an expanded top fluid bed
Authors: Avidan Amos , Yerushalmi Joseph
Published: June 2004

This study investigated solids mixing of a group A fine powder in a 0.15 m ID expanded top fluid bed with a ferromagnetic tracer. The superficial gas velocity was raised from 0.075 to 1.1 m/s, causing the bed to go through bubbling, slugging, and turbulent fluidization regimes. A countercurrent flow model described the data well at low gas velocities. The bed assumed a more homogeneous appearance at higher gas velocities; a one‐dimensional axial dispersion model was used to correlate the data. Axial dispersion coefficients increased with gas velocity. The data agree well with literature data for low gas velocities.
Heat and mass transfer in water‐laden sandstone: Microwave heating
Authors: Wei Chen Kou , Davis H. T. , Davis E. A. , Gordon Joan
Published: June 2004

Our previous theoretical model was extended to predict the heat and mass transfer phenomena in microwave‐heated porous materials. A water‐filled sandstone was heated in microwaves and its drying rates and temperature profiles were measured. Predictions agree well with observations. Besides moisture loss rates and temperature profiles, the model also predicts local moisture content, gas densities, and pressure. These latter quantities were not measured in our work, but are of interest since they reveal the basic mechanisms of heat and mass transfer in internally heated porous media.
Mathematical modeling of catalytic converter lightoff. Part II: Model verification by engine‐dynamometer experiments
Authors: Oh S. H. , Cavendish J. C.
Published: June 2004

A transient mathematical model has been developed which describes the behavior of packed‐bed catalytic converters during warmup. Model predictions agree very well with the results of engine‐dynamometer experiments for three Pt‐alumina catalysts of widely different properties, thus demonstrating the validity of the model.
Mathematical modeling of catalytic converter lightoff. Part III: Prediction of vehicle exhaust emissions and parametric analysis
Authors: Oh S. H. , Cavendish J. C.
Published: June 2004

The converter warmup model developed previously (Oh and Cavendish, 1985) has been used to simulate the performance of a packed‐bed converter during the cold‐start portion of vehicle emissions tests. Despite the highly transient converter inlet conditions, the model successfully predicts tailpipe mass emissions as a function of time.
Porosity effects on catalytic char oxidation. Part II: Experimental results
Authors: Su J. L. , Perlmutter D. D.
Published: June 2004

Oxidation rates of Na2CO3‐ and K2CO3‐impregnated char samples were measured in an isothermal kinetic control regime. The results were analyzed by a previously developed model to extract the intrinsic catalytic reactivities, freed from superimposed noncatalytic and structural effects. Although the overall catalyzed rates are only several times greater than their uncatalyzed counterparts, the intrinsic catalytic rates were found to be four orders of magnitude greater. The results further indicate that the function of the catalyst is to increase the number of active sites without affecting the activation energy. The overall reaction kinetics are demonstrated to contain the combined contributions of both catalytic and noncatalytic reactions, and in this context the effects of multiple catalysts as well as of the pore structure development during reaction can be understood and interpreted.
Adsorption of gaseous hydrocarbons on activated carbon: Characteristic kinetic curve
Authors: Costa E. , Calleja G. , Domingo F.
Published: June 2004

The internal diffusion coefficients, Di, of pure methane, ethane and ethylene as well as some of their binary and ternary mixtures, have been calculated at 20°C for solid particles of a commercial activated carbon. It has been observed that the contribution of the surface migration mechanism to the global mass transfer process inside the adsorbent particles can be as much as 70–80%. Values for the surface migration coefficient Ds have also been calculated from the relation Di = Dg + KDs, where K is a dimensionless mean slope factor. Values found for both coefficients are of the same order of magnitude as those reported in the literature for similar systems.

All the values for the internal diffusion coefficients of these pure components and their mixtures fit into a single correlation curve, the characteristic kinetic curve of the adsorbent.
On dense phase voidage and bubble size in high pressure fluidized beds of fine powders
Authors: Weimer A. W. , Quarderer G. J.
Published: June 2004

Dense phase voidage, εD, dense phase superficial gas velocity, uDo, and absolute bubble rise velocity, uB, were measured at pressures up to 8300 kPa in a pilot‐scale, fluidized bed of Group A and boundary Group A/B powders. The mean equivalent bubble diameter, db, near the top of the bed was inferred from uB, and known bed operating conditions. Increased pressure at fixed superficial gas velocity, uo, increased εD and uDo and decreased db for Group A powders. The marked decrease in inferred maximum bubble size, d with increased pressure could not be explained by a decrease in gas contributing to bubble flow, uBo, but rather appeared to be the result of a bubble instability phenomenon limiting bubble growth.
Determination of mass transfer coefficients for bubble‐free devolatilization of polymeric solutions in twin‐screw extruders
Authors: Collins G. P. , Denson C. D. , Astarita G.
Published: June 2004

Theoretical and experimental studies have been conducted on the mass transfer rates which occur during the continuous devolatilization of bubble‐free polymeric solutions in a corotating twin‐screw extruder. Experimental measurements of the mass transfer rates, when reported in terms of the product of the individual liquid phase mass transfer coefficient and the surface area for mass transfer per unit volume of empty extruder, were found to correlate well with screw speed in accordance with the predictions of a model based on penetration theory. It is shown, however, that significant differences exist between the measured and predicted values for the rates of mass transfer, which leads to the conclusion that the surface area for mass transfer is substantially smaller than the value computed on the basis that continuous films are formed on the surfaces of the screws and the barrel wall.
Nonisothermal gas absorption with chemical reaction
Authors: Asai Satoru , Potter O. E. , Hikita Haruo
Published: June 2004

The temperature rise at a gas‐liquid interface due to heat evolution and the relevant enhancement factor for gas absorption rate are analyzed for absorption, with an instantaneous irreversible reaction and with a first‐order irreversible reaction allowing for the temperature dependence of the major physicochemical properties. The analysis reveals that, unlike isothermal absorption, the film theory solutions with the replacement of any system parameters do not give a reasonable approximation to the realistic penetration theory solution, except in the case of the physical absorption regime. However, the modified Danckwerts analysis, in which the physicochemical properties are evaluated at the time‐averaged interface temperature, is shown to be useful in obtaining the approximate penetration theory solutions with satisfactory accuracy.
Kinetics of CO oxidation over Co3O4/γ‐Al2O3. Part II: Reactor dynamics
Authors: Perti Deepak , Kabel R. L.
Published: June 2004

The transient responses of a fixed‐bed reactor to step increases and decreases in CO, O2, and/or CO2 feed concentrations were measured and interpreted. It is shown that dynamic methods yield vastly more phenomenological and mechanistic information than steady state measurements, with significantly less experimental effort.
Short‐lived sites in nucleate boiling
Authors: Myers J. E.
Published: June 2004

An hypothesis is proposed to explain the origin of short‐lived sites observed in nucleate pool boiling. Conditions are postulated under which microbubbles might circulate into the superheated liquid region and serve as the source of these nucleation sites. Consequences of this possible mechanism are examined for explanations of hysteresis effects and scatter of results in boiling research.
Wave formation on a vertical falling liquid film
Authors: Alekseenko S. V. , Nakoryakov V. Ye. , Pokusaev B. G.
Published: June 2004

The method of integral relations is used to derive a nonlinear two‐wave equation for long waves on the surface of vertical falling liquid films. This equation is valid within a range of moderate Reynolds numbers and and be reduced in some cases to other well‐known equations.

The theoretical results for the fastest growing waves are compared with the experimental results concerning velocities, wave numbers, and growth rates of the waves in the inception region. The validity of the theoretical assumptions is also confirmed by direct measurements of instantaneous velocity profiles in a wave liquid film.

The results of the experimental investigation concerning nonlinear stationary waves and the evolution of initial solitary disturbances are presented.
An MILP formulation for heat‐integrated distillation sequence synthesis
Authors: Andrecovich M. J. , Westerberg A. W.
Published: June 2004

In this paper the problem of distillation sequence synthesis with heat integration is formulated and solved as a mixed integer linear superstructure optimization problem. Allowing both conventional and multieffect distillation, two alternatives for generating a superstructure are shown, then a formulation is presented which approximates the synthesis problem as a mixed integer linear programming (MILP) problem. Examples illustrate the method. Reported computer times suggest that earlier algorithmic methods for discovering the better sequences among those allowed by the problem formulation, and without the option of multieffecting, are an order of magnitude slower than this approach.
Utility bounds for nonconstant QΔT for heat‐integrated distillation sequence synthesis
Authors: Westerberg A. W. , Andrecovich M. J.
Published: June 2004

In earlier work the authors presented a simple method to synthesize heat‐integrated distillation sequences through the use of simple sketches on a diagram displaying temperature vs. enthalpy. Embedded in that work is the useful but in‐correct assumption that the reboiler/condenser heat loads and the temperature‐difference across the column are independent of the temperature (pressure) level at which the column is operated. This assumption of constancy is removed here, and it is shown how to calculate the minimum utility target using a small linear programming formulation. It is also shown how to use the results of this calculation to synthesize distillation sequences that approach the bound discovered. For the example problems solved, the minimum utility target calculated increases about 25 to 60% over that calculated assuming constant QΔT. The sequences synthesized based on this improved target are virtually the same as the constant QΔT method produces, suggesting that the earlier method is indeed a useful approach.
Finite amplitude waves in stratified two‐phase flow: Transition to slug flow
Authors: Ahmed Rafi , Banerjee Sanjoy
Published: June 2004

In horizontal two‐phase flow, transition from stratified to slug flow occurs due to the nonlinear instability of finite amplitude interfacial waves. The nonlinear equations describing interfacial waves in stratified two‐phase flow are solved by a multiple scales perturbation method. Instability criteria and amplification factors are determined. The phase velocities that are calculated to lead to amplification of finite amplitude interfacial waves are well below those based on linear stability criteria. This is in agreement with existing experimental data on transition from stratified to slug flow in horizontal channels.
Effects of intraparticle heat and mass transfer during devolatilization of a single coal particle
Authors: Bliek Alfred , Van Poelje W. M. , Van Swaaij W. P. M. , Van Beckum F. P. H.
Published: June 2004

The objective of the present work is to elucidate the influence of intraparticle mass and heat transfer phenomena on the overall rate and product yields during devolatilization of a single coal particle in an inert atmosphere. To this end a mathematical model has been formulated which covers transient devolatilization kinetics and intraparticle mass and heat transport. Secondary deposition reactions of tarry volatiles also are included. These specific features of the model allow a quantitative assessment to be made of the impact of major process conditions such as the coal particle size, the ambient pressure and the heating rate on the tar, gas and total volatile yield during devolatilization. Model predictions are compared to a limited number of experimental results, both from the present work and from various literature sources.
Gas separation by pressure swing adsorption: A pore‐diffusion model for bulk separation
Authors: Yang R. T. , Doong S. J.
Published: June 2004

An experimental and theoretical study is performed for bulk separation of gas mixture by pressure swing adsorption, a process widely used commercially for gas purification. By cycling the pressure of a bed of activated carbon between 3 and up to 500 psig (0.021 to 3.445 MPa), at the ambient temperature, a 50/50 H2/CH4 mixture is separated into two products with well over 90% purity and recovery at high throughputs. All process characteristics can be predicted by a pore‐diffusion model. A fundamental understanding of the function of each step in the cyclic process is given.
Diffusion of benzene, toluene, naphthalene, and phenanthrene in supercritical dense 2,3‐dimethylbutane
Authors: Sun C. K. J. , Chen S. H.
Published: June 2004

The conditions under which the Taylor‐Aris dispersion phenomenon can be employed to generate accurate tracer diffusion data in supercritical dense fluids are established. The technique is used to determine the diffusivities of benzene, toluene, naphthalene, and phenanthrene in supercritical dense 2,3‐dimethylbutane as a function of temperature and pressure. A molecular theory incorporating the Sung‐Stell formulation of molecular dynamic correlations in smooth‐hardsphere fluids and the Baleiko‐Davis molecular roughness for polyatomics with the Enskog‐Thorne dense gas diffusivity relationship is found to represent our experimental data to within ±4%. The values of the effective hard‐sphere diameters involved in the present theory can be predicted fairly accurately from the critical volumes of the solutes and solvent considered here.
Pressure swing adsorption. Part II: Experimental study of a nonlinear trace component isothermal system
Authors: Hassan M. M. , Raghavan N. S. , Ruthven D. M. , Boniface H. A.
Published: June 2004

The recently developed mathematical model for simulation of a PSA system (Raghavan et al., 1985) has been extended to a nonlinear Langmuir equilibrium system. The pressure swing adsorption separation of a small concentration of ethylene from helium has been studied experimentally on 4A and 5A molecular sieves. In the 4A system mass transfer is controlled by intracrystalline diffusion and is slow, whereas in the 5A system mass transfer is very much faster and is controlled by macropore diffusion. With rate and equilibrium parameters derived from experimental breakthrough curves, the theoretical model provides a good representation of the experimentally observed behavior of both PSA systems.
Effects of London‐van der Waals forces on the thinning and rupture of a dimpled liquid film as a small drop or bubble approaches a fluid‐fluid interface
Authors: Hahn Phil‐Soo , Chen Jing‐Den , Slattery J. C.
Published: June 2004

When a small drop or bubble approaches a fluid‐fluid interface, a thin liquid film forms between them and begins to drain. As the thickness of the draining film become sufficiently small [about 1,000 Å (100 nm)], the effects of the London‐van der Waals forces and of the repulsive force of any electrostatic double layer become important. Lin and Slattery (1982b) developed a hydrodynamic theory for the first portion of the coalescence process: the drainage of the thin liquid film while it is sufficiently thick that the effects of London‐van der Waals forces and of electrostatic forces can be ignored. Here the effect of the London‐van der Waals forces are included. Given only the drop radius and the required physical properties, the configuration of the film as a function of time is predicted. For the case of a negative disjoining pressure, it is possible to estimate an upper bound for the coalescence time or the time during which a small drop or bubble appears to rest at a phase interface before it coalesces under the influence of London‐van der Waals forces.
Effect of air shear on gas absorption by a liquid film
Authors: McCready M. J. , Hanratty T. J.
Published: June 2004

Rates of oxygen absorption from turbulent air by a concurrently flowing liquid film were measured in an enclosed 2.54 cm × 30.5 cm rectangular channel. The effect of liquid viscosity is varied by using water and a water‐glycerine solution. The results are interpreted by arguing that flow fluctuations in the liquid that control mass transfer are associated with waves of small wavelength at the interface.
Aerosol reactor theory: Stability and dynamics of a continuous stirred tank aerosol reactor
Authors: Pratsinis S. E. , Friedlander S. K. , Pearlstein A. J.
Published: June 2004

The stability characteristics of an aerosol reactor in a continuous stirred tank configuration have been investigated theoretically. Three dimensionless parameters, the surface tension group ∑, reaction rate group R, and residence time group θc, suffice to determine the dynamic behavior of this system. The stability of the unique steady state was investigated using linear analysis. Numerical integration of the full nonlinear equations shows that the dynamic behavior was in accord with the predictions of the linear stability theory. The system exhibits limit‐cycle behavior in the unstable part of the parameter space. In the unstable region, a simple linear relation was found between the period of the numerically computed solutions and the bifurcation parameter, θc. The results of this study are in qualitative agreement with the experimental results of Badger and Dryden (1939).