bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of hindered sedimentation of polydisperse mixtures
Authors: Zimmels Y.
Published: June 2004

The theory and application of hindred sedimentation is reviewed. Polydisperse mixtures with size and density distributions are considered. A general solution technique is established for steady‐flow regimes where a standard drag correlation for monodisperse systems is applied to each component. Solutions for discrete and continuous particle‐size and density distributions are outlined. Results are presented for the sedimentation of mixtures made up of particles of uniform density and varying size suspended in a fluid with fixed properties. Under these conditions, the sedimentation velocities of the components vary significantly with the size distribution of the particles and the total volume fraction occupied by the particles In this context, topics such as maximum flux of particles, classification and density separation are considered.
Fluidized‐bed reactor model with generalized particle balances. Part I: Formulation and solution
Authors: Overturf B. W. , Reklaitis G. V.
Published: June 2004

The changes to the solid phase which occur within fluidized‐bed gas‐solid reactors may have a significant impact on the performance of this class of reactors, particularly in coal conversion applications. In this paper a particle balance model is developed which accommodates particle distributions dependent on both size and density as well as populations consisting of multiple solids. The fast double collocation method used for solving the associated PDE permits this calculation to be performed within the framework of a Davidson‐Harrison bubbling‐bed model. A modification of the iteration procedure for the emulsion‐phase state variables of the D‐H model is reported which allows the composite reactor model to be executed reliably and efficiently. A general purpose program has been implemented, whose application is presented in a companion paper.
Effective diffusion and conduction in two‐phase media: A unified approach
Authors: Chang Hsueh‐Chia
Published: June 2004

A multiscale analysis based on two widely different length scales that exist instagnant two‐phase media is carried out to investigate diffusion and conduction in periodic and random systems. A variational form of the resulting unit cell equations allows one to demonstrate its equivalence to the cell equations of other independent approaches, thus unifying these widely different methods. The variational approach is also shown to facilitate numerical studies and to provide a link between random and periodic media by yielding an upper bound for the effective diffusivity in random media in terms of the periodic one.
Mobilization of oil ganglia
Authors: de la Cruz V. , Spanos T. J. T.
Published: June 2004

Following secondary recovery processes in conventional light oil reservoirs, more than half the original oil in place may remain trapped as a discontinuous phase. During the previous recovery processes these oil ganglia have been pinched off by capillary forces and remain immobile while the continuous phase which surrounds them is able to flow freely. Furthermore if a portion of this oil is mobilized in a tertiary recovery process the conditions required to apply Darcy's equation to the flow of either phase are violated. These are also problems which are encountered during in‐situ recovery techniques in tar sands where the mobilization of the heavy oil occurs as a discontinuous phase. In this paper the relevant flow equations are derived. Also a parameter is deduced which directly determines the criterion for mobilization.
Convective diffusional deposition and collection efficiency of aerosol on a dust‐loaded fiber
Authors: Kanaoka Chikao , Emi Hitoshi , Tanthapanichakoon Wiwut
Published: June 2004

A three‐dimensional stochastic model, which is effective for the convective diffusional deposition of aerosol particles, was developed starting from Langevin's equation. The model was utilized to simulate collection and agglomeration processes of particles on a cylindrical fiber. By obtaining the distribution of captured particles on a fiber and the evolution of the collection efficiency of a dust‐loaded fiber through the simulation, the effect of Peclet number, interception parameter, and the accumulated mass of particles on them were discussed. Further, the collection efficiency of a dust‐loaded fiber was correlated by using a linear function of the accumulated mass of particles in a unit filter volume. Dependence of coefficient in the linear function, collection efficiency raising factor on Peclet number, and interception parameter were also discussed.
Prediction of heat transfer in turbulent falling liquid films with or without interfacial shear
Authors: Yih Siu‐Ming , Liu Jung‐Liang
Published: June 2004

A unified approach is proposed for the prediction of heat transfer coefficients in turbulent falling films undergoing heating, evaporation or condensation for both of the cases with or without interfacial shear. A modified van Driest eddy viscosity model, which incorporated a damping factor f and takes into account the effect of variable shear stress, is used to predict the hydrodynamics of turbulent falling films. The calculated film thicknesses are in good agreement with the Nusselt‐Brauer correlations for the non‐sheared film and the Dukler prediction for highly sheared film. Also, by including a van Driest type turbulent Prandtl number model, the asymptotic heat transfer coefficients are accurately predicted and show better agreement with the extensive literature data and correlations than do most of the existing turbulence models proposed to date.
Applicability of axial dispersion model to analyze mass transfer measurements in bubble columns
Authors: Deckwer W.‐D. , Nguyen‐Tien K. , Kelkar B. G. , Shah Y. T.
Published: June 2004

The applicability of axial dispersion model (ADM) for the measurement of the gas‐liquid mass transfer coefficient (kLa) in bubble columns is discussed. It is shown that the misinterpretation of the concentration jump near the column inlet can lead to wrong conclusions regarding the mass transfer rates. It is further illustrated that some reported kLa dependencies on the superficial liquid velocity and the axial distance are resulted from the use of an incorrect model and can be rectified by an application of ADM. Finally, it is shown that ADM can be effectively used to calculate kLa a for: (a) highly viscous liquids, (b) in the presence of chemical reaction, (c) slurry reactors, and (d) the columns with different liquid inlet locations.
Theory on colloidal double‐layer interactions
Authors: Papadopoulos Kyriakos D. , Cheh Huk Y.
Published: June 2004

The potential energy between two interacting colloidal particles is derived by a knowledge of the energy of interaction of two parallel flat plates. The proposed method maps pairs of infinitesimal surface elements from the two interacting bodies to parallel plate‐like elements. The results obtained from this theory are compared with the Derjaquin approximation for large kR and the Levine and Dube approximation for small kR.
Noncatalytic gas‐solid reactions in a vertical pneumatic transport reactor
Authors: Fan Liang‐Shih , Satija Sunil , Kim B. C. , Nack H.
Published: June 2004

A heterogeneous model is developed to account for noncatalytic gas‐solid reactions in a vertical pneumatic transport reactor. The model takes into consideration both the positive and negative variations of the solid porosity and the variation of the gas diffusivity with the reaction. The method of lines utilizing the second order centered finite difference scheme for the spatial discretization is employed to obtain the model solution.

Experiments utilizing a vertical pneumatic transport reactor of a laboratory scale are performed to study the reaction between limestone and sulfur dioxide generated from coal combustion. The reactor is of 16.2 cm ID and 610 cm in length. The experimental data for sulfur retention are reported for various superficial gas velocities and calcium‐sulfur molar ratios. Verification of the model with experimental data is conducted. The agreement between the model prediction and experimental data is satisfactory.
Slow second‐order reactions in a deflected buoyant jet
Authors: Forney L. J. , Oakes L. A.
Published: June 2004

An integral method including the entrainment hypothesis of Hoult, Fay and Forney (1969) is used to predict the concentration of product formed in a buoyant jet in a crossflow. The analysis is restricted to a slow, irreversible, second‐order reaction with premixed reactants. Reliable laboratory data are presented for the oxidation of nitric oxide by the reaction 2NO + O2 → 2NO2 with excess O2 and these results are correlated with the theory. Additional measurements are recorded to provide information on the magnitude of the turbulent parameters necessary for proper closure of the rate expressions.
Analytical model for excess Gibbs energy of nonspecific liquid metal interactions
Authors: Cox K. R. , Eckert C. A.
Published: June 2004

A physical model for the very strong intermolecular forces in liquid metal mixtures is proposed, involving the combined effects of ion‐ion, ion‐electron, and electron‐electron interactions plus the charge density effects on the electron kinetic energy. The resulting excess Gibbs energy expression contains a single cross‐energy parameter which must be evaluated either from the eutectic point or from one mixture datum. The applicability of the model is limited to systems without strong specific solvation, but it does effectively predict both negative and positive deviations from Raoult's law, including the asymmetry arising from size differences. Applications are shown for vapor‐liquid, liquid‐liquid and solid‐liquid equilibria.
Estimation of true moments from truncated data
Authors: Skopp Joseph
Published: June 2004

Moment analysis is a powerful tool in reactor bed analysis. Weighted moments is a technique which has been introduced to increase the accuracy of moment estimation. The supposed advantage of weighted moments is reevaluated utilizing an optimum truncation point. The resulting coefficient of variation in the moment estimates is shown to be superior to an arbitrary truncation point for all weighting factors. When an optimum truncation point is used, little advantage is observed for weighted moments.
Regeneration of carbon containing sodium dodecylbenzene sulfonate—cyclic regeneration with steam in fluidized beds
Authors: Umehara Tadashi , Smith J. M.
Published: June 2004

Cyclic regeneration of activated carbon containing adsorbed sodium dodecyl‐benzene sulfonate (DBS) was studied in fluidized beds at 1119 K and 101.3 kPa. Optimum restoration of adsorption capacity (97.2% per cycle) resulted when gasification with 21.5% steam was continued for 200 s. At that time, about 85% of the DBS added to the carbon during the adsorption process had been removed. Because of the adsorbed inorganic residue from DBS, these results are somewhat different from earlier studies with the sucrose‐carbon system. With sucrose, maximum restoration of adsorption capacity was achieved when a weight equivalent to 100% of the adsorbed sucrose was removed by thermal decomposition and steam gasification.
Optical methods and results of dew point and deposition rate measurements in salt/ash‐containing combustion gases—B2O3(I) deposition rates by interference methods and comparisons with theory
Authors: Seshadri K. , Rosner D. E.
Published: June 2004

This study is focused on deposition rate processes leading to inefficiency and “hot corrosion” in fossil‐fuel‐fired furnaces and engines. The inorganic compounds which deposit on heat exchanger surfaces and blades are formed in combustion product gases when the fuel and/or ingested air contains inorganic impurities. An improved understanding of the coupled thermodynamic, kinetic, and transport processes governing the deposition rate of inorganic oxides and salts from hot gases containing these compounds (or their precursors) can suggest more efficient test strategies and control measures. Accordingly, an optical interference method for accurately measuring the growth rate of deposits well before the onset of run‐off under laboratory burner conditions has been developed.

To demonstrate the technique and provide data suitable for theoretical model development, a deliberately simple chemical system and target geometry are used. BCl3(g) is introduced into a premixed C3H8‐air flat flame at atmospheric pressure. The growth rate of B2O3(I) on an electrically heated platinum ribbon is then measured interferometrically over a range of fuel/air ratios and seed levels. However, the very existence of B2O3(I) deposition at the present seed levels and surface temperatures (about 1,200–1,300 K) clearly demonstrates the importance of kinetic restrictions on B2O3(I) gasification reactions. Optically measured film growth rates are obtained at film thicknesses small enough to neglect condensate run‐off, hence they yield vapor deposition rates directly. These deposition rates are found to be in good agreement with the predictions of a recently developed multicomponent mass‐transfer boundary layer (BL) theory, with a constrained equilibrium ((HBO2)3 precluded) boundary condition. Remarkably, at a constant value of the BCl3 flow rate, the Pt ribbon temperature above which there is no B2O3 condensate (i.e., the so‐called dew point) is observed to depend on the fuel/air ratio. Whereas previous equilibrium‐based deposition models cannot embrace such phenomena, a semi‐quantitative argument, based on the nonequilibrium chemistry of B2O3 precursor formation and (HBO2)3‐formation barriers, explains these potentially significant trends. These encouraging results suggest a more general applicability for the optical methods and chemically frozen (CF) BL theory described herein, and demonstrate the important role of heterogeneous and homogeneous kinetic barriers in determining dew points and deposition rates in combustion systems.
Meandering of water rivulets
Authors: Culkin J. B. , Davis S. H.
Published: June 2004

Water rivulets are produced on inclined flat plates made of high‐density polyethylene, Mylar, Plexiglas and acetate film. Conditions are obtained for straight rivulets to begin to meander and for measuring rivulets to cease their unsteadiness. These critical conditions are correlated using a one‐dimensional theory of high Reynolds number slender rivulets in which pressure gradients generated by curvature, surface tensionand contact‐angle hysteresis balance.
Generalized correlation for friction loss in drag reducing polymer solutions
Authors: Darby Ron , Chang Hsun‐Fu D.
Published: June 2004

The definition of the pipe flow friction factor has been extended to include the effect of fluid viscoelastic properties on energy dissipation in turbulent tube flow. The resulting friction factor includes a characteristic fluid relaxation time, which can be determined directly from rheological measurements, and reduces to the usual Fanning friction factor for inelastic fluids. The use of this more general friction factor enables turbulent tube flow data for both fresh and shear degraded “concentrated” drag reducing polymer solutions of various concentrations in various tube sizes to be correlated by the usual f vs. NRe relation for Newtonian fluids in smooth tubes.
Modeling of growth rate dispersion of citric acid monohydrate in continuous crystallizers
Authors: Berglund K. A. , Larson M. A.
Published: June 2004

A mathematical model for prediction of the crystal size distribution from a continuous crystallizer is presented. The kinetic data used for the model were obtained from batch contact nucleation experiments with citric acid monohydrate. In these experiments, the distribution of growth rates as well as the initial size distribution were estimated. Results from the model indicate that the excess number of crystals usually present at small sizes in continuous crystallizers is due to growth rate dispersion (where crystals of the same size may have different growth rates) and not size dependent growth.
Hydrodynamics of cocurrent gas‐liquid‐solid semifluidization with a liquid as the continuous phase
Authors: Chern Song‐Hsing , Fan Liang‐Shih , Muroyama K.
Published: June 2004

The hydrodynamic behavior of a cocurrent gas‐liquid‐solid semifluidized bed was investigated. A separate investigation was performed on a packed bed and a fluidized bed under gas‐liquid flow conditions similar to that for the semifluidized bed. Parameters of the semifluidized bed under extensive study include pressure drop, gas holdup, onset liquid velocity for semifluidization, and the height of the packed bed section and the fluidized section. The pressure drop of the semi‐fluidized bed obtained experimentally was compared favorably with that predicted by the model equations.
Measurement and modelling of droplet coalescence and breakage in a pulsed‐plate extraction column
Authors: Garg M. O. , Pratt H. R. C.
Published: June 2004

Droplet coalescence and breakage rats in a pulsed‐plate extraction column have been measured using the colorimetric method of Hamilton and Pratt (1980). The results were interpreted in terms of rate constants, defined appropriately for the mixer‐settler and emulsion regions of operation respectively, using a discrete population balance model. It is shown that the resulting values of these constants can be used to predict accurately the steady‐state droplet‐size distribution and apparent coalescence rate. Computations for a typical extraction system indicated that the effect of polydispersivity on performance is surprisingly small for the pulsed plate column.
Dynamic behavior of a porous char particle burning in an oxygen‐containing environment: Part II: Transient analysis of a shrinking particle
Authors: Sotirchos S. V. , Amundson N. R.
Published: June 2004

The diffusion and reaction model developed in a previous paper is extended allowing for shrinkage of the char particles. It is shown that possible shrinkage, arising from disintegration of the solid structure at a certain conversion level, modifies severely the extinction behavior of the reacting particles. Specifically, the region of ambient temperature and particle radius in which the predictions of the nonisothermal and of the isothermal versions of the model differ significantly becomes smaller. However, the particle shrinkage does not affect the ignition phenomena observed since a particle usually ignites at low conversion levels where the radius change is still negligible.
Gels as size selective extraction solvents
Authors: Cussler E. L. , Stokar M. R. , Varberg J. E.
Published: June 2004

We have successfully used cross‐linked, partially‐hydrolyzed, polyacrylamide gels to concentrate solutions of high molecular weight solutes. The gels are sizeselective, concentrating solutes whose diameter exceeds 3 nm. They can be easily regenerated by means of pH‐induced changes in gel swelling; this regeneration is consistent with that inferred from existing theories of gel swelling. The resulting separation process is a good alternative to ultrafiltration.
Liquid‐phase diffusion and adsorption of pyridine in porous silica‐alumina pellets
Authors: Van Vuuren D. S. , Stander C. M. , Glasser David
Published: June 2004

The adsorption and effective diffusivity of pyridine dissolved in heptane were measured in silica‐alumina pellets using a specially developed single‐pellet continous‐flow diffusion cell. The measured diffusivities varied between 0.43 × 10−9 and 3.25 × 10−9 m2·s−1; the temperature dependence of the diffusivities indicated that both pore volume diffusion and surface diffusion play a role in the mass transfer.
Lateral migration of a rigid sphere in torsional flow of a viscoelastic fluid
Authors: Karis T. E. , Prieve D. C. , Rosen S. L.
Published: June 2004

A single polystyrene sphere of radius a, between 141 and 275 micron, when in jected into a disk‐plate (torsional) flow of polybutene (viscosity 36 poise, Mn ∼680), migrates radially inward at a rate that is dramatically increased by dissolving 1% of a high‐molecular‐weight polyisobutylene (Mv ∼106) to make the fluid viscoelastic. The torsional flow field was created by rotating a 21‐cm‐diameter disk at a rate ω of 6–9 rpm with a gap H of 3.7–5.4 mm between this and a ground glass plate with the fluid in the gap. Lateral migration toward a lower shear rate increased with increasing shear rate and with increasing shear rate gradient in the manner predicted by Brunn (1976) or Chan and Leal (1977). Shear rates up to 25 s−1 were investigated. Below a shear rate of 8 s−1 the radial migration velocity is of the form vr = − L(ωa/H)2r, where L is a positive constant containing the fluid properties, and r is the radial position of the particle.
Interpretation of equilibrium exchange rates for nonelementary reactions
Authors: Willcox Dave , Kung H. H.
Published: June 2004

In a system that is close to chemical equilibrium, the relaxation of each elementary step toward equilibrium obeys the linear laws of nonequilibrium thermodynamics. For a series reaction in which the concentration of the intermediate species are low or do not change with time, the relaxation can be characterized by one time constant, which can be associated with an overall equilibrium exchange rate for the overall reaction. The relationship between the overall equilibrium exchange rate and the equilibrium exchange rates of the individual steps is analogous to that between the overall conductance and the individual conductances of a network of electrical resistors in series. A numerical example is presented to show the range of validity of this relationship. Finally, a condition for the determinability of exchange rates is presented. Exchange rates are independently determinable if and only if the determinant of the matrix, whose elements are made up of squares of the inner products of the vectors that are made up of the stoichiometric coefficients of the species in the reactions, is non‐zero.
Bilayer film model for the interaction between adsorption and bacterial activity in granular activated carbon columns part I: Formulation of equations and their numerical solutions
Authors: Wang S‐C P. , Tien Chi
Published: June 2004

The diffusion‐reaction film model proposed by Andrews and Tien (1981) for the interaction between adsorption and bacterial activities in carbon columns was generalized. The microbial film was assumed to be composed of two regions of distinctively different microbial activity, depending on the presence or absence of dissolved oxygen. Governing equations were derived to describe the dynamics of the carbon columns in which the interaction between adsorption and bacterial growth and methods for solving these equations were developed.
Bilayer film model for the interaction between adsorption and bacterial activity in granular activated carbon columns part II: Experiment
Authors: Wang S‐C P. , Tien Chi
Published: June 2004

Experiments were conducted on the degradation of valeric acid in aqueous solutions by bacteria in attached growth and on the removal of valeric acid from aqueous solutions in granular activated carbon columns. The first type of experiment was intended to obtain results necessary to determine the values of the relevant parameter of biofilm kinetics. These parameters were then used in conjunction with the model developed in Part I to predict the performance of carbon columns for removing valeric acid. Comparisons between experiments and predictions constitute the necessary model validation.
Mass transfer with chemical reaction in liquid foam reactors
Authors: Shah P. S. , Mahalingam R.
Published: June 2004

Mass transfer studies were conducted in a stable liquid foam reactor under various operating conditions to evaluate gas holdup, effective interfacial area, liquid‐phase mass transfer coefficient and a modified interfacial mass transfer coefficient to include the surface‐active agents employed. Gas holdup and effective interfacial area were evaluated experimentally. The interfacial mass transfer coefficient was evaluated semitheoretically, by considering the interfacial region as a separate phase and using the experimental data developed for mass transfer accompanied by a fast first‐order chemical reaction. The liquid‐phase mass transfer coefficient was also evaluated semitheoretically, using Danckwert's theory for the liquid phase and the experimental data on mass transfer accompanied by a slow pseudofirst‐order chemical reaction.

An experimental unit was set up to provide a stable flowing foam column, simulating the foam reactor. Mass transfer rates were studied for superfacial gas velocities in the range from 1.5 × 10−2 m/s to 5 × 10−2 m/s, giving gas residence times in the range from 20 to 55 seconds. A cationic and nonionic surface‐active agent and three different wire mesh sizes, giving bubble size distributions in the range from 2.2 to 5.4 mm Sauter mean diameters, were employed.

It is observed that gas holdup is insensitive to the type of surface‐active agent; it is however, dependent on wire mesh size and gas velocity. The bubble diameter and, hence, the interfacial area are found to be insensitive to gas velocity in the range studied; they are, however, strong functions of wire mesh size. The liquid‐phase mass transfer coefficient increases with increase in gas velocity. The surface‐active agent introduces additional resistance to mass transfer in both reaction cases, this being the controlling one in the case of the fast reaction. A comparison with conventional packed bed contactors indicates the mass transfer rates to be about 8 times lower for the foam reactor, for the fast reaction case; for slow reactions, the foam reactor has mass transfer rates approximately 2‐4 times higher than those for conventional packed bed contactors.
Analysis of staged liquid surfactant membrane operations
Authors: Hatton T. A. , Wardius D. S.
Published: June 2004

Graphical and numerical procedures are presented for the design and analysis of cocurrent and countercurrent multistaged mixer‐settler units for liquid membrane extraction operations—these are based on the recently developed Advancing Front Model of Ho et al. (1982) and Hatton et al. (1983). The numerical results indicate that the extraction efficiency in a countercurrent cascade is only slightly improved over that for cocurrent operation. However, for any given stage, marked improvements in extraction efficiency are indicated if an external emulsion recycle over the mixer settler unit is used to ensure adequate holdup ratios in the mixer. Premixing of the emulsion feed and recycle streams will impair the extraction performance, however,
Theory and operational characteristics of the magnetic value for solids: Part I: Grate design
Authors: Jaraiz‐M. Eladio , Wang Yang , Zhang Guo‐Tai , Levenspiel Octave
Published: June 2004

The operational characteristics of the grate‐type MVS with screen were studied in detail. First, theory was developed to predict how the current needed to operate the valve was related to the valve geometry. Then experiments were made to see how bed height, screen aperture, grate spacing, the presence of nonmagnetic solids in the mixture all affected the current needed to operate the valve and on the mass flux of solids. The response time of the valve was also determined.

The experiments were compared with the predictions of the theory.
Tracer diffusion of carbon tetrachloride, S‐trioxane, 12‐crown‐4, 15‐crown‐5, 18‐crown‐6 in acetonitrile, benzene, and chlorobenzene
Authors: Yumet Eduardo , Chen Hang‐Chang , Chen Shaw‐Horng
Published: June 2004

Tracer diffusivities measured with the Taylor dispersion technique are reported for carbon tetrachloride, s‐trioxane, 12‐crown‐4, 15‐crown‐5, and 18‐crown‐6 in acetonitrile, benzene, and chlorobenzene across ranges of temperature. It is demonstrated that Stokes' law corrected with a microfriction factor successfully accounts for the diffusion behavior of even disk‐shaped crown ethers. Solute and solvent molecules being effectively spherical in the context of Stokes' law, the tracer diffusion of crown ethers is found to be satisfactorily represented by a rough‐hard‐sphere model for molecular diffusion. The degree of success increases with decreasing solvent polarity. The diffusion data for carbon tetrachloride are also used to extend the basis of the recently developed reduced equation for the tracer diffusion of nonelectrolytes in liquids over wide temperature ranges.
Radiotracer measurement of local deposition profiles, friction reentrainment, and impaction reentrainment in an electrostatic precipitator
Authors: Felder Richar D. M. , Arce‐Medina Enrique
Published: June 2004

A radiotracer‐based method of measuring local particle deposition profiles and reentrainment rates in an electrostatic precipitator has been developed and demonstrated. In tests performed on a pilot‐scale precipitator, differences in local deposition profiles obtained with and without a predeposited layer of dust on the plate were observed. Rates of reentrainment due to gas friction (aerodynamic drag) and to particle impaction on the plate were measured separately, and correlated with a semiepirical formula. Both friction and impaction reentrainment rates were found to vary as powers of the difference between the gas velocity and a minimum velocity required for reentrainment. The impaction reentrainment was found to vary as a power of the inlet dust loading.
Synthesis of optimal serial reactor structures for homogeneous reactions. Part I: Isothermal reactors
Authors: Chitra S. P. , Govind Rakesh
Published: June 2004

The reactor synthesis problem can simply be stated as follows: Given the reaction mechanism and kinetics, what is the optimum type and arrangement of the reactor(s) that would maximize product yield? Extensive studies for simple reaction systems (series, parallel, consecutive, etc.) using idealized plug flow and continuous stirred tank reactors have been presented in the literature. However, these studies fail to provide a systematic procedure for selecting the reactor(s) type and the rangement for complex reaction schemes.

In this paper simple rules with geometrical interpretations have been developed for synthesizing isothermal reactor configurations for complex reaction schemes. A computer program capable of specifying the optimum reactor structure from a generalized configuration has also been described.
Synthesis of optimal serial reactor structures for homogeneous reactions. Part II: Nonisothermal reactors
Authors: Chitra S. P. , Govind Rakesh
Published: June 2004

In Part I of this paper a methodology for the synthesis of optimal isothermal serial reactor structures for complex reactions was presented. This has been extended to nonisothermal systems in this paper.

A complete review of the relevant background has been included in this paper. A graphical procedure has been presented for Type II complex reactions and a computer program has been described for Type III complex reactions. Two cases for the Van de Vusse reaction scheme and a naphthalene oxidation example have been used to illustrate the synthesis approach.
Two‐component laser doppler velocimeter studies of submerged jets of dilute polymer solutions
Authors: Berman N. S. , Tan Hung
Published: June 2004

Axisymmetric submerged jets of dilute solutions of poly(ethylene oxide) and polyacrylamide of high molecular weight were studied using a two‐component laser Doppler velocimeter. At from 40–60 jet diameters from the source the small eddies are suppressed in the solutions studied. The behavior of the large eddies depends upon the elastic nature of the solution.
Improved dead‐time compensator controllers
Authors: Palmor Z. J. , Powers D. V.
Published: June 2004

It is shown that the conventional Smith dead‐time compensator can be modified in a fashion which leads to significant improvements in its regulatory capabilities for measurable disturbances or inputs. The proposed modification utilizes effectively the existing prediction capabilities of the conventional dead‐time compensator and eliminates the need for a separate feedforward controller in many circumstances under which it is normally employed. The modified dead‐time compensator possesses simultaneous feedforward and feedback actions. An additional tuning parameter which controls the degree of dead‐time cancellation allows the designer to shape the response according to requirements. Illustrative examples show the advantages of the modified scheme.
A heat transfer model for tubes immersed in gas fluidized beds
Authors: Chandran R. , Chen J. C.
Published: June 2004

A model for local heat transfer between a gas‐fluidzed bed and a submerged tube is proposed based on combined dense‐phase and lean‐phase transport. The heat transfer process during dense‐phase contact at the tube surface is modeled by packet renewal mechanism and the transfer process during lean‐phase contact by fluid convection mechanism. The model predictions show good agreement with experimental local and average heat transfer coefficient data for horizontal tubes.
Effect of temperature on crystallization and dissolution processes in a fluidized bed
Authors: Budz Jerzy , Karpiński P. H. , Nuruć Zbigniew
Published: June 2004

The influence of temperature on crystallization and dissolution kinetics in a fluidized bed was investigated. Values of activation energies were determined and a correlation between the rate constants of secondary nucleation and of the surface integration step of crystal growth was presented.
Fixed bed with catalyst deactivation: On‐line estimation of deactivation, control, and design
Authors: Hong Jan‐Chen , Lee Hong H.
Published: June 2004

On‐line measurements of temperature and concentration and the global rate for fresh catalyst can be used to estimate a measure of catalyst deactivation. A feedback control policy is obtained from this measure of catalyst deactivation for maintaining the reactor outlet conversion constant with time at a desired level. This feedback control enables one to maintain the desired conversion without any knowledge of deactivation kinetics. These results are applicable to any type of deactivation. The optimal control can easily be taken into consideration for reactor design. This combination of process design and control with due consideration of catalyst deactivation for both is shown to result in a substantial improvement of the reactor performance.
Thermal behavior of shell molybdena‐alumina catalysts
Authors: Duncombe P. R. , Weller S. W.
Published: June 2004

Heat treatment of “shell” molybdena‐alumina catalyst pellets results in macroscopic redistribution of the molybdena. Redistribution is minimal at 625°C but extensive at 750°C. After 6 hours at 750°, a sharp maximum is observed in the radial distribution. This is a result of opposing factors: radial diffusion inward from the initial shell, and preferential sintering of the alumina support in the shell region. Loss of molybdena by vaporization is not appreciable at 750°C but is serious at 875°C. A computer program has been developed to convert SEM‐EDAX (scanning electron microscopy energy‐dispersive analysis of x‐ray) data for unpolished pellet section to a quantitative, smooth profile of Mo concentration as a function of reduced radial position.
A novel radioactive particle tracking facility for measurement of solids motion in gas fluidized beds
Authors: Lin J. S. , Chen M. M. , Chao B. T.
Published: June 2004

Measurements of solids motion in a fluidized bed have been made in a computer‐aided particle tracking facility. A radioactive tracer particle, dynamically identical to the solid particles to be studied, was mixed with the solids in the bed. The gamma radiation from the tracer was continuously monitored by a large number of scintillation detectors located around the bed, providing information on the tracer's instantaneous location. Prudent use was made of the purposely introduced redundant distance data to achieve improved accuracy. The recognition of the existence of secondary emission due to the interaction of the primary radiation and other system materials and the subsequent devising of a scheme to mitigate its effect contribute much to the success. Results for a bed with a uniform air distributor plate show the existence of two counter‐rotating toroidal vortices whose relative sizes and strengths vary with the fluidizing velocity. Fluctuating motions at low frequencies ranging from 1.6 to 16 Hz have been observed at various locations in the bed.
Transport processes in narrow (capillary) channels
Authors: Acosta R. E. , Muller R. H. , Tobias C. W.
Published: June 2004

Rates of mass and momentum transport in narrow flow channels (gaps 0.2–0.5 mm) have been determined over a wide range of flow velocities, 220–7,700 cm/sec (Re 1,300 to 22,000). Existing correlations that apply to smooth channels of much larger hydraulic diameter were found to be valid for the narrow channels as well. However, in the turbulent regime the condition of hydraulic smoothness could be satisfied only when the walls were optically smooth. Transport rates to rough walls were also measured. The ratio of the mass transport to the momentum transport in the form ofjD/(f/2)—a measure of the improved mass transfer compared to the increased pressure drop—is given for the smooth and rough‐wall cells over the Re range studied.
Separation of adsorption and surface reaction rates: Dynamic studies in a catalytic slurry reactor
Authors: Ahn Bum‐Jong , McCoy B. J. , Smith J. M.
Published: June 2004

Dynamic experiments provide an opportunity to determine, separately, values of the adsorption and surface reaction rates occurring in a heterogeneous, catalytic reaction. In this method it is not necessary to assume that either adsorption, surface reaction, or desorption controls the rate, in contrast to the procedure used for analyzing steady state rate data.

The dynamic method is applied to experimental data for the oxidation of sulfur dioxide in a three‐phase aqueous‐slurry reactor using activated carbon as the catalyst. The results for 274.5 K show that both rates of reversible adsorption of oxygen and the subsequent, irreversible surface reaction affect the overall rate. Neither process can be considered to be controlling.

The data required for the analysis are the zero and first moments of the response in the effluent gas to a disturbance in the feed, the adsorption equilibrium constant for oxygen, and appropriate mass transfer coefficients.
Stability of a viscous compound fluid drop
Authors: Landman K. A.
Published: June 2004

A compound drop composed of viscous Newtonian core and shell fluids is disturbed away from its motionless spherical state. The physical characteristics of the drop determine the decay rates of any disturbance. This damping process is accompanied by out‐of‐phase displacements of the two interfaces. Special limiting cases of a thin and thick shell are investigated.
Enhanced paraxylene selectivity in a fixed‐bed reactor
Authors: Do D. D.
Published: June 2004

Simulations of enhanced paraxylene selectivity in a fixed‐bed reactor are presented in this paper. The primary reaction of alkylation of toluene with methanol and the secondary isomerization of the xylene products occurring inside zeolite catalysts ZSM‐5 are considered. The selectivity of paraxylene is enhanced due to the great difference between the effective diffusivities of xylene isomers. Such enhancement is found to decrease with toluene conversion along the reactor. Behaviors of intracrystal concentration profiles of three xylene isomers and toluene are also investigated.
Analysis of distributed pore closure in gas‐solid reactions
Authors: Bhatia S. K.
Published: June 2004

The recent random‐pore model (Bhatia and Perlmutter, 1980, 1981a; Gavalas, 1980) is further developed to account for distributed pore reaction in gas‐solid systems. Numerical solutions for the resulting equations are presented for the case when the reaction is accompanied by an increase in volume of the solid phase. It is shown that in such situations pore closure begins with the smaller pores and progresses to the larger ones. For certain pore size distributions seemingly incomplete conversion is found even when sufficient initial porosity exists so that complete pore closure cannot occur.
On the kinetics of ice crystallization in batch crystallizers
Authors: Shirai Yoshihito , Nakanishi Kazuhiro , Matsuno Ryuichi , Kamikubo Tadashi
Published: June 2004

The population balance equation with respect to ice crystal size in a batch crystallizer was solved, taking into account the crystal size dependency of growth rate, and the temperature change with crystal growth was calculated. Both the temperature change and the crystal size distribution obtained theoretically were in fairly good agreement with the experimental factors measured in pure water and in a 5% dextran solution.
An equation of state: Its development from argon data and its application to other substances
Authors: Wilsak R. A. , Thodos George
Published: June 2004

Using PVT measurements available in the literature for argon, the following equation of state involving the excess properties π and τ was developed:

where α, β, and ψ are density‐dependent functions. The results of this relationship for argon have been compared with those obtained using the BWR and the Stewart et al. (1981) equations of state. The present expression was applied in a generalized manner to nitrogen, methane, carbon dioxide, and ammonia. In addition, comparisons have been made using these four substances with three generalized relationships: a truncated virial, a modified Redlich‐Kwong, and the Hirschfelder‐Buehler‐McGee‐Sutton equations of state.
The effect of natural convection on ice crystal growth rates in salt solutions
Authors: Huang J. S. , Barduhn A. J.
Published: June 2004

Many measurements of ice growth rates in NaCl solutions have been made to determine the role of natural convection in the control of such growth rates. The results of two analyses are presented. In one, only thermal natural convection is treated for growth in pure water. The second treats the simultaneous effects of both mass and thermal natural convection in salt solutions. This second analysis correctly predicts higher ice growth rates in dilute salt solutions than in pure water.
Correlating diffusion coefficients in concentrated carbohydrate solutions
Authors: Oosting E. M. , Gray J. I. , Grulke E. A.
Published: June 2004

The diffusivities and the vapor‐liquid equilibrium coefficients of two organic components, 1‐hexanol and 2‐butanone, were measured in concentrated maltodextrin solutions using newly developed techniques. Accurate determination of these quantities required complete material balances of the two phases and control of the water concentration in the experimental cell. The diffusion coefficients of these solutes correlated with solution viscosity to the 1/2 power over a range of temperatures and concentrations. Other literature data for diffusion coefficients in concentrated malto‐dextrin and sugar solutions are shown to correlate with viscosity.
Char attrition during the batch fluidized bed combustion of a coal
Authors: Chirone R. , D'Amore M. , Massimilla L. , Mazza A.
Published: June 2004

Batchwise fluidized bed combustion of a coal has been carried out to investigate the generation of elutriable carbon fines by attrition of the burning char, Differences between the purely mechanical attrition and the combustion‐assisted attrition of the char have been outlined. The time required to “activate” the char surface as regards attrition explains certain features of carbon elutriation curves. Attrition rate constants determined from these curves are compared with those previously found by continuous fluidized combustion of the same coal.
Solid‐liquid mass transfer in packed beds with cocurrent gas‐liquid downflow
Authors: Rao V. G. , Drinkenburg A. A. H.
Published: June 2004

Local instantaneous solid‐liquid mass transfer coefficients were measured in two‐phase gas‐liquid downflow through packed columns for 3 × 3 mm and 6 × 6 mm cylinders. An electrochemical technique was used. Liquid flow rates from 3.0 to 26.6 kg/m2·s and gas flow rates from 0.07 to 1.16 kg/m2·s covered the gas‐continuous, ripple, and pulse flow regimes. Time‐averaged mass transfer coefficients in trickle flow and in pulse flow for the pulse proper and the base (outside the pulse) were found to increase with increasing gas and liquid rates. Correlations are presented in terms of liquid phase Reynolds numbers and in terms of Kolmogoroff numbers. The mass transfer coefficients in the pulse were found to correspond closely to the coefficients that would be attained in the dispersed bubble flow regime.
Cold flow mixing rates in confined, recirculating coaxial jets with angular secondary injection
Authors: Hedman P. O. , Leavitt D. R. , Sharp J. L.
Published: June 2004

The mixing of gases and particles in confined, coaxial jets with angular secondary steam injection into suddenly expanded mixing chambers was studied. The effects of secondary stream injection angle, mixing chamber diameter and length, primary jet solids loadings, particle size, and secondary stream velocity on particle and gas mixing rates were determined. Gas mixing was much faster than particle mixing. Angular secondary injection significantly increased the initial gas and particle mixing rates but had little effect on the overall length of duct needed for complete mixing. The effects on initial gas mixing rate of combined angular secondary injection and increased secondary velocity were additive.
Multiplicity in continuous MSMPR crystallizers. Part II: Temperature multiplicity in a cooling crystallizer
Authors: Tavare N. S. , Garside John , Akoglu Koksal
Published: June 2004

This paper demonstrates the application of the theory of temperature multiplicity to the continuous mixed‐suspension, mixed‐product removal (MSMPR) cooling crystallizer as described by the coupled solute and energy balances along with the associated population balance transformed into moment equations. Exact uniqueness and multiplicity criteria are developed. Applications to specific cases together with diagrams depicting the effects of the important variables on the regions of multiplicity and uniqueness are presented.
The effects of surfactants on the motion and transport mechanisms of a condensing droplet in a high reynolds number flow
Authors: Chang Tae‐Ho , Chung J. N.
Published: June 2004

The motion and transport mechanisms of a condensing droplet initially contaminated with insoluble monolayer surfactant material are examined through a theoretical approach. The surface tension gradient force induced by the surfactant and the shear stress from the relative motion between droplet and its ambient vapor are evaluated on the droplet surface as major forces affecting the internal motion of the droplet. The strength of the internal motion ranges from one order of magnitude smaller than the free stream velocity for slight surfactant contamination to almost a complete stop in motion for high surfactant concentration.
The influence of a grid‐generated turbulence on the development of chemical reactions
Authors: Bennani A. , Gence J. N. , Mathieu J.
Published: June 2004

The evolution of slow, irreversible, isothermal, second‐order chemical reactions between two nonpremixed species is experimentally studied in a field of quasiisotropic grid turbulence developing in a water tunnel. The experiments provide some basic data on the interaction between the turbulent mixing and the reaction, which tends to remove the mixed species.