bluuebunny/crossref_metadata_2025_split huggingface dataset:
Settling of polydisperse particles with thin double layer at small péclet number
Authors: Wang H. , Wen C. S. 
Published: April 2004

AbstractThe special‐function expansion method is used to solve the sedimentation problem of polydisperse colloid particles with thin double layer. The pair‐distribution function is expanded into Legendre polynomials. The recurrence formulas for calculating the coefficients of the Legendre polynomials and the expressions for calculating the sedimentation coefficient are deduced analytically. Then, the sedimentation of polydisperse particles with thin double layer at small Péclet number is analyzed numerically by the perturbation method. Results indicate that the sedimentation of potential interacting particles is more complex than that of the hard spheres, and the existence of the thin double layer affects the particles settling heavily. Critical double‐layer thickness exists, without which a colloid system may change from a stable one into an unstable one and the hindered settling may change into accelerated settling.
Possible air separations with superconducting membranes
Authors: Gordon Ryan D. , Cussler E. L. 
Published: April 2004

AbstractPermeabilities of oxygen, nitrogen and helium across porous, superconducting membranes with 5‐μm pores are consistent with those across nonsuperconducting membranes with well‐defined pores of similar sizes. This is true both at ambient and superconducting temperatures. Transport can occur by Knudsen diffusion, Poiseuille flow, capillary condensation, and turbulent flow. There is no evidence of surface diffusion. Theoretical considerations of superconducting membranes are consistent with these results, indicating when superconductivity might play a role. However, past reports concerning air separation with superconducting membranes with these micrometer‐sized pores are questionable.
Liquid‐phase sorption‐enhanced reaction process
Authors: Sircar S. , Rao M. B. 
Published: April 2004

AbstractA process for carrying out simultaneous liquid‐phase reaction and separation of desired products is described. It uses a fixed packed column of an admixture of a catalyst and an adsorbent that selectively removes a reaction byproduct from the reaction zone. The adsorbent is periodically regenerated using the concepts of liquid‐phase concentration swing adsorption. The integrated process allows production of multiple products at high purity with high conversions. For an endothermic reaction, the process permits much higher conversions of reactants to products at a substantially lower temperature than would be necessary by a plug‐flow reactor using the catalyst alone. The concept is demonstrated for hydrolysis of methyl acetate to produce acetic acid and methanol.
Nonequilibrium cell model for multicomponent (reactive) separation processes
Authors: Higler Arnoud , Krishna R. , Taylor Ross 
Published: April 2004

AbstractA generic nonequilibrium cell model for multicomponent separation processes, including liquid‐phase chemical reactions, was developed. Its important features include the use of Maxwell‐Stefan equations to describe interphase mass transfer and the use of a multiple cell per stage approach to consider various mixing characteristics of vapor and liquid phases. A finite difference approach was used for solving the diffusion‐reaction equations in each fluid phase to properly account for effects of reactions on mass transfer. The multiple cells per stage approach was adopted to take into account the effect of concentration and temperature profiles on a tray on the local reaction rates. The model was compared to several case studies by Kooijman (1995). Comparison of various flow models showed only minor differences between Kooijman's model and the nonequilibrium cell model. The differences were found only for cases in which the phases are assumed to be imperfectly mixed and to be caused by different ways of modeling the interface concentration profiles in various flow models. In addition, some calculations are described for reactive distillation operations described by Okasinski and Doherty (1998) and Marek (1956). These examples show that staging in both flow directions influences overall column performance considerably.
Effect of tube size and obstacles on explosion limits in flowing gases
Authors: Bolk Jeroen W. , Westerterp K. Roel 
Published: April 2004

AbstractIn a large pilot plant the upper explosion limit of ethene–air–nitrogen mixtures was experimented in 3.0‐m‐long and 21‐, 50‐, and 100‐mm‐dia. tubes at different flow rates, pressures, and temperatures. The upper explosion limit, influenced by the gas velocity, becomes smaller and shifts to higher oxygen concentrations for increasing flow rates. The results of these tubes could be correlated based on the tube Reynolds number. A cooling effect of the tube wall, which might influence the explosion region, was not observed. An increase in pressure lowers the critical oxygen content as does an increase in temperature, thus the explosion region becomes larger. Different obstacles were tested, which alter the hydrodynamics. Reaction fronts could only propagate for increased oxygen concentrations through a structured Sulzer laboratory gauze packing or a sudden reduction in diameter from 50 to 20 mm. In the experiment, where the tube was completely filled with glass spheres, propagation of reaction fronts through this packed bed was not possible, even at very low gas velocities and very high oxygen concentrations. In a deep dead zone connected to the tube, the gas was ignited and reacted without igniting the gas outside the dead zone. After some time the reaction stopped because of oxygen starvation. However, dead zones with another geometry, where renewal of the combustible gas can occur, still may be dangerous.
Laser‐induced fluorescence technique for the quantification of mixing in impinging jets
Authors: Unger David R. , Muzzio Fernando J. 
Published: April 2004

AbstractA laser‐induced fluorescence (LIF) technique is implemented to measure concentration profiles and mixing performance in two impinging jet geometries. Experimental results are reported for steady and unsteady (transitional) mixing of initially segregated miscible fluids. Flow structures are visualized by imaging concentration distributions at five vertical planes throughout the mixers. Mixing is quantified for each Reynolds number examined by calculating the overall intensity of segregation. Mixing performance varies substantially as a function of Reynolds number. Optimum operating conditions are identified for both impinging jet geometries. The results demonstrate the ability of laser‐induced fluorescence to quantitatively capture small‐ and large‐scale flow structures and accurately and reproducibly quantify mixing performance in real time for industrially‐relevant mixing devices. The LIF technique proves to be an accurate and versatile method to quantify mixing performance of miscible fluids.
Variation of gravure coating thickness during early stages of doctor blade wear
Authors: Hanumanthu R. 
Published: April 2004

AbstractWith all operating parameters fixed, the mean coated thickness in gravure coating should ideally be a constant fraction of the volume factor of the engraving, and, hence, invariant over coated distance. Experimental data presented, however, reveal an unexpected variation of gravure coating thickness over the first few thousand meters of coated web. The observed variation is attributed to wear of the blade tip. The lubrication approximation is invoked to model a series of steady‐state flows between blade tips of various profiles and a smooth surface at a fixed gap away from them. The blade tip profiles are chosen to simulate those of a continously wearing blade tip. The resulting four‐parameter model is used to “fit” experimental data of gravure coating thickness variation. Then, the model is used to predict the effects of various operating parameters, including coating liquid properties, blade thickness, blade setup, and web speed, on this phenomenon.
Mass transfer and dispersion around active sphere buried in a packed bed
Authors: de Carvalho João R. F. Guedes , Alves Manuel A. M. 
Published: April 2004

AbstractMass transfer around single spheres in granular beds of inerts (packed or fluidized) was analyzed for transport by advection and diffusion/dispersion. Fluid flow in the granular bed around the spheres was assumed to follow Darcy's law; at each point, dispersion of solute was assumed to be determined by the coefficients of transverse and longitudinal dispersion, respectively, in the cross‐stream and streamwise directions. The elliptic equation resulting from a differential mass balance was solved numerically over a wide range of the relevant parameters. Resulting values of the Sherwood number are represented accurately by the product of two terms: the solution for advection plus molecular diffusion, which depends only on the Peclet number relative to the active sphere; the enhancement brought about by convective dispersion, which depends only on the Peclet number relative to the inert particles.
Experimental and computational study of multiphase gas/particle flow in a CFB riser
Authors: Mathiesen Vidar , Solberg Tron , Arastoopour Hamid , Hjertager Bjørn H. 
Published: April 2004

AbstractThe flow behavior in the riser of a circulating fluidized‐bed reactor was studied experimentally and computationally. Laser Doppler anemometry was applied to measure the flow behavior of FCC catalysts. Particle diameter and mean and fluctuating velocity for different particle sizes were measured at different flow conditions. A typical core‐annulus flow with a relative velocity between particles of different sizes was obtained. A significant radial segregation of the mean diameter was measured in the riser. A multifluid computational fluid dynamics model was developed and verified against the experimental results. The flow model is based on a Eulerian description of the phases where the kinetic theory for granular flow forms the basis for the turbulence modeling in the solid phases. The model is generalized for one gas phase and N number of solids phases to enable a realistic description of the particle‐size distribution in gas/solid flow systems. Each solid phase is characterized by a diameter, form factor, density, and restitution coefficient. Simulations with one gas and two solid phases were conducted, and the computational results agreed generally well with the measurements.
Experimental and modeling study on tubular dense membranes for oxygen permeation
Authors: Xu Nanping , Li Shiguang , Jin Wanqin , Shi Jun , Lin Y. S. 
Published: April 2004

AbstractTubular La0.6Sr0.4Co0.2Fe0.8O3–δ perovskite‐type membranes were prepared by isostatic pressing. A mathematical model was developed to simulate the performance of the tubular perovskite‐type dense membranes for oxygen permeation. The experimental oxygen permeation fluxes of tubular La0.6Sr0.4Co0.2Fe0.8O3–δ perovskite‐type membrane increased with decreasing downstream oxygen partial pressure and increasing helium flow rate, which coincided with the results of the oxygen permeation modeling study. Parametric study indicated that air should be supplied sufficiently during the oxygen permeation operation. Modeling oxygen permeation fluxes as a function of the tubular membrane length and tubular membrane thickness are discussed in detail. The oxygen flux slightly decreased after long‐term operation over 110 h. EDS and XRD analysis indicated that SrSO4, CoSO4, SrO, Co2O3, and La2O3 were formed on the surfaces of the tubular membrane due to the interaction with trace SO2 in the air and the helium, and segregation of surface elements. The oxygen permeation of tubular La0.6Sr0.4Co0.2Fe0.8O3–δ membrane was stable after SO2
in the air and the helium has been removed.
Scaleup experiments on seeded batch cooling crystallization of potassium alum
Authors: Doki Norihito , Kubota Noriaki , Sato Akira , Yokota Masaaki , Hamada Osamu , Masumi Fumio 
Published: April 2004

AbstractPotassium alum was crystallized by natural cooling in two well‐mixed laboratory‐scale (12.2 L) and pilot‐scale (600 L) crystallizers. When unimodal product crystals of grown seeds were used, no scaleup effect on product crystal‐size distribution (CSD) was observed if enough seeds were loaded over a critical seed concentration. Cooling rate, crystal yield (crystal suspension density), and stirring condition do not seriously affect the product CSD under such a seeding condition. Low supersaturation peak caused by the growth of enough seeds, the short period of nucleation, and the agglomeration of nuclei to the growing seed crystals are considered to be mechanisms working to produce unimodal product crystals of grown seeds. Simple design calculations are demonstrated to determine the amount of seed with the help of a critical seed concentration, which can be determined easily from laboratory‐scale experiments. Crystallizer volume was calculated simply from a mass balance.
Stochastic modeling of carbon oxidation
Authors: Chen Wei‐Yin , Kulkarni Advait , Milum Jeremy L. , Fan L. T. 
Published: April 2004

AbstractRecent studies of carbon oxidation by scanning tunneling microscopy indicate that measured rates of carbon oxidation can be affected by randomly distributed defects in the carbon structure, which vary in size. Nevertheless, the impact of this observation on the analysis or modeling of the oxidation rate has not been critically assessed. This work focuses on the stochastic analysis of the dynamics of carbon clusters' conversions during the oxidation of a carbon sheet. According to the classic model of Nagle and Strickland‐Constable (NSC), two classes of carbon clusters are involved in three types of reactions: gasification of basal‐carbon clusters, gasification of edge‐carbon clusters, and conversion of the edge‐carbon clusters to the basal‐carbon clusters due to thermal annealing. To accommodate the dilution of basal clusters, however, the NSC model is modified for the later stage of oxidation in this work. Master equations governing the numbers of three classes of carbon clusters, basal, edge and gasified, are formulated from stochastic population balance. The stochastic pathways of the three different classes of carbon during oxidation, that is, their means and the fluctuations around these means, have been numerically simulated independently by the algorithm derived from the master equations, as well as by an event‐driven Monte Carlo algorithm. Both algorithms have given rise to identical results.
Wet oxidation of an azo dye: Lumped kinetics in batch and mixed flow reactors
Authors: Donlagic Jelka , Levec Janez 
Published: April 2004

AbstractOxidation of a dilute aqueous solution of a model azo dye pollutant (Orange II) was studied in batch and continuous well‐mixed (CSTR) reactors. Both reactors operate at 200–250°C, and total pressures up to 50 bar and at oxygen partial pressure from 10 to 30 bar. The model pollutant concentrations were in a range between 100 and 1,000 mg/L, which may be found in industrial wastewaters. The dye oxidation undergoes a parallel‐consecutive reaction pathways, in which it first decomposes thermally and oxidatively to aromatic intermediates and via organic acids to the final product carbon dioxide. To develop a kinetic equation capable of predicting organic carbon reduction, all organic species present in solution were lumped by total organic carbon (TOC). The lumped oxidation rate in batch reactor exhibited second‐order behavior, whereas in the CSTR it was found linearly proportional to its TOC concentration. The lump behavior in batch reactor was dominated by the refractory low molecular mass aliphatic acids formed during the oxidation.
Development of a metal hydride electrode waste treatment process
Authors: Bianco J. C. , Martin D. , Ansart F. , Castillo S. 
Published: April 2004

AbstractManufacturing residues of metal hydride electrodes for nickel–metal hydride batteries were chemically processed to recover the metal part and heat treated for the organic part. Chemical recovery yielded Ni‐Co alloy after electrolysis of the solution and hydroxides of other metals, mainly rare earths. The organic part, pyrolyzed at 700°C, led to separation between carbon and fluorinated matter. Infrared coupling at the output of the pyrolysis furnace was used to identify the pyrolysis gases.
Infinite dilution activity coefficients from ab initio solvation calculations
Authors: Lin Shiang‐Tai , Sandler Stanley I. 
Published: April 2004

AbstractA Group Contribution Solvation (GCS) model was developed to calculate infinite dilution activity coefficients (γ∞) based on modern computational chemistry. The GCS model results in an average error of 7% in γ∞ for the limited number of data points among water, n‐hexane, acetonitrile and n‐octanol, whereas the errors are 47% and 52% with the UNIFAC model and the modified UNIFAC model, respectively. GCS was also used to calculate infinite dilution partition coefficients, which can be used to determine how a dilute solute partitions between two solvents. Solutes were examined in three different liquid‐liquid systems: water/n‐hexane, water/acetonitrile, and water/n‐octanol. With GCS, the average errors are 22% (for 18 solutes), 18% (for 14 solutes) and 14% (for 15 solutes) for these solvent systems, while comparable errors are 237%, 286% and 226% with UNIFAC; and 342%, 414% and 306% with modified UNIFAC. The GCS model is a powerful new tool to predict the octanol‐water partition coefficients.
Equation‐of‐state parameters for pure polymers by molecular dynamics simulations
Authors: Fermeglia Maurizio , Pricl Sabrina 
Published: April 2004

AbstractTwo new procedures, based on molecular mechanics and molecular dynamics computer simulations, are presented for estimating the PHSCT EOS and the LF EOS parameters of a set of four polymers of industrial relevance and to predict their PVT behavior. These new, original methods offer good results, are relatively inexpensive, are absolutely general, and can be applied in principle to any equation of state, provided the model parameters have a well‐defined physical meaning.
Estimation of cell traction and migration in an isometric cell traction assay
Authors: Knapp David M. , Tower Theodore T. , Tranquillo Robert T. , Barocas Victor H. 
Published: April 2004

AbstractA quantitative analysis of data from an in vitro assay presented allows for simultaneous study of cell migration within as well as cell traction on tissue equivalents (collagen gels seeded with tissue cells to serve as model tissues). Using our anisotropic biphasic theory for modeling tissue equivalents, the ability of the model to simulate the data was validated by accurately predicting the alignment of fibroblasts and collagen fibrils in the compacting collagen gels and the effects of gel aspect ratio on gel compaction. The effects of migration and adhesion modulating factors (platelet‐derived growth factor‐BB and an anti‐β1 integrin antibody), as well as mechanical stress in the collagen network (attached vs. floating gels), on cell migration and traction during compaction were investigated. In all cases, cell migration was negatively correlated with cell traction. The relevance of the results to wound contraction is discussed.
Internal mass flux through frost
Authors: Fukada Satoshi , Inoue Kunihiro 
Published: April 2004

AbstractAn experimental method is developed for determining the internal mass flux through frost with a dendrite structure. The theory and experimental procedures of the measurements using water slightly concentrated with deuterium are described. The internal mass flux determined from variations in the deuterium concentration in frost with time shows an almost linear decrease in the frost depth direction from the surface. The profile of the local frost density is almost flat in the depth direction. The frost uniformity is kept independent of the cooled‐plate temperature and the total pressure in the container unless part of the frost melts. The cause for the uniformity of frost density is discussed in terms of the frost temperature profile and microscopic crystal growth.
Magnetic resonance imaging of the filtration process
Authors: Dirckx Conrad J. , Clark Simon A. , Hall Laurance D. , Antalek Brian , Tooma Joe , Hewitt J. Michael , Kawaoka Ken 
Published: April 2004

AbstractThis article demonstrates that 3‐D magnetic resonance imaging (MRI) provides sufficient spatial resolution to visualize accurately the internal architecture of a 10‐in. cartridge filter and housing. A paramagnetic material (<5‐μm iron‐oxide particles) used as the contaminant, together with a gradient‐echo imaging sequence, enables location of the areas on the filter surface where the particles are deposited, even at the earliest stages of blocking. The magnetic susceptibility contrast mechanism of MR imaging sequence and particulate matter produces a far larger volume reduction in MR signal than that generated by the actual displacement of fluid by the particles. Using this spatial amplification effect, the temporal performance of the filter was studied by imaging the deposition of 3.75 g of the particulate material at ten incremental stages of blocking. Blocking is heterogeneous initially, both longitudinally along the filter length and radially across the transverse sections, and continues to be heavier in the areas of initially greater deposition as more material is entrapped. The correlation between the areas of heavy blocking and the internal support structure of the filter cartridge is discussed, since those regions appear to be strongly related to the cartridge body design. In a separate set of experiments, the 3‐D flow field of a Newtonian fluid through the filter system was measured for an unblocked filter. These measurements also show some correlation between the spatial heterogeneity of particulate deposition and the heterogeneous flow paths of liquid through the filter.
Colloidal gas aphrons (CGA): Dispersion and structural features
Authors: Jauregi Paula , Mitchell Geoffrey R. , Varley Julie 
Published: April 2004

AbstractColloidal gas aphrons (CGA) have previously been defined as surfactant stabilized gas microbubbles and characterized for a number of surfactants in terms of stability, gas holdup and bubble size even though there is no conclusive evidence of their structure (that is, orientation of surfactant molecules at the gas–liquid interface, thickness of gas–liquid interface, and/or number of surfactant layers). Knowledge of the structure would enable us to use these dispersions more efficiently for their diverse applications (such as for removal of dyes, recovery of proteins, and enhancement of mass transfer in bioreactors). This study investigates dispersion and structural features of CGA utilizing a range of novel predictive (for prediction of aphron size and drainage rate) and experimental (electron microscopy and X‐ray diffraction) methods. Results indicate structural differences between foams and CGA, which may have been caused by a multilayer structure of the latter as suggested by the electron and X‐ray diffraction analysis.