bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rheological properties of mixed polysaccharides and polysaccharide‐thickened emulsions
Authors: Pal Rajinder 
Published: June 2004

AbstractSteady flow and viscoelastic properties of mixed‐polysaccharides and mixed‐polysaccharide‐thickened oil‐in‐water emulsions are investigated with a cone‐and‐plate system using a controlled‐stress rheometer. The mixed‐polysaccharide system studied is xanthan gum and guar gum. The rheological properties of the mixed‐polysaccharide systems exhibit strong synergistic effects. For a total polysaccharide concentration of 0.75 wt. % investigated, the synergistic effect is maximum at a xanthan:guar ratio of 15:85. The oil‐in‐water emulsions, prepared from a mixed‐polysaccharide system as the suspending medium, are strongly shear thinning and highly viscoelastic in nature. The rheological parameters such as apparent viscosity, storage, and loss moduli increase with an increase in the oil concentration of the emulsion.
Extraction of spray particles with supercritical fluids in a two‐phase flow
Authors: Wagner Henning , Eggers Rudolf 
Published: June 2004

AbstractA new process for extractive separation with supercritical fluids is described. It is characterized by mixing a liquid feed with a dense gas in a special mixing device and the formation of spray particles when this mixture is injected into an extraction zone where the fluid phase is loaded with the extracts. By dividing the extraction into two process steps, mixing and loading, it is possible to adjust the devices and apparatuses for different media. For example, a static mixer or a fluid‐assist atomizer can be used as mixing devices. Since the viscosity behavior of the mixture and the surface tension in dense gases are important for the formation of spray particles, carbon dioxide was measured at pressures up to 70 MPa and the geometry of the extraction zone was optimized by residence times and fluid dynamics.Two different materials were tested in an apparatus on a semiindustrial scale with different mixing devices and extraction zones. By measuring fluid loading in the extraction zone, the mass‐transfer parameter of a mathematical extraction model could be adapted. The model considers particle formation in the mixing zone, the fluid dynamic in the loading zone, and the mass transfer between spray particles and fluid phase. Calculated concentration profiles make it possible to determine the residence time and the size of the extraction zone for given geometries and fluid dynamics.
New decline pattern of filtrate flux in cross‐flow microfiltration of dilute suspension
Authors: Murase Toshiro , Ohn Than 
Published: June 2004

AbstractThe cross‐flow microfiltration flux is assumed to fall smoothly with a decreasing slope from startup to the steady state. Under actual operating conditions beyond a critical level, however, an anomalous decline pattern arises; initially cross‐flow medium filtration occurs and then thin‐cake filtration. At the earlier stage, fine particles in polydispersed suspensoids are filtered out on the surface of the membrane and/or captured within the latter, clogging the membrane pores gradually. After the membrane surface is covered by the deposit, further filtration occurs by the buildup of filter cake on the initial deposit. Among the many operating variables, three major controlling factors for the earlier stage are confirmed: solids concentration, relative size of solids and pores, and relative force of sweeping and capturing of suspensoids. Because suspended solids are separated by medium‐ and cake‐law filtration in a series, a method for evaluating the time dependence of flux with the new pattern is derived. Reliable flux analysis is achieved for the transient flux of the dilute suspension forming a low compressibility fouling layer, which helps understand efficient flux performance.
Hollow‐fiber gas‐membrane process for removal of NH3 from solution of NH3 and CO2
Authors: Qin Yingjie , Cabral Joaquim M. S. , Wang Shichang 
Published: June 2004

AbstractA hollow‐fiber supported gas membrane process for the separation of NH3 from aqueous solutions containing both NH3 and CO2 was investigated theoretically and experimentally. A lumen laminar flow and radial diffusion model was applied to calculate the membrane wall transfer coefficient from the data stripping a single volatile component, NH3 or CO2, from their individual aqueous solutions. Influence of the type of membranes and operating conditions on mass‐transfer rate were discussed, especially the influence of the membrane transfer coefficient on the film mass‐transfer coefficient in the lumen. Appropriate configurations of the hollow‐fiber modules for stripping of a single component were analyzed to optimize mass transfer. To predict the stripping of NH3 from a solution containing NH3 and CO2, a mathematical model incorporating local chemical equilibria and Nernst–Planck diffusion was developed to describe the mass transport. The models described the experimental data fairly well. The experimental results showed that the supported gas membrane process can be used to remove NH3 effectively from aqueous media containing NH3 and CO2.
Surface fractality of wood charcoals through small‐angle X‐ray scattering
Authors: Venkatraman A. , Boateng A. A. , Fan L. T. , Walawender W. P. 
Published: June 2004

AbstractGeometrical properties of the pore‐solid interfaces of devolatilized charcoals from the pyrolysis of fuel woods in a bench‐scale fluidized‐bed reactor were investigated through small‐angle X‐ray scattering. Specifically, surface morphological features of the interfaces were characterized by a single parameter indicative of the degree of surface roughness, that is, the surface fractal dimension, dSF, at various retention times. The surface fractal dimensions of the original wood samples prior to devolatilization were approximately identical for all species within the range between 2.00 and 2.15, over a length scale from 55 to 600 Å, and those for the respective charcoals from these wood samples were influenced to different degrees by the retention time, τ, in the reactor. The dSF's of the mesopores of charcoals of all the species attained maxima at a value of τ equal to 35 s and decreased subsequently with an increase in τ. The analysis of this unexpected trend was facilitated by the values of the mean radii of gyration of the pores, estimated through the Guinier plots. The results imply that when the retention time of the charcoals in the reactor is prolonged, the mechanism of pore enlargement and smoothening of the interfaces can play a dominant role in altering the surface morphology and thereby influence significantly the kinetics of chemical reactions in heterogeneous porous systems.
Perturbation analysis of Thomas and Windle's model of Case II transport
Authors: Durning C. J. , Edwards D. A. , Cohen D. S. 
Published: June 2004

AbstractThomas and Windle's model of Case II transport is analyzed for a semiinfinite medium by a singular perturbation technique. Two adjacent boundary layers separate equilibrated and dry regions. A thin boundary layer of width ∼ O(M−1/2/ln M), where M (≫1) dictates how rapidly the mixture's viscosity decays with liquid concentration, sits next to the equilibrated outer left region. Here, quasi‐steady diffusion balances relaxation. A thicker intermediate layer of width ∼ O(M−1/2) separates the lefthand boundary layer and the dry outer region on the right, where both relaxation and unsteady diffusion participate in the transport. Matching the solutions at leading order specifies the moving front's speed, v: v ∼ M1/2. The analysis indicates that relaxation significantly affects the nearly dry region just ahead of the moving front. This disagrees with the widely accepted view that ordinary diffusion dominates in the nearly dry righthand region. Approximating that ordinary diffusion dominates in this region leads to a stepexponential concentration profile at the front and a simple analytical solution for the front speed, v with the correct M scaling. This approximate result accurately predicts the values of v determined by direct numerical solutions.
Gas‐separation membrane cascades utilizing limited numbers of compressors
Authors: Agrawal Rakesh , Xu Jianguo 
Published: June 2004

AbstractA systematic procedure is presented to drawn n‐compressor membrane cascades for gas‐separation applications with n ≥ 1. In this method, a parent cascade structure is created that contains the n‐compressor cascades as substructures. These substructures are then revealed by systematically eliminating unwanted membrane stages and recycle compressors from the parent cascade. The procedure is illustrated by generating arrays of one‐ and two‐compressor cascade schemes. It is found that these arrays contain the cascade schemes known from the literature and also lead to some new schemes. This procedure increases the likelihood of finding an economically viable membrane cascade for a given separation application.
Dynamic rectification of data via recurrent neural nets and the extended Kalman filter
Authors: Karjala Thomas W. , Himmelblau David M. 
Published: June 2004

AbstractThe presence of autocorrelated measurement errors and/or measurement bias in process measurements poses serious problems in the rectification of data taken from dynamic processes. The proposed procedure to resolve these problems involves the use of recurrent neural networks (RNN) and the extended Kalman filter (EKF). By interpreting RNNs within a nonlinear state‐space context, a state‐augmented EKF can be used to optimally estimate both the states of the RNNs and noise and bias models. RNN models can be identified off‐line and utilized for data rectification within the extended Kalman filter in process environments in which badly autocorrelated measurement errors exist in the data. The same technique is also used to estimate measurement bias present in both process input and output variables. This approach has the advantage that models developed from “first principles” are not required and that rectification can be performed solely on the basis of the contaminated dynamic data.
Reaction kinetics of photoactive defects in semiconductor dissolution
Authors: Robertson Eric A. , Fogler H. Scott 
Published: June 2004

AbstractUniformity and predictability are the principal qualities sought for all wet chemical etches. The establishment of these qualities, however, is hindered by a number of factors, such as nonuniformities in the starting material and random fluctuations in the local temperature and reactant concentration, which can lead to variations in etch rate across the surface of a wafer. The effects of variations in the local etch rate on the morphological development of an etching surface and on the overall etch rate of the semiconductor are discussed. The system studied was an Al0.4Ga0.6As/GaAs heterostructure photodissolved in nitric acid using 730‐nm laser light. Defects in the AlGaAs layer, which etched faster than the surrounding material, were responsible for variations in the etch rate. The defects also exhibited a degree of photosensitivity that has not been previously observed. It was also found that not all of the defects spanned the AlGaAs epilayer. A model for the overall etch rate was based on a system of noninteracting cylindrical defects with a distribution in depths.
Crack propagation in catalytic pellets due to thermal stresses
Authors: Boshoff‐Mostert L. , Viljoen H. J. 
Published: June 2004

AbstractCatalytic combustion reactions and reacting systems that operate in the parameter sensitivity region of the kinetic regime are likely to experience sudden temperature changes, resulting in the development of thermal stress in the catalyst support. The unified theory of Hasselman is used to study the onset and extent of crack propagation in catalyst support media. This theory is based on the principle that cracks propagate (terminate) when the total energy of the system increases (decreases) with additional crack growth. It is shown that the total energy of the medium (elastic and fracture energy) varies with time and position in the medium, and the extent of crack growth also varies from one point to the other. Within the limitation of the assumption that the crack density is low enough, the model provides valuable insight into the durability and mechanical strength of ceramic support media.
Application of artificial neural networks in modeling limestone–SO2 reaction
Authors: Bandyopadhyay Jayanta K. , Annamalai Senthil , Gauri K. Lal 
Published: June 2004

AbstractFour varieties of limestone distinguished on the basis of pore‐size distributions were exposed in dynamic 10‐, 20‐ and 50‐ppm SO2 atmospheres for up to 500 h at 25°C and 100% rh. The resulting conversion of the limestone was measured as a function of the reaction product formed and the change in porosity. These conversions could be predicted correctly using either the shrinking unreacted core model or the distributed pore model. An artificial neural network (ANN) was also trained for the purpose. All three approaches predicted conversions that fitted well with the observed data; however, those predicted by ANN were the most accurate. Further, the weights determined for ANN on the basis of three limestone varieties also accurately predicted the conversions of the fourth variety for which no information was supplied in the training phase, showing that ANN can also be used successfully to estimate gas–solid noncatalytic reactions.
Impact of tank geometry on the maximum turbulence energy dissipation rate for impellers
Authors: Zhou Genwen , Kresta Suzanne M. 
Published: June 2004

AbstractThe maximum turbulence energy dissipation rate per unit mass, εmax, is an important variable in dispersion systems, particularly for drop breakup and coalescence, and for gas dispersion. The effect of tank geometry (number of baffles, impeller diameter, and off‐bottom clearance) on εmax for four impellers (the Rushton turbine, RT; the pitched blade turbine, PBT; the fluidfoil turbine, A310; and the high‐efficiency turbine, HE3) is examined. Mean and fluctuating velocity profiles close to the impellers were measured in a cylindrical baffled tank using laser doppler velocimetry. Local and maximum turbulence energy dissipation rates in the impeller region were estimated using ε = Av3/L with A = 1 and L = D/10 for all four impellers. Factorial designs were used to test for the effects of single geometric variables under widely varying conditions and interactions between variables. Several factorial designs were used to ensure that real effects were separated from effects that appeared as an artifact of the experimental design. Results show that the tank geometry has a significant effect on εmax, primarily with respect to variations in impeller diameter and interactions between the off‐bottom clearance and impeller diameter. For the same power input and tank geometry, the RT consistently produces the largest εmax and/or εmax scaled with N3D2.
Investigation of ion separation by microporous nanofiltration membranes
Authors: Rios G. M. , Joulie R. , Sarrade S. J. , Carlès M. 
Published: June 2004

AbstractTwo new nanofiltration membranes, an organomineral (titania‐Nafion) medium and an inorganic (γAl2O3) medium, were studied using single or mixed solutions of monovalent or divalent ions. The experimental results not only confirm previous findings concerning the treatment of electrolytic solutions using charged nanofiltration membranes, but provide additional data notably for microporous membranes. A simple model based on the Nernst–Planck equation is proposed; its simplicity is related to the nature of the two membranes tested, for which the diffusion terms may easily be disregarded. It highlights the importance of the potential difference that forms on the membrane and explains most of the observed rejection results. In addition, ionic plugging of micropores may play a part with regards to rejection and flow depending on working conditions.
Simultaneous optimal bottom linewidth and side‐wall curvature control of wet etching
Authors: Zhou Bo , Ramirez W. Fred 
Published: June 2004

AbstractEtching is one of the critical steps in the fabrication of microelectronics devices. A time‐optimal control problem with a dual‐term terminal cost including both bottom linewidth and side‐wall curvature is formulated to implement an optimal open‐width design principle. A singular‐arc solution does not exist and the control action is bangbang. The optimal switching time is analytically calculated. The feasibility and effectiveness of this technique are illustrated by simulation studies. This design and control philosophy can easily be applied to other microelectronics manufacturing processes.
Dispersion effects on membrane reactor performance
Authors: Koukou M. K. , Papayannakos N. , Markatos N. C. 
Published: June 2004

AbstractA mathematical model has been developed that predicts the effects of design parameters, operating variables and physical properties on the performance of a membrane reactor with a permeselective wall. The model consists of the full set of partial differential equations that describe the conservation of mass, momentum and chemical species, coupled with chemical kinetics and appropriate boundary conditions for the physical problem. The solution of this system is obtained by a finite‐volume technique. The model was applied to study the dehydrogenation of cyclohexane. Two membrane types in tubular form were studied: a selective porous glass with low gas permeabilities and a porous alumina with very high gas permeabilities. It is concluded that gas separation and reactor performance are strongly influenced by dispersion effects only in the latter membrane reactor, while in both cases radial concentration profiles do not correspond to those obtained with plug flow. Therefore, simulations of this type of problem should be based on complex dispersion models rather than the existing ideal plug‐flow ones.
General method for the transformation of chord‐length data to a local bubble‐size distribution
Authors: Liu Weidong , Clark Nigel N. , Karamavruc Ali Ihsan 
Published: June 2004

AbstractBubble‐size distributions influence the behavior of multiphase systems, but are not readily measured directly using probes. The chord lengths may be transformed into bubble sizes by modeling the bubble shapes as ellipsoids. Previous research on the transformation of chord‐length data into bubble‐size distributions using a numerical backward transformation revealed an instability problem. This problem was overcome by transforming the chord‐length data to a local bubble‐size distribution directly by using a Parzen window function and summing to yield the whole distribution. The best estimate of the local bubble‐size density distribution depends on the Parzen window width that was chosen by proposing a measure of performance. An empirical relationship was also offered to determine the best Parzen window width. Chord lengths were generated using the example of a Rayleigh bubble‐size distribution and Monte‐Carlo simulation. The window approach transformed the chord lengths back into the bubble‐size distribution with good agreement.
Shear‐induced alignment of nonspherical Brownian particles near walls
Authors: Nitsche Johannes M. , Roy Partha 
Published: June 2004

AbstractA theoretical investigation is presented of the convection‐diffusion of model nonspherical solutes in shear flow over a plane wall. The analysis proceeds by formulating the underlying configuration‐space Brownian transport equation for the distribution over accessible positions and orientations. Geometrical constraints are imposed via boundary conditions preventing wall penetration, and some of the calculations incorporate hydrodynamic interactions with the wall. The analysis is brought to fruition by regular perturbation expansion in the rotary Péclet number, and solution of the resultant boundary‐value problems by a Galerkin technique. Three specific mechanistic conclusions result from the analysis. First, steric constraints imposed by the wall impedes the shear‐induced solute alignment (producing a more nearly uniform distribution over orientations relative to the unbounded‐fluid case) near the wall. Second, although the first effect of flow is to counteract the equilibrium depletion of solute centers near the wall, flow reinforces this depletion at higher order in the shear rate. Third, solute‐wall hydrodynamic interactions act to strengthen the shear‐induced solute alignment near the wall. This last phenomenon occurs because hydrodynamic wall effects significantly decrease the rotary diffusivity, but have little effect on the angular velocity, thereby locally increasing the effective rotary Péclet number (the effective flow strength). Correspondingly, solute‐wall hydrodynamic interactions reinforce the flow effects on the near‐wall depletion just noted. Steric and hydrodynamic wall effects typically are of order 15–20% near the wall.
Analysis of two‐stage heterogeneous separation processes
Authors: Sridhar L. N. 
Published: June 2004

AbstractIn this article, rigorous mathematical analysis is used to prove that the necessary condition for multiple steady‐state solutions to exist in two‐stage separation process problems involving ternary mixtures is the tendency of the mixture to exhibit a second liquid phase. The unrealistic solution multiplicity that exists in these problems, when phase splitting is not included in the model equations used to solve them, vanishes when phase splitting is included. The standard specification of reflux ratio and bottoms flow rate has been investigated.
Fundamental study of the dissolution of calcium phosphonates from porous media
Authors: Browning F. Henry , Fogler H. Scott 
Published: June 2004

AbstractPhosphonate‐scale inhibitors are commonly used to prevent scale formation in many industrial processes involving high‐salinity brine solutions. To effectively prevent scale formation in these industrial processes, one must have a fundamental understanding of how phosphonates are released into high‐salinity brines. Because phosphonates can precipitate with divalent cations such as calcium, their release into aqueous media is often governed by many dissolution mechanisms. This study focuses on the release of calcium‐phosphonate precipitates from porous media (as related to oil‐field applications) and a mathematical model describing these release mechanisms based on mechanistic studies of pore‐level phenomena. The phosphonate used was 1‐hydroxyethylidene‐1,1‐diphosphonic acid (HEDP). The release of two distinct calcium‐HEDP precipitates from porous media was studied: soluble, fibrous 1:1; insoluble, spherical 2:1. Visual studies using etched‐glass micromodels showed that five distinct regimes govern the release of 1:1 calcium‐HEDP precipitate from porous media. Conversely, the release of 2:1 calcium‐HEDP precipitate was dominated by two distinct regimes. A continuum model developed describes the release of both precipitates from porous media by mathematically describing each of the distinct release regimes and defining conditions under which the transition between release regimes occurred. Experimental data agreed excellently with model simulations for both precipitates.