bluuebunny/crossref_metadata_2025_split huggingface dataset:
A bubbling fluidization model using kinetic theory of granular flow
Authors: Ding Jianmin , Gidaspow Dimitri 
Published: June 2004

AbstractDetailed knowledge of solids circulation, bubble motion, and frequencies of porosity oscillations is needed for a better understanding of tube erosion in fluidized bed combustors. A predictive two‐phase flow model was derived starting with the Boltzman equation for velocity distribution of particles. The model is a generalization of the Navier‐Stokes equations of the type proposed by R. Jackson, except that the solids viscosities and stresses are computed by simultaneously solving a fluctuating energy equation for the particulate phase. The model predictions agree with time‐averaged and instantaneous porosities measured in two‐dimensional fluidized beds. Observed flow patterns and bubbles were also predicted.
Correlation of aqueous Henry's constants from 0°c to the critical point
Authors: Harvey Allan H. , Sengers J. M. H. Levelt 
Published: June 2004

AbstractRecent theoretical results (Japas and Levelt Sengers, 1989) for the temperature dependence of Henry's constant near the solvent's critical point are used to obtain a linear expression which, for aqueous solutions of nonpolar gases, fits experimental Henry's constant data at temperatures from water's critical point down to roughly the normal boiling point. A small correction with only one additional adjustable parameter extends the correlation to 0°C. The final result is a three‐parameter correlation, covering the entire range of temperatures, which fits the available data as well as or better than existing four‐parameter empirical expressions and better than a recently proposed three‐parameter expression. Since the correct near‐critical behavior is built in, the new correlation should be especially useful for estimating Henry's constants in systems where little or no data exist at high temperatures. Fitted parameters are given for ten nonpolar gases in H2O and six nonpolar gases in D2O.
Study of restricted diffusion in porous catalysts by NMR
Authors: Cheng W. C. , Luthra N. P. , Pereira C. J. 
Published: June 2004

AbstractThe diffusion of 1,3,5 tri‐tert‐butylbenzene (TTB) into cylindrical γ‐alumina extrudates of varying micropore diameter and macropore volume has been studied by NMR spectroscopy. The proton NMR signal of the methyl proton of TTB in the micropores of the alumina extrudate was found to be well resolved and shifted upfield relative to that in the bulk liquid by 0.55 ppm. The area under the shifted peak is proportional to the liquid concentration of TTB in the micropores. The change in the intensity of this peak as a function of time and measurements of the amount of TTB absorbed on the surface alumina at equilibrium were used to calculate the effective diffusivity of TTB in each extrudate. Measured values of the effective diffusivity are in reasonable agreement with predictions using correlations in the literature. These observations suggest a new method for measuring the liquid‐phase effective diffusivity in porous materials.
Elastohydrodynamics of blade coating
Authors: Pranckh F. R. , Scriven L. E. 
Published: June 2004

AbstractBlade coating is the most common method of coating paper, and it is applied in coating magnetic suspensions and adhesives. Typically, the blade's upstream edge is clamped into a rigid holder so that the blade and substrate form a converging wedge. The translating substrate drags liquid into the wedge, where liquid forces develop and deflect the elastic blade, but it is loaded externally to counteract the deflection. Liquid dragged past the blade and thus the coating thickness depend on the elastohydrodynamic interaction among blade, liquid, and loading. Shell theory and lubrication flow theory describe the interaction by means of differential equations that are shown to be equivalent to Saita and Scriven's (1985) earlier formulation but that lead to a computationally more efficient analysis. Predictions computed agree with those of the earlier formulation and with experiments. Moreover, the new predictions illustrate effects of normal force loading and broaden the theory of blade coating.
Axial dispersion for turbulent flow with a large radial heat flux
Authors: Beckman Lawrence V. , Law Victor J. , Bailey Raymond V. , Von Rosenberg Dale U. 
Published: June 2004

AbstractIn 1954, G. I. Taylor derived an expression for an apparent axial dispersion coefficient for mass transfer in turbulent flow under the assumption of no mass transport between the tube wall and the fluid inside the tube. Taylor's expression has been verified in a number of experimental efforts for both mass and heat transfer.This work extends the results of Taylor to the case where there is a significant transport of heat from the tube wall to the fluid in the tube, such as in a double‐pipe heat exchanger. Using an analysis similar to Taylor's, it is shown that the apparent axial dispersion coefficient is about one order of magnitude larger when a large radial gradient is present. Experimental data on a double‐pipe heat exchanger show significantly improved correspondence with a dispersion‐based model of the system when the larger dispersion coefficients are used.
Dynamics of pulsing flow in trickle beds
Authors: Dankworth David C. , Kevrekidis I. G. , Sundaresan S. 
Published: June 2004

AbstractA macroscopic model of two‐phase flow in packed beds, based on the volume‐averaged equations of motion for the gas and liquid phases, was analyzed in an attempt to understand the onset and evolution of fully‐developed pulsing flow in trickle beds. By assuming that solutions take the form of waves travelling at constant speed, periodic solutions to these equations are found which can be associated with long‐time, asymptotic behavior of pulses in a very long bed. Families of one‐dimensional waves which exist at a particular set of mass fluxes can be characterized by infinite period bifurcations in the travelling wave frame. We numerically follow these bifurcations as the fluxes are changed, generating bifurcation diagrams for the original model. The results predict that properties of one‐dimensional pulses should correlate with the total superficial velocity through the bed. A hysteresis in the trickling‐pulsing transition is also predicted.
Collocation analysis of a boundary‐layer model for crossflow fractionation trays
Authors: Young Thomas C. , Stewart Warren E. 
Published: June 2004

AbstractA nonequilibrium model for fractionation trays with lateral dispersion is analyzed by a collocation method. Mobile‐interface turbulent boundary‐layer theory is used to describe the local heat and mass transfer rates with allowance for vapor superheat, liquid subcooling, and net molar transfer between the phases. Multicomponent transport is incorporated by a linearized matrix method. Numerical integration of the gradients through the tray permits use of local flows and states, as well as local phase equilibrium expressions. A collocation scheme solves the model efficiently; two grid points normally suffice to represent a tray. The model contains just two adjustable coefficients, a00 and Pe; the dependence of these on tray geometry and hydrodynamics remains to be investigated.
Hydrodynamics of gas‐agitated liquid‐liquid dispersions
Authors: Hatzikiriakos Savvas G. , Gaikwad Rajendra P. , Nelson Philip R. , Shaw John M. 
Published: June 2004

AbstractGas‐agitated liquid‐liquid dispersions arise in applications as diverse as direct hydrogenation processes for bitumen and coal, and the manufacture of iron and steel. The transfer of gas‐phase constitutents to the dispersed liquid phase and/or elution of dispersed‐phase drops have been identified as potential limiting phenomena in these processes. Consequently, mean drop size and drop size distribution are key design variables. In this paper, the impact of gas flux and the physical properties of dispersed‐phase constitutents on the steady‐state size distribution of liquid drops in lean liquid‐liquid dispersions is quantified. The physical properties of the dispersed phase are shown to have a significant impact on drop size and drop‐size distribution at low gas fluxes. Sauter mean drop size is correlated using theoretical models for drop break‐up and coalescence. All results are compared with stirred tank analogues.
Stability of multilayer extrusion of viscoelastic liquids
Authors: Anturkar N. R. , Papanastasiou T. C. , Wilkes J. O. 
Published: June 2004

AbstractA linear stability analysis of multilayer plane Poiseuille flow of Oldroyd‐B liquids with shear rate dependent viscosities is performed for an arbitary number of layers. Asymptotic solutions at long wavelengths and numerical solutions at wavelengths of O(1) are obtained for two‐dimensional infinitesimal disturbances. The asymptotic solutions are identical for viscoelastic and Newtonian liquids in two‐ and three‐layer flows, except for nearly geometrically symmetric configurations in three‐layer flows. Multilayer flows of viscoelastic liquids can be stable at all wavelengths; thus, operating diagrams of stable flows can be constructed. Symmetric and nearly symmetric configurations in three‐layer flows are unstable when the core layer is more viscous than the cuter layers. For highly elastic liquids, stability is not influenced by elasticity, whereas shear thinning always destabilizes the flow. The analysis provides guidelines to avoid interfacial instabilities, which originate inside dies of multilayer extrusion.
A kinetic model for industrial gas‐phase ethylene copolymerization
Authors: McAuley K. B. , MacGregor J. F. , Hamielec A. E. 
Published: June 2004

AbstractA dynamic kinetic model describing gas‐phase olefin copolymerization using a multiple active site Ziegler‐Natta catalyst is presented. This model is capable of predicting production rate, molecular weight, and copolymer composition changes observed in an industrial reactor. The model also explains how broad molecular weight distributions and bimodal copolymer compositions can occur as has been observed for commercial linear polyethylenes.
RF plasma synthesis of amorphous AIN powder and films
Authors: David M. , Babu S. V. , Rasmussen D. H. 
Published: June 2004

AbstractAmorphous powder and thin films of aluminum nitride (AIN) are deposited in a parallel‐plate RF plasma reactor starting from trimethylaluminum (TMA) and ammonia. Film deposition is favored at lower pressures and NH3/TMA ratios; particle deposition occurs under higher pressures and NH3/TMA ratios. Electron microscopy, x‐ray diffraction, IR spectroscopy, and UV reflectance measurements are used for product characterization. Films of AIN grown at 250°C are transparent, pure, and have high UV reflectivity. AIN powder is amorphous and has a particle size of 10–20 nm and surface area of about 85 m2/g. Amine impurities present in the as‐deposited powder are removed by heat treatment at 600°C. The IR spectra of as‐deposited powders do not show the characteristic Al‐O bonding peak found in powders deposited by other methods.
Effective thermal conductivity of composites containing spheroidal inclusions
Authors: Lu Shih‐Yuan , Kim Sangtae 
Published: June 2004

AbstractThe effective thermal conductivity of composite materials containing perfectly‐conducting, perfectly‐aligned, spheroidal inclusions has been computed to O(c2), where c is the volume fraction of the inclusions, by incorporating two‐particle interactions in a rigorous fashion. Relevant two‐particle problems were solved by boundary collocation and method of reflections in the near and far fields, respectively. Our results for the effective thermal conductivity are rigorous extensions of Maxwell's theory in the form of an expansion in small cℓα, where ℓ is the spheroid aspect ratio (α = 1 for oblate and α = 2 for prolate spheroids). The influence of microstructure was examined with two ad hoc model distribution functions: 1. a uniform distribution and 2. a stretched hard‐sphere pair distribution. The latter yielded superior results over a greater range of c, as judged by comparisons with Willis' (1977) bounds developed from variational methods.
Self‐propagating solid‐solid noncatalytic reactions in finite pellets
Authors: Varma Arvind , Cao Giacomo , Morbidelli Massimo 
Published: June 2004

AbstractThe method of self‐propagating high‐temperature synthesis (SHS) can be utilized to synthesize certain advanced ceramic materials, such as metal carbides, borides and silicides, directly from the elements in powder form. The method involves mixing the powders, preparing pellets from the mixture, and igniting one end of the pellet. Owing to high exothermicity of the reactions, a combustion wave can propagate through the pellet. The influence of processing conditions on propagation of the combustion wave is investigated extensively in this modeling study for pellets of finite length. It is shown that unlike infinitely long systems, the combustion wave for a finite pellet does not propagate in constant pattern. It is also shown that radiative heat losses play a major role in SHS, while convective heat losses are not relatively important.
Bouncing motions of liquid drops between tilted parallel‐plate electrodes
Authors: Mochizuki T. , Mori Y. H. , Kaji N. 
Published: June 2004

AbstractThe paper reports on experimental and analytic studies on translational motions of liquid drops in an immiscible, dielectric liquid confined by a pair of tilted parallel‐plate electrodes, across which a steady electric field is being applied. With an increase of the strength of the field, drops begin to bounce back and forth between the electrodes while falling down along the axis of tilt of the electrodes. The bouncing motions are found to be predictable with a reasonable accuracy by using a simple model constructed within the framework of conventional fluid mechanics and electrostatics.
On‐line state and parameter Identification of positive photoresist development
Authors: Carroll Thomas A. , Ramirez W. Fred 
Published: June 2004

AbstractThe development phase of the optical photolithography process has long been considered the most crucial, as it is the final image‐forming step. Process monitoring methods have focused primarily on end point detection and have not used other inferable on‐line information. This paper examines the use of mathematical models in conjunction with on‐line development penetration data to determine process changes. An on‐line sequential parameter identification scheme is used to calculate a current rate parameter value for the development model, and a Kalman filter is used to reduce erroneous observations caused by measurement noise. A powerful development monitor system results from the combination of real‐time data, and on‐line parameter and state estimation theory.
Two‐dimensional analysis of a dust explosion
Authors: Aldis David F. , Gidaspow Dimitri 
Published: June 2004

AbstractPeak pressures and propagation velocities for dust explosions have for many years been studied as a function of particle concentration. There are, however, no multidimensional models in the literature which can be used to compute local pressures and impluses needed to access the potential damage caused by a detonation.A two‐dimensional two‐phase hydrodynamic computer model was developed in this study to predict pressure propagation in dust explosions. Two cases of detonation of dispersed powders injected into a rectangular cavity were analyzed. The ignition of an idealized, uniformly distributed powder in a box produced a pressure peak that propagated through the powder with an increasing amplitude from the ignition source at one corner. The computational maximum pressure agreed with an approximate calculation of the Chapman‐Jouguet pressure. The pressure propagation for the more realistic nonuniform initial particle distribution produced several peaks not unlike those observed on the ground below the detonation. Computed pressures agreed roughly with the measured average pressure peaks.
Displacement effect in multicomponent chromatography
Authors: Gu Tingyue , Tsao George T. , Tsai Gow‐Jen , Ladisch Michael R. 
Published: June 2004

AbstractThe study of interference effects is of fundamental importance in understanding multicomponent chromatography. In this work, a displacement effect is examined and shown to be able to explain the dominating interference effects in three major modes of chromatography—frontal, elution, and displacement—involving competitive isotherms. It is concluded that the concentration profile of a component usually becomes sharper due to the displacement effect from another component, while the concentration front of the displacer is usually diffused. Five factors that escalate the displacement effect in multicomponent elution were investigated. A binary elution with a competing modifier in the mobile phase was also discussed. This study was carried out using computer simulations based on a general nonlinear multicomponent rate equation model that considers axial dispersion, external mass transfer, intraparticle diffusion, and Langmuir isotherms. The use of the general model helps the visualization of the multicomponent interactions in chromatography under mass transfer conditions.
Percolation theory of creation and mobilization of foams in porous media
Authors: Rossen W. R. , Gauglitz P. A. 
Published: June 2004

AbstractA percolation model of foam mobilization in porous media is developed. This model indicates that there is a minimum pressure gradient or, equivalently, a minimum gas velocity required to initiate mobilization of foam. As a result, for most foam enhanced oil recovery processes, where the surface tension is not low, deep foam penetration depends on propagation of foam formed at a high pressure gradient near the well. Low surface tension makes mobilization of CO2 foams feasible, however, at pressure gradients found throughout much of the formation in a typical field application. The theory further predicts, and data confirm, that the minimum velocity for foam mobilization during steady flow of liquid and gas decreases as injected liquid volume fraction increases. The theory suggests a better strategy for foam generation: alternate injection of small slugs of liquid and gas.
Analysis of bioproduct separation using gel‐enclosed adsorbents
Authors: Nigam Somesh C. , Siahpush Ali R. , Wang Henry Y. 
Published: June 2004

AbstractThe concept of “gel‐enclosed” adsorbents was recently introduced for whole fermentation broth processing. The term “gel‐enclosed adsorbents” in this paper refers to small adsorbent particles such as the ones used in affinity or ion‐exchange chromatography enclosed within a protective, spherical, semipermeable gel barrier. The barrier can be in the form of an entrapment matrix where a porous gel matrix in itself contains entrapped adsorbent particles, or in the form of an encapsulating membrane where an aqueous spherical core containing the adsorbent particles is enclosed by a gel membrane. Both experimental and theoretical analyses were carried out to elicit a more fundamental view of the diffusion and adsorption phenomena occurring within these forms of adsorbents. Furthermore, the effective porosity of the gel matrix and the effective diffusivities of the species being separated, as well as their adsorption behavior combined result in what is here termed “kinetic selectivity”.
Polymer melt devolatilization mechanisms
Authors: Albalak Ramon J. , Tadmor Zehev , Talmon Yeshayahu 
Published: June 2004

AbstractScanning electron microscopy (SEM) was used to study the mechanism of falling‐strand devolatilization of polymer melts. Polystyrene and low‐density polyethylene were enriched with styrene and hexane, respectively, and were subsequently extruded as thin strands at various conditions. The polymer strands were exposed to superheat conditions for preset periods of time ranging from tenths to tens of seconds. The strands were then frozen, fractured, and studied by SEM. Devolatilization was found to proceed through a blistering mechanism, both on the surface of the strands and on the surfaces of volatile bubbles formed within the core of the melt. At all volatile concentrations surface blistering and foaming preceded bubble growth in the core, and occurred before the strands foamed. A mechanism for the observed polymer melt devolatilization is proposed.
Prediction of liquid circulation in viscous bubble columns
Authors: Rice Richard G. , Geary Nicholas W. 
Published: June 2004

AbstractA new theory to predict liquid circulation was derived and compared with applicable literature data. A single dimensionless group, ε(gRd2/v2c), is shown to control mixing intensity under low‐viscosity conditions, but two separate groups (ε and gRd2/v2c) are necessary for viscous systems. Closure was accomplished using the Prandtl model for Reynolds stress. Locally varying mixing length was taken to be proportional to bubble size and bubble concentration. The model was constructed based on the premise that two distinct zones exist: a mainly turbulent core joined to a thin viscous wall layer.
Feedforward/feedback control of multivariable nonlinear processes
Authors: Daoutidis Prodromos , Soroush Masoud , Kravaris Costas 
Published: June 2004

AbstractThis paper concerns general MIMO nonlinear processes, whose dynamic behavior is described by a standard state‐space model of arbitrary order, including measurable disturbances. The concept of relative order of an output with respect to an input, extended to include disturbance as well as manipulated inputs, is generalized in a MIMO context and it is used to obtain a characterization of the dynamic interactions among the input and the output variables. A synthesis formula is calculated for a feedforward/state feedback control law that completely eliminates the effect of the measurable disturbances on the process outputs and induces a linear behavior in the closed‐loop system between the outputs and a set of reference inputs. The input/output stability and the degree of coupling in the closed‐loop system are determined by appropriate choice of adjustable parameters. A MIMO linear controller with integral action completes the feedforward/feedback control structure. The developed control methodology is applied to a continuous polymerization reactor and its performance is evaluated through simulations.
Stochastic analysis of a three‐phase fluidized bed: Fractal approach
Authors: Fan L. T. , Neogi D. , Yashima M. , Nassar R. 
Published: June 2004

AbstractThree‐phase fluidized beds have played important roles in various areas of chemical and biochemical processing. The characteristics of such beds are highly stochastic due to the influence of a variety of phenomena, including the jetting and bubbling of the fluidizing medium and the motion of the fluidized particles. A novel approach, based on the concept of fractals, has been adopted to analyze these complicated and stochastic characteristics. Specifically, pressure fluctuations in a gas‐liquid‐solid fluidized bed under different batch operating conditions have been analyzed in terms of Hurst's rescaled range (R/S) analysis, thus yielding the estimates for the so‐called Hurst exponent, H. The time series of the pressure fluctuations has a local fractal dimension of dFL = 2 − H. An H value of ½ signifies that the time series follows Brownian motion; otherwise, it follows fractional Brownian motion (FBM), which has been found to be the case for the three‐phase fluidized bed investigated.