bluuebunny/crossref_metadata_2025_split huggingface dataset:
Designing a commercial ion‐exchange carousel to treat DOE wastes using CST granules
Authors: Huckman M. E. , Latheef I. M. , Anthony R. G. 
Published: April 2004

AbstractA column carousel system was designed to treat nuclear waste at the Savannah River Site. A carousel model was used to simulate cesium removal in an ion‐exchange carousel loaded with crystalline silicotitanate (CST) granules. The model accounts for axial dispersion and resistance to film and intraparticle diffusion. The effect of resistance to intraparticle diffusion on the required column volumes is significant. Values of the effective diffusivity of 0.25 to 0.6×10−10 m2/s were estimated from bench‐scale column experiments. This range of values resulted in a variation of column volumes by a factor of 3. The Zheng‐Anthony‐Miller equilibrium model was used to estimate Cs isotherms. The largest carousel volume did not result from waste with the lowest equilibrium loading. For wastes with low equilibrium loadings, the switching interval increased, which increases the volume of CST required to treat the same volume of waste.
Modeling for simulation of fluidized‐bed incineration process
Authors: Marias F. , Puiggali J. R. , Flamant G. 
Published: April 2004

AbstractA mathematical model for the fluidized‐bed incineration process was developed using the waste composed of wood, cardboard and polyvinyl chloride. It is based on heat and mass balances of the gas held within the five zones representing both the bubbling bed and freeboard and including heat transfer with sand and reacting particles of char (pyrolysis residue). The mixture fraction concept and assumption of chemical equilibrium are used to compute temperature and species concentration fields resulting from volatile combustion. These fields are affected by char combustion, which relies, in turn, on a model based on surface reaction and a full population balance. The formation of pollutants (NOx, SOx ) was also taken into account. The main steps involved by the numerical resolution of the model are discussed, and some results are shown for a 1 MW unit.
Predictive model and deterministic mechanism in a bubbling fluidized bed
Authors: Zhao Gui‐Bing , Chen Ji‐Zhong , Yang Yong‐Rong 
Published: April 2004

AbstractA predictive model based on the theory of phase space reconstruction was proposed to study the determinism and predictability of dynamics underlying pressure fluctuations by measuring and analyzing the time series of pressure signals at different locations in a bubble bed with 0.3 m in dia. and 3 m in height. Chaotic invariants (correlation dimension, K2 entropy, and Lyapunov exponent spectrum) of measured and model‐generated time series of pressure signals were nearly the same. The model captured some important nonlinear characteristics of the real system, which can be used to study the dynamics of fluidizing system. Deterministic dynamics underlying pressure signals were confirmed to exist. A new characteristic index defined as the determining level of dynamics was used to analyze deterministic degrees at different gas velocities and locations of the wall in the bed. Since prediction errors of pressure fluctuations grow exponentially with time at short time scales and the exponent separation rate between predicted and measured values is proportional to the maximal Lyapunov exponent, the long‐term predictability of pressure fluctuations is impossible. This verified chaotic properties of fluctuation dynamics in the fluidized bed with deterministic mechanism and sensitive dependence on initial conditions.
Synthesis of silica‐carbon particles in a turbulent H2‐air flame aerosol reactor
Authors: Kammler Hendrik K. , Mueller Roger , Senn Omri , Pratsinis Sotiris E. 
Published: April 2004

AbstractSynthesis of flame‐made nanostructured powders was studied, for the first time, at high production rates (up to 700 g/h) in a turbulent diffusion flame reactor, addressing also the required safety concerns. A commercial hydrogen‐air burner was used for synthesis of pure silica and composite silica‐carbon particles by oxidation of hexamethyldisiloxane. The product powder was collected continuously in a baghouse filter unit and cleaned periodically by air‐pressure shocks. The effect of the fuel (hydrogen) flow rate, powder production rate and total oxidant flow rate on product particle size, morphology, and composition was also investigated. Nitrogen adsorption, transmission electron microscopy and thermogravimetric analysis coupled with a mass spectrometer, and a CO2 ‐analyzer were employed to characterize specific surface area and powder composition. Typically, aggregates of silica‐carbon composite particles (0 to 1.4 wt. % carbon) were made on specific surface areas of 75 to 250 m2/g at production rates of 125 to 700 g/h, which correspond to particle concentrations of 17 to 93 g/m3 (2–10% solid fraction by weight).
Protein ion‐exchange adsorption kinetics
Authors: Wesselingh J. A. , Bosma J. C. 
Published: April 2004

AbstractThe kinetics of the adsorption of the protein BSA on the ion exchanger Q‐Sepharose FF were measured for several values of the pH and ionic strength, using several techniques. The measurements were best described with a model incorporating both surface and pore diffusion and with the chemical potential gradient as the driving force for diffusion. The surface‐diffusion coefficients from this model show an inverse exponential dependency on the binding strength. This dependency can be explained by an activated jump mechanism. The pore‐diffusion coefficient is much lower than that in free solution, which is probably caused by a combination of steric and electric exclusion.
Mass‐transport dynamics, activity, and structure of sulfate‐reducing biofilms
Authors: Beyenal Haluk , Lewandowski Zbigniew 
Published: April 2004

AbstractFactors limiting hydrogen sulfide production were identified in a two‐species biofilm containing sulfate‐reducing bacteria (Desulfovibrio desulfuricans) and nonsulfate‐reducing bacteria (Pseudomonas fluorescens). Profiles of hydrogen sulfide (H2S) concentration, pH, local mass‐transport coefficient, local flow velocity, and local relative effective diffusivity in the biofilm were measured using microelectrodes. Biofilms had a heterogeneous structure consisting of cell clusters separated by voids. Typically, the H2S concentration was lower in the voids than in the adjacent cell clusters, demonstrating that the voids acted as transport channels for removing H2S from cell clusters. The extent of biofilm heterogeneity was directly correlated with the flux of H2S from cell clusters. At flow velocities below 2 cm/s, the flux of H2S from cell clusters depended on the flow velocity. We concluded that at these flow velocities the H2S production rate was limited by the delivery rate of sulfate ions to the biofilm. At flow velocities above 2 cm/s, the H2S production rate was nearly constant and did not depend on the flow velocity. At high flow velocities (>2 cm/s) the H2S production rate was limited by metabolic reactions in the biofilm. Local intrabiofilm flow velocity profiles were influenced strongly by biofilm heterogeneity without significant pH variation within biofilms. Surprisingly, profiles of local relative effective diffusivity indicated that the biofilm was made up of two layers, which could be related to the specimen with a two‐species biofilm.
Effects of reactant concentrations on reactive miscible viscous fingering
Authors: Nagatsu Yuichiro , Ueda Toshihisa 
Published: April 2004

AbstractEffects of reactant concentrations on the characteristics of reactive miscible viscous fingering in a Hele‐Shaw cell at low finger‐growth velocity were studied both experimentally and theoretically. The product distribution varies with the variations in the initial reactant concentrations and depends on the location of a reaction zone. When the reaction zone is located in the more‐viscous‐liquid region the product concentrates at the fingertips, but when it is located in the less‐viscous‐liquid region, the product spreads in a relatively broad area inside the fingers. This significant difference in the reaction pattern resulting from variations in the reactant concentrations is caused by the large difference of molecular diffusivity in the two liquids, that is, of viscosity which is one of the important factors for viscous fingering. These results are confirmed theoretically by one‐dimensional diffusive–reactive analysis.
Simple stochastic model of spontaneous imbibition in Hele‐Shaw cells
Authors: Rodríguez R. F. , Salinas‐Rodríguez E. , Hayashi J. A. , Soria A. , Zamora J. M. 
Published: April 2004

AbstractThe imbibition of water in oil in Hele‐Shaw cells is described as an asymmetric random walk of water in a globally disordered medium. The disorder is modeled by an external, nonwhite, dichotomic noise, and the resulting random walk is described in terms of an effective Markovian master equation. The solution to this equation is given, and the mean‐squared‐displacement (MSD) of fluid particles in an effective ordered medium is calculated. This same quantity was also measured in squared cells with a fixed separation, where Soltrol 170 was displaced by twice‐distilled water. The flow generated by spontaneous displacement of oil presented three sequential stages, each with a characteristic speed and advancing front structure. In the first and third stages viscous fingering was not detected, but in the intermediate development stage it was observed. From the recorded time evolution of the front, its average displacement speed and the MSD of water in oil as a function of time were determined. Imbibition of water shows an enhanced diffusion regime in the first stage where MSD varies with t2, without any external noise effect. This is followed by a simple diffusion behavior in an effective medium in the second stage, where the external noise effect is large. In the third stage Gaussian diffusion prevails again. Numerical regression techniques were used to determine the best values of model parameters that fit experimental values for different stages, so that the sum of squared errors between theoretical predictions and experimental measurements is minimized. Good agreement was found with average errors of 14.3%, 5.9% and 0.6%, respectively.
Effect of mixing on product quality in semibatch stirred tank reactors
Authors: Verschuren Iris L. M. , Wijers Johan G. , Keurentjes Jos T. F. 
Published: April 2004

AbstractSemibatch stirred tank reactors with a turbulent flow field are used frequently in the chemical process industry to accomplish mixing tasks. Mixing in a turbulent flow consists of several processes. Descriptions for these processes from literature are used to construct a model to calculate the selectivity of a mixing‐sensitive reaction in a semibatch stirred tank reactor. The model is validated by determining the effects of various process parameters on the selectivity of the third Bourne reaction. Calculation of the selectivity requires information on the hydrodynamic parameters of the stirred vessel studied. The essential detailed description of these hydrodynamic parameters to obtain a good agreement between measured and calculated selectivities was determined. The model proved to be successful in predicting the product distribution of a competitive reaction, making it useful for the design and scale‐up of stirred‐tank reactors.
Liquid‐liquid extraction of aroma compounds with hollow fiber contactor
Authors: Baudot Arnaud , Floury Juliane , Smorenburg Herbert E. 
Published: April 2004

AbstractThe extraction of aroma compounds through a commercial hollow‐fiber contactor from model aqueous feeds to sunflower oil was tested. The stripping efficiency of this membrane‐based solvent extraction operation was systematically studied as a function of the oil/water partition coefficient of the permeants, and the flow and location of the feeds in the contactor (in the shell side or in the lumen of the fibers). The mass transfer between the two phases was modeled based on the resistances‐in‐series approach. In particular, a correlation describing the mass transfer with a transverse flow in the shell is proposed. With similar operating conditions, the stripping of the aroma compounds was more efficient when flowing the aqueous feed phase in the shell side than inside the fibers.
Mass transfer in low‐density xerogel catalysts
Authors: Heinrichs Benoît , Pirard Jean‐Paul , Schoebrechts Jean‐Paul 
Published: April 2004

AbstractTexture and morphology of a Pd‐Ag/SiO2 hydrodechlorination low‐density xerogel catalyst prepared by a cogelation sol‐gel process were characterized in detail to examine mass transfer in such catalysts. The catalyst consists of active Pd‐Ag nanocrystallites trapped inside elementary 20 nm microporous silica particles arranged in larger aggregates, which constitute the macroscopic pellet. To reach active sites, reactants must first diffuse through large pores located between aggregates of SiO2 particles and then through smaller pores located between those elementary particles inside the aggregates. Finally, they diffuse through micropores located inside silica particles. Diffusion in such a “funnel” structure cannot be described assimilating the pellet to a pseudo‐continuum. Diffusion should be examined carefully at three levels of decreasing size: the macroscopic pellet, the aggregate of silica particles, and the elementary silica particle. This approach shows that cogelled xerogel catalysts have remarkable mass‐transfer properties.
Reliable density‐functional‐theory calculations of adsorption in nanoscale pores
Authors: Maier Robert W. , Stadtherr Mark A. 
Published: April 2004

AbstractA popular approach for the modeling of adsorption phenomena is density‐functional theory (DFT). A new methodology described here is the first completely reliable technique for finding all solutions to the nonlinear equation systems arising in the lattice‐DFT modeling of adsorption in porous materials. The method is based on interval analysis, in particular on an interval Newton/generalized bisection algorithm, which provides a mathematical and computational guarantee that all solutions are enclosed. The method is demonstrated using a model, formulated using DFT for a confined lattice, of adsorption in slit‐like nanoscale pores. In addition to confirming solutions found previously, the method also found on several test problems a number of additional, previously unreported solutions.
Electromagnetics, heat transfer, and thermokinetics in microwave sterilization
Authors: Zhang H. , Datta A. K. , Taub I. A. , Doona C. 
Published: April 2004

AbstractSterilization of solid foods using microwave power was studied using numerical modeling and specialized experimental verification. Maxwell's equations and the heat conduction equation were coupled using two separate finite‐element programs and specially written modules to couple the programs. Spatial distributions of thermal‐time, representing sterilization, were calculated from time‐temperature history and first‐order kinetics. Experimentally, concentrations of marker compounds formed during heating were measured and taken as indices of thermal‐time. Experimental data on marker formation combined with numerical calculations provide an accurate and comprehensive picture of the sterilization process and represent a major step in establishing the efficacy of microwave sterilization processing. Unlike conventional sterilization, heating patterns can change qualitatively with geometry (shape and size) and properties (composition) of the food material, but optimal heating is possible by choosing suitable combinations of these factors. Combined with marker yield measurements, the numerical model can give comprehensive descriptions of the spatial time‐temperature history, and thus can be used to verify the sterilization process.
Controlling particle size during anatase precipitation
Authors: Sathyamoorthy Sekhar , Moggridge Geoff D. , Hounslow Michael J. 
Published: April 2004

AbstractTitanium dioxide particles in the form of anatase are precipitated from concentrated titanyl sulfate solution in the sulfate process, which are then recovered by a filtration process downstream of the precipitation stage. A previous study by Sathyamoorthy et al. showed that the final anatase particles are aggregates (1‐2 μm) consisting of numerous crystals (7–8 nm) arranged in primary agglomerates (60–100 nm). Pigment quality is determined by crystal and primary agglomerate size. One way of improving filtration rate is by the formation of larger aggregates, while maintaining the crystal and primary agglomerate size at optimum values. In a new seeding procedure proposed, the controlled inoculation of seeds used in industry is combined with a new type of seed (Large Seeds). The new seeding procedure has the potential to increase downstream filtration efficiency by increasing aggregate size, while maintaining crystal and primary agglomerate sizes close to the values correctly obtained in industry. High yield in the precipitation process is also maintained.
Experimental studies of gas permeation through microporous silica membranes
Authors: Yoshioka Tomohisa , Nakanishi Eisuke , Tsuru Toshinori , Asaeda Masashi 
Published: April 2004

AbstractPermeation mechanism of inorganic gases was studied experimentally and theoretically through microporous silica membranes prepared by the sol–gel method. Inorganic gas permeation was measured using the membranes with subnano pores in diameter. The permeance of He increased with increasing temperature for various cases, while that of CO2, O2 and N2 decreased. In particular, the observed temperature dependency of CO2 was greater than those of other gases. In such small pores, the interaction energy between a permeant molecule and the pore wall can affect gas‐permeation properties. A simple gas‐permeation model is used considering the effect of the attractive or repulsive pore‐wall potential field, which deviates from the ambient gas phase of the gas molecule concentration (pressure) in a pore. The model can explain the experimental gas‐permeation properties successfully. Potential curves of CO2 and N2 in a silica pore were also calculated to predict the permeation ratio of CO2/N2. This model can help understand further the gas‐permeation mechanism in micropores.
Extended PLS approach for enhanced condition monitoring of industrial processes
Authors: Kruger U. , Chen Q. , Sandoz D. J. , McFarlane R. C. 
Published: April 2004

AbstractAn extended partial‐least squares (EPLS) algorithm is introduced to correct a deficiency of conventional partial least squares (PLS) when used as a tool to detect abnormal operating conditions in industrial processes. In the absence of feedback control, an abnormal operating condition that affects only process response variables will not be propagated back to the process predictor (or input) variables. Thus monitoring tools developed under the conventional PLS framework and based only on the predictor matrix will fail to detect the abnormal condition. The EPLS algorithm described removes this deficiency by defining new scores that are based on both predictor and response variables. The EPLS approach provides two monitoring charts to detect abnormal process behavior, as well as contribution charts to diagnose this behavior. To demonstrate the utility of the new approach, the extended algorithm and monitoring tools are applied to a realistic simulation of a fluid catalytic cracking unit and to a real industrial process that involves a complex chemical reaction.
Viscoplastic fluid flow through a sudden axisymmetric expansion
Authors: Jay Pascal , Magnin Albert , Piau Jean Michel 
Published: April 2004

AbstractNumerical experiments were carried out for yield‐stress fluid flows through a 1:4 sudden axisymmetric expansion using the Herschel‐Bulkley and Bingham models with a two‐viscosity approximation. The influence of shear thinning, inertia and yield‐stress values on the structure of the flow and on pressure and head losses was studied. The detailed structure of flow in the expansion shows an initial vortex. The yield stress generates two toroidal rigid dead zones, one located in the corner of the expansion and one located close to the stagnation point that appears between the vortex and the downstream flow. Inertia and yield stress act in opposite ways. When inertia increases, the vortex increases in size and the rigid dead zone decreases. Conversely, when yield stress increases, the vortex decreases in size and the rigid dead zone increases. Shear thinning reduces the dimensions of both vortices and dead zones. Pressure loss increases with yield stress. In addition, the numerical results are consistently compared with experimental ones.
A simulation‐optimization framework for research and development pipeline management
Authors: Subramanian Dharmashankar , Pekny Joseph F. , Reklaitis Gintaras V. 
Published: April 2004

AbstractThe Research and Development Pipeline management problem has far‐reaching economic implications for new‐product‐development‐driven industries, such as pharmaceutical, biotechnology and agrochemical industries. Effective decision‐making is required with respect to portfolio selection and project task scheduling in the face of significant uncertainty and an ever‐constrained resource pool. The here‐and‐now stochastic optimization problem inherent to the management of an R&D Pipeline is described in its most general form, as well as a computing architecture, Sim‐Opt, that combines mathematical programming and discrete event system simulation to assess the uncertainty and control the risk present in the pipeline. The R&D Pipeline management problem is viewed in Sim‐Opt as the control problem of a performance‐oriented, resource‐constrained, stochastic, discrete‐event, dynamic system. The concept of time lines is used to study multiple unique realizations of the controlled evolution of the discrete‐event pipeline system. Four approaches using various degrees of rigor were investigated for the optimization module in Sim‐Opt, and their relative performance is explored through an industrially motivated case study. Methods are presented to efficiently integrate information across the time lines from this framework. This integration of information demonstrated in a case study was used to infer a creative operational policy for the corresponding here‐and‐now stochastic optimization problem.
Operational envelopes for batch processes
Authors: Samsatli Nouri J. , Sharif Mona , Shah Nilay , Papageorgiou Lazaros G. 
Published: April 2004

AbstractBatch processes are often subjected to a number of sources of variability, which are frequently overlooked due to operating policy implementation. In many pharmaceutical and speciality chemical processes, which are predominantly batch in nature, a high proportion of the operating procedure is implemented manually, which can lead to significant variability. The effect of this variability is typically neglected at all stages in process development and even when full‐scale production begins. The result of any variability can have a dramatic effect on some process stages (particularly sensitive ones such as crystallization), and it is therefore important to understand how variability in any of the operating variables affects the overall process. Ideally, one would like to design processes that are less sensitive to variability and specify precisely the limits of any allowable variability. A method for designing batch processes using “operating envelopes” that specify process operation in terms of a region within which the operating variables should be maintained to guarantee feasible and profitable operation of the process is presented. The problem is formulated as a multiscenario dynamic optimization problem, and an efficient hierarchical solution procedure is presented. Finally, the applicability of the procedure is demonstrated by using two example problems.