bluuebunny/crossref_metadata_2025_split huggingface dataset:
Activator effects on urease kinetics
Authors: Choi C. Y. , Perlmutter D. D. 
Published: June 2004

AbstractAn experimental study of the effects of amino acid additives on the rates of urease kinetics showed that the degree of enhancement is sensitive to the relative levels of additives and substrate, and that enhancement can turn to inhibition at especially low concentrations of either arginine, DL‐alanine, or glycine. Kinetic models developed to interpret these and prior literature data showed that all the data are consistent in the framework of the steady state model proposed but contradict the expectations that would follow from an equilibrium based treatment.
An analysis of carrier facilitated transport in heterogeneous media
Authors: Stroeve Pieter , Smith Kenneth A. , Colton Clark K. 
Published: June 2004

AbstractA theoretical model is developed for steady state diffusion in reactive heterogeneous media in which simultaneous reversible chemical reactions occur between diffusible carrier species and the transported species. The heterogeneous systems analyzed are those for which one phase is dispersed as uniform spheres in a second continuous phase, and either or both phases may be reactive. The results have a simple physical interpretation in terms of additivity of resistances. The theory is applied to oxygen diffusion in blood.
Vortex free downflow in vertical drains
Authors: McDuffie Norton G. 
Published: June 2004

AbstractPerformance of flush drains in gas‐liquid separators has been evaluated under conditions of variable gas flow and pressure, liquid height and flow rate, and drain diameter. For the two‐phase flow regime, liquid flow rate is found to be independent of vessel pressure or gas flow rate. Transition from weir control to orifice control of liquid flow rate occurs over the range of H/D ratios from 0.4 to 1.5. In this range, simple orifice equations do not apply. Revised design equations for use to determine minimum liquid height for maintenance of single‐phase downflow in gas‐liquid separators are presented.
The characterization of fixed beds of porous solids from pulse response
Authors: Bashi Haseeb , Gunn Donald 
Published: June 2004

AbstractThe response of a fixed bed of porous particles through which fluid flows to a pulse of tracer gas has been analyzed by a number of methods. It is found that analysis of the Fourier transformed and the Laplace transformed response curves for small values of the parameters of the integrals provides accurate estimates of intraparticle diffusivity and Peclet group for axial dispersion when additional information provided by the experiments is used to resolve interaction between the process coefficients in the dynamic response.
Degrees of anisotropy for fluid flow and diffusion (electrical conduction) through anisotropic porous media
Authors: Neale Graham 
Published: June 2004

AbstractThis work involves a quantitative comparison between diffusion (or electrical conduction) and fluid flow occurring in the principal directions of certain simple anisotropic porous media, namely, clusters of parallel circular (or elliptic) cylindrical fibers. The degrees to which the observed macroscopic properties, permeability, and effective diffusivity (electrical conductivity) depend upon the direction of flow are determined analytically. Systems of parallel fibers are shown to be considerably more anisotropic with respect to fluid flow than with respect to diffusion (or electrical conduction), this effect being very pronounced with flattish fibers. It would not appear that any general analogy exists between diffusion (electrical conduction) and fluid flow occurring within anisotropic porous media.
A group contribution molecular model of liquids and solutions
Authors: Nitta Tomoshige , Turek E. A. , Greenkorn R. A. , Chao K. C. 
Published: June 2004

AbstractA group contribution molecular model is developed for the thermodynamic properties of polar and nonpolar liquids and their solutions, including energy of vaporization, ρVT relations, excess properties, and activity coefficients. The model is based on the cell theory in which the repulsive forces of molecules are expressed with a modified cell partition function derived from the Carnahan‐Starling equation of state for hard spheres. The attractive forces are made up of group pair interaction contributions. Group and interaction properties have been determined for methyl, methylene, hydroxyl, and carbonyl. Extensive comparisons are made of predictions of the model with data for pure liquids and their solutions.
Influence of Schmidt number on the fluctuations of turbulent mass transfer to a wall
Authors: Shaw Dudley A. , Hanratty Thomas J. 
Published: June 2004

AbstractMeasurements are presented on the influence of Schmidt number on the frequency of the mass transfer fluctuations at a solid boundary. The shape of the spectral function is similar at all Schmidt numbers. A relation between the mass transfer fluctuations and the fluctuating velocity field can be obtained only at high frequencies. A comparison of the scale and the frequency of the mass transfer fluctuations and the velocity fluctuations suggests that the rate of mass transfer is controlled by convective motions in the flow oriented eddies described by a number of previous investigators. However, the concentration fluctuations caused by these convective motions are greatly dampened close to the wall by molecular diffusion. Thus the mass transfer fluctuations reflect only the scale and not the frequency of the convective motions in the flow oriented eddies.
Effect of partial segregation on conversion in continuous stirred‐tank reactors
Authors: Bhatt Bharat L. , Ziegler Edward N. 
Published: June 2004

AbstractA model is described which accounts for partial segregation in continuous stirred‐tank reactors by considering packets circulating within a completely micromixed continuous regime. The packets have a nonideal residence time and concentration distribution. Mass transport occurs between these packets and the continuous phase of uniform composition in proportion to their concentration gradients. Laplace transformed tracer responses establish the diffusion and mixing parameters. Over 90% of the system is segregated in unstirred aqueous solutions. Addition of polymer increases segregation by over 40% at a 100 rev/min stirrer speed.
Multicomponent liquid phase adsorption in fixed bed
Authors: Hsieh J. S. C. , Turian Raffi M. , Tien Chi 
Published: June 2004

AbstractAlthough multicomponent, liquid phase adsorption is often encountered in industrial application, most of the studies concerning fixed‐bed sorption processes have been dealt primarily with systems containing one adsorbable species. The present work provides a numerical solution to the fixed‐bed, multicomponent adsorption problem, taking into account both separately or in combination the effect of liquid and/or solid phase mass transfer resistance and of variation of the assumed governing adsorption isotherm. Numerical solutions of several example problems are presented and compared with results based on equilibrium theory and a simplified method developed by Cooney and co‐workers previously (1972).
Analysis of heat transfer for laminar power law pseudoplastic fluids in a tube with an arbitrary circumferential wall heat flux
Authors: Faghri Mohammad , Welty James R. 
Published: June 2004

AbstractAn analysis is performed to obtain an exact solution to the problem of thermal entry region heat transfer in a circular tube with an arbitrary circumferential wall heat flux for pseudoplastic fluids using the power law constitutive model. The solution is expanded in a power series form, with expansion coefficients and related constants obtained numerically. A simple result is presented for a cosine heat flux distribution around the periphery of the tube which illustrates the simultaneous influence of circumferential wall heat flux variation and non‐Newtonian fluid behavior on heat transfer.
Growth rate of an ice crystal in subcooled pure water
Authors: Kallungal Joshy P. , Barduhn Allen J. 
Published: June 2004

AbstractNew and extensive experimental data on the rate of growth of ice crystals in the a axis direction in quiescent and slow flowing subcooled pure water show conclusively that thermal natural convection is an important heat transfer mechanism controlling the growth rate. At zero and low forced velocities, steady growth is observed only when the crystals grow horizontally or upward. Steady downward growth does not occur in quiescent water. This is consistent with the physical properties of water and the phenomenon of thermal natural convection.Growth rates at high water flow rates vary as the square root of the forced velocity and the 3/2 power of the subcooling and follow the theory of Fernandez and Barduhn (1967) with the ice‐water interfacial energy set at 52 mJ/m2 (52 erg/cm2).
Phase distribution and residence time in a spouted bed
Authors: Suciu G. C. , Pǎtraşcu M. H. 
Published: June 2004

AbstractParticle movement in the core and in the annulus of a semicircular, vertical, spouted bed was examined by high‐speed tracer photography. Use of a functional analogy with a free jet establishes an equation correlating core air velocity and relative bed height. Dependence of bed void fraction and particle throughput vs. relative bed height shows good agreement with previous work. Particle mean retention time and air flow distribution in the annulus and the spout were obtained by calcualtional estimates.
Optimal catalyst distribution in a dual enzyme sequential system
Authors: Choi C. Y. , Perlmutter D. D. 
Published: June 2004

AbstractThe dual enzyme sequential reactions that decompose arginine to ammonia were investigated experimentally to determine appropriate rate equations and to test predictions of optimal distribution of the two enzymes (arginase and urease) immobilized in a packed‐bed reactor.The kinetics of this system were experimentally found to be of the kind that calls for a bang‐band control with a well‐defined switching point between the two immobilized enzyme catalysts. At low values of reactor residence time, the optimum switching point is shown to approach a limiting position which depends on the kinetic order of the second reaction. In the higher ranges of residence time, the switching point moves into the latter half of the reactor, but exceptions to this generalization are found when Michaelis‐Menten kinetics are applicable to both reactions. For the special circumstance where the two reactions are of zero and first order, respectively, the optimal distribution of the two catalysts is independent of the first rate constant. The experimental results are, in general, consistent with these expectations, and secondary deviations are discussed. A suboptimal policy alternative is also treated analytically and tested by experiment.
Hydrodesulfurization of gas oil, reaction rates in narrow boiling ranges fractions
Authors: Yitzhaki Dan , Aharoni Chaim 
Published: June 2004

AbstractThe hydrodesulfurization of gas oil is treated as a sum of parallel reactions taking place in narrow boiling range fractions. The component reactions are approximately first order for fractions with boiling ranges of 20°C and mid boiling points between 250° and 350°C. The experimental procedure involves desulfurization of the gas oil, fractionation of samples of feed and products at various residence times, and determination of sulfur concentration in the fractions. The effect of the particle size of the catalyst and of the viscosity of the oil on the reaction rate can be assessed from Thiele's equation.
On the surface diffusion of adsorbable gases through porous media
Authors: Ponzi Marta , Papa Jose , Rivarola Juan B. P. , Zgrablich Giorgio 
Published: June 2004

AbstractA model is proposed for the hopping mechanism of surface diffusing molecules, adsorbed on porous solids, which allows a simple calculation of the mean hopping distance as a function of surface coverage.Surface permeabilities calculated with this model are compared to new experimental data. A satisfactory agreement is obtained, and the values of the parameters involved turn out to be very reasonable.
A single‐pore model for gas‐solid noncatalytic reactions
Authors: Ramachandran P. A. , Smith J. M. 
Published: June 2004

AbstractAnalysis of single‐pore behavior in a porous pellet of reactant is used to develop a new model for predicting the conversion‐time relationship for gas‐solid noncatalytic reactions. The model accounts for the influence of pore diffusion, diffusion through the product layer which builds upon the pore walls, and surface reaction. By focusing attention on one pore, it is possible to include the effects of the changes in pore geometry that occur during reaction. Thus, both pore‐mouth clocure and uniform deposition of product throughout the pellet can be predicted by using appropriate values for the diffusional and physical properties of the reaction system. The key parameters of the model are the effective pore length and effective diffusivity in the product layer. Numerical values of these quantities can be approximated from measurements of the pore volume and surface are of the unreacted and reacted forms of the pellet, or they may be evaluated from a limited amount of conversion vs. time data. The use of the model for predicting conversion‐time curves is illustrated with available data for the reduction of nickel oxide pellets with carbon monoxide and for the reaction of sulfur dioxide with calcium carbonate.
Electrochemical extraction of copper from scrap steel
Authors: Chin Der‐Tau 
Published: June 2004

AbstractA packed‐bed electrochemical method is presented for the removal of copper from scrap steel. The method is based on the principle that at certain potentials, steel can be passivated in a suitable electrolyte, whereas copper dissolves anodically. A rotating hemispherical electrode was used to determine the polarization curves of copper and mild steel in various electrolytes. Extraction tests were carried out with an electrochemical cell composed of a cathodic carbon packed bed and an anodic bed packed with synthesized steel scrap.
Influence of fines dissolving on crystal size distribution in an MSMPR crystallizer
Authors: Juzaszek Pawel , Larson M. A. 
Published: June 2004

AbstractA laboratory mixed suspension mixed product removal (MSMPR) crystallizer was operated with and without continuous fines segregation and destruction. Predicted improvements in product‐crystal size were observed. By carefully representing the crystallizer flow pattern, quantitative agreement of crystal size distribution with prediction was achieved.
The prediction of hydrate formation in condensed systems
Authors: Ng Heng‐Joo , Robinson Donald B. 
Published: June 2004

AbstractThe experimental work reported here gives hydrate forming conditions in the water liquid‐hydrocarbon liquid‐hydrate region for five mixtures of methane and n‐butane. Data available in the literature were used to establish the parameters in a computer program for predicting hydrate forming conditions in condensed systems. The method is shown to be reliable for several systems of widely variable composition.
The effect of mass transfer on apparent ascorbic acid autoxidation kinetics
Authors: Davidson Robert S. , Grieger‐Block Richard A. 
Published: June 2004

AbstractPrevious studies of copper‐ion catalyzed ascorbic acid autoxidation have indicated zero‐order, first‐order, or Michaelis‐Menten dependence of rate on ascorbic acid or copper concentrations and first‐ or half‐order dependence on oxygen concentration. A simple mathematical model of gas‐liquid mass transfer with liquid phase reaction accounts for the various behaviors. Use of an experimental technique that eliminates the mass transfer step shows that the oxidation rate dependence is first order in copper, half order in oxygen, and Michaelis‐Menten in ascorbic acid concentrations.
Magnetothermal convection of oxygen gas in nonuniform magnetic fields
Authors: Clark Donald C. , Honeywell Wallace I. 
Published: June 2004

AbstractNatural convection heat transfer through oxygen gas may be significantly altered by the application of a nonuniform magnetic field. An additive contribution to the point velocity arises from the temperature dependence of the magnetic body force on the fluid. Theoretical predictions are in close agreements with experimental results.
System structures for process simulation
Authors: Evans Lawrence B. , Joseph Babu , Seider Warren D. 
Published: June 2004

AbstractThe plex data structure is proposed for use in an advanced computing system to model chemical processes. The plex is shown to permit increased modularity and flexibility over systems with dimensioned array structures. Two methods are suggested to create and operate upon the plex: the problem oriented language and the problem oriented calling programs. The concept of a routing plex is introduced as a means for specifying the path of calculations when building block routines call upon other routines and choices exist at each level.
Elongational flow behavior of viscoelastic liquids: Part II. Definition and measurement of apparent elongational viscosity
Authors: Pearson Glen , Middleman Stanley 
Published: June 2004

AbstractThe collapse of a single spherical gas bubble within a large body of fluid creates a uniaxial elongational flow in the surrounding fluid. Collapse under constant bubble pressure is observed to produce nearly constant strain rate kinematics. If the steady state stress at the bubble/fluid boundary could be measured, it would be possible to estimate the elongational viscosity of the fluid.Unfortunatley the experiment does not yield the desired stress data, except in the special case of the Newtonian fluid. We are led to define an apparent elongational viscosity, and for specific constitutive models we can evaluate the deviation between the apparent and true viscosity. The experimental and theoretical work indicate that the apparent elongational viscosity provides a good estimate of true elongational viscosity for the tow viscoelastic solutions studied so far.
Multivariable computer control of a butane hydrogenolysis reactor: Part III. On‐line linear quadratic stochastic control studies
Authors: Jutan Arthur , Wright J. D. , MacGregor J. F. 
Published: June 2004

AbstractA linear low‐order state space dynamic model for a catalytic butane hydrogenolysis reactor which has been fitted to reactor dynamic data is used to develop a multivariable linear quadratic feedback control algorithm for regulatory control of the reactor exit concentrations using temperature measurements only. Kalman filter theory is used to obtain state estimates for the system. The control algorithm developed is implemented on the pilot plant reactor in a series of DDC control studies. The controller is shown to perform very well and considerably better than a single loop PI controller with a feedback on the hot spot temperature. Performance is evaluated both under the normal stochastic disturbances in the system and under a severe deterministic load disturbance. Exit concentrations predicted by the model and used in the performance index are shown to compare very favorably with actual concentrations obtained from a process gas chromatograph.
Measurement of zeolitic diffusivities and equilibrium isotherms by chromatography
Authors: Shah Dhananjai B. , Ruthven Douglas M. 
Published: June 2004

AbstractThe chromatographic method has been used to study the sorption and diffusion of methane, ethane, propane, and cyclopropane in 5A molecular sieve. Both the equilibrium isotherms and the time constants for zeolitic diffusion, obtained from the chromatographic peaks, agree well with the values obtained previously by the gravimetric method, thus confirming the validity of the experimental technique. The results obtained in several previously reported chromatographic studies are reviewed, and it is shown that the apparent discrepancies between chromatographic and gravimetric data arise mainly from differences in the way in which the micropore diffusivity is defined. The relative advantages and disadvantages of the gravimetric and chromatographic methods are briefly considered.
Synthesis of heat exchange networks by mixed integer optimization
Authors: Kelahan R. C. , Gaddy J. L. 
Published: June 2004

AbstractProcess synthesis involves manipulation of the process arrangement, while studying the variables of each arrangement, to arrive at the optimal process. If each process arrangement is treated as a discrete variable, process synthesis becomes a mixed integer optimization problem. This paper examines the synthesis of heat exchanger networks using the adaptive random search procedure, which can be used to search continuous and discrete independent variables simultaneously. The means of handling the heat exchanger arrangement as a discrete variable is discussed, and the incorporation of various synthesis heuristics is presented. The results of synthesis of 2 × 2, 2 × 3, and 3 × 3 networks are presented and compared with other methods of synthesis.
The relationship between one‐dimensional and two‐dimensional separation processes
Authors: Wankat Phillip C. 
Published: June 2004

AbstractOne‐dimensional, time dependent separations are analogous to two‐dimensional, steady state separations, and the equations for the former can be transformed to the latter by the transform t → θ/w. This analogy is used to develop and provide the solutions for the two‐dimensional analogues of several variations of chromatography, parametric pumping, and pressure swing adsorption.
Generalized vapor pressure behavior of substances between their triple points and critical points
Authors: Gomez‐Nieto Mateo , Thodos George 
Published: June 2004

AbstractSeveral approaches are utilized for the estimation of the parameters associated with the normalized vapor pressure equation

to develop a capability for the prediction of vapor pressures consistent with the theorem of corresponding states. In this development, conditions and restrictions associated with the critical point and the normal boiling point were used to establish the vapor pressure parameters α, β, γ, and m. For the evaluation of these parameters, five different approaches were applied, and vapor pressures calculated with each of them were compared with corresponding experimental values presented in the literature. These comparisons were further examined using the results of four other well‐known vapor pressure equations available in the literature.This evaluation included 138 substances of all types and involved a total of 7,633 literature reported vapor pressure values to show that improved results are possible through the involvement of the generalized vapor pressure equation of this investigation.
Gas backmixing, solids movement, and bubble activities in large scale fluidized beds
Authors: Nguyen H. V. , Whitehead A. B. , Potter O. E. 
Published: June 2004

AbstractThis paper illustrates the interrelation between bubbles, solids movement, and gas backmixing in large fluidized beds by presenting experimental data obtained with a 1.22 m square bed. The results demonstrate a close relationship between gas backmixing, solids movement, and bubble coalesence, with the behavior altering markedly as bubble coalescence patterns change.
An analytical study of single particle char gasification
Authors: Arri Luis Ernesto , Amundson Neal R. 
Published: June 2004

AbstractThe gasification of a single particle of porous char surrounded by a boundary layer with oxygen and water vapor in its environment, taking into consideration the six main reactions along with the appropriate heat and mass transport effects, is considered using a shell‐progressive model. Much can be done analytically, and the numerical treatment of the model equations for a variety of parameters elucidates the structure of the problem which is much more complicated than anticipated, in spite of the fact that the model is a relatively simple one. The flame front of burning hydrogen and carbon monoxide can be at the core surface, in the ash layer, or in the boundary layer depending upon the ambient conditions of temperature and oxygen concentration.