bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydrodynamics of soil immobilization in the immobilized soil bioreactor
Authors: Karamanev Dimitar G. , Chavarie Claude , Samson Réjean 
Published: June 2004

AbstractThe hydrodynamic characteristics of a new type of reactor, the immobilized soil bioreactor, were studied. This apparatus is a practical new engineering concept (soil immobilization) based on entrapment of soil particles, which contain pollutant‐degrading microorganisms, in the pores of a geotextile to activate the indigenous microorganisms. The soil immobilization is the third on the size scale of immobilization processes, coming after (1) that of molecules in heterogeneous catalysis (in Angstrom) and (2) that of microbial cells and their fragments in immobilized cells and enzymes biocatalysis (in micron). The size of immobilized soil particles is in the range of a millimeter. A mathematical model of liquid flow within the reactor is proposed, which qualitatively explains the distribution of the immobilized soil in space. The dynamics of soil immobilization within the bioreactor has been studied as a function of the particle size, initial slurry concentraion and air flow rate. A mathematical model of the process of soil immobilization was proposed based on deep filter mechanics. The process can be described by a second‐order kinetic model. This study will be of great importance for the design of immobilized soil bioreactors for degradation of recalcitrant soil pollutants.
Minimum liquid fluidization velocity in gas‐liquid‐solid fluidized beds
Authors: Briens L. A. , Briens C. L. , Margaritis A. , Hay J. 
Published: June 2004

AbstractAccurate detection of minimum liquid fluidization is essential to the successful operation of gas‐liquid‐solid fluidized beds, especially when particle or liquid properties evolve. A gas‐liqid‐solid system of 3‐mm glass beads exhibits three distinct flow regimes as the liquid velocity is increased: compacted, agitated and fluidized‐bed regmes. Measurements showed that the bed is not fluidized in the agitated bed regime. Pressure gradient and bed height measurements do not provide the minimum liquid fluidization velocity; instead, they offer the velocity between the compacted and agitated bed regimes. Time‐averaged signals are not reliable for determining the minimum liquid fluidization velocity. It can be obtained from the standard deviation, the average frequency, the Hurst exponent and the V statistic of the cross‐sectional average conductivity, which can be measured under many industrial conditions.
Electrostatic partitioning in slit pores by Gibbs ensemble Monte Carlo simulation
Authors: Chun Myung‐Suk , Phillips Ronald J. 
Published: June 2004

AbstractEquilibrium partitioning of spherical solutes between slit pores and bulk solution is investigated by the Gibbs ensemble Monte Carlo method. Two types of perturbatins are performed in this simulation: a random displacement of solutes that ensures equilibrium within both bulk and pore regions, and random interchanges of solutes that equalize the interaction potentials between the two regions. To study the effects of electrostatic interactions, interaction energies between the solutes and pore walls and between pairs of solutes are evaluated by using a singularity method. Partition coefficients calculated for neutral solutes, which experience purely steric interactions, increase with increasing solute concentration and agree well with existing theoretical results. For pores and solutes of like charge, results for the limit of infinitely dilute solute concentration show a sharp decline in partition coefficient with decreasing ionic strength of solution. As the solute concentration increases, the interplay of solute–wall and solute–solute interactions becomes increasingly important, and the partition coefficient increases accordingly. The density profiles indicate unambiguously that, whether solutes and proes are uncharged or of like charge, solute–solute interaction promotes enhanced concentrations near the wall, causing the partition coefficient to increase. Even at solute concentrations as low as 5%, effects of solute–solute interactions caused by electrostatic charge can more than compensate for sphere–wall repulsive interactions, indicating that concentration effects should be considered at least as important as electrostatic effects in partitioning phenomena.
Estimating radial velocity of fixed beds with low tube‐to‐particle diameter ratios
Authors: Cheng Zhen‐Min , Yuan Wei‐Kang 
Published: June 2004

AbstractThe Ergun equation based on the effective spherical diameter is universally valid for various shapes of granular packings. It, however, was derived from the assumption of infinite tube‐to‐particle diameter ratio without considering the wall effect. Although some improvements were made by Mehta and Hawley (1969) to correct this, the application of the Ergun equation is still restricted to cylindrical columns with a packing porosity of less than 0.5. To modify the Ergun equation to noncylindrical flow space with or without a wall, it was substituted into the empty tube pressure drop equation by introducing an effective tube diameter so that the pressure drop can be predicted just from the free flow space and the wetted area involved. This treatment offers the basis for a new method in velocity distribution prediction.
Destruction and removal of toluene and MEK from gas streams with silent discharge plasmas
Authors: Chang Moo Been , Chang Chun‐Cheng 
Published: June 2004

AbstractThe effectiveness of applying silent discharge plasmas (SDP) for destroying and removing volatile organic compounds (VOCs) from gas streams is experimentally evaluated with a laboratory‐scale reactor. The VOCs selected for study include toluene and methyl ethyl ketone (MEK). Direct collision with energetic electrons and reaction with generated gas‐phase radicals are two major mechanisms responsible for destruction and removal of VOCs from gas streams. Operating parameters investigated include applied voltage, gas residence time, and temperature and composition of the gas stream. Experimental results indicate that the removal efficiency of toluene and MEK achieved with SDP can be enhanced by operating the system at a higher gas temperature and applied voltage due to the generation of more energetic electrons and radicals. O2 is essential for removing VOCs from gas streams with SDP. More than 80% removal efficiencies were achieved with this system for both toluene and MEK. SDP can potentially serve as an alternative control technology for removing VOCs from gas streams.
Biofiltration of isopentane in peat and compost packed beds
Authors: Wang Zhao , Govind Rakesh 
Published: June 2004

AbstractCommercially available biofiltration systems have used natural bioactive materials in packed beds due to low media cost and easy availability. Detailed understanding and modeling of biofiltration systems are lacking in existing literature. Experimental studies on the isopentane treatment in air using peat‐ and compost‐packed beds were conducted with inlet isopentane concentrations of 360 to 960 ppmv, and empty‐bed gas‐phase residence times of 2 to 10 min. High removal efficiences (> 90%) were achieved at low contaminant concentrations ( < 500 ppmv) and large empty‐bed gas‐phase residence times ( > 8 min). For both peat and compost biofilters, there was an “optimal” water content that gave the highest removal efficiency. For higher water content, mass transfer of isopentane through the liquid phase controlled the biofiltration removal efficiency. At low water content, irreversible changes in the bioactivity of peat and compost occurred, resulting in an irrecoverable loss of removal efficiency. Increases in biofilter bed temperature from 25 to 40°C improved the removal efficiency. A mathematical model incorporating the effect of water content and temperature was developed to describe the packed‐bed biofilter performance. Model predictions agreed closely with experimental data.
Modeling flow in disordered packed beds from pore‐scale fluid mechanics
Authors: Thompson Karsten E. , Fogler H. Scott 
Published: June 2004

AbstractNetwork models are an effective means of incorporating pore‐scale heterogeneity into flow models of porous materials. The drawback to these models used to be the inability to obtain quantitative macroscopic parameters representing larger (experimental‐scale) media. However, recently developed modeling techniques, combined with more widely available computational resources, make the simulation of macroscopic parameters from a network approach viable. A network model for the slow flow of an incompressible fluid in disordered packed beds is presented. Fundamental fluid mechanics equations are solved at the pore scale and then translated to macroscopic behaviour using a network approach. The results reproduce experimental permeabilities and show excellent quantitative fits to residence time distributions for mechanical dispersion in real beds. Simulations of the RTD are of special interest, because they are definitive links between pore‐scale flow behavior and macroscopic responses.
Influence of dynamic interfacial properties on droplet breakup in plane hyperbolic flow
Authors: Janssen J. J. M. , Boon A. , Agterof W. G. M. 
Published: June 2004

AbstractDroplet breakup in laminar flows is important in emulsification processes and polymer blending. The influence of surfactants on droplet deformation and breakup in a plane hyperbolic flow was studied experimentally in an opposed‐stream device. As in the case of simple shear flow, the inhomogeneity of the surfactant distribution along the droplet interface has a pronounced effect. Our results are qualitatively consistent with other numerical studies for droplet breakup in an axisymmetric elongational flow. Also a striking similarity is noted with other experimental observations for the deformation and breakup of polymeric drops in a quasi‐steady‐plane hyperbolic flow. The critical capillary number for droplet breakup in the experiments correlates with the interfacial viscoelasticity, and a reformulation of the numerical framework in terms of interfacial elasticity parameters is suggested for future numerical work including other linear flows.
Oil‐assisted agglomeration for toner deinking: Population balance model and experiments
Authors: Snyder Bret A. , Berg John C. 
Published: June 2004

AbstractThis study examines the selective agglomeration of hydrophobic toner particles from a repulped paper fiber slurry by adding an immiscible oil that preferentially wets the toner particles. Effects of cationic starch additives, agitation rate, time, temperature and oil composition are examined experimentally in terms of the dynamic and steady‐state evolution of the particle‐size distribution produced. A simple, but effective, population balance model is solved numerically to simulate the agglomeration process and provides quantitative relationships between process variables and the effectiveness and rate of agglomeration. These relations are simple and clear. The process is shown to be controlled by the composite effect of the aforementioned variables on the aggregation and breakup rates, and the observed hehavior is understood in these terms. Practical recommendations for agglomeration, a process potentially useful for deinking toner‐printed paper, are deduced from the results.
Application of almost‐everywhere singular distributions in chemical engineering
Authors: Giona Massimiliano , Patierno Oreste 
Published: June 2004

AbstractAlmost‐everywhere singular (AES) distributions, usually referred to as multifractal measures, provide an intermediate link between atomic distributions (distributions represented by a countable superposition of Dirac's delta terms) and smooth regular distributions. This article shows how AES distributions can be rigorously treated in connection with distributed‐parameter models and presents closed‐form expressions and/or recursive, uniformly converging approximation methods for integral transforms (Laplace and Stieltjes). In particular, exact results are obtained and discussed for linear and uniform nonlinear kinetcis and for transport schemes in the presence of continuous mixtures. The physical origin of AES distributions in real systems is also detailed.
Experimental study on wetting of fibers with non‐Newtonian liquids
Authors: Ghannam Mamdouh T. , Esmail M. Nabil 
Published: June 2004

AbstractParameters of wetting dry fibers with non‐Newtonian liquids are studied experimentally. Rheological tests show that seven of the 13 test liquids adhere to Newtonian behavior with a wide range of viscosities 3 < μ < 30,000 mPa·s. The other six liquids show shear‐thinning behavior with different flow indices. Some of the liquids exhibited viscoelastic behavior. Diameters of the fibers are in the range 0.033 < D < 0.071 cm. Experimental measurements cover contact angles, interfacial depths and diameters, as well as the critical wetting speed of entraining visible small air bubbles in the liquid volume. Dynamic contact angles are strong functions of the apparent viscosity of the liquid at the particular wetting speed regardless of whether the liquid is Newtonian or non‐Newtonian. Higher values of contact angles correspond to wetting of fiber with larger diameter for less viscous liquid are generally higher than those for Newtonian liquids. Depressions created in the surface of different test liquids can be classified into three different scales, corresponding to three scales of liquid viscosities.
Efficient high‐pressure state equations
Authors: Harstad Kenneth G. , Miller Richard S. , Bellan Josette 
Published: June 2004

AbstractA method is presented for a relatively accurate, noniterative, computationally efficient calculation of high‐pressure fluid‐mixture equations of state, especially targeted to gas turbines and rocket engines. Pressures above 1 bar and temperatures above 100 K are addressed. The method is based on curve fitting an effective reference state relative to departure functions formed using the Peng‐Robinson cubic state equation. Fit parameters for H2, O2, N2, propane, methane, n‐heptane, and methanol are given.
New correlation for sieve‐tray point efficiency, entrainmnt, and section efficiency
Authors: Bennett Douglas L. , Watson Dana N. , Wiescinski Marie Anne 
Published: June 2004

AbstractA comprehensive composite database for distillation sieve‐tray efficiency is used to develop point efficiency and entrainment correlations based on a model that considers the fluid on the distillation tray to be contained in a liquid‐continuous region near the tray deck and a vapor‐continuous region on top of the liquid‐continuous region. This model allows estimates of the portion of the mass transfer that occurs in each region and the mass‐transfer resistance that occurs on the liquid side and vapor side of the interface. For most cases, most of the mass transfer occurs within the liquid‐continuous region. The liquid side resistance is often significant.The entrainment correlation is consistent with the work of Bennett et al., which relates entrainment to the ratios of the liquid to vapor density and the froth height to the tray spacing. A simple liquid continuous‐only mass‐transfer model containing only four empirical parameters correlates the point efficiency data to within 6.4%. Despite a twofold change in vapor Schmidt number, no dependency on vapor Schmidt number is seen. Important dimensionless groupings are the Reynolds number based on the hole velocity, effective froth density, ratio of the liquid inventory to the perforation diameter, and fraction of the tray area perforated. Mathematically simple and accurate methods allow the prediction of the section efficiency for trays operating in cross or parallel flow. They address vapor and liquid mixing, entrainment and a criterion to avoid significant degradation of the tray efficiency due to weeping.
Gas–liquid flow through horizontal tees of branching and impacting type
Authors: Hatziavramidis Dimitri , Sun Bing , Gidaspow Dimitri 
Published: June 2004

AbstractIn gas–liquid flows through tee junctions, because of the difference in inertia between the phases, the flowing mass fractions for an individual phase at the outlet sides differ from those at the inlet. This phase separation is an important consideration in delivering fluids and energy through pipe networks in the power and process industry. In this work, air–water and steam–water flows through branching and impacting tee junctions are considered. Under certain conditions (when the volumetric fraction of the liquid drops does not change appreciably and their bulk density is much higher than the gas density, and when the flow rates and/or the gas volumetric fraction are high), these flows can be approximated as irrotational flows of incompressible, inviscid fluids and are amenable to potential flow methods, for example, conformal mapping. For the general case of gas–liquid flows through a branching or impacting tee, a CFD code is utilized to conduct transient flow simulations. Predictions of phase separation for both types of tee junction agree well with experimental data.
Synthesis of crystallization–distillation hybrid separation processes
Authors: Berry David A. , Ng Ka M. 
Published: June 2004

AbstractA systematic method to synthesize crystallization–distillation hybrid separation processes is presented. Two classes of hybrids are identified for binary mixtures. The first bypasses azeotropes and tangent pinches, while the second bypasses eutectics. Guidelines for flow‐sheet selection are proposed based on an analysis of simple eutectic, constant relative volatility systems. In addition, the hybrids are compared to both extractive and adductive crystallization in order to determine the conditions under which solvent‐based crystallization techniques outperform the proposed hybrid configurations. The method is extended to ternary mixture. The use of stream combination and complex distillation columns is also considered.
“Tunable” diffusion of D2O in CO2‐swollen poly(methyl methacrylate) films
Authors: Vincent M. F. , Kazarian S. G. , Eckert C. A. 
Published: June 2004

AbstractOpportunities exist to exploit the unique properties of carbon dioxide to process polymers for advanced applications. The diffusion of deuterated water in poly(methyl methacrylate) films swollen by carbon dioxide at 35°C over the pressure range 0 to 90 bar (corresponding density range: 0.0 to 0.66 g/cm3) was measured using in situ FTIR spectroscopy. The mechanism and time scale of the diffusion of deuterated water in PMMA are easily controlled by manipulation of the applied CO2 density. The enhancement of mass transport rate is consistent with the degree of plasticization of the polymer due to the absorption of carbon dioxide.
Lumen mass transfer in hollow‐fiber membrane processes with constant external resistances
Authors: Qin Yingjie , Cabral Joaquim M. S. 
Published: June 2004

AbstractHollow‐fiber membrane processes with a constant external resistance having a constant or variable shell concentration resulting from an operational mode of cocurrent or countercurrent are studied. By solving numerically the continuity mass‐conservation equation with the corresponding boundary conditions, the lumen laminar mass‐transfer coefficients for both cases are correlated. The correlations greatly improve the calculating accuracy of the overall mass‐transfer coefficient and can be used to obtain the lumen mixed‐cup concentration by an algebraic equation substituting the partial differential equation. A separation factor m' is introduced to characterize the effect of the operational mode. Calculation results demonstrate that the lumen mass‐transfer coefficient is independent of the real lumen and shell concentrations, but it is greatly influenced by m'. The countercurrent mode, compared to the cocurrent mode, provides not only a higher mean driving force, but a higher lumen mass‐transfer coefficient. This conclusion is novel and valid for the tube‐shell heat or mass‐transfer processes and is supported by the experimental data in the literature and our gas membrane separation experiments.
Kinetically driven instabilities and selectivities in methane oxidation
Authors: Park Young K. , Vlachos Dionisios G. 
Published: June 2004

AbstractIgnitions, extinctions, and Hopf bifurcations in methane oxidation were studied as a function of pressure and inlet fuel composition. A continuous stirred‐tank reactor was modeled with numerical bifurcation techniques, using the 177 reaction/31 species mechanism. Sensitivity and reaction pathway analyses were performed at turning points to identify the most important reactions and reactive species. Then, simulations were compared with experimental data. Multiple ignitions and extinctions as well as oscillations that are purely kinetically driven were found. Ignition to a partially ignited state with considerable reactivity of methane indicates possible narrow operation windows with high selectivities to partial oxidation products. At 0.1 atm, we found a selectivity of up to 80% to CO at 70% CH4 conversion. The ignition to a fully ignited branch is associated with high selectivity to CO2 and H2O. The C2 chemistry inhibits the ignition of methane to the partially ignited branch. The methane ignition temperature exhibits two branches with respect to pressure, with only the low‐pressure branch being dominant. Reaction path analysis at ignition conditions shows that the preferred pathway of CH4 oxidation is to form CO and CO2 through CH2O and CH2(s) intermediates. However, at intermediate to high pressures, the recombination of CH3 to C2 H6 also becomes quite significant.
Analytical description of the Lennard‐Jones fluid and its application
Authors: Tang Yiping , Lu Benjamin C.‐Y. 
Published: June 2004

AbstractA simplified exponential (SEXP) approximation, combining the exponential approximation and the first‐order mean spherical approximation, is proposed to improve the equation of state for the Lennard‐Jones (LJ) fluid. The SEXP approximation, which can be implemented in an analytical manner, yields better radial distribution functions of the LJ fluid. Extensive comparisons with two typical perturbation theories show that the SEXP approximation is more appropriate to describe the behaviors of the LJ fluid. The latest 33‐parameter modified Benedict‐Webb‐Rubin equation, also calculated, is inadequate in the region of phase coexistence. The SEXP approximation is applied to the calculation of methane properties with much better results than the Peng‐Robinson equation of state for saturated liquid densities and second virial coefficients.
Separation of bulk hydrogen sulfide–hydrogen mixtures by selective surface flow membrane
Authors: Parrillo D. J. , Thaeron C. , Sircar S. 
Published: June 2004

AbstractThe separation performance of binary hydrogen sulfide–hydrogen mixtures by a nanoporous carbon membrane called selective surface flow (SSF) membrane is described. The membrane selectively permeates H2S from H2, and a H2‐enriched stream is produced at the feed‐gas pressure. A two‐stage embodiment of the SSF membrane is described for production of high‐purity H2 with high H2 recovery from an equimolar H2S‐H2 feed gas. A novel protocol for operation of the two‐stage membrane is needed to achieve that separation goal.