bluuebunny/crossref_metadata_2025_split huggingface dataset:
Role of particle geometry and surface contacts in solid‐phase reactions
Authors: Kostogorova J. , Viljoen H. J. , Shteinberg A. 
Published: April 2004

AbstractGiven the surface areas of three different species A, B, and C, what is the most likely contact area between A and B? This problem finds many applications, but it is of specific importance in solid‐phase reactions. Reactions in powder mixtures depend strongly on contact area between reactants, even when one species may melt. The surface of particles is meshed with small “tiles,” and a combinatorial problem is formulated to map all tiles onto each other. The number of different contacts of n constituents is \documentclass{article}\pagestyle{empty}\begin{document}$\sum\limits_{i = 1}^n i$\end{document}; if pores are present, they are considered a constituent. The combinatorial problem for n > 3 is computationally overwhelming, but for two or three species, the desirable contacts can be calculated. The model was developed for contact between three different species (two species are included as a special case). This could constitute three different powders at 100% MTD, or a mixture of two powders that includes pores where the latter phase acts as a third species. The combinatorial approach is used to find the discrete probability‐distribution function (PDF), viz., p(z, A, B, C), where z is the number of desirable contacts (for example, A∖︁B), given the surface areas (A, B, C). The first moment of the PDF gives the expectancy value Ψ (A∖︁B, A, B, C) for contact between species A and B. The theory was demonstrated by two examples. A simple contact problem is solved for two powders that also contain pores. The second example compares kinetic rates for different shapes and sizes of particles.
Linear control of nonlinear systems: Interplay between nonlinearity and feedback
Authors: Eker S. Alper , Nikolaou Michael 
Published: April 2004

AbstractA rigorous and general theory, as well as an associated efficient computational methodology, was developed that addresses the question of when and what linear control is adequate for a nonlinear process. A number of computer simulation examples illustrate the power of the proposed approach. Several potential future developments are outlined.
LF‐LPV input/output data‐based predictive controller design for nonlinear systems
Authors: Yoo Kee‐Youn , Rhee Hyun‐Ku 
Published: April 2004

AbstractMost control engineers concentrate on finding a controller given the plant model or identifying a model from the data. There is no doubt that model‐based control and system identification are closely related, simply because one depends strongly on the other. In this work a subspace identification algorithm for LF‐LPV (linear‐fractional linear parameter‐varying) models is reformulated from a control point of view. This algorithm is referred to as an input/output data‐based predictive control, in which an explicit model of the system to be controlled is not calculated at any point in the algorithm. It allows for the construction of a nonlinear model predictive controller for an unknown nonlinear system directly from a set of its open‐loop measurements. As an example of the input/output data‐based predictive control, the styrene solution polymerization in a continuous reactor system is considered to prove the superior performance of LF‐LPV input/output data‐based predictive controller for polymer quality control. This approach gives a new angle for attacking the problem of identifying and controlling nonlinear systems.
Design of homogeneous biphasic catalytic processes
Authors: Singh Divya J. , Samant Ketan D. , Ng Ka M. 
Published: April 2004

AbstractA systematic procedure for the design of homogeneous catalytic processes with special emphasis on biphasic reactions was developed. First, the reaction kinetics were determined, and then a generic stirred cell model for biphasic homogeneous catalytic reactions was used to elucidate the interplay of reaction and mass transfer and the impact of phase equilibria. The optimal range of reactor conditions, as captured by the Damköhler numbers, was then related to reactor attributes. Process alternatives for catalyst recovery and recycle were considered.
Pattern matching in historical data
Authors: Johannesmeyer Michael C. , Singhal Ashish , Seborg Dale E. 
Published: April 2004

AbstractFor many engineering and business problems, it would be very useful to have a general strategy for pattern matching in large databases. For example, the analysis of an abnormal plant condition would benefit if previous occurrences of the abnormal condition could be located in the historical data. A new pattern‐matching strategy is proposed for multivariate time series based on statistical techniques, especially principal‐component analysis (PCA). The new approach is both data‐driven and unsupervised because neither training data nor a process model is required. Given an arbitrary set of multivariate data, the new approach can be used to locate similar patterns in a large historical database. The proposed pattern‐matching strategy is based on two similarity factors: the standard PCA similarity factor and a new similarity factor that characterizes the pattern of alarm violations. An extensive simulation study for a chemical reactor demonstrates that this strategy is more effective than existing PCA methods and can successfully distinguish between 28 different operating conditions.
Nucleation, growth, and agglomeration in barium sulfate turbulent precipitation
Authors: Marchisio Daniele L. , Barresi Antonello A. , Garbero Mirko 
Published: April 2004

AbstractIn this work barium sulfate precipitation is studied in a tubular reactor in a wide range of operating conditions. The effect of reactant concentrations and barium or sulfate excess on crystal‐size distribution and morphology is investigated. Experimental results show that ion excess has a strong influence and that at high concentration aggregation takes place. Computational fluid dynamics is coupled with the finite‐mode probability density function approach for taking into account both macro‐ and micromixing, whereas the population balance is treated by using the standard moment method. Comparison with experimental data suggests that when micromixing and agglomeration are properly taken into account, the agreement is improved. However, this statement is partially affected by the lack of knowledge in barium sulfate kinetics.
Improvement of hydrogen storage by adsorption using 2‐D modeling of heat effects
Authors: Delahaye A. , Aoufi A. , Gicquel A. , Pentchev I. 
Published: April 2004

AbstractThe use of hydrogen storage based on an adsorption process for cars operating on a fuel cell will be seriously considered when the amount of stored gas is high enough, the tank safe and economically viable, and the filling process fast enough. To maximize the storage capacity for rapid filling, it is necessary to minimize heating of the adsorbent bed and to imagine means to extract energy toward the outside. Numerical simulation of such a hydrogen storage tank, based on a 2‐D model where mass and thermal energy balances are coupled, is presented. Results from simulations agreed well with experiments, when various modified parameters were calculated. Solutions for improving adsorbent beds for hydrogen storage tanks are then proposed.
Mechanisms of mixing and creation of structure in laminar stirred tanks
Authors: Alvarez M. M. , Zalc J. M. , Shinbrot T. , Arratia P. E. , Muzzio F. J. 
Published: April 2004

AbstractAlthough stirred tanks have been the most commonly used fluid mixing devices since the beginnings of the industrial era, little is known about how and why they mix, and, therefore, about how to improve their performance, particularly when operated in the laminar regime. In laminar conditions, chaos is the only route to achieve efficient mixing. From the body of research in 2‐D chaotic flows, very minute perturbations in the velocity field can lead to widespread chaos and substantial enhancement of mixing performance, but these observations have not been systematically applied to industrially relevant 3‐D flows. Using planar laser induced fluorescence and direct numerical simulations, the mechanisms of creation and evolution of mixing structures were studied in Newtonian and non‐Newtonian flows. The observed dynamical behaviors are related to geometric features of the system. In Newtonian flow systems, the passing of the impeller blades triggers the onset of chaos by introducing small perturbations to the underlying regular 2‐D flow that is observed when impellers are substituted with discs. In non‐Newtonian viscoelastic systems, nonlinearity in the stress field introduced by the fluid rheology drives the system to spontaneous chaos even when concentric discs are used to stir the fluid.
Tracer mixing dynamics during aggregation and fragmentation
Authors: McCoy Benjamin J. , Madras Giridhar 
Published: April 2004

AbstractFor many chemical systems consisting of particles, liquid droplets, or gas bubbles undergoing concurrent (reversible) aggregation and fragmentation in a stirred immiscible fluid, evolution of the particle distribution and mixing of chemical species are important fundamental issues. A dynamic model for dispersive mixing systems presented here illustrates the time dependence of the particle‐size distribution (PSD) and the tracer mass distribution (TMD). For rapid tracer diffusion, the population balance equations (PBEs) for the PSD and TMD are identical (only the initial conditions differ) for binary aggregation and fragmentation rate coefficients that do not depend on particle size or tracer mass. The integrodifferential PBE is solved by a numerical method, and results agree with the moment solution. Measures for the degree of tracer mixing are related to the variance or polydispersity index and to the mixing entropy. The kinetics are reversible, allowing the PSD, TMD, and mixing entropy to approach stationary states. Results are partially compared with a similarity solution for the PSD.
Monitoring of batch processes using spectroscopy
Authors: Gurden Stephen P. , Westerhuis Johan A. , Smilde Age K. 
Published: April 2004

AbstractThere is an increasing need for new techniques for the understanding, monitoring and the control of batch processes. Spectroscopy is now becoming established as a means of obtaining real‐time, high‐quality chemical information at frequent time intervals and across a wide range of industrial applications. In this article, the role of spectroscopy for batch process monitoring is discussed in terms of both current and potential advances. The emphasis is on how to handle the measured data to extract maximum information for improved process performance and efficiency. In particular, the use of spectroscopy for statistical process monitoring is detailed and considered as complementary to the use of engineering process data. A case study of the ultraviolet‐visible monitoring of a first‐order biochemical conversion reaction is described, as well as the advantages of spectroscopy for process fault detection and diagnosis. Future prospects for the use of on‐line spectroscopy are also discussed.
Foaming mechanisms in surfactant free particle suspensions
Authors: Bindal S. K. , Sethumadhavan G. , Nikolov A. D. , Wasan D. T. 
Published: April 2004

AbstractPhysical mechanisms for foam formation in the presence of colloidal particles are poorly understood. This study is aimed at enhancing the basic understanding of the mechanisms that produce foaming in a three‐phase system, containing solid, liquid, and gas, and identifying key parameters that aggravate foaming in the absence of surface‐active agents. The foaming ability of a system (“foaminess”) was investigated by aerating a suspension of nanosized hydrophilic silica particles. We observed that the foaminess was directly proportional to particle concentration and inversely proportional to particle size. However, even a small degree of bidispersity in particle size drastically reduced foaminess. To explain these observations, the drainage of a single foam lamella containing nanosized particles was studied using a novel capillary force balance apparatus, which incorporates the microinterferometric technique. The single foam lamella thins in a stepwise manner, as the colloidal particles self‐organize into a layered structure between the gas bubbles. This layer provides a barrier against coalescence of bubbles, thereby stabilizing the foam lamella. The number of stepwise film thickness transitions increased with particle concentration and decreased with the increase in the particle size, consistent with the results from foaming experiments. Particle bimodal distribution greatly decreases the foam‐lamella stability, consistent with the theoretical prediction.
Interpretation of ethane hydrate equilibrium data for porous media involving hydrate‐ice equilibria
Authors: Zhang Wu , Wilder Joseph W. , Smith Duane H. 
Published: April 2004

AbstractEquilibrium pressures for the dissociation of ethane hydrate confined in silica gel pores of nominal radii 7.5, 5.0 or 3.0 nm were measured over a range of temperatures. Each of these porous media contained a broad distribution of pore radii. At higher temperatures, the pressures were larger than previously reported for bulk hydrates, and generally increased with a decrease in nominal pore radius for those data where the equilibria involved liquid water. However, at the lowest temperatures (where the equilibria involved ice), the pressures were identical (within expected experimental uncertainties) for all three silica gels and the same as reported by various authors for the bulk hydrate. The lack of any dependence of the equilibrium pressure on pore size at the lowest temperatures (where the equilibrium involves ethane hydrate, ethane gas, and ice) indicates that, below the quadruple point temperature of the smallest pore in which hydrate formed, there is no detectable effects on the equilibrium pressure due to the restricted geometries of the porous media. It suggests that the interface relevant to the formation of hydrate in silica gel pores is that between the hydrate and aqueous phase (Henry et al., 1999) and that within experimental error the surface energy between the hydrate and aqueous phase can be approximated by that between ice and the appropriate aqueous phase.
Colloid‐associated contaminant transport in porous media: 2. Mathematical modeling
Authors: Sen Tushar Kanti , Nalwaya Nitesh , Khilar Kartic C. 
Published: April 2004

AbstractA comprehensive mathematical model developed describes the colloid‐associated contaminant transport in groundwater flows based on equilibrium adsorption of contaminants, hydrodynamic release, migration, and capture of colloidal fines in groundwater flows. This model is more realistic than the existing models in that the physics of migration of colloidal fines is adequately incorporated. It also accounts for the entrapment and plugging of fine particles and, therefore, predicts both facilitation and retardation of the transport of contaminants depending on the flow and other conditions. The conditions leading to inhibition/retardation of contaminant transport due to plugging are: high release coefficient, low initial porosity, high inlet fines concentration, and high initial permeability. The mobilization and migration of colloidal fines, kaolin and their role on plugging, as well as on Ni2+ contaminant transport through kaolin‐sand packed beds, were studied, and the model was tested with published experimental measurements, as well as with our laboratory column results. The plugging‐based retardation of contaminant transport can be used to develop a new containment technique.
Modeling intra‐ and extra‐particle processes of wood fast pyrolysis
Authors: Di Blasi Colomba 
Published: April 2004

AbstractA detailed single‐particle model, including a description of transport phenomena and a global reaction mechanism, is coupled with a plug‐flow assumption for extraparticle processes of tar cracking, in order to predict the fast pyrolysis of wood in fluid‐bed reactors for liquid‐fuel production. Good agreement is obtained between predictions and measurements of product yields (liquids, char, and gases) as functions of temperature. Particle dynamics are very affected by the convective transport of volatile products. The average heating rates are on the order of 450–455 K/s, whereas reaction temperatures vary between 770 and 640 K (particle sizes of 0.1–6 mm and a reactor temperature of 800 K). The effects of several factors, such as size, shape, and shrinkage of wood particles, and external heat‐transfer conditions are also examined.
Hydrodynamic transport properties of concentrated suspensions
Authors: Chang Chingyi , Powell Robert L. 
Published: April 2004

AbstractA method of estimating the dependency of the relative viscosities and average sedimentation velocities of particle dispersions on the particle packing behavior, which is related to the shape (sphericity or aspect ratio) of the particle and the ruggedness of the particle surface is proposed. For each ensemble of microstructures, as determined by the flow system in which measurements are made (such as steady shear flow, high‐frequency dynamic shear flow, or sedimentation in a static fluid), a single master curve is obtained. These curves allow direct estimates of the relative viscosities or sedimentation velocities to be made if the maximum packing fraction is known.
Fluid mechanics of laminated sheet manufacture
Authors: Eames I. , Wright N. , Gilbertson M. A. 
Published: April 2004

AbstractThe fluid mechanics of laminated sheet manufacture was studied by pouring a liquid filler from a point source onto an inclined moving sheet and then passing it under a narrow gap below a pinch bar that spreads the liquid under the influence of gravity. The liquid filler must pass under the pinch bar before it starts to solidify. The spreading of a viscous liquid as it undergoes this process was studied theoretically and experimentally. Steady similarity solutions were obtained based on a vertically averaged formulation of the mass and momentum equations for viscous flows. Experimental measurements of the spread of the fluid and the time taken for fluid to travel from the source to the pinch bar agreed well with theoretical predictions. The new models are applied to the operation of the manufacturing process and the implications are discussed.
Analysis on nanoparticle growth by coagulation in silane plasma reactor
Authors: Kim Dong‐Joo , Kim Kyo‐Seon 
Published: April 2004

AbstractThe particle growth in a silane plasma reactor by coagulation between particles was analyzed by using a discrete‐sectional model, considering effects of a particle charge distribution based on the Gaussian distribution function. At the start of the plasma discharge, there is the high concentration of small‐size particles, and later large‐size particles appear and grow by coagulation between small‐size particles. Some fractions of small‐size particles are in a neutral state or even charged positively. The positively charged small‐size particles coagulate faster and more selectively with large‐size particles, which are charged more negatively than with medium‐size particles. Also, the particle‐size distribution in a plasma reactor becomes bimodal and large‐size particles become quite monodisperse. As the mass generation rate of monomers increase or as the monomer diameter decreases, large‐size particles grow more quickly and the particle‐size distribution becomes bimodal earlier. The plasma reactor can be a good candidate to produce monodisperse, nanosized particles.
Intrapellet diffusivities from TAP pulse responses via moment‐based analysis
Authors: Colaris A. H. J. , Hoebink J. H. B. J. , de Croon M. H. J. M. , Schouten J. C. 
Published: April 2004

AbstractMoment‐based analysis was applied to determine successfully inter‐ and intrapellet diffusion coefficients from experimental TAP outlet pulse responses over a one‐zone bed with porous particles. Different temperatures, gas molar masses, and pellet sieve fractions were used to validate the Knudsen diffusion relation for inert gases inside porous catalyst pellets. The zeroth to third moments of the outlet pulse response were analytically derived for rectangular, cylindrical and spherical pellets. The third moment provides a significantly more accurate access to the intrapellet diffusivity than the second moment does. The experimental window of the TAP reactor is explored for porous silica as catalyst support bed filling. The relevance of concentration gradients inside the pellet is illustrated with model simulations.
Effects of diffusion‐controlled reactions on atom‐transfer radical polymerization
Authors: Delgadillo‐Velázquez Omar , Vivaldo‐Lima Eduardo , Quintero‐Ortega Iraís A. , Zhu Shiping 
Published: April 2004

AbstractA kinetic model incorporating effects of diffusion‐controlled reactions on atom‐transfer radical polymerization (ATRP) was developed. The reactions considered to be diffusion‐controlled are monomer propagation, bimolecular radical termination, chain transfer between propagating radical and catalyst, and transfer to small molecules. Model predictions indicate that a diffusion‐controlled propagation reduces the “living” behavior of the system, whereas a diffusion‐controlled termination enhances its livingness. When diffusion‐controlled transfer between chains and catalyst is considered the same in the forward and backward directions, the livingness of the system is enhanced, but if one of them is kept unchanged while the other is increased, the livingness of the system is reduced. When diffusion‐controlled termination is important, our simulations show that the overall effect of diffusion‐controlled phenomena in ATRP is to enhance the livingness of the system. Experimental data from the literature for styrene, methyl methacrylate, and methyl acrylate ATRP homopolymerizations validate the kinetic model.
Continuous atom transfer radical block copolymerization of methacrylates
Authors: Shen Youqing , Zhu Shiping 
Published: April 2004

AbstractA column reactor packed with silica‐gel‐supported copper bromide (CuBr)–hexamethyltriethylenetetramine (HMTETA) was developed for the continuous‐transition–metal‐mediated living/controlled radical polymerization [atom transfer radical polymerization (ATRP)] for homo‐ and block copolymerization of methyl methacrylate (MMA). The reactor showed good stability (>100 h) in both catalyst activity and molecular weight of the poly(methyl methacrylate) (PMMA) produced. The MMA conversion decreased as the flow rate increased. The polymerization in the reactor was in first order with respect to monomer concentration. The molecular weight of the resulting PMMA increased linearly with MMA conversion, exhibiting the characteristic feature of living polymerization. Thus, simply changing the flow rate of MMA, which in turn determined the MMA conversion, readily controlled the molecular weight of PMMA. The block copolymerization of MMA with n‐butyl methacrylate (nBMA) was carried out using two reactors connected in series. The block copolymers were slightly contaminated by PMMA prepolymer from the first column. The molecular weight of the nBMA block could be changed by the flow rate of the nBMA in the second reactor. This packed column reactor technology is feasible for continuously synthesizing polymers or block copolymers with controlled molecular weights that are readily adjustable by changing the monomer flow rates.