bluuebunny/crossref_metadata_2025_split huggingface dataset:
Flow along porous media by partical image velocimetry
Authors: Saleh S. , Thovert J. F. , Adler P. M. 
Published: June 2004

AbstractVelocity measurements near porous media are performed by particle image velocimetry. Fully established laminar flows along flat media are studied and compared with the predictions of classical models. Five types of porous media are investigated. Two‐dimensional pictures of the flow, average velocities, and local fluctuations are discussed.
Mathematical modeling of heat and mass transfer in packed‐bed adsorbers/regenerators
Authors: Gouvalias G. S. , Markatos N. C. 
Published: June 2004

AbstractNonisothermal adsorption is studied by incorporating its mathematical description into a model consisting of the full two‐dimensional Navier‐Stokes equations and energy and species concentration equations to simulate the processes in fixed‐bed industrial adsorbers/regenerators. The model partial‐differential equations are solved numerically by using well‐established computational fluid dynamics techniques. The equilibrium between gas and solid is considered nonlinear, which is described by Freundlich‐type equations. The transport and adsorption of a compound from a solvent to and into an adsorbent are described by a two‐step process: transport through the “film” to the outer surface of the particle and diffusion into the porous particle. The effect of fill resistance is discussed, as well as a two‐equation turbulence model. Solutions obtained for a typical industrial adsorber/regenerator demonstrate the potential of this method. The computed results for various flow ratios and parameters in the Freundlich equations are shown to be physically plausible.
Chemical vapor infiltration: Dispersed and graded depositions for ceramic composites
Authors: Chung G. Y. , McCoy B. J. , Smith J. M. , Cagliostro Domenick E. 
Published: June 2004

AbstractA structured‐geometry model for dispersed and graded deposits was developed for chemical vapor infiltration of multiply‐woven substrates of carbon filters. An earlier model was modified to allow for two reactants in the feed. The model predicts gas‐phase concentration profiles in the voids of substrates and deposition amounts of two reactants as a function of time and location. Results are shown for feeding reactant gases simultaneously for dispersed deposition and periodically for the study of the graded deposition for a typical substrate. The variation in relative contents of reactants in the feed with time shows how the composition of the deposit varies. Porosities and changes of dimensions with time everywhere in the substrate are also predicted. This is an advantage of the structured‐geometry model vs. a simplified homogeneous geometry for the substrate. Such a simplification may preclude predicting failure, such as delamination, which would require a local description of the composite structure.Sensitivity to input parameters such as temperature, pressure, and reactant feed concentration is discussed, and two substrate geometries are compared.The behavior of the system is predicted to be dominated by the times to fill gaps between filaments at the ply surfaces and the outermost space between plies. Furthermore, faster kinetics and slower reactant diffusion favor deposition of one material near the surface of a ply or the matrix and the other near the center of the ply or matrix. By manipulating feed rates of reactants, uniformity of material and overall porosity of the composites are predicted to be enhanced.
Robust stability analysis of constrained l1‐norm model predictive control
Authors: Genceli Hasmet , Nikolaou Michael 
Published: June 2004

AbstractSufficient conditions for robust closed‐loop stability of a class of dynamic matrix control (DMC) systems are presented. The l1‐norm is used in the objective function of the on‐line optimization, thus resulting in a linear programming problem. The ideas of this work, however, are expandable to other DMC‐type controllers. The keys to the stability conditions are: to use an end‐condition in the moving horizon on‐line optimization; to have coefficients of the move suppression term in the objective function of the on‐line optimization satisfy certain inequalities; and to express the uncertainty as deviations in the unit pulse response coefficients of the nominal plant. These deviations and disturbances must also satisfy certain inequalities.An off‐line tuning procedure for robust stability and performance of a class of DMC controllers is also included, which determines an optimal moving horizon length and optimal values for coefficients of the move suppression term. The applicability of our approach is elucidated through numerical simulations.
Effects of molecular structure upon complex‐support interactions
Authors: Bruce David , Bertrand J. Aaron , White Mark G. 
Published: June 2004

AbstractTwo cationic, copper metal complexes with different ligands were synthesized: ethylenediamine (en) [Cu(C2N8N2) (ClO4)2] and diethanolamine (Deta) {[Cu‐C8H21N2O4]ClO4}. These complexes were mounted on Cab‐O‐Sil using nonaqueous impregnation techniques, and the loadings were determined at which multilayers formed. These samples were analyzed for copper, carbon, nitrogen and hydrogen content to determine if ligand dissociation occurred during the impregnation. Samples were decomposed in a thermal gravimetric apparatus to determine the kinetics of the thermolysis reaction in air, and the evolved gases were analyzed by gas chromatograph‐mass spectrometry to determine the products of the thermolysis reaction. The results of these and earlier studies are summarized in a model that describes the effects of molecular structure upon complex‐support interactions. Complexes with the ability to form hydrogen bond interactions between the ligand and the support form strong interactions with the surface of silica, whereas complexes without such hydrogen bond interactions are only weakly attracted to the silica surface. Strong interactions with the surface may also arise as a result of ligand dissociation and direct interaction of the metal ion with the surface oxygens. The charge on the complex and its shape play less important roles in determining the affinity of the metal complex with the silica.
Electrochemical membrane process for flue gas desulfurization
Authors: McHenry Dennis J. , Winnick Jack 
Published: June 2004

AbstractA flue gas desulfurization process being developed for coal‐fired power plants removes and concentrates sulfur oxides (SOx). The key element is an electrochemical cell using a sulfur oxide selective membrane. It achieves 90% sulfur oxide removal with near 100% electric current efficiency.Recent research has focused on improving the structure of the electrochemical membrane and its interface with the electrodes. The capillary forces of the membrane and porous electrodes establish an equilibrium. To maintain electrode surface area enhancement, it is necessary to retain the electrolyte in the membrane and allow only wetting of the electrode pores. Chemically‐stable matrix materials for the membrane have been identified; several fabrication techniques were used to prepare the actual membrane structure. A new electrode material, (LiO)xNiO, possesses the proper chemical stability and electrical properties in the corrosive environment. These modifications have led to an order of magnitude increase in flux and operating lifetime.
Generalized quartic equation of state for pure nonpolar fluids
Authors: Shah Vinod M. , Bienkowski Paul R. , Cochran Hank D. 
Published: June 2004

AbstractA generalized quartic equation of state has been developed for pure nonpolar fluids. The equation of state contains four parameters which depend on three properties of the fluid—critical temperature, critical volume, and acentric factor. A mathematical approximation based on previously reported hard‐sphere molecular dynamics simulations has been used to model repulsive contributions to the pressure. Attractive forces were modeled using an empirical term. While the quartic equation yields four roots, one root is always negative and hence physically meaningless, and three roots behave like three roots of a cubic equation. Thus, the new equation of state has the advantages of a cubic, simplicity and unequivocal identification of the roots, while correctly modeling the attractive and repulsive contributions to the pressure. The new equation of state is more accurate than either the Peng‐Robinson or a previously proposed quartic equation of state. Accuracy in the supercritical and compressed liquid regions is improved substantially.
Minimum entrainer flows for extractive distillation: A bifurcation theoretic approach
Authors: Knapp Jeffrey P. , Doherty Michael F. 
Published: June 2004

AbstractIn addition to a minimum reflux, every extractive distillation exhibits a maximum reflux, above which the desired separation is impossible, and a minimum entrainer flow rate, below which the separation is also impossible. Both of these quantities correspond to bifurcations of the finite difference equations describing the middle section of the column and, given a VLE model, can be easily calculated knowing only information about the column feed and the desired product compositions, that is, prior to any column design calculations.Both maximum reflux and minimum entrainer flows have important implications for the design and operation of extractive distillations. By limiting the range of feasible operating reflux ratios, the maximum reflux affects the flexibility, operability and controllability of the column. Ranking a set of feasible extractive entrainers according to their minimum entrainer flows provides a simple effective method for identifying the most promising candidates. Near optimal design values of the entrainer flow can then be estimated using the heuristic presented.
Kinetic modeling of free‐radical graft polymerization
Authors: Chaimberg Mark , Cohen Yoram 
Published: June 2004

AbstractThe kinetic model of free‐radical surface graft polymerization developed is based on a conservational polymerization and molecular‐weight distribution (CPMWD) numerical algorithm. The CPMWD model uses an implicit numerical technique to solve for the coupled monomer, surface site, and total growing polymer differential rate equations, which ensure that conservation of mass is maintained. The model formulation allows for the incorporation of kinetic rate coefficients, which are a function of the chain length of the reacting species, the solution viscosity, and the concentration of surface grafted polymer. The model also makes it possible to evaluate the monomer conversion, the graft yield and the molecular weight distributions of the homopolymer and surface‐grafted polymer for the complete duration of the graft polymerization reaction. Its application was demonstrated for a model system of vinylpyrrolidone graft polymerization onto the surface of a silica substrate.
A thermodynamic model for structure‐H hydrates
Authors: Mehta Ajay P. , Dendy Sloan E. 
Published: June 2004

AbstractA statistical thermodynamics model based on the original work of van der Waals and Platteeuw is presented for structure‐H hydrates. The model is an extension of the hydrate prediction method generalized by Parrish and Prausnitz for structure‐I and‐II hydrates. Four structure‐H‐forming systems, methane+ adamantane, methane+ neohexane, methane+isopentane, and methane+methylcyclohexane, were considered. Optimized Kihara core parameters are presented for each of the large hydrocarbon guest molecules. The optimized reference chemical potential difference and reference enthalpy difference for structure‐H hydrates are also presented. The results show good agreement with the experimentally determined phase‐equilibria conditions. A sensitivity analysis is presented for the parameters in the model, and their relative order of influence on the accurate evaluation of the quilibrium pressure is determined.
Activated carbon catalyzes reactions of phenolics during liquid‐phase adsorption
Authors: Cooney David O. , Xi Zhenpeng 
Published: June 2004

AbstractVarious phenolic compounds in aqueous buffer solutions were contacted batchwise with powdered activated carbon. Relatively slow, but continual, decreases in the solution phenolic concentrations were measured over a period of several weeks. The decreases were due to oxidative coupling reactions of the phenolics which occurred on the carbon surface subsequent to adsorption. The effects of time, pH, dissolved oxygen, and the molecular nature of the phenolic were determined.
Prediction of micromixing effects in precipitation: Case of double‐jet precipitators
Authors: David René , Marcant Bruno 
Published: June 2004

AbstractMixing effects are evaluated for double jet semibatch and continuous stirred precipitators by a model which gives the variation of the primary nucleation flux from the mixing conditions. The predicted trends are compared with results of various authors, including those from a new study of calcium oxalate semibatch double‐jet precipitation. Satisfactory qualitative agreement is found for the different chemical systems as a function of feed rate, stirring speed and feed locations for calcium oxalate precipitation. Two types of precipitation systems are demonstrated, depending on the ratio added/tank volume, the initial supersaturations and the intrinsic stiffness factor of a given precipitation. The difference between the two types depends on the increase or reduction of the primary nucleation flux by imperfect mixing with respect to the reference primary nucleation flux obtained with perfect mixing.
Modeling, simulation and kinetic parameter estimation in batch crystallization processes
Authors: Farrell Robert J. , Tsai Yen‐Cheng 
Published: June 2004

AbstractA dynamic model of a seeded batch crystallizer is used to investigate the process‐dependent aspects of nucleation and growth kinetic parameter estimation by computer simulation. The satisfactory identification of all parameters in power‐law‐type kinetics with respect to supersaturation requires the use of nonlinear parameter transformations. The proper choice for transformation is problem‐dependent, becoming more sensitive as nucleation rates increase, and the percentage of crystals below the measurable range increases.
Application of Voronoi tessellation for modeling randomly packed hollow‐fiber bundles
Authors: Chen Vicki , Hlavacek Marc 
Published: June 2004

AbstractInfluence of local voids on flow maldistribution in randomly packed fiber bundles is examined by Voronoi tessellation. A theoretical expression for the local void distribution caused by random placement of fibers is developed by using a randomcell model. Simulations and packing experiments have been conducted to assess the accuracy of the theoretical distribution of cell sizes. In the case of shell side, laminar flow parallel to the fibers, the theoretical distribution is used to estimate fRe (friction factor times Reynolds number) and volumetric flows, and to compare results with ordered arrays and experimental data from literature. The results are used to assess the contributions of local voidage variation to flow bypass. This has implications for the prediction of pressure drop and heat and mass transfer in hollow‐fiber module applications where transport is dominated by flow on the shell side.
Removal of hydrogen sulfide from natural gas through an electrochemical membrane separator
Authors: Alexander Steven Ray , Winnick Jack 
Published: June 2004

AbstractAn advanced process is developed for the separation of H2S from natural gas through an electrochemical membrane. H2S is removed from natural gas by reduction to the sulfide ion and H2 at the cathode. The sulfide ion migrates to the anode through a molten salt electrolyte suspended in an inert ceramic matrix. Once at the anode it is oxidized to elemental sulfur and swept away for condensation in an inert gas stream. The natural gas is enriched with H2. Order‐of‐magnitude reductions in H2S concentration have been repeatedly recorded on a single pass through the cell. This process allows removal of H2S, while producing H2 and elemental sulfur directly. No absorbents are used, and there is no need for subsequent treatment of a concetrated H2S stream as with conventional gas sweetening technology. This makes the process economically attractive, since it is much less equipment‐intensive than conventional technology.
Application of electrolyte theory to extractive separations using hydrotropes
Authors: Narayanan K. V. , Ananth M. S. 
Published: June 2004

AbstractThe use of polar hydrotropes in extractive and in liquid‐liquid extraction has been extensively reported in the literature. In this article, the effect of hydrotropes on increasing the effectiveness of separation is explained in terms of the effect of the dipole‐induced dipole and the ion‐induced dipole interactions on the activity coefficients of the neutral solutes in the aqueous phase. The self‐consistent local composition theory is used to correlate quantitatively the observed behavior in systems involving liquid‐liquid equilibria. The theory yields composition‐dependent expressions for the effect of each independent pair interaction on the activity coefficient of a neutral solute in the aqueous phase. The ratio of the activity coefficients of the two solutes is of interest in this context. The resulting expression for the separation factor is elegant and admits simple physical interpretation. The essential features of hydrotrope‐assisted extraction are correctly described by the theory. The ability of the theory to correlate data is demonstrated for two systems.
Thermodynamics of phase equilibria in aqueous‐organic systems with salt
Authors: Zerres H. , Prausnitz J. M. 
Published: June 2004

AbstractA semiempirical thermodynamic method is developed to establish a framework for calculating vapor‐liquid and liquid‐liquid equilibria in ternary systems containing water, an organic solvent, and a salt. Careful attention is given to precise definition of standard states. Short‐range ion‐solvent forces are taken into account primarily by a chemical‐equilibrium method based on stepwise ion solvation; however, physical contributions also contribute. Water‐cosolvent nonideality is described by an extended equation of the van Laar form. Long‐range electrostatic forces between ions are taken into account by an extended Debye‐Hückel equation with corrections for transferring from a McMillan‐Mayer to a Lewis‐Randall framework.The new method is illustrated with results for several systems including saturated aqueous mixtures of LiBr or LiCl with methanol where the salt concentration exceeds 20 molal. The method developed here is of particular interest for process calculations in extractive crystallization, a low‐energy operation for producing salt from aqueous solution.
Simulation and optimization of NOx absorption system in nitric acid manufacture
Authors: Suchak N. J. , Joshi J. B. 
Published: June 2004

AbstractA mathematical model has been developed for the prediction of the optimum design of packed and plate columns for the manufacture of nitric acid. The effects of inlet NOx composition, extent of oxidation and extent of absorption in each stage, temperature, and pressure have been included in the model. The optimization of the preoxidizer and the condenser has also been discussed.
Concentric‐tube airlift reactors: Effects of geometrical design on performance
Authors: Merchuk J. C. , Ladwa N. , Cameron A. , Bulmer M. , Pickett A. 
Published: June 2004

AbstractPressure drops, gas holdup, and mass‐transfer coefficients were measured in two concentric‐tube airlift reactors of 30 and 300 L (nominal volume). The aspect ratio and the ratio of riser to downcomer cross section were the same for both reactors, but the geometry of the gas separation section was different. The influence of the bottom and top clearances was studied using water and carboxymethyl cellulose solutions and covering a range of effective viscosity from 10−3 to 25 × 10−3 Pa·s. The pressure drop results expressed as a Euler number were satisfactorily correlated with Fr, Ga, and a bubble disengagement group M. Correlations are presented also for the gas holdup in the riser, downcomer, and gas separator. The last‐mentioned coincides with the correlation for the total holdup in the reactor. The gas‐liquid mass‐transfer coefficients for all the liquids and geometric variables in both reactors were successfully correlated as Sherwood numbers.
Prediction of pH in complex aqueous mixtures using a group‐contribution method
Authors: Achard Christian , Dussap Claude‐Gilles , Gros Jean‐Bernard 
Published: June 2004

AbstractExpressions that suitably describe the behavior of weak electrolytes in aqueous systems are developed. A new numerical procedure is presented to allow for partial dissociation phenomena and so consider the whole species in solution. It is based on mass balances, the electroneutrality assumption, and dissociation constants of electrolytes. Combining it with a modified UNIFAC electrolyte group‐contribution model based on the solvation concept directly allows calculation of pH, activities, and concentrations of species. The validity and usefulness of the expressions are tested using data for the pH of buffer solutions and complex aqueous mixtures such as fermentation media and liquid foods: pH values accurate to within ±0.05 pH units were obtained.
Heavy metal removal and recovery by contained liquid membrane permeator
Authors: Guha Asim K. , Yun Chang H. , Basu Rahul , Sirkar Kamalesh K. 
Published: June 2004

AbstractHeavy metals like Cu2+, Cr6+, and Hg2+ were removed successfully from wastewater and concentrated in a strip aqueous solution for recycle using the hollowfiber‐contained liquid membrane (HFCLM) technique. Using cotransport, Cr6+ and Hg2+ present as anions in the feed solution were transferred individually through a liquid membrane containing tri‐n‐octylamine in xylene and concentrated in an alkaline solution on the strip side. The removal efficiency of each heavy metal was studied as a function of the aqueous feed flow rate in an HFCLM permeator. Copper present as cation Cu2+ was removed and concentrated by countertransport using LIX84 in n‐heptane as the liquid membrane. The efficiency of copper removal was studied as a function of feed copper concentration, feed flow rate, strip flow rate, and area ratio between the feed fiber set and strip fiber set. The strip side flow rate did not affect the Cu2+ transfer rate. A theoretical model presented predicts the copper transport rate from the feed solution to the strip solution in an HFCLM permeator with a variable feed to strip‐side membrane area. Both feed aqueous boundary layer and interfacial complexation reaction on the feed side dominate the observed Cu2+ removal process through LIX 84 in n‐heptane for feed concentration levels used 90–500 mg/L. It was verified by providing two times larger liquid‐liquid interfacial area in the feed aqueous side or in the strip aqueous side. The model can be used to design the membrane area required on the feed and strip fiber sides to remove essentially all of the copper from a given wastewater stream.
X‐ray computed tomography studies of gas storage and transport in Devonian shales
Authors: Lu X. , Miao P. , Watson A. T. , Pepin G. P. , Moss R. M. , Semmelbeck M. 
Published: June 2004

AbstractDevonian shales and other unconventional resources can be highly fractured and may have significant amounts of gas stored by adsorption. Conventional experiments are not well suited for characterizing the properties important for describing gas storage and transport in these media. Here, X‐ray computed tomography scanning is used to determine gas storage in dynamic gas flow experiments on Devonian shale samples. Several important properties are obtained from these experiments, including fracture widths, adsorption isotherms, and matrix porosities and permeabilities.