bluuebunny/crossref_metadata_2025_split huggingface dataset:
Flow distribution in the fiber lumen side of a hollow‐fiber module
Authors: Park Joong Kon , Chang Ho Nam 
Published: June 2004

AbstractLittle 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

AbstractNew 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

AbstractA 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

AbstractA 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

AbstractA 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

AbstractHighly 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

AbstractA 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

AbstractIn 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

AbstractKinetics 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

AbstractClassification 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

AbstractIn 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

AbstractTwo 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

AbstractLiquid 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

AbstractThe 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

AbstractVibrational 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

AbstractModel‐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

AbstractThe 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

AbstractAsymmetric 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

AbstractThe 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

AbstractAn 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

AbstractVessel 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

AbstractReactant 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

AbstractDrops 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

AbstractDispersion‐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

AbstractThe 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

AbstractMany 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

AbstractExperimental 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.