bluuebunny/crossref_metadata_2025_split huggingface dataset:
Redistribution of adsorbed VOCs in activated carbon under electrothermal desorption
Authors: Cheng Z.‐M. , Yu F. D. , Grevillot G. , Luo L. , Tondeur D. , Yuan W. K. 
Published: April 2004

AbstractElectrothermal desolption is an electricity‐promoted desolption technology developed only in the last decade. It is extremely eficient and straightforward when the adsorbent is electrically conductive, since heating can be achieved by the Joule effect. The volatile organic compound (VOC) vapors desorbing from micropores might redistribute and condense in mesopores with high concentration, which is possible since no dilution occurs. To study this problem, benzene and activated carbon were used as the working system, and a theoretical analysis was developed. In a wide temperature range up to 400°C, no VOC vapor could be condensed in mesopores with the strong micropore adsorption effect. With the weak micropore adsorption effect, however, mesopore condensation will occur, but it only takes place in mesopores smaller than 3 nm in diameter, and the amount is generally negligible. To prevent any possible condensation, the desorption temperature should at least equal the liquid boiling point calculated in a 2‐nm capillary tube.
Transient measurements of adsorption and diffusion in H‐ZSM‐5 membranes
Authors: Gardner Tracy Q. , Flores Ana I. , Noble Richard D. , Falconer John L. 
Published: April 2004

AbstractA transient permeation method presented here not only determines the adsorption and diffusion properties of the pores that are the transport pathways through zeolite membranes, but nondestructively estimates the effective thickness of the membrane. Transient responses of the permeate concentration to step changes in the feed were measured on two H‐ZSM‐5 tubular membranes and modeled assuming Maxwell‐Stefan diffusion and Langmuir adsorption. The adsorption isotherms determined from these transient measurements at 298 K of N2 and CO2 were nearly identical to those measured by calorimetry on H‐ZSM‐5 powders. The CH4 isotherm at 298 K was similar to isotherms measured by calorimetry and gravimetric techniques on Na‐ZSM‐5 and silicalite powders. The similarity of the isotherms indicates that transport of these light gases occurs mainly through zeolite pores. The Maxwell‐Stefan diffusion coefficients DMS depended on concentration and were higher for higher feed partial pressures. Average DMS values for the two membranes were 7.5, 5 and 1.5×10−10 m2/s for N2, CH4, and CO2, respectively; these are in the same range and order as diffusion coefficients measured in zeolite crystals.
Product‐centered processing: Manufacture of chemical‐based consumer products
Authors: Wibowo Christianto , Ng Ka M. 
Published: April 2004

AbstractA systematic framework for product‐centered processing is useful particularly in developing chemical‐based consumer product manufacturing processes. The objective is to provide directions and guidelines toward the development of a process for manufacturing a product with the desired performance in reduced time and effort. The product performance, represented by several quality factors, is related to product ingredients and structural attributes, as well as the process flowsheet and operating conditions. The procedure consists of five steps. First, the product functionality, form, and packaging are defined. Second, relevant quality factors are identified. Third, necessary ingredients are selected and product microstructure is determined. Fourth, the manufacturing process is designed in light of the desired product properties. Limitations on achievable product quality are also identified. Finally, the product and process are evaluated with the help of experimental data. The framework is illustrated using industrial examples, including the production of dry toner, laundry detergent, shampoo, and cosmetic lotion.
Solubilities of nonvolatile solutes in polymers from molecular thermodynamics
Authors: Fornasiero F. , Olaya M. M. , Wagner I. , Brüderle F. , Prausnitz J. M. 
Published: April 2004

AbstractBecause there is no simple, general method for measuring solubilities of nonvolatile solutes in a polymer, this work presents a thermodynamic framework for estimating such solubilities from infinite‐dilution distribution‐coefficient data for aqueous solutions of the solute in equilibrium with the polymer. The experimental infinite‐dilution distribution coefficient is related to that calculated from a molecular‐thermodynamic model (Flory–Huggins). The three binary Flory parameters are obtained from water–solute and water–polymer data, and from the solute's distribution coefficient. Solubilities of 19 nonvolatile aromatic solutes were estimated in three polymers: ethyl‐vinyl acetate copolymer (EVAc) with 33 (EVAc33), 45 (EVAc45) wt. % vinyl acetate content, and poly(vinyl acetate) (PVAc) at 25°C, where most of the solutes are solids. For some of these systems, predicted solubilities are compared with new experimental results. The calculations reported here may be useful for various applications, including the design of membrane processes or drug‐delivery systems, and for packaging technology for foods, chemicals, and pharmaceuticals.
Generalized model for predicting phase behavior of clathrate hydrate
Authors: Yoon Ji‐Ho , Chun Moon‐Kyun , Lee Huen 
Published: April 2004

AbstractAn improved and generalized model was developed to predict the dissociation pressures of hydrate‐forming gases and the complicated phase behavior of multicomponent hydrate systems. Based on the van der Waals‐Platteeuw theory with the Kihara spherical‐core potential function, a new equation for the water fugacity in the filled hydrate phase is provided. Instead of vapor pressures of ice for conventional approaches, it adopts the molar enthalpy difference between ice and liquid water. Since it always maintains its unique form whether the hydrates coexist with ice or water, it can be successfully applied to predict the multiphase equilibria of simple and mixed hydrate systems. The fugacities of all components in vapor and liquid phases coexisting with hydrates were calculated by the Soave‐Redlich‐Kwong (SRK) equation of state incorporated with the modified Huron‐Vidal second‐order mixing rule. Lower and upper quadruple points and neighboring four three‐phase curves around these quadruple points were described correctly by this model calculation. The Kihara potential parameters for the interaction between water and gas molecules are presented by fitting experimental dissociation pressures. Various types of systems involving hydrate mixtures containing either two guest components or inhibitors were extensively tested to examine the model's potential applicability to predicting the complicated phase equilibria.
Pore‐scale modeling of fluid transport in disordered fibrous materials
Authors: Thompson Karsten E. 
Published: April 2004

AbstractThe modeling of fluid transport in fibrous materials is important for many applications. Most models operate at the continuum level, which requires an a priori knowledge of spatially averaged transport parameters. Alternatively, highly detailed models, in which the momentum equations are solved directly, require major simplifying assumptions. Thus, it is desirable to use intermediate‐level techniques that model transport using first principles, but that are appropriate for real engineering processes. In this work, pore‐scale network modeling is adapted for fibrous materials and tested for a large range of fibrous structures and solid volume fractions. A novel technique is used to generate prototype network structures from Voronoi diagrams. The Voronoi networks are coupled with two different multiphase flow algorithms, enabling the modeling of various displacement processes relevant to engineering. Permeability predictions agree well with known values. Effects of dynamics, wettability, and material structure on displacement were studied. This modeling technique not only allows for better quantification of how microscale properties affect macroscopic transport, but helps reduce the number of experiments required to predict continuum transport parameters for various materials and processes.
Antierosion in a 90° bend by particle impaction
Authors: Fan J. R. , Yao J. , Cen K. F. 
Published: April 2004

AbstractRibbed bend protection, a new method to protect duct bends against erosion in gas–solid flows, was studied theoretically. In this method, ribs are evenly welded on the outer wall of the inside bend at 20°–80°, and the material of the bend is medium carbon steel. An experimental system is set up to perform 3‐D numerical work simultaneously. Experimental and numerical results agree well and confirm that the method is simple and efficient for erosion protection. Numerical simulation is used to study the axial gas‐flow characteristics along the bend and the secondary flow at the cross section. Detailed analyses involving the impact of velocity and the incidence angle of particle–metal (particle‐rib or particle‐duct) impact show the mechanism of the antierosion effect. As a result, both experimental and theoretical predications demonstrate that the average erosion rate of ribbed bends is only one‐third of the bare bend under test conditions, and that rectangular ribs possess greater antierosion ability than square ribs do. Besides, the predictions suggest that the erosion of the wall is more serious than that of the ribs on a ribbed bend, while the wear distribution pattern remains unchanged after adding ribs at the bend.
CFD simulation of flow and turbulence in a slurry bubble column
Authors: Matonis Diana , Gidaspow Dimitri , Bahary Mitra 
Published: April 2004

AbstractTo develop a predictive, experimentally verified computational fluid dynamic model for gas–liquid–solid flow, a 3‐D transient computer code for the coupled Navier–Stokes equations for each phase was developed. The principal input into the model is the viscosity of the particulate phase, which was determined from a measurement of the random kinetic energy of the 800‐micron glass beads and a Brookfield viscometer. The computed time‐averaged particle velocities and concentrations agree with PIV measurements of velocities and concentrations, obtained using a combination of gamma‐ray and X‐ray densitometry, in a slurry bubble column, operated in the bubbly‐coalesced fluidization regime with a continuous flow of water. Both the experiment and simulation show a downflow of particles in the center of the column, and an upflow near the walls, and a nearly uniform particle concentration. Normal and shear Reynolds stresses were constructed from the computed instantaneous particle velocities. The PIV measurement and the simulation produced similar nearly flat horizontal profiles of turbulent kinetic energy of particles.
Convection cells and segregation in a vibrated granular bed
Authors: Hsiau Shu‐San , Wang Pai‐Chei , Tai Chi‐Hwang 
Published: April 2004

AbstractGranular materials may be circulated in a container with two symmetric convection cells under external vertical vibration conditions. Effects of the container geometry on the convection strength and segregation process are studied experimentally. First, the wall tilted outward angles are changed to observe the direction of the convection roll and convection strength. The strength of the normal convection rolls decreases by increasing the wall angles of the container from 0° (vertical walls). The convection rolls become reversed when the wall tilted outward angles are greater than a transition angle. The wall roughness and vibration velocity amplitude are also changed to investigate their influences on the convection cell strength. The segregation of a larger disk induced by the convection cells of smaller disks shows that the normal convection rolls induce the upward motion of the larger disk, and the reverse convection rolls result in the downward motion of the larger disk. The separation velocity increases linearly with the convection flow rate.
Using discrete distributions to analyze CSD data from MSMPR crystallizers
Authors: Jones Christopher M. 
Published: April 2004

AbstractA novel technique for treating continuous mixed‐suspension, mixed‐product removal (MSMPR) crystal‐size distribution (CSD) data uses a discrete probability distribution to represent the growth rate distribution of crystals in a crystallizer. It is based on the premise that individual crystals in a population each have their own intrinsic growth rate, but the growth rates of crystals in the population may vary. Treatment of CSD data using this discrete distribution technique enables the calculation of crystallizer kinetics data, including the nucleation rate and characterization of the nuclei growth rate distribution and using both graphical representation and descriptive statistics. Previously published data for a system exhibiting growth rate dispersion is used to demonstrate the efficacy of the technique. Furthermore, the results of the data analysis using the discrete distribution technique are compared to the results of data analysis using the continuous distribution technique.
New adsorbents for purification: Selective removal of aromatics
Authors: Takahashi Akira , Yang Ralph T. 
Published: April 2004

AbstractAdsorption of benzene and cyclohexane on various Y‐zeolites was investigated to develop sorbents for the purification of aliphatics by removal of aromatics. Ag‐Y showed superior benzene/cyclohexane selectivities to Na‐Y, Pd‐Y, and H‐USY. Separation factors greater than 105 were obtained with Ag‐Y at low concentrations of benzene. High selectivities were achieved by the strong interaction between benzene and Ag‐Y, while the interaction with cyclohexane was not influenced by the cations. Molecular orbital calculation revealed that benzene formed a classic π‐complexation bond with Ag‐Y: donation of electron charges from the p‐orbitals of benzene to the vacant s‐orbital of the silver (σ donation) and, simultaneously, back donation of electron charges from d‐orbitals of silver to π*‐orbital of benzene (d–π* back donation). Grand canonical Monte Carlo simulations were also performed for adsorption isotherms. Potential parameters of benzene on Ag‐Y, including π‐complexation, were developed first. Simulation and experiments of GCMC agreed excellently for adsorption of benzene on Y‐zeolites.
Modeling of air separation in a LSCF hollow‐fiber membrane module
Authors: Tan Xiaoyao , Li K. 
Published: April 2004

AbstractMixed ion‐conducting ceramic membranes are promising in oxygen separation from air due to their infinite permselectivity. Hollow‐fiber‐shaped membranes can provide a high surface area for such an application. A mathematical model for a hollow‐fiber La0.6Sr0.4Co0.2F0.8O3−δ(LSCF) membrane module for air separation was developed and a performance of the module at various operating conditions was studied theoretically. The simulation results reveal that the cocurrent is a better operating flow pattern than the countercurrent flow pattern. The vacuum operation on the lumen side of the membrane module is preferable to the elevated pressure operation on the shell side for achieving high oxygen productivity. A high vacuum level and a desired membrane area are essential to produce the pure oxygen and nitrogen simultaneously. Experimental results and kinetic parameters in the literature obtained from the LSCF membrane for air separation agreed satisfactorily with the theoretical solutions.
Development of fluidized catalytic reactors: Screening and scale‐up
Authors: Kelkar Vaibhav V. , Ng Ka M. 
Published: April 2004

AbstractA systematic procedure that helps develop gas‐solid and gas‐liquid‐solid catalytic fluidized‐bed reactors has two components—screening and scale‐up. In screening, a reactor type is selected first from the variety of multiphase reactors. If fluidized‐bed reactors are chosen, further screening is carried out using experimentally verified models to account for the detailed hydrodynamic features of the reactor. Decisions are made on the fluidization regime, heat management scheme, solid recirculation, use of reactor internals, and so on. In addition, heuristics are presented to anticipate and address issues such as catalyst agglomeration, breakage and deactivation, and changes in the nature of fluidization over the long term. The second component provides criteria to directly scale up the bench reactor to the production reactor, while maintaining a selected reactor performance index such as conversion, product yield, and selectivity.
Reaction and transport kinetics for depolymerization within a porous body
Authors: Krug Steffen , Evans Julian R. G. , ter Maat Johan H. H. 
Published: April 2004

AbstractPolyoxymethylene is used as the organic vehicle for ceramic and metal powder injection moulding. It is ideal for studies of shrinking‐core reaction kinetics in porous systems because it decomposes exclusively to monomer in the solid state in the presence of nitric acid vapor. The solid–gas reaction interface can be defined to within 3 μm by electron microscopy and about 50 μm optically. Reaction rates were measured in crowded powder assemblies containing 56 vol % alumina powder by observation of the boundary; a method that avoids the ambiguities of gravimetry. The reaction‐rate constant and the effective diffusion coefficient of gas in the porous reacted layer were calculated from the shrinking core kinetics. The diffusion coefficient was in good agreement with theoretical estimates involving counterdiffusion. The time for complete depolymerization of a moulding was estimated for different powder characteristics, geometries, and volume fractions.
Experiments on chaotic mixing in a screw channel flow
Authors: Hwang W. R. , Jun H. S. , Kwon T. H. 
Published: April 2004

AbstractMixing patterns of a passive dye were investigated experimentally in an unwound screw channel flow with periodic barriers that serve to induce a chaotic flow. Continuous cross‐sectional and longitudinal mixing patterns were observed as a function of the barrier fraction and were interpreted in terms of dynamical systems theory, along with 3‐D numerical simulations. Observations include: periodically invariant cross‐sectional mixing patterns due to the resonance bands; pile‐up of dye streaks caused by stretching and folding of manifolds near hyperbolic points; unmixed zones due to KAM tori; longitudinal deformation patterns with exit time distributions; and effects of the barrier fraction on the size of unmixed islands, the thickness of the band of dye streaks, and the distribution of exit times.
Silicon array of elongated through‐holes for monodisperse emulsion droplets
Authors: Kobayashi Isao , Nakajima Mitsutoshi , Chun Kyoseok , Kikuchi Yuji , Fujita Hiroyuki 
Published: April 2004

AbstractMonodisperse emulsions are of great significance in both scientific and industrial fields, since they have advantages such as their better stability and simplified physical properties. A novel micromachined emulsification device has been developed for monodisperse emulsion droplets. It has uniformly sized through‐holes, called straightthrough microchannel (MC), on a silicon microchip. An oblong straightthrough MC successfully yielded monodisperse oil‐in‐water (O/W) emulsion droplets with an average droplet diameter of 32.5 μm and a coefficient of variation below 2% by forcing the dispersed phase into the continuous phase through the straightthrough MC. On the other hand, a circular straightthrough MC yielded polydisperse emulsion droplets. Straightthrough MC emulsification revealed that an elongated cross‐sectional shape in the oblong straightthrough MC contributes significantly to the spontaneous formation of monodisperse emulsion droplets without any turbulent mixing.
Connections between density waves in fluidized beds and compressible flows
Authors: Johri Jayati , Glasser Benjamin J. 
Published: April 2004

AbstractUnder certain simplifying assumptions, model equations of motion and continuity for the particles in a fluidized bed can be related to those of a compressible fluid acted on by a density dependent force. A linear stability analysis shows that the base state of the compressible flow equations can lose stability in the form of plane density waves. The plane waves emerge through a Hopf bifurcation and propagate through the bed as traveling waves. Through a bifurcation analysis coupled with parameter continuation, the solution structure of the fully‐developed plane waves was computed. As the amplitudes of the plane waves increase, they lose stability in the lateral direction. A comparison of these results with previous work on gas‐fluidized beds shows that salient features of the instability of a gas‐fluidized bed are captured by the basic physics of compressible flows.
Mass transport and flow regimes in centrifugal partition chromatography
Authors: Marchal L. , Legrand J. , Foucault A. 
Published: April 2004

AbstractCentrifugal partition chromatography (CPC) is a support‐free liquid–liquid separation process that depends for efficiency on the behavior of the two liquid phases. Hydrodynamics of phases was studied according to flow rate and centrifugal acceleration, using a transparent column and a stroboscopic video system. For the heptane‐methanol two‐phase system, three main flow regimes—stuck film, oscillating sheet, and atomization—are observed, highlighting the coriolis acceleration effect as well as the influence of the column shape. Mass transport in the CPC column is modeled by a plug flow with axial dispersion and mass transfer with a stagnant volume. Model parameters (residence time, Péclet number, partition ratio, and mass‐transfer coefficient) are fitted on solute residence‐time distribution. Off‐column dispersion is an important source of peak broadening in CPC, whereas its irregular geometry provides a plug flow for mobile phase. Importance of flow pattern on mass transfer is demonstrated. CPC interest for preparative applications is confirmed.
Modeling ultrafiltration of complex biological solutions
Authors: Darnon E. , Belleville M. P. , Rios G. M. 
Published: April 2004

AbstractThe ultrafiltration of a single protein (β‐lactoglobulin) solution was compared with a mixture of yeast extract and β‐lactoglobulin to show that, even when all the compounds of a complex biological solution interfere with the results of filtration, it can estimate its performance just using some major assumptions connected to a mass‐transfer model. Preliminary experiments based on these assumptions showed that the filtration of a single rejected protein like β‐lactoglobulin builds a dynamic layer at the wall, the selectivity and resistance of control by the protein concentration and formation of this dynamic membrane. Adding yeast extract, a complex biological medium, can alter this layer. But at neutral pH, away from the protein isoelectric point, these modifications are weak and their effects more negligible than those arising from a modified concentration. Using these assumptions, a model based on the theory of thermodynamics of irreversible processes is proposed that provides the correct description of selectivity and flux during the filtration of such complex and badly known mixtures.