bluuebunny/crossref_metadata_2025 huggingface dataset:
Design of set point regulators for processes involving time delay
Authors: Sanathanan C. K. , Quinn S. B.
Published: June 2004

An efficient frequency domain methodology for the design of set point regulators for high‐order process models involving relatively large pure time delay is presented. The unique advantage of the methodology is that it enables the designer to rapidly visualize the structure of the required controller as soon as the time and frequency domain specifications are stipulated for the closed‐loop system. Optimizing the parameters of an appropriate structure improves the robustness of the controller. The method does not require order reduction of the original model, and time delay is handled directly. Also, only output feedback is utilized.
General conditions of collinearity at the phase boundaries of fluid mixtures
Authors: Eubank P. T. , Barrufet M. A.
Published: June 2004

The general collinearity conditions at phase boundaries for mixtures are proved by thermodynamic identities for density and for entropy as functions of temperature, pressure, and composition. In the case of density/temperature/pressure/composition collinearity is always found at the cricondentherm or any temperature extremum, whereas for entropy/temperature/pressure/composition collinearity is always found at the cricondenbar or any pressure extremum. Qualitative phase diagrams for a typical binary system are presented in accordance with the derived inequalities. Whether a particular slope, involving the above variables, from the homogeneous side of the phase boundary is greater or less than that from the heterogeneous side depends on location on the phase boundary with respect to cricondentherm, critical point, and cricondenbar.
Heat transfer from a circulating fluidized bed to membrane waterwall surfaces
Authors: Wu R. L. , Lim C. J. , Chaouki Jamal , Grace J. R.
Published: June 2004

Average and local heat transfer coefficients were measured for transfer from circulating fluidized beds of sand particles (mean size 188 and 356 μm) to two water‐cooled membrane wall surfaces located on one face of a 152 mm square by 7.3 m tall column. The measurements cover a range of superficial gas velocities from about 4 to 7 m/s, suspension densities from about 8 to 130 kg/m3, suspension temperatures from 150 to 400°C, and secondary‐to‐primary air ratios of 0 to 1.5. Heat transfer coefficients, averaged over a 1.53 m length of the membrane waterwall surfaces, depend strongly on suspension density, but show almost no separate dependence on gas velocity, bed temperature, or secondary‐to‐primary air ratio for the conditions studied. For the surface nearest the top of the unit, the coefficient decreases with distance measured downward from the top, suggesting that particles travel downward along the surface. As a result, averaged coefficients are lower and the influence of particle size is less than for previously reported circulating fluidized bed heat transfer measurements where miniature heat transfer surfaces were employed.
Non‐premixed simple reaction in homogeneous turbulence
Authors: Kosály George
Published: June 2004

In turbulent flow the equations governing the development of conversion vs. distance are not closed because of the contribution of the concentration fluctuations to the average reaction rate. Toor's hypothesis permits closure from data obtained for mixing without reaction. This paper presents a critical review of the derivation of the hypothesis and discusses its validity.
Use of a finite‐element method to interpret rheological effects in blade coating
Authors: Sullivan Tim , Middleman Stanley , Keunings Roland
Published: June 2004

Data and finite‐element simulations are presented for the blade coating of a series of Newtonian and non‐Newtonian fluids. Numerical simulations for purely viscous fluids show good agreement with coating thickness data for Newtonian and relatively inelastic non‐Newtonian liquids, including geometries for which lubrication theory is inaccurate. These simulations account for the shape of the free surface, with surface tension included, and incorporate realistic inflow and outflow boundary conditions. By comparing pressure distributions generated with the finite‐element technique to those calculated using lubrication theory, it is shown that the simple lubrication theory analysis suffers from inadequate inflow and outflow boundary conditions. Comparison of these simulations with new experimental results for three well‐characterized viscoelastic liquids, having nearly identical steady shear viscosities but different normal stress behavior, confirms speculations of earlier work with respect to the effect fluid rheology has on coating thickness.
Modeling of free‐radical polymerization of styrene by bifunctional initiators
Authors: Choi K. Y. , Lei G. D.
Published: June 2004

A detailed kinetic model for the bulk styrene polymerization initiated by symmetrical diperoxyester bifunctional initiators is presented. When chain termination occurs via a combination termination mechanism, six distinct polymeric species are identified in accordance with the nature of the polymer end units. It is shown that the unequal thermal decomposition characteristics of the peroxides of the bifunctional initiator system lead to the formation of polymers having considerably higher molecular weight than those obtained by the monofunctional intiator systems. It has also been found that high monomer conversion, high molecular weight, and narrow molecular weight distribution can be obtained simultaneously by using the bifunctional initiators at high reaction temperatures. This is due to the reinitiation and propagation of inactive polymers carrying undecomposed peroxides. The molecular‐weight‐increasing effect of the bifunctional initiator is more pronounced at high reaction temperatures. The new possibilities of increasing the monomer conversion and controlling the polymer molecular weight properties more effectively through the use of bifunctional initiators are discussed.
Computer generation of reaction schemes and rate equations for thermal cracking
Authors: Hillewaert L. P. , Dierickx J. L. , Froment G. F.
Published: June 2004

Reaction schemes for the thermal cracking of paraffins, naphthenes, olefins, and aromatics, and the associated rate equations, are generated by an algorithm based upon Boolean relation matrices. In order to reduce calculation times for the heavier components, a self‐learning system is introduced. This self‐learning system avoids repetition of identical calculations by recognizing intermediate species, for which the reaction schemes have already been generated. The software includes routines for standardizing the representation of the species, an information retrieval system, and libraries containing the necessary information for recognition of the species and the reaction schemes for these species.
Narrowing diagnostic focus using functional decomposition
Authors: Finch F. E. , Kramer M. A.
Published: June 2004

The problem of diagnosing faults in chemical plants can be efficiently addressed by a hierarchical procedure involving successive narrowing of the space in which the fault search is conducted. A technique is presented for narrowing diagnostic focus useful in the first stages of a diagnostic search. Based on a decomposition of the process according to function, the technique assesses the functionality of process systems based on measurements of controlled and manipulated variables. A procedure for identification of possibly faulty systems and units from the system states is outlined. Detailed diagnosis, not treated in this paper, would be applied after candidate systems or units are located. An example is presented using a hypothetical chemical reaction process.
Pore evolution and channel formation during flow and reaction in porous media
Authors: Hoefner M. L. , Fogler H. S.
Published: June 2004

A theoretical and experimental study on the dissolution of porous media by flowing acid has been carried out. Dissolution of the media results in an evolution of the pore geometry and the formation of random flow channels. The goal is to predict the range of conditions under which channels will form, and the effects of various parameters on the structure of the channels and on their rate of propagation through the media. A random network model is used to describe the behavior of the stochastic, rootlike channels that form during flow and dissolution in carbonate rock and in other systems. The structure of the flow channels that form as a result of acid attack are characterized and studied using a Wood's metal casting technique. A comparison of model results shows that the rates of channel formation and growth are intimately related to the developing structure of the channels (size of branches and degree of branching), which in turn is controlled by factors such as the fluid velocity and the rate of reaction. Depending on the experimental conditions, the channels range from a single conduit with a minimum of branching to a highly branched, spongy network of channels. The dependence of permeability increase and channel branchedness on injection rates and acid diffusion rates is described by the Damkohler number for flow and reaction.
Micellar‐enhanced ultrafiltration of chromate anion from aqueous streams
Authors: Christian S. D. , Bhat S. N. , Tucker E. E. , Scamehorn J. F. , El‐Sayed D. A.
Published: June 2004

Micellar‐enhanced ultrafiltration can be used to remove multivalent anions or cations from aqueous streams. In the removal of chromate ions (CrO), the cationic surfactant hexadecylpyridinium chloride is added to the solution, and the chromate ions preferentially adsorb at the surface of the highly charged surfactant micelles. The solution is processed by ultrafiltration, using a membrane with pore sizes small enough to block the passage of the micelles and adsorbed ions. The permeate solution has a chromate concentration less than 0.1% that in the original stream. A new equilibrium model, combining the simple two‐phase polyelectrolyte theory of Oosawa with thermodynamic activity, material‐balance, and charge‐balance equations, successfully correlates ultrafiltration and equilibrium dialysis results for chromate solutions.
Flooding, holdup, and drop size measurements in a multistage column extractor
Authors: Kirou V. I. , Tavlarides L. L. , Bonnet J. C. , Tsouris C.
Published: June 2004

The hydrodynamics of a pilot plant multistage mixer column extractor was studied for the toluene/water physically equilibrated system. The effects of rotational speed, and continuous and dispersed phase flow rates were investigated under a variety of operating conditions. Dispersed phase axial holdup profiles, determined by a noninvasive ultrasonic method, showed a strong nonuniformity. Depending on the operating conditons, holdup profiles can change from a concave shape to a sigmoidal form with a maximum in the bottom of the column. Sauter mean diameter and drop size distribution profiles are strongly affected by rotational speed. Significant, but weaker, are the effects of continuous and dispersed phase flow rates. Continuous monitoring of the holdup profile in the proximity of flooding leads to the formulation of proper criteria for the prediction of flooding. These criteria are appropriate for models allowing for axial variation of the holdup along the contactor.
Stability and tensile strength of liquids exhibiting density maxima
Authors: Debenedetti P. G. , D'Antonio M. C.
Published: June 2004

If a given liquid exhibits a density maximum anywhere in its phase diagram, thermodynamic consistency dictates that such a point cannot be isolated: a density maxima locus must necessarily exist. For a fluid that does not also exhibit density minima, the pressure‐temperature projection of such a locus is negatively sloped, and can only end at a stability limit. There exist two thermodynamically consistent ways in which such an intersection can occur, and they correspond, respectively, to the highest and lowest possible temperatures at which a liquid can exhibit a negative coefficient of thermal expansion. These theoretical predictions are confirmed by experimental observations. The existence of density anomalies anywhere in a liquid's phase diagram is shown to have a profound influence in determining the shape of such a fluid's stability boundary.
Recycle continuous‐flow electrophoresis: Zero‐diffusion theory
Authors: Gobie William A. , Ivory Cornelius F.
Published: June 2004

Recycle continuous‐flow electrophoresis (RCFE) is a modification of Hannig's thin‐film CFE device in which eluant is continuously recycled to the chamber inlet. Shifting the recycled eluent laterally a specific distance prior to reinjection enables the RCFE to separate any two solutes to arbitrary purity. This paper studies solute transport in an idealized RCFE in the absence of diffusion. The model is solved analytically by means of a two‐sided Laplace transform. Three distinct types of solute distribution are found, and guidelines for construction and operation of an RCFE are derived.
Recursive identification of gross errors in linear data reconciliation
Authors: Crowe Cameron M.
Published: June 2004

In the reconciliation of measurements of flows and concentrations so that they conform to conservation laws and other constraints, any gross errors in the measurements must be identified in order that they can be either corrected or deleted.

A new method is derived for the recursive prediction of the changes in the objective function, and of the statistical tests for the measurements, which would result from the deletion of suspect measurements. Inverses of large matrices are not required and the reconciliation can also be easily calculated for any set of deletions. It is shown that the decrease in the objective function caused by deletion of a single measurement equals the square of the corresponding maximum power measurement statistic, calculated prior to that deletion. An algorithm for the detection of suspect sets of gross errors, whose deletion leads to acceptable values of all statistical tests and process flow rates, is proposed and illustrated.
Particle dynamics and heat transfer under plasma conditions
Authors: Vardelle M. , Vardelle A. , Fauchais P. , Boulos M. I.
Published: June 2004

A study was carried out of the momentum and the heat transfer to fine alumina particles injected into a DC plasma jet. Measurements are reported of particle number flux distribution, particle velocity, and inflight particle surface temperature under different operating conditions. The results show that the particle trajectories and associated particle flux distribution depends to a large extent on the particle injection velocity. The maximum particle velocity and surface temperature are noted, however, to remain close to the centerline of the jet, independent of the particle injection conditions. The maximum surface temperature reached by the particles increases with increasing plasma power and the use of an Ar/H2 plasma gas (17 vol. % H2) compared to that for a pure argon plasma.

The particle velocity data are in good agreement with the predictions of a two‐dimensional mathermatical model used for the calculation of the particle trajectories and temperature history. The model predictions, however, agreed only in trend with the measured particle surface temperatures. Deviations between the two could still be observed at large distances from the point of injection of the powder. The computed particle number flux distributions were narrower than the measured profiles, which can be attributed to the fact that the model did not include, at this stage, turbulent particle diffusion effects.
On‐line optimizing control of a packed‐bed immobilized‐cell reactor
Authors: Hamer John W. , Richenberg Carl B.
Published: June 2004

On‐line optimizing control has been used to find and track the economically optimal operating conditions of a packed‐bed reactor. The continuous reactor under study converts the ammonium salt of fumaric acid to aspartic acid using whole cells immobilizing in K‐carrageenan beads. The on‐line optimizing control was performed using a leastsquares recursive estimation algorithm with a variable forgetting factor to estimate the parameters in a linear discrete‐time model. A Newton optimization procedure used these parameters to calculate the direction and distance to the optimal conditions. Features found to enhance the speed and stability of the algorithm included the use of a variable forgetting factor algorithm, both low‐ and high‐pass filtering of the data, outlier rejection, and linearizing input‐outupt transformations.
Galvanic interactions on periodically regular heterogeneous surfaces
Authors: Morris Rael , Smyrl William
Published: June 2004

A heterogeneous electrode surface has been modeled using a regular distribution of circular anodes in a surrounding coplanar cathodic matrix. In the absence of mass transport effects, galvanic currents and potentials have been calculated using finite‐element analysis, with nonlinear electrode kinetics. For a fixed ratio of anodic to cathodic areas on a heterogeneous surface, calculated galvanic currents increase linearly with the active perimeter between cathodic and anodic regions. Furthermore, the current is independent of the shapes and distributions of anodic regions in a surrounding cathodic plane provided that the ratio of overall anodic area to active perimeter is conserved. Thus, due to its longer active perimeter, a surface represented by a large number of tiny anodic islands dispersed in a cathodic sea will exhibit much greater galvanic currents than an equivalent surface represented by a small number of large anodic continents.
Global phase behavior of mixtures of short and long n‐alkanes
Authors: Peters C. J. , De Arons J. Swaan , Sengers J. M. H. Levelt , Gallagher J. S.
Published: June 2004

The perturbed‐hard‐chain model of Beret, Donohue, and Prausnitz, in the simplified version of Kim et al., is compared with recent VLE data on mixtures of ethane and n‐alkanes with carbon numbers from 16 to 24. By using and extrapolating the linear relations between the three adjustable model parameters and the carbon number, as given by Kim et al., we find that the experimental isothermal bubble curves are well represented up to the critical pressure without the use of any adjustable parameters. Experimental Henry constants for ethane in eicosane are well predicted at all temperatures. We find this global model more accurate than the Soave‐Redlich‐Kwong equation, even if the latter is fitted isotherm‐by‐isotherm to individual mixtures with temperature‐dependent mixing parameters.
Fixed‐bed adsorption of gases: Effect of velocity variations on transition types
Authors: LeVan M. Douglas , Costa Carlos A. , Rodrigues Alirio E. , Bossy Alain , Tondeur Daniel
Published: June 2004

In fixed‐bed adsorption or desorption of gases, velocity variations accompany changes in gas composition, and these variations affect the transition types (spreading waves or shocks). A general criterion is developed for determining the transition type for isothermal monovariant systems (one adsorbable component in inert gas or two adsorbable components with no inert gas). Several examples are given to illustrate the determination of transition types for simple waves, contact discontinuities, shocks, and combined waves.
Robust nonlinear state feedback under structured uncertainty
Authors: Kravaris Costas , Palanki Srinivas
Published: June 2004

This work follows the global input/output linearization approach for the design of control systems for nonlinear plants of Kravaris and Chung. A robust nonlinear state feedback is proposed for uncertainties considered as a class of bounded perturbations to the state model. A Liapunov‐based approach is used to guarantee uniform ultimate boundedness.
Representation of the solubility behavior of amino acids in water
Authors: Nass Kathryn K.
Published: June 2004

Expressions suitable for the description of the behavior of small biological zwitterions in aqueous systems are developed. The validity and usefulness of the expressions are tested by correlating data for the activity coefficients of several amino acids in water. Development of rational expressions for the solid‐liquid equilibria (SLE) of amino acids, in terms of the heat of solution at infinite dilution, is also presented. The solubility data of phenylalanine, tyrosine and diiodotyrosine as a function of pH are successfully correlated using the approach developed here. In addition, simultaneous correlation of the pH and temperature dependence of solubility data for diodotyrosine in water gives very good representation. The expressions described here should prove useful for the design and optimization of separation processes, such as crystallization, with minimal experimental information.
Nonlinear dynamic matrix control for high‐purity distillation columns
Authors: Georgiou Apostolos , Georgakis Christos , Luyben William L.
Published: June 2004

The performance of Dynamic Matrix Control (DMC) for different product purity distillation columns is studied and compared with a conventional multiloop proportional‐integral control structure (LV). The load‐rejection capability (regulatory response) of DMC becomes worse than that of the conventional structure as product purity increases. Large load disturbances take the highly nonlinear system away from the nominal linear model, adversely affecting the performance of DMC. The LV structure is less sensitive to process nonlinearities. However, simple nonlinear output transformations suggested by the fundamental design equations of the process give models that are quite insensitive to nonlinearities of the process. This results in a nonlinear version of DMC that has better performance than the standard DMC and it is much simpler than the gain and time constant scheduling DMC or adaptive DMC. The complexity of DMC when it is applied on systems with very large time constants is also addressed. Suggestions to overcome this problem are proposed.
Origin of roll waves in horizontal gas‐liquid flows
Authors: Bruno Kenneth , McCready M. J.
Published: June 2004

The mechanism of formation of roll waves on a horizontal liquid layer sheared by a gas flow is examined. Measurements of the wave amplitude spectrum show that, for liquid film Reynolds numbers greater than about 100, roll waves evolve from disturbances that initially have wave‐lengths much longer than the film thickness and which grow slowly with distance. Predictions of linear stability analysis are shown to agree well with the observation of these instabilities and not the visual transition to roll waves as was suggested in earlier studies. For very thin films, the data do not give conclusive proof of the origin of roll waves, but it is speculated that these are actually solitary waves which have begun to break.
Heat capacity and heat of dissociation of methane hydrates
Authors: Rueff Roger M. , Dendy Sloan E. , Yesavage Victor F.
Published: June 2004

The objective of this study was to determine the heat capacity and heat of dissociation of methane hydrates. A technique has been devised which circumvents the two major problems encountered in measuring gas hydrate heat capacity: the need to impose a mechanical pressure during the measurement and the need to have an absolutely pure hydrate sample. The technique was shown to be successful utilizing high‐pressure, constant‐volume cells in a differential scanning calorimeter.
A linear chemical‐physical theory model for liquid metal solution thermodynamics
Authors: Howell Wayne J. , Lira Carl T. , Eckert Charles A.
Published: June 2004

The simplified chemical‐physical theory (SCPT) for compound‐forming liquid metal solutions is improved by a reduction in the number of modeling parameters using an adaptation of the group contribution approach. A group contribution technique is applied to linearize the Gibbs energy (and enthalpy) of formation of intermetallic compounds. As a result, the activities or Gibbs energies of many binary liquid alloy systems are represented successfully with only a single parameter for the chemical interactions and another for the physical interactions. Similarly, the enthalpies of mixing are modeled well using only the temperature derivatives of these two parameters.
Application of thin films to porous mineral oxides using two‐dimensional solvents
Authors: Wu Jengyue , Harwell Jeffrey H. , O'Rear Edgar A. , Christian Sherril D.
Published: June 2004

Thin polymeric films have been applied to the surface of a porous material in a novel process. Nitrogen sorption, a conventional tool for measuring surface areas and pore size distributions, can be employed for determining the thickness of such films through a comparison of the pore size distribution curves before and after film formation. The thickness of a polystyrene film on a porous alumina powder is determined and compared with the theoretical thickness for styrene polymerized inside a two‐dimensional solvent, which consists of a partial bilayer of sodium dodecyl sulfate physically adsorbed from an aqueous solution onto the powder. Film thicknesses ranged from 1.8 to 0.4 nm while BET surface area decreased from 94.7 to 57.8 m2/g. The powder surface changes from hydrophilic to hydrophobic while retaining the basic pore structure.
Monte Carlo simulation of supported metal catalyst sintering and redispersion
Authors: Glen Campbell W. , Lynch David T. , Wanke Sieghard E.
Published: June 2004

Monte Carlo simulations of sintering and redispersion of supported metal catalysts, based on an atomic migration mechanism, are presented. The support surface was modeled as a square grid with metal atoms located at various grid points. Interaction energies between metal atoms, and between metal atoms and support sites were specified. The probability of movement of each metal atom during one time increment (iteration) was calculated from the interaction energies. The effects of interaction energies, metal loading and initial distribution of the metal were examined. The model predictions are in good qualitative agreement with experimental observations. The model predicts “apparent” movement, splitting and coalescence of entire metal particles; these experimentally observed phenomena have usually been cited as evidence that sintering occurs by a particle migration mechanism.
Optimal production of secreted protein in fed‐batch reactors
Authors: Park Seujeung , Fred Ramirez W.
Published: June 2004

The optimal control policy for the maximization of the secreted heterologous protein in a fed‐batch bioreactor was obtained using SEY2102 as a model host yeast and SUC2‐s2 as a model secretory protein. A dynamic model for host cell growth, gene expression, and the secretion of expressed polypeptides was formulated. The optimal system trajectory contains multiple singular arcs that are distinct from one another. Optimal control requires transitions between these singular arcs. Optimal transitions between multiple singular arcs with bounded controls are uniquely located in observance with the Minimum Principle of Pontryagin. An iterative numerical search strategy for determining the optimal control showed successful convergence properties.
Molecular thermodynamics of aqueous two‐phase systems for bioseparations
Authors: King Robert S. , Blanch Harvey W. , Prausnitz John M.
Published: June 2004

Aqueous polymer‐polymer two‐phase systems provide a powerful method for separating biomolecules by extraction. When a complex mixture of biomolecules (e.g., a fermentation broth or a solution of lysed cells) is added to such a system, biomolecules partition uniquely between the two phases, achieving separation.

A thermodynamic framework is presented for optimizing extraction performance in biological separations. First, a molecular‐thermodynamic model, based on the osmotic virial equation, is proposed to describe phase equilibria for dilute aqueous mixtures containing polymers and protein. Second, experimental phase‐equilibrium data (protein partition coefficients) are reported for a number of model proteins including albumin, lysozyme, and α‐chymotrypsin. To interpret and correlate the experimental data, Low‐Angle Laser‐Light Scattering (LALLS) measurements were made to determine osmotic second virial coefficients for aqueous mixtures containing polymers, proteins, salts (KCl, KH2PO4 and K2SO4 at concentrations of 50 and 100 mM) and several combinations of polymer‐polymer and polymer‐protein pairs. Combined with electrochemical measurements (differences in potential between the two phases and protein net charge), these data provide parameters for the model to calculate the desired phase equilibria. A comparison of calculated and experimental results indicates that the virial‐equation model provides good prediction of binodals and a reliable basis for estimating infinite‐dilution protein partition coefficients for biotechnical process design.
Rule‐based mineral sequences in geochemical flow processes
Authors: Novak Craig F. , Schechter Robert S. , Lake Larry W.
Published: June 2004

The infiltration of an aqueous solution into a permeable medium generally results in the dissolution of some of the minerals initially present and the possible precipitation of others. When the infiltration velocities are small, as is the case for many natural processes, conditions of local equilibrium apply and the dissolution and precipitation processes exhibit a wave‐type behavior reminiscent of chromatogrphic fronts. Zones of constant composition (state) will be separated by narrow regions within which the aqueous and solid phase concentrations exhibit sharp changes. Because of this wave‐like structure, an algebraic solution of the coupled material balance equations exists, but in a form that involves a trial and error solution procedure which has heretofore discouraged its application. This paper describes the essence of a scheme which uses a combination of graph theory and heuristics to minimize trials and thereby render the algebraic solution practical. The scheme offers an alternative to time‐sequencing solutions (e.g., finite difference) of the set of partial differential equations.
Conversion distribution in diffusion‐governed chlorination of poly(vinyl chloride)
Authors: Wachi Shun , Morikawa Hisashi , Inoue Hakuai
Published: June 2004

Conversion distribution in particles of chlorinated poly(vinyl chloride) (CPVC) is conceptually described based on balance equations involving mass transfer and chemical reaction. In the physical sorption of chlorine in poly(vinyl chloride) (PVC) as measured by the constant volume cell method, equilibrium concentration and diffusion rate obeyed Henry's law and Fick's law. The rate process of photo chlorination of PVC, which was investigated by the gravimetric method, could be well predicted by theoretical calculation of chlorine diffusion in PVC accompanying the infinitely fast chemical reaction. In a free grain of PVC synthesized by suspension polymerization, the chlorination rate was governed by the polymer‐phase diffusion within agglomerates of coalesced primary particles.

To produce homogeneously chlorinated PVC, a periodic photo‐irradiation method was theoretically proposed and experimentally demonstrated. The effect of the periodic operation on the thermal property of CPVC was evaluated by DSC.
A discretized population balance for nucleation, growth, and aggregation
Authors: Hounslow M. J. , Ryall R. L. , Marshall V. R.
Published: June 2004

The population balance for batch aggregation of particulate suspensions is recast in a form that may be solved simply and accurately. The transformed equation is deduced with the introduction of only one additional parameter, which is found to be a constant for all cases. The transformed equation is tested by comparison with some analytical solutions with which it is found to be in excellent agreement. In particular, the equation is shown to predict correctly the rate of change of total particle number and volume. Compatible descriptions of linear growth and nucleation are developed with similar success.

The method is then applied to modeling the in vitro growth and aggregation of kidney stones (calcium oxalate monohydrate crystals). It is found that these phenomena are well described by McCabe's ΔL law, a size‐independent coalescence kernel, and first‐order kinetics. Simulated particle size distributions and their moments are in excellent agreement with the experimental results.
Onset of pulsing in two‐phase cocurrent downflow through a packed bed
Authors: Grosser K. , Carbonell R. G. , Sundaresan S.
Published: June 2004

In cocurrent downflow of a gas and a liquid through a packed column, a transition from trickling flow to pulsing flow is observed as one increases the flow rates. A simple macroscopic model for the two‐phase flow is analyzed to examine whether this regime transition should be viewed as the loss of stability of a steady state or the loss of existence of any solution for the steady‐state equations of motion. The former appears to be a more reasonable interpretation and an explicit algebraic criterion for the onset of pulsing is presented.
Number of passage distribution functions with application to dispersive mixing
Authors: Tadmor Zehev
Published: June 2004

Number of passage distribution (NPD) functions in batch and continuous recirculating systems are presented, and their application to dispersive mixing of plastics and rubber is discussed. Dispersive mixing requires a process of repeated ruptures of the dispersed phase. This is accomplished by repeated passages in special regions of the system where stress levels above a given threshhold value are imposed on the liquid. The application of NPD functions to certain batch and continuous mixers and compounders is discussed.
Modeling chromate ion‐exchange processes
Authors: Sengupta Arup K. , Lim Lois
Published: June 2004

In spite of chromate's very high selectivity at acidic pH, fixed‐bed chromate‐exchange processes always suffer from severe gradual breakthroughs of chromate during column runs. Earlier, Sengupta and Clifford confirmed that such a gradual breakthrough is an equilibrium phenomenon and provided the underlying ion‐exchange mechanism. An algorithm, developed with the aid of the governing chromate ion‐exchange mechanism, is presented here to predict the salient properties of chromate‐exchange processes in a multicomponent system. The model predicts the gradual chromate breakthroughs during column runs fairly accurately and also accounts for other unusual characteristics of chromate ion exchange. Average separation factor models, often used for designing fixed‐bed ion‐exchange processes, are unable to predict the gradual breakthrough characteristics of a preferred component such as chromate.
Comparative SO2 reactivity of CaO derived from CaCo3 and Ca(OH)2
Authors: Bruce Kevin R. , Gullett Brian K. , Beach Laura O.
Published: June 2004

Experimental data on sulfation rates of CaO particles derived from CaCO3 are compared to those derived from Ca(OH)2 using a product layer diffusion control model differing only in the shape of the CaO grain. Both the model and the experimental data indicate slightly higher reactivity for the Ca(OH)2‐derived oxide due to the observed difference in grain shape. This effect is considered as a contributor to the greater performance of Ca(OH)2 in pilot‐scale SO2 removal studies.
The theory of precipitation/dissolution waves
Authors: Helfferich Friedrich G.
Published: June 2004

The concepts of coherence and composition paths, originally developed for multicomponent chromatography, are used to establish a simple theory of transport in systems with precipitation and dissolution in the course of multicomponent, single‐phase flow in permeable media. Composition route construction in phase diagrams in combination with distance‐time diagrams yields concentration profiles without recourse to trial‐and‐error procedurs. Detailed results are given for systems with three ions A, B, and X and up to two precipitates AX and BX. The extension to systems with additional, nonprecipitating species is described. The new approach confirms most conclusions of Bryant's earlier theory, removes assumptions stipulated in the latter, and is simpler to handle.
Methane steam reforming, methanation and water‐gas shift: I. Intrinsic kinetics
Authors: Xu Jianguo , Froment Gilbert F.
Published: June 2004

Intrinsic rate equations were derived for the steam reforming of methane, accompanied by water‐gas shift on a Ni/MgAl2O4 catalyst. A large number of detailed reaction mechanisms were considered. Thermodynamic analysis helped in reducing the number of possible mechanisms. Twenty one sets of three rate equations were retained and subjected to model discrimination and parameter estimation. The parameter estimates in the best model are statistically significant and thermodynamically consistent.
Flow in driven cavities with a free surface
Authors: Canedo Eduardo L. , Denson Costel D.
Published: June 2004

A study of the flow of viscous liquids contained in an open cavity driven by a moving wall has been undertaken as a first step toward understanding interphase heat and mass transport in polymer processing equipment where rolling pools of liquid are generated. Solutions to the equations of motion for creeping flow in cavities of different aspect ratios were obtained using a finite‐differences technique for circumstances when the wall moves in the same direction as the gravitational field.

Experimental studies of the flow patterns in cavities of various aspect ratios were found to be in good agreement with the creeping flow predictions for cavity Reynolds numbers Re < 50 and aspect ratios a < 1. The structure of the flow in this geometry was found to be similar to that in closed cavities of the same shape. The position and strength of the principal vortex were observed to be nearly independent of the existence of a free surface, and the gas‐liquid interface was found to significantly stabilize the rotational motion in shallow cavities.
Thermophoretic properties of nonspherical particles and large molecules
Authors: Garcia‐Ybarra Pedro , Rosner Daniel E.
Published: June 2004

The Knp ≫ 1 gas‐kinetic approach of Waldmann (1959, 1961) is extended to predict the thermophoretic properties of nonspherical aerosol particles, and massive nonspherical gas molecules. Calculations are presented for sphero‐cylindrical particles (molecules) of arbitrary aspect ratio, L/R, predicting that in a local temperature gradient grad T they will thermophoretically drift: (i) more rapidly when their major axis is aligned with −grad T; (ii) at a velocity different from that of a sphere of radius R equal to the cylinder radius; (iii) at an angle with respect to −grad T when their major axis is not parallel to, nor perpendicular to, −grad T; and (iv) without a net torque tending to orient the particle with respect to −grad T. Important corollaries are that nonspherical particles in a temperature gradient should also experience new thermophoretically‐induced coagulation mechanisms. We predict that the orientation‐averaged thermal diffusion factor αT should increase approximately linearly with particle (molecule) length.
The optimal design of dynamic experiments
Authors: Espie D. , Macchietto S.
Published: June 2004

A robust and efficient algorithm is developed to calculate dynamic inputs for optimal experimental designs. Different objective functions are presented to allow designs for both model discrimination and the improvement of parameter precision. Time‐varying inputs are calculated by reformulating the optimal design problem as an optimal control problem. This approach can provide large improvements in the ability to discriminate among a series of models, and then increase the accuracy of the resulting parameters.
Mass transfer studies of external‐loop airlifts and a bubble column
Authors: Popovic Milan K. , Robinson Campbell W.
Published: June 2004

Gas holdups (ϵGR) and liquid‐phase volumetric oxygen transfer coefficients (kLaT) were measured for a bubble column (BC) and three different external‐circulation‐loop airlift (ECL‐AL) fermentors of 50 to 60 L working volume, using viscous non‐Newtonian aqueous solutions of various carboxymethylcelluloses. Some measurements also were done with a viscous Newtonian system (51.8 wt. % sucrose solution).

Discussed in this paper are correlations of ϵGR and kLaT with riser superficial gas velocity (0.02 ≦ UGR ≦ 0.26 m/s), the ratio of the downcomer and riser crosssectional areas (0[BC] ≦ Ad/Ar ≦ 0.444), and the effective viscosity of the liquid phase (0.02 ≦ ηeff ≦ 0.5 Pa · s), over the parameter ranges indicated. It is shown that both ϵGR and KLaT are highly dependent upon UGR and Ad/Ar. The effective viscosity has a significant effect on KLaT, but has only a relatively weak affect on ϵGR. The KLaT correlation developed for non‐Newtonian systems was extended to include the results obtained for the viscous Newtonian system studied by incorporating the effects of liquid‐phase molecular diffusivity, density, and interfacial tension as determined by Nakanoh and Yoshida (1980).
The rheology of suspensions containing polymerically stabilized particles
Authors: Mewis Jan , Frith William J. , Strivens Trevor A. , Russel William B.
Published: June 2004

The non‐Newtonian viscosities of polymerically stabilized colloidal suspensions are usually predicted and correlated on the basis of data and scaling principles for Brownian hard spheres. Here, the specific effect of the stabilizer layer is investigated using suspensions of monodisperse PMMA particles with a chemically attached stabilizer layer. The ratio between particle radius and stabilizer layer thickness is changed between 5 and 61. At high values of this ratio the data show Brownian hard sphere behavior. At lower values deviations appear. As a first approximation, the “softness” of the particles can be characterized through the concentration at maximum packing. A more detailed comparison with hard sphere data provides a measure for softness that changes with concentration and shear rate. A theoretical estimate of the concentration effect is in line with the experiments. The critical shear stress (or Peclet number) is not a constant but goes through a maximum when the concentration is increased.
Lumping coupled nonlinear reactions in continuous mixtures
Authors: Chou M. Y. , Ho T. C.
Published: June 2004

A lumping procedure proposed previously is applied to two types of continuous reaction mixtures: one in which the constituents undergo reactions of a Langmuir‐Hinshelwood (LH) type, the other in which the constituents undergo reactions of a bimolecular type. It is shown that both mixtures initially can behave qualitatively like lumped first‐order reactions. At large times, the behavior of the lumps can be described by power law kinetics, with the bimolecular lump displaying a higher overall reaction order. In particular, if the feed contains a nonzero amount of unconvertible species, the LH lump at large times decays at a second‐order rate, whereas the bimolecular lump decays at a third‐order rate. To complement the asymptotic results, expressions describing the behavior of the lumps at any time are derived.
Reactions in continuous mixtures
Authors: Aris Rutherford
Published: June 2004

A continuous mixture is one which is so complex that it is no longer worthwhile to distinguish individual chemical species; instead, an index, such as the simulated boiling point, is chosen and ci, the concentration of the species Ai, is replaced by c(x)dx, the concentration of material with index in the interval (x, x + dx). It has been long known that the total concentration of a suitably distributed mixture, each of whose components disappears by a first‐order reaction with constant k(x), will appear to disappear according to a higher order of reaction. The generalization of this to a mixture that requires two indices for its description is worth considering for three reasons: First, there may well be materials that are so complex as to require this. Second, the second index may be considered to distribute reaction time. Third, this approach seems to answer the mathematical question of how to generalize from the continuum of first‐order reactions to one of parallel Nth‐order reactions.
Model predictive optimal averaging level control
Authors: Campo Peter J. , Morari Manfred
Published: June 2004

The infinite‐horizon, discrete‐time optimal averaging level control problem for surge tanks, with minimization of the rate of change of outlet flow as its objective, is formulated and a solution is presented. A finite moving‐horizon approximation is introduced and analytical solutions are obtained for two important special cases. These results provide a quantitative measure of the impact of a secondary objective, integral action, on flow filtering. The problem is then generalized to include nonconstant level and outlet flow constraints. A model predictive control formulation is presented which addresses the objectives of the generalized problem. The resulting controller minimizes the maximum rate of change of outlet flow, provides integral action, and handles constraints on the tank level and outlet flow rate. The proposed controller includes a single adjustable parameter that directly effects the trade‐off between the incompatible objectives of good flow filtering and rapid settling time. Examples are presented to demonstrate the properties of the model predictive controller. An implementation, involving imbedded feedback, is developed which guarantees internal stability of the model predictive scheme for open‐loop unstable processes (such as integrators).
Interaction measures for nonsquare decentralized control structures
Authors: Reeves D. E. , Arkun Y.
Published: June 2004

A block relative gain measure for nonsquare systems has been derived. Evaluated at steady state, this measure serves as a performance‐related tool for evaluating control structures prior to controller design. Both the nonsquare dynamic block relative gain and the relative sensitivities have been presented as dynamic interaction measures that depend on the controller tuning and are consequently applicable to design of nonsquare decentralized controllers. Rigorous relationships between the dynamic block relative gain and the performance and stability of a closed‐loop system have been established.
Hydrodynamics of a lamella electrosettler
Authors: Gidaspow Dimitri , Shih Yang‐Tsai , Bouillard Jacques , Wasan Darsh
Published: June 2004

Using the principles of conservation of mass and momenturn for each phase, a theory is developed for describing quantitatively the sedimentation of colloidal particles in vessels having electrodes that are inclined to the vertical.

As a limiting case, a kinematic settling formula was derived that describes the motion of settling fronts of colloidal alumina particles suspended in tetralin as a function of angle of inclination and strength of applied electric field in terms of electrophoretic mobilities. A hydrodynamic computer model shows the flow patterns and settling behavior of such lamella settlers with and without an applied electric field. The predicted motions of the settling fronts and the thicknesses of the clear boundary layers above the upper wall of the inclined vessels globally agreed with the experimental observations.