bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transport in heterogeneous media: Tracer dynamics in complex flow networks
Authors: Başağaoğlu Hakan , Ginn Timothy R. , Green Christopher T. , McCoy Benjamin J. 
Published: April 2004

AbstractLarge‐scale inhomogeneities in natural porous media profoundly affect the dynamic response of conveyed tracers. It is proposed that tracer dynamics in heterogeneous porous media can be represented by temporal moments based on parallel and series unit models of homogeneous columns, stirred volumes, or mass‐transfer‐connected closed compartments. The rules of combining the moments for elementary volumes are based on units (1) in series, where output from the preceding units is the input to the succeeding unit, and (2) in parallel, where the splitting or joining flow paths control the response. For a network of elementary volumes in series or parallel, fate and transport of contaminants in heterogeneous media can be analyzed simply in a deterministic framework. Results for several simple series and parallel models show the wealth of responses that can be quantitatively described by this procedure.
Gas–liquid mass transfer to single bubbles: Effect of surface contamination
Authors: Vasconcelos Jorge M. T. , Orvalho Sandra P. , Alves Sebastião S. 
Published: April 2004

AbstractThe dissolution of single bubbles of gases of low solubility kept stationary in a downward stream of water was studied. In “clean” water, two regimes are identified. Initially, the process is fast, consistent with the theory for circulating bubbles. Then, the mass‐transfer rate falls sharply to that predicted for solid spheres. Transition times and transition diameters vary widely with experimental conditions. In untreated water, only the second regime is found. Results are explained in terms of the kinetics of trace surfactant accumulation at the interface. An adaptation of the stagnant‐cap model is proposed, with surface immobilization expressed in terms of interface dynamics. The model yields good prediction of the transition point for a very large set of conditions, including different gases at various concentrations in the liquid stream and a wide range of initial bubble diameters.
Design and analysis of nonequilibrium separation processes
Authors: Sridhar L. N. , Maldonado Carlos , Garcia Ana Maria 
Published: April 2004

AbstractDesign and analysis of nonequilibrium separation process problem are discussed. Even though there have been published articles on the design and analysis of equilibrium separation process problems, these issues have not been addressed in great detail as far as nonequilibrium problems are concerned. Strategies are developed for drawing residue curve maps using mass‐transfer model equations. In addition the multistage nonequilibrium separation process problem is rigorously analyzed and it is shown that, as in the single‐stage case, any multiplicity that occurs is a result of the multiplicity that occurs here in the phase equilibrium calculations at the interface.
Statistical process monitoring based on dissimilarity of process data
Authors: Kano Manabu , Hasebe Shinji , Hashimoto Iori , Ohno Hiromu 
Published: April 2004

AbstractMultivariate statistical process control (MSPC) has been widely used for monitoring chemical processes with highly correlated variables. In this work, a novel statistical process monitoring method is proposed based on the idea that a change of operating condition can be detected by monitoring a distribution of process data, which reflects the corresponding operating conditions. To quantitatively evaluate the difference between two data sets, a dissimilarity index is introduced. The monitoring performance of the proposed method, referred to as DISSIM, and that of the conventional MSPC method are compared with their applications to simulated data collected from a simple 2 × 2 process and the Tennessee Eastman process. The results clearly show that the monitoring performance of DISSIM, especially dynamic DISSIM, is considerably better than that of the conventional MSPC method when a time‐window size is appropriately selected.
Simulating cyclohexane millisecond oxidation: Coupled chemistry and fluid dynamics
Authors: O'Connor R. P. , Schmidt L. D. , Deutschmann O. 
Published: April 2004

AbstractCyclohexane partial oxidation over a 40‐mesh Pt–10% Rh single‐gauze catalyst can produce ∼85% selectivity to oxygenates and olefins at 25% cyclohexane conversion and 100% oxygen conversion, with cyclohexene and 5‐hexenal as the dominant products. A detailed 2‐D model of the reactor is solved using density‐functional theory (with 35 reactions among 25 species) and computational fluid dynamics. Rapid quenching in the wake of the wires allows highly nonequilibrium species to be preserved. The simulations show that the competition between cyclohexyl and cyclohexylperoxy radicals is crucial in determining product selectivities. At high temperatures and low pressures, the cyclohexyl radical is favored, leading to high selectivities to cyclohexene. At lower temperatures or high pressures, cyclohexylperoxy radicals are favored, allowing the formation of parent oxygenates to dominate. Numerical simulations suggest ways to tune reactor operation for desired product distributions and allow the investigation of dangerous or costly operating conditions, such as high pressure.
Molecular thermodynamics for fluid‐phase equilibria in aqueous two‐protein systems
Authors: von Solms Nicolas , Anderson Camille O. , Blanch Harvey W. , Prausnitz John M. 
Published: April 2004

AbstractWith saline water as the continuous medium, a two‐component McMillan‐Mayer equation of state is used to describe liquid–liquid phase equilibria in a two‐protein system. The equation of state is based on a hard‐sphere reference with perturbations introduced through a potential of mean force to account for electrostatic forces and for attraction between protein particles. To illustrate the thermodynamic framework, one parameter each is fitted to experimental precipitation data for aqueous saline one‐protein systems containing either lysozyme or ovalbumin. A lysozyme–ovalbumin interaction parameter is then introduced to calculate phase behavior in the aqueous two‐protein system. These calculations are remarkably similar to classic vapor–liquid equilibrium calculations using an equation of state. For the aqueous two‐protein system, calculations give the light‐phase composition as well as the lysozyme and ovalbumin partition coefficients for a given dense‐phase composition. Agreement with sparse experimental data is reasonable over a range of pH and high ionic strength provided by the common precipitant ammonium sulfate.
Mapping of sonochemical reactors: Review, analysis, and experimental verification
Authors: Gogate Parag R. , Tatake Prashant A. , Kanthale Parag M. , Pandit Aniruddha B. 
Published: April 2004

AbstractThe erratic behavior of cavitational activity exhibited in a sonochemical reactor poses a serious problem in its design and scale‐up. Several previous studies in the past dealt with mapping of sonochemical reactors, which have been critically analyzed and recommended for efficient scale‐up strategies. There have been no efforts to link the primary effects (local pressure field) of ultrasound activity with the observed secondary effects (such as chemical reaction). In this work an ultrasonic horn (standard immersion‐type reactor), and an ultrasonic bath (rectangular geometry with transducers located at the bottom in triangular pitch) reactors were mapped with the help of local pressure measurement (using a hydrophone), and liberated iodine was estimated using the Weissler reaction, and a quantitative relationship was established between the two. In estimating chemical reaction rates, the effect of microscopic variation in the type of microreactor used (test tube in this case) on the extent of degradation was also investigated. Measured local pressure pulses were used in theoretical simulations of bubble dynamics equations to check the type of cavitation taking place locally, and to estimate the possible collapse of the pressure pulse in terms of the maximum bubble size reached during the cavitation phenomena. A relationship also was established between observed iodine liberation rates and the maximum bubble size reached. The engineers can easily use these unique relationships in an efficient design, since the secondary effect can be directly quantified.
Supercritical fluid extraction of surfactant from Si‐MCM‐41
Authors: Kawi S. , Lai M. W. 
Published: April 2004

AbstractSupercritical fluid extraction has been carried out on as‐synthesized Si‐MCM‐41 in a study to evaluate the efficiency of SFE in the recovery of the organic template cetyltrimethylammonium hydroxide (CTMAOH) from the pores of Si‐MCM‐41. Effects of different extraction parameters on the extraction efficiencies were investigated. The results show that modified CO2 is required to extract CTMAOH. High extraction efficiencies are obtained at 85°C and at both 100 and 350 bar, while the lowest efficiency is obtained at 150 bar. The extraction efficiency also increases initially on increasing the modifier concentration and reaches a limiting value when the concentration is increased further. Among a series of modifiers studied, methanol and acidic methanol (modified with acetic acid) are effective. The modifiers used in the extraction have a significant impact on the properties of the final material. The compound extracted was characterized and identified as CTMAOH.
A new image reconstruction method for tomographic investigation of fluidized beds
Authors: Liu Shi , Wang Haigang , Jiang Fan , Yang W. Q. 
Published: April 2004

AbstractIt is important to investigate the behavior of circulating fluidized beds (CFB) for efficient coal combustion. Electrical capacitance tomography (ECT) was applied to the measurement of gas/solids distribution in square CFBs. An iterative method was used to achieve improved image reconstruction over the commonly used linear back‐projection algorithm. The solids concentration profile, temporal variation of average solids concentration, and frequency spectra, which were obtained from the ECT data, are presented.
Equilibrium theory analysis of rectifying PSA for heavy component production
Authors: Ebner Armin D. , Ritter James A. 
Published: April 2004

AbstractAn isothermal equilibrium theory analysis, based on linear isotherms and a binary feed stream, was carried out to evaluate the feasibility of a rectifying PSA process for producing a pure heavy component at high recovery. Analytic expressions were derived to describe the performance of this process at the periodic state. The performance was also analyzed in terms of the different concentration and velocity profiles exhibited during various cycle steps that included the analysis of complex shock and simple wave interactions. Based on a parametric study, periodic behavior was established for a wide range of process conditions; and a design study with the PCB activated carbon–H2–CH4 system at 25°C further demonstrated the feasibility of a rectifying PSA cycle for producing a 100% CH4 stream from a dilute feed stream (y = 0.01) with a respectable recovery (80%), and reasonable process conditions. It also demonstrated the potential usefulness of an actual rectifying PSA process for bulk gas separation and purification.
Pore‐size effects on activated‐carbon capacities for volatile organic compound adsorption
Authors: Huang Mei‐Chiung , Chou Chia‐Huei , Teng Hsisheng 
Published: April 2004

AbstractGas‐phase adsorption of acetone and n‐hexane by activated carbons with different pore structures was investigated. The carbons were prepared from a bituminous coal with KOH activation. Increasing the activation temperature increased both the porosity and pore size. The equilibrium adsorption capacity for the organic compounds increased with the carbon porosity, but not proportionally. The percentage of pore volume utilized showed a decreasing trend with the porosity development for acetone adsorption, while an increasing trend was observed for n‐hexane. By incorporating pore size distribution with the Dubinin‐Radushkevich equation using an inverse proportionality between the micropore size and adsorption energy, the isotherms for adsorption onto different carbons can be well predicted. Simulations indicated that the adsorption energy, which is an inverse function of the micropore size, determines the adsorption capacity. Different effects of porosity development were observed for different adsorbates.
Mathematical modeling of rice cooking and dissolution in beer production
Authors: Davey Malcolm J. , Landman Kerry A. , McGuinness Mark J. , Jin Hong N. 
Published: April 2004

AbstractWhen beer is brewed in Asia, rice is traditionally used as an adjunct to provide additional sugars for the fermentation process. Under sufficiently high temperatures, the grain, which is primarily composed of starch, takes up water. The starch undergoes a gelatinization reaction when the moisture content is sufficiently high. Stirring and enzyme activity facilitate the removal of the outer gelatinized rice layers, and this starch dissolves into solution. The starch molecules are subsequently broken down by enzymes. The water uptake, gelatinization, and dissolution processes are modeled using a modified diffusion approach. The mass of starch molecules dissolved in solution as the cooking proceeds is determined. The dissolution process increases the speed of gelatinization, and the gelatinization front speed and the thickness of the gel layer are constant with time. The modeling takes into account different temperature regimes and a distribution of rice size. Such models help understand and optimize the total dissolved solids from this cooking process.
Engineering kinetics for hydrothermal oxidation of hazardous organic substances
Authors: Vogel Frédéric , Smith Kenneth A. , Tester Jefferson W. , Peters William A. 
Published: April 2004

AbstractSupercritical water oxidation (SCWO) can decontaminate hazardous organic wastes, including mixtures whose constituents vary widely in their susceptibility to oxidation. The SCWO kinetics of complex organic wastes are analyzed using a mathematical model that eliminates the substantial input requirements and computationally demanding mathematics of multistep, component‐specific rate expressions. The approach assumes that SCWO occurs by an infinite set of independent, parallel, first‐order chemical reactions, with a continuous distribution of activation energies. The resulting model, distributed activation energies model (DAEM), was applied by earlier workers to other kinetics problems of comparable complexity, inter alia, decay of molecular defects in solids, and coal pyrolysis. A three‐parameter DAEM is shown to correlate the SCWO kinetics of eight organic wastes, including several complex mixtures. These wastes are: JP‐5 aviation fuel, Velsicol H537 hydraulic fluid, aqueous methanol solutions, NaOH and NH4OH hydrolysates of solid rocket propellants, an orange military dye marker, municipal sewage sludge, and alcohol distillery waste water. The model was separately parameterized for each waste by best fitting its predictions of conversion as affected by residence time and/or temperature to experimental data from various investigators. A satisfying correlation resulted for each case. Illustrative reactor engineering calculations demonstrate DAEM's superiority to a single reaction model in sizing a PFR for SCWO of a complex organic mixture. The times required to achieve 99.99% destruction of different wastes depend strongly on the nature of the waste and differ by about three orders of magnitude from the most labile waste to the most refractory waste.
Influence of swelling and diffusion‐induced convection on polymer sorption processes
Authors: Alsoy Sacide , Duda J. L. 
Published: April 2004

AbstractUnsteady‐state sorption of a vapor or liquid by a polymer is modeled to include the influence of the moving phase boundary associated with the polymer swelling and diffusion‐induced convection. A formulation presented clearly elucidates the influence of these two effects on the overall sorption process. Numerical solutions of the model equations indicate the errors that can be induced when swelling or convection are neglected. For most polymer‐solvent systems, the influence of the diffusion‐induced convection associated with volume changes in mixing can be neglected in the analysis of sorption processes. In contrast, the correction for the moving boundary or swelling of the polymer phase can be quite significant, particularly when a large step change in solvent concentration is considered.
Transport across a turbulent air‐water interface
Authors: Law C. N. S. , Khoo B. C. 
Published: April 2004

AbstractTurbulence structure in the immediate vicinity of the air–water interface has a dominant influence on the mass transfer across it. In this work, investigations on near‐surface turbulence and mass‐transfer rate were carried out for two distinct flow conditions: one with turbulence generated from beneath the interface, the other via wind shear from above the interface. Turbulence measurement with respect to the fluctuating interface was performed and Hanratty's β, the gradient of the linear variation of vertical velocity at the interface, was quantified. It is found that incorporating a near‐surface turbulence parameter such as β provides a reasonable model for interfacial mass transfer, applicable to the two vastly different flow conditions studied.
Gas–solid two‐phase flow in FCC riser
Authors: Fan Yiping , Ye Sheng , Chao Zhongxi , Lu Chunxi , Sun Guogang , Shi Mingxian 
Published: April 2004

AbstractFCC riser performance was examined in a large cold‐riser model made of 0.186‐m‐ID plexiglass. In the prelift zone, distributions of particle velocity and local density in six cross sections were investigated, and the experimental results indicated that the whole prelift zone can be divided into three subzones in the axial direction. In the feedstock injection zone, some new flow parameters were introduced and five flow parameters in five different cross sections were measured. When a nozzle jet was injected, secondary flow of the jet exited in the vicinity of the riser wall due to vortices, and this flow moved forth at first and then merged into the main stream. Based on the gas–solid two‐phase flow characteristics in each zone, the whole feedstock injection zone of the riser can be divided into four subzones. A new axial particle backmixing model and a simplified method for computing the radial distribution of the nozzle jet concentration in a different riser cross section can predict flow parameters of particles and the jet.
Gas and solids mixing in a turbulent fluidized bed
Authors: Du Bing , Fan Liang‐Shih , Wei Fei , Warsito W. 
Published: April 2004

AbstractGas and solids mixing characteristics in the bubbling and turbulent regimes of a gas‐solid fluidized bed are examined using helium and phosphor tracer techniques to obtain the gas and solids dispersion coefficients, respectively. The real time, quasi‐3‐D flow behavior is qualified and quantified by the electrical capacitance tomography (ECT) technique. The mixing behavior varies significantly with the flow regimes. As the gas velocity increases, axial and radial gas dispersion coefficients increase in the bubbling regime, reach a peak at Uc, the transition velocity from the bubbling to turbulent regimes, and then decrease. In contrast, as the gas velocity increases, axial and radial solids dispersion coefficients increase in the bubbling regime and continuously increase through Uc to the turbulent regime. Temperature and pressure have little effect on the gas and solids mixing behavior. A small quantity of fine particles is noted to drastically affect the gas and solids mixing behavior in the turbulent fluidized bed. The axial and radial dispersion coefficients of gas and solids reach their maximum when the fines content is about 15%. The ECT measurements illustrate the effect of adding fines on the flow behavior in the bed. A small quantity of fine particles disintegrate the bubble/void phase, significantly modifying bubble/void‐ and emulsion‐phase mixing behavior.
Enantiomer separation in a cascaded micellar‐enhanced ultrafiltration system
Authors: Overdevest Pieter E. M. , Hoenders Marc H. J. , van't Riet Klaas , van der Padt Albert , Keurentjes Jos T. F. 
Published: April 2004

AbstractThe increasing demand for optically pure compounds (enantiomers) stimulates the development of new enantiomer separation processes on an industrial scale. The separation of enantiomers by ultrafiltration of enantioselective micelles was studied in a cascaded system. The feasibility of this separation concept was proven by a cascade of five lab‐scale units and a bench‐scale system using an industrial membrane module. Model calculations show that the separation is not improved greatly at enantioselectivities (ratio of affinity constants) above 10 and the affinity of the enantioselective micelles for the substrate (enantiomers) plays a crucial role in the performance of the separation process. Modeling the separation as a function of the dimensionless affinity number (affinity constant · enantiomer feed concentration) shows that there is an operation window in which the separation satisfies its criterion of high yield and high enantiomeric excess. For countercurrent affinity systems, this implies that any research effort should focus on developing (microheterogeneous) media characterized by weak interactions with the substrate to allow for operation at high feed concentrations, not on high affinity systems.
Scrubbing of fly‐ash laden SO2 in modified multistage bubble column scrubber
Authors: Meikap B. C. , Kundu G. , Biswas M. N. 
Published: April 2004

AbstractThe emission of SO2 from various chemical industries is associated with particulate (fly‐ash), mostly concentrations of particulate laden sulfur dioxide in and around these plants overshoot the danger point. Prediction of fly‐ash laden SO2 removal efficiency is very important for the selection of pollution control equipment. Experimental investigations were conducted on the scrubbing of fly‐ash laden SO2 in the modified multistage bubble column scrubber using water. Experimental results show that almost zero penetration (100% removal efficiency) of fly‐ash laden SO2 can be achieved in this system. A correlation was developed for predicting the percentage collection efficiency of sulfur dioxide in the presence of fly‐ash. Experimental results agreed excellently with the correlation. Enhancement of SO2 collection due to the presence of fly‐ash was also quantified.
Modeling and design of vapor‐phase biofiltration for chlorinated volatile organic compounds
Authors: Den Walter , Pirbazari Massoud 
Published: April 2004

AbstractA mathematical model was developed for biofilter design and performance prediction with reference to the purification of contaminated gas streams. The model incorporated important aspects such as mass transfer, biodegradation, and adsorption processes. A systematic modeling protocol incorporated the development of a scale‐up strategy based on dimensional analysis and similitude. Trichloroethylene (TCE) was employed as the model contaminant for biofiltration testing and model verification. The biokinetic and adsorption parameters for the contaminant were determined independently from a series of minibiofilter and miniadsorber column experiments, specifically designed to simulate the actual biofilter operational regimes in a miniature scale. Bench‐scale biofilter experiments employing granular activated carbon columns indicated the good predictive capability of the model for the removal of TCE. Dynamic simulation studies were performed to assess the transient‐ and steady‐state behavior of the model under various operating conditions. Model sensitivity was studied to evaluate the influence of adsorption equilibrium, transport and biological parameters on the biofilter dynamics. The results demonstrated that the biofilter performance was greatly influenced by the Monod coefficients and the biofilm thickness.