bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrodynamics of gas‐liquid‐solid annular fluidization
Authors: Fan Liang‐Shih , Kitano Kunihiro , Kreischer B. E.
Published: June 2004

In a strict sense, operation of the three‐phase ebullated bed reactor used in the H‐Oil process is not characterized by conventional three‐phase fluidization, but by annular three‐phase fluidization. In annular three‐phase fluidized beds differences in the hydrodynamic behavior over that found in conventional beds occur through changes in the bubble behavior. The addition of a concentrically located inner column in a gas‐liquid‐solid fluidized bed promotes bubble coalescence. This increase in coalescence can be observed either through changes in the liquid velocity of transition from the coalesced bubble regime to the dispersed bubble flow regime or through changes in holdup behavior. A hydraulic diameter defined for the annulus region proves suitable when comparing different annular systems having the same outside column diameter, but unsuitable when comparing systems having different outside column diameters.
Measurement of critical temperatures of thermally unstable n‐Alkanes
Authors: Smith R. L. , Teja A. S. , Kay W. B.
Published: June 2004

A modified sealed‐tube apparatus has been developed for the measurement of the critical temperatures of thermally unstable fluids. The apparatus has been used to measure the critical temperatures of the normal alkanes from n‐octane to n‐hexadecane. Since the higher alkanes (with more than 10 carbon atoms) decompose at temperatures well below their critical temperatures, a new method of analysis of the apparent critical temperature vs. time data has been developed. This method employs reaction kinetics based on an irreversible first‐order reaction and is used to linearize the data and to perform an unambiguous extrapolation to the critical temperature of the undecomposed substance. The method is successful because the temperature history of the substance is recorded by computer, and ampoule contents are analyzed at the completion of the experiment. The critical temperatures of the n‐alkanes reported in this paper have been compared with values found in previous studies.
A scaling procedure for the structural and interaction analysis of dynamic models
Authors: Bonvin Dominique , Mellichamp D. A.
Published: June 2004

Many techniques that are used for analyzing the structure of large‐scale, interactive systems (including the structural dominance analysis and singular‐value decomposition methods) require a careful scaling of input and output variables to yield useful results. A suitable scaling procedure motivated by physical arguments and aimed at expressing input and output variables in common terms is presented and illustrated through several examples, including nonlinear lumped‐parameter and distributed‐parameter models.
Alkali‐alumina sorbents for high‐temperature removal of SO2
Authors: Gavalas G. R. , Edelstein Sergio , Flytzani‐Stephanopoulos M. , Weston T. A.
Published: June 2004

The high‐temperature removal of SO2 by sorbents consisting of sodium and lithium salts supported on α‐Al2O3 has been investigated with emphasis on the chemistry of regeneration. The sulfated sorbents were regenerated by reduction with CO at 700–800°C in a thermogravimetric analyzer and a packed‐bed microreactor. Sulfur removal from the sorbent and distribution of gaseous products were measured at different alkali loadings, temperatures, and CO concentrations. The results are interpreted in terms of a network of reactions wherein alumina is important as a catalyst and as a reactant. During regeneration sulfate is converted to aluminate and sulfide, the fraction of aluminate defining the extent of regeneration. The rate and extent of sulfur removal increase with the ratio of alumina to alkali and are higher in the presence of lithium. The product gas consists of SO2, COS, and elemental sulfur, the latter compound constituting up to 35% of the sulfur removed.
A cautious self‐tuning controller for chemical processes
Authors: Papadoulis A. V. , Tsiligiannis C. A. , Svoronos S. A.
Published: June 2004

An adaptive controller is presented that is able to perform effectively in the presence of nonlinearities and of model uncertainty typical of industrial processes. The controller incorporates a minimum variance part and a caution part. The latter is independent of the estimated model and becomes dominant in the case of a large mismatch between plant and estimated model. Application to a simulated nonlinear continuous stirred‐tank reactor demonstrates its effectiveness, even when other adaptive controllers give unsatisfactory performance.
Design of enzyme‐pH electrodes
Authors: Varanasi Sasidhar , Stevens R. L. , Ruckenstein E.
Published: June 2004

A theoretical framework useful for predicting the steady state response of enzyme‐pH electrodes is developed. The model takes into account that the catalytic activity of the enzymes as well as the degree of dissociation of the product acids and bases is strongly dependent upon the local pH, and that buffering salts present in solution facilitate the transport of H+ ions. It is shown that the electrode should operate under substrate diffusion‐limited conditions and the concentration of H+ ions should not have steep variations within the enzymic membrane. This condition can be fulfilled by adjusting the buffer concentration in the bulk solution. In the latter conditions the electrode response does not depend on the actual kinetics of the enzymic reaction, and can be predicted by an algebraic equation. The predictions are in excellent agreement with the experiments on penicillinase‐pH and urease‐pH electrodes.
Feedback control of CSD in a KCL crystallizer with a fines dissolver
Authors: Randolph A. D. , Chen Li , Tavana Aria
Published: June 2004

On‐line crystal size distribution control in an 18 L KCl crystallizer, equipped with a fines dissolver, was experimentally studied using inferential control of nuclei density. The control algorithm used was proportional control of inferred nuclei density by manipulation of fines removal rate. A sudden 5–8°C drop in the temperature of the crystallizer was used as a standard upset, which produced a fairly reproducible burst of nuclei. Nuclei density was then estimated from the fine crystal distribution in the fines loop using a light‐scattering instrument. The control study was implemented by a computer program that used the current value of nuclei density to calculate updated set points of the fines removal rate. Simple proportional control of nuclei density in response to changes in fines removal rate was shown to be an effective way to minimize fluctuations in the product crystal size distribution that are caused by nucleation disturbances.
Singular optimal control strategy for a fed‐batch bioreactor: Numerical approach
Authors: Menawat Anil , Mutharasan R. , Coughanowr D. R.
Published: June 2004

The production of bakers' yeast in a fed‐batch bioreactor can be maximized by controlling the substrate feed rate. This leads to a singular optimal control problem. An exact solution initially based on a heuristic argument and later quantified by the generalized Legendre‐Clebsch convexity condition is obtained. A numerical technique, obtained by embedding the singular problem in a sequence of nonsingular problems that converge to the singular one in a limit as ϵ → ∞ is demonstrated.
Flow of a thin liquid layer due to ambient disturbances
Authors: Ruschak K. J.
Published: June 2004

A closed‐form solution for the transient deformation of a thin liquid layer caused by ambient pressure disturbances predicts the level of disturbances that will produce significant flow in the time available. The effects of viscosity, gravity, surface tension, and a soluble surface‐active agent are included in the analysis. The major simplification is the use of the lubrication approximation to the equations of flow. Nearly stationary pressure disturbances are found to be more dangerous than moving disturbances. Surface tension gradients arising from convection of surfactant in the surface oppose flow and reduce the film deformation. The thermodynamic properties of the surfactant, as well as its diffusion coefficient, are important in determining whether significant surface tension gradients develop. However, the effectiveness of a surfactant at minimizing film deformation also depends upon flow parameters such as the natural time scale for flow.
Scanning electron microscopy studies of polymer melt devolatilization
Authors: Albalak R. J. , Tadmor Z. , Talmon Y.
Published: June 2004

The devolatilization mechanism of polystyrene was studied by scanning electron microscopy. Strands of molten polystryene, containing 2,300 ppm styrene, and molten polystyrene containing 5% pentane, were extruded into a heated vacuum chamber. The strands were abruptly frozen, then fractured under liquid nitrogen and their morphology studied with scanning electron microscopy. A rich variety of morphological features in the core and on the surface of strands was discovered. These include micro‐ and miniblisters, fibrous structures, and crusty nodules on the inner surfaces of large macrobubbles. The source of these morphological features and their relevance to devolatilization is discussed.
Panel movement effects on solution flow in through‐holes of printed circuit panels
Authors: Galasco R. T. , David A. P. , Shaffer R. R.
Published: June 2004

A hydrodynamic model is developed relating the movement of printed circuit panels to solution flow in through‐holes. Qualitative and quantitative model verification is experimentally established. Effects of external gas bubbling on hole solution transport are elucidated. Based on the hydrodynamic model, panel motion criteria for contamination‐free and fast chemical processing are introduced. Limits of mechanical panel movement as a method for processing holes of different geometry with typical wet chemical process baths are addressed.
A mechanistic model for two‐phase annular‐mist flow in vertical pipes
Authors: Yao S. C. , Sylvester N. D.
Published: June 2004

The physical phenomena associated with two‐phase annular‐mist flow in vertical pipes are considered. A new mechanistic model is developed to predict liquid entrainment, liquid film thickness, in situ velocities, and pressure drop. The model is compared to field data and found to be superior to the three commonly used empirical correlations.
Self‐tuning control with decoupling
Authors: Chien I‐Lung , Seborg D. E. , Mellichamp D. A.
Published: June 2004

A new method to design adaptive, self‐tuning controllers is presented that incorporates decoupling for multivariable control problems. The algorithm is shown to result from two very different derivations. The first approach employs multiple single‐input/single‐output self‐tuning controllers but with a classical decoupling scheme incorporated; the second approach utilizes a novel selection of design parameters in an existing multivariable self‐tuning control method. The decoupling self‐tuning controller is capable of handling unknown or time‐varying time delays. Simulation studies utilizing two distillation column models show that the controller can provide excellent control even for highly nonlinear and highly interacting processes.
An experimental study of the effect of turbulent mixing on the selectivity of competing reactions
Authors: Mehta R. V. , Tarbell J. M.
Published: June 2004

An experimental study of the effect of turbulent mixing on the selectivity of a parallel‐consecutive reaction system (A + B → R; R + B → S) has been carried out in an unmixed feedstream (multijet) tubular reactor. Fluid mechanical characterization of the reactor by pulsed ultrasound Doppler velocimetry reveals that the mean and rms velocity fields are nearly constant over eight‐ninths of the reactor length. Axial profiles of mean product concentration (R and S) have been measured spectro‐photometrically with a fiber‐optic probe under constant hydrodynamic conditions but with variable feed concentration conditions. The concentration profiles (particularly the S profile) show very large deviations from the perfect mixing (classical plug flow reactor) limit. These data provide a good basis for discriminating among the many models of mixing and reaction available in the literature. This is demonstrated with two examples: the four‐environment model, which fits the data well, and the interaction by exchange with the mean model, which does not.
The kinematics of fountain flow in mold‐filling
Authors: Coyle D. J. , Blake J. W. , Macosko C. W.
Published: June 2004

Moldability criteria and process optimization for both reactive and thermoplastic injection molding hinge on the mold‐filling step. The fluid mechanics of the filling step is typically described in terms of a one‐dimensional main flow and a complex two‐dimensional flow near the advancing front, often termed the “fountain flow.” A unique apparatus which permits direct observation of the fountain flow in a rectangular cavity is described. The motion of tracer lines as well as the pathlines have been photographed for both Newtonian and shear‐thinning liquids. The data show clearly the main flow, the transition to the front flow, and the deceleration and acceleration zones in the fountain flow, which lead to a “mushrooming” of the tracer line.

In addition, Galerkin finite‐element analysis is used to predict the isothermal free‐surface flow of a Newtonian liquid near the advancing front between parallel plates. The most interesting visualization of the calculated flow is obtained by tracking lines of material, thus producing numerical tracer experiments. The calculations show the widely varying residence times and the complex shear and extensional deformation histories of fluid elements as they move through the fountain flow region. The calculations are in agreement with the experiments and clarify previous results, both theoretical and experimental, that did not capture the details of the entire flow field.
The role of porosity in filtration. Part XI: Filtration followed by expression
Authors: Tiller F. M. , Yeh C. S.
Published: June 2004

This paper addresses the question of the relative amounts of liquid removed during filtration and expression as a function of cake compressibility. As liq
uid flows through a porous cake, the accumulative drag collapses the particulate structure, thereby increasing the solid content and displacing the liquid. The use of pump pressure in filtration represents the simplest hydraulic deliquoring process. In expression operations, pistons, membranes, rollers or belts are employed to squeeze the particulate cake after filtration is complete.

Filtration followed by expression at constant pressures ranging from 0.6 to 24.7 MPa (6.1‐243.6 atm) was investigated theoretically and experimentally. During filtration and the early stages of expression, the flow rate and average liquid content of highly compressible attapulgite were virtually unaffected by increasing pressure in the range investigated.
Averting extinction in autothermal catalytic reactor operations
Authors: Metchis S. G. , Foss A. S.
Published: June 2004

A multiloop control system and an on‐line reactor operability analysis were developed for the purpose of detecting and averting extinction of the autothermal state of a laboratory catalytic reactor. The reactor system consisted of a feed‐effluent heat exchanger and two packed beds in which the exothermic reaction between hydrogen and oxygen occurred.

The strategy of control was based on the preservation of the relative stability of the autothermal steady state when the reactor experienced large changes in feed concentration and flow rate. Such a strategy involved a model‐based prediction of reactor conditions that so preserved stability, and a procedure to guide the process rapidly and smoothly to those new conditions. Experiments demonstrated the successful avoidance of extinction and the orderly attainment of new operating conditions in about three reactor‐system time constants. The procedures developed could serve as a component of an on‐line expert system for safe reactor operations.
Phase holdups in three‐phase fluidized beds
Authors: Lee S. L. P. , de Lasa H. I.
Published: June 2004

The local bubble frequency, the local phase holdups and the local bed porosity in three‐phase fluidized beds were measured. Air, water, and 250 μm glass beads were used as the gas, liquid, and solid phases. The effects of gas and liquid velocities on phase holdups were studied. Time‐averaged local gas holdup and bubble frequency were measured by an optical fiber probe. Mass balances were performed at various axial positions along the fluidized beds to check the accuracy of the measurements.
Hindered transport of large molecules in liquid‐filled pores
Authors: Deen W. M.
Published: June 2004

Transport in liquid‐filled pores of molecular dimensions plays an important role in membrane separations, in various forms of chromatography, and in catalysis, to name a few examples. A frequent observation is that if the pore dimensions are of the same order as those of a solute molecule, the apparent diffusion coefficient of that solute is much lower than in bulk solution. Likewise, rates of convective transport of such solutes are generally lower than the product of bulk concentration and volume flow rate. Thus, solute transport is typically “hindered” or restricted. A key objective of research on hindered transport is to be able to predict the applicable transport coefficients from such fundamental information as the size, shape, and electrical charge of the solutes and pores. The present status of this research is reviewed.
Trickle‐bed reactors: Liquid diffusional effects in a gas‐limited reaction
Authors: Beaudry E. G. , Duduković M. P. , Mills P. L.
Published: June 2004

A model is developed for predicting the performance of a partially wetted trickle‐bed reactor for a gas‐limiting reaction of order less than or equal to one. The model indicates that under certain conditions the liquid reactant may affect the reaction rate due to its inability to rapidly diffuse to catalyst areas that are in direct contact with the gas. This model is the first to explain and predict on a rational basis the experimental results for the hydrogenation of diluted ć‐methylstyrene and aqueous maleic acid reported in the literature. A criterion that determines when liquid reactant effects can be expected is developed and reported.
Gas absorption with exothermic bimolecular (1,1 order) reaction
Authors: Bhattacharya A. , Gholap R. V. , Chaudhari R. V.
Published: June 2004

Gas absorption with a nonisothermal, bimolecular (1,1 order), and irreversible reaction are analyzed and approximate film theory solutions are obtained for interfacial temperature rise and enhancement factor. The model of Mann and Moyes is extended to incorporate depletion of liquid reactant concentration at the gas‐liquid interface and also the variation of dissolved gas concentration in the bulk liquid, leading to a generalized solution independent of the regime of absorption. The effect of heat generation, heat dissipation, and reaction rate parameters on enhancement factor and interfacial temperature rise is discussed. The system showed multiplicity behavior under certain conditions, but at higher values of heat dissipation parameters and for some combinations of heat generation and reaction rate parameters, unique solutions were obtained. However, even the unique solutions of enhancement factor are substantially different from the values obtained under isothermal conditions. Since depletion of liquid reactant concentration is incorporated, asymptotic values of enhancement factor (at large \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt M $\end{document}) were observed to be the same as those obtained in the instantaneous reaction regime of isothermal absorption and reaction process. The model presented does not require a priori assumption of the regime of absorption and hence can be useful in modeling nonisothermal reactors.
Control configuration selection for distillation columns
Authors: Skogestad Sigurd , Morari Manfred
Published: June 2004

Most two‐product distillation columns can be described as 5 × 5 plants, but the control system design is usually simplified by means of the following procedure:

Choose two manipulated inputs for composition control (corresponding to a specific control configuration).

Design the level and pressure control system (usually three SISO controllers).

Design a 2 × 2 controller for composition control.

This paper provides guidelines for step 1, which is considered the most important. Ratios (e.g., L/D or V/B) are frequently chosen as manipulated inputs in step 1. It is shown that the ratio configurations are effectively complex multivariable controllers that provide, among other features, improved flow disturbance rejection.
Fines migration in porous media
Authors: Sharma M. M. , Yortsos Y. C.
Published: June 2004

A model developed by Sharma and Yortsos (1987a) is applied to the processes of fines migration and fines injection in a porous medium. The first is a problem frequently encountered in oil reservoirs when release of fines is triggered by physicochemical interactions of the porous formation with the injected fluids. The second may be a problem in the filtration of relatively large particulates. Simple solutions are provided for both processes by considering size exclusion as the dominant particle retention mechanism. The solutions developed provide expressions for the particle concentration profiles, the open pore density and pore size distribution profiles, as well as the permeability reduction. These expressions are of importance in the evaluation of the extent and depth of formation damage and can be used as designing tools for remedial treatment, such as acidizing or fracturing.
Predicting fluid‐bed reactor efficiency using adsorbing gas tracers
Authors: Krambeck F. J. , Avidan A. A. , Lee C. K. , Lo M. N.
Published: June 2004

Gas tracers have been used frequently to predict conversion in chemical reactors. But in heterogeneous systems such as fluid‐bed reactors, tracer residence time data usually overpredict actual contact time and conversion. In this work, the general two‐phase countercurrent flow model is extended to include tracer adsorption, which is important in predicting contact time. The tracer used was SF6, whose adsorption on the solids could be varied over a wide range. The apparent reactor efficiency, calculated directly from tracer response, is shown to approach that estimated from the two‐phase model when the fluid bed approached homogeneity. This is the case for many large‐scale reactors that are operated in the turbulent fluidization regime. The use of horizontal baffles in methanol‐to‐gasoline cold flow models is shown to improve bed efficiency by staging the bed.
Dynamic modeling of deep‐bed filtration
Authors: Mackie R. I. , Horne R. M. W. , Jarvis R. J.
Published: June 2004

Previous attempts to model the effect of deposition on removal efficiency in deep‐bed filtration have relied heavily on the determination of empirical parameters even for monosized suspensions. A newly developed mathematical model not only significantly reduces this reliance, but takes full account of the polydispersity of suspensions. The results of eight runs on an experimental filter are compraed with the predictions of the mathematical model. Qualitative agreement is good; quantitative agreement is fair.
Solubility in binary mixtures at the immiscibility critical point
Authors: Ludmer Z. , Shinnar R. , Yakhot V.
Published: June 2004

It is shown that the solubility of organic solids in binary mixtures of partially miscible liquids is singular at the immiscibility critical point. The theoretically predicted maximum of solubility in the vicinity of the critical point is found experimentally. The effect is similar to the phenomenon observed near the gas‐liquid critical point. The similarity of these two critical phenomena may have interesting technical applications and may provide guidelines for identifying promising new solvents for separation processes.
A random contact point model for second virial coefficients in dilute solutions
Authors: Bloemendal Michael , Marcus Yizhak
Published: June 2004

A simple latticelike random contact point model is presented to correlate and predict second virial (or pair interaction) coefficients of thermodynamic quantities in dilute solutions. With this model it is possible to correlate pair interaction coefficients in different solvents with one equation and a single set of group interaction parameters. Enthalpic pair interaction coefficients of alkanes and alkanols dissolved in ten different alkan‐1‐ols and water, and of amides dissolved in N,N‐dimethylformamide, N‐methylformamide, and water are discussed in terms of the model. Corresponding group interaction parameters in water, alkan‐1‐ols, and amides are found to be equal within experimental error. When applied to aqueous solutions, the model yields the empirical equations of Savage and Wood, which are thus given some theoretical basis. The model also provides values of the higher interaction coefficients on the basis of the pair terms.
Quantification of flow hydrodynamics in pulse thermogravimetric analysis systems
Authors: Dadyburjor D. B. , Dean J. W.
Published: June 2004

A test has been designed and used to compare flow hydrodynamics in different thermogravimetric analysis (TGA) systems used as pulse microreactors. The test involves passing a pulse of injectant over the sample pan containing an adsorbent. Water and zeolite are used in the present case. The technique is easily performed and is insensitive to variations in temperature. A model is developed by which the fraction of gas pulse bypassing the sample pan within the TGA can be obtained. In gas/solid reactions, either catalytic or noncatalytic, the test should prove useful for comparing TGA extent‐of‐conversion data to similar measurements taken from other reactor configurations, carrier flow rates, and flow geometries.
Gas and solids behavior in a baffled and unbaffled slurry bubble column
Authors: O'Dowd W. , Smith D. N. , Ruether J. A. , Saxena S. C.
Published: June 2004

New data and analyses are presented for describing gas and solids behavior in a slurry bubble column. Axial solids concentration and bubble size distributions were measured in a 0.108 m ID slurry bubble column apparatus operated at steady state conditions. The column was operated with and without internal baffles. The slurry and gas superficial velocities ranged from 0.0077 to 0.009 m/s and from 0.031 to 0.24 m/s, respectively. The solid phase consisted of glass spheres in a narrow size range with a mean diameter of 96.5 μm; the liquid phase consisted of tap water.

With a one‐dimensional sedimentation‐dispersion model, the data have been used to predict average solids loadings and axial distributions of the solids for specified operating conditions. Local bubble size and concentration measurements indicate that the slurry bubble column was operated in the churn‐turbulent flow regime throughout the entire range of operating conditions used in this study. The impact of internal baffles and solids concentration on the gas and solids behavior is discussed.
Modeling of slow dynamics in the oxidation of CO over supported silver
Authors: Shanks B. H. , Bailey J. E.
Published: June 2004

The oxidation of CO over aluminum‐supported Ag was studied at 147°C using transient experiments. Long‐time‐scale dynamics were observed that could not be explained by previously postulated kinetic mechanisms for this reaction system. A model is presented with kinetic parameters estimated from steady state and transient data that is able to reproduce a variety of cycled feed stream experiments. The model incorporates a slow reversible step which forms an adsorbed oxygen species that blocks reaction sites.
Monte Carlo simulation of diffusion and chemical reaction in catalyst pores
Authors: Zielinski J. M. , Petersen E. E.
Published: June 2004

Diffusion and chemical reaction in a catalyst pore is simulated as a Monte Carlo process. In this analysis the average diffusion distance, calculated for a large number of wall collisions, and the reaction probability are computed as two independent statistical events. This formulation yields results that compare very well with the theoretical values, yet uses minimal computer time. Results reported include typical concentration profiles and effectiveness factors for first‐ and second‐order isothermal reactions using the method described. These results show promise of extension to more complex systems where analytical solutions are not available.
Study of two‐phase flow by laser image processing
Authors: Hanzevack E. L. , Bowers C. B. , Ju Chi‐Hong
Published: June 2004

A new, unobtrusive method for liquid‐liquid two‐phase flow data collection was proved to be reliable in this research. Drop size distributions and concentration profiles were determined for a dilute water‐inkerosene system under horizontal straight pipe flow using this technique, and the Segev model for predicting concentration profiles was tested with the data collected here.

The drop size distributions were found to follow a Rosin‐Rammler function for a limited droplet diameter range, and the average value of the exponent in the Rosin‐Rammler equation was determined to be 2.0. The velocity where the flow regime makes a transition from stratified to adequately dispersed flow was found to be between 2.0 and 2.2 m/s. Concentration profiles predicted by the Segev model were in general agreement with the profiles determined in this work, and using the proper choice of model parameters noticeably improves the model predictions.
Extreme solvent effects on reaction rate constants at supercritical fluid conditions
Authors: Johnston K. P. , Haynes Charles
Published: June 2004

The reaction rate constant was adjusted continuously over two orders of magnitude for the unimolecular decomposition of α‐chlorobenzyl methyl ether using the supercritical fluid solvent 1, 1 diffluoroethane. Activation volumes were observed as low as −6,000 cm3/mol, which is about an order of magnitude more negative than those reported previously in the literature for a homogeneous reaction. Spectral shift (solvatochromic) data were measured for phenol blue in the same fluid in order to interpret the rate data. A method is presented to predict solvent effects on rate constants at supercritical fluid conditions.
Transient response of continuous‐flow stirred‐tank polymerization reactors
Authors: Cozewith Charles
Published: June 2004

The transient behavior of polymer properties following a step change in feed conditions during copolymerization in a continuous‐flow stirred‐tank reactor has been investigated by both modeling and experiment. For kinetics appropriate to Ziegler catalyzed olefin polymerization, the dynamic response of polymer molecular weight and composition is predicted to be relatively slow; four to six reactor turnovers could be required to reach steady state. In addition, response time depends on the direction and magnitude of change and is generally shorter when a property value is decreased. These model predictions were confirmed by measurement of the transient response of copolymer composition and molecular weight for ethylene‐propylene‐ethylidene norbornene terpolymerization.

The model equations also were used to simulate reactor startups, and it was found that steady state following a startup can be reached in about three reactor turnovers. The initial absence of polymer in the reactor causes the dynamic response to be faster for a startup than for reactor control.
Effect of natural convection on spontaneous combustion of coal stockpiles
Authors: Brooks Kevin , Balakotaiah Vemuri , Luss Dan
Published: June 2004

Spontaneous combustion may occur in a coal stockpile when the heat generated within the pile cannot be dissipated at near ambient temperature. Under practical conditions, natural convection enhances the rate of heat removal from the bed and shifts the ignition to lower particle sizes (higher reactivities). Analysis of three limiting cases of a one‐dimensional model yields criteria predicting the conditions under which ignition occurs as well as those for which a low‐temperature (extinguished) state exists for all particle sizes. A simple asymptotic relation predicts the ignition point at large Rayleigh numbers.
Mass transfer in falling films: Influence of finite‐amplitude waves
Authors: Barrdahl R. A. G.
Published: June 2004

An analytical, theoretical investigation of mass transfer in a Newtonian, isothermal falling film displaying periodic, finite‐amplitude waves is presented. The solution derived provides full information on the mass transfer rate as expressed exclusively in terms of physical properties of the liquid and the completely determined flow.
Design of tubular flow reactors for monodisperse aerosol production
Authors: Kodas T. T. , Friedlander S. K.
Published: June 2004

Design equations are derived for calculating the properties of an aerosol generated in a tubular flow reactor operated at a constant rate of formation of condensable monomer. These equations lead to a set of characteristic dimensionless groups. Independently, it is shown that nearly monodisperse aerosols can be generated by: (1) separating particle formation and growth processes, (2) operating with a narrow residence time distribution, and (3) minimizing monomer concentration gradients. These criteria can be used in solving the design equations over ranges of the dimensionless groups suitable for monodisperse aerosol production. In general, high rates of monomer formation are desirable, subject to the desired particle size and concentration, but an upper bound may result from coagulation.
Computer‐Aided planning of purge operations
Authors: Fusillo R. H. , Powers G. J.
Published: June 2004

A strategy is proposed for synthesizing operating procedures for purging species from chemical processing systems during start‐up. This strategy is based in part on the artificial intelligence methods of planning with constraints and symbolic functional modeling of chemical processing systems. Techniques are introduced for identifying chemical species to be purged, choosing methods and auxiliary fluids for executing purge tasks, and allocating chemical species to their final destinations. The implementation of this strategy is illustrated with the example of purging a hydrocarbon chlorination system during start‐up.
Phase equilibria of continuous fossil fuel process oils
Authors: Abbasian M. Javad , Weil Sanford A.
Published: June 2004

Fossil fuel process oils consist of such a large number of components that their only proper description is in terms of continuous distribution functions of a suitable characteristic variable. A methodology is presented to describe the oils in terms of a generalized distribution function. The characteristic variable is determined from measurements of the equilibrium ratios of two test oils, at ambient pressure. Application of the proposed methodology to a sequence of operations shows that, unlike the pseudocomponents technique, the level of accuracy can be maintained.
Tracer dispersion in sintered glass beads with a bidisperse size distribution
Authors: Hulin J. P. , Charlaix E. , Plona T. J. , Oger L. , Guyon E.
Published: June 2004

An experimental study was made of tracer dispersion in bidisperse sintered glass materials prepared from mixtures of two sizes of beads with mean diameters of 325 and 95 μm. The equivalent dispersion coefficient increases by a factor of 30 when the porosity decreases from 30 to 12%; this variation is similar to that measured in monodisperse samples. The variation of dispersion can be characterized by the ratio R = ℓd/L1 where ℓd is a length scale deduced from the equivalent dispersion coefficient and L1 is obtained from conductivity and permeability measurements. It is shown that the increase of ℓd/L1 correlates with the loss of porosity during the sintering process. Lightly sintered samples with a percentage of small beads around the minimum of porosity display a nearly Gaussian behavior, with a dispersion coefficient close to that obtained in homogeneous equivalent mixtures. This result is in contrast with very large anomalies observed by other authors. These results imply that dispersion in consolidated samples is sensitive to large‐scale inhomogeneities of the materials rather than to their detailed structure.
Multicomponent efficiencies in two types of distillation column
Authors: Biddulph M. W. , Kalbassi M. A. , Dribika M. M.
Published: June 2004

A study of the efficiencies of two plate distillation columns is reported. One column had three rectangular trays with a flow path length of about 1 m, the other was a modified glass Oldershaw column with one tray of 38 mm dia. Tray efficiencies were measured in both columns and point efficiencies were deduced for the rectangular column.

The systems studied were ternary and quaternary mixtures of alcohols and water. The results showed that for thermodynamically nonideal systems significant differences existed among the individual component point efficiencies. In the case of an ideal system the component point efficiencies were effectively equal, but tray efficiencies were different due to differing volatilities and composition profiles across the large trays.

This study illustrates the need to allow for the above effects in large‐column designs for multicomponent systems. The possibility of using laboratory‐scale point efficiencies in these designs is explored.
Heuristic synthesis of nonsharp separation sequences
Authors: Bamopoulos George , Nath Ravindra , Motard Rodolphe L.
Published: June 2004

The preliminary synthesis of ordinary distillation schemes for separating a single feed into desired products is examined. Nonsharp products are emphasized, i.e., when components are desired in more than one product. Such sets lead naturally to columns with incomplete separation of the key components, including one‐section columns. Stream bypassing around separators and limited stream splitting are permitted. Sequences cannot have separators with identical key components, and only limited product fragmentation is considered. A heuristic ordering of separation options, coupled with a depth‐first application on a pictorial or a matrix representation of a stream, is proposed. Subsequently a best‐first search identifies the few better schemes. Partial sequences are (sub)optimized heuristically. Employing the present methodology on an example problem of four components and products resulted in annual cost savings of 42%, compared to the best sequence isolating the feed components.
Liquid‐liquid flows in an inclined pipe
Authors: Vigneaux P. , Chenais P. , Hulin J. P.
Published: June 2004

Experimental measurements are reported of oil‐water flows in a 20 cm ID pipe at mean velocities between 2.7 and 35 cm/s, at deviation angles θ from vertical between 0 and 65°, and at water flow rate fractions between 30 and 100%. The distribution of the water volume fraction αw across a pipe section is obtained using local high‐frequency probes. The mean water volume fraction in the section and the slip velocity Vs between oil and water are also determined. High Vs values (up to 50 cm/s) are measured at large deviation angles; they are associated with oil droplet swarms or continuous oil phase zones. Both αw profiles and Vs values depend only on the mean water volume fraction and not on the total flow rate Qt in the range investigated. At low oil volume fractions αo, all droplets are concentrated close to the upper side of the pipe. At larger αo values, a slower linear variation of αw with the distance y from the axis is measured. A model is suggested relating the slope ∂αw/∂y in a vertical plane to the existence of internal density waves in the stratified mixture.
A nonrandom factor model for the excess gibbs energy of electrolyte solutions
Authors: Haghtalab A. , Vera J. H.
Published: June 2004

A new approach to represent the deviations from ideality of electrolyte solutions is derived on the basis of the assumptions of specific interactions of Brönsted and of local electroneutrality of Chen. The model consists of two contributions due to long‐range forces, represented by the Debye‐Hückel theory, and to short‐range forces, represented by local compositions through nonrandom factors. With only two adjustable parameters per electrolyte, the model is valid for the whole range of electrolyte concentration, from dilute solution up to saturation. Results are compared with those obtained from two‐parameter or one‐parameter models of Meissner, Bromley, Pitzer, and Chen et al. The model presented in this work consistently produces better results and reproduces the experimental values from the dilute region up to saturation.
Turbulent mixing in baffled stirred tanks with vertical‐blade impellers
Authors: Komori Satoru , Murakami Yasuhiro
Published: June 2004

Mixing time and power consumption have been measured in baffled, paddle‐agitated cylindrical tanks with single‐ and double‐impellers, and mixing efficiency has been defined by a reciprocal of the product of the mixing time and power consumption. The mixing efficiency and mixing time of double‐impeller agitation have been compared with those of single‐impeller agitation, and they have been related, through a circulation time, to the flow patterns obtained from the measurements of mean axial and radial velocities.
Simulation of particle dispersion in a two‐dimensional mixing layer
Authors: Chein Reiyu , Chung J. N.
Published: June 2004

Particle dispersion in a two‐dimensional mixing layer is analyzed numerically by calculating the particle trajectories in a free shear layer simulated by discrete vortices. Important global and local flow quantities reported in experimental measurements are reasonably simulated.

The particle dispersion results demonstrate that the extent of particle dispersion depends strongly on the Stokes number St, the ratio of particle aerodynamic response time to the characteristic time of the mixing layer flow. Particles with relatively small St values are dispersed at approximately the fluid dispersion rate. Particles with large St values are dispersed at a rate that is less than the fluid rate. Particles with intermediate values of St may get flung outside of the vortex structures in the mixing layer and therefore get dispersed at a higher rate than the fluid. This result is in agreement with some previous experiments in plane and axisymmetric jets. It is also found that a higher dispersion rate is associated with the particles introduced to the flow from the low‐speed side and from near the middle of the mixing layer.
Efficient implementation of VLE procedures in equation‐oriented simulators
Authors: Macchietto S. , Maduabueke G. I. , Szczepanski R.
Published: June 2004

Modern equation‐oriented simulators solve systems of equations and procedures using Newton's method or its variants. Partial derivatives of the output variables of procedures with respect to their input variables are required and are usually approximated by perturbation or quasi‐Newton methods. Here it is shown how this partial derivative information can be computed exactly for procedures in general, with particular applications to flash and multicomponent distillation procedures. Results indicate that 1. physical property procedures should provide analytical derivatives of properties in addition to point values; 2. commonly used procedures for vapor‐liquid equilibria calculation can easily be modified, and should be, to also return output/input gradients; and 3. the use of exact derivatives at all levels results in significant improvements in efficiency over present methods.
Scaling rules for isocratic elution chromatography
Authors: Wankat Phillip C. , Koo Yoon‐Mo
Published: June 2004

Scaling rules for both linear and nonlinear elution chromatography with independent solutes are discussed. The scaling method utilizes smaller diameter particles with high mass transfer rates. The column length, diameter, and cycle time are then scaled so that pressure drop, separation, and throughput are the same or better than in the old design. The new design uses much less packing and cycles more rapidly than the old design. Mathematical derivation shows that the scaling rules for systems with linear and nonlinear isotherms are the same in certain circumstances. Gaussian solutions are used for studying linear systems. Mass transfer zone and diffusive wave analyses are used for constant and proportional patterns, respectively, to describe elution when plateaus form at the feed concentration. Numerical examination of the constant‐pattern elution curve using the Thomas solution shows that the scaling rules are applicable to short columns, which means that there is a negligible entrance effect on the scaling rules. The Thomas solution also shows that the mass transfer resistance has little effect on the scaling rules for the proportional‐pattern wave of a nonlinear solute. Shock and diffusive wave analyses based on the local equilibrium model are employed to describe the separation when the elution curves do not have plateaus. The calculated results show that the scaling rules are followed exactly when pore diffusion controls. Separation of two noninteracting nonlinear components and of a linear and a nonlinear component remains constant when these scaling rules are followed. Several example calculations are used to demonstrate the method.
Electrophoresis in a dilute dispersion of colloidal spheres
Authors: Chen Shing B. , Keh Huan J.
Published: June 2004

An analytical study of the electrophoretic motion of two freely‐suspended, nonconducting spheres with thin electrical double layers is presented using a method of reflections. The particles may differ in radius and/or in zeta potential at the surface, and they are oriented arbitrarily relative to the direction of applied electric field. Corrections to Smoluchowski's equation due to particle interactions are determined in a power series of 1/r12 up to 0(r), where r12 is the center‐to‐center distance between the particles. It is found that the electrophoretic particles do not interact with one another when they have equal zeta potentials. For the specific case of spheres with identical radii, our results agree well with the exact calculations using bipolar coordinates. Based on a microscopic model, the results for two particles are used to find the effect of volume fractions of particles of each type on the mean particle velocities in a bounded dispersion. Of particular interest is the electrophoresis of a suspension of particles with arbitrary size distribution but with identical zeta potentials, in which the sole factor influencing the mean particle velocity is the volume fraction of all particles. In general, the effect of particle interactions on electrophoresis is much weaker than that on sedimentation.
Evaluation and control of particle properties in aerosol reactors
Authors: Wu Jin Jwang , Nguyen Hung V. , Flagan Richard C. , Okuyama Kikuo , Kousaka Yasuo
Published: June 2004

The production of powders by aerosol routes spans a wide range of operating temperatures depending on the type of aerosol reactors used. The dominant mechanism of particle growth and evolution depends highly on the rate at which the reactions producing the condensible species are carried out. Numerical solutions of the discrete‐sectional aerosol general dynamic equation that accounts for the interactions of the discrete clusters were obtained for conditions representative of the different types of aerosol reactors used for powder production today. Simplified reaction and coagulation equations that give fast and useful prediction of the evolution of aerosols associated with chemical reactions were derived, and a simple reaction‐coagulation model was developed. The effects of reaction rate, initial vapor concentration, residence time, seed particles, and temperature profile on the properties of tine particles produced by gas‐phase chemical reactions were evaluated using both models. Results show good agreement between the two.