bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanism of heat transfer in bubbly liquid and liquid‐solid systems: Single bubble injection
Authors: Kumar Samir , Kusakabe K. , Raghunathan K. , Fan L.‐S. 
Published: June 2004

AbstractLocal instantaneous changes in heat‐transfer coefficients due to the passage of gas bubbles in liquid and liquid‐solid systems are measured. A special heat‐transfer probe is developed and located within the bed to trace the instantaneous local heat‐transfer rate during the passage of single gas bubbles. A microfoil heat flow sensor is attached to a foil heater, and the sensor‐heater probe assembly can accurately measure the heat flux and the surface temperature over a small area. Signals from the sensor are amplified and interfaced with the microcomputer data acquisition system. Simultaneous visualization is performed using a high‐speed video camera and a borescope to establish the correspondence between the visual and sensor signals, and hence relate the local instantaneous hydrodynamics to the heat‐transfer rate. Local heat‐transfer coefficient vs. time traces are analyzed in conjunction with visual signals. The heat‐transfer coefficient exhibits a sharp peak in the bubble wake. In both liquid and liquid‐solid systems, the observed local maximum in heat‐transfer coefficient behind a rising bubble is due to the bubble‐wake‐induced surface renewal. Enhancement in heat transfer due to the bubble increases with the size because of increased surface renewal caused by larger bubble wake and stronger vortices. The local maximum in heat transfer, however, is more pronounced in liquid than in liquid‐solid systems.
Zirconium transport dynamics in the Purex solvent extraction process
Authors: DeMuth Scott F. , Counce Robert M. 
Published: June 2004

AbstractThe primary objective of this study was to develop and validate experimental and mathematical procedures that can be used to determine the fundamental mechanisms of the Purex (plutonium and uranium) extraction process. The mechanisms of this solvent extraction process have been established by classical chemical engineering principles.In the past, modeling of transport phenomena for the solvent extraction of spent nuclear fuel by the Purex process has typically (1) relied solely on diffusion, (2) relied solely on chemical reaction, (3) combined diffusion and chemical reaction in a semiempirical fashion, or (4) combined diffusion and chemical reaction in a nonclassical chemical engineering manner.This study was conducted with the single Purex species, aqueous Zr4+, to simplify the chemistry and modeling mathematics. The validated procedures and model are applicable to most all Purex species.
Uranium adsorption characteristics of a circulating fluidized‐bed adsorber
Authors: Ito Yoshiro , Nakamura Susumu , Shirakashi Masataka , Kanno Masayoshi 
Published: June 2004

AbstractA new type of fluidized bed, called a circulating fluidized‐bed adsorber (CFBA), was developed for processing a large quantity of water with high efficiency. Its fluid mechanical characteristics are reported, as well as recovery of uranium from natural seawater using a small CFBA. Using hydrous titanium oxide, granulated with polyacrylonitrile (PAN‐HTO), as an adsorbent, CFBA ran stably for six days, the period required for the adsorbent to collect a practical amount of uranium. To predict the uranium adsorption performance of a plant‐size CFBA, a numerical model simulating the adsorption kinetics was developed. The result of the numerical calculation by the model was in good agreement with the experimental data.
Modeling and scale‐up of multiwafer LPCVD reactors
Authors: Badgwell Thomas A. , Edgar Thomas F. , Trachtenberg Isaac 
Published: June 2004

AbstractThe deposition of thin films in a hot‐wall multiwafer low‐pressure chemical vapor deposition (LPCVD) reactor is an important unit operation in the manufacture of modern integrated circuits. In this article, our previously published model for the multiwafer LPCVD reactor has been combined with in‐situ temperature measurements to accurately predict the axial and radial film thickness distributions for a polysilicon deposition process. The model describes in detail multicomponent mass transport, the reactor's thermal environment based on in‐situ temperature measurements, and the reactor geometry including inlet and outlet sections as well as downstream injectors. Model predictions were compared with experimental data from two industrial‐scale polysilicon reactors at SEMATECH and from a smaller research reactor. Approximate scale‐up rules for the important special case of larger wafers were derived from the model equations and tested by simulation. The rules compare well with the results from a nonlinear program in which the axial variation of film growth rate was minimized.
Continuous kinetic lumping of catalytic cracking processes
Authors: Cicarelli Paolo , Astarita Gianni , Gallifuoco Alberto 
Published: June 2004

AbstractProcesses, in which a multicomponent mixture of chemically similar compounds undergoes cracking reactions governed by nonlinear kinetics, are analyzed. Cracking reactions in general imply cleavage of chemical bonds between monomeric units. The article focuses on the case of the “uniform” kinetics. To obtain an analytical solution of the kinetic equations describing this process, we present an approach based on a continuous description of the mixture. The resulting nonlinear integrodifferential equation has been linearized by a warped time scale, and a formal solution has been obtained via a regular perturbation method. The perturbation parameter is twice the inverse of the initial average number of monomeric units in excess of the minimum number that can be cracked by the reactions considered.
Global volumetric phase fractions in horizontal three‐phase flows
Authors: Lahey Jr. R. T. , Açikgöz M. , França F. 
Published: June 2004

AbstractGeneralized drift‐flux expressions for horizontal three‐phase (gas/water/oil) conduit flows have been derived. A detailed set of phasic volume fraction data were measured for the various flow regimes observed in air/water/oil flows. This article shows that drift‐flux techniques can be used to predict the phasic volumetric fractions for horizontal three‐phase flows, such as those which may occur in off‐shore oil well lines.
Effect of column inclination on the performance of three‐phase fluidized beds
Authors: Del Pozo M. , Briens C. L. , Wild G. 
Published: June 2004

AbstractInclining a fluidized bed column by as little as 1.5 degrees greatly affects the bed characteristics. The bed contracts, the particle‐liquid mass‐transfer and heat‐transfer coefficients increase by up to 30%, and the gas‐liquid mass‐transfer coefficient can either be increased by up to 15% or decreased by up to 20%.
Creeping axisymmetric flow around a solid particle near a permeable obstacle
Authors: Michalopoulou A. C. , Burganos V. N. , Payatakes A. C. 
Published: June 2004

AbstractThe hydrodynamic interaction between a solid particle and a porous obstacle, both of spherical shape, the former moving slowly along the line of their centers and the latter held stationary in an external axisymmetrical flow field, is analyzed. Owing to the linearity of the creeping motion equations and the boundary conditions, this general problem can be decomposed into two simpler problems: I. the motion of the solid sphere relative to the porous one in a fluid at rest; II. an axisymmetrical streaming flow past the two spheres held stationary. The solution to problem II requires further decomposition into the problem of undisturbed flow in the absence of the two spheres and that of the two spheres following each other in a fluid at rest (problem III). The above component flow problems are solved analytically using the stream function formulation in bispherical coordinates. The flow and pressure fields, and the drag forces exerted on both spheres are determined as functions of the permeability, the slip factor, the gap length, and the relative size of the two spheres. In problem I it is found that the drag force exerted on the solid particle increases with decreasing permeability for any value of the gap length. The opposite behavior is observed in problems III (and II). In all cases, however, the drag force exerted on the porous sphere increases as the permeability decreases for any separation distance. In the region of very small separation distances the drag forces on the two spheres in problem I attain a weak maximum at a critical gap length which is a function of the obstacle permeability and the sphere size ratio. The behavior of the drag forces in problems II (and III) is more complicated and depends strongly on the sphere size ratio. The effects of the slip velocity and the particle to streaming velocity ratio (in the composite problem) on the values of the drag forces are also examined.
Fluid flow in compressible porous media: I: Steady‐state conditions
Authors: Jönsson K. Ann‐Sofi , Jönsson Bengt T. L. 
Published: June 2004

AbstractThis is the first of two articles dealing with fluid flow in compressible porous media. In this article a model describing fluid flow and pressure‐induced variations in porosity under stationary conditions is developed. In a forthcoming article the dynamic behavior during filtration and wet pressing of compressible porous media are presented.Fluid flow through rigid porous media is generally described by Darcy's law. The corresponding expression for compressible materials is derived in this article. This expression, the steady‐state flow (SSF) equation, allows the steady‐state flow to be easily calculated, either numerically, or by using the approximative analytical solutions that are also presented here. In the SSF equation optional empirical and/or theoretical permeability and compressibility relationships may be combined. Further, a new compressibility model which also applies for viscoelastic materials is presented. The influence of the compressibility of the material and the influence of precompression is illustrated.
Unique adsorption properties and potential energy profiles of microporous pillared clays
Authors: Baksh M. S. A. , Yang R. T. 
Published: June 2004

AbstractThe adsorption isotherms of O2, N2, CH4, CO2, SO2, and NO on five pillared clays (Zr, Al, Cr, Fe, and Ti‐PILCs) are measured. The equilibrium selectivity of CH4/N2 on Al‐PILC is greater than 5.0, which exceeds all known sorbents by a large margin. In addition, high SO2/CO2 equilibrium selectivities are observed on these pillared clays. The sorption characteristics of these pillared clays (PILCs) exhibit characteristic trends that are better understood with the aid of the potential energy profiles. A new semi‐empirical approach is presented for the calculations of the potential energy profiles of PILCs. This approach requires the adsorption isotherms and an isotherm equation that accounts for the structural heterogeneity of the adsorbents. A comparison of the energy profiles obtained using the semi‐empirical approach with the corresponding results obtained via the Kirkwood‐Muller formalism, where only dispersion forces are taken into account, provides a measure of the importance of the electrostatic forces in the sorption characteristics of these PILCs. Sizable differences are observed for the potential energy profiles, indicating that the electrostatic forces are not negligible, and can significantly enhance the adsorption potential, resulting in large increases in the amounts adsorbed on these PILCs.
Magnetic determination of average catalyst temperatures in fluidized beds
Authors: Cale Timothy S. , Merson J. A. 
Published: June 2004

AbstractA magnetic method to measure the time and spatial average temperature of supported nickel catalysts in fluidized beds is detailed. It is an extension of a magnetic method developed in this laboratory to study fixed beds. The RMS output voltage of an AC permeameter is used to follow changes in the magnetic moment, hence temperature, of the catalyst upon starting or stopping ethane hydrogenolysis. The theory of the thermometry in fluidized beds is detailed and the observed RMS output voltage vs. time traces for typical experiments are explained. Simulations indicate that signals generated by the moving particles are largely averaged out, since the direction of the magnetic moment of each catalyst particle follows the applied field and is independent of movement. Filtering in the frequency domain can be used to further reduce the effects of particle movement. Calibrations needed to convert AC permeameter output voltage changes to changes in sample temperature during experiments on two distinctly different fluidized beds are the same as for the respective fixed beds. Depending somewhat on the sample moment, the average solid temperature can be determined with a repeatability of a few tenths of a degree.
A hybrid neural network‐first principles approach to process modeling
Authors: Psichogios Dimitris C. , Ungar Lyle H. 
Published: June 2004

AbstractA hybrid neural network‐first principles modeling scheme is developed and used to model a fedbatch bioreactor. The hybrid model combines a partial first principles model, which incorporates the available prior knowledge about the process being modeled, with a neural network which serves as an estimator of unmeasured process parameters that are difficult to model from first principles. This hybrid model has better properties than standard “black‐box” neural network models in that it is able to interpolate and extrapolate much more accurately, is easier to analyze and interpret, and requires significantly fewer training examples. Two alternative state and parameter estimation strategies, extended Kalman filtering and NLP optimization, are also considered. When no a priori known model of the unobserved process parameters is available, the hybrid network model gives better estimates of the parameters, when compared to these methods. By providing a model of these unmeasured parameters, the hybrid network can also make predictions and hence can be used for process optimization. These results apply both when full and partial state measurements are available, but in the latter case a state reconstruction method must be used for the first principles component of the hybrid model.
Inaccessible pore volume formation during sulfation of calcined limestones
Authors: Sotirchos Stratis V. , Zarkanitis Solon 
Published: June 2004

AbstractA mathematical model for transport, reaction and structure evolution in gas‐solid reactions with solid product is used to analyze a set of experimental data for the sulfation of calcines derived from three stones of high (>95%) calcium carbonate content. The analysis of the experimental data places emphasis on the formation of inaccessible pore space and its effects on the efficiency of calcined limestones as sorbents for SO2 removal. Our results show that the ultimate capacity of calcined limestones for SO2 uptake is influenced strongly by the formation of inaccessible pore space, which in turn is determined by their pore‐size distribution and the connectivity (degree of interaction) of the pores. For the three specimens used in our study, the ultimate conversion (measured experimentally) increased and the inaccessible pore space formed during pore closure (predicted by the mathematical model) decreased with decreasing grain size in the rock precursors, indicating that the morphological texture of the precursors plays a major role in determining the topological features of the pore structure of the resulting calcines.
Analysis of effective axial diffusion in branching networks
Authors: Federspiel William J. 
Published: June 2004

AbstractDiffusional transport in a network of branching conduits is considered. The branching network is idealized as an ensemble of identical branching segments. Starting with the general species continuity equation, multiscale perturbation analysis is used to derive a one‐dimensional, effective transport equation for species concentration. The macrotransport equation contains an effective diffusion coefficient, D*, which arises naturally from the analysis. D* can be computed from a local diffusion problem posed on an individual branching segment of the ensemble network. The local relations defining D* bear clear similarity to their counterparts for transport in spatially periodic porous media. Although this study was originally directed toward describing gas diffusion in the peripheral airspaces of the lung, the results provide insight for other transport processes occurring in branching networks.
Modeling the formation of boron carbide particles in an aerosol flow reactor
Authors: Xiong Yun , Pratsinis Sotiris E. , Weimer Alan W. 
Published: June 2004

AbstractThe formation of submicron crystals of boron carbide (B4C) by coagulation and sintering by the rapid carbothermal reduction of intimately mixed carbon‐boron oxide powders in an aerosol flow reactor at temperatures above the boiling point of boron oxide is investigated. High heating rates (105K/s) force rapid evaporation of boron oxide and suboxides from the precursor powder, resulting in its rupture and formation of boron carbide molecular clusters that grow to macroscopic particles by coagulation. Consequently, the formation and growth of B4C particles are described by simultaneous interparticle collision and coalescence using a two‐dimensional particle‐size distribution model that traces the evolution of both size and shape characteristics of the particles through their volume and surface area. In addition to the coagulation term, the governing population balance equation includes a coalescence contribution based on B4C sintering law. The predicted evolution of the two‐dimensional particle‐size distribution leads to a direct characterization of morphology as well as the average size and polydispersity of the powders. Furthermore, model predictions of the volume and surface area of boron carbide particles can be directly compared with experimental data of B4C specific surface area and an effective sintering rate of B4C is deduced.
Prediction of the effective diffusivity in pore networks close to a percolation threshold
Authors: Zhang Lin , Seaton Nigel A. 
Published: June 2004

AbstractThe problem of diffusion in pore networks that are close to a percolation threshold is considered. Such networks arise: if the network is poorly connected; if the diffusing molecules are of a comparable size to the pores so that the fraction of the network accessible to the molecules is close to the percolation threshold; and in solids with multimodal pore‐size distributions in which the pores belonging to the largest mode form a network close to the percolation threshold. We have investigated diffusion in such networks, using a new method in which the mass balance equations for diffusion on a regular lattice are solved using a Monte Carlo approach, coupled with a renormalized effective medium approximation. The method is accurate both close to and far from the percolation threshold, and is fast enough for routine calculations, such as in catalyst design applications.
Chemically active liquid membranes in inorganic supports for metal ion separations
Authors: Yi Jongheop , Tavlarides Lawrence L. 
Published: June 2004

AbstractCeramic membranes with pores filled with organic chelation acid show promise as the basis for inorganic membrane separator units for metal ion separations from dilute aqueous streams. The performance of such membranes in disk geometry is evaluated experimentally for a model system. The proposed model describes the metal ion flux through the membrane, and a batch or continuous operated separator using these membranes is analyzed. Copper ion fluxes through α‐alumina/silica disks impregnated with 2‐hydroxy‐5‐nonylacetophenone oxime were determined from a rotating diffusion cell apparatus for feed solution concentration of copper 0.03 mol/L, feed solution pH 3, strip solution pH of 0.3, and rotation speed of 130 rpm. Flux values range from 5.4 × 10−6 to 2.2 × 10−5 mol/cm2·h and compare well with the reported values for metal ion transport through polymeric supporting membranes (Largman and Sifniades, 1978; Babcock et al., 1981; Teramoto and Tanimoto, 1983; Kojima and Miyauchi, 1981).The proposed steady‐state flux model describes the metal flux through chemically active liquid membranes in inorganic supports. The model includes film resistance to mass transfer in both liquid films, complexation and stripping reactions at the liquid‐liquid interface in the membrane pores on both surfaces of the membrane, and metal ion/complex diffusion through the membrane. Separately designed experiments were executed using a precise pH‐static technique to obtain the physical and chemical parameters of diffusivities, kinetic coefficients and equilibrium coefficients. Calculated fluxes compare well with experimentally determined values from batch experiments (average standard error, 11%).The proposed lumped parameter linear kinetic rate model for the surface reaction rates interprets the kinetic data for the copper chelation reaction. The model is based on a multistep reaction mechanism and has the following form for the extraction reaction for the above mentioned conditions:

A similar expression is presented for the strip reaction.An analytical solution for the mathematical model predicts the performance of the chemically active liquid membrane reactor for the batch or continuous operation of the rotating diffusion cell. Calculated results describe expected trends and agree well with the experimental results.
Brownian diffusion of hard spheres at finite concentrations
Authors: Selim M. Sami , Al‐Naafa M. A. , Jones M. C. 
Published: June 2004

AbstractWe investigated the effect of concentration on the Brownian diffusion of uncharged rigid spheres. Monosize silica spheres were prepared according to the method of Stöber (1968). The particles were sterically stabilized by chemisorption of stearic alcohol at their surface by the method developed by van Helden (1981).Particle radius was 14.5 nm from electron micrographs of the coated particles. Osmotic pressure measurements of the sterically stabilized particles dispersed in cyclohexane showed that the particles behaved as hard spheres. The measurements agreed well with predictions from the Carnahan‐Starling equation over the concentration range 0.0458 < ϕ < 0.37 where ϕ is the volume fraction of the particles in the suspension. Viscosity measurements of silica dispersions were made over the concentration range 0 < ϕ < 0.25. The relative viscosity over the range 0 < ϕ < 0.2 was fitted by ηr = 1 + 2.4ϕ + 7.1ϕ2. The coefficients 2.4 and 7.1 in this equation are in good agreement with the theoretical values of 2.5 and 6.2 obtained by Einstein(1906) and Batchelor(1977), respectively. The Brownian diffusion coefficient of the particles dispersed in cyclohexane was measured over the concentration range 0.0055 < ϕ < 0.248 using Taylor's hydrodynamic stability method. A laser fiber‐optic system was used to measure the transient concentration profile along the capillary as indicated by a fluorescent dye. This technique offers the advantage of being direct and nonintrusive. The experimental diffusivity data were found to be well described by the generalized Stokes‐Einstein equation(Batchelor, 1976) over the entire concentration range studied.