bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microwaves in soil remediation from VOCs. 1: Heat and mass transfer aspects
Authors: Acierno Domenico , Barba Anna A. , d'Amore Matteo 
Published: April 2004

AbstractA novel technique presented performs in situ remediation of soils contaminated by volatile organic compounds (VOCs) based on the use of electromagnetic fields for heating operations. Attention is focused on heat and mass transfer occurring in porous‐moisturized media like a soil matrix. The microwave induced steam distillation process is investigated. Measurements are reported of temperature, humidity, residual contaminant concentration, and permittivity during the process. The crucial role is elucidated that the changes of the dielectrical properties of the soil matrix play on the electromagnetic field propagation. A mathematical model of the remediation process relating all the parameters above is proposed and validated.
Efficient simulation of time‐dependent flows: Application to a twin screw extruder
Authors: Raut Janhavi S. , Naik Vijay M. , Jongen Thibauld R. 
Published: April 2004

AbstractAn efficient, versatile technique was developed for detailed simulation of flows in complex processing equipment with multiple moving parts. It uses a suitably modified finite‐volume CFD simulation algorithm to deal with the problems posed by the relative motion of moving parts in processing equipment. A fixed grid is used to discretize the mass and momentum transport equations for the contents of the entire equipment volume. The motion of the solid moving parts within this domain is accounted for by assigning velocities to nodes of the grid representing the location of these parts at any moment of time. The technique was first validated for a single screw extruder by comparing the results predicted by conventional techniques involving body fitted mesh and a rotating frame of reference. Because of its inherent nonbody fitted mesh characteristics, the fixed grid method resulted in a rough, time‐dependent boundary for the moving parts. The extent of error arising from this artifact was also evaluated. The benefits of this technique were demonstrated by simulating complex three‐dimensional (3‐D) flow in an industrially important processing equipment with multiple moving parts—an intermeshed counterrotating twin screw extruder. The time required for geometry generation and meshing using this approach was very small, and the relevant geometric parameters including those associated with the moving parts can be varied by simply modifying values in the analytical expressions used to define them. This technique does not require recreating or remeshing the entire geometry, thus making it easy to optimize the design of complex equipment via quick parametric studies.
Electrochemical measurement of velocity gradient at the wall of a helical tube
Authors: Galier Sylvain , Issanchou Sébastien , Moulin Philippe , Clifton Michael J. , Aptel Philippe 
Published: April 2004

AbstractAn electrochemical technique was used for measuring the wall velocity gradient in two coiled pipes: a torus and a helix. An electrochemical oxidation reaction was employed with its rate limited by mass transfer. Measurement of the diffusion‐limited current at a microelectrode embedded flush with the wall allows the wall shear rate to be determined. The flow velocity was varied through both the laminar and turbulent regimes. Measurements were made for different electrode positions on the pipe circumference and, as expected, the highest shear rate was found at the outside of the curve, with the lowest value at the inside. In the case of the helical pipe, maxima and minima in shear rate were shifted slightly away from the positions observed for the torus.
Effect of density homogeneity on the dynamic response of powder beds
Authors: Yanagida T. , Matchett A. J. , Coulthard J. M. , Asmar B. N. , Langston P. A. , Walters J. K. 
Published: April 2004

AbstractHomogeneous and inhomogeneous powder beds subjected to low‐magnitude vibration are compared in terms of the dynamic response. The inhomogeneous samples were segregated into two phases: loose and dense phases, layering the two phases horizontally or vertically. An apparent mass, defined as a ratio of the base force to base acceleration, was measured. Comparison of homogeneous and segregated data demonstrated a significant density gradient dependence on the apparent mass data. First, homogeneous systems showed a resonant peak, which gave the longitudinal elastic modulus of the bed via the velocity of longitudinal stress wave propagation. Second, vertically segregated systems exhibited two significant peaks at low frequencies, corresponding to the resonance of each phase. In addition, the apparent mass values at the two peaks were related to the quantity of each phase. Third, horizontally segregated systems exhibited a resonant peak, whose frequency was approximately equal to homogeneous data, but the apparent mass value at the peak differed from homogeneous data. A model based on the fourth‐power scaling law, two‐phase theory and Rayleigh's energy method gave an interpretation for the insensitivity of the peak frequency to the density gradient in the vertical direction.
Predicting adsorption of water/organic mixtures using molecular simulation
Authors: Jorge Miguel , Seaton Nigel A. 
Published: April 2004

AbstractThe use of Monte Carlo simulation to predict the adsorption of mixtures of polar and nonpolar species on activated carbon was investigated using water and ethane on BPL carbon as a prototype system. The structure of the adsorbent was modeled by an array of slit‐shaped pores, characterized by a pore‐size distribution. The chemical heterogeneity of the carbon was taken into account by including oxygen‐containing sites on the surface of the pores. The pore‐size distribution was obtained from pure‐ethane adsorption on the same carbon sample, while the concentration and distribution of surface sites were determined by analyzing pure‐water adsorption. Model predictions agree well with experimental multicomponent data.
Parameter estimation for industrial polymerization processes
Authors: Bindlish Rahul , Rawlings James B. , Young Robert E. 
Published: April 2004

AbstractThe parameter estimation problem and its application to industrial data obtained from polymerization processes are analyzed. The polymerization process model consists of the material balances with the polymerization kinetics for the reactor and a simplified dynamic model for the downstream separator. The estimable kinetic parameters in the process model are obtained for plant data by analyzing the associated optimization problem. Two kinetic parameters are estimable for the copolymer data and the homopolymer data based on the information in the available industrial plant data. The identified process model forms the basis for a monitoring and feedback control system for these processes.
Coordinating feedback and switching for control of hybrid nonlinear processes
Authors: El‐Farra Nael H. , Christofides Panagiotis D. 
Published: April 2004

AbstractA robust hybrid control strategy for a broad class of hybrid nonlinear processes with actuator constraints and uncertain dynamics is proposed. These variable‐structure processes comprise a finite family of constrained uncertain continuous nonlinear dynamical subsystems, together with discrete events that trigger the transition between the continuous subsystems. The proposed control strategy is predicated on the idea of coordinating the hierarchical tasks of lower‐level feedback‐controller synthesis and upper‐level switching logic design. Using multiple Lyapunov functions, a family of bounded robust, nonlinear feedback controllers are initially designed to robustly stabilize the constituent modes of the hybrid process, subject to uncertainty and constraints. The region of guaranteed closed‐loop stability is then explicitly characterized for each mode in terms of the magnitude of actuator constraints and the size of the uncertainty. A set of stabilizing switching laws that track the energy evolution of the constituent modes are then derived to orchestrate safe transitions between the stability regions of the constituent modes and their respective controllers, in a way that respects actuator constraints and guarantees robust stability of the overall uncertain hybrid closed‐loop system. This hybrid control method is applied through computer simulations to robustly stabilize an exothermic chemical reactor with switched dynamics, model uncertainty, and actuator constraints at an unstable steady‐state and to design a fault‐tolerant control system for chemical reactors through switching between multiple constrained control configurations.
Feedback control of growth rate and surface roughness in thin film growth
Authors: Lou Yiming , Christofides Panagiotis D. 
Published: April 2004

AbstractA method for multivariable feedback control of surface roughness and growth rate in thin film growth using kinetic Monte‐Carlo (MC) models is proposed. The method is applied to the process of thin film growth in a stagnation flow geometry including atom adsorption, desorption, and surface migration as the three processes that shape film microstructure and determine film growth rate. A multiscale model involving coupled partial differential equations to model the gas phase and a kinetic MC simulator, based on a large lattice, for the modeling of film growth, is used to simulate the process. A roughness and growth rate estimator constructed allowed computing estimates of the surface roughness and growth rate at a time‐scale comparable to the real‐time evolution of the process. The estimator involves kinetic MC simulators based on small lattice models, adaptive filters used to reduce stochastic fluctuations of the outputs of the small lattice MC simulator outputs, and measurement error compensators used to reduce the errors between the estimates and measurements. The interactions between the inputs (substrate temperature and inlet precursor mole fraction) and outputs (growth rate and surface roughness) in the closed‐loop system are studied and found to be significant. A multivariable feedback controller, which uses the state estimator and explicitly compensates for the effect of input/output interactions, is designed to simultaneously regulate the growth rate and surface roughness by manipulating substrate temperature and inlet precursor mole fraction. Application of the estimator/controller structure to the multiscale process model demonstrates successful regulation of the surface roughness and growth rate to the desired set point values. This approach is shown to be superior to control of the growth rate and surface roughness using two independent feedback control loops.
General hybrid multizonal/CFD approach for bioreactor modeling
Authors: Bezzo F. , Macchietto S. , Pantelides C. C. 
Published: April 2004

AbstractA critical issue in the modeling of aerobic bioreactors is the close interaction between fluid flow and the biological reactions. In particular, shear rate has a large effect on the broth viscosity which, in turn, affects the rate of mass transfer of oxygen from the gas to the liquid phase. We demonstrate how a generic hybrid multizonal/computational fluid dynamics (CFD) modeling approach can be applied to take account of these interactions. The approach to multizonal modeling presented characterizes the flow rates between adjacent zones, and also the fluid mechanical quantities, such as the shear stress, that have important effects on the process behavior within each zone, by means of steady‐state CFD calculations. An unstructured model for xanthan gum production in a batch aerobic bioreactor is used for this purpose. The hybrid modeling approach is also applied to structured models involving distributions of cell mass within each zone.
Effect of active species mobility on soot‐combustion over Cs‐V catalysts
Authors: Fino Debora , Russo Nunzio , Badini Claudio , Saracco Guido , Specchia Vito 
Published: April 2004

AbstractThe soot combustion process promoted by some of the most promising diesel particulate combustion catalysts (Cs2O·V2O5, Cs4V2O7, CsVO3) is discussed on the grounds of a theoretical analysis and an experimental test campaign involving reaction runs in microreactors (either in isothermal or in temperature‐programmed conditions) and in a DSC apparatus. Such investigations, beyond the prevalent kinetic parameters (activation energy, oxygen reaction order, preexponential kinetic constant), led to a definition of the role of catalyst‐to‐carbon contact conditions on the conversion rate. Particularly, the role of formation of eutectic liquid phases, which dominates the catalytic behavior of the Cs2O·V2O5 catalyst, was fully elucidated on the grounds of either DSC runs or visual inspection through a heated optical microscope.
Electrohydrodynamic mixing in microchannels
Authors: Tsouris C. , Culbertson C. T. , DePaoli D. W. , Jacobson S. C. , de Almeida V. F. , Ramsey J. M. 
Published: April 2004

AbstractElectrohydrodynamic flow generated by the motion of charge carriers in an electric field was investigated for rapid mixing in microchannel devices. A “tee” geometry of channels ranging from 40 to 110 μm in width and 30 to 60 μm in depth was used to contact two miscible fluids, such as alcohols. A fluorescent dye (Rhodamine B) was used to quantify mixing. A potential difference ranging from 0 to 900 V was applied between two electrodes separated by a distance of 450 μm, resulting in field strengths ranging from 0 to 2 × 106 V/m. Results show that when no electric field is applied, mixing of the two streams is driven by diffusion and is, therefore, slow. The mixing length, at which the concentration across the channel becomes essentially uniform, decrease significantly as the applied voltage was increased. There seems to be a threshold of applied voltage below which mixing is not enhanced by the electric field under the conditions studied. In strong electric fields, the mixing length was less than 150 μm, while in the absence of an electric field, the mixing length was greater than 5,000 μm.
Aqueous speciation of arsenic in sulfuric acid and cupric sulfate solutions
Authors: Casas J. M. , Etchart J. P. , Cifuentes L. 
Published: April 2004

AbstractPhysicochemical data for arsenic speciation calculations, and the development and application of an equilibrium model were determined numerically and experimentally to simulate the speciation of arsenic and copper in aqueous sulfuric acid solutions. Results show that concentrations of dissolved species depended highly on temperature, acidity, and solution concentration. A range of species can be formed, depending on pH and temperature. In acidic solutions, the principal ones are: HSO4−, H+, Cu2+, CuSO4(aq), H3AsO3(aq), and H3AsO4(aq); arsenic ions are present in low concentrations. Association degrees increase with temperature and concentration, the solutes being partially dissociated. Calculations of metal solubilities, pH, and ionic conductivity showed good agreement with experimental data. The model can be applied to study the aqueous speciation in industrial copper hydrometallurgical solutions, as well as to define and to evaluate purification strategies for the treatment of industrial effluents.
Dynamics of isoelectric precipitation of casein using sulfuric acid
Authors: Hofland G. W. , Berkhoff M. R. , Witkamp G. J. , van der Wielen L. A. M. 
Published: April 2004

AbstractThe acid precipitation of casein from skim milk is an interesting and complex operation, as it involves several mechanistic steps occurring simultaneously. Research has focused so far on the influence of static variables such as temperature and final pH on the curd properties. Here the dynamics of the process was investigated. From a characteristic times analysis it was concluded that the most important mechanistic steps in the acid precipitation of casein were acid mixing, aggregation/breakup, and transport in/out of the precipitate particles. Experiments in a fed batch setup using sulfuric acid as the precipitant showed how the precipitation influenced the pH profile and demonstrated the large influence of process variables, such as the acid addition rate, the mixing intensity, and aging time on particle‐size distributions and the release of minerals from the casein.
Chemical processing and micromixing in confined impinging jets
Authors: Johnson Brian K. , Prud'homme Robert K. 
Published: April 2004

AbstractRapid processes such as certain organic reactions or precipitations at high supersaturation require the rapid mixing provided by jet mixers. Micromixing in a confined impinging jets (CIJ) mixer was characterized employing the Damköhler number to correlate processing. A scaling theory for the characteristic micromixing time, proportional to momentum diffusion starting at the Kolmogorov microscale, is shown as sufficient to express the micromixing performance of the CIJ mixer. A recently characterized second‐order competitive reaction set is used as a “chemical ruler” to assign an absolute value to the mixing time in the CIJ mixer. A wide range of characteristic time (320 to 5 ms) is evaluated with hydrochloric acid competing for sodium hydroxide neutralization or 2,2‐dimethoxypropane acid catalyzed hydrolysis. This reaction set was sensitive enough to detect the onset of a turbulent‐like flow at a Re of 90 and was able to demonstrate a decrease in undesired products up to the highest Re tested, 3,800 or a jet velocity of 19 m/s. It represents a significant advancement to the reaction sets and techniques used for previous mixing studies, which are reviewed. Experiments verify the characteristic mixing time in a CIJ mixer scales as the inverse of the jet velocity to the three halves power, and the “mesomixing volume” (the volume over which the majority of flow energy was dissipated) is best approximated as proportional to the internozzle separation cubed. For each of the different jet diameters, chamber diameters and outlet configurations tested, the selectivity of the reaction scaled linearly with the Damköhler number, as determined from the known reaction kinetics and the calculated Kolmogorov diffusion time. The first full characterization is provided of micromixing in impinging jets that allows the prediction of mixing performance, reaction selectivity, and scale‐up criteria.
Thermophoresis of an aerosol sphere parallel to one or two plane walls
Authors: Keh Huan J. , Chen Po Y. 
Published: April 2004

AbstractThe steady thermophoretic motion of a spherical particle in a gaseous medium located in an arbitrary position between two infinite parallel‐plane walls is studied theoretically in the absence of fluid inertia and thermal convection. The Knudsen number is assumed small to describe the fluid flow by a continuum model with a temperature jump, thermal slip, and frictional slip at the particle surface. The imposed temperature gradient is constant and parallel to the two plane walls, which may be insulated or prescribed with the far‐field temperature distribution. The presence of neighboring walls causes two basic effects on the particle velocity: the local temperature gradient on the particle surface is enhanced or reduced by the walls, to speed up or slow down the particle; the walls increase viscous retardation of the moving particle. A boundary collocation method is used to solve the thermal and hydrodynamic governing equations of the system. Numerical results for the thermophoretic velocity of the particle relative to that under identical conditions in an unbounded gaseous medium are presented for various relative thermal conductivity and surface properties of the particle, as well as relative separation distances between the particle and two plates. For thermophoretic motions of a spherical particle parallel to a single plate and on the central plane of a slit, the collocation results agree well with the approximate analytical solutions obtained by a method of reflections. The presence of lateral walls can reduce or enhance the particle velocity, depending on the relative thermal conductivity and surface properties of the particle, the relative particle‐wall separation distances, and the thermal boundary condition at the walls. In general, the boundary effect on thermophoresis is complicated and weaker than that on sedimentation.
Slip velocity and drag law in a liquid‐liquid homogeneous dispersed flow
Authors: Augier Frédéric , Masbernat Olivier , Guiraud Pascal 
Published: April 2004

AbstractLocal measurements of phase velocities and phase fraction in a dense liquid‐liquid homogeneous flow were done based on an application of PIV with a refractive index matching technique. This technique allowed to measure simultaneously both phase velocities and phase fraction fields, as well as the drop mean diameter in a vertical cocurrent flow of n‐heptane dispersed in an aqueous solution of glycerin. The evolution of the relative velocity as a function of the phase fraction (0–0.4) was studied with moderate particle Reynolds numbers (10–100) for drops behaving as spherical rigid particles. A local drag coefficient was derived from these measurements. The calculated mean relative velocity as a function of the local phase fraction with existing classical drag coefficient laws showed significant discrepancies with the measurements overestimated. Thus, the drag coefficient variation rate as a function of the phase fraction was underestimated by the models. The evolution of the normalized velocity (by the terminal velocity) as a function of the phase fraction was predicted correctly with mixture viscosity models in a creeping flow regime.
Hydrodynamic similarity of solids motion and mixing in bubbling fluidized beds
Authors: Sanderson John , Rhodes Martin J. 
Published: April 2004

AbstractSolids motion and solids mixing behavior are important in many fluidized‐bed applications, and yet, in the evaluation of hydrodynamic similarity criteria, relatively few studies have considered these phenomena directly. This work reports on a series of physical experiments involving solids motion and solids mixing undertaken in a number of freely bubbling fluidized beds scaled using the “simplified” scaling criteria. In the first set of experiments, the motion of large neutrally buoyant particles in bubbling beds of a finer material was compared using a simple float‐tracer experiment in beds that were 300 mm, 600 mm, and 1,560 mm in dia. The distribution of circulation times for the float‐tracers was found to scale well across the majority of gas velocities considered when the scaling law was followed, but discrepancies were noted when either the bulk bed material or large tracer particle sizes were mismatched. These results demonstrate that the circulation of large neutrally buoyant particles within the correctly scaled bubbling beds is indeed a “scaleable” phenomenon across a wide range of bed sizes, and this has useful consequences for fluidized‐bed applications involving floating bodies. In the second set of experiments, solids downflow velocities were compared in scaled beds that were 146 mm and 300 mm in dia. using a novel application of electrical–capacitance tomography (ECT). The measured solids downflow velocities showed qualitative agreement with the scaling law and correlations in the literature. The novel tracer technique was only moderately successful in this application, but is worthy of further investigation, as the approach may serve to enhance the capabilities of existing ECT equipment.