bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractA 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

AbstractIn 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

AbstractThe 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

AbstractExperiments 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

AbstractMass 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

AbstractGraphical 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

AbstractThe 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

AbstractTracer 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

AbstractA 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

AbstractThe 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

AbstractIn 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

AbstractAxisymmetric 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

AbstractIt 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

AbstractA 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

AbstractThe 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

AbstractOn‐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

AbstractHeat 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

AbstractMeasurements 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

AbstractRates 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

AbstractDynamic 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

AbstractA 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

AbstractSimulations 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

AbstractThe 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

AbstractThe 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

AbstractUsing 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

AbstractMany 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

AbstractThe 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.