bluuebunny/crossref_metadata_2025 huggingface dataset:
Effective interfacial area determination by gas absorption accompanied by second‐order irreversible chemical reaction
Authors: Matheron Erik R. , Sandall Orville C.
Published: June 2004

Oxygen and carbon dioxide were absorbed by aqueous sodium hydroxide solutions in an agitated vessel, and the experimental results were interpreted in terms of the surface renewal theory in order to deduce effective interfacial areas. The simultaneous physical and chemical absorption experiments permitted a determination of the enhancement factor under identical physicochemical and hydrodynamic conditions. It was found that for the unbroken interface case, the effective areas for physical and chemical absorption are equal when the Danckwerts parameter γ is approximately unity. γ is defined as the ratio of the increase in absorption capacity of the liquid to the enhancement factor. For the case where the gas is sparged through the liquid, it was found that the effective interfacial area is a strong function of agitator speed (above a critical speed) and gas flow rate, whereas the mass transfer coefficient was found to be nearly independent of agitator speed and gas sparge rate.
Turbulence characteristics and mass transfer at air‐water surfaces
Authors: Davies John T. , Lozano Francisco J.
Published: June 2004

The turbulence intersities and spectra in water very close to an air interface have been measured with a hot wire anemometer. The turbulence in the water has been induced in three ways: with a stirrer, by a submerged jet, and by flow of a thin film of water over inclined plates, both rough and smooth.

We find that the root‐mean‐square fluctuation velocity Ṽx′ shows for the first system no regular trend with the distance y below the surface, while for the second system Ṽx′ increases markedly as the surface is approached. In water films over the rough plates, Ṽx′ can be as high as four times the shear stress velocity.

The turbulence energy spectra close to the surfaces in the first and second systems show (Figure 6) no extended region of slope −5/3, whereas for flow over the plates, there is an appreciable subrange of this slope (Figures 8 and 9).

Intensities of turbulence in the surface region are as high as 30 to 50% in the first system, up to 100% in the second system, and 17% over smooth plates and up to 60% over rough plates.

These turbulence characteristics can be related to the rates of mass transfer for oxygen absorbing into water by comparing plots of k/D1/2 with the square roots of the different eddy frequencies. The Levich treatment [interpreted by Equation (15)] gives good agreement with the stirred cell and jet results. For the smooth and rough plates, mass transfer depends on eddies intermediate in size between the x directional and the y directional large eddies. In all cases, the Kolmogoroff eddy frequencies are much too high to correlate with mass transfer rates.

Further, the energy spectra show that 60 to 80% of the total eddy energy lies in the larger eddies, with only 1% (or less) in the Kolmogoroff range.

We conclude that the Prandtl sized eddies, and even larger eddies, determine mass transfer rates at a free surface.

Direct measurement of concentration fluctuation frequencies, using platinum microelectrodes, was found to be unsatisfactory because of the poor frequency response of the amplified signals.
Staged approach of percolation processes
Authors: Rodrigues Alírio E. , Beira Eduardo C.
Published: June 2004

Sorption processes in a perfectly mixed reactor are analyzed by using two models: The equilibrium model and a kinetic model which considers the effect of the external mass transfer resistance. In both cases, a general non‐linear equilibrium isotherm is considered.

The influence of the different model parameters on the response of the perfectly mixed sorber and their effect on a design parameter (the breakthrough time) are discussed.

A criterium is derived in order to predict when the equilibrium model is valid.
Growth of ice in a saltwater drop falling in an organic phase
Authors: Bustany S. T. , Harriott Peter , Wiegandt H. F.
Published: June 2004

Data on the ice formation rate are presented for a salwater drop suspended by drag forces in a flowing cold organic liquid. The effects of refrigerant undercooling, salt concentration, drop size, and time were studied. Ice formation rates in drops of 3 wt % sodium chloride solution were two to three times lower than in pure water drops. A parallel plate model was used to correlate the data and predict ice formation rates for other drops and refrigerants.

Dispersing drops of brine or fruit juices in a countercurrent cold organic refrigerant is a method of desalination (or freeze concentration) that deserves further study.
Fully developed viscous flow and heat transfer in curved semicircular sectors
Authors: Masliyah Jacob H. , Nandakumar K.
Published: June 2004

The Navier‐Stokes equation in stream function‐vorticity form and the energy equation are solved numerically for a fully developed flow of a Newtonian fluid in coiled circular sectors having zero pitch. Two heat transfer cases are studied: axially uniform heat flux with uniform peripheral temperature and axially uniform temperature with mixed conditions along the periphery. Solutions are presented for curvature ratios in the range of 5 to 30, Prandtl numbers in the range of 0.7 to 100, and Dean numbers up to 300. In all cases studied, the heat transfer performance for the curved tubes was superior to that of a straight tube geometry.
Concentration forcing of catalytic surface rate processes: Part I. Isothermal carbon monoxide oxidation over supported platinum
Authors: Cutlip Michael B.
Published: June 2004

Periodic feed switching between carbon monoxide/argon and oxygen/argon mixtures to a gradientless reactor has been found to significantly increase the average reaction rate as compared to the steady state rate, when the time averaged feed concentrations in both cases are stoichiometric. The rate enhancement achieved during periodic reactor operation is attributed to the attainment of more desirable surface concentrations on the platinum catalyst which dramatically increase the surface rate processes leading to carbon dioxide production.
Numerical analysis of variable property heat transfer to a single sphere in high temperature surroundings
Authors: Sayegh N. N. , Gauvin W. H.
Published: June 2004

A theoretical study has been conducted to investigate the effects of large temperature differences on the rate of pure heat transfer from a very hot gas to stationary spheres.

In the numerical analysis, the momentum and energy equations for variable property flow past a sphere were solved simultaneously, using finite difference techniques. Results were obtained for Reynolds numbers up to 50 and surface temperature to gas temperature ratios varying between 0.25 and unity. These ranges cover most of the conditions commonly encountered in heterogeneous plasmas, transferred arc, and other high temperature chemical engineering processes. The flow behavior, drag coefficients, and Nusselt number were calculated for each case.

The constant property solutions were in excellent agreement with numerical and experimental results reported in the literature, thus justifying the validity of the model and of the underlying assumptions. In general, the effect of variable properties was to drastically increase the flow velocity, vorticity, and temperature and vorticity gradients near the surface.

A generalized heat transfer correlation was derived which, in addition to constant property conditions, included the effect of large variations in the physical properties of the fluid as a result of large temperature differences.
Equilibrium and kinetics studies of hydrogen isotope exchange on vanadium hydride
Authors: Wong Y. W. , Hill F. B.
Published: June 2004

Chromatography experiments and pressure‐composition isotherm measurements were carried out on the vanadium‐hydrogen system in order to obtain an understanding of the equilibrium and kinetic factors affecting hydrogen isotope exchange. Analysis of the results yielded values of the hydrogen equilibrium distribution coefficient, the tritium‐protium separation factor, the rate of the gas‐solid exchange reaction, and the axial dispersion coefficient.
Surface ablation in the impingement region of a liquid jet
Authors: Swedish Michael J. , Epstein Michael , Linehan John H. , Lambert George A. , Hauser George M. , Stachyra Larry J.
Published: June 2004

A theoretical and experimental investigation of a water jet impinging on a melting solid surface has been carried out. Ice, octane, p‐xylene, and olive oil served as the meltable solid materials, comprising a Prandtl number range of 5 to 2 800. An available laminar stagnation flow model was utilized to describe melting heat transfer in the jet impingement region. Melting rate measurements were found to agree quite well with the values predicted with this model.
Mass transfer between a flowing fluid and a solid wavy surface
Authors: Thorness Charles B. , Hanratty Thomas J.
Published: June 2004

This paper considers the transfer of mass or heat between a fluid and a small amplitude solid wavy surface. A periodic variation of the transfer rate can occur because of wave induced variations of the normal convective flow and of the properties of the turbulence. Solutions of the mass balance equations are presented for the laminar flow at a large Schmidt number or Prandtl number and for turbulent flow at large and small wave numbers. For turbulent flows at intermediate wave numbers, the prediction is limited by inadequacies of present theories that model the wave induced variation in the turbulent diffusion of heat or mass. In order to provide guidance for this modeling, new measurements on the variation of the mass transfer rate along a solid wavy surface are presented for a Schmidt number of 729. An analogy between momentum and mass transfer is explored as a means for evaluating the turbulent diffusion terms.

The amplitude of the function describing the mass transfer variation is found to decrease with decreasing wave number and the phase to increase with decreasing wave number. The phase angle and the amplitude of the variation in the mass transfer rate relative to the average mass transfer rate are insensitive to changes in Schmidt number or Prandtl number. For turbulent flows, the phase change can be large enough that the maximum in the mass transfer rate can exist somewhere in the trough of the wave. This result is of considerable significance in interpreting wavelike dissolution patterns.
Estimation of phase diagrams and solubilities for aqueous multi‐ion systems
Authors: Kusik C. L. , Meissner H. P. , Field E. L.
Published: June 2004

Calculation of the phase diagram for saturated aqueous multi‐ion solutions of strong electrolytes, based upon use of the thermodynamic solubility products, is illustrated for the four‐ion system: Na+, K+, Mg++, SO4=. Solid phases are identified along with the ion concentrations of the associated saturated solutions.
Calculation of sulfate and nitrate levels in a growing, reacting aerosol
Authors: Peterson Thomas W. , Seinfeld John H.
Published: June 2004

The temporal variation of particle size and chemical composition of a marine aerosol exposed to SO2, NH3, NO, NO2, H2SO4 and H2O vapor is studied to determine the effect of these parameters on the sulfate and nitrate levels in the particle. Results show that, for gas phase SO2 oxidation to sulfate, and liquid phase nitrate formation, those parameters that enhance sulfate formation tend to inhibit nitrate formation, and vice versa. Further, for the situation considered, the ratio predicted for sulfate and nitrate ions to ammonium ions is very nearly that found if all these ions were present in the form of NH4NO3 and (NH4)2SO4. This compares favorably with data on sulfate, nitrate and ammonium levels in the Los Angeles area. The model used is capable of representing a general growing, reacting aerosol; other cases studied by this approach are briefly outlined. Limitations of its use are discussed.
Effects of acceleration, deceleration and particle shape on single‐particle drag coefficients in still air
Authors: Marchildon E. K. , Gauvin W. H.
Published: June 2004

Measurements were made of the drag coefficients of smooth solid particles moving singly through still air at Reynolds numbers in the range of 103 to 104. Spheres were observed during acceleration, deceleration and at terminal velocity. Discs were tested during acceleration and at steady velocity. Other particles in the shapes of discs, circular cylinders and rectangular parallelepipeds were tested at steady velocity in their preferred and, in some cases, non‐preferred orientations. The effects of non‐steady velocity and of particle form were determined. An unexpected influence of particle density was observed for some of the particles.
Diffusivities of low‐volatility species in light gases
Authors: Ravindran Periasamy , Davis E. J. , Ray A. K.
Published: June 2004

Gas‐phase diffusivities for high boiling point organics in common gases are determined by evaporating a single submicron aerosol droplet of the organic species, while it is suspended in an electric field in the path of a polarized laser beam. The droplet size is measured as a function of time by using Mie theory to determine the size from the light scattering data of intensity versus angle. In addition to diffusivities, the Lennard‐Jones molecular interaction potential parameter, ϵii, and the collision diameter σii, are found, by applying the molecular theory of gases to interpret the evaporation rate data. Results are compared with available empirical and semi‐theoretical correlations for diffusivities and Lennard‐Jones parameters. The low vapor pressure organics used here are dioctyl phthalate (DOP), dibutyl sebacate (DBS) and dibutyl phthalate (DBP), and the carrier gases are helium, nitrogen and carbon dioxide.
Sweetening of sour natural gases by mixed‐solvent absorption: Solubilities of ethane, carbon dioxide, and hydrogen sulfide in mixtures of physical and chemical solvents
Authors: Rivas O. R. , Prausnitz J. M.
Published: June 2004

Solubilities of ethane, carbon dioxide, and hydrogen sulfide have been measured in propylene carbonate, N‐methyl‐2‐pyrrolidone and tetramethylene sulfone (sulfolane); and in mixtures of these physical solvents with monoethanolamine and diglycolamine, in the range −10 to 100°C. Thermodynamically consistent equations are given for gas absorption with chemical reaction at equilibrium. Henry's law describes physical equilibrium between the acidic gas in the vapor phase and free acid solute in the liquid phase. Equilibrium constants describe chemical equilibria for the absorbed gas and the chemical solvent.

Preliminary design calculations for sweetening natural gases by absorption with mixed solvents suggest that, under some circumstances, mixed‐solvent absorption may be more economical than using conventional aqueous alkanolamine.
Computation of phase and chemical equilibrium: Part I. Local and constrained minima in Gibbs free energy
Authors: Gautam Rajeev , Seider Warren D.
Published: June 2004

Several methods are reviewed for determining compositions in multiphase, reacting mixtures at equilibrium. Wolfe's quadratic programming algorithm is applied and results compared with the Rand method (Dluzniewski and Adler 1972), NASA method (Gordon and McBride 1971) and the George et al. (1976) implementation of Powell's method. For poor guesses in compositions, local and constrained minima in Gibbs free energy may arise, giving incorrect phase distributions.
A thermodynamic‐combinatorial approach to the design of optimum heat exchanger networks
Authors: Flower John R. , Linnhoff Bodo
Published: June 2004

This article describes a novel approach to the systematic synthesis of heat exchanger networks. For a given synthesis problem, this approach leads to a complete listing of all solutions which exist, using a prescribed degree of energy recovery, the minimum number of exchangers, heaters and coolers, and no split streams. The approach is combinatorial, with a variety of thermodynamic criteria used to minimize the problem size by preventing infeasible solutions being generated. Two examples (5SPI and 6SPI) are discussed to illustrate complete solution by hand.
Moving‐bed solids flow in an inclined pipe leading into a fluidized bed: Part II. The solids flow properties
Authors: Chen Te‐Yu , Walawender Walter P. , Fan L. T.
Published: June 2004

The purpose of part II of this paper is to theoretically analyze and experimentally examine moving‐bed solids flow in an inclined pipe connecting a fluidized bed and a solids storage vessel. The macroscopic momentum balance equation is simplified and applied to the present system. A friction factor correlation is developed. Based on the flow curves constructed, we found that the power law model is suitable for describing moving‐bed solids flow.
Analysis of the phase inversion characteristics of liquid‐liquid dispersions
Authors: Arashmid M. , Jeffreys G. V.
Published: June 2004

Correlations of the collision frequency and the coalescence frequency of an agitated dispersion are combined with models relating drop sizes and hold‐up to agitator speed, to predict the ambivalence range and phase inversion composition of liquid‐liquid dispersions. Our model was tested by comparing predicted and experimental phase invesrion compositions of the system toluene‐water ad carbontetrachloride‐water. In addition, the predicted results have been compared ith published results for the system kerosene‐water, and in all cases, agreemet between predicted and experimental resutls are excellent.
Effectiveness and deactivation of a diluted catalyst pellet
Authors: Varghese Philip , Wolf Eduardo E.
Published: June 2004

In this article, we analyze the performance of a dluted catalyst pellet consisting of inert and active particles under diffusion influenced conditions and pore‐mouth poisoning. First, we establish the requirements for validty of the analytical soltuions of the diluted pellet equations. Secondly, we show that, under pore‐mouth poisoning conditions, a diluted pellet can display considerably longer lifetimes than a uniformly impregnated catalyst. Conversely, for the same lifetime, use of a diluted pellet can result in savings of the catalytic agent. These advantages are not offset by difficulties in catalyst manufacture, as is the case for previous designs.
Structural analysis of multicomponent reaction models: Part I. Systematic editing of kinetic and thermodynamic values
Authors: Sorensen Jan P. , Stewart Warren E.
Published: June 2004

The consistency of a chemical reaction scheme depends in part on the numerical values given for its kinetic and thermodynamic constants. Part I of the present two‐part treatment provides (1) a systematic procedure to reduce the given values to a self‐consistent form, and (2) a proper selection of parameters whenever the values are to be improved by a subsequent regression analysis. Various completeness and consistency tests are described, including a search for illegal reaction loops arising from assumptions of irreversibility. The procedure is implemented on a computer and is illustrated with two examples.
The facilitated transport of carbon monoxide through cuprous chloride solution
Authors: Smith Douglas R. , Quinn John A.
Published: June 2004

The facilitated transport of carbon monoxide through thin, immobilized films of cuprous chloride solutions is investigated, using a tracer C14O technique. Steady‐state tracer flux measurements are used to determine the second‐order forward rate constant and equilibrium constant for the reversible reaction of CO with cuprous ion. The enchanced results at low CO partial pressures can be interpreted in terms of a consecutive reaction model. The cuprous ion is remarkably effective as a carrier for CO. The CO permeation rate in the presence of cuprous ion can be increased by two orders of magnitude over the nonfacilitated flux. As such, the cuprous ion is an attractive facilitating agent for use in a membrane separation system.
The effect of an expanded section on slugging
Authors: Yang W.‐C. , Keairns D. L.
Published: June 2004

Slugging experiments were performed in a semicircular Plexiglas column 5.6 m in height to study the effect of an expanded section on slugging. The bottom section of the column (3.05 m long) is 28.6 cm in inside diameter and the expanded section 40.6 cm. Both the bed height and the fluidizing velocity were varied during the study, and the results were successfully correlated with a theoretically derived equation. The implications in designing a bed with an expanded section to reduce the slugging effectively are also discussed.
Three phase slurry reactors
Authors: Chaudhari R. V. , Ramachandran P. A.
Published: June 2004

This article reviews the major developments in the engineering and design of three‐phase slurry catalytic reactors. A general theoretical analysis for predicting the overall rate of reaction in a slurry reactor for various kinetics is presented, incorporating all the transport effects. Modeling of semi‐batch reactors is discussed and design procedures are indicated. Some major correlations and methods for determining gas‐liquid and liquid‐solid mass transfer coefficients and effective diffusivity in liquid filled pores are reviewed. Slurry reactors are compared with other three‐phase reactors, such as trickle bed or packed bed reactors, and relative merits are pointed out.
Studies in the synthesis of control structures for chemical processes: Part II: Structural aspects and the synthesis of alternative feasible control schemes
Authors: Morari Manfred , Stephanopoulos George
Published: June 2004

The classification of control objectives and external disturbances in a chemical plant determines the extent of the optimizing and regulatory control structures (see Part I). In this article we discuss the structural design of alternative regulatory control schemes to satisfy the posed objective. Within the framework of hierarchical control, criteria are developed for the further decomposition of the process subsystems, reducing the combinatorial problem while not eliminating feasible control structures. We use structural models to describe the interactions among the units of a plant and the physicochemical phenomena occurring in the various units. The relevance of controllability and observability in the synthesis of control structures is discussed, and modified versions are used to develop all the alternative feasible regulatory structures in an algorithmic fashion. Various examples illustrate the developed concepts and strategies, including the application of the overall synthesis method to an integrated chemical plant.
Studies in the synthesis of control structures for chemical processes: Part III: Optimal selection of secondary measurements within the framework of state estimation in the presence of persistent unknown disturbances
Authors: Morari Manfred , Stephanopoulos George
Published: June 2004

When primary control objectives cannot be measured directly, secondary measurements have to be selected and used in conjunction with estimators to infer the value of the unmeasurable variables. Unmeasured process disturbances (state excitation noise) are assumed to be of major importance, dominating the errors caused by measurement noise. Since the white noise assumption is generally insufficient for the persistent disturbances commonly occuring in the Chemical Engineering, environment, a nonstationary noise model has been employed, and is shown to yield superior estimations under these circumstances. New necessary and sufficient conditions have been developed for the observability of the dynamic system augmented to include the noise model.

A variety of new measurement selection criteria is presented here, with the goal of minimizing estimation error. One class of criteria aims at minimizing the transient estimation error when a static estimator is used. The other class minimizes the measurement error caused by the unobservable subspace. The design of state reconstruction procedures (which are able to handle persistent unmeasured process disturbances) is explained in a stochastic and a deterministic framework. Finally, the synthesis of reduced order control schemes is discussed. The power of the selection criteria and the superiority of a Kalman filter design employing a nonstationary noise model is demonstrated in many examples.
Dynamics of bubbles and entrained particles in the rotating fluidized bed
Authors: Chevray Rene , Chan Yau Nam I. , Hill Frank B.
Published: June 2004

Trajectories of bubbles and entrained particles in the rotating fluidized bed were obtained from equations expressing a balance among inertial, centrifugal, Coriolis, gravity and drag forces. The solutions led to information on the behavior of isolated bubbles, bubbles swarms and the elutriation characteristics of the rotating fluidized bed.
Electrically stimulated aerosol filtration in packed beds
Authors: Harriott G. M. , Saville D. A.
Published: June 2004

Since charged particles are quite mobile in an electric field, charge is often added to aerosol particles to facilitate capture; indeed, provision for such charging is an indispensable part of electrostatic precipitators. Nevertheless, calculations disclose that a very slight amount of charge may suffice when the distance the aerosol particle must travel to the collector surface is small, contrary to the usual situation. In the experiments described, here, a model aerosol containing 0.5 μm polystyrene particles passed through a radioactive charge neutralizer to deliberately reduce the charge as much as practicable and then through a packed bed under the influence of a fairly large external electric field. Filtration efficiencies approaching 100% were obtained owing to the influence of the field on small amounts of residual charge.
Solvent losses in gas absorption. Solubility of methanol in compressed natural and synthetic gases
Authors: Lazalde‐Crabtree H. , Breedveld G. J. F. , Prausnitz J. M.
Published: June 2004

Experimental results are reported for the solubility of methanol in compressed nitrogen, methane, ethane and carbon dioxide in the region −45° to +10°C and 17 to 62 bars.

New and previously published experimental data are used to obtain (or estimate) second virial coefficients for all binary pairs in mixtures containing hydrogen, nitrogen, carbon monoxide, methane, ethane, propane, carbon dioxide, hydrogen sulfide and methanol. These coefficients, combined with experimental data for the vapor pressure of methanol and with Henry's constants, partial molar volumes and Margules coefficients for dissolved gases in methanol, yield a correlation for calculating solvent losses as a function of temperature, pressure and gas composition. For a large‐scale natural‐gas absorption process, these losses may represent a significant economic factor in plant design.
An introduction to the nonlinear theory of adsorptive reactors
Authors: Schweich Daniel , Villermaux Jacques , Sardin Michel
Published: June 2004

Coupling between transient chemical reaction at equilibrium and a linear and isothermal chromatographic separation is studied when a nonlinear chemical mass action law is assumed to hold between the species. It is shown that the qualitative features of the chromatograms can be predicted by simple algebraic calculations. Two novel properties of the adsorptive (or chromatographic) reactor are demonstrated. The improvement of the theory, with regard to quantitative predictions, is discussed.
A single‐particle char gasification model
Authors: Srinivas B. , Amundson Neal R.
Published: June 2004

A model is developed for the gasification of a single‐char particle in an environment of water, hydrogen, carbon dioxide, carbon monoxide and methane, existing in the gasification zone of a reactor. The model, consisting of the mass and energy conservation equations, together with the Stefan‐Maxwell relations includes the intraparticle effects and the change in internal surface area. It is found that the intraparticle effects and the surface area effects are significant and hence cannot be neglected, and the situation becomes more acute with increasing particle size and high temperatures. Comparisons with other models and existing empirical relations show that the model agrees well when diffusional effects are minimal, but at higher temperature and large pariticle size there is a significant difference. The model may be used to discriminate among various idealized models such as the homogeneous and the shrinking core model. The conyective terms in the Stefan‐Maxwell relations have negligible influence. The analysis can be directly used in the modeling studies of gasification reactors and will be so applied in a later paper.
Emulsion phase residence time and its use in heat transfer models in fluidized beds
Authors: Ozkaynak Taner F. , Chen John C.
Published: June 2004

Heat transfer from a vertical tube in fluidized beds was investigated by measurement of emulsion packet residence times. The root‐square‐mean residence times were then used in a modified packet model to successfully predict effective heat transfer coefficients.
The continuous membrane column
Authors: Hwang Sun‐Tak , Thorman John M.
Published: June 2004

The continuous membrane column provides a revolutionary separation technique. Both the most and the least permeable components can be separated continuously to any degree without cascading. Experimental data for several binary systems show good agreement with theory.
An optimal arrangement of simultaneous linearized equations for general systems of interlinked, multistoged separators
Authors: Hidalgo S. R. , Correa V. A. , Gomez M. A. , Seader J. D.
Published: June 2004

The simultaneous solution of all the equations for a general system of interlinked, multistaged separators is considered. The interlinks may be simple streams or reciprocal streams, and a particular separator may have bypassing streams (for example, pumparounds). Algorithms are developed that automatically arrange the linearized equations so that for a Newton‐Raphson type of solution procedure using, for example, the Naphtali‐Sandholm technique, a minimum or nearly minimum number of nonzero blocks occur outside the tridiagonal band so that computational memory and time requirements are minimized. The nonzero and nonidentity blocks are stored in a single vector of variable dimension.
Sulfur dioxide transport through aqueous solutions: Part II. Experimental results and comparison with theory
Authors: Roberts Daryl L. , Friedlander Sheldon K.
Published: June 2004

Measurements were made of the steady state flux of sulfur dioxide through films of water and solutions of neutral and alkaline sodium salts (0.1 to 2.0 M sodium chloride, 10−3 to 3.0M sodium hydroxide, NaHSO3 or sodium sulfite) with sulfur dioxide partial pressures between 10 and 100Pa. In agreement with equilibrium theory (Part I), data from water and sodium chloride solutions show that HSO is responsible for 83 to 95% of the flux (facilitation factor F between 5 and 19). In alkaline solutions, HSO and other sulfur containing species cause F to be as large as 1 370. Equilibrium theory, however, overpredicts F by up to a factor of 7. The NEBLA (Part I) accounts for this deviation.
Throughflow drying and conditioning of beds of moist porous solids: A simple method for the quantitative prediction of moisture and temperature fronts
Authors: Basmadjian Diran
Published: June 2004

A simple procedure previously developed for the prediction of fixed bed adiabatic sorption operations (Basmadjian, 1980b) has been extended to the throughflow drying and conditioning of beds of moist porous solids. The method eliminates time consuming numerical solutions of the model PDE's and yields satisfactory agreement with reported experimental data.
Transport accompanied by chemical reaction in stagnation flow
Authors: Balaraman K. S. , Mashelkar R. A. , Doraiswamy L. K.
Published: June 2004

There are many industrially important reactions in which the chemical kinetics and external diffusion govern the observed reaction rate, and the observed kinetics differ drastically from the true kinetics. This study shows that the forward stagnation flow region of a circular cylinder can be a convenient system for studying the true kinetics of a solid catalyzed reaction owing to its unique property of uniform accessibility.
A comprehensive model for fluidized bed coal combustors
Authors: Rajan Renga R. , Wen C. Y.
Published: June 2004

A comprehensive model for the simulation of fluidized bed coal combustors (FBC) is developed, capable of predicting the combustion efficiency, char and limestone elutriation and the corresponding particle size distribution in the bed and in the entrained materials, solids withdrawal rate from the bed, bed temperature profile, sulfur dioxide retention, sulfur dioxide and NOx emissions, concentrations of oxygen, carbon monoxide, carbon dioxide, volatiles, sulfur dioxide and NOx along the combustor height. The model can also simulate combustors with varying cross section along the bed height. The performance of the model is compared with the data obtained from four different combustors. Agreement between the computed results and the data is good. The salient features in the model which need further investigation are pointed out.
Chlorination kinetics of zirconia in an RF chlorine plasma tail flame
Authors: Biceroglu O. , Gauvin W. H.
Published: June 2004

The chlorination kinetics of zirconia were studied in a single stationary particle reactor system. A plasma of pure chlorine generated by an induction torch provided both the high enthalpy field and the reacting gas. The influence on the rate of conversion of such parameters as temperature, chlorine concentration (in the presence of argon) and particle diameter and porosity were investigated. Based on experimental and theoretical studies, rate equations were developed under different rate controlling mechanisms.

The chlorination of zirconia in the particle temperature range of 1 540° to 2 480°K obeyed a shrinking core reaction model. The reaction was chemically controlled below 1 950°K, and above this temperature both chemical and mass transfer resistances were important. The experimental results confirmed the theoretical analysis.
Application of a variable time‐step finite‐difference method for the one‐dimensional melting problem including the effect of subcooling
Authors: Yuen W. W. , Kleinman A. M.
Published: June 2004

A new numerical method is proposed for the one‐dimensional melting problem. Unlike many of the existing numerical techniques which either immobilize the moving interface by a suitable coordinate transformation or search for the moving interface under a fixed grid, fixed‐time‐step finite‐difference formulation, the present method was a fixed grid, variable time‐step approach. Each time step in the computation is determined iteratively by requiring that the interface be located at a mesh point, one grid space from the previous interface location.

Results of two sample calculations show that the present method is superior to the conventional finite‐difference method both in its accuracy and computational efficiency. The formulation is mathematically simple and can be applied with no difficulty to problems with nonplanar geometry and initial subcooling. The present method is applied to the analysis of the melting of a finite slab subjected to a constant heat flux boundary condition. Some interesting effects of initial subcooling on the physics of melting are illustrated and discussed.
Gas absorption with consecutive second‐order reactions
Authors: Huang D. T. ‐J. , Carberry J. J. , Varma A.
Published: June 2004

For gas absorption accompanied by two consecutive second‐order reactions, the reaction factors of the film and penetration theories were solved by the orthogonal collocation method. For equivalent definition of the other physico‐chemical parameters, the reaction factors from the two theories differ only slightly. In film theory, it is shown that the film‐bulk boundary condition is of importance only for small values of M. It is also shown that the difference between the point yields of the film and penetration theories is generally small, although it is larger than the difference in reaction factors for the two theories.
Influence of condensable vapor on strength of powders
Authors: Elbirli B. , Vergara‐Edwards Luis , Coughlin Robert W.
Published: June 2004

Diametrically different influences of small moisture contents upon strength are often measured in beds of different kinds of particles. Here we explain such opposing trends in terms of capillary forces exerted by condensed liquid rings at the points of particle contact. The effects of such rings are opposite for different particle shapes at the point of contact, namely, at spherical or at sharp angular contact points. In addition to the theoretical development, data are given for two different illustrative types of particles.
Heat and mass diffusion with chemical reaction: A moving boundary analysis in a particle
Authors: Essoh Djedjess C. , Klinzing George E.
Published: June 2004

Goodman's integral heat and mass balance method is applied to the problem of a moving boundary in a spherical particle. The moving boundary was fixed by a suitable transformation for ease in solution. The mean value theorem was used to treat the nonlinearities when they occurred. Relations for the heat and mass boundary positions are obtained for the most general conditions. These expressions reduce in their limiting cases to known results.
The synthesis of distillation trains with heat integration
Authors: Morari Manfred , Faith Don C.
Published: June 2004

Due to rising energy costs, there is an increasing need to include the goal of energy conservation as an integral part of process synthesis. This paper discusses the problem of finding the optimum sequence of distillation columns for separating a multicomponent mixture, when heat exchange is permitted between the columns. The major difficulties are associated with the nonserial nature of the problem, the large combinatorial variety and the size of the optimization task. The synthesis strategy presented here overcomes these problems by the use of a bounding technique together with the Lagrangian theory from nonlinear programming. Accurate lower bounds on the optimal costs permit the elimination of nonoptimal sequences with minimal computational effort.
The mixing of Granular solids in a rotary cylinder
Authors: Mu Jacob , Perlmutter D. D.
Published: June 2004

A model is derived for solids mixing and material transport in a continucus flow rotary dryer or reactor. Detailed analysis of the particle motions in the turnover process provides an opportunity to apply well‐known reactor models to several subregions and to relate the overall results to different design geometries and operating conditions. The essential parameters of the model are the number of stages, the volume fractions of mixed flow and plug flow in each stage, the recycle ratio and the bypass ratio.
Studies in the synthesis of control structures for chemical processes: Part IV. Design of steady‐state optimizing control structures for chemical process units
Authors: Arkun Yaman , Stephanopoulos George
Published: June 2004

The design of the steady‐state optimizing control for a single unit is formulated within the framework of the nonlinear mathematical programming theory. Alternative implementational strategies are developed and a multilevel screening procedure is proposed to arrive at the best optimizing control configuration. Numerical examples on a fluid catalytic cracking unit and a distillation column demonstrate the systematic design and the synthesis of the most promising optimizing control structures for these systems.
Analysis of drop size distributions in lean liquid‐liquid dispersions
Authors: Narsimhan Ganesan , Ramkrishna Doraiswami , Gupta Jai P.
Published: June 2004

Experimental measurements of transient drop size distributions in a stirred liquid‐liquid dispersion (with low dispersed phase fraction) have been used concomitantly with population balance theory to recover the transition probability of droplet breakage, based on a similarity concept. The data remarkably uphold the proposed similarity hypothesis, and the estimated probability function displays the same qualitative trend as the model due to Narsimhan et al. (1979).
A novel rotated disc electrode and time lag method for characterizing mass transport in liquid‐membrane systems
Authors: Gough David A. , Leypoldt John K.
Published: June 2004

A time lag method is described for use with a membrane‐covered, rotated disc electrode that allows determination of the partitioning and diffusivity of small molecules in hydrophilic gel membranes and membrane permeability from a single measurement. This new technique takes into account the concentration boundary layer in the solution adjacent to the membrane and reaction at the electrode surface of solutes that are diffusion‐ or kinetic‐limited. Examples are given of the use of this method for characterizing mass transfer in a commercial cellulosic membrane with oxygen, hydroquinone, ferrocyanide, and glucose as solutes.
Oscillatory states in the oxidation of carbon‐monoxide on platinum
Authors: Sheintuch M.
Published: June 2004

The trend observed on variation of the operating conditions during CO oxidation on platinum in a CSTR is as follows: stable states → simple oscillations → multipeak oscillations → stable states. Analysis of the experimental results indicates that a third or higher order system of differential equations is necessary to describe most of the observations.
Kinetics of selective oxidation of toluene and methanol over supported V2O5‐alkalimetal sulfates
Authors: Sharma R. K. , Srivastava R. D.
Published: June 2004

The catalytic activity of supported V2O5‐alkalimetal sulfate catalysts was studied by oxidizing toluene and methanol to aldehydes and water. An isothermal, fixed‐bed reactor, operating at atmospheric pressure and temperatures of 320, 345, and 370°C, was used to obtain the reaction rate data for different partial pressure combinations of the reaction components of these two systems. Three different approaches, Langmuir‐Hinshelwood, Hinshelwood, and two‐step redox mechanisms, have been used to study the kinetics, with statistical data interpretation.
Oxygen mass transfer in bubble columns working at large gas and liquid flow rates
Authors: Alvarez‐Cuenca M. , Nerenberg M. A.
Published: June 2004

One of the most persistent obstacles in the study of oxygen mass transfer in bubble columns is the technical difficulty of using large liquid and gas flow rates economically. This experimental limitation is reflected in the present, very incomplete, understanding of the mass transfer characteristics of these two‐phase systems. In this work, a new experimental technique has been developed and used.

The use of computer‐calculated concentration contour diagrams permitted a detailed study of the mass transfer characteristics of the zone near the distributor. No similar study has been reported in the literature until now. The ability of the axial dispersion and two‐zone models to describe the experimental data is analyzed.

Finally, liquid side volumetric mass transfer coefficients have been calculated for both models. The results indicate that KLa increases, often linearly, with the superficial gas velocity. Furthermore, for the liquid‐phase range [0, 10] cm/s, KLa had a minimum at Vl ∼ 7.5 cm/s. For larger liquid superficial velocities, an increase in KLa was found. These observations were valid for the axial dispersion (ADM), plug flow (PFM) and two‐zone (T‐ZM) models.
Bacterial population dynamics in batch and continuous‐flow microbial reactors
Authors: Nishimura Y. , Bailey J. E.
Published: June 2004

Calculations of the distribution of states in cell populations grown in well‐mixed, isothermal batch and continuous flow reactors are presented. By restricting the analysis to a class of bacteria for which cell division control may be modeled using overlapping timers, analytical results are obtained for many cell population characteristics in terms of the growth rate history. This required growth rate trajectory is evaluated using a separate overall reactor model. The simulation results conform qualitatively to available experimental data and suggest new experiments for further testing of the single‐cell model.
Effective diffusivity by the gas chromatography technique: Analysis and application to measurements of diffusion of various hydrocarbons in zeolite NaY
Authors: Hsu L.‐K. P. , Haynes H. W.
Published: June 2004

The gas chromatography technique was applied to measurements of diffusion of n‐butane in zeolite NaY. The linear chromatography theory failed to explain these results quantitatively, and a significant system nonlinearity was demonstrated. This nonlinearity is likely associated with non‐Fickian diffusion. Order of magnitude estimates of the diffusivity could still be obtained, however. Over the range of temperatures 105 to 240°C, the n‐butane diffusivities were in the range 10−8 to 10−6 cm2/s. Similar results were obtained with n‐hexane and calculated diffusivities were about an order of magnitude smaller than the corresponding n‐butane values. In contrast, limited experiments with cyclohexane, 2, 2‐dimethylbutane, and trans‐decalin were entirely consistent with the linear chromatography theory. At the measurement temperatures, the intracrystalline diffusion was too rapid to be detected in any of these systems. Attempts to operate at lower temperatures where diffusion might be significant were frustrated by extensive peak broadening and concomitant loss of detector response.
Steady‐state multiplicity of a nonadiabatic bubble column with fast reactions
Authors: Huang D. T.‐J. , Varma Arvind
Published: June 2004

A steady‐state model is developed for a nonadiabatic bubble column with fast pseudo‐nth‐order reactions. A priori bounds are obtained for steady‐state temperature and conversion, and analytic necessary and sufficient criteria are derived for the prediction of uniqueness and multiplicity of the steady states as a function of system physico‐chemical parameters. For the special case of pseudo‐first‐order reactions, the occurrence of multiple steady states is shown to be more possible in a bubble column than in a gas‐liquid CSTR for equivalent system parameters.
Design and experimental evaluation of controllers for process undisturbability
Authors: Shah S. L. , Fisher D. G. , Seborg D. E.
Published: June 2004

Selected state and/or output variables can be made undisturbable, i.e., invariant, to arbitrary, unmeasured changes in specific input variables by properly designed feedback and feedforward controllers. Simulation and experimental applications to a computer‐controlled, pilot plant evaporator gave results superior to conventional controllers.

Necessary and sufficient conditions for undisturbability are expressed in terms of the structure of the coefficient matrices of the state space model and equivalently of the corresponding eigenvector matrix. The design procedure normally includes arbitrary specification of all closed‐loop eigenvalues and up to r elements of each eigenvector, where r is the number of control (manipulated) variables.
Regeneration of powdered activated carbon. Part I. Thermal decomposition kinetics
Authors: Chihara Kazuyuki , Smith J. M. , Suzuki Motoyuki
Published: June 2004

Kinetics of thermal regeneration of powdered activated carbon containing adsorbed sucrose was studied from 298 to 1033 K. Most of the data were obtained (by measuring mass vs. time of spent carbon samples) in a thermal gravimetric apparatus. The regeneration process was interpreted in terms of a two‐step process: (1) low‐temperature decomposition to an adsorbed intermediate and gaseous products; and (2) a higher temperature decomposition of adsorbed intermediate into adsorbed residual carbon and gaseous products.

Surface area measurements indicated that most of the original carbon surface, but not all, could be recovered by thermal (with inert gas) regeneration up to 773 K. If permanent loss in surface is to be avoided during continued, cyclical use of the carbon, reaction with an oxidizing gas would be required after thermal regeneration.