bluuebunny/crossref_metadata_2025 huggingface dataset:
A group contribution molecular model of liquids and solutions
Authors: Nitta Tomoshige , Turek E. A. , Greenkorn R. A. , Chao K. C.
Published: June 2004

A 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

Measurements 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

A 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

Although 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

An 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

New 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

Particle 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

The 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

The 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

A 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

Analysis 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

A 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

A 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

The 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

Previous 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

Natural 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.
Discrete flow modeling: A general discrete time compartmental model
Authors: Chang Feg‐Wen , Fitzgerald Thomas J.
Published: June 2004

A general flow model is developed which is discrete both in time and space. The stirred‐tank network model (continuous time compartmental model) is summarized and compared with the discrete flow model. Efficient methods for model fitting are given and demonstrated with numerical examples.
Estimation of flows and temperatures in process networks
Authors: Stanley G. M. , Mah R. S. H.
Published: June 2004

It is shown that temperatures and flows in a process network can be estimated from a quasi steady state model and a discrete Kalman filter. The data needed for such an application are readily available in many operating plants, and the computational requirements are within the capabilities of available process computers.
System structures for process simulation
Authors: Evans Lawrence B. , Joseph Babu , Seider Warren D.
Published: June 2004

The 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

The 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.
Critical point criteria in legendre transform notation
Authors: Reid Robert C. , Beegle Bruce L.
Published: June 2004

Legendre transform theory is used to develop two general critical point criteria for a classical thermodynamic system. The problem of indeterminacy is discussed, as is the option of employing mole fractions (rather than mole numbers).
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

A 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

The 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

Process 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

One‐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

Several 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

This 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

The 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.
Char gasification in a countercurrent reactor
Authors: Amundson Neal R. , Arri Luis Ernesto
Published: June 2004

A model is developed for the countercurrent char gasifier of Lurgi form. Char particles are fed to the top and oxygen, inert, and steam in the bottom. The combustion zone is defined as the zone in which there is a nonzero molfraction of oxygen. In the gasification zone, the particles are assumed to be a lumped system in which the Johnson reaction kinetic expressions are assumed to be valid with the water gas shift reaction at equilibrium. All of the reactions between oxygen and carbon and water and carbon are assumed to take place in the combustion zone but with the carbon‐oxygen reaction predominating to form a shell progressive system within the particles. Radiation is taken into account, and parametric computations are made on temperatures, compositions, flow rates, and char reactivity. The maximum temperature is strongly influenced by radiation and its position is a sensitive function of the solid flow rate producing an ash layer at the bottom of varying thickness.
Synthesis of kinetic structure of reaction mixtures of irreversible first‐order reaction
Authors: Lee Hong H.
Published: June 2004

A synthesis method for the kinetically consistent structure of reaction mixtures is developed based on elementary structures of reaction mixtures and rate expressions for product lumps of nth order. Knowledge of product lumps and experimental kinetic data on each of the lumps are required for the synthesis of kinetic structure. Rate constants for all reaction paths and initial lumps from which all the product lumps originate can be determined.
Kinetic behavior of weak base anion exchangers
Authors: Hübner Pavel , Kadlec Vaclav , Dukla Čkd
Published: June 2004

In this work, twelve different weak base anion exchangers were studied as to their decrease of breakthrough capacity with increasing specific loading. From the curves, the rate coefficients were calculated and correlated with the values characterizing the ion exchanger. It was found that the sorption rate of acid increases with decreasing average molality of functional groups in the ion exchanger.
On singular policies in the optimal distribution of a bifunctional catalyst: Part I. Effect of reaction kinetics
Authors: Choi C. Y. , Perlmutter D. D.
Published: June 2004

Results are presented on the affects of kinetic changes on optimal, bifunctional, catalyst distribution policies for a consecutive two‐reaction sequence in a plug flow tubular reactor. Earlier results on singular control arising from reversible reactions are extended to include inhibition or activation. These may arise from the affects of any reactant or product on the rate or from a subsequent or preceding reaction in a sequence. The system equations are written in dimensionless form to provide efficient computations and to allow analytic interpretation of numerical results from previous studies.
An analysis of flow separation in hydrodynamic chromatography of polymer latexes
Authors: Silebi Cesar A. , McHugh Anthony J.
Published: June 2004

An analysis is presented for the flow separation process in hydrodynamic chromatography along with comparisons to experimental data. The flow separation model is based on calculations for the convected Brownian motion of colloidal particles in a capillary tube in the presence of a force field. The results indicate the role of the relevant experimental parameters in the separation process.
Solubilities of heavy hydrocarbons in compressed methane, ethane, and ethylene: Dew‐point temperatures for gas mixtures containing small and large molecules
Authors: Kaul Bal K. , Prausnitz John M.
Published: June 2004

Solubilities of heavy hydrocarbons in compressed gases were measured in the region 50° to 170°C for hexadecane, bicyclohexyl, diphenylmethane, and 1‐methyl naphthalene and in the region 165° to 272°C for eicosane and squalane. Measurements were made in the pressure region 9 to 80 atm. The solubility data were reduced to yield second virial cross coefficients B12. To interpret the B12 data, a square‐well potential was used; the characteristic size of the large molecule is given by the mean radius of gyration which takes into account the variety of molecular conformations. Calculated results give good agreement with new as well as previously published B12 data.

Illustrative calculations indicate how the results obtained here may be used to make dew‐point calculations in multicomponent systems containing both small and large molecules.
Kinetics of oxidation of sodium dithionite by flow thermal method
Authors: Singh D. K. , Sharma R. N. , Srivastava R. D.
Published: June 2004

The homogeneous kinetics and inhibition of sodium dithionite oxidation in an aqueous solution were studied by means of a flow thermal method. Results on the oxidation study of dithionite solutions at 30°C show that the reaction is first order with respect to dithionite and zero order with respect to oxygen. An activation energy of 17.5 kcal/g‐mole has been calculated for this reaction. The inhibiting effects of manganese chloride, manganese sulfate, and triethanolamine were inversely proportional to 0.8, 0.9, and 0.2 power, respectively.

A free radical chain mechanism has been proposed, and the rate expressions derived are in good agreement with the experimental data.
A modification of regular solution theory to incorporate an improved approximation for pair distribution functions in mixtures
Authors: Gonsalves Joseph B. , Leland Thomas W.
Published: June 2004

The radial distribution functions for pairs in a fluid mixture can be closely approximated from known data on pair distribution functions pure components evaluated at a mean density determined by a properly defined average of molecular interaction parameters in the mixtures. This approximation has been used to replace the assumption about structure in mixtures inherent in the traditional regular solution theory. The result is a modified regular solution theory which gives an improvement in predicting excess thermodynamic functions and activity coefficients in mixtures involving appreciable differences in molecular size and shape.
Backmixing in gas‐liquid reactors
Authors: Shah Y. T. , Stiegel G. J. , Sharma M. M.
Published: June 2004

This review evaluates the present state of the art on backmixing in gas‐liquid and gas‐liquid‐solid reactors. A brief outline of numerous techniques for measuring residence time distribution (RTD) of various phases in a multiphase reactor is presented. This is followed by a brief description of differential and stagewise models for characterizing backmixing from RTD measurements. Both simple (that is, single‐parameter axial dispersion model) and more complex (that is, two‐, three‐, or four‐parameter models) models are evaluated. Backmixing characteristics of various gas‐liquid columns such as trickle beds, spray columns, mechanically agitated columns, plate columns, fluidized bed columns, etc., are subsequently evaluated. The performance of a bubble column under various reaction conditions is analyzed. Criteria for the elimination of backmixing in packed‐bed reactors are presented, and the effect of backmixing on the multiple steady states in a gas‐liquid reactor is briefly reviewed. Finally, the scale‐up problems associated with gas‐liquid reactors with various degrees of backmixing and the recommendations for the future work in RTD and macromixing models are outlined.
Theory of draw resonance: Part II. Power‐law and maxwell fluids
Authors: Hyun Jae Chun
Published: June 2004

Employing the same kinematic wave theory used in the previous paper on Newtonian fluids (Part I), draw resonance in isothermal spinning is solved analytically for both power law and Maxwell fluids. The critical drawdown ratios at the onset of draw resonance are again found by equating twice the throughput wave residence time to the thread‐line residence time yielding the same results reported by others through numerical calculations (Pearson and Shah, 1974; Fisher and Denn, 1976), thus confirming the premise that draw resonance is the result of the propagation of throughput waves.
The design of gas sparged devices for viscous liquid systems
Authors: Bhavaraju S. M. , Russell T. W. F. , Blanch H. W.
Published: June 2004

Design procedures for gas sparged contractors for both low and high viscosity liquids were developed to predict overall kLa. Bubble size close to the orifice, for moderately high gas rates, was found to increase at a rate proportional to one third power of gas rate and one tenth power of liquid viscosity. Bubble breakup phenomenon was shown to be related to liquid turbulence in the vessel rather than gas turbulence in the orifice. Procedures were developed through a simple liquid circulation model to obtain a criterion for the onset of bubble breakup. Results indicate that intense liquid mixing and high interfacial area can be achieved in low viscosity liquids by gas sparging alone. In high viscosity fluids, bubble breakup was not observed. The liquid circulation model predicts laminar flow at these experimental conditions over the complete range of gas rates observed.
Cold flow mixing rate data for pulverized coal reactors
Authors: Memmott Vincent J. , Smoot L. Douglas
Published: June 2004

Mixing rates of particles and gases in confined, coaxial jets are reported for tests with conditions simulating those of pulverized coal gasification and combustion processes. Gas velocity, particle mass flux, and gas composition were measured at various radial and axial locations downstream of the primary jet exit plane. Effects of inlet velocity, density, injection angle, particle loading level, and particle size on the rates of mixing were determined. Increasing injection angle and secondary velocity significantly increased gas and particle mixing rates, while effects of other variables were much less significant. Dispersion of particles lagged that of the gas in all cases investigated.
Mass transfer on a single sieve plate column operated with periodic cycling
Authors: Duffy G. J. , Furzer I. A.
Published: June 2004

A single sieve plate column operated with periodic cycling was mathematically modeled using the assumption of zero weeping rate and plug flow of liquid during the liquid drain period. Zero weeping rates could only be obtained by introducing baffles to control fluid oscillations on the plate. Experimental measurements of the ratio of the slopes of the equilibrium and operating lines λ, the Murphree plate efficiency ε, the fraction of the liquid holdup transferred per cycle η, and the separation factor X on a computer controlled column provided the first reliable confirmation of the improvements in separating ability, predicted by the theory.
A rigorous method for calculating minimum reflux rates in distillation
Authors: Chien Henry H. Y.
Published: June 2004

A computer method has been developed to calculate the minimum reflux rate for a specified distillation separation. The method makes no unnecessary simplifying assumptions of the distillation process model. The limitation of the method is that it cannot solve problems in which the minimum reflux rate is determined by a point of tangent between the operating line and the equilibrium line on a McCabe‐Thiele diagram (see Figure 1).
Synthesis of heat exchanger networks: II. Evolutionary generation of networks with various criteria of optimality
Authors: Linnhoff Bodo , Flower John R.
Published: June 2004

An evolutionary method is presented for the synthesis of heat exchanger networks. Starting from feasible solutions which preferably exhibit maximum energy recovery,

The synthesis of such solutions has been discussed in Part I (see Linnhoff and Flower, 1978).

the method allows systematic promotion of desired design features such as low overall cost, suitability for starting‐up procedures, observation of safety constraints, etc. Seven examples based on standard literature problems are used to illustrate the method.
Dynamics and control of the activated sludge wastewater process
Authors: Attir Uri , Denn Morton M.
Published: June 2004

The dynamics of the activated sludge process are governed under certain conditions by interactions between the reactor and settler through sludge recycle. Settler underloading can lead to extremely sluggish system response, indicating that effective sludge height regulation is an important control objective. This objective may be in conflict with the need to maintain small variations in reactor solids concentration. An effective compromise can be achieved by using ratio control on both sludge recycle and settler underflow. This control policy does not require sludge storage.
Nucleation and growth rates of ammonium chloride in organic media: Development of an on‐line measurement technique
Authors: Shadman Farhang , Randolph Alan D.
Published: June 2004

Nucleation and growth rates of small ammonium chloride crystals precipitated from organic mother liquors were measured with an electronic particle counter using an on‐line measurement and data reduction technique. Current values for nucleation and growth rates could be obtained within a period of 3 min, thus permitting rapid scanning of variables affecting crystal size distribution. Population average sizes of 1 to 3μ were typically measured in these organic liquors. The average size of particles increased with increase in ammonium chloride solubility. Addition of surfactants (sodium dodecylbenzene sulfonate, sodium oleate) either had no effect on nucleation or inhibited growth and nucleation equally, thus did not change particle size. The average size of particles was slightly increased with addition of magnesium chloride.
A model for moving‐bed coal gasification reactors
Authors: Yoon Heeyoung , Wei James , Denn Morton M.
Published: June 2004

A steady state model of moving‐bed coal gasification reactors has been developed. Model predictions are in agreement with published commercial plant data for Lurgi pressurized gasification reactors and a pilot plant slagging gasifier. The dependence of reactor performance on operating variables has been studied for Illinois and Wyoming coals. For a given coal, maximum efficiency is determined by the coal‐to‐oxygen feed ratio. The location of the maximum temperature, which defines the combustion zone, is an important operating variable. Efficient operation of the dry ash reactor cannot be carried out below a critical feed gas temperature because of insufficient gasification and excessive carbon loss in the ash.
Electrification of particles by impact on inclined metal plates
Authors: Masuda Hiroaki , Iinoya Koichi
Published: June 2004

The electrification of particles falling onto metal surfaces was well correlated with the normal component of the impact velocity, showing that the electrification was mainly caused by the deformation of contact bodies. The current generated by the electrification at higher impact velocities was proportional to the velocity, while the current at lower velocities showed a different tendency. The elastic and plastic‐elastic collision theory including particle roundness was used to explain these experimental results. Further, the coefficient of restitution, which was related to the work done by normal impulse, was determined by means of the velocity at the elastic limit obtainable from electrification data.
Prediction of the sorptional equilibrium relationship for the drying of foodstuffs
Authors: Rotstein Enrique , Cornish Alan R. H.
Published: June 2004

After existing correlations were reviewed to predict the equilibrium of foodstuffs with moist air, it was found that they were not adequate. A new equilibrium expression is presented on the basis of equal chemical potentials in the external and internal phases. The resulting equation can be used over most of the range of moisture contents of sugar based foodstuffs including the high moisture region; it also provides simple analytical expressions for the partial derivatives of moisture content with respect to temperature and to water vapor activity.
Optimal determination of the vapor pressure critical exponent
Authors: Walton Clifford W. , Mullins Joseph C. , Holste James C. , Hall Kenneth R. , Eubank Philip T.
Published: June 2004

Correlations producing thermodynamic property tables employ the concepts of scaling with increasing frequency in the vapor‐liquid critical region. One of the important concepts is that the vapor pressure equation should provide infinite curvature and finite slope ψc at the critical point. The vapor pressure critical exponent θ describes the divergent curvature in a power law expression.

This paper provides an extensive study of θ. We have determined an optimal value of θ by two general approaches: a curve fit method (CFM) which employs least‐squares analyses, and a numerical derivative method (NDM). The CFM is interpolative but requires a vapor pressure equation, while the NDM is extrapolative but is independent of the vapor pressure equation.

The vapor pressure equations, which satisfy scaling concepts most closely, exhibit a very flat minima for the CFM. As a result, the values of θ which provide reasonable correlations vary over an appreciable range (depending upon the compound, form of the equation, and the temperature range). The NDM did not present any particular difficulties. Our overall weighted average for θ is 0.199 with a standard deviation of 0.052, while the overall numerical average was 0.225 with a standard deviation of 0.045; the final recommended value of θ is 0.22 ± 0.04.
An approximate theory of interfacial tensions of multicomponent systems: Applications to binary liquid‐vapor tensions
Authors: Winterfeld P. H. , Scriven L. E. , Davis H. T.
Published: June 2004

Formulas obtained by approximation of the rigorous expression for the interfacial tension of multicomponent, polyatomic fluids are shown to provide accurate and simple estimates of the composition dependence of the surface tension of nonaqueous, binary solutions at low vapor pressures. Similar formulas are recommended for multicomponent (that is, more than two components) solutions.
Hydrodesulfurization of dibenzothiophene catalyzed by sulfided CoO‐MoO3γ‐Al2O3: The reaction network
Authors: Houalla Marwan , Nag N. K. , Sapre A. V. , Broderick D. H. , Gates B. C.
Published: June 2004

Kinetics experiments have determined the reaction network in the hydrodesulfurization of dibenzothiophene catalyzed by sulfided CoO‐MoO3/γ‐Al2O3 at 573°K and 102 atm. The predominant reaction is a direct sulfur extrusion, giving biphenyl and hydrogen sulfide; the biphenyl is subsequently hydrogenated slowly to give cyclohexylbenzene and then bicyclohexyl. Dibenzothiophene also undergoes a primary hydrogenation reaction preceding sulfur removal, but it is about one thousand times slower than the sulfur extrusion reaction.
Combined forced and free convection in a reverse osmosis system
Authors: Chang C. Y. , Guin J. A.
Published: June 2004

The influence of combined forced and free convection on the performance of a reverse osmosis system in a horizontal circular pipe is examined. The free convective motion, which is superimposed upon the main axial flow, is caused by buoyancy forces arising from the buildup of a dense solute boundary layer near the membrane surface. The three‐dimensional convective diffusion problem is solved by dividing it into a perturbation part accounting for the buoyancy effects present for Ra ≠ 0 and a nonperturbation part for the intrinsic convective flow pattern present even when Ra = 0.

An approximate solution to the nonperturbation equations is obtained from the literature, and the perturbation equations are solved using a stream function‐vorticity scheme valid for high Schmidt numbers. The effects of rejection parameter, Rayleigh number, and pressure parameter on the Sherwood number and concentration polarization are studied. Correlations are developed for the asymptotic Sherwood number and the effective axial length at which free convection becomes significant. The numerical results are in reasonable agreement with limiting analytical solutions and with the experimental asymptotic Sherwood numbers measured by Derzansky and Gill (1974) and Hsieh et al. (1976).
Time resolution of rapid processes using numerical calculation and inversion of Laplace transforms
Authors: Hahn W. A. , Wendt J. O. L.
Published: June 2004

A method for the interpretation of data which results from a signal altered by a process of known weighting function was developed. The method is based on the numerical evaluation and inversion of the Laplace transform. For two different weighting functions, it is shown how narrow a signal can be interpreted accurately. The method is then applied to coal volatilization data.
Experimental evaluation of analytical and Smith predictors for distillation column control
Authors: Meyer C. B. G. , Wood R. K. , Seborg D. E.
Published: June 2004

Two time delay compensation techniques, the Smith predictor and the analytical predictor, are used for bottom composition control of a pilot scale methanol‐water distillation column. The closed‐loop performance of the two predictor schemes is compared to that for a proportional‐integral controller in experimental and simulation studies. The predictors resulted in improved control for both set point and feed flow disturbances.
Origin and size distribution of secondary nuclei
Authors: Garside John , Rusli I. T. , Larson M. A.
Published: June 2004

Microscopic observations and Coulter counter measurements of the secondary nuclei produced when a parent crystal of potash alum was contacted with a solid rod suggest that these nuclei are born by an attrition mechanism which appears to be dependent on the growth rate of the crystal. The nuclei can be up to 50 μm in size. The nuclei smaller than about 4 μm are relatively insensitive to supersaturation, whereas the number greater than about 4 μm is approximately linear in supersaturation.
Continuous phase mass transfer during formation of drops from jets
Authors: Skelland A. H. P. , Huang Y‐F.
Published: June 2004

This study enables the extension of a recent design procedure for perforated plate extraction columns to include operation under jetting conditions. Correlations of experimental data are given for jet length, jet contraction, drop size, and mass transfer rates in continuous phase controlled liquid‐liquid systems. Systems exhibiting very low mass transfer rates were used, and this gave significantly different results from those obtained earlier with moderate rates of mass transfer.
Safety and reliability synthesis of systems with control loops
Authors: Kumamoto Hiromitsu , Henley Ernest J.
Published: June 2004

A method of a reliability synthesis for a system with control loops is proposed by introducing a concept which we call a critical transition set. The set is an extended set of an exact failure mode and is important in that each occurrence of the system failure has to correspond to a mode in the set. This means that the system can be improved in such a way as to eliminate all the dominant modes in the set.

First, the system diagram is obtained by connecting outputs of components to the inputs of succeeding components. Time delays are introduced in the feedback loops to represent the internal system state (memory). Then, the components are modeled by decision tables. The critical transition set can be obtained easily by simple tabular manipulations once the system failure is defined. Finally, the system reliability and availability improvements are made based on the set.
Solution of material balances for flowsheets modelled with elementary modules: The unconstrained case
Authors: Sood Mohinder K. , Reklaitis G. V. , Woods J. M.
Published: June 2004

A study is made of the structure and properties of material balance simulation problems, and a technique is developed for their efficient solution. The method requires neither simultaneous solution of all balance equations nor iterative convergence methods. Instead, for each stream mixing point in the flow sheet, a vector balance equation is developed which contains as unknowns only mixer output streams. This unique set of vector equations is sequenced for solution by using precedence ordering and substitution techniques. It is shown that only as many vector equations need to be solved simultaneously as there are streams which would require iteration in the conventional sequential approach. Once the mixer output streams are calculated, the remaining intermediate process streams are evaluated directly with no further equation solving. Computational results are presented showing the efficiency of the method.
Enhancement of heat transfer and thermal homogenity with motionless mixers
Authors: Nauman E. B.
Published: June 2004

Motionless mixers are well suited to augment heat transfer and to provide a uniform thermal environment in laminar flow reactors. Heat transfer performance can be characterized with the Nusselt number, while the degree of thermal homogeneity can be characterized using the thermal time distribution which is the nonisothermal analogue of the residence time distribution. Theoretical results, calculations, and design strategies are presented for a variety of mixer types including flow inverters as well as the more common flow dividers. Two‐channel, partial flow inversion is an excellent, near optimal, strategy for cooling or other situations such as polymerizations which give elongated velocity profiles. For flattened velocity profiles, perfect mixing can sometimes give better results. In practice, however, partial inverters can be expected to outperform those motionless mixers which are primarily flow dividers.
A population balance approach to the modeling of solid phase reactions
Authors: Bhatia Suresh K. , Perlmutter D. D.
Published: June 2004

A population balance approach is used to model solid phase reactions in terms of nuclei of the product phase dispersed in the reactant matrix. A conversion‐time relationship is obtained by the solution of a set of moment equations derived from the population balance. Some previously known solutions for both homogeneous and heterogeneous nucleation are developed by this approach to demonstrate the relative ease of solution when compared with previously used integral techniques. A model for nucleus impingement at low conversions is formulated and applied to published data on the oxidation of cuprous iodide to illustrate the practical use of this technique. The classical Avrami model (Avrami, 1939, 1940, 1941) is modified to include the initial volume of a nucleus, and it is shown that insensitivities in the original model are removed by this improvement. The need for direct measurements of nucleation and growth rates is emphasized.