bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron and hole transport in degenerate semiconductors
Authors: Orazem M. E.
Published: June 2004

Concentration‐dependent activity coefficients were used in conjunction with dilute‐solution transport equations to show the effect of degeneracy on the apparent physical properties of semiconductors and on the performance of photovoltaic cells. The approach presented here allows convenient treatment of degenerate semiconductors in a manner that is both thermodynamically consistent and consistent with the Fermi‐Dirac distribution for electrons. These calculations show that neglect of the concentration dependency of the activity coefficients has a large effect on the calculated values for local concentrations in a photovoltaic device, but affects the calculated values of power density and cell potential only slightly. Neglect of the concentration dependency of the activity coefficients does have a significant effect on the calculation of the resistivity of the semiconductor.
Synthesis of decentralized process control structures using the concept of block relative gain
Authors: Manousiouthakis Vasilios , Savage Robert , Arkun Yaman
Published: June 2004

The concept of block relative gain (BRG) is introduced to define a measure of interaction for decentralized control structures. This new theoretical development generalizes the original Bristol's relative gain array (RGA) to block pairing of inputs and outputs that are not necessarily single‐input single‐output pairings. Various properties of BRG are rigorously derived and formulated in a mathematical framework suited to analysis and synthesis. Based on these important properties, a methodology is developed for the systematic generation and selective screening of alternative decentralized control structures. Subsequently, a controller design procedure for the most promising decentralized structures is given. A boiler furnace and a system of heat‐integrated reactors are used to illustrate the significance and the utility of the proposed method for industrial processes.
Computer simulation of turbulent mass transfer at a mobile interface
Authors: McCready M. J. , Vassiliadou Eleni , Hanratty T. J.
Published: June 2004

Numerical solutions to the unaveraged mass balance equation for the case of a flat mobile interface reveal that both high‐ and low‐frequency velocity fluctuations can contribute to mass transfer. This is in contrast to transport to a solid boundary where only low‐frequency fluctuations, normal to the wall, are important. The average mass transfer coefficient is found to depend on Schmidt number to the −0.5 power, in agreement with classical theories. It is related to the velocity field in the liquid primarily through the mean‐square value of the gradient of normal velocity fluctuations at the interface.
Fractionating condensation and evaporation in plate‐fin devices
Authors: Tung Hsien‐Hsin , Davis J. F. , Mah R. S. H.
Published: June 2004

A model that describes fractionation with condensation and evaporation in a plate‐fin device has been formulated. It is capable of evaluating profiles of composition, temperature, and flow rate for both liquid and vapor streams in an extended surface device. The device may be adiabatic or nonadiabatic and the surface may be incompletely wetted. Compared to experimental measurements, the model predictions showed ± 1 number of transfer unit deviation along the length of the device. The predictions of the top and bottom flow rate ratio showed a 5–10% deviation for adiabatic and condensation runs and a 25% deviation for evaporation runs.
The mutual diffusion coefficient of methanol–n‐hexane near the consolute point
Authors: Clark W. M. , Rowley R. L.
Published: June 2004

The composition and temperature dependence of the mutual diffusion coefficient near the liquid‐liquid critical point of methanol–n‐hexane mixtures has been determined by Gouy interferometry. The critical exponent was found to be 0.685. Constant‐temperature extrapolation to zero diffusivity located the spinodal curve. Spinodal loci calculated from the NRTL model are inconsistent with the experimentally determined values.
Mechanism of potassium‐catalyzed carbon/CO2 reaction
Authors: Sams D. A. , Shadman Farhang
Published: June 2004

The mechanism of potassium‐catalyzed C/CO2 reaction is studied by a temperature and concentration programmed reaction (TCPR) technique. The proposed redox mechanism contains three surface complexes: –CO2K, –COK, and –CK. The oxide groups are the intermediates during C/CO2 gasification. The completely reduced form, –CK, is the end product of catalyst reduction and is the precursor for K loss. The stoichiometries of these surface groups are confirmed by oxygen and potassium balances.
The formation and growth of protein precipitates in a continuous stirred‐tank reactor
Authors: Glatz C. E. , Hoare Michael , Landa‐Vertiz Jaime
Published: June 2004

Product particle size distribution data are obtained for the isoelectric precipitation of protein in a continuous stirred reactor in order to evaluate the kinetics of aggregate growth in processes for protein recovery via precipitation. Data are modeled using population balances to verify the postulated mechanism and provide a basis for evaluating results for other reactor configurations. Aggregate breakage was found to be the dominant phenomenon.
A mathematical model of drying for hygroscopic porous media
Authors: Stanish M. A. , Schajer G. S. , Kayihan Ferhan
Published: June 2004

A mathematical model is developed to simulate the drying of hygroscopic porous media and, in particular, of wood. Drying rate experiments were performed using wood specimens and a nonhygroscopic porous ceramic solid and were simulated using the appropriate version of the drying model. Calculated model predictions are in very satisfactory agreement with experimental results. An examination of the relative impacts on drying of the transport mechanisms that comprise the model leads to meaningful interpretations of observed drying behavior. Controlling rate factors can be identified and different types of drying behavior specific to a given material or drying condition can be explained and understood through model simulation studies. Such capability can provide important guidance for drying process design and control.
A receding interface model for the drying of slurry droplets
Authors: Cheong H. W. , Jeffreys G. V. , Mumford C. J.
Published: June 2004

A receding interface model of the drying of single drops of slurries of sodium sulfate decahydrate has been developed to describe the drying characteristics of this material and to estimate the drying rates of particulate slurries. The simultaneous heat and mass transfer rate equations have been solved numerically, and the results obtained have been compared with those obtained experimentally by drying single drops suspended on the tip of a glass filament.

Single drops of slurries, 1.0 to 1.5 × 10−3 m dia., were suspended on the tip of a flexible glass cantilever inserted in a vertical wind tunnel. A 50μm dia. nickel wire passed through the center of the glass beam and the outer surface was coated with a thin film of copper, thereby forming a thermocouple that measured the temperature of the core of the drop; the deflection of the beam gave the loss in weight during drying. In this way the instantaneous drying rate and drop temperature were determined and compared with those predicted by the receding interface model. In all cases the agreement between the predictions of the model and experimental results was good.
A composite statistical test for detecting changes of steady states
Authors: Narasimhan S. , Mah R. S. H. , Tamhane A. C. , Woodward J. W. , Hale J. C.
Published: June 2004

A statistical procedure for determining whether process variables have undergone a change of steady states is developed by using a composite statistical test. Factors influencing the power of the test and the probability of Type I errors were studied through theoretical analysis, computer simulation, and application to plant data. They include the number of variables to be tested together, the number of measurements used in time averaging, the levels of significance of the tests, and the appropriate formulation of the hypotheses. The procedure developed here is useful in process data reconciliation and in applications that require an analysis of process trends.
A new similarity rule for fluidized bed scale‐up
Authors: Horio Masayuki , Nonaka Akira , Sawa Yoshitaka , Muchi Iwao
Published: June 2004

A rule of hydrodynamic similarity for a scale change of fluidized beds has been developed based on the governing equations of bubble and interstitial gas dynamics. When geometrically similar scale‐up is to be carried out maintaining hydrodynamic similarity, the proposed similarity rule requires that two conditions be satisfied. The first condition assures a similarity in bubble coalescence. The second assures the similarities in bubble splitting and in the interstitial flow pattern. The present work proves theoretically that these two conditions are the necessary, and almost sufficient, conditions for hydrodynamic similarity. They consider not only bubble coalescence but also bubble splitting. The theory proposed was first tested by previous correlations for bubble diameter and grid zone structure, and second by experiment. It has been proved that as long as the present rule is satisfied, the longitudinal distribution of the average bubble diameter, stochastic variation around it, and the radial distribution of superficial bubble velocity can be maintained similar for a scale change.

Application of the present rule to predict the bubbling and solid circulation characteristics in a large‐scale unit by a small‐scale experiment has thus proved promising, at least for Geldart group B particles. In order to further study the possibility of a similarity in mass transfer and chemical reactions, computation was carried out using the three‐phase bubble assemblage model. If the effect of molecular diffusion is negligible, as in the case of fluidized bed combustion, even a chemical similarity is found to be possible.
Kinetics of sodium bicarbonate decomposition
Authors: Hu Wang , Smith J. M. , Doǧu Timur , Doǧu Gülsen
Published: June 2004

A thermal gravimetric method was used to measure rates of decomposition of NAHCO3 particles. Such decomposition produces a highly porous Na2Co3 that reacts with SO2 rapidly and completely at moderate temperatures. Hence, NaHCO3 decomposition provides a reactant with attractive features for SO2 removal. The rapid rate of decomposition combined with the high heat effect prevented determining intrinsic rates by constant temperature runs when the temperature level was above 400 K. However, rising‐temperature runs, which allowed time for heat transfer to equilibrate temperatures of the thermocouple and particles, gave reliable results at high temperatures. The activation energy was 102 kJ/mol. Porosimeter data verified the large increase in pore volume (from 0.03 to 0.39 × 10−3 m3/kg) on converting the NaHCO3 particles to Na2CO3. First‐order kinetics were observed up to high conversions, after which the apparent order decreased. However, the sodium bicarbonate could be completely converted to Na2CO3.
Small pore closure and the deactivation of the limestone sulfation reaction
Authors: Simons G. A. , Garman A. R.
Published: June 2004

The sulfation model of Simons and Rawlins (1980) is extended to include the effect of product deposits. The model includes: 1. the plugging of the smallest pores and the subsequent loss in the internal surface area, 2. the diffusion of the SO2 through the product deposits, and 3. the loss of intraparticle diffusion due to the complete plugging of the largest pores. It is shown that the plugging of the smallest pores is generally rate‐controlling.
Molecular thermodynamics for fluids at low and high densities. Part I: Pure fluids containing small or large molecules
Authors: Cotterman R. L. , Schwarz B. J. , Prausnitz J. M.
Published: June 2004

A correlation is presented for the thermodynamic properties of pure fluids containing small or large molecules. The residual Helmholtz energy is given in terms of perturbed‐hard‐chain (PHC) theory, extended to polar fluids with a multipolar expansion. The novel feature of this correlation is a separation of the Helmholtz energy into low‐density and high‐density contributions. The low‐density contribution follows from a virial expansion and the high‐density contribution from a perturbation expansion. For intermediate densities, a continuous function is used to interpolate between the two density limits. This modification of PHC theory improves agreement with experimental second virial coefficients, vapor pressures, and saturated liquid densities. Since all molecular parameters used here have a well‐defined physical significance, they can be reliably estimated for high‐molecular‐weight‐fluids where experimental data are scarce. More important, separation into low‐density and high‐density contributions allows separate mixing rules for each density region; this flexibility in mixing rules significantly improves representation of mixture properties, as discussed in Part II.
Hydration of isobutene in liquid‐full and trickle‐bed reactors
Authors: Leung Pak , Zorrilla C. , Recasens F. , Smith J. M.
Published: June 2004

Rates of hydration of isobutene were measured with Amberlyst‐15 catalyst particles in a differential, liquid‐full recycle reactor operating at atmospheric pressure and 303 to 333 K. Catalysts pretreated in two different ways were studied. Liquid‐to‐particle mass transfer had a small but measurable effect on the rate. Intraparticle diffusion was more significant, as indicated by effectiveness factors from 0.26 for the larger catalyst particles (dp = 1.04 × 10−3 m) at 333 K to 0.84 for the smaller particles (dp = 0.45 × 10−3 m) at 303 K. The intrinsic rate was first‐order in isobutene concentration with an activation energy of 67 kJ/mol. The intraparticle diffusion resistance is due to the macropores surrounding the very small gel‐type microparticles of which the particles were composed.

Some data were obtained for reaction rates in trickle‐bed operation. Global rates were somewhat lower in the trickle‐bed operation than in the liquid‐full runs. Using the previously determined intrinsic kinetics and effectiveness factors, the liquid‐to‐particle mass transfer coefficients could be approximated for the trickle‐bed operation.
Flow distribution in the fiber lumen side of a hollow‐fiber module
Authors: Park Joong Kon , Chang Ho Nam
Published: June 2004

Little attention has been paid to the flow distribution among many thousands of fibers in the hollow‐fiber modules of artificial kidney, ultrafiltration, and reverse osmosis devices despite its potential importance in the efficiency of the module. Numerical study by a finite‐difference method, as well as experiment by direct sampling from individual fibers and high‐speed photography of a color tracer, has shown that there exists a significant degree of nonuniformity in the flow distribution, which depends on the manifold design, the Reynolds number, and the pressure drop along the fibers.
Crystallization kinetics of potassium sulfate in an MSMPR agitated vessel
Authors: Jones A. G. , Budz Jerzy , Mullin J. W.
Published: June 2004

New data are reported on the crystallization kinetics of potassium sulfate solutions in a laboratory‐scale continuous MSMPR cooling crystallizer. Population density distributions determined down to 1 μm by laser light scattering and sieve analysis are corrected for the effects of crystal agglomeration and shape variation and are used to determine accurate growth and nucleation rates. The crystal growth rate is strongly size‐dependent, second order with respect to supersaturation, with a high overall activation energy. The surface reaction contribution to the growth process is comparatively large, with a diffusion dependency that increases with crystal size and temperature. While largely consistent with most previous studies, a marked deviation is detected in growth rates at small sizes at which very strong curvature is exhibited in the population density distributions. Secondary nucleation rates vary linearly with suspension density, and the zero size order and activation energy are similar to those of growth but significantly are both much lower at a larger effective size. These observations support the view that growth rate dispersion may be responsible in large part for the substantial variation in reported secondary nucleation kinetics.
Gas separation by high‐flux, asymmetric hollow‐fiber membrane
Authors: Pan C. Y.
Published: June 2004

A mathematical model of multicomponent permeation systems with high‐flux, asymmetric hollow‐fiber membranes is presented. The model takes into account the permeate pressure variation inside the fiber. In the special case of negligible permeate pressure drop, the model yields a simple analytical solution for membrane area calculation that eliminates the numerical integration step required in existing methods. Laboratory multicomponent permeation experiments have verified the mathematical model and have demonstrated the technical feasibility of using the high‐flux asymmetric cellulose acetate hollow fiber for H2, CO2, and H2S separation. It is shown that the selectivity of the cellulose acetate membrane is ideally suited to the recovery of hydrogen from the purge gas of reactor recycle loops. For the separation of high‐concentration CO2or H2S, the test data show that the permeabilities of the individual components in mixed gas permeation are significantly different from those of pure gases.
Computational aspects of equations of state: Fact and fiction
Authors: Mathias P. M. , Benson M. S.
Published: June 2004

A detailed study has been made of the computing times for several common equations of state used by industry. The cubic equations are approximately equivalent to more complicated equations (e.g., perturbed hard chain and BWRS) for systems with eight or more components. Thus, it is not justified to choose cubic equations over other forms purely on the basis of computational advantage. Further, the study identifies mixing‐rule summations as the dominant consumer of computing time.
Surface shear near the contact line of a binary evaporating curved thin film
Authors: Parks C. J. , Wayner P. C.
Published: June 2004

A model for surface shear in the contact line region of a steady state two‐component evaporating thin film in the shape of a meniscus is developed. A constant vapor pressure boundary condition at the liquid‐vapor interface is combined with experimental meniscus profile data to obtain temperature and composition profiles. The results are used to delineate the relative effects of meniscus shape, temperature, and composition on fluid flow toward the higher temperature in an evaporating meniscus. For the system analyzed, it is found that surface shear due to composition gradients and temperature gradients is the single most important contribution to flow in the evaporating, two‐component capillary meniscus in the film thickness range 10−6 m ≤ δ ≤ 10−5 m. The effect of concentration on the vapor pressure leads to a maximum evaporation rate at a thickness of approximately 6 μm for the conditions studied. Theoretical results are discussed in the light of experimental observations.
Effect of electrolyte on the rheological properties of coal‐water mixtures
Authors: Kaji Ryuichi , Muranaka Yasushi , Miyadera Hiroshi , Hishinuma Yukio
Published: June 2004

Highly concentrated coal‐water mixtures were prepared using two different types of dispersants, anionic and nonionic. Through experimental investigations of the effect of the electrolytes on their rheological properties, the mechanisms of the particle dispersion in both mixtures have been elucidated.
On‐line optimization of constrained multivariable chemical processes
Authors: Jang Shi‐Shang , Joseph Babu , Mukai Hiro
Published: June 2004

A two‐phase approach to the control and operation of complex chemical processes at their optimum operating conditions is presented. The first phase consists of on‐line parameter identification and state estimation of approximate nonlinear dynamic process models using on‐line and off‐line measurements. In the second phase, the optimum operating strategy is determined by integrating and optimizing this identified process model over a selected time horizon into the future. The method is particularly suited to those processes that exhibit slow dynamic responses and are subject to disturbances that have a significant economic impact. Examples include batch chemical reactors, large distillation towers, and processes with significant holdup times such as large fluidized‐bed reactors.
A new solution to the inverse problem of optimal regulator control
Authors: Tan Li‐Yang , Weber T. W.
Published: June 2004

In chemical process control, the application of an optimal control strategy, dictated by the theory of the linear quadratic problem, does not always guarantee the best process performance. The main problem is that the unspecified weighting matrices in the quadratic performance index have a pronounced effect on the optimal control law derived from linear quadratic theory. In the past, values of the weighting matrices have been selected by experimenting with the process in much the same manner as a PID controller is tuned. The objective of the present study is to resolve the inverse problem of optimal regulator control, limiting the performance index in the quadratic form with two independent weighting matrices which are investigated. A new criterion has been developed such that the computation of determining those matrices can be carried out off‐line in advance, and then stored in a computer for real‐time use.
Carbochlorination of metal oxides with phosgene
Authors: Adelman D. J. , Burnet George
Published: June 2004

Kinetics of the carbochlorination with phosgene of an alumina‐silica material are reported for a temperature range of 723 to 1,023 K and a phosgene partial pressure range of 4 to 90 kPa. The oxides react in a constant ratio over most of the conversion range and the grain model accurately predicts conversion as a function of time.
Observability and redundancy classification in multicomponent process networks
Authors: Kretsovalis Alexandros , Mah R. S. H.
Published: June 2004

Classification of variables and measurements in multicomponent flow networks is treated in this paper. Classification rules are derived that exploit the relationship between cutsets of the process graph and certain graphs derived from it, and the solvability of the relevant equations. These rules are incorporated in two graph‐oriented algorithms for observability and redundancy classification.
Theory of batchwise centrifugal filtration
Authors: Sambuichi Masao , Nakakura Hideo , Osasa Kunihisa , Tiller F. M.
Published: June 2004

In centrifugal filtration, centrifugal forces serve as the driving force in the production of cakes. Centrifugal sedimentation leads to formation of a clear supernatant followed by a slurry and a cake that grows and compacts simultaneously. The slurry concentration is independent of radius but decreases everywhere within the suspension at the same rate with respect to time. The theoretical analysis of centrifugal filtration presented here takes cake compressibility and variable permeability into account. Experiments were carried out under low driving forces with a centrifuge having a diameter of 150 mm and speeds of 1,000–2,000 RPM. With centrifugal accelerations of 75–300 g and pressure differentials under 1 atm, the sedimentation process was relatively slow and could be observed experimentally with ease.
Growth rate dispersion by initial growth rate distributions and growth rate fluctuations
Authors: Zumstein R. C. , Rousseau R. W.
Published: June 2004

Two distinctly different mechanisms that lead to growth rate dispersion have been observed experimentally. One of the mechanisms involves an initial growth rate distribution among nuclei, while the other allows crystal growth rates to fluctuate. The model formulated in the present work includes both phenomena. Solutions to population balances in a continuous mixed‐suspension, mixed‐product removal continuous crystallizer and a constant‐supersaturation batch crystallizer are obtained in terms of parameters characterizing the two mechanisms.
Liquid‐side ion exchange mass transfer in a ternary system
Authors: Kataoka Takeshi , Yoshida Hiroyuki , Uemura Toshifumi
Published: June 2004

Liquid phase mass transfer in a ternary system [R – A] + (B + E) has been analyzed according to the Nernst‐Planck equation. The equilibrium isotherm was represented by the mass action law. In the case of DA > DB > DE, the resin phase concentration of B ion with time showed a peak. The height of the peak was influenced by the diffusivity ratio, equilibrium constant, and ionic valence. When the modified equilibrium constant K′ ≧ 100 in the case of A ion and K′ ≧ 500 in the case of B and E ions, the exchange rates of the ions could be obtained by approximating K′ = ∞.

Experimental data on the change of the resin phase concentration y with time are represented. In a [R – H+] + (Na+ + Zn2+) system, the change of yNa with time showed a high peak. In a [R – H+] + (Na+ + Li+) system, the change of yLi with time showed a small peak. No peaks arose in a [R – Na+] + (H+ + Li+) system. The data agreed reasonably well with the values calculated according to the theoretical equations.
A visual study of pulp floc dispersion mechanisms
Authors: Lee C. W. , Brodkey R. S.
Published: June 2004

The dispersion of artificially produced softwood pulp flocs in controlled, plane, turbulent Couette flow was studied by using both monocular and stereoscopic film techniques. The mechanisms of controlled floc formation and of dispersion are proposed. For the latter, two mechanisms were observed, one global that involves deformation, breaking, and fragmentation, and one local that involves surfac erosion. The effect of the flow field stress level on the time and rate of dispersion is presented.
Vibrational control of an exothermic reaction in a CSTR: Theory and experiments
Authors: Cinar Ali , Deng Jian , Meerkov S. M. , Shu Xianshu
Published: June 2004

Vibrational control is a method for modification of dynamic properties of linear and nonlinear systems by introducing fast, zero‐average oscillations in the system's parameters. In this paper, forced oscillations introduced in the input flow rates of an exothermic continuous stirred‐tank reactor (CSTR) are shown to result in a modification of the S‐shaped steady state curve. This modification leads to a possibility of operating a CSTR at an asymptotically stable period regime located in the vicinity of an unstable steady state of the reactor system with stationary input flow rates. Thus, vibrations of the input flow rates can be viewed as a stabilizing mechanism for exothermic CSTR's.
Linear model‐dependent control
Authors: Svoronos S. A.
Published: June 2004

Model‐dependent control for single‐input/single‐output discrete‐time linear systems is introduced. It is a powerful controller design method that effectively handles open‐loop instability, inverse response, and time delays. Only two parameters need to be tuned, and these directly influence control quality and robustness. Two examples demonstrate the power and versatility of the method.
Facilitated transport of CO2 in ion exchange membranes
Authors: Way J. D. , Noble R. D. , Reed D. L. , Ginley G. M. , Jarr L. A.
Published: June 2004

The facilitated transport of CO2 through ion exchange membranes containing organic amine counterions was studied. Steady state CO2 fluxes were measured from pure gas streams and mixtures with CH4. Facilitation factors for CO2 up to 26.7 were calculated from transport data. Transport measurements were binary mixtures of CO2 and CH4 yielded ratios of CO2 flux to CH4 flux ranging from 29.0 to 264. Conversion of flux ratios to permeabilities yielded separation factors up to 551 for CO2 over CH4, which are compared to literature data for polymeric membranes. The transport data support a mobile, reactive‐carrier facilitated transport mechanism with a carbamate zwitterion complex. Effective diffusivities for CO2 and the carrier‐gas complex were determined from transport data. A reaction equilibrium model predicted facilitation factors that were in very good agreement with experimental values. Potential applications are also discussed.
Film‐splitting flows of shear‐thinning liquids in forward roll coating
Authors: Coyle D. J. , Macosko C. W. , Scriven L. E.
Published: June 2004

Asymmetric film‐splitting of shear‐thinning liquid between rotating cylinders in forward roll coating is analyzed with the Carreau model of shear‐sensitive liquid. The mass and momentum conservation equations for steady, two‐dimensional flow are solved by means of the Galerkin finite‐element method. A simpler model is also developed from the lubrication approximation and its range of validity is established. The major results are that the greater the shear thinning, the farther out of the gap the splitting meniscus moves, the higher the flow rate through the gap, and the more symmetrical the film split than with Newtonian liquid. Experiments reported in the literature confirm some of these predicted trends.
Fiber spinning of viscoelastic liquid
Authors: Papanastasiou T. C. , Macosko C. W. , Scriven L. E. , Chen Zhao
Published: June 2004

The fiber spinning process of viscoelastic liquid is successfully analyzed by means of a nonlinear integral constitutive equation, finite‐element discretization, and Newton iteration. The process is cast and studied both as an initial value problem, which requires the specification of the drawing force, and as a two‐point boundary value problem, which requires the specification of the draw ratio. Solutions are obtained up to high elasticity, high draw ratio, and large drawing force. The results agree with the analytic asymptotic solution for Newtonian liquid, with existing numerical solutions in the limiting case of the upper‐convected Maxwell liquid, and with available experimental data on spinning of polystyrene melt at 170°C and low‐density polyethylene at 150°C.
Diffusion coefficients for binary alkane mixtures to 573 K and 3.5 MPa
Authors: Matthews M. A. , Akgerman Aydin
Published: June 2004

An automated Taylor dispersion apparatus, designed to operate from 298 to 573 K and 101 to 3,450 kPa (14.7 to 500 psia), was used to measure diffusion coefficients at infinite dilution for the solutes n‐octane, n‐decane, n‐dodecane, n‐tetradecane, and n‐hexadecane in the solvents n‐heptane and n‐dodecane. Dodecane viscosity and density also were measured at all conditions. Various predictive theories are tested in light of the new data, and a correlation based on the data at high temperature and pressure is presented. The data are well represented by a free‐volume expression of the form \documentclass{article}\pagestyle{empty}\begin{document}$ D_{AB} /\sqrt T = \beta \,(V - V_D) $\end{document}. The data given here extend the available data base for alkane/alkane diffusion by 100 to 200 K, and allow evaluation of predictive theory over an extended range of temperatures.
Overpressure during emergency relief venting in bubbly and churn‐turbulent flow
Authors: Leung J. C.
Published: June 2004

Vessel overpressure behavior during emergency relief venting in both bubbly and churn‐turbulent flow regimes was obtained analytically. The transient predictions are shown to be in good agreement with the more exact numerical integration scheme. The applications of current results in relief vent sizing for both reactor vessels and storage tanks are demonstrated via numerical examples.
Effect of segregation on the course of unpremixed polymerizations
Authors: Fields S. D. , Ottino J. M.
Published: June 2004

Reactant segregation and mixing effects can be represented by a one‐dimensional distribution of alternating reactive liquid layers. This paper reports a theoretical study of the influence of this configuration on the course of three‐component, random block copolymerizations. Two models that follow the interdiffusion of the reacting species and the catalyst are considered. The first employs a lumped competitive‐parallel kinetic scheme to represent the formation of hard and soft segments; the second uses a moment formulation to handle the polymerization. The results are intended for the description of mixing‐activated three‐component polyurethane systems, but conclusions of a general nature are obtained. Several unexpected results are presented regarding the molecular weight buildup and spatial product segregation in the system. In particular, it is established that reactant segregation may severely influence product segregation (layering), the average molecular weight, and the maximum molecular weight achieved.
Turbulent dispersion of aqueous drops in organic liquids
Authors: Haas P. A.
Published: June 2004

Drops sizes for turbulent dispersion of aqueous solutions in organic liquids were determined and correlated for three types of dispersion devices: small‐diameter tubes, motionless mixer units, and a rotating annular disperser with Couette flow. Empirical correlation based on dimensional analyses were useful for application of these devices to gel‐sphere processes. The results support the Kolmorogoff theory of turbulence as a dispersion mechanism for a range of 104 for the rate of energy dissipation.
Solvent extraction with microporous hydrophilic and composite membranes
Authors: Prasad Ravi , Sirkar K. K.
Published: June 2004

Dispersion‐free solvent extraction using microporous hydrophobic membranes has been extended to hydrophilic and composite hydrophobic‐hydrophilic membranes. Excess phase pressure conditions, if needed for dispersion‐free operation, have been identified. Boundary layer and membrane resistances to solute transport have been isolated and simple relations developed for the overall mass transfer coefficient in such systems. A variety of flat microporous membranes have been utilized. Previous investigations by others had interpreted the membrane mass transfer resistance using the notion of unhindered diffusion through tortuous pores of the membrane. We have studied here the applicability and limitations of such a model for a number of membrane‐solute‐solvent systems.
Electrokinetic behavior of colloidal particles with thin ionic double layers
Authors: Natarajan Ramesh , Schechter R. S.
Published: June 2004

The phenomenological equations that govern the nonequilibrium behavior of the ionic diffuse double layer surrounding an isolated, charged coloidal particle are considered. An approximate solution is constructed that is valid when the ratio of the Debye length to the characteristic particle dimension is small. This solution is applicable to a particle that is subjected to an external perturbation composed of an arbitrary linear combination of steady, axisymmetric electrical, hydrodynamical, or concentration gradient fields. Hence, this analysis provides a unified approach to the treatment of the entire class of admissible problems in the thin double layer approximation. Specific applications are shown to the problems of electrophoresis and dilute shear viscosity of a suspension of uniform, noninteracting spherical colloidal particles. Comparison with the numerical results of previous investigators shows that the solutions are accurate over much of the parameter range of practical interest in colloidal suspensions. The role of the zeta potential and the mobilities, valences, and concentrations of the dissolved ions on electrokinetic phenomena are examined.
On the optimization of differential‐algebraic process systems
Authors: Cuthrell J. E. , Biegler L. T.
Published: June 2004

Many chemical engineering problems require the optimization of systems of differential and algebraic equations. Here a method is presented based on finite‐element collocation, which converts differential equations to algebraic residual equations with unknown coefficients. A nonlinear program is then formulated, with residuals incorporated as equality constraints and coefficients as decision variables. Also, adaptive knot placement is used to minimize the approximation error, with necessary and sufficient conditions for optimal knot placement incorporated as additional equality constraints in the nonlinear program. All equality constraints are then solved simultaneously with the optimization problem, thus requiring only a single solution of the approximated model. Finally, problems with discontinuous control profiles can be treated by introducing an extra level of elements (superelements) as decisions in the optimization problem. This approach is demonstrated on a simple optimal control problem as well as a reactor optimization problem with steep temperature profiles and state variable constraints.
Heterogeneous azeotropic distillation: Experimental and simulation results
Authors: Kovach J. W. , Seider W. D.
Published: June 2004

Experimental measurements for an industrial azeotropic distillation tower that dehydrates secondary butyl alcohol (SBA) show erratic operation that only approaches a steady state. These are explained with steady‐state simulations which show that slight variations in the aqueous reflux rate cause many trays to shift from homogeneous to heterogeneous operation, accompanied by significant changes in the SBA purity, with water or entrainer contaminating the bottoms product. When other methods failed, an arc‐length homotopy‐continuation method made small adjustments in the reflux ratios to obtain close agreement with the measurements.
Thermodynamics of highly dilute solutions and the quest for ultrapurity
Authors: Sciamanna S. F. , Prausnitz J. M.
Published: June 2004

Since very high purity is sometimes required for health‐related (and other) products, it is useful to reexamine the common thermodynamic relations that describe the chemical potential of a solute at very high dilution. Because Stirling's approximation is not valid for small numbers, the usual thermodynamic relations must be reformulated for small systems, i.e., for a solute in a small bubble or drop. A simplistic analysis indicates that in a small bubble or drop, the chemical potential of a solute goes to a finite value as the mole fraction of solute goes to zero, in contrast to the conventional result, where that chemical potential goes to negative infinity. This simplistic analysis has profound implications for separation science; it implies that (in theory) ultrapurity may be attained by conventional diffusional methods. While serious objections can be raised to invalidate the simplistic analysis, it may nevertheless be useful for chemical engineers to consider separation methods using highly dispersed systems.
A multivariable nonlinear self‐tuning controller
Authors: Agarwal Mukul , Seborg D. E.
Published: June 2004

A new self‐tuning controller (STC) has been developed for a general class of nonlinear multiinput, multioutput process models. These models can include arbitrary, known nonlinear functions of the old inputs and outputs as well as the products of these functions and any powers of the most recent inputs. A very general control algorithm has been proposed that allows different numbers of inputs and outputs, different time delays for each input‐output pair, and a performance index that can include different penalties on the outputs and on the incremental changes in the outputs. Simulation results are presented for two‐point composition control of a pilot‐scale distillation column. The results demonstrate that the new nonlinear STC performs significantly better than conventional STC's based on linear models.
Generalized likelihood ratio method for gross error identification
Authors: Narasimhan S. , Mah R. S. H.
Published: June 2004

A new method for detecting, identifying, and estimating gross errors in steady state processes is described in this paper. The generalized likelihood ratio method is based on the likelihood ratio statistical test and provides a general framework for identifying any type of gross error that can be modeled. The procedure is illustrated with gross errors caused by measurement biases and leaks. One significant advantage of the method is that the identification of gross errors is not confounded by departure from steady state conditions, which may now be accounted for by “leaks”. Also proposed is a new strategy for identifying multiple gross errors using serial compensation of gross errors, which may be applied to all types of gross errors including leaks and biases and which requires less computing time than the existing strategies.
Kinetics of the sodium carbonate–sulfur dioxide reaction
Authors: Kimura Shoichi , Smith J. M.
Published: June 2004

The Kinetics of the SO2‐Na2CO3 reaction were studied at 353 to 413 K and atmospheric pressure with thermal gravimetric analysis data. Since the reaction is very fast, special precautions were taken to operate at conditions such that transport effects did not influence results. The data indicated that Na2SO3 was formed by two paths: direct reaction, and adsorption of SO2 followed by conversion of adsorbed SO2 to adsorbed CO2 and finally desorption to final product. Rate constants were evaluated for each step in the proposed mechanism. Product distribution predicted from the rate constants agreed well with the distribution calculated from the experimental data at temperatures from 353 to 413 K. At 413 K the results suggested a change in mechanism.
Effect of film size on drainage of foam and emulsion films
Authors: Malhotra A. K. , Wasan D. T.
Published: June 2004

All available theoretical analyses for the drainage of thin plane‐parallel liquid films, such as those existing between two approaching liquid droplets or bubbles in the coalescence process, predict essentially the same dependence of rate of thinning of the intervening film on its size as is described by the Reynolds equation—that is, drainage time increases with the square of the film radius. Recently, we have reported experimental data for both foam and emulsion films which showed that the measured drainage times increase with about a 0.8 power of the film radius, a value much smaller than the theoretically predicted value of 2.0. Here we present a hydrodynamic analysis to predict the experimentally observed effect of film size on the kinetics of thinning of emulsion and foam films. We extend the applicability of the Reynolds model by accounting for the flow in the Plateau borders as well as the London‐van der Waals forces in the thin film phase. Our theoretical predictions are in good agreement with the experimental data on the dependence of drainage time of both foam and emulsion films on their radii.
Effect of solids on oxygen transfer in agitated three‐phase systems
Authors: Mills D. B. , Bar Raphael , Kirwan D. J.
Published: June 2004

A dynamic response method was used to measure the volumetric mass transfer coefficient for oxygen in a mechanically agitated vessel containing an aqueous suspension of 66 μm glass beads. At constant stirring speed and superficial gas velocity the volumetric gas transfer coefficient kLa was found to decrease with solids loading. A generalized equation correlated the results in terms of the volume concentration of the solids, the total power input per slurry volume, and the superficial gas velocity.
Compressed fluid technology: Application to RIE‐developed resists
Authors: Ziger D. H. , Wolf T. M. , Taylor G. N.
Published: June 2004

A novel plasma‐developed resist lithographic process is described that uses compressed CO2 to extract nonvolatile siloxane molecules from host organic polymers. The process is capable of at least 0.75 μm resolution with an X‐ray sensitive guest siloxane‐host polymer system. A processing window was investigated and defined to eliminate or minimize film damage during compressed fluid extraction. Polymer deformation was usually avoided by using supercritical CO2 rather than liquid CO2, provided that film thicknesses were ≤1 μm. Increased solute concentrations in the host polymer also adversely affected the quality of extracted films. An in situ capacitance process monitoring scheme was developed which indicated that film damage, when observed, was primarily caused by explosive decompression of the solvent from the host polymer.
STICT model for surface thermodynamics of liquid metal solutions
Authors: Howell W. J. , Eckert C. A.
Published: June 2004

A new model, called STICT for surface thermodynamics using ideal chemical theory, is developed for the surface tension of liquid metal alloys. It uses the Guggenheim approach to relate surface phase properties to those in the bulk. For strongly solvated metal mixtures, ideal chemical theory is used to characterize bulk properties. The STICT model fits experimental data well for the seven systems for which sufficient data exist. Moreover, calculations of bulk and surface true compositions give some guidance to the tailoring of the surface properties of alloys for various applications.
Diffusion in pore networks: Effective medium theory and smooth field approximation
Authors: Burganos V. N. , Sotirchos S. V.
Published: June 2004

The problem of diffusion in pore networks of a certain class is considered, and a procedure for estimating effective diffusivities is formulated. The effective‐medium theory is used to obtain an effective conductance for the network, which is then used to determine the effective diffusivity starting from first physical principles and utilizing the observation that a network of pores of uniform conductance satisfies the smooth field approximation. Comparison of the estimated intraparticle diffusivities with those obtained from the exact solution of the transport equation for large networks reveals high accuracy and reliability of the method. Results for a number of pore networks show that the smooth field assumption should not be employed arbitrarily since it always predicts higher effective diffusion coefficients than the exact ones, by more than one order of magnitude in some cases.
Crystallization kinetics of potassium chloride from brine and scale‐up criterion
Authors: Qian Ru‐Ying , Chen Zu‐De , Ni He‐Gen , Fan Zhang‐Zhang , Cai Fu‐Di
Published: June 2004

A systematic study of potassium chloride crystallization shows that constant tip speed, TIPS, is the agitation criterion for scale‐up. Three hydrodynamic regions are identified by a group MT TIPS3. Thus, a new generalized kinetic equation is proposed: B° = KGi(MT TIPS)j.

The values of the power index j are 0.7 and 1.2 for low and high ranges of MT TIPS3, respectively. At even higher MT TIPS3, j scatters due to the breakage of crystals. The power index i is independent of hydrodynamic conditions and depends only on the crystallization temperature, e.g., it is 2.8 at 313.2 K.
A generalized bubble diameter correlation for gas‐solid fluidized beds
Authors: Horio Masayuki , Nonaka Akira
Published: June 2004

A new bubble diameter correlation is derived to predict bubbling characteristics of fluidized beds of varieties of powders. The present model is founded on the postulate that the steady bubble size, which is often called the maximum stable diameter, observed in a bed of Geldart group A powder is formed as a result of an equilibrium of successive coalescence and splitting. For the cases of group B powders the present correlation automatically converges to the conventional correlation of Mori and Wen (1975), whose predictions are close to those of Rowe (1976) and Darton et al. (1977). For group A powders the present correlation is validated by comparison with experimental data in the literature. Based on this correlation a theoretical explanation is presented for the fact that the maximum bubble diameters observed were up to 50 to 100 times as large as those from the stable bubble theory of Harrison et al. (1961).