bluuebunny/crossref_metadata_2025 huggingface dataset:
Flows of nonlinear fluids through porous media
Authors: Sheffield Robert E. , Metzner Arthur B.
Published: June 2004

The conventional “cylindrical tube” model of porous media is shown to be inapplicable to flows of nonlinear fluids. A more precise geometric description of the converging‐diverging pore geometry appears to enable accurate pressure drop‐flow rate descriptions but requires further development.
On the extension of the model of matrix acid stimulation to different sandstones
Authors: Fogler H. S. , McCune C. C.
Published: June 2004

A model was developed for the acidization of various sandstone cores which successfully describes the flow and reaction in the porous media during acidization. A comparison of the experimental results of various investigators shows excellent agreement with the results predicted by the authors with the model.
The modeling of hematite reduction with hydrogen plus carbon monoxide mixtures: Part I. The behavior of single pellets
Authors: Tsay Q. T. , Ray W. H. , Szekely Julian
Published: June 2004

On the assumption of shrinking core behavior, a mathematical model was developed for representing the reduction of hematite disks with a mixture of hydrogen and carbon monoxide. In the model, experimentally measured values were used for the porosity, and the effective pore diffusivities were calculated from pseudo binary formulas. Literature data were used for the activation energies of the reactions, while the preexponential factors were obtained by data fitting. The model was found to provide a good means for representing experimental measurements of Szekely and El‐Tawil (1976), both with regards to the effect of temperature and gas composition.
Studies in chemical process design and synthesis: III. A Simple and practical approach to the optimal synthesis of heat exchanger networks
Authors: Nishida N. , Liu Y. A. , Lapidus Leon
Published: June 2004

An algorithmic‐evolutionary approach to the systematic synthesis of minimum cost networks of exchangers, heaters, and coolers is proposed. The new approach is easy to apply by hand calculations, requiring no special mathematical background and computational skill from the user. In addition to generating many cheaper networks for sample problems ranging in size from 4 to 10 streams as compared to previous studies, the proposed method provides an explicit theoretical guidance on the optimal exchange among hot and cold streams and on the optimal locations of heating and cooling utilities in the network. It also has a provision for the use of stream splitting and for generating a cyclic network. The new method is particularly effective in the synthesis of minimum cost networks for industrial crude unit preheat recovery.
Methanol, past, present, and speculation on the future
Authors: Stiles Alvin B.
Published: June 2004

Methanol is overviewed from the standpoint of history: how the history relates to the present and how it could relate to the future. The overview includes ingredients (fuels, catalysts, etc.), synthesis gas generating procedures, processing techniques, and equipment and other considerations for the present and the near and more distant term future.
Statistical analysis of material balance of a chemical reactor
Authors: Madron Frantisěk , Veverka Vladimir , Vaněček Vojtěch
Published: June 2004

A method is suggested for a complex statistical treatment of the material balance of a chemical reactor, based on the stoichiometric characteristics of reactions taking place in the reactor. Statistically adjusted values of the balance variables are obtained, and the hypothesis that the material balance data do not contain gross errors is tested. The calculation procedure is demonstrated by an illustrative example of the material balance of a fermentation process.
Distillation with secondary reflux and vaporization: A comparative evaluation
Authors: Mah R. S. H. , Nicholas J. J. , Wodnik R. B.
Published: June 2004

A novel distillation scheme which makes use of secondary reflux and vaporization to enhance thermal efficiency is presented. Low operating temperatures, close boiling mixture, and tight product specifications appear to favor this scheme over the conventional distillation. Computer simulation indicates a potential utility reduction of 50 to 75%.
Pyrite oxidation in aqueous ferric chloride
Authors: King W. E. , Perlmutter D. D.
Published: June 2004

The rate of pyrite oxidation in aqueous ferric chloride was determined for two distinct solid particle systems: industrial grade pyrite and coal particles containing pyrite. The oxidation rate for the pyrite particle system was found to increase significantly with increasing temperature (40° to 100°C), ferric chloride concentration (0.1 and 1.0 M), and pyrite loading (2 to 20 g/l); the rate decreased with increasing particle size (−325 to 140 mesh). Agitation did not have a significant effect, and a kinetic model was developed and fit to the experimental data.

For the coal particle system used in this study, the most important variable was particle size. The oxidation rate of pyrite in coal smaller than 325 mesh was much greater than in larger coal particles. The effect of temperature (80° to 100°C) on the oxidation of pyrite in coal was not significant, nor was the effect of pretreatment with 0.1N hydrochloric acid. Approximately half of the detected ferric iron reduction was attributable to pyrite oxidation; the balance arises from other coal reactions.
Experimental study of eddy diffusion model for heated turbulent free jets
Authors: Kataoka Kunio , Takami Tohru
Published: June 2004

Prandtl's eddy diffusion model was successfully extended to turbulent momentum, energy, and mass transfer in nonisothermal free jets by taking into account the effect of change in volume of traveling eddies. The present model was experimentally confirmed for the high temperature, low velocity, turbulent free jets produced by combustion of methane gas.
Evaluation of parameters for nonlinear thermodynamic models
Authors: Anderson T. F. , Abrams D. S. , Grens E. A.
Published: June 2004

A method based on the maximum likelihood principle has been developed for the determination of model parameters from experimental data when all the measured variables are subject to error. In addition to the best estimates of the parameters, this method also yields information useful in selection of appropriate models and evaluation of the accuracy of the data. Application of the method is illustrated in the reduction of binary vapor‐liquid equilibrium data.
Adsorption rate on molecular sieving carbon by chromatography
Authors: Chihara Kazuyuki , Suzuki Motoyuki , Kawazoe Kunitaro
Published: June 2004

Diffusivities in the micropore and adsorption equilibrium constants were determined for neon, argon, krypton, xenon, nitrogen, methane, ethylene, ethane, propylene, propane, n‐butane, and benzene on molecular sieving carbon by chromatographic measurement and moment analysis. Isosteric heat of adsorption was found to be 2.6 times heat of vaporization for the gases examined here. Two separate linear relations were obtained between activation energies of diffusion in micropore and isosteric heats of adsorption for rare gases, methane, and benzene, and for n‐paraffin and n‐olefin except methane.
The mixing of solids in slugging gas fluidized beds
Authors: Thiel William J. , Potter Owen E.
Published: June 2004

Measurements have been made of axial solids mixing in fluidized beds of 0.05, 0.1, and 0.22 m diameter with a variety of materials at atmospheric pressure. Round nosed slugs, raining slugs, and turbulent bubbling have been investigated. Raining slugs occur with coarser materials. With cracking catalyst round nosed slugs form readily in the smaller diameter beds, but in the largest bed, breakdown to the turbulent state was normal. A model has been developed to predict the axial solids mixing in a slugging fluidized bed containing round nosed slugs. The model supposes that each slug is followed by a well‐mixed wake and a piston flow region. The model predicts well the scale effect noted by W. G. May. Axial mixing is fast for round nosed slugs, falls for turbulent bubbling, and is low for raining slugs.
Convective mass transfer in the presence of polarizing fields: Dispersion in hollow fiber electropolarization chromatography
Authors: Reis Joaquim F. G. , Ramkrishna Doraiswamy , Lightfoot Edwin N.
Published: June 2004

An effective means is developed for describing two‐dimensional convective dispersion in the presence of polarizing fields. Explicit results are given for planar fields applied across Poiseuille flows, and these are used to characterize hollow fiber electropolarization chromatography (EPC).
Influence of polymer additives on the gas‐liquid mass transfer in stirred tanks
Authors: Ranade V. R. , Ulbrecht J. J.
Published: June 2004

The influence of polymer additives upon the gas‐liquid mass transfer in stirred tanks is examined. While the addition of sodium carboxymethyl‐cellulose brings about a reduction of the overall liquid side mass transport coefficient which is in line with the predictions by earlier works, the reduction ofkLain polyacrylamide solutions of equal viscosity is much stronger. This is explained by the viscoelasticity of the PAA solutions, and an empirical correlation is proposed.
Selective copper recovery with two types of liquid membranes
Authors: Lee Kyung‐Hee , Evans D. F. , Cussler E. L.
Published: June 2004

Copper can be selectively separated and concentrated by diffusion across liquid membranes. These membranes are effective either as thin films supported by porous polymer sheets or as liquid microcapsules or liquid surfactant membranes.
Relaxation oscillations in chemical reactors
Authors: Gilles E. D. , Eigenberger Gerhart , Ruppel Wilhelm
Published: June 2004

This paper deals with a particular type of limit cycle in chemical reaction systems, the so‐called relaxation oscillation. This phenomenon can be caused by thermal or kinetically induced instabilities in a loop reactor or a CSTR, but can also occur in a catalytic fixed‐bed reactor for an endothermic reaction with self‐inhibiting or self‐accelerating steps.
Cold flow mixing rates with recirculation for pulverized coal reactors
Authors: Tice Christopher L. , Smoot L. Douglas
Published: June 2004

The mixing of particles and gases in confined, coaxial jets in the presence of recirculation was studied. Particle and gas mixing rates were measured for conditions simulating processes involving pulverized coal combustion and entrained gasification. The effects of mixing chamber diameter, gas velocity, particle size, and particle loading level on mixing rates were determined from particle mass flux and gas tracer measurements. In every case, the gas mixed much faster than did the particles. Introduction of an expanded mixing chamber of larger diameter (with recirculation zone) significantly increased both gas and particle mixing rates over that for a smaller mixing chamber without recirculation. However, this observed increase was not strongly dependent upon the diameter of the larger mixing chamber. Increasing secondary velocity also increased mixing rates significantly.
Magnetically enhanced thermal convection in oxygen gas
Authors: Honeywell W. I. , Vevai J. E.
Published: June 2004

The effects of static magnetic fields on heat transfer in oxygen gas have been measured at temperatures between 78 and 112°K and pressures between 2.01 and 4.77 kN/m2. After the data are corrected for ordinary thermal conductivity behavior, comparison with theory suggests that the phenomenon is magnetically enhanced thermal convection.
Heat transfer in plane Couette flow with additional pressure gradient including entrance effects for a non‐Newtonian fluid
Authors: Mitwally Essam M.
Published: June 2004

Analytical solutions are presented for laminar plane Couette flow of a power law non‐Newtonian fluid. Effects of an additional negative pressure gradient were included in solving for the velocity distribution. The contributions due to the entrance heating region and the viscous dissipation effects were included in arriving at the temperature distribution and also the variation of the local Nusselt number at the stationary plate.
A model for short residence time hydropyrolysis of single coal particles
Authors: Russel William B. , Saville Dudley A. , Greene Marvin I.
Published: June 2004

The chemical reactions and mass transfer processes occurring within a single coal particle during high temperature hydropyrolysis are described mathematically and the model is tested using extant experimental data. A significant feature of the model is the treatment of bulk flow due to the evolution of volatiles and the resulting balance between diffusion, bulk flow, and chemical reaction. Predictions of the variations in conversion due to changes in total pressure, hydrogen partial pressure, and particle size agree quantitatively with experimental data.
Annular two‐phase flow of gases and non‐Newtonian liquids
Authors: Eisenberg Fred G. , Weinberger Charles B.
Published: June 2004

Two‐phase, annular flow of gases and non‐Newtonian liquids through horizontal pipes is modeled, and a prediction method for pressure drop and gas volume fraction is proposed. The prediction method consists of a modification, based upon shear rate dependence of the apparent viscosity of the liquid phase, of Lockhart‐Martinelli correlations for Newtonian liquids. The model applies to the case of laminar flow of the annular liquid film. Experimental data, obtained with several aqueous polymer solutions and air, agree closely with predicted values of pressure drop and void fraction.
Infinite dilution volatilities of polar solutes in hydrocarbons
Authors: Won K. W.
Published: June 2004

Infinite dilution volatility data have been correlated for alcohols, esters, aldehydes, ketones, and sulfur containing hydrocarbon solutes in aliphatic hydrocarbon solvents over a wide temperature range using a temperature dependent energy parameter for the pure solute.

When a polar solute molecule is surrounded entirely by nonpolar molecules, polar molecular interactions such as hydrogen bonding do not play an important role. Therefore, a single, pure solute parameter is sufficient for correlation.

Calculated heats of solution at infinite dilution agree well with published calorimetric data.
Simulation of the dynamic behavior of deep bed filters
Authors: Tien Chi , Turian Raffi M. , Pendse Hemant
Published: June 2004

A simulation procedure for predicting the dynamic behavior of a deep bed filter over the entire practicable range of filter operation is developed. The method is based on synthesizing available quantitative results relating to filtration, and to porous media flows, within an overall framework which views the process to consist of two principal stages dominated by appropriate limiting deposition modes. Evaluation of the results through comparison with available data indicates, to the extent the nature of these types of data permits, that the method is surprisingly effective and even capable of predicting on satisfactorily quantitative basis some intricate details of observed filter behavior.
The simulation of binary adsorption in continuous countercurrent operation and a comparison with other operating modes
Authors: Liapis A. I. , Rippin D. W. T.
Published: June 2004

Simulation studies are presented of three different modes of operating a two‐component adsorption system. The efficiency with which an activated carbon adsorbent is utilized is compared for a single fixed bed, a periodic countercurrent system in which the adsorbent is equally distributed over two, four, and six beds and a continuous countercurrent system. The carbon utilization in the single fixed bed was shown to be one third to one half of that in a continuous countercurrent adsorber of the same length, whereas the periodic countercurrent system achieved a utilization of 79 to 98% of that in the continuous system.

The mathematical models used to describe the three different modes of column operation include the effects of axial diffusion in the columns, mass transfer resistance in the boundary layer surrounding each particle, and fluid diffusion within the porous particles.
Mixing with helical ribbon agitators: Part II. Newtonian Fluids
Authors: Patterson W. Ian , Carreau P. J. , Yap C. Y.
Published: June 2004

Of necessity, the mixing process is sometimes restricted to the laminar regime, although turbulent mixing is generally more desirable. Common examples of laminar mixing are found when the fluid has a very high viscosity, or when one of the mixture components is shear sensitive. It has been pointed out that the helical ribbon agitator (HRA) is admirably suited to the low Reynolds number mixing process. This work derives a model to predict the power consumption of the HRA. The model has been developed with the aid of experimental data and tested extensively using literature data. For a wide range of mixer geometries and sizes, it predicts power consumption with an average deviation of 13%.

The concept of relative efficiency of mixers is also described as an aid to comparing different HRA mixer geometries. Finally, the problem of scale‐up of different HRA configurations is discussed.
Analysis of solid‐solid reactions: A review
Authors: Tamhankar S. S. , Doraiswamy L. K.
Published: June 2004

This paper reviews some important aspects of the analysis of solid‐solid reactions which include: fundamental considerations, experimental techniques, analysis of pellet‐pellet reactions, analysis of mixed powder reactions, role of the gas phase, and reactor design. Illustrations are given wherever necessary. Examples of industrial applications, important systems studied, and the models used are tabulated.
Efficient single‐jet mixing in turbulent tube flow
Authors: Forney L. J. , Kwon T. C.
Published: June 2004

A similarity law is proposed to provide effective jet penetration and mixing of a tracer in turbulent tube flow. The scaling law is derived from approximate solutions to the equations of motion for the case of a single, fully developed turbulent jet issuing normally to the flow. Jet properties are correlated with experimental measurements on a methane tracer.
Hot wire measurement in the interacting two‐plane parallel jets
Authors: Yuu Shinichi , Shimoda Fumio , Jotaki Tomosada
Published: June 2004

This study presents the data of turbulence properties in the two‐plane parallel air jets which merge as they issue into still surroundings. These turbulent properties (time averaged and root mean square velocities, Eulerian auto and cross correlation coefficients, various scales of turbulence, energy spectra, and probability density functions of fluctuating velocities) were measured in both the converging and combined regions of the jets by using the X array, hot wire anemometers.

The negative high shear stress existed in the merging region. Strictly speaking, the turbulent flow in this region is not isotropic. In the combined region, the turbulent mechanics of these jets are essentially the same as that of the single plane jet. All of the spectra in these jets had a slope of 5/3 over about one decade of the wave number space. The probability density functions were Gaussian except for the boundary to the surrounding air.
Absorption of carbon dioxide into aqueous monoethanolamine solutions
Authors: Hikita Haruo , Asai Satoru , Katsu Yoshio , Ikuno Seiichi
Published: June 2004

The rates of absorption of pure carbon dioxide into aqueous monoethanolamine solutions with a surface active agent were measured at 15°, 25°, 35°, and 45°C in a liquid jet column and a wetted wall column. Experimental results were analyzed with the chemical absorption theory based on the penetration model. Physical solubility of carbon dioxide in aqueous monoethanolamine solutions was determined from the absorption rates measured in a near pseudo first‐order reaction regime and was shown to be considerably larger than the physical solubility in water. The measured absorption rates were in good agreement with the theoretical predictions for gas absorption with an irreversible second‐order reaction, when the variation of the physical solubility of carbon dioxide due to the change in the composition of the solution during the absorption process was taken into account.
Calcium silicates: A new class of highly regenerative sorbents for hot gas desulfurization
Authors: Yang Ralph T. , Shen Ming‐Shing
Published: June 2004

A study has been conducted on the utilization of calcium silicates and the silica supported lime as regenerative sorbents for desulfurization of hot combustion gases. Except for γ‐Ca2SiO4 and Ca3SiO5, all the calcium silicates and the silica supported calcium oxide are equally or more reactive than calcium oxide, and the regeneration rates of these sorbents are substantially higher than that of calcium oxide. There was no tendency of decaying of the reactivity after eight cycles of sorption and regeneration.
Drag coefficient and relative velocity in bubbly, droplet or particulate flows
Authors: Ishii Mamoru , Zuber Novak
Published: June 2004

Drag coefficient and relative motion correlations for dispersed two‐phase flows of bubbles, drops, and particles were developed from simple similarity criteria and a mixture viscosity model. The results are compared with a number of experimental data, and satisfactory agreements are obtained at wide ranges of the particle concentration and Reynolds number. Characteristics differences between fluid particle systems and solid particle systems at higher Reynolds numbers or at higher concentration regimes were successfully predicted by the model. Results showed that the drag law in various dispersed two‐phase flows could be put on a general and unified base by the present method.
Electroforced sedimentation of thick clay suspensions in consolidation region
Authors: Shirato Mompei , Aragaki Tsutomu , Manabe Akira , Takeuchi Nobuhiko
Published: June 2004

It is shown that the slow settling rates of thickened Gairome clay slurries, when initial concentrations are sufficiently concentrated for settling due to the so‐called consolidation mechanism from the beginning of settling, can be greatly enhanced by application of D.C. voltages. Equations for settling due to the consolidation mechanism are developed in view of the influence of the gravitational and the applied electric field. It is demonstrated that the settling rates increase remarkably with increasing electric field intensity. The settling rates and the porosity distributions in settling sediments calculated by the new equations compare favorably with experimental observations.
Multivariable controller design for linear systems having multiple time delays
Authors: Ogunnaike B. A. , Ray W. H.
Published: June 2004

A multivariable, multidelay compensator, capable of handling general, linear time delay problems is derived in a form applicable both in continuous and discrete time. The controller developed is shown to have the same structure as the linear‐quadratic optimal feedback controller for input delays and reduces to the Smith predictor (and the analytical predictor) for the special case of a single time delay. Some examples representative of engineering practice are used to demonstrate the effectiveness of the controller.
Statistical analysis of constrained data sets
Authors: Knepper Jay C. , Gorman John W.
Published: June 2004

Practical, comprehensive computer‐based methods for analyzing data sets are developed. Methods for calculating data adjustment, parameter values, variance‐covariance of adjusted data and parameters and for detecting aberrant data are presented. A simple calculation algorithm and application of the methods for design of experimental measurements are proposed.
Forced convective boiling in vertical tubes for saturated pure components and binary mixtures
Authors: Bennett Douglas L. , Chen John C.
Published: June 2004

Over 1000 sets of data for forced convective boiling of distilled water, ethylene glycol and aqueous mixtures of ethylene glycol are reported. Most of these data were taken in the annular flow regime. These data indicate a previously unrecognized Prandtl number effect on the boiling heat transfer for both pure components and mixtures. A significant reduction in the heat transfer coefficient is observed for mixtures attributable to mass transfer effects. An expression is developed which accounts for both of these effects and correlates the experimental data to within a mean deviation of 14.9%. This correlation reduces to the standard Chen correlation for pure fluids with Prandtl numbers close to unity.
Identification and linear multivariable control in an absorption‐desorption pilot plant
Authors: Albrecht J. J. , Kershenbaum L. S. , Pyle D. L.
Published: June 2004

A study of the identification of the dynamics of a pilot scale absorption‐desorption system and the subsequent design of a multivariable control scheme are reported. A multivariable transfer function model was obtained from experimental input‐output data in which the inputs (steam supply and liquid circulation rate) were perturbed simultaneously using uncorrelated pseudo random sequences. A two‐step, least‐squares estimator was employed for the identification of the model.

A multivariable controller was then designed on the basis of the direct Nyquist array method. The implementation of the controller design indicated the utility of the design procedure as compared to independent single input, single output control loops; there is, however, some scope for additional tuning.
A random capillary model with application to char gasification at chemically controlled rates
Authors: Gavals George R.
Published: June 2004

Porous particles are described by a random capillary model predicting the frequency of pore intersections and the evolution of pore volume and surface area during reaction. The model is applied to char gasification at chemically controlled rates, and the results are compared with data from the literature.
Viscous heat generation in slit flow
Authors: Ybarra Robert M. , Eckert Roger E.
Published: June 2004

The onset of significant departure from isothermality caused by viscous energy dissipation in flow through a slit is determined for isothermal and adiabatic walls. A series solution of the energy equation enables calculation of dimensionless profiles for any power law fluid. Such solutions provide useful standards for judging performances of numerical schemes for solving complex nonisothermal flows.
Fundamental investigations and electrochemical engineering aspects concerning an advanced concept for alkaline water electrolysis
Authors: Fischer Juergen , Hofmann Hans , Luft Gerhard , Wendt Hartmnt
Published: June 2004

A thorough search for electrocatalysts for anodic oxygen evolution from caustic potash solution together with an investigation for the main reasons of ohmic potential drops in the interelectrode gap has lead to a new concept for an advanced medium temperature (150° to 200°C), medium pressure (30 to 100 bars) alkaline water electrolysis. The new concept will allow electrolytic water decomposition at temperatures between 160° and 200°C with current densities of 1 to 1.5 A/cm2 and cell voltages between 1.55 and 1.65 V.
Dynamics of mixed cultures of microorganisms: Some topological considerations
Authors: Stephanopoulos Gregory
Published: June 2004

Structural relationships between the numbers of the various types of steady states exhibited by a mixed culture of microorganisms growing in a chemostat have been obtained. The analysis is based on the degree theory and utilizes Hopf's index theorem. Useful information concerning the culture growth and general conclusions pertaining to the nature of the possible steady states are obtained from these relationships. An alternate method of stability analysis, based on the above results, has also been developed and applications to several cases of growth of indirectly interacting populations which demonstrate the efficiency of the method are presented.
Optimal sensor location with an application to a packed bed tubular reactor
Authors: Harris T. J. , Macgregor J. F. , Wright J. D.
Published: June 2004

A number of approaches to the optimal selection of sensor locations are presented, and some of these are applied to determine optimal thermocouple positions in a packed bed tubular reactor. As expected, the optimal locations were found to be those surrounding the hot spot location. The theory also revealed that for good state estimation and for goodlinear quadratic control of the reactor, only one or two well located temperature measurements are necessary rather than the entire temperature profile.
Substrate‐inhibited kinetics with catalyst deactivation in an isothermal CSTR. II. Multiple pseudosteady states and reactor failure
Authors: Do Duong D. , Weiland Ralph H.
Published: June 2004

Analytical expressions are derived for the time and magnitude of failure of an isothermal CSTR with substrate‐inhibited kinetics, caused by slow catalyst deactivation under three types of parallel and series mechanisms. Reactors operating at high space velocity are found to be most susceptible to early failure and poisoning by product is more dangerous than by reactant. The magnitude of the jump across steady states depends solely on the Langmuir‐Hinshelwood kinetic parameters and a detailed analysis of reactor behavior during the jump itself is given.
Simultaneous measurement of size and velocity of bubbles or drops: A new optical technique
Authors: Semiat Raphael , Dukler A. E.
Published: June 2004

Accurate information on both the size and velocity of a dispersed phase is of importance to many problems in heat or mass transfer and reaction. Existing experimental methods are limited in their applicability, difficult to use, provide only size or velocity, and are of low statistical reliability. A new method is developed here which overcomes most of these shortcomings and permits accurate simultaneous measurement of the size and two dimensional velocity of the dispersed phase.
Laser doppler anemometry measurements in gas‐solid flows
Authors: Lesinski J. , Mizera‐Lesinska B. , Fanton J. C. , Boulos M. I.
Published: June 2004

Laser Doppler Anemometry (LDA) was used for the simultaneous measurement of the gas and particle velocities in a gas‐solid, two‐phase flow. The flow configuration consists of an air jet at ambient temperature in which a spherical glass powder of a mean particle diameter of 97.0 or 13.7 μm was injected from one side using a secondary air jet. Both principal and secondary jets were also seeded with talcum powder with a mean particle diameter of about 1 μm which served as a tracer.

The probability density distribution function (PDF) of the LDA output showed two distinct peaks corresponding to the particle and gas velocities. As the particles were accelerated by the flow, the slip velocity between the gas and the particles decreased causing the gap between these two peaks to narrow. The measured mean particle velocity profiles were in agreement with the predictions of a theoretical model.

The objectives of the present investigation was to obtain experimental data on the dependence of the particle trajectories and their mean velocities on the injection conditions in a free jet stream. The principal question, however, was whether such data could be obtained using Laser Doppler Anemometry (LDA). In other words, whether LDA could be effectively used in two‐phase flow systems for the simultaneous measurement of the gas and particle velocities? Obviously, the answer to this last question can affect far beyond this particular study and more than justified the effort for this detailed investigation. It should be pointed out that, while LDA has been known for sometime, and the necessary equipments for an LDA system are available on a commercial bases, relatively little attention has been given to its application to other than single‐phase, fluid‐flow measurements.
Properties of bismuth oxide catalysts for oxidative dehydrogenation dimerization of propylene
Authors: White M. G. , Hightower J. W.
Published: June 2004

The electronic properties of bismuth oxide shed light on the mechanism of its catalytic activity for the oxidative dehydrogenation dimerization of propylene. Variations in the electrical conductivity and thermoelectric power, as the gas phase contacting a pellet of this p‐type semiconductor was changed, provided information about the nature of species adsorbed at reaction temperature.
A stochastic model for turbulent diffusion of particles or drops
Authors: Lee N. , Dukler A. E.
Published: June 2004

A stochastic model is presented for turbulent diffusion of particles or drops in a turbulent field. The model is free of arbitrary adjustable constants and is applicable to realistic situations where the flow is nonhomogeneous such as in boundary layers or in pipe flow. New experimental data is presented for dispersion of glass beads in the boundary layer of the University of Houston Environmental Wind Tunnel. Good agreement with the theoretical model is demonstrated.
Estimation of activity coefficients in concentrated sulfite‐sulfate solutions
Authors: Rosenblatt G. M.
Published: June 2004

The electrolyte theory of Pitzer and coworkers is used to estimate geometric mean‐ion activity coefficients in strong electrolyte solutions at 25–55°C. By using Pitzer's equations with ion‐pair parameters estimated in this paper, one can calculate activity coefficients to moderately high ionic strengths in aqueous mixtures containing the following ions: Na+, K+, Mg2+, Ca2+, Cl−, ClO, ClO, HCO, HSO, CO, SO, SO, and S2O. Mixtures containing these ions are present in CaO/CaSO4 flue gas desulfurization units and in laboratory experiments aimed at understanding the chemistry occurring in such units. The computed activity coefficients are relatively insensitive to the values of the estimated quantities. The basis of the estimates, as well as their effect on calculated activity coefficients, is discussed. It is concluded that activity coefficients are estimated with an accuracy of ±25% or better.
Kinetics of nonisothermal sorption: Systems with bed diffusion control
Authors: Ruthven D. M. , Lee Lap‐Keung
Published: June 2004

A theoretical model is presented to describe the kinetics of nonisothermal sorption for a system in which the main resistance to mass transfer is the macrodiffusional resistance of the absorbent particle bed while the main resistance to heat transfer is the resistance at the external surface of the adsorbent sample. The model is used to interpret experimental kinetic data for the sorption of several hydrocarbons in 10X and 13X zeolite crystals. By varying the configuration of the sample bed and the size of the zeolite crystals it is shown that, for n‐heptane and iso‐octane in 13X, the intracrystalline diffusional resistance is negligible even in 40‐μm crystals. The assumption of intracrystalline diffusion control which has been made in earlier kinetic studies of similar systems is therefore incorrect.
Studies in the synthesis of control structures for chemical processes. Part V: Design of steady‐state optimizing control structures for integrated chemical plants
Authors: Arkun Yaman , Stephanopoulos George
Published: June 2004

This paper addresses the question of how to design the steady‐state optimizing control system for a large scale interconnected chemical plant. The integrated design approach is structured within the framework of the hierarchical control theory and is based on the concepts of constraint control, hierarchical decomposition and nonlinear mathematical programming. Theoretical developments lead to the generation of alternative operational policies of practical value. An imbedded branch and bound screening strategy is given to select the best policy, which will be implemented on‐line by the optimizing plant controllers. The general design approach has the broad applicability to any interconnected large scale system, and its application is demonstrated on a gasoline polymerization plant.
Revision of kynch sedimentation theory
Authors: Tiller Frank M.
Published: June 2004

Much of the theory of gravity sedimentation has been based on the work of Coe and Clevenger (1916) and Kynch (1952). They provided methods for obtaining rates of sedimentation in batch, static tests which are presently used for design of continuous thickeners. Kynch assumed that a first order partial differential equation controlled the entire sedimentation process. His equation was based on: (1) continuity balance; and (2) sedimentation velocity being a unique function of solid particulate concentration. A general solution was presented in the form of volume fraction of solids ϕs = f(x − vt). During the constant rate fall of the upper interface, the boundary condition of uniform initial concentration combines with the Kynch equations to adequately describe the sedimentation phenomena. Kynch ignored the sediment rising from the bottom of the settling chamber, and assumed that the characteristics y = x − vt originated at the origin of coordinates (height, time) during the first falling rate period. The characteristics actually originate at the surface of the rising sediment where the upward liquid velocity affects the rate of fall of the particulates. New equations have been derived based upon the assumption that the characteristics emanate from the rising sediment.
Effects of molecular size and configuration on diffusion in microporous membranes
Authors: Deen W. M. , Bohrer M. P. , Epstein N. B.
Published: June 2004

Effects of molecular size and configuration on hindered diffusion were examined by measuring diffusion of two series of uncharged macromolecules through track‐etch membranes with uniform and well‐defined pore geometry. At any given Stokes‐Einstein radius, diffusivities in small pores were lower for ficoll (crosslinked structure) than for dextran (more nearly linear structure).
Optimal operation of integrated processing systems. Part I: Open‐loop on‐line optimizing control
Authors: Garcia Carlos E. , Morari Manfred
Published: June 2004

A new algorithm for the continuous tracking of the optimal economic operating conditions of an integrated chemical plant has been developed. The method does not make use of fundamental models of the plant but is based on an on‐line search using experimental moves of the independent variables. The results of these moves provide the data for the identification of a dynamic process model. This model allows one to determine the gradient of the objective function and thus guides the next move of the independent variable eventually leading to the optimum. The advantages of the new technique over other methods are demonstrated in simulation examples:

The speed of tracking is equally fast or faster than the relaxation speed of the system after a step change.

The noise insensitivity allows safe tracking of the optimum despite significant measurement errors.

As a key feature a decentralized form of the algorithm is developed making it suitable for distributed microprocessor implementation.
Analysis of particulate removal in venturi scrubbers—role of heat and mass transfer
Authors: Placek T. D. , Peters L. K.
Published: June 2004

In a previous paper, a theoretical model of venturi scrubber performance was presented in which the operating variables, scrubber geometry, and droplet and dust size distributions are specified. The present paper examines the roles that heat and mass transfer have in determining the particle collection efficiency. The mechanisms of inertial impaction, interception, and diffusiophoresis are analyzed simultaneously to account realistically for heat and mass transfer effects on particle collection. Operation at elevated gas temperatures can substantially reduce collection, primarily due to the increase in gas density which occurs as the gas contacts the spray liquid. Mass transfer effects are important only when condensation onto the drops occurs, such as that during the scrubbing of saturated gas streams or when using cold liquid sprays. Under these conditions, mass transfer effects increase the collection efficiency.
Unsteady heat transfer in laminar non‐Newtonian boundary layer over a wedge
Authors: Gorla Rama Subba Reddy
Published: June 2004

The transient thermal response of a power‐law type non‐Newtonian, laminar boundary layer flow over a wedge is investigated. Consideration is given to the case of a step change in surface temperature. Details of the transient heat flux and the temperature field are obtained and have been presented graphically. The range of Prandtl numbers investigated is from 5 to 1000 while the viscosity index was allowed to vary from 0.1 to 5.0.
An analysis of bacterial growth in fluidized‐bed adsorption column
Authors: Andrews G. F. , Tien Chi
Published: June 2004

An analysis is presented to described the dynamics of fluidized bed adsorption columns. A microbial film model (recently proposed by the authors) is used to characterize the bacterial activity and its interaction with adsorption and solids mixing. Solids mixing and mixing in the liquid phase are included in the analysis, as is the effect of microbial film growth on the settling velocity of the adsorbent particles. The interplay of film growth, bed stratification and solids mixing is discussed in detail.
Numerical solution for the flow of highly viscous fluid in agitated vessel with anchor impeller
Authors: Kuriyama M. , Inomata H. , Arai K. , Saito S.
Published: June 2004

Fluid motion in an agitated vessel with an anchor impeller is characterized by flow in a horizontal plane induced by the vertical arms of the impeller rotating near the vessel wall. A numerical algorithm of the two‐dimensional flow in the horizontal plane is established using an iterative method for the determination of the boundary values of stream function. The computational results of the velocity profiles and agitation power are compared with those of the experiments, and it is shown that the numerical method used in this study is very useful to analyze the flow past the vertical arms of an anchor impeller.
A study of fast tracer desorption in molecular sieve crystals
Authors: Kärger Jörg
Published: June 2004

A modification of the customary NMR (Nuclear Magnetic Resonance) pulsed field gradient technique is shown to allow the observation of tracer desorption phenomena in a time interval of 4 … 1 000 ms. The processes observed are only limited by molecular transport in the individual crystallites. Other influences, such as intercrystalline transport resistances and the finite rate of adsorbate supply or adsorption heat dissipation, as known from traditional sorption experiments, can be excluded.

The method is applied to several zeolitic adsorbate‐adsorbent systems: methane…hexane/NaX; ethane/NaCaA. The tracer desorption curves show the expected dependences on paraffin chain length, sorbate concentration and crystallite size. Comparison with the coefficients of intracrystalline diffusion shows that desorption is limited by intracrystalline transport, excluding the existence of structural surface resistance for these systems. Application of the technique to small zeolite crystallites allows the observation of molecular transport phenomena considerably slower than accessible until now by customary NMR techniques.
Effect of lateral heat losses on the stability of thermal displacement fronts in porous media
Authors: Yortsos Y. C.
Published: June 2004

Previous studies have shown that heat transport by horizontal conduction in thermal displacement processes in porous media has a stabilizing effect on condensation fronts. This paper expands the stability analysis by also including the description of heat transfer lateral heat losses by conjungate (vertical) conduction. A marginal stability condition is derived in terms of a parameter Λ representing the relative magnitude of heat transfer by conjugate conduction. It is shown that lateral heat losses ask a significant stabilizing effect on the front. This effect should be important in thermal oil recovery processes such as steam injection and in‐situ combustion.
Finite difference calculation of current distributions at polarized electrodes
Authors: Prentice G. A. , Tobias C. W.
Published: June 2004

The changing geometry of electrodes undergoing electrodeposition or dissolution can be simulated by successive solutions of Laplace's equation with nonlinear boundary conditions. To overcome the instability in the finite‐difference calculation caused by nonlinear boundary conditions, a weighting algorithm to compute the new surface potential on successive iterations has been developed.
Theoretical and experimental study of radiant heat transfer in a solar fluidized‐bed receiver
Authors: Flamant G.
Published: June 2004

The temperature profile, total emissivity, flux density distribution, and effective mean penetration distance were determined from measurements in high‐temperature solar fluidized beds. A theoretical model is proposed to describe the complex heat transfer phenomena in the radiation penetration zone of the fluidized layers. The results correlated well at incipient fluidizing conditions for beds of silicon carbide and chamotte but were found imprecise for beds of zirconia and silica sand.
Intraparticle‐forced convection effect in catalyst diffusivity measurements and reactor design
Authors: Rodrigues A. E. , Ahn Bum J. , Zoulalian André
Published: June 2004

Intraparticle forced convection was considered in order to explain experimentally observed changes in effective diffusivity (apparent) with flowrate, when measures are carried out in fixed beds.

A complete model taking into account intraparticle diffusion and forced convection together with film diffusion is derived in order to analyze diffusivity measurements by physical methods, both in perfectly mixed reactors and fixed beds.

The experiments were carried out with hydrogen tracer in a partial oxydation catalyst.

Implications of the use of such “apparent” effective diffusivities in reactor design are discussed, showing that errors of 100% can be made.
Factors affecting secondary nucleation rate of sodium chloride in an evaporative crystallizer
Authors: Grootscholten P. A. M. , De Leer B. G. M. , De Jong E. J. , Asselbergs C. J.
Published: June 2004

Crystallization kinetics of sodium chloride have been studied in a Continuous Mixed Suspension Mixed Product Removal evaporative crystallizer at 50°C. A marine propeller was found to give a substantially lower nucleation rate than a pitched blade impeller under identical conditions. The crystal turnover time did not affect the effective nucleation rate.
In situ gravimetric studies of the regenerative mechanism for water‐gas shift over magnetite: Equilibrium and kinetic measurements in CO2/CO and H2O/H2 gas mixtures
Authors: Kubsh J. E. , Dumesic J. A.
Published: June 2004

In situ gravimetric measurements were used to study oxygen removal from (or incorporation into) chromia‐promoted magnetite in CO2/CO and H2O/H2 gas mixtures at 637 K. The equilibrium and kinetic data could be described by two reversible, oxidation‐reduction reactions: surface‐oxygen removal by CO and surface oxygen replenishment by H2O, with the corresponding reverse reaction involving CO2 and H2. These reactions form a regenerative mechanism that is able to predict qualitatively both the measured rate and rate expression for water‐gas shift. It is concluded that this regenerative mechanism is a primary pathway for water‐gas shift over magnetite.