bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetics of microbubble–solid surface interaction and attachment
Authors: Yang Chun , Dabros Tadeusz , Li Dongqing , Czarnecki Jan , Masliyah Jacob H. 
Published: April 2004

AbstractMicrobubble–solid surface interaction and attachment under the influence of hydrodynamic and physicochemical forces were studied experimentally and theoretically. An impinging‐jet technique was developed to measure bubble‐attachment flux onto a flat solid surface in an impinging‐jet stagnation flow. A video imaging system enables direct observation of the attachment behavior of hydrogen microbubbles onto two different collector surfaces: hydrophilic untreated glass and hydrophobic methylated glass. Experimental results showed that the attachment flux depends on both hydrodynamic flow and electrolyte concentration. A mass‐transfer model developed computes bubble‐attachment flux, considering hydrodynamic convection, Brownian diffusion, migration under gravitational buoyancy, and DLVO surface forces (that is, van der Waals and electric double‐layer forces). At high flow rates, the numerical predictions for attachment rates onto methylated glass generally agreed well with the experimental data. However, a difference exists between theoretical and experimentally determined attachment rates for both untreated and methylated glass when the Reynolds number of the flow is low. Several mechanisms are proposed to account for this discrepancy.
Retrograde melting behavior in polyolefin + solvent + antisolvent solutions
Authors: Adidharma Hertanto , Radosz Maciej , Luszczyk Marek 
Published: April 2004

AbstractThe SAFT1 equation of state captures the melting retrograde behavior for a ternary system of poly(ethylene‐co‐octene‐1) + isooctane + ethylene. The melting temperature minimum depends on the polymer branch density, solvent composition, polymer concentration, and polymer molecular weight, in decreasing order of sensitivity. Furthermore, the effects of the solvent/antisolvent ratio and polymer concentration on the melting temperature are nonmonotonic, that is, their sign may change in going from low to high pressures. Finally, the sign of the slope of the melting curve depends only on the difference between the partial molar volume of polymer in solution and the molar volume of pure solid polymer.
Population balance equations for cell and microbial cultures revisited
Authors: Fredrickson A. G. 
Published: April 2004

AbstractThe first chemically structured model of growth of a microbial or cell population proposed in 1967 by Fredrickson et al. took account of the particulate nature of the population. This model assumed implicitly that cells passed through the cell cycle continuously without transitions between recognizable cell cycle phases. This article discusses how to generalize or revise the first model so that passages of cells through a series of recognizable cell cycle phases can be accounted for. The 1967 article assumed that cell fission can occur anywhere in state space, although with high probability only in a limited domain of that space. Extension of this concept to cell cycle transitions leads to a model that violates a principle of determinism. Revised models that subdivide state space into nonoverlapping subdomains associated with each phase of the cell cycle are developed to obviate this unacceptable situation. The new models introduce the need for information about cell behavior that does not currently exist and thereby provide motivation for an experimental program aimed at supplying the data necessary for their identification and validation.
Using MR techniques to probe permeability reduction in rock cores
Authors: Johns M. L. , Sederman A. J. , Gladden L. F. , Wilson A. , Davies S. 
Published: April 2004

AbstractPolymer solutions are used commonly in oil‐recovery applications to reduce water production. While the polymer treatment is known to modify the permeability of the rock, the mechanism by which this occurs is poorly understood, and, hence, the ability to optimize either the polymer solution or its application is restricted. In this work, the pulsed‐gradient spin‐echo nuclear magnetic resonance technique is used to determine displacement propagators (distributions) for brine solution flowing through a Bentheimer sandstone rock core, both before and after treatment of the rock core with a polyacrylamide polymer solution. A novel simulation strategy employing the lattice–Boltzmann method is then proposed to interpret the differences in these propagators in terms of the location of polymer retained within the pore structure of the rock following treatment. The results suggest that the polymer is preferentially trapped in comparatively low permeability pores.
Bed nonhomogeneity in turbulent gas‐solid fluidization
Authors: Du Bing , Warsito W. , Fan Liang‐Shih 
Published: April 2004

AbstractBed dynamic behavior in a gas‐solid fluidization system is measured in real time using ECT based on the NNMOIRT recently developed. The ECT results reveal the time‐averaged and transient characteristics of the bubble/void phase and the emulsion phase, which is of value to the verification of the 3‐D computation codes with real physical systems. In the turbulent regime, the time‐averaged solids holdup distribution exhibits radial symmetry, which is not the case for the bubbling regime. The standard deviations of the fluctuations of the cross‐sectional, averaged bubble/void phase fraction, and the cross‐sectional, averaged solids holdups in the bubble/void phase and in the emulsion phase, all peak at the transition velocity from the bubbling to the turbulent regimes Uc. The addition of 10% fine particles decreases the solids holdup in the emulsion phase due to the breakup of large bubbles. The ECT study indicates that optical fiber probe measurement of the bubble/void phase fraction may yield significantly different results depending on the threshold level selected for the measured solids holdup distribution. The bubble/void phase fraction measured by the optical fiber probe does not vary with bed temperature up to 400°C; the emulsion phase voidage is observed to increase as the bed temperature increases.
Simulation and optimization of pressure‐swing adsorption systems for air separation
Authors: Jiang Ling , Biegler Lorenz T. , Fox V. Grant 
Published: April 2004

AbstractOver the past 20 years, PSA processes have gained increasing commercial acceptance as an energy‐efficient separation technique. After a startup time, the system reaches cyclic steady state (CSS), at which the conditions in each bed at the start and end of each cycle are identical. Contrary to the traditional successive substitution method, we apply a direct determination approach using a Newton‐based method with accurate sensitivities to achieve fast and robust convergence to CSS. Trust region methods and scaling are used to handle ill‐conditioning and model nonlinearities. When design specifications are imposed, this approach is easily extended to include design constraints. This eliminates trial‐and‐error experiments and determines all the operating parameters simultaneously. In addition, we modify a standard flux limiter in order to deal with nondifferentiable terms and ensure computational accuracy and efficiency. Optimal PSA processes are designed by means of state‐of‐the‐art rSQP‐based optimization algorithms. The simultaneous tailored approach incorporates detailed adsorption models and specialized solution methods. Here, CSS convergence is achieved only at the optimal solution and the time‐consuming CSS convergence loop is eliminated. Applications of several nonisothermal VSA O2 bulk gas separation processes are presented to illustrate all of these approaches.
Quadrature method of moments for population‐balance equations
Authors: Marchisio Daniele L. , Pikturna Jesse T. , Fox Rodney O. , Vigil R. Dennis , Barresi Antonello A. 
Published: April 2004

AbstractAlthough use of computational fluid dynamics (CFD) for simulating precipitation (and particulate systems in general) is becoming a standard approach, a number of issues still need to be addressed. One major problem is the computational expense of coupling a standard discretized population balance (DPB) with a CFD code, as this approach requires the solution of an intractably large number of transport equations. In this work the quadrature method of moments (QMOM) is tested for size‐dependent growth and aggregation. The QMOM is validated by comparison with both Monte Carlo simulations and analytical solutions using several functional forms for the aggregation kernel. Moreover, model predictions are compared with a DPB to compare accuracy, computational time, and the number of scalars involved. Analysis of the relative performance of various methods for treating aggregation provides readers with useful information about the range of application and possible limitations.
Steam reforming of methane and water‐gas shift in catalytic wall reactors
Authors: Venkataraman K. , Wanat E. C. , Schmidt L. D. 
Published: April 2004

AbstractCatalytic wall reactors permit high heat‐transfer rates between exothermic and endothermic reactions taking place catalytically on opposite sides of a thin wall, because they eliminate resistance to heat transfer in thermal boundary layers, thus making them compact and efficient. A parallel plate catalytic wall reactor was built in which exothermic methane combustion on platinum and endothermic methane steam reforming on rhodium occurred on walls in alternate channels. This reactor gave 95% conversion of methane to synthesis gas with a residence time of ∼70 ms at a steam/methane ratio of 1/1 with a thermal efficiency of ∼60%. A preheat pass was added on the combustion side that enabled heat exchange between hot combustion products and cold combustion inlet gases to increase temperature upstream and decrease it downstream. This two‐pass reactor gave H2/CO ratios of ∼14/1 with a residence time of ∼170 ms at a steam/methane ratio of 4/1. To increase the H2/CO ratio, the endothermic channel length was also extended, with a platinum‐ceria wall coating on the extended region to further reduce downstream temperatures and promote water‐gas shift. This reactor gave downstream temperatures as low as 200°C, and produced H2/CO ratios as high as 42/1 with a residence time of ∼300 ms at a steam/methane ratio of 4/1. The extended reactor shows good potential for producing high H2/CO ratio product streams suitable for preferential oxidation and subsequent use in fuel cells in a scalable configuration.
Formation process of three‐dimensional arrays from silica spheres
Authors: Ishikawa Keiji , Harada Hironori , Okubo Tatsuya 
Published: April 2004

AbstractElucidating the formation process of 3‐D arrays from submicrometer‐sized particles is a key to creating an optimal fabrication process of photonic crystals. In this research, the spontaneous sedimentation of silica spheres is imaged by in situ confocal laser scanning microscopy, and the dynamics is studied. When the pH is 7.0 and 10, the rate of the formation process of a hexagonal structure is attributed to the transport of spheres in the early stage of precipitation, and can be reproduced by a simple equation for Langmuir‐type adsorption, ignoring the desorption part. In a later stage, however, the rate becomes smaller. In the first layer, even after drying, the nearest two spheres are separated, while maintaining a hexagonal structure. From the results, the formation process of three‐dimensional arrays from silica spheres is illustrated.
Methane hydrate nonstoichiometry and phase diagram
Authors: Huo Zhongxin , Hester Keith , Sloan E. Dendy , Miller Kelly T. 
Published: April 2004

AbstractA previous study discovered that, when formed from different ethylene oxide (EO) feed solutions, hydrates had different small‐cage occupancies with essentially total occupation of the large cavities of sI hydrate. An EO + H2O isobaric phase diagram was proposed with a solid solution range to explain this phenomenon. Since methane and CO2 also occupy both small cages and large cages of sI hydrate, new phase diagrams were proposed which allowed the methane or CO2 hydrate composition to vary as a function of feed composition at fixed p‐T conditions. Raman spectroscopy experiments now show that H2O + CH4 hydrates formed at the vapor–liquid interface have a different composition than dendrites growing into the water below the interface. Interfacial hydrates were typical laboratory samples formed with excess gas, while dendrites coexisted with excess water and were similar to seafloor hydrate. Integrated peak intensities were used to calculate relative cage occupancies in Raman data analysis. Interfacial hydrates had an average of 95.4% small cages occupied at 30 MPa and 275.15 K, while dendrite hydrates had only 82.8% small‐cage occupancy at the same conditions. This result suggests that hydrates in the ocean floor may have lower methane concentrations than hydrates formed under normal laboratory conditions at the same pressure and temperature.
Modeling wet‐gas annular/dispersed flow through a venturi
Authors: van Werven M. , van Maanen H. R. E. , Ooms G. , Azzopardi B. J. 
Published: April 2004

AbstractA theoretical model for gas–liquid annular/dispersed flow through a venturi meter is reported. It is based on an earlier model developed for venturi scrubbers. Changes implemented are based on new research and on the different physics between the two cases. The predictions of the model have been tested using information from recent experiments on venturi meters employed for measuring wet‐gas flows with a liquid volume fraction up to 10%. The model gives good predictions with appropriate values of a small set of input variables.
Population balance PSD model for emulsion polymerization with steric stabilizers
Authors: Immanuel Charles D. , Doyle Francis J. , Cordeiro Cajetan F. , Sundaram Sekhar S. 
Published: April 2004

AbstractA detailed population balance model is developed for the particle‐size distribution (PSD) in the emulsion copolymerization of vinyl acetate and butyl acrylate, with nonionic poly(ethylene oxide) surfactants and a redox initiator pair (t‐butyl hydrogen peroxide and sodium formaldehyde sulphoxylate). The model accounts for the effects of the nucleation, growth, and coagulation events on the evolution of the PSD. The study addresses the modeling of the coagulation kernel (time‐varying and size‐dependent intrinsic coagulation rate) under nonionic surfactants. The coagulation‐inclusive model results show significant differences from the results generated by a coagulation‐free model (even under low solids conditions). More importantly, the coagulation‐inclusive model predicts to a reasonable accuracy the experimental data on the full PSD.
Novel multifunctional optical‐fiber probe: II. High‐density CFB measurements
Authors: Liu Jinzhong , Grace John R. , Bi Xiaotao 
Published: April 2004

AbstractThe novel parallel three‐fiber optical probe described in Part I of this article is applied to determine simultaneously local instantaneous solids volume concentration, velocity, and flux in multiphase suspensions. Radial distributions of local particle concentration, velocity, and flux and their fluctuations in a high‐density circulating fluidized bed (HDCFB) are presented. A strong correlation exists between fluctuations of local particle velocity and particle concentration. The optical probe is shown to provide a means of evaluating alternative measurement techniques that have commonly been employed in earlier studies.
Optimal design of interconnected bioreactors: New results
Authors: Harmand Jérôme , Rapaport Alain , Trofino Alexandre 
Published: April 2004

AbstractThe optimal design of two interconnected continuous stirred bioreactors in which a single reaction occurs is presented. The term “optimal” should be understood here as the minimum of the total volume of the reactors required to perform a given conversion rate, given a quantity of matter to be converted per time unit. In determining the optimal volume, it is assumed that the input flow may be distributed among the tanks and also that a recirculation loop can be used. The analysis of the optimal configurations is investigated, and the concept of “steady‐state equivalent biological system” is highlighted. The class of growth functions for which the results of this study hold is quite wide and includes, in particular, Monod, Haldane, and Aiba kinetics.
Shortcut method for kinetically controlled reactive distillation systems
Authors: Lee J. W. , Brüggemann S. , Marquardt W. 
Published: April 2004

AbstractA geometric‐based shortcut method for reactive distillation is addressed. The rectification body method for nonreactive distillation, the concept of critical Damköhler numbers, and the geometric design method for reactive distillation are combined with a new eigenvector analysis of pinch points. This shortcut method provides a minimum or reasonable Damköhler number for a given heat duty, as well as the design implication of how to effectively distribute reaction zones inside a column. This method can be used for a fast screening of process design alternatives and for an initialization of rigorous optimization.
Theory of trickle‐bed magnetohydrodynamics under magnetic‐field gradients
Authors: Iliuta Ion , Larachi Faïçal 
Published: April 2004

AbstractExternal inhomogeneous magnetic fields exert a body force (magnetization force) on electrically nonconducting and magnetically permeable fluids. The force acts on both paramagnetic and diamagnetic fluids and can be used to compensate for or to amplify the gravitational body force, unlike the Lorentz braking force that manifests only for electrically conducting liquids, such as liquid metals. The ability to influence two‐phase flows through porous media by the application of external inhomogeneous magnetic fields is of interest in the operation of trickle‐bed reactors for catalytic process intensification, particularly in oxidation catalysis, where the O2 paramagnetic properties may be propitious to macrogravity operation for enhancing liquid holdup and wetting efficiency. An isothermal 1‐D two‐fluid magnetohydrodynamics model based on volume‐average mass and momentum balance equations to describe the gas‐liquid downflow under a spatially uniform magnetic‐field gradient. The slit model approximation was used for the derivation of drag force closures intervening in the momentum equations. The evolution of the trickle‐bed magnetohydrodynamics was theoretically investigated in terms of liquid holdup and pressure drop under four gas‐liquid combinations. Advantages of this novel approach of process intensification were rationalized in terms of catalytic reactions.
Modeling structure effects on aggregation kinetics in colloidal dispersions
Authors: Sandkühler Peter , Sefcik Jan , Lattuada Marco , Wu Hua , Morbidelli Massimo 
Published: April 2004

AbstractThe time evolution of the cluster‐mass distribution (CMD) during colloidal aggregation can be modeled using population balance equations, given that the matrix of the aggregation rate constant (kernel) is known. Although numerous aggregation kernels have been proposed, their validity is still a major open problem, particularly when the role of the internal structure of the aggregates is referred to. A procedure is presented for the discrimination among possible kernel expressions including the structure effect. For aggregation processes in the submicron range, information about size and structure of aggregates can be obtained by dynamic and static light‐scattering measurements, for example, in terms of the average hydrodynamic (Rh) and gyration (Rg) radii. These quantities can also be calculated from the cluster‐mass distribution when accounting for the aggregate structure by the fractal concept and for the angular and rotational diffusion dependence of Rh. Since Rh and Rg represent different averages of the CMD, their simultaneous fitting is a severe test for a given kernel due to its inclusion of information on the average and width of the distribution. This procedure allows differentiation among several types of kernels proposed in the literature for DLCA and RLCA based on their ability to describe experimental data.
Hydrogen storage in carbon nanotubes: Residual metal content and pretreatment temperature
Authors: Lueking Angela , Yang Ralph T. 
Published: April 2004

AbstractHydrogen storage in MWNT was enhanced via the catalytic activity of NiMgO. The magnitude of the hydrogen to metal ratio for the MWNT/NiMgO system, combined with temperature programmed adsorption and desorption studies, showed hydrogen spillover from the catalyst to the carbon surface. Metal doping combined with temperature activation studies showed that both nickel and magnesium are active in the catalytic process. The yield, quality, and carbon‐metal contact were shown to affect hydrogen uptake. Higher pretreatment temperatures enhanced uptake, for both low‐ and high‐pressure measurements, due to increased carbon‐metal contact and activation of the catalyst. At 69 bar (or 1,000 psia), the hydrogen adsorption and desorption of the MWNT/NiMgO system were 3.7% and 3.6%, respectively.
Comparing flow‐reversal and inner recirculation reactors: Experiments and simulations
Authors: Ben‐Tullilah Moshe , Alajem Einat , Gal Rina , Sheintuch Moshe 
Published: April 2004

AbstractThe operation of reactors with flow reversal operate similar to a reactor with internal recirculation, which the feed enters through one (say, inner) reactor and then turns around and flows out through (the outer) another, when the heat‐transfer coefficient between the tubes is large. In this study, we compare the behavior of a packed‐bed reactor operating in flow‐reversal or internal‐recirculation modes, using ethylene oxidation on Pt/Al2O3 as a model reaction. The reactor was built from two concentric tubes (with 28.5 and 42.5 mm in diameter), both packed with a 20 cm catalytic bed and 10 cm inert beds (of alumina‐pellets) on each side. An adjustable opening between the tubes allowed for an internal recycle mode and the whole system could be operated with periodic flow reversal. The reactor can be employed then either as a simple once‐through bed or as a bed with flow reversal in the inner tube or as bed with internal recirculation flowing from the inner to outer tube, or in the opposite direction, as well as an internal‐recirculation reactor with flow reversal. Due to heat losses, the latter two modes were inferior to the others. The experiments, backed by simulations using a homogeneous model with independently determined parameters, showed that the technically‐simpler inner‐outer internal‐recycle reactor operated better at low flow rates, than that with flow reversal, but the conclusion is reversed at high flow rates. The domain where the internal‐recirculation reactor is superior depends on the heat‐transfer coefficient between the streams. By lowering the feed concentration, the extinction point was determined for each mode highlighting again the conclusions drawn above that inner‐recirculation operation may be superior to flow reversal at low flow rates. Simulations revealed also the existence of solutions with stationary fronts or oscillatory fronts.