bluuebunny/crossref_metadata_2025_split huggingface dataset:
Volume‐explicit equation of state for hard chains, their mixtures, and copolymers
Authors: Hamad Esam Z. 
Published: April 2004

AbstractVolume‐explicit equations of states for hard chains, their mixtures, and copolymers were developed. The equations accurately represent the simulation data. They also predict the correct volume at high pressures (close packing), unlike the common pressure‐explicit equations, which predict a physically unattainable volume. Entropic demixing is also predicted by the proposed equations. The developed equation can be used as the repulsive pan in developing volume‐explicit real polymer equations of state or excess Gibbs energy models.
Practical friction‐based approach to modeling multicomponent diffusion
Authors: Zielinski John M. , Hanley Brian F. 
Published: April 2004

AbstractAlthough most industrial drying and separation technologies are based on transport of multiple components, a convenient and practical means of describing multicomponent diffusion over wide temperature and concentration ranges has not been developed for polymer solutions or even for simple liquid mixtures. We have been able to demonstrate that all of the diffusion coefficients required to describe molecular transport in multicomponent systems can be easily predicted from self‐diffusion coefficients and thermodynamic information when the mass flux with respect to the mass‐average velocity is expressed in terms of the frictional force experienced by a molecule as it undergoes Brownian motion. This approach enables the flux equations for any combination of materials to be written in terms of experimentally measurable quantities. The model was tested by: (1) predicting literature data for principal diffusion coefficients in a ternary system; (2) applying the diffusion model to predict the drying behavior of three ternary systems; (3) predicting experimental values of the principal and cross coefficients for a ternary organic solvent mixture from self‐diffusion data measured by PFG‐NMR and available thermodynamic data; and (4) examining whether the limiting cases in this model are physically realistic. The applicability of the model to gas transport and polymer interdiffusion is also briefly examined.
Large eddy simulations on the flow driven by a Rushton turbine
Authors: Derksen Jos , Van den Akker Harry E. A. 
Published: April 2004

AbstractLarge eddy simulations were performed on the flow in a baffled stirred tank, driven by a Rushton turbine at Re = 29,000. The simulation procedure consisted of a lattice–Boltzmann scheme for discretizing the Navier–Stokes equations, and a force‐field technique for representing the action of the impeller on the fluid. The subgrid‐scale model was a conventional Smagorinsky model with a Smagorinsky constant cs = 0.12. The uniform, cubic computational grid had a size of about 6 × 106 nodes. The computer code was implemented on a parallel, shared‐memory computer platform. The results on the phase‐resolved average flow, as well as on the turbulence characteristics, are compared with phase‐resolved experimental data. The trailing vortex structure in the vicinity of the impeller was well represented by the simulations.
Deposition of sodium sulfate in a heated flow of supercritical water
Authors: Rogak Steven N. , Teshima Paul 
Published: April 2004

AbstractWastes that can be treated by supercritical water oxidation often contain salts. Salts are almost insoluble under supercritical conditions and can result in severe fouling. A simple heat‐ and mass‐transfer model was developed and tested experimentally for sodium sulfate in a fully turbulent flow of water at 25 MPa. This model uses empirical heat‐transfer correlations to estimate mass‐transfer rates. The diffusion coefficient of the salt is calculated from the Stokes‐Einstein relation using a hydrodynamic diameter of 2 to 6 Å. New measurements of solubility showed that the solubility of sodium sulfate decreases by a factor of about 1,000 as the temperature increases from 380°C to 400°C. Salt deposition rates, inferred from the outside temperature of a heated test section, were reasonably close to the model predictions.
Sorption‐enhanced reaction process for hydrogen production
Authors: Hufton J. R. , Mayorga S. , Sircar S. 
Published: April 2004

AbstractA novel concept called Sorption Enhanced Reaction Process (SERP) for hydrogen production by steam‐methane reformation (SMR) reaction uses a fixed packed column of an admixture of an SMR catalyst and a chemisorbent to remove carbon dioxide selectively from the reaction zone. The chemisorbent is periodically regenerated by using the principles of pressure swing adsorption. The SERP process steps allow direct production of high‐purity hydrogen (>95 mol %) at high methane to hydrogen conversion (>80%) with dilute methane (<5 mol%) and trace carbon oxide (∼50 ppm) impurities at the reaction pressure by operating the reactor at a low temperature of 450°C. A conventional plug‐flow reactor packed with catalyst alone not only needs to be operated at a much higher temperature (>650°C) to achieve the same methane to hydrogen conversion, but produces a much lower purity of hydrogen product (∼75 mol %) with a large quantity of carbon oxide (∼20 mol %) impurities. A novel chemisorbent, which reversibly sorbs carbon dioxide in the presence of excess steam at a temperature of 300–500°C, was developed for application in the SERP and the process is experimentally demonstrated in a bench‐scale apparatus.
Perovskite‐related ZrO2‐doped SrCo0.4 Fe0.6O3‐δ membrane for oxygen permeation
Authors: Li Shiguang , Jin Wanqin , Huang Pei , Xu Nanping , Shi Jun , Hu Michael Z.‐C. , Payzant E. Andrew , Ma Y. H. 
Published: April 2004

AbstractA typical perovskite La0.2Sr0.8Co0.2Fe0.8O3‐δ (LSCF) membrane and a novel perovskite‐related ZrO2‐doped SrCo0.4Fe0.6O3‐δ (SCFZ) membrane were successfully prepared. The sintered membranes were characterized by an in‐situ high‐temperature X‐ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. Oxygen permeabilities of the two dense membranes were measured in the temperature range of 923 to 1,173 K under a fixed oxygen partial pressure gradient. The results of the oxygen permeation experiment and high‐temperature X‐ray diffraction in argon atmosphere indicate that the perovskite‐related SCFZ membrane has higher oxygen fluxes and is stable than that of the LSCF membrane at elevated temperatures and reduced oxygen partial pressures.
Isolation enhanced principal component analysis
Authors: Gertler Janos , Li Weihua , Huang Yunbing , McAvoy Thomas 
Published: April 2004

AbstractPrincipal component analysis (PCA) may reduce the dimensionality of plant models significantly by exposing linear dependences among the variables. While PCA is a popular tool in detecting faults in complex plants, it offers little support in its original form for fault isolation. However, by utilizing the equivalence between PCA and parity relations, all the powerful concepts of analytical redundancy may be transferred to PCA. Following this path, it is shown how structured residuals, which have the same isolation properties as analytical redundancy residuals, are obtained by PCA. The existence conditions of such residuals are demonstrated, as well as how disturbance decoupling is implied in the method. The effect of the presence of control constraints in the training data is analyzed. Statistical testing methods for structured PCA residuals are also outlined. The theoretical findings are fully supported by simulation studies performed on the Tennessee Eastman process.
On reaction kinetics for the thermal decomposition of hydrogen sulfide
Authors: Karan Kunal , Mehrotra Anil K. , Behie Leo A. 
Published: April 2004

AbstractNew kinetic data for the hydrogen sulfide decomposition reaction obtained from quartz tubular reactors over a temperature range of 800–1,250°C are reported. The study shows that the overall decomposition reaction has a first‐order dependency on H2S concentrations at these temperatures. The regression of our experimental data gave an overall hydrogen sulfide decomposition reaction rate constant as k (m3/kmol·s) = (1.68±0.86)×1011 exp [(−28,940±840)/T]. Moreover, for the first time, kinetic data from higher temperature (1,500–3,100°C) shock‐tube studies (Olschewski et al., 1994; Woiki and Roth, 1994) and the lower temperature flow reactor study (this work) are reconciled. A single rate constant for H2S decomposition reaction, k (m3/kmol·s) = (1.12±0.11)×1011 exp [−(28,360±200)/T] over a wide temperature range of 800–3,100°C was found to represent satisfactorily the three sets of data.
Coupling of hydrodynamics and chemical reaction in gas‐lift reactors
Authors: Márquez M. A. , Sáez A. E. , Carbonell R. G. , Roberts G. W. 
Published: April 2004

AbstractA model was developed to study the strong coupling between hydrodynamics and chemical reaction that occurs in external‐loop gas‐lift reactors. The model predicts the liquid circulation rate, as well as the axial profiles of gas holdup, pressure, gas and liquid velocity, and reactant conversion in the riser. The study on the first‐order, irreversible, isothermal reaction in the gas phase nA→B with a change in the number of moles on reaction shows that for n>1, the gas holdup decreases along the riser, the liquid circulation rate is lower than that in the absence of reaction, and liquid circulation decreases as n and k increase. The bubble radius at the sparger and the inlet gas composition can have important effects on reactor performance. Scale‐up strategies that involve increasing the reactor length result in higher reactant conversion, but a lower ratio of liquid circulation rate to gas feed rate.
Effect of small branch inclination on gas–liquid flow separation in T junctions
Authors: Ottens Marcel , Hoefsloot Huub C. J. , Hamersma Peter J. 
Published: April 2004

AbstractA model developed calculates the mass intake fraction of gas and liquid phase during gas–liquid flow with small liquid holdup values (ϵL ≤ 0.1) through regular T junctions with small branch inclinations. It was derived from the steady‐state macroscopic mechanical energy balance (extended Bernoulli equation) applied to the “inlet‐to‐run” streamline and “inlet‐to‐branch” streamline of both gas and liquid phases. The model results are compared with experimental data of the system air/water–glycerol (0, 33, and 60 wt. %) flowing through a regular (D1 = D2 = D3 = 0.051 m) T junction with branch inclinations ranging from 0° to 0.5°. It was found that the gas–liquid flow split behavior is affected strongly by the liquid viscosity and by branch inclinations of 0.1° and higher. The results predicted with the model agree well with experimental results obtained in a regular T junction with a horizontal inlet run and an inclined side arm.
Bifurcation study of kinetic effects in reactive distillation
Authors: Venimadhavan Ganesh , Malone Michael F. , Doherty Michael F. 
Published: April 2004

AbstractSimple distillation with multiple chemical reactions of arbitrary stoichiometry is described, with emphasis on effects of chemical kinetics. For low and high Damköhler number, the lightest and heaviest boiling components or azeotropes are known or can be found by known methods. In those limits, the products from a distillation can be anticipated and feasible separation structures can be identified. Feasible structures in these cases are not the same, however, and there are one or more transitions so that different structures can appear for different ranges of the Damköhler number. The transition points correspond to bifurcations, and using bifurcation analysis and continuation methods a systematic method that represents these changes was developed. The practical implication is that the feasibility and product purities for a reactive distillation may depend on production rate, catalyst level, and liquid holdup. The approach is illustrated for the production of methyl‐tert‐butyl ether (MTBE), where a critical Damköhler number for the disappearance of a distillation boundary is found. The influence of pressure on byproduct reactions in methyl acetate synthesis is also studied. A study of the synthesis of isopropyl acetate illustrates how the bifurcation method captures the essential kinetic effects in reactive distillation, including a critical Damköhler for the birth of a reactive azeotrope.
Analysis for the catalytic ignition of methane in a stagnation‐point flow
Authors: Treviño C. 
Published: April 2004

AbstractThe catalytic ignition of a mixture of methane and air in a planar stagnation‐point flow over a platinum foil is studied. The heterogeneous reaction mechanism is modeled with twelve heterogeneous reactions, including the adsorption processes of both reactants, the desorption kinetics of reactants and main products, and a set of surface reactions of the Hinshelwood–Langmuir type. The critical conditions for the catalytic ignition are found using high activation energy asymptotics of the desorption kinetics of the adsorbed reactant O(s). The analytical results are compared with published experimental data. The agreement is good, at least qualitatively.
Solid–liquid equilibria for solutions of binary globular‐protein mixtures
Authors: Hino Toshiaki , Prausnitz John M. 
Published: April 2004

AbstractA theory of the van der Waals form is used to establish solid–fluid phase diagrams for aqueous solutions containing two kinds of globular proteins. Theory is based on a one‐fluid model that uses a composition‐dependent hard‐sphere diameter and a composition‐dependent solvent‐mediated effective temperature to represent protein solutions. The hard‐sphere reference equation of state is based on the model of Young that correlates computer simulations of fluid–solid coexistence curves for binary hard‐sphere mixtures. The attractive perturbation term uses the inverse‐power potential with variable exponent n. Based on the correlation of George and Wilson and Rosenbaum et al., the optimum range of effective temperature is determined for protein crystallization. For binary protein systems, as the size difference increases, the mutual solubility of unlike proteins declines sharply in the precipitated solid phase. The theoretical results obtained here may be useful for design of protein‐separation processes by crystallization.
Characteristics of microencapsulated PCM slurry as a heat‐transfer fluid
Authors: Yamagishi Yasushi , Takeuchi Hiromi , Pyatenko Alexander T. , Kayukawa Naoyuki 
Published: April 2004

AbstractThe hydrodynamic and heat‐transfer characteristics of slurry containing microencapsulated phase‐change materials (MCPCMs) were investigated experimentally for use as a heat‐transfer fluid. Pressure drop and local convective heat‐transfer coefficients of the slurry flows in a circular tube with uniform heat flux were measured. Slurries consisting of octadecane (C18H38) contained in 2–10‐μm‐dia. microcapsules and pure water were used. The particle volume fractions in the slurry were varied up to 0.3. Results showed that increases in particle volume fractions caused the slurry flow structure to change from turbulent to laminar, and the pressure‐drop reduction of the slurry flow relative to a single‐phase water flow was under the same flow‐rate conditions. The heat‐transfer performance of the slurry also depended on the change in flow structure. When the MCPCMs melted, the local heat‐transfer coefficients for turbulent slurry flows increased relative to those for nonmelting slurry. This phenomenon was influenced by the MCPCM fraction, the degree of turbulence, and the heating rate at the tube wall. The experimental data will be useful in the design of thermal‐energy transportation systems using MCPCM slurry.
Modeling of solid–liquid fluidization in the stokes flow regime using two‐phase flow theory
Authors: Thelen Travis V. , Ramirez W. Fred 
Published: April 2004

AbstractTwo‐phase theory is applied to solid–liquid fluidization in the Stokes flow regime. Because inertial terms can be neglected in the Stokes flow regime, the momentum balances are simplified to an algebraic relation between drag, buoyant, and diffusive forces. The resulting convection‐dispersion model is then applied to an experimental expanded‐bed adsorption system. Two flows are investigated, namely, step changes in the fluidization velocity and step changes in the fluid properties. Experimental data and model simulations are in excellent agreement for both flow configurations. Furthermore, the two‐phase model provides an accurate prediction of the observed time delay in bed expansion for step changes in fluid properties, as well as a mechanistic explanation for its observation.
Optimal operation of multivessel batch distillation columns
Authors: Furlonge H. I. , Pantelides C. C. , Sørensen E. 
Published: April 2004

AbstractIncreased interest in unconventional batch distillation column configurations offers new opportunities for increasing the flexibility and energy efficiency of batch distillation. One configuration of particular interest is the multivessel column, which can be viewed as a generalization of all previously studied batch column configurations. A detailed dynamic model was used for comparing various optimal operating policies for a batch distillation column with two intermediate vessels. A wide variety of degrees of freedom including reflux ratios, product withdrawal rates, heat input to the reboiler, and initial feed distribution were considered. A mixture consisting of methanol, ethanol, n‐propanol and n‐butanol was studied using an objective function relating to the economics of the column operation. Optimizing the initial distribution of the feed among the vessels improved column performance significantly. For some separations, withdrawing product from the vessels into accumulators was better than total reflux operation in terms of energy consumption. Open‐loop optimal operation was also compared to a recently proposed feedback control strategy where the controller parameters are optimized. The energy consumption of a regular column was about twice that of a multivessel column having the same number of stages.
Optimal design of solvent blends for environmental impact minimization
Authors: Buxton Andrew , Livingston Andrew G. , Pistikopoulos Efstratios N. 
Published: April 2004

AbstractA systematic procedure proposed here selects optimal solvent blends for nonreactive, multicomponent absorption processes accounting for plant‐wide point source environmental interactions. This approach, based on the optimal design technique for pure solvents developed in our earlier work, involves the identification of all agent‐based operations (such as gas absorption and liquid extraction) within the process of interest, the determination of a list of candidate solvent blends satisfying separation task operational and environmental constraints, and the selection of an optimal solvent blend candidate based on global plant‐wide process and environmental constraints. The procedure features new property and operational feasibility constraints, a refined task‐based problem formulation, and a new solution strategy. Two examples are presented to demonstrate the approach, and trade‐offs between cost and environmental impact objectives are discussed.
Improving cubic EOSS near the critical point by a phase‐space cell approximation
Authors: Fornasiero Francesco , Lue Leo , Bertucco Alberto 
Published: April 2004

AbstractCubic equations of state (EOSs) are widely used to model the thermodynamic properties of pure fluids and mixtures. However, because they fail to account for the long‐range fluctuations existing in a fluid near the critical point, they do not accurately predict the fluid properties in the critical region. Recently, an approximate renormalization group method was developed that can account for these fluctuations. A similar method is applied to provide corrections to a generalized cubic EOS for pure fluids, which is able to represent all classic cubic EOSs. The proposed approach requires two additional parameters: c̄RG and Δ. The value of c̄RG is correlated to experimental critical compressibility data, while Δ is set equal to 1. The method is applied to predict the saturated liquid density of fluids of different polarity, and the corrections to the original EOS are found to significantly improve the predictions of this property both far from and close to the critical point. Finally, a correlation is presented for the direct evaluation of the parameter c̄RG from the value of the critical compressibility factor.
Design of a simulated moving bed in the presence of mass‐transfer resistances
Authors: Azevedo Diana C. S. , Rodrigues Alírio E. 
Published: April 2004

AbstractTwo different strategies presented determine the sets of operating conditions that yield desired product purities for an SMB separator. The search was performed numerically by solving the analogous true‐moving‐bed model equations. A linear equilibrium binary mixture and mass‐transfer effects were taken into account by using a bilinear driving force approximation to describe intraparticle diffusion. The strategies are equivalent and produce the same results. Comparison with the linear equilibrium model strategy indicates that there are new limiting values for the flow‐rate constraints in the presence of mass‐transfer effects. The constraints on sections I, II and III were more restrictive than those derived from equilibrium models, whereas the constraint on section IV was less affected. Qualitative observations drawn from a model of intermediate complexity were also presented to confirm our results.
Emulsion breakdown: Mechanisms and development of multilayer membrane
Authors: Kawakatsu Takahiro , Boom Remko M. , Nabetani Hiroshi , Kikuchi Yuji , Nakajima Mitsutoshi 
Published: April 2004

AbstractPhase inversion phenomena of oil‐in‐water (triolein in water‐containing sodium lauryl sulfate, SDS) emulsions permeating through hydrophobic micropores were visualized using an optically accessible array of well‐defined microchannels and a microscope video system. Oil droplets coalesced on the hydrophobic microchannel surface and permeated to form a continuous oil layer at the outlet. Water was repelled from the surface, and large, irregular‐sized water droplets were created at the outlet. To evaluate the emulsion breakdown mechanism practically, the emulsions were filtered with hydrophobic polytetrafluoroethylene membranes of several pore sizes. In all cases, the permeate was separated into two phases, an oily and an aqueous one. The three pore sizes, 1‐, 5‐ and 10‐μm membranes, were stacked into a layer, and with the multilayer membrane the breakdown ability of the 1‐μm membrane was effectively combined with the oil droplet growth ability of the 5‐ and 10‐μm membranes.
Structural design for on‐line process optimization: II. Application to a simulated FCC
Authors: Loeblein C. , Perkins J. D. 
Published: April 2004

AbstractA previously proposed methodology for analyzing the economic performance of different structures of an integrated model predictive regulatory control and on‐line optimization system is illustrated using the simulated case study of a fluid‐catalytic cracker. The economic performance of two previously proposed regulatory control structures, the conventional and riser‐regenerator control structures, is assessed both in isolation and as part of a real‐time optimization system. The results show that the economic performance of the conventional structure is superior when operated in isolation. The theory, however, predicts that an optimally configured real‐time optimization system based on the riser‐regenerator structure will deliver superior performance overall. The predictions of the method were confirmed using Monte Carlo simulations.