bluuebunny/crossref_metadata_2025 huggingface dataset:
Desorption of carbon dioxide from supersaturated water in an agitated vessel
Authors: Hikita Haruo , Konishi Yasuhiro
Published: June 2004

The rates of desorption of carbon dioxide from supersaturated water solutions into pure carbon dioxide or nitrogen gas stream were measured at 15,25, and 35°C in a baffled agitated vessel with a flat gas‐liquid interface operated in a continuous manner. The volumetric liquid‐phase mass transfer coefficients for the bubbles generated in the agitated liquid and the enhancement factors of the volumetric liquid‐phase mass transfer coefficient for the free liquid surface due to the bubbling were calculated from the measured desorption rates and correlated as functions of the relative supersaturation of the solution and the liquid‐phase Reynolds number.
Fundamentals of gas‐liquid‐solid fluidization
Authors: Muroyama Katsuhiko , Fan Liang‐Shih
Published: June 2004

The successful design and operation of a gas‐liquid‐solid fluidized‐bed system depend on the ability to accurately predict the fundamental properties of the system, specifically, the hydrodynamics, the mixing of individual phases, and the heat and mass transfer properties. Identification of the flow regimes under which the system operates is crucial to an understanding of both the variations of these properties and overall system performance. This timely, comprehensive review describes in a systematic manner the status of fundamental gas‐liquid‐solid fluidization behavior. This review also discusses the areas in which current knowledge is deficient and further research is needed.
Intermediate storage in noncontinuous processes involving stages of parallel units
Authors: Karimi I. A. , Reklaitis G. V.
Published: June 2004

A model is developed to study holdup in intermediate storage as a function of system parameters such as processing unit delay times. General results concerning the periodicity of the required storage volume, the allowable unit delay times, and the calculation of the volume are presented. Analytical expressions for the limiting volume are obtained for several special network configurations. A simple upper bound is derived for purposes of quick estimates of the limiting volume for the general case, and a gradient based algorithm is reported for obtaining the minimum volume schedule for general networks.
Reactor selectivity based on first‐order closures of the turbulent concentration equations
Authors: Brodkey R. S. , Lewalle Jacques
Published: June 2004

Toor's (1969) hypothesis is extended to the second‐order, series‐parallel reaction. A second closure relates the mixing for the second reaction to the first. The equations are solved for conversion and selectivity for a turbulent reactor configuration. The analysis is extended to incorporate concepts of residence time distribution, segregation, and maximum mixedness.
Particle collection in magnetically stabilized fluidized filters
Authors: Albert R. V. , Tien Chi
Published: June 2004

A study was conducted on the use of magnetically stabilized fluidized (MSF) filters for removing fine particles from gases. The effect on filter performance of a number of variables was examined, including the applied field strength, gas velocities, and bed height. The dynamic behavior of MSF filters was found to be characterized by a decreasing collection efficiency with time as a result of significant particle re‐entrainment.
Influence of secondary flow on diffusion with reaction
Authors: Mashelkar R. A. , Venkatasubramanian C. V.
Published: June 2004

Coiling of a tube produces a profound change in the internal flow patterns due to the generation of a centrifugally driven secondary flow. This change strongly influences the transport processes in a coiled tube. The present paper investigates the influence of such secondary flow on a process of convective diffusion with reaction. The findings have an important bearing on a better understanding of a coiled tube reactor.
A moving‐front transition boiling model
Authors: Kao Y. K. , Weisman J.
Published: June 2004

In accordance with visual observations, a transition boiling model that assumes a quench front which alternately advances and retreats in the water flow direction, is proposed. With appropriate choice of a quench zone width and heat transfer rate when the surface is wet, the model predictions are in the same range as the observed temperature oscillations. An extension of the model leads to heat transfer rate predictions in general agreement with experimental observations.
Aerosol behavior in temperature and concentration gradient fields in nonisothermal tube flow
Authors: Nadkarni A. R. , Mahalingam R.
Published: June 2004

A general aerosol dynamics equation is derived for nonisothermal steady flow in cylindrical geometry. A scheme for the numerical solution of this equation is presented and its application is illustrated for a practical case incorporating condensation, nucleation, and thermophoresis effects. Additionally, the results of the numerical computations are compared with laboratory experimental measurements of changes in aerosol concentrations and size distributions for nonisothermal flow through a horizontal circular tube.
A single particle approach for analyzing flow systems. Part III: Multiple fluids
Authors: Rubinovitch Michael , Mann Uzi
Published: June 2004

This paper provides a stochastic model for general flow systems with several inlets and outlets, where different fluids are fed through the various inlets. Several process characteristics are derived and discussed. They include the distribution, mean, and variance of the number of visits and total residence time of the various fluid elements to flow regions and the fraction of each fluid that avoids a flow region or a group of flow regions. It is shown that for any fluid and any specified region, the local flow rate through the region is equal to the product of the net flow rate through the system and the mean number of visits to the region by a fluid element of this type. Expressions are also derived for the compositions of material at the outlet streams and at individual flow regions exits, as well as for the composition of material inside each flow region. These results may be employed to verify flow models of physical systems and to determine model parameters.
Low backmixing in multistage agitated contactors used as reactors
Authors: Vidaurri F. C. , Sherk F. T.
Published: June 2004

The objective of the study was to test the validity of an available backmix correlation in the low backmix regime required by multistage agitated contactors used as reactors. The correlation was found to be inapplicable, and new equation forms were developed to fit the new experimental data. Keys to low backmix rates are a small annular area around the shaft compared to the column cross‐sectional area and an extended annular path length.
A model for parison behavior in the extrusion blow molding process
Authors: Dealy J. M. , Orbey Nese
Published: June 2004

A simple, lumped‐parameter model has been developed to predict the length and shape of a parison on the basis of experimental swell data and the storage modulus of the resin. The applicability and limitations of the model are demonstrated by comparing its predictions with experimental observations of parison behavior.
Rapid hydropyrolysis of softening coal particles—A modeling study. Part II: Model predictions and comparison with experimental results
Authors: Schaub Georg , Peters W. A. , Howard J. B.
Published: June 2004

The mathematical model described in Part I is applied to predict CH4 and tar yields in rapid hydropyrolysis of softening coal particles. Predicted effects of pressure and particle size agree with trends previously measured in a screen heater apparatus.
Porosity effects on catalytic char oxidation. Part I: A catalyst deposition model
Authors: Su J. L. , Perlmutter D. D.
Published: June 2004

Six char samples generated from two coals were impregnated by solutions with different concentrations of Na2CO3 and /or K2CO3. The catalyst solution penetration was studied, the catalyst uptake was measured, and the effects of impregnation on the char pore structure were determined experimentally. The results indicate that the impregnated catalysts reside only on particle exteriors without significant penetration. The overall rate of reaction is therfore the combination of catalytic reaction on particle exteriors and noncatalytic reaction on the pore surfaces inside the particle. A kinetic model is presented that takes these findings into account.
Effect of pore structure on char oxidation kinetics
Authors: Su J.‐L. , Perlmutter D. D.
Published: June 2004

Prior studies have demonstrated that char gasification rates vary with conversion, showing a maximum at an intermediate level. In this work experimentally determined char‐air reaction rates and corresponding pore structures are compared to assess the applicability of a previously proposed random pore model and to extract pertinent chemical and physical parameters. Results on six different chars are presented and analyzed to obtain structure parameters, intrinsic kinetics, and activation energies. Agreement between two independent evaluations of the structure parameters demonstrates the degree of applicability of the random pore model and supports the view that rate variations with conversion are controlled by pore structural changes, even though overall rates also include contributions of intrinsic reactivity.
Incipient fluidization condition for a centrifugal fluidized bed
Authors: Fan L. T. , Chang C. C. , Yu Y. S. , Takahashi Teruo , Tanaka Zennosuke
Published: June 2004

A model has been proposed for the condition of incipient fluidization in a centrifugal fluidized bed. The model is based on the balance between the overall forces, including the centrifugal and fluid frictional forces, exerted on the fluidized particles and the overall effective weight of the particles. Equations have been derived from the model for predicting the critical fluidizing velocity and the maximum pressure differential (or pressure drop) through the centrifugal bed. A series of experiments was carried out with different solid particles, bed rotational speeds, and bed heights. The resultant data for the critical fluidizing velocity and the maximum pressure drop of the bed indicate that the proposed model is valid and the derived equations are of practical use.
A model for pressure drop in two‐phase gas‐liquid downflow through packed columns
Authors: Rao V. G. , Drinkenburg A. A. H.
Published: June 2004

The nature of the interaction between the flowing phases in a cocurrent gas‐liquid downflow through packed beds depends on the type of the flow regime. The interaction is poor and geometric in nature in gas‐continuous flow and becomes high and dynamic in pulse flow due to gas dispersion, acceleration, and mixing of the liquid in the pulses. Models to calculate pressure drop in each of the flow regimes are presented, taking into account the respective interactions. Experimental data on pressure drops and liquid holdups were measured in gas‐continuous flow for 3 mm glass spheres and 6 mm Raschig rings. An air‐water system is used. The literature data on pressure drops and the experimental data, covering liquid velocities from 0.001 m/s to 0.029 m/s and gas velocities from 0.097 m/s to 2 m/s, were compared with the calculated values. It was found that the pressure drop due to dynamic interaction can be as low as 10% and as much as 80% of the total pressure drop for the data examined in this work. An empirical correlation for holdup in gas‐continuous flow is given for Rashig rings.
Adsorption equilibrium constants and intraparticle diffusivities in molecular sieves by tracer‐pulse chromatography
Authors: Hyun S. H. , Danner R. P.
Published: June 2004

A perturbation chromatography technique using radiotracer gases has been developed to determine the adsorption equilibrium constants and diffusivities in molecular sieves. The ethane and ethylene 13X molecular sieve systems were studied in regions of high concentration. The data obtained by this technique are shown to be in agreement with equilibrium data obtained by static methods and with kinetic data obtained by adsorption uptake and chromatographic methods, but not with kinetic data obtained using NMR techniques. The tracer‐pulse chromatographic technique is much more efficient for obtaining gas adsorption equilibria and intraparticle diffusivities and is considerably easier to adapt to wide pressure and temperature ranges than the conventional methods.
A study of inertial effects in granular bed filtration
Authors: Gal E. , Tardos G. , Pfeffer R.
Published: June 2004

The filtration efficiency of a granular bed filter was investigated in the domain where inertial effects are dominant. A filtration model predicting single sphere and total bed efficiencies based on trajectory calculations of dust particles in the voids of the granular bed was developed. The model uses the flow field in a bed of spheres arranged in a body‐centered cubic array for which the filtration efficiency was found to be a function of a modified Stokes number defined by St′ = St × F where the function F depends only on the Reynolds number. The value of the function F can be found experimentally or predicted from the Ergun correlation to be F = 1 + 0.0157 Re. The filtration efficiency calculated using the model agrees well with experimental results obtained in beds of dense cubic packing of spheres especially at relatively low Reynolds numbers (Re < 200) and relatively high Stokes numbers (St′ > 0.01). The prediction of the theoretical model also agrees well with experimental data for randomly packed beds at low porosities and low Reynolds numbes.
Turbulent flow in stirred tanks. Part I: Turbulent flow in the turbine impeller region
Authors: Placek Jiri , Tavlarides L. L.
Published: June 2004

The concept of the trailing vortex introduced by van't Riet and Smith (1975) is used for evaluation of the mean velocity and intensity of periodic velocity fluctuations in the turbine impeller discharge flow. From the analysis of forces acting on the trailing vortex, it follows that geometric similarity in the impeller discharge flow can be expected for the Reynolds number range Re ε 〈1.5 × 104; 9.0 × 104〉 and for the radial distance up to one‐tenth of the impeller diameter. The calculated profiles of mean velocity and intensity of periodic velocity fluctuations agree with published data and permit the declaration of boundary conditions for the impeller discharge flow for numerical modeling of turbulent fluid flow in turbine impeller agitated tanks.
Relation of oil yield to the structure of the thermal wave in the combustion processing of oil shale
Authors: Hiskakis Miltiadis , Hanratty T. J.
Published: June 2004

The combustion retorting of oil shale is analyzed. By using coordinate systems moving at the same velocity as reaction zones, a model is obtained for the fully developed thermal wave which would exist after the wave has progressed a sufficient distance into the bed. Of particular interest is the interpretation of oil yield in terms of the structure of the wave and of operating variables.
Chemical kinetics of the reaction of carbon dioxide with ethanolamines in nonaqueous solvents
Authors: Sada E. , Kumazawa H. , Han Z. Q. , Matsuyama H.
Published: June 2004

The kinetics of the reaction of carbon dioxide with mono‐ and diethanolamine in such nonaqueous solvents as methanol, ethanol, and 2‐propanol and in water were studied using a stirred tank absorber with a plane gas‐liquid interface at 303 K. The reaction was found to be of first order with respect to carbon dioxide for every solvent. The order of reaction with respect to ethanolamine was found to be unity only for an aqueous solution of monoethanolamine and for the other solutions, ranged from 1.4 to 2, depending on the solvent species. The reaction order was increased in the order of water, methanol, ethanol, and 2‐propanol. The variation of the reaction order with the solvent species could be explained in terms of a reaction scheme via a zwitterion. Almost linear dependence of the logarithm of the reaction rate constant on the solubility parameter of the solvent was derived.
Hot purge gas regeneration of adsorption beds with solute condensation: Experimental studies
Authors: Friday D. K. , LeVan M. D.
Published: June 2004

Activated carbon beds with adsorbed n‐octane are regenerated using hot air. Effects of pressure, feed temperature, and initial loading on temperature and concentration breakthrough curves are studied. For moderate and high values of these variables, effluent vapors are found to be saturated with hydrocarbon during part of the heating step, indicating the presence presence of liquid within the bed. Regeneration behavior is predicted with reasonable accuracy using a nonisothermal stage model.
Discrete cell model of fixed‐bed adsorbers with rectangular adsorption isotherms
Authors: Do D. D.
Published: June 2004

Adsorption of organics inot activated carbon particles within a fixed‐bed adsorber is modeled using the concept of mixing cells. The adsorption isotherm of these organics is taken to be rectangular because of the commonly observed strong affinity of organics into activated carbons. The model equations are solved by a singular perturbation method, and this results in a graphical procedure similar to that of McCabe and Thiele used in distillation column design. Such a graphical procedure provides a quick means to determine the adsorbate profiles along the adsorber for a given time and also the breakthrough curve, which reflects the performance of the adsorber.
Dynamics of deep‐bed filtration. Part II: Experiment
Authors: Chiang Hsu‐Wen , Tien Chi
Published: June 2004

Filtration experiments were conducted using granular beds composed of nearly monosized filter grains and monodispersed suspensions. The experimental data obtained are histories of filtrate quality and pressure drop across the filter bed, from which local filter coefficient and pressure gradient were determined as functions of the specific deposit. The experimental results, together with the results of the analyses of the two limiting situations presented in Part I, were used to develop a general correlation which accounts for the change in filter performance caused by particle deposition.
Evaluating significant economic trade‐offs for process design and steady‐state control optimization problems
Authors: Fisher W. R. , Doherty M. F. , Douglas J. M.
Published: June 2004

An order‐of‐magnitude analysis that evaluates the significant economic trade‐offs for the process design optimization problem allows rapid screening of flowsheet alternatives. The optimization problem is simplified by eliminating all but the most important design variables and by including only the dominant cost functions for each trade‐off. Quantitative parameters are defined which allow a straightforward selection of these elements and identify the incentive for optimization. A new optimization criterion helps to prevent the rigor of the optimization analysis from exceeding the accuracy of the design and economic models used.
Perturbation solution and moment expansion for nonlinear adsorption in a CSTR
Authors: Allal K. , Hinds B. C. , McCoy B. J.
Published: June 2004

Regular perturbation theory is applied to determine the response to an impulse input in a continuous‐flow stirred‐tank reactor (CSTR) with nonlinear adsorption. A series expansion for temporal moments is a result of the procedure. This moment expansion allows the usual restriction of linearity in analysis of experimental data by moments to be waived. The response at each order can be expressed as an expansion in Laguerre polynomials involving moments, which, in the present example, converges to the exact solution.
Selectivity modification in electroorganic reactions by periodic current control: Electroreduction of nitrobenzene
Authors: Fedkiw P. S. , Chao J. C.
Published: June 2004

The electroreduction of nitrobenzene in deoxygenated acid solution generates predominantly either p‐aminophenol or aniline via the common electrochemically generated intermediate, phenylhydroxylamine. Square wave current control increases the reaction selectivity for p‐aminophenol, which is produced in a chemical pathway from the intermediate over that obtained at the average current of the oscillation. Data collected under electrokinetic‐controlled reaction conditions on a planar copper electrode in a water‐propanol‐sulfuric acid medium show an order of magnitude increase in selectivity at 100 Hz over that measured at the average direct current. The electrode is depolarized under periodic current control which results in lower rates of undesired electrochemical reactions with a consequential increase in chemical product selectivity. Implications and limitations of periodic electrochemical reaction rate control are discussed.
The surface rejuvenation theory of wall turbulence for momentum, heat and mass transfer: Application to moderate and high schmidt (Prandtl) fluids
Authors: Loughlin K. F. , Abul‐Hamayel M. A. , Thomas L. C.
Published: June 2004

The surface rejuvenation model of the turbulent burst process, already developed for the momentum and heat transfer processes, is applied to the field of mass transfer. The range of applicability of the theory, previously shown to be valid for the Prandtl number range 0.7 to 64 is extended to Schmidt numbers of 6,500 without introducing any new parameters. Concentration and temperature profiles for high Schmidt and Prandtl numbers are in agreement with experimental data. Theoretical expressions for Sherwood and Stanton numbers are calculated and shown to be in agreement with experimental data over five orders of magnitude.
Design of cyclic fixed‐bed adsorption processes. Part II: Regeneration and cyclic operation
Authors: Costa Carlos , Rodrigues Alirio
Published: June 2004

Regeneration of polymeric adsorbents saturated with phenol in a fixed bed is modeled by an “equilibrium model” and a “reaction front model.” These models were previously tested over CSTR experiments.

A package for the design of cyclic fixed‐bed adsorbers was then prepared by linking the reaction front model for regeneration with a pore‐diffusion model for saturation described in Part I (Costa and Rodrigues, 1985) and a model for washing. Predicted and experimental results were compared in a cyclic run.
Application of the fractional derivatives method to bubble growth/dissolution processes with or without first‐order chemical reaction
Authors: Hong Juan , Woo H. S.
Published: June 2004

A new application of the fractional derivatives technique is presented to analyze bubble growth/dissolution processes with or without first‐order chemical reaction. The second‐order partial differentail equation with moving boundary conditions is converted to a first‐order ordinary differential equation using the fractional derivatives technique. The first‐order differential equation can be simplified to the quasistationary and the quasisteady‐state equations under appropriate conditions. The predictions of the fractional derivatives solution (FDS) are in excellent agreement with those by numerical methods over a wide range of the dimensionless parameter Na, which describes the extent of gas saturation. The versatility of FDS encompasses various approximate solutions.
Analysis of deep bed filtration data: Modeling as a birth‐death process
Authors: Fan L. T. , Nassar R. , Hwang S. H. , Chou S. T.
Published: June 2004

To simulate the performance of a deep bed filter in terms of the pressure drop dynamics under a constant flow condition, a fairly general stochastic model, namely, the birth‐death process, which takes into account both blockage of the pores by suspended particles and scouring of deposited particles, is combined with the Carman‐Kozeny equation. This model is relatively simple in that the entire bed is spatially lumped and it contains only two parameters, α and β, which are fairly easy to identify. In spite of this simplicity, the model is capable of representing the majority of the available experimental data.
Diffusion and adsorption of moisture in desiccant sheets
Authors: Raghavan Vaikuntam , Gidaspow Dimitri
Published: June 2004

The simultaneous diffusion and adsorption of water vapor into specially prepared silica gel and activated carbon desiccants was experimentally studied for laminar flow through an isothermally maintained parallel‐plate channel. The equilibrium characteristics and tortuosities of the various desiccant sheets used were experimentally determined.

The data were compared with a modified Rosen model. The Rosen model predicts outlet concentrations from the knowledge of adsorption equilibrium constants, diffusion, and mass transfer coefficients. A comparison of computed and measured concentrations as a function of sorption time shows that with independently measured equilibrium and effective diffusion coefficients, the modified Rosen model became completely predictive.
A simultaneous‐modular approach to process flowsheeting and optimization. Part II: Performance on simulation problems
Authors: Chen Hern‐Shann , Stadtherr M. A.
Published: June 2004

The performance of the simultaneous‐modular approach on five simulation problems, ranging in complexity from very simple to moderately complex, is studied. Numerical experiments comparing different computational strategies for implementing the simultaneous‐modular approach are also performed. Full‐block perturbation is found to be the most suitable technique for obtaining the flowsheet‐level Jacobian. On process simulation problems the simultaneous‐modular approach, as implemented in SIMMOD, is found to be as reliable as the sequential‐modular approach, and competitive with or sometimes much better than the sequential‐modular approach in terms of computational efficiency.
A simultaneous‐modular approach to process flowsheeting and optimization. Part III: Performance on optimization problems
Authors: Chen Hern‐Shann , Stadtherr M. A.
Published: June 2004

The performance of the simultaneous‐modular approach on four process optimization problems is studied, and numerical experiments using different computational strategies are also performed. The simultaneous‐modular approach is found to be very effective on process optimization problems, and the strategies used in our implementation SIMMOD are found to be more efficient than those used in previous implementations of the simultaneous‐modular approach for process optimization.
Transient ion exchange and solubilization of limestone in an oil field sandstone: Experimental and theoretical wavefront analysis
Authors: Schweich D. , Sardin M.
Published: June 2004

The competition between calcium‐sodium ion exchange and the solubilization of calcium carbonate is studied in a column packed with a sandstone from an oil field. An equilibrium model accounting for this coupling is described. It is shown that the preflush used to eliminate the exchangeable calcium has only a transient efficiency and that the salinity of the water after the preflush can no longer be decreased to a very low level when the solubilization process occurs.
Hydrogenation of butynediol to cis‐butenediol catalyzed by Pd‐Zn‐CaCO3: Reaction kinetics and modeling of a batch slurry reactor
Authors: Chaudhari R. V. , Parande M. G. , Ramachandran P. A. , Brahme P. H. , Vadgaonkar H. G. , Jaganathan R.
Published: June 2004

An experimental study of the kinetics of hydrogenation of butynediol has been reported using Pd‐Zn‐Ca3 catalyst in a slurry reactor. The effects of catalyst loading, butynediol concentration, H2 partial pressure, butenediol (product concentration, temperature, and agitation speed on the rate of hydrogenation have been studied using a stirred pressure reactor). The initial rate data shwoed that the rate is proportional to the square root of H2 pressure, while increase in butynediol concentration inhibited the reaction. A Langmuir‐Hinshelwood‐type rate model has been proposed based on these data and the kinetic parameters evaluated. The values of the activation energy E and the heat of adsorption of butynediol (−ΔH) evaluated were 38.30 kJ/mol and –9.87 kJ/mol, respectively.

Batch reactor models were derived based on the rate expression obtained from the initial rate data for variable pressure as well as constant pressure conditions. The prediction of the model were compared with experimental data obtained over a wide range of conditions. The predictions of the model were compared with experimental data obtained over a wide range of conditions. The results agreed well within 5–7% error. Use of the pressure vs. time data for evaluation of kinetic and mass transfer parameters is also demonstrated.
A nonequilibrium stage model of multicomponent separation processes. Part III: The influence of unequal component‐efficiencies in process design problems
Authors: Krishnamurthy R. , Taylor R.
Published: June 2004

The conventional equilibrium‐stage model that uses a component‐independent stage efficiency and a nonequilibrium‐stage model, in which mass transfer rate equations are solved simultaneously with the stage conservation equations, are employed to solve four representative distillation design problems. There are large differences between the number of stages predicted by the two models for a specific separation of the more volatile component. The differences arise from two causes: the way in which the liquid phase resistances and equilibrium equations are used in the models, and the consequences of diffusional interaction effects. Neglect of the latter may lead to an underdesigned column; there is between a 9 and 15% difference in the stage requirements predicted by the nonequilibrium model with a rigorous mass transfer model and a nonequilibrium model which ignores interaction effects.
Regeneration of activated carbons used in waste‐water treatment by a moving‐bed regenerator
Authors: Hashimoto Kenji , Miura Kouichi , Kyotani Susumu
Published: June 2004

A method was developed for calculating the distributions of weight loss and temperature of spent activated carbon in a moving‐bed regenerator in which the solid flow was regarded as being plug flow. A kinetic model developed earlier, which was based on regeneration consisting of many first‐order reactions each with different frequency factors and different activation energies, was successfully applied to a design method for the regenerator. The flow pattern of the solid particles and heat transfer characteristics in a small moving bed were clarified experimentally, and the information obtained was used to calculate the distributions of weight loss of the spent carbon and temperature in the moving‐bed regenerator by means of the design method. The calculated results were in fairly good agreement with the experimental data obtained in a small moving‐bed regenerator. The adsorption capacity of the regenerated carbon was comparable to or greater than that of the virigin carbon.
Analytic reduced‐order dynamic models for large equilibrium staged cascades
Authors: Celebi Caglayan , Chimowitz E. H.
Published: June 2004

A model reduction technique based upon modal analysis is presented for modeling the dynamics of general, large equilibrium staged cascades encountered in chemical processes. The analysis is general enough to encompass quite complex cascades involving multiple fee and/or product streams with nonideal thermodynamic behavior. The low‐order models proposed have a number of desirable features: the state variables have physical significance and model parameters are clearly related to the fundamental process parameters which are easily obtainable from steady‐state plant data. Quantitatively it is shown that the low‐order models proposed are in excellent agreement with the complete (high‐order) dynamic models on a range of problems some of which involve complex, nonideal cascades.
Zero‐gravity distillation utilizing the heat pipe principle (micro‐distillation)
Authors: Seok D. R. , Hwang Sun‐Tak
Published: June 2004

Separation of ethanol‐water and methanol‐water mixtures has been accomplished experimentally using a horizontal zero‐gravity distillation column. A countercurrent flow between liquid and vapor phases was established utilizing the principle of the heat pipe. The concentration profile along the column has been investigated with various product rates. A high degree of separation was achieved in a relatively short column lined with capillary wicks. The flexible column orientation can also be a tremendous advantage as compared to the necessarily vertical operation of the conventional distillation columns.
The vacancy solution model of adsorption—improvements and recommendations
Authors: Cochran T. W. , Kabel R. L. , Danner R. P.
Published: June 2004

The vacancy solution model of adsorption which uses an activity coefficient equation of the Wilson form has been improved (1) by incorporating temperature dependency into the model, and (2) by development of a functional relationship between the adsorbate‐adsorbate binary interaction parameters. This reduces the number of regression parameters and improves the predictive capabilities of the model. Comparisons of this improved model with the Flory‐Huggins activity coefficient form of the vacancy solution model are presented for binary and ternary systems. For a priori predictions from pure‐component data, the Flory‐Huggins form is recommended. If experimental binary data are available for all pairs, the form that most accurately correlates the binary data should be used to predict higher‐order systems.
Study of coal gasification in an experimental fluidized bed reactor
Authors: Neogi D. , Chang C. C. , Walawender W. P. , Fan L. T.
Published: June 2004

Thermal gasification has been proposed as one technical option for the conversion of coal to gaseous fuels and/or chemicals to supplement supplies presently derived from petroleum and natural gas. In the present study, a bench‐scale fluidized bed reactor was used for the gasification of coal with steam as the fluidizing medium. A mixture of sand and limestone used as the bed material made it possible to gasify a caking coal without the problem of agglomeration. The gas composition and yield of the hydrogen‐rich product gas were studied as a function of temperature.

To study the heterogeneous reactions taking place in the reactor and also the transient behavior of the system, a mathematical model was developed. The model assumed a reaction mechanism that accounted for the devolatilization of coal, cracking of volatiles, char gasification, and the water‐gas shift reaction. Both the dynamic behavior and steady state performance of the gasifier were simulated based on the model. The steady state results of the simulation were compared with the experimental data. This comparison enabled us to ascertain that the proposed reaction mechanism and dynamic model predicted the correct trends.
Experimental study on the separability of reaction‐deactivation kinetics: Thermal desorption of alcohols from fresh and Na‐poisoned γ–Al2O3
Authors: Forzatti Pio , Borghesi Massimo , Pasquon Italo , Tronconi Enrico
Published: June 2004

Temperature programmed desorption (TPD) of methanol and ethanol from fresh and Na‐poisoned γ–Al2O3 has been employed to investigate experimentally the separability of reaction‐deactivation kinetics. The analysis of the TPD spectra has provided both an energetic characterization of the nonhomogeneous catalytic surface and the kinetic parameters of the desorption reaction, and has allowed quantitative discussion of the separability of the expression for the rate of desorption. The results obtained have been related to the chemical causes of nonseparability of reaction‐deactivation kinetics; they also demonstrate the influence of catalyst decay on selectivity. For the systems considered, it appears that the assumption of separable deactivation kinetics is generally not a satisfactory approximation.
A radioisotopic tracer method for measurement of solids concentration in a settling bed of solids
Authors: Watson J. S. , Brown C. H. , Byers C. H. , Clinton S. D. , Perona J. J.
Published: June 2004

A new and improved radiotracer technique provides information on both the particulate concentration and the movement during sedimentation of monodispersed and binary mixtures. In studies of sedimentation with 44 and 62 μm ion exchange particles, several solids concentrations, three fluid viscosities, and three mixtures with different ratios of the two size particles, the results all lie close to a correlation proposed by Richardson and Zaki.
A new model for entrainment from fluidized beds
Authors: Briens C. L. , Bergougnou M. A.
Published: June 2004

A model describing the entrainment of solid particles from gas‐fluidized beds of mixed‐size particles is proposed. It was tested with the limited experimental data published to date and was shown to be superior to existing models and correlations. The model demonstrates that the concentration of very fine particles in the bed can have a significant effect on entrainment.
Reconciliation of process data with process simulation
Authors: Stephenson G. R. , Shewchuk C. F.
Published: June 2004

The SACDA group at the University of Western Ontario has developed an equations‐oriented modular process simulation program called MASSBAL. A model of a process is constructed by selecting and flowsheeting standard building blocks describing fundamental operations such as the mixing and separating of streams. Building blocks are also provided by which equipment operating or design equations may be incorporated into the model. Reconciliation of the inconsistency and redundancy of process measurements is an optional feature of the program. The measurements are reconciled by minimizing a weighted least‐squares criterion while satisfying the model equations and any modeling constraints. The minimum is obtained directly, avoiding the need for laborious searching techniques.
Parametric sensitivity in fixed‐bed catalytic reactors: The role of interparticle transfer resistances
Authors: Morbidelli Massimo , Varma Arvind
Published: June 2004

The parameteric sensitivity behavior of a plug‐flow catalytic fixed‐bed reactor with negligible intraparticle mass and heat transfer resistances is examined for any positive‐order irreversible reaction. By combining information about multiplicity and runaway, a complete picture of the steady state reactor behavior is obtained. Calculations of the parametrically sensitive region for various values of the involved dimensionless parameters are reported.
The hydrodynamics of trickling flow in packed beds. Part II: Experimental observations
Authors: Levec J. , Sáez A. E. , Carbonell R. G.
Published: June 2004

The liquid holdup and the pressure drop for two‐phase trickling flow in a packed bed were measured experimentally. Different values of those parameters were obtained as the liquid flow rate was increased and then decreased, indicating a multiplicity in hydrodynamic states. This behavior was observed even when the gas flow rate was zero in the bed. It was determined that the hysteresis exhibited by the process is due to imperfect wetting of the packing and to the difference between advancing and receding contact angles at the gas‐liquid‐solid contact lines. The reduced wetting conditions are also the cause of the increase in liquid holdup observed when the surface tension of the liquid is decreased. In this case, the amount of liquid retained in the bed is controlled by the extension of the wetted regions due to the more favorable contact angles as the surface tension decreases. The transition from the trickling to the pulsing flow regime was also dependent on the history of the process.

A new correlation for predicting liquid holdups and pressure drops for trickling flow in packed beds is proposed for the decreasing liquid flow rate operating mode. This correlation is based on the experimental determination of the liquid phase relative permeability as a function of the the liquid phase reduced saturation and the determination of the gas phase relative permeability as a function of the gas phase saturation and the gas phase Reynolds number. The new data are analyzed in the light of the theory developed in the first part of this paper.
Effect of recycle structure on distillation tower time constants
Authors: Kapoor Naveen , McAvoy T. J. , Marlin T. E.
Published: June 2004

Recycle of material or energy can change the effective dynamic behavior of a process. Distillation towers are inherently recycle processes. Published tower time constants based on linear analysis have been substantially in error when compared to actual responses for many cases. The reason for this error is shown to be the recycle nature of distillation towers. An improved method of estimating time constants, which can be extended to industrial towers, is presented.
Effect of radial velocities on laminar flow, tubular reactor models
Authors: McLaughlin H. S. , Mallikarjun Ramesh , Nauman E. B.
Published: June 2004

Existing models for laminar flow in tubular reactors neglect radial velocities in the momentum transport equation. The axial velocity distribution is calculated assuming fully developed flow wherein axial velocities are in local equilibrium with the radial viscosity profile. A test of this assumption has been devised using a representative model of the Newtonian viscosity, μ(r, z), and by reconstructing the radial velocity components using the continuity equation. The assumption of fully developed flow is shown to be a valid approximation for typical polymerization reactions. However, the fact that radial velocities are negligible with respect to momentum transport does not mean they are negligible with respect to convective diffusion of heat and mass. Radial convection is shown to be important for typical polymerization and heat transfer examples.
Dynamic interfacial tensions in acidic crude oil/caustic systems. Part I: A chemical diffusion‐kinetic model
Authors: Borwankar R. P. , Wasan D. T.
Published: June 2004

A chemical diffusion‐kinetic model is developed for the acidic oil/caustic system of alkaline flooding by proposing a set of interfacial reactions leading to in situ generation of surfactants. The rate constants of interfacial reactions are independent of aqueous phase compositions. In Part I, the model is applied for determining these rate constants from its correlation with dynamic interfacial tension data obtained using the spinning drop tensiometer. The relative magnitudes of the rate constants characterizing the adsorption/desorption barriers are shown to govern the extent of dynamic interfacial tension minimum.
Aerobic coupling of aqueous phenols catalyzed by binuclear copper: Ring substituent effect and the kinetics of the coupling of o‐methylphenol
Authors: Cha J. A. , Berry K. B. , Lim P. K.
Published: June 2004

The substituent effect on the aerobic and catalytic coupling of aqueous phenols conforms to a Hammett correlation in which the reaction constant is −2.16; the results are very similar to that of the enzymatic coupling reaction, in which the reaction constant is −2.4. Deviations from the Hammett correlation are attributed to steric factor, product inhibition, and the blocking of coupling sites on phenoxy radicals. Available evidence indicates that catalytic and enzymatic coupling reactions are strikingly similar in many respects. The striking resemblance suggests a common reaction mechanism in which binuclear metal (copper or iron) plays a key role. The common mechanistic features of the coupling reactions are suggested, and the implications of the findings are discussed with reference to (1) the design of a novel dephenolization scheme, (2) the elucidation of the widely occurring but poorly understood enzymatic coupling reactions, and (3) the synthesis of active polymer‐bound coupling catalysts.
Dynamic contact angles on moving plates
Authors: Ishimi Kosaku , Hikita Haruo , Esmail M. N.
Published: June 2004

A simple model for advancing dynamic menisci of the interface between two immiscible fluids is proposed on the hypothesis that there is a monomolecular film which precedes an apparent contact line and that a frictional force due to the solid surface is balanced with the interfacial tension forces on the film. An analytical solution for dynamic contact angles on vertical and inclined solid surfaces of plates is obtained as a function of the interfacial capillary number, the static contact angle, and the parameters of Langumuir's duplex film model. An analytical solution for dynamic meniscus heights is also derived. The analytical solutions are compared with previous experimental data. The agreement between the theoretical and experimental results is found to be fairly good, average deviations being 3.8 and 12%, respectively, for dynamic contact angles and dynamic meniscus heights at the solid surface.
Cocurrent flow of gas‐particulate mixtures through helical tubular colis: Particle velocity measurement and prediction
Authors: Shu Ming‐Tsai , Hamshar J. A. , Weinberger C. B.
Published: June 2004

Particle velocities are measured for the cocurrent flow of air and coal particles through helical colis. The ratio of average particle velocity to gas velocity, Vg, is nearly independent of Vg at 0.25 ± 0.1. This ratio would be above 0.95 for similar flow conditions in straight, horizontal tubes. The particle velocities also depend slightly on other variables, decreasing with larger particles, larger solids feed rate, and smaller helix diameters. Visual observations reveal that the particles slide along the outer periphery of the coil, in a fashion similar to the sliding action at saltation conditions in horizontal flow. A model that permits prediction of particle velocity in helical geometries is proposed; this model is based on the modification of existing saltation velocity correlations by substituting centripetal acceleration for gravitational acceleration. Approximate agreement between experiment and prediction is obtained.
The effective diffusivity of fibrous media
Authors: Koch D. L. , Brady J. F.
Published: June 2004

A procedure based on averaging the conservation equations in a homogeneous, disordered fibrous medium is used to demonstrate that in the limit of long times, macroscopic versions of Fick's and Fourier's laws may be used to relate the average flux to the average gradient in driving force. The asymptotic behavior in the limit of low volume fraction of the effective diffusivity (or conductivity) in such a medium is determined for all values of the Peclet number, P = Ua/Df, where U is the average velocity through the bed, a is the fiber radius, and Df is the molecular diffusivity of the solute in the fluid. The convective disturbance caused by the fibers is found to have a large influence on the rate of mass transfer even at moderate Peclet numbers and low volume fraction.
Kerogen decomposition at subpyrolysis temperatures
Authors: Yucelen Fusun , Smith J. M. , Wakao N.
Published: June 2004

The thermal decomposition of Colorado oil shale was studied at subpyrolysis temperatures, 533 to 611 K, as part of an investigation of rates of supercritical extraction. Thermal degradation followed by solution in the solvent is a possible, partial explanation for the enhanced solubility at supercritical conditions for a complex mixture such as kerogen.

In the region of the critical temperature of toluene, up to 26% of the kerogen in the original shale was converted by thermal reactions to gases and soluble (in toluene at 298 K and 101 kPa) products. The kinetics of the decomposition of the insoluble organics in shale could be explained by a combination of series and parallel reactions.
Effective heat transfer parameters for transient packed‐bed models
Authors: Dixon A. G. , Cresswell D. L.
Published: June 2004

A general theory is presented for the prediction of effective axial conductivity and overall radial heat transfer coefficient for fluid flow through packed beds, under either transient or steady state conditions. The parameters to be used in each case may be quite different, depending on the dominant phase for heat transfer. The theory unifies all previous results and explains conflicting conclusions arrived at by different workers. The ability of a pseudohomogeneous model to reproduce packedbed transients is shown to depend upon the choice of effective parameters.