bluuebunny/crossref_metadata_2025 huggingface dataset:
Longitudinal and lateral dispersion in packed beds: Effect of column length and particle size distribution
Authors: Han Neung‐Won , Bhakta Jayendra , Carbonell R. G.
Published: June 2004

Longitudinal and lateral dispersion coefficients were measured at various axial positions in a packed bed in the Peclet number range from 102 to 104. Three different types of packings were used: uniform size particles, a narrow size distribution, and a wide size distribution. For the case of uniform particles the longitudinal dispersivities were found to be strong functions of position in the bed unless the dispersion length satisfies a constraint dependent on the value of the Peclet number. Generally, the larger the Peclet number, the larger the required length for constant axial dispersivities to be achieved. For the case of the wide size distribution, longitudinal dispersivities were larger than in the uniform particle case, and they required a longer dispersion length to achieve a constant value. This suggests a characteristic length for dispersion larger than the mean hydraulic radius. The lateral dispersivities were found to be insensitive to the distribution of particle sizes or location in the bed.
Chemical kinetics of carbon dioxide reactions with diethanolamine and diisopropanolamine in aqueous solutions
Authors: Savage D. W. , Kim C. J.
Published: June 2004

Differential rates of carbon dioxide absorption into aqueous monoethanolamine (MEA), diethanolamine (DEA), and diisopropanolamine (DIPA) were measured over a wide range of carbonation ratios. Analysis of the chemical‐reaction‐rate‐controlled data showed that the chemical reaction rates for all three aminoalcohols are first order with respect to the free‐amine concentration.
Carrier‐mediated transport across phospholipid‐composite membranes containing valinomycin
Authors: Sada Eizo , Katoh Shigeo , Terashima Masaaki , Takada Yoshihiro
Published: June 2004

Artificial membranes containing a phospholipid and valinomycin were prepared. Valinomycin in these membranes acts as an ionophore (a mobile carrier for potassium ions) at a temperature above the phase transition point of the phospholipid. Experimental data were explained by the theory of carrier‐mediated transport accompanying formation of a carrier‐ion pair complex.
A hierarchical decision procedure for process synthesis
Authors: Douglas J. M.
Published: June 2004

A new procedure for synthesizing process flow sheets and base‐case designs has been developed. The procedure is evolutionary in nature and proceeds through a hierarchy of decision levels, where more fine structure is added to the flow sheet at each decision level. Heuristics are used to obtain some of the structural elements of the flow sheet, and other heuristics are used to make some of the decisions required at the various decision levels. In many cases, no heuristics are available, so that process alternatives are generated. The analysis protion of the procedure has strong focus on the economic tradeoffs that are associated with the significant design variables.
A Simple Synthesis Method Based on Utility Bounding for Heat‐Integrated Distillation Sequences
Authors: Andrecovich M. J. , Westerberg A. W.
Published: June 2004

In this paper a new method is presented which will enable engineers to select better heat‐integrated distillation systems quickly and easily. The key to this method is making the assumption that QΔT, the product of the condenser or reboiler duty and the temperature difference between the reboiler and condenser, is constant for a single distillation task over a wide range of pressures. Using this assumption and the principles of multieffect distillation, a lower bound on the utility use for single distillation tasks and for distillation sequences is readily calculated for designs involving simple two‐product columns that may not be multieffected. This paper also describes methods which can be used to synthesize distillation systems which approach these bounds. Finally, an algorithm is presented which develops the least cost distillation system for separating a multicomponent feed. The methods in this paper are illustrated with a five‐component example problem.
High‐temperature mutual solubilities of hydrocarbons and water. Part II: Ethylbenzene, ethylcyclohexane, and n‐octane
Authors: Heidman J. L. , Tsonopoulos C. , Brady C. J. , Wilson G. M.
Published: June 2004

In Part I (Tsonopoulos and Wilson, 1983), the mutual solubilities of three C6 hydrocarbons (benzene, cyclohexane, n‐hexane) and water were experimentally investigated and, together with critically selected literature data, were correlated up to the three‐phase critical end point. The present paper extends this analysis to the mutual solubilities of three C8 hydrocarbons (ethylbenzene, ethylcyclohexane, n‐octane) and water, which have been measured at the three‐phase equilibrium pressure up to the critical temperatures (568, 561 and 539 K, respectively). A thermodynamic analysis of these new measurements and of available literature data has been performed up to the three‐phase critical end point. Information is also provided on vapor‐phase equilibrium compositions. The solubility of hydrocarbons in water has been used to calculate Henry's constants, while the solubility and volatility of water in hydrocarbons has been successfully correlated with several modifications of the Redlich‐Kwong equation of state.
Numerical simulation of a PSA system. Part I: Isothermal trace component system with linear equilibrium and finite mass transfer resistance
Authors: Raghavan N. S. , Hassan M. M. , Ruthven D. M.
Published: June 2004

A numerical simulation of a pressure swing adsorption process is presented for a system in which a small concentration of an adsorbable component is separated from an inert carrier. Linear equilibrium and a linear rate expression are assumed. The model equations were solved by orthogonal collocation and by finite difference methods with consistent results. The theory is shown to provide a good representation of the experimental data of Mitchell and Shendalman (1973) for the system CO2‐He‐silica gel.
An NRTL model for representation and prediction of deviation from ideality in electrolyte solutions compared to the models of Chen (1982) and Pitzer (1973)
Authors: Ball F. X. , Fürst W. , Renon H.
Published: June 2004

A new method of representation of electrolyte solution nonideality is derived, on the basis of similar assumptions, from a model applied by Cruz and Renon (1978) to binary electrolyte solutions. In order to test the validity of the model for representation of strong electrolyte properties, parameters were fitted to osmotic coefficient data for single, completely dissociated salts in aqueous solutions and were used to calculate osmotic coefficients of mixed aqueous electrolytes. Results are compared with those given by Chen's local composition model (Chen et al., 1982; Aspen, 1983) and Pitzer's truncated model (Pitzer, 1973, 1979; Pitzer and Mayorga, 1973; Pitzer and Kim, 1974), the same number of adjustable parameters being used in each case.

The average standard deviations for single electrolytes are within 1% in the case of 1–1 salts for the three models, and within 2% in the other cases, except for Chen's model (5%). As for predicted results, both local‐composition models yield standard deviations of less than 2%, while the accuracy given by the Pitzer model is better than 1.5%.
High performance displacement chromatography: Calculation and experimental verification of zone development
Authors: Frenz John , Horváth Csaba
Published: June 2004

Effluent concentration profiles from high performance displacement chromatography were calculated by using the theory of equilibrium chromatography of Helfferich and Klein (1970). The close agreement between predictions of the theory neglecting mass transfer resistances and experimental results demonstrates that conditions close to ideal chromatography are attainable in HPLC. Individual adsorption isotherms, as measured by frontal development, closely followed Langmuirian behavior.
Synthesis of control structures by singular value analysis: Dynamic measures of sensitivity and interaction
Authors: Lau Henry , Alvarez Jesús , Jensen K. F.
Published: June 2004

A strategy for synthesizing regulatory control structures is developed within the framework provided by singular value decomposition (SVD). Quantitative measures of interaction and sensitivity for the nodes, as well as for the entire system, are established with this method. The approach enables analysis of the control struture over a range of frequencies which are of practical importance for a particular processing unit, thus insuring that both static and dynamic effects are encompassed. In addition, this method allows the designer to identify the modeling aspects which are important in determining the performance of the synthesized control structures. A series of examples, presented in order of increasing complexity, demonstrate the usefulness and versatility of this procedure. The technique is implemented as an interactive computer package.
A nonequilibrium stage model of multicomponent separation processes. Part I: Model description and method of solution
Authors: Krishnamurthy R. , Taylor R.
Published: June 2004

A nonequilibrium stage model is developed for the simulation of countercurrent multicomponent separation processes. A feature of the model is that the component material and energy balance relations for each phase together with mass and energy transfer rate equations and equilibrium equations for the phase interface are solved to find the actual separation directly. Computations of stage efficiencies are entirely avoided. A procedure for solving the model equations simultaneously using Newton's method is outlined.
The separation of electrolytes by a “solventing‐out” process
Authors: Alfassi Z. B.
Published: June 2004

The analytic expression found before for the precipitated function of an electrolyte as a function of the added volume of a miscle organic solvent (MOS) to a saturated aqueous solution was used to discuss the required conditions for separation of two electrolytes.
Partial molar excess properties, null spaces, and a new update for the hybrid method of chemical process design
Authors: Lucia Angelo
Published: June 2004

A new thermodynamically consistent quasi‐Newton formula is proposed for building iterative representations of the approximated part of the Jacobian matrix in the hybrid method of chemical process design. This update exploits the fact that the excess enthalpy and activity coefficient functions are homogeneous functions of degree zero in mole numbers which, in turn, gives rise to a natural null space for the approximated part of the Jacobian matrix that is defined by the component molal flow rates. The new formula builds iterative approximated parts that satisfy this null space constraint in addition to the usual overall secant condition and the desired sparsity constraints.

The new quasi‐Newton formula is derived using the variational calculus approach first for the nonsparse case. This solution is then extended to the sparse case.

The new updating formula, which is applicable to any chemical process design problem that involves nonideal phase equilibria and/or enthalpy of mixing considerations, is compared to the modified Schubert update in the context of the hybrid method. It is also compared to an implementation of Newton's method in which the approximated part of the Jacobian matrix is calculated by finite differences. Using an adiabatic single stage flash problem for a binary mixture with strongly nonideal liquid phase behavior, it is shown that the new updating formula compares favorably with finite differencing and can result in solutions to problems for which the original hybrid method fails.
Longitudinal and lateral thermal dispersion in packed beds. Part II: Comparison between theory and experiment
Authors: Levec J. , Carbonell R. G.
Published: June 2004

The thermal response of a packed bed subject to step changes in fluid temperature was measured in the Peclet number range from 10 to 103. Fluid temperature and particle temperatures were measured independently at six different axial locations in the bed as a function of time. From the temperature breakthrough curves we were able to calculate the spatial separation between the fluid and solid temperature fronts. The measured values were higher by a factor of 2 to 3 than those predicted by traditional heat transfer models. Longitudinal effective thermal conductivities were also computed and compared to theoretical predictions. The new heat transfer model developed in a previous paper is able to account for these differences between experimental results and the predictions of the dispersionconcentric and continuous solid phase models used by previous investigators. Steady‐state experiments were used to measure lateral effective thermal conductivities. A temperature gradient was imposed at the top of the bed perpendicular to the flow direction and its spread was measured at different axial locations in the Peclet number range from 10 to 103. The predicted lateral effective thermal conductivities calculated using mass transfer data to estimate the hydrodynamic dispersion effect were significantly lower than the measured values. This is possibly due to the influence of viscosity and density gradients in the flow field in the packed bed.
An index for operational flexibility in chemical process design. Part I: Formulation and theory
Authors: Swaney R. E. , Grossmann I. E.
Published: June 2004

One of the key components of chemical plant operability is flexibility—the ability to operate over a range of conditions while satisfying performance specifications. A general framework for analyzing flexibility in chemical process design is presented in this paper. A quantitative index is proposed which measures the size of the parameter space over which feasible steady‐state operation of the plant can be attained by proper adjustment of the control variables. The mathematical formulation of this index and a detailed study of its properties are presented. Application of the flexibility in design is illustrated with an example.
An index for operational flexibility in chemical process design. Part II: Computational algorithms
Authors: Swaney R. E. , Grossmann I. E.
Published: June 2004

Procedures for the numerical computation of an index for operational flexibility in chemical processes are considered. Two types of algorithms are proposed which rely on the assumption that critical points for feasible operation lie at vertices or extreme values of the uncertain parameters. The first algorithm is a direct search procedure that features a heuristic variant to avoid exhaustive enumeration of all vertices. The second algorithm employs an implicit enumeration scheme based on a lower bound for monotonic constraints. These algorithms are applied to several example problems to demonstrate both the use of the flexibility index in process design and the computational efficiency of the algorithms.
A dynamic study of CO oxidation on supported platinum
Authors: Barshad Yoav , Gulari Erdogan
Published: June 2004

Catalytic oxidation of CO on alumina‐supported platinum was studied in a tubular isothermal reactor with applied concentration transients. A completely automated reactor system capable of switching frequencies as high as 0.2 Hz was constructed.

Concentration cycling resulted in reaction rates that were much higher than the maximum rate achievable at steady‐state operation. Mapping of the time‐averaged carbon dioxide production rate in the time‐period duty‐fraction plane, resulted in a unique global maximum. We find that the maximum in rate occurs when the switching times are comparable to the characteristic time of the surface reaction. Results of our experiments also rule out significant contribution from the Eley‐Rideal mechanism at the temperature range of this work (below 120°C).
On‐line optimizing control of a nonadiabatic fixed bed reactor
Authors: Lee K. S. , Lee Won‐Kyoo
Published: June 2004

A scheme of on‐line optimizing control is presented for a nonadiabatic fixed bed reactor which experiences a highly exothermic reaction. The control scheme has been devised to perform adaptive control of bed temperature and on‐line steady state optimization simultaneously.

Experiments were conducted with a pilot scale fixed bed reactor where partial oxidation of n‐butane to maleic anhydride occurs. The reactor system was interfaced with a microcomputer for real‐time control and optimization. With an objective function consisting of a net profit by producing maleic anhydride plus a penalty term on high bed temperature, it was clearly shown that the reaction conditions were driven to the expected optimum region.
Simple, analytical criteria for the sequencing of distillation columns
Authors: Malone M. F. , Glinos K. , Marquez F. E. , Douglas J. M.
Published: June 2004

A quantitative criterion for the selection of simple distillation sequences is derived for ideal mixtures. A simple cost model, along with a short‐cut solution of Underwood's equations, gives an analytical form for the total vapor rate, which is the key design variable. The results for column sequencing that are based on the analytical criterion agree well with more exact solutions, but they indicate that in numerous situations the commonly accepted heuristics are incorrect.
Solid‐solid and gas‐gas mixing properties of a new two‐impinging‐streams mixer
Authors: Tamir Abraham , Luzzatto Kfir
Published: June 2004

A new device for solid‐solid and gas‐gas continuous mixing, based on the impingement of two streams, was developed and successfully tested. It was found that in comparison to other available solid‐solid pneumatic mixers, such as the fluidized bed, spouted bed, air mixer, and mixing silo, the new device is very convenient and easy to operate and more energy‐efficient. This is also true for gas‐gas mixing when compared with a fluidized bed. A model for the gas phase behavior in the mixing of two gases was successfully tested, which supplements the picture of the solid particles behavior predicted from a model previously derived by the authors.
Some details of developing slugs in horizontal two‐phase flow
Authors: Kordyban Eugene
Published: June 2004

A photographic study has been carried out to uncover the details of development of slugs in horizontal two‐phase flow. Based on the observations, it is proposed that the slugs originate as a consequence of local Kelvin‐Helmholtz instability at the wave crest, rather than the instability of the whole wave. The findings are in reasonable agreement with published results on the transition to slug flow.
Thermal resistance models of packed‐bed effective heat transfer parameters
Authors: Dixon A. G.
Published: June 2004

Simple thermal resistance models of packed‐bed heat transfer can be used to derive predictive formulas for the effective axial and radial thermal conductivities and apparent wall heat transfer coefficient. In particular, the behavior of the heat transfer parameters over the entire range of Reynolds number can be explained by considering the two asymptotic cases of low Re (solid phase dominant) and high Re (fluid phase dominant).
Density of an equimolar mixture of ethane and methyl chloride
Authors: Eubank P. T. , Kreglewski Aleksander , Hall K. R. , Holste J. C. , Mansoorian Hamazasm
Published: June 2004

We have measured the density of an equimolar gas mixture of C2H6–CH3Cl between 323.15 and 473.15 K at pressures to 14.0 MPa. Interaction second virial coefficients and dew‐point pressures are extracted from the measurements. Intermolecular force constants for the Lennard‐Jones and Stockmayer models are determined optimally for like and unlike pair interactions. Recent methods of prediction for second virial coefficients, both pure and interaction, are tested against experiment.
Dynamic modeling of emulsion polymerization reactors
Authors: Penlidis A. , MacGregor J. F. , Hamielec A. E.
Published: June 2004

This paper is a survey of recent published works on the dynamic and steady state modeling of emulsion homo‐ and copolymerization in batch, semicontinuous, and continuous latex reactors. Contributions to our understanding of diffusion‐controlled termination and propagation reactions, molecular weight, long chain branching and crosslinking development, polymer particle nucleation, and of the dynamics of continuous emulsion polymerization are critically reviewed.
The diffusivity of potassium chloride and sodium chloride in concentrated, saturated, and supersaturated aqueous solutions
Authors: Chang Y. C. , Myerson A. S.
Published: June 2004

The diffusion coefficients of potassium chloride and sodium chloride were measured in concentrated, saturated, and supersaturated solutions at 25°C employing Gouy interferometry. The results indicate a maximum in the diffusivity vs. concentration curve near saturation followed by a rapid decline in diffusivity toward zero with increasing concentration in the supersaturated region. This behavior supports the idea that the diffusion coefficient approaches zero at the spinodal concentration. The data were successfully correlated by modifying an empirical activity coefficient equation (Robinson and Stokes, 1955) to account for molecular cluster effects and employing the calculated activity coefficients along with a predictive equation for diffusivity in electrolytes (Robinson and Stokes, 1955).
Interfacial drag and film height for vertical annular flow
Authors: Asali J. C. , Hanratty T. J. , Andreussi Paolo
Published: June 2004

New measurements are presented for film height and pressure drop for vertical gas‐liquid annular flows. Improved methods for predicting the film height and interfacial friction factor are developed for situations in which the liquid film flow rate is known.
Rapid hydropyrolysis of softening coal particles—A modeling study. Part I: Model formulation and parameter values
Authors: Schaub Georg , Peters W. A. , Howard J. B.
Published: June 2004

A mathematical model is developed for rapid hydropyrolysis of softening coal particles. It is aimed to represent previously measured effects of pressure and particle size on product yields. The model includes a global chemical reaction scheme combined with diffusional transport of hydrogen dependent on the transient physical properties of the coal. Model predictions are compared with experimental data in a companion paper.
Catalysis and synergism in the reduction smelting of lead sulfide with carbon and lime
Authors: Rao Y. K. , El‐Rahaiby S. K.
Published: June 2004

The catalyzed direct reduction of lead sulfide with carbon and lime was investigated at several temperatures and under two different inert gas atmospheres. The catalyzed reduction kinetics were determined both with a nitrogen atmosphere and a helium‐rich helium‐nitrogen atmosphere. The reduction kinetics under the latter were decidedly superior to those under the former. The differences were interpreted in terms of faster diffusion rates in a helium medium and synergistic effects. The catalyst used was a ternay eutectic mixture (K, Li, Na)2CO3, which amounted to 2.5 wt. % of the PbS:4CaO:4C reaction mixture.
The role of zeolite pore structure during deactivation by coking
Authors: McLaughlin K. W. , Anthony R. G.
Published: June 2004

Residues accumulating within the cavities of a small‐pore zeolite, isolated by extraction, are composed of a series of aromatics up to a distinct cutoff at pyrene. Similar analysis of partiall‐regenerated catalyst reveal pathways by which residue oxidation can occur and pathways by which these residues can participate during methanol decomposition.
Effects of surface viscosities on the stability of a draining plane parallel liquid film as a small bubble approaches a liquid‐gas interface
Authors: Hahn P.‐S. , Slattery J. C.
Published: June 2004

When a small bubble is driven through a liquid phase to a liquid‐gas interface, a thin liquid film forms between them and drains until an instability forms and coalescence occurs. Following Lin and Slattery (1982b), Chen et al. (1984) and Hahn et al. (1985) analyzed this process, neglecting the effects of electrostatic forces and of the surface viscosities. Here we extend their theory to include the effects of the surface viscosities. We employ a modification of the development by Barber and Hartland (1976; Flumerfelt et al., 1982) for a draining film bounded by parallel planes.

For a large intermediate range of the surface viscosities, the coalescence time is a strong function of these parameters. Inclusion of the surface viscosities acts to moderate or even reverse trends previously established for the dependence of the coalescence time on the bubble radius, the viscosity of the film liquid, the interfacial tension, the strength of the London‐van der Waals forces, and the density difference between the two phases.
Stochastic modeling of a fluidized‐bed reactor
Authors: Too J. R. , Fox R. O. , Fan L. T. , Nassar R.
Published: June 2004

In this work dispersive mixing and chemical reactions are treated simultaneously by resorting to the theory of stochastic processes. A fluidized‐bed reactor is modeled by discretizing it into ideally stirred tanks of various sizes corresponding to bubble, cloud, and emulsion phases. All parameters in the model are correlated with known or experimentally obtainable quantities. Examples using a complex chemical reaction are given to demonstrate the applicability of the approach.
Surface phenomena and mass transfer interactions in liquid‐liquid systems
Authors: Thornton J. D. , Anderson T. J. , Javed K. H. , Achwal S. K.
Published: June 2004

The surface dynamics of pendant aqueous droplets forming at a submerged nozzle in an immiscible organic solvent have been studied using a novel laser‐activated photochromic tracer technique. This enabled a small element of surface to be labeled so that its subsequent history could be recorded photographically.

Results for aqueous droplets forming in toluene in the absence of any mass transfer indicated only a slow interfacial circulation from the front to the rear, and there was no indication of any surface renewal as a result of hydrodynamic flow even at nozzle Reynolds numbers as high as 300. By contrast, the introduction of any one of a number of organic solutes into the toluene phase led to sporadic Marangoni‐type interfacial disturbances, which in turn resulted in rapid replacement of elements of the droplet surface. It is proposed that renewal of the droplet surface is dependent on solute diffusion in the present instance and that the processes of surface renewal and mass transfer are likely to be interactive.
Continuous thermodynamics of multicomponent systems
Authors: Kehlen Horst , Rätzsch M. T. , Bergmann Joachim
Published: June 2004

Based on a continuous distribution function instead of the mole fractions of individual components, a consistent building of continuous thermodynamics is presented. It may be favorably used in all cases where there are a large number of very similar chemical species such as in polymers, in heavy petroleum fractions, or in coal‐derived liquids.
Molecular theory of transport in fluid microstructures: Diffusion in interfaces and thin films
Authors: Adolf D. , Tirrell M. , Davis H. T.
Published: June 2004

Gradient theory of equilibrium fluid microstructures is extended to nonequilibrium isothermal processes. The theory is applied to steady diffusion across liquid‐liquid interfaces. It is shown that local equilibrium across a fluid‐fluid interface is maintained even in the presence of very high diffusion fluxes and that the concept of an interface acting as an applied potential energy for a diffusing species is of limited utility. The theory is suited for practical, semiempirical calculations of structure, stress, and isothermal transport in systems containing interfaces.
Performance studies of the measurement test for detection of gross errors in process data
Authors: Iordache C. , Mah R. S. H. , Tamhane A. C.
Published: June 2004

The measurement test proposed by Mah and Tamhane (1982) allows the gross error associated with a measurement to be directly identified without a separate procedure. In this paper a comprehensive evaluation of this test was carried out based on two different definitions of its power. The influence of constraints, network configuration, position of measurement, magnitudes of gross error and standard deviations, number of measurements, and other factors were summarized as rules and guidelines for the application of this test. The simulation procedure developed in this investigation may be used to design a gross error detection scheme for any specific application.
Representation of deviation from ideality in concentrated aqueous solutions of electrolytes using a mean spherical approximation molecular model
Authors: Ball Francois‐Xavier , Planche Henri , Fürst Walter , Renon Henri
Published: June 2004

A semiempirical expression for the Helmholtz energy of mixed electrolyte solutions in solvents mixtures is obtained from the solution of the mean spherical approximation given by Planche and Renon (1981) for a nonprimitive model of interactions. A consistent set of analytical equations for the related thermodynamic properties was further derived and used to represent osmotic coefficient data of strong aqueous electrolytes at 25°C. Data correlation was performed on more than 80 systems up to a 6 M molality using generally one adjustable parameter for each single electrolyte; from these parameters the properties of mixtures can be calculated in a predictive manner without additional parameters.
Hydrodynamic simulation of periodic cycled plate columns
Authors: Thompson M. F. , Furzer I. A.
Published: June 2004

A mathematical model of the hydrodynamic processes occurring in a periodic cycled plate column is developed and experimentally confirmed. The model is applied to the prediction of the holdup distribution and the investigation of hydrodynamic problems. An effective manifold arrangement is proposed to minimize the uneven liquid draining encountered in previous experimental studies.
Absolute rates of the carbon‐carbon dioxide reaction
Authors: Yang K. L. , Yang R. T.
Published: June 2004

The etch‐decoration transmission electron microscopy technique was used to measure the turnover frequencies of the C‐CO2 reaction in the temperature range 600–900°C. The absolute rate constants of the elementary rate steps were determined, and were in reasonably good agreement with statistical theories. The rates on monolayer steps of graphite were higher than those on multilayer steps by approximately four orders of magnitude at 800°C, because the CO bond in the reaction intermediate is stronger by about 9 kcal/mol on the monolayer steps. The rates of vacancy formation in the lattice were also determined. The vacancies are formed by atomic oxygen dissociated from CO2.
A theory for the most stable variable viscosity profile in graded mobility displacement processes
Authors: Gorell S. B. , Homsy G. M.
Published: June 2004

The stability of the displacement of a viscous fluid in a porous medium by a less viscous fluid containing an additive is considered. For the case in which the total amount of injected additive is fixed, a theory has been formulated to find the graded mobility profile which minimizes the instability due to an adverse mobility ratio. The result is a constrained nonlinear eigenvalue problem in which the mobility ratio of the fluids, α, and the total dimensionless amount of additive,N, appear as parameters. Estimates showNis typically large for practical situations. An asymptotic solution for largeNis developed which shows that the optimal mobility profile is always an exponential curve at leading order. It is shown that although the optimal mobility profile is nearly exponential, the optimal concentration profile is not necesarily so, contrary to previous suggestions in the literature. Furthermore, it is shown that, unlike the case of a mobility jump, a graded mobility process under optimal conditions has amplifications independent of displacement velocity. We also discuss a possibile stabilization mechanism due to the very long wavelength disturbances which occur under optimal conditions.
Tracer diffusion of aromatic hydrocarbons in liquid cyclohexane up to its critical temperature
Authors: Sun C. K. J. , Chen S. H.
Published: June 2004

Tracer diffusion coefficients in liquid cyclohexane of benzene, toluene, p‐xylene, mesitylene, naphthalene, and phenanthrene have been determined from 298.2 to 523.2 K (TR = 0.54 ∼ 0.95) using the Taylor dispersion method. Positive deviations from the Arrhenius relationship are observed as the critical temperature is approached, but a rough‐hard‐sphere theory is found to be adequate for describing the data across the entire temperature range. On the basis of the computer simulation results for hard‐sphere fluids, correlations involving solute and solvent critical volumes and their molecular weights have also been developed for practical applications. Tracer diffusivities in supercritical carbon dioxide are also adequately represented by the proposed correlation, as the fluid density is not far removed from that of liquid carbon dioxide.
Deterministic variability analysis for intermediate storage in noncontinuous processes: Part II: Storage sizing for serial systems
Authors: Karimi I. A. , Reklaitis G. V.
Published: June 2004

The allowability conditions derived in Part I of this series are applied to develop intermediate storage sizing expressions for serial systems subjected to process parameter variations. Multiple variations in either starting moments, transfer flow rates, or transfer fractions are considered first. These results are then combined using a worst‐case analysis to develop size estimates under general variations. A simple statistical basis is given for the bounds on the cumulative variations which are employed in the sizing expressions. An example serial system is discussed to illustrate the results.
Hollow fiber gas membranes
Authors: Qi Zhang , Cussler E. L.
Published: June 2004

Gas membranes can be used to rapidly remove volatile solutes like hydrogen sulfide and sulfur dioxide from dilute aqueous solutions. The gas membranes are supported by microporous hydrophobic hollow fibers. The aqueous feed containing the volatile component flows down the fiber lumen, and an aqueous stripping solution bathes the outside fiber surface. Thus the membrane consists of gas trapped in the hydrophobic pores. The fluxes across these membranes, which can be much faster than those across polymer films, are consistent with a nonlinear mechanism which includes solute ionization.
Characteristics of slugging regime and transition to turbulent regime for fluidized beds of large coarse particles
Authors: Satija Sunil , Fan Liang‐Shih
Published: June 2004

Slugging characteristics, including slug velocity and frequency and the height of the slugging bed, for a slugging bed of four different types of coarse particles ranging from 1 to 7 mm in size are determined based on pressure fluctuation behavior of the bed. The slugging characteristics of coarse particle slugging beds are found to be much different from those of the particle slugging beds reported in the literature. The pressure fluctuation behavior in a coarse particle turbulent bed and the transition velocity from a slugging bed to a turbulent bed is also examined.
An analysis of the lyophilization process using a sorption‐sublimation model and various operational policies
Authors: Millman M. J. , Liapis A. I. , Marchello J. M.
Published: June 2004

The freeze‐drying process is studied under various operational policies through the use of a sorption‐sublimation model. The operational policy that provides the shortest drying times keeps the pressure at its lowest value. The upper and lower heating plates are independently controlled so that the material constraints are encountered and held throughout the free water removal phase.

Under certain conditions, and for the case of samples of small thickness, the sorbed water profiles may have segments whose bound water concentrations are higher than those at the start of the free water removal phase. It is shown that the criterion used in terminating the freeze‐drying process is of extreme importance, since it may lead to an undesirable sorbed water profile which may deteriorate the quality of the dried product.
Behavior of nucleation sites in pool boiling
Authors: Sgheiza J. E. , Myers J. E.
Published: June 2004

The behavior of active boiling site populations was monitored for pool boiling on an electrically heated 1‐mil stainless steel sheet. The boiling sites were located using a high‐speed infrared camera focused on the underside of the boiling surface. Experiments were conducted to determine factors affecting the origin, concentration, and lifetime of active sites.
Design of cyclic fixed‐bed adsorption processes. Part I: Phenol adsorption on polymeric adsorbents
Authors: Costa Carlos , Rodrigues Alirio
Published: June 2004

A model for the adsorption of phenol in a fixed bed of a polymeric adsorbent is developed. Model parameters (equilibrium parameters, capacity factor, axial dispersion, film mass transfer coefficient, and intraparticle effective diffusivity) are experimentally determined from independent experiments. Numerical solution of the model equations uses the method of lines with double orthogonal collocation in finite elements. The model is used for the prediction of breakthrough curves and is part of a package for the design of cyclic processes.
Knudesen diffusion in random assemblages of uniform spheres
Authors: Huizenga D. G. , Smith D. M.
Published: June 2004

Experimental measurements have been conducted of Knudsen diffusion through a model porous medium fabricated by the pelleting of monodisperse silica spheres. Tortuosity factors for this random‐assemblage‐of‐spheres porous solid are calculated and compared with values obtained from both theory and measurements made in the bulk diffusion regime. Evidence is presented to support the use of a mean pore radius calculated as twice the ratio of pore volume to surface area, as opposed to values obtained from mercury porosimetry or sorption isotherm analysis.
Mixing/segregation in two‐ and three‐dimensional fluidized beds: Binary systems of equidensity spherical particles
Authors: Rice R. W. , Brainovich J. F.
Published: June 2004

A comparison was made of the equilibrium mixing/segregation behavior of binary mixtures of different‐sized, equal‐density glass beads in two‐ and three‐dimensional fluidized beds. Several empirical equations for mixing index were examined, all involving a dimensionless function of excess gas velocity. This function, which appeared to largely account for the effect of aspect ratio, was found to optimally correlate the data for both types of beds. However, a much better fit was obtained for the threedimensional bed data, most probably because wall effects significantly retarded mixing in the two‐dimensional bed.
Application of percolation theory to noncatalytic gas‐solid reactions
Authors: Yortsos Y. C. , Sharma M.
Published: June 2004

Previous models of noncatalytic gas‐solid reactions are based primarily on parallelpore representations, thus excluding important topological effects of the porous medium. This paper utilizes network representations and percolation theory to develop expressions for pore closure time and the evolution of accessible volume, effective diffusivity, and conversion rates.
Self‐tuning control of chip level in a Kamyr digester
Authors: Belanger P. R. , Rochon L. , Dumont G. A. , Gendron S.
Published: June 2004

A study is presented of the application of a self‐tuning regulator to the control of the level of wood chips in a Kamyr digester, used in the production of wood pulp. Following an initial phase of experiments and model structure selection, two control schemes were studied, using respectively the blow flow and the outlet device speed as manipulated variables. The approach finally adopted uses the outlet device as the primary control. The control has been in operation for several months and has provided significantly improved control and a high degree of operator acceptance.
Optimal averaging level control
Authors: McDonald K. A. , McAvoy T. J. , Tits André
Published: June 2004

An optimal averaging level control problem is defined and solved for a surge tank system. Two averaging level controllers, the ramp controller and the optimal predictive controller are developed utilizing the optimal control policy. These controllers are compared with previously reported averaging level controllers for step and sinusoidal disturbances in inlet flow rate. The OPC results in improved disturbance filtering characteristics for most of the disturbances considered and is very simple to implement.
A model for flow regime transitions in cocurrent down‐flow trickle‐bed reactors
Authors: Ng K. M.
Published: June 2004

A study of the nature of interstitial flows within trickle‐bed reactors is presented. Based on physical concepts, a theory is developed to predict the transition boundaries for various flow regimes for nonfoaming liquids. The effects of factors such as bed porosity, size of monodispersed spherical catalyst particles, interfacial tension, viscosity, density, and the gas and liquid flow rates, on flow transitions are considered. Experimental data in the literature are used to confirm the theory and the agreement is good.
Stage‐wise parameter estimation for stiff differential equations
Authors: Srinivasan V. , Aiken R. C.
Published: June 2004

The use of singular perturbation approximation for estimating parameters in stiff ordinary differential equations is illustrated. A sequential parameter estimation approach, in which the difficult‐to‐estimate parameters are introduced in higher‐order terms of the perturbation solution, is developed and illustrated. This approach is shown to provide excellent initial estimates, to be computationally efficient, and to be insensitive to initial guesses for the parameters. Aspects of data requirements for this problem estimation are discussed.
Automatic synthesis of optimum heat exchanger network configurations
Authors: Floudas C. A. , Ciric A. R. , Grossmann I. E.
Published: June 2004

This paper addresses the problem of automatically generating heat exchanger network configurations that feature minimum investment cost subject to minimum utility cost and fewest number of units. Based on the linear programming and the mixed‐integer linear programming (MILP) transshipment models for heat integration, a superstructure that has embedded many alternative configurations is proposed. This superstructure, which has as units the matches predicted by the MILP transshipment model, includes options for series and parallel matching, as well as stream splitting, mixing, and bypassing. Many of the implied stream connections in the superstructure are reduced to zero flow with a nonlinear programming formulation that leads to realistic and practical designs. Theoretical properties as well as the implementation aspects of the proposed procedure for the automatic generation of networks are presented. The method is illustrated with three example problems.
Evaluation of diffusivities in electrolyte solutions using Stefan‐Maxwell equations
Authors: Pinto N. DeG. , Graham E. E.
Published: June 2004

The Stefan‐Maxwell equations have been used to predict single‐electrolyte diffusion and ternary tracer diffusion in concentrated electrolyte solutions. Variations in diffusivity due to concentration have been shown to be related to the relaxation effect and viscosity changes of solution. Specific equations are presented to evaluate the ion‐ion and ion‐solvent interaction coefficients appearing in the Stefan‐Maxwell equations. These equations, when tested against experimental data, gave an accurate description of the process at up to 4.0 M concentrations and for trace species mobilities differing by a factor of ten.
Bulk separation of multicomponent gas mixtures by pressure swing adsorption: Pore/surface diffusion and equilibrium models
Authors: Doong S.‐J. , Yang R. T.
Published: June 2004

A theoretical and experimental study is performed for the bulk separation of a ternary mixture by pressure swing adsorption. Three concentrated products can be obtained by cycling the pressure in the adsorber. Three models are formulated for the cyclic process: equilibrium, Knudsen diffusion, and Knudsen plus surface diffusion. The latter model provides the best results when compared with the experimental data, due to the important contribution of surface flux to the total flux in the sorbent pores.
Dynamic interfacial tensions in acidic crude oil/caustic systems. Part II: Role of dynamic effects in alkaline flooding for enhanced oil recovery
Authors: Borwankar R. P. , Wasan D. T.
Published: June 2004

A model for caustic propagation in a core during continuous injection is combined with the considerations of interfacial reactions proposed in Part I in order to examine the role of dynamic effects in continuous alkaline flooding. Axial dispersion of caustic and its reversible uptake by the reservoir rock are taken into account. From this model, the interfacial tension between an isolated oil globule and the surrounding flood water can be predicted as a function of time using the knowledge of the kinetics of interfacial reactions, the rock adsorption equilibria, and the longitudinal dispersion coefficient.
Thermally coupled system of distillation columns: Optimization procedure
Authors: Fidkowski Zbigniew , Krolikowski Lechoslaw
Published: June 2004

An analytical solution of thermally coupled system (TCS) optimization was found. Energy requirements of the TCS were minimized provided that the ternary solution being separated is ideal. The TCS is energetically profitable in comparison with other sequences of distillation columns. The solution method can be used for the synthesis of separation systems and for screening calculations, due to the great simplicity of the result.
Dynamic hydrogenation studies in a catalytic slurry reactor
Authors: Ahn Bum‐Jong , Smith J. M. , McCoy B. J.
Published: June 2004

Hydrogenation of α‐methyl styrene with Pd/Al2O3 catalyst was studied in a three‐phase stirred slurry reactor. Responses to step inputs of H2 in N2 carrier gas provided temporal moments that allowed estimation of separate values for reversible adsorption and irreversible surface reaction rates for reactant H2. Mass transfer resistances are either estimated from other sources and shown to be small, or are evaluated from the flow rate dependence of the moments. The adsorption equilibrium constant for H2 on the catalyst was measured with reaction product cumene as the solvent. For temperatures between 290 and 322 K adsorption appears to have the dominant influence on the overall rate of hydrogenation. The energy of activation for the adsorption step was found to be 8 kcal/mol.
Reconciliation of process flow rates by matrix projection. Part II: The nonlinear case
Authors: Crowe C. M.
Published: June 2004

Flow rate and concentration measurements in a steady state process are reconciled by weighted least squares so that the conservation laws and other constraints are obeyed. Two projection matrices are constructed in turn, in order to decompose the problem into three subproblems to be solved in sequence. The first matrix eliminates all unmeasured component flow rates and concentrations from the equations; the second then removes the unmeasured total flow rates. The adjustments to component flow rates are iteratively determined, starting with guessed values of unmeasured total flow rates.

Chi‐square and normal test statistics are derived by linearizing the equations, to allow detection of gross errors in imbalances and adjustments of measurements.
Linear process calculations as convergence accelerators in flowsheet‐sequenced programs
Authors: Milani S. M. , Findley M. E.
Published: June 2004

Linear process calculations were developed for use in conjunction with flow‐sheet‐sequenced calculations, as methods of convergence acceleration. Two such methods were compared with the successive substitution and Wegstein methods on relatively simple processes. “Linear Process Simulation,” which requires user‐derived equations, produced the best results.