bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optimal design of batch‐storage network using periodic square wave model
Authors: Yi Gyeongbeom , Reklaitis Gintaras V. 
Published: April 2004

AbstractThis study is to find the analytic solution for determining the optimal capacity (lot size) of a multiproduct, sequential, multistage production and inventory system to meet the finished product demand. It overcame the limitation of the classical lot sizing method developed based on the single product and single‐stage assumption. The superstructure of the plant consisted of a network of serially and/or parallel interlinked batch processes and storage units. The processes involve chemical reactions with multiple feedstock materials and multiple products, as well as mixing, splitting, or transportation of materials. The objective function for optimization is minimizing the total cost composed of setup and inventory holding costs, as well as the capital costs of constructing processes and storage units. The resulting simple analytic solution can greatly enhance the proper and quick investment decision for the preliminary plant design problem confronted with diverse economic situations.
Control‐relevant scheduling of polymer grade transitions
Authors: Mahadevan Radhakrishnan , Doyle Francis J. , Allcock Andrew C. 
Published: April 2004

AbstractGrade transition is a critical step in the operation of a polymerization reactor. The nonlinear input‐output behavior of the reactor can lead to severe differences in the dynamic response of different grade transitions. These differences are analyzed under the assumption that the polymerization reactor is regulated by a linear controller. The cost of each transition is calculated based on a linear first‐order model of the transition. Robust control theory is employed to propose screening tools and heuristics for the identification of the transitions that are “difficult” from an operational perspective in the presence of uncertainty. The dependence of the transition cost on the gain and the time constant of various transitions is analyzed to determine the effect of process nonlinearities on the scheduling problem. This approach is demonstrated on the problem of scheduling grade transitions in an isothermal methyl methacrylate polymerization reactor.
Process modeling by Bayesian latent variable regression
Authors: Nounou Mohamed N. , Bakshi Bhavik R. , Goel Prem K. , Shen Xiaotong 
Published: April 2004

AbstractLarge quantities of measured data are being routinely collected in various industries and used for extracting linear models for tasks such as process control, fault diagnosis, and process monitoring. Existing linear modeling methods, however, do not fully utilize all the information contained in the measurements. A new approach for linear process modeling makes maximum use of available process data and process knowledge. Bayesian latent‐variable regression (BLVR) permits extraction and incorporation of knowledge about the statistical behavior of measurements in developing linear process models. Furthermore, BLVR can handle noise in inputs and outputs, collinear variables, and incorporate prior knowledge about regression parameters and measured variables. The model is usually more accurate than those of existing methods, including OLS, PCR, and PLS. BLVR considers a univariate output and assumes the underlying variables and noise to be Gaussian, but it can be used for multivariate outputs and other distributions. An empirical Bayes approach is developed to extract the prior information from historical data or maximum‐likelihood solution of available data. Examples of steady‐state, dynamic and inferential modeling demonstrate the superior accuracy of BLVR over existing methods even when the assumptions of Gaussian distributions are violated. The relationship between BLVR and existing methods and opportunities for future work based on this framework are also discussed.
Large‐scale oscillations of a feedstream inside a stirred tank reactor
Authors: Verschuren Iris L. M. , Wijers Johan G. , Keurentjes Jos T. F. 
Published: April 2004

AbstractRecent studies have shown feedstreams inside stirred tank reactors to oscillate. When multiple feed points are used, these oscillations can cause feedstreams to overlap. The objective of this study is to determine a description of the oscillations that can be used to prevent the feedstreams to overlap. The oscillations are analyzed by determining the displacements of the centers of the mass of a feedstream in radial cross sections. The growth of the root‐mean‐square radius of these displacements with time is linear, corresponding to the “initial growth stage.” The growth rate of the root‐mean‐square radius with time proved to equal the velocity fluctuations related to turbulent motions with a size larger than the diameter of the feedstream, indicating that these large‐scale turbulent motions are responsible for large‐scale oscillations. With the description obtained for the root‐mean‐square radius, the minimal distance between two feed pipes necessary to prevent the overlap of the feedstreams can be calculated.
Experimental measurement of radiative heat transfer in gas‐solid suspension flow system
Authors: Han Guiyoung , Tuzla Kemal , Chen John C. 
Published: April 2004

AbstractAn experimental measurement of the radiative heat flux from a gas‐solid suspension to wall was made in a water cooled heat exchanger. The heat‐transfer test section was 5 cm ID and 90 cm long. Operating temperature ranged from 200 to 600°C and the gas velocity at the inlet of the test section varied from 6 to 11 m/s. The suspension densities covered a range from 3 to 35 kg/m3. Time‐averaged radiative heat flux was directly measured using a radiometer, which allowed to determine suspension emissivity using a measured suspension temperature. Radiative heat flux and suspension emissivity showed strong dependence on the suspension density. The effect of particle size on suspension emissivity was also studied by using two different sizes of particles. Experimentally determined suspension emissivities, which ranged from 0.3 to 0.85, agreed well with the predictable suspension emissivities based on an independent scattering theory. The contribution of radiation to total heat transfer was about 40–50% for the operating condition used in this study.
Separation of mono‐ and dibranched hydrocarbons on silicalite
Authors: Jolimaitre E. , Ragil K. , Tayakout‐Fayolle M. , Jallut C. 
Published: April 2004

AbstractBreakthrough curves for mixtures of C5 and C6 hydrocarbons with different degrees of branching were obtained experimentally on a silicalite molecular sieve by fixed‐bed experiments. The kinetic separation of di‐ from monobranched hydrocarbons was feasible on this type of zeolite: dimethyl molecules enter silicalite crystals very slowly, whereas monomethyl molecules are quickly adsorbed. Experimental results were compared to a theoretical isothermal model, considering the variation of diffusivity with concentration according to the Maxwell–Stefan theory. The parameters of the model (adsorption equilibria and diffusivities) were determined from single‐component breakthrough curves. Experimental curves were generally well represented by the model, but the variation of diffusivity with concentration, as predicted by the Maxwell–Stefan theory, did not significantly improve the model prediction of experimental breakthrough curves by using a mean value of diffusivity.
Vacancy solution theory for binary adsorption equilibria in heterogeneous carbon
Authors: Ding L. P. , Bhatia S. K. 
Published: April 2004

AbstractA heterogeneous modified vacancy solution model of adsorption developed is evaluated. The new model considers the adsorption process through a mass‐action law and is thermodynamically consistent, while maintaining the simplicity in calculation of multicomponent adsorption equilibria, as in the original vacancy solution theory. It incorporates the adsorbent heterogeneity through a pore‐width‐related potential energy, represented by Steele's 10–4–3 potential expression. The experimental data of various hydrocarbons, CO2 and SO2 on four different activated carbons—Ajax, Norit, Nuxit, and BPL—at multiple temperatures over a wide range of pressures were studied by the heterogeneous modified VST model to obtain the isotherm parameters and micropore‐size distribution of carbons. The model successfully correlates the single‐component adsorption equilibrium data for all compounds studied on various carbons. The fitting results for the vacancy occupancy parameter are consistent with the pressure change on different carbons, and the effect of pore heterogeneity is important in adsorption at elevated pressure. It predicts binary adsorption equilibria better than the IAST scheme, reflecting the significance of molecular size nonideality.
Nonlinear model predictive control of end‐use properties in batch reactors
Authors: Valappil Jaleel , Georgakis Christos 
Published: April 2004

AbstractSignificant economic benefits can be derived from reducing the variability of product properties around their specification targets in batch reactors. End‐use properties in batch reactors using dynamic models that relate the operating conditions to the end‐use properties are related through a static nonlinear model to the molecular properties of the product and are controlled directly. Their values are required to lie in a desired target region in the property space. The control of end‐use product properties is formulated as a nonlinear model predictive control problem, and an efficient numerical technique using successive linearizations is utilized for the solution. A parameter adaptive extended Kalman filter is used for state estimation of the molecular properties that are not measured directly. The emulsion polymerization of styrene is chosen as a case study, and an approximate mathematical model is developed. The model is detailed enough to predict the end‐use properties, which depend on both the molecular weight and particle‐size distributions of the product. The end‐use product properties, such as tensile strength and melt index, are controlled in desired target regions by adding a monomer and a chain transfer agent, as well as the flow rate of the coolant, as the manipulated variables.
YSZ‐SrCo0.4Fe0.6O3‐δ membranes for the partial oxidation of methane to syngas
Authors: Gu Xuehong , Jin Wanqin , Chen Changlin , Xu Nanping , Shi Jun , Ma Y. H. 
Published: April 2004

AbstractThe perovskite‐related yttria‐stabilized zirconia promoted SrCo0.4Fe0.6O3‐δ (SCFZ) oxides were used to construct membrane reactors for the partial oxidation of methane to syngas (POM). The oxygen permeability study of the SCFZ membrane in the air/helium gradient showed that the apparent activation energy was about 69±5 kJ/mol at 1,023∼1,223 K, and the oxygen flux was controlled by the bulk diffusion and surface exchange rate. In a cofeed reactor packed with SCFZ pellets and a blank SCFZ membrane reactor without any catalyst packing, the SCFZ oxides showed low catalytic activity for POM in the fixed‐bed reactor and no POM catalytic activity in the membrane reactor. An SCFZ membrane reactor with NiO/Al2O3 catalyst was continuously running for over 220 h under constant operational conditions. While about 64% of methane was converted with 100% CO selectivity after reaching the steady state, the oxygen flux was about 10 times the value of the air/helium gradient, in the reactor packed with the catalyst. The oxygen flux of SCFZ membranes in the reducing atmosphere could be limited by the surface reaction rate at the reaction side.
Using CFD to understand chaotic mixing in laminar stirred tanks
Authors: Zalc J. M. , Szalai E. S. , Alvarez M. M. , Muzzio F. J. 
Published: April 2004

AbstractHigh‐accuracy CFD results for laminar flow in a stirred tank agitated by three Rushton turbines are used as a starting point for an in‐depth analysis of mixing. Asymptotic mixing performance is investigated as a function of the Reynolds number by means of Poincaré sections, which reveal large segregated regions with sizes and shapes that vary greatly over a relatively small range of Reynolds numbers. The spatial distribution of mixing intensities is also examined by computing the stretching field, which can be used to optimally choose injection locations for dispersing additives in the tank. When mixing dynamics is examined by particle tracking, the structures observed at short times expose the mechanism of laminar mixing by Rushton turbines. The computed mixing structures are compared with experimental images of dye concentration using planar laser‐induced fluorescence. A remarkable agreement is observed for the short‐term, as well as the asymptotic evolution, of mixing patterns. Simulations of dye concentration fields as a function of Re confirm large differences in mixing behavior for the four different flow conditions. Strong axial segregation revealed by the stretching field, as well as the location of poorly mixing regions, are accurately predicted.
Scaling of granular flow processes: From surface flows to design rules
Authors: Ottino J. M. , Khakhar D. V. 
Published: April 2004

AbstractScale‐up of granular processes is notoriously difficult and there is little guidance at the present time. This is true even in the simplest case of noncohesive powders consisting of spherical grains, the scenario considered here. However, flows in granular materials are often restricted to thin regions of rapid surface flow with the rest of the material suffering only slow plastic rearrangements. This seemingly trivial observation leads to understanding of the entire system and to the concept that an understanding of surface flows constitutes the key element for scale‐up of granular flow processes. A surface flow is characterized primarily by its thickness and the shear rate. For large particles, both are controlled primarily by the Froude number and the particle‐size ratio (particle diameter to cylinder radius), whereas material properties have a secondary effect. Modern experimental techniques are yielding further insight into the physics of shear flows and theoretical analysis is providing guidance and scaling insights. The assembly of experimental and theoretical components opens the class of problems dominated by surface flows to serious engineering analysis and predictability. Current understanding is extended and integrated, the governing scaling laws are made explicit, and the results obtained in terms of rules are summarized. The use of the integrated knowledge by means of an example is exemplified.
High‐dimensional solid‐liquid phase diagrams involving compounds and polymorphs
Authors: Wibowo Christianto , Samant Ketan D. , Ng Ka M. 
Published: April 2004

AbstractA systematic procedure for the generation and visualization of high‐dimensional isobaric phase diagrams for systems exhibiting compound formation and/or polymorphism is presented. Such phase diagrams are useful in synthesizing crystallization‐based separation processes for systems involving compounds and polymorphs, which are common in the production of pharmaceuticals. Polythermal as well as isothermal phase diagrams of multicomponent systems can be generated. Examples are provided to illustrate the procedure.
Equilibria for adsorption of phosphates on OH‐type strongly basic ion exchanger
Authors: Yoshida Hiroyuki , Galinada Wilmer A. 
Published: April 2004

AbstractThe equilibrium isotherms for adsorption of phosphate ions using an OH‐type, strongly basic ion exchanger, DIAION SA10A, were studied experimentally and the results appeared technically feasible. Four different types of phosphate ions, H3PO4, H2PO, HPO, and PO, were used. In all the systems considered, the experimental adsorption isotherms showed a high amount of phosphate adsorption. Moreover, differences in the adsorption behaviors were observed. These differences were highly influenced by the pH of the equilibrated solutions. The ion‐exchange reaction models were then proposed. By the mass action law, the theoretical equations for the adsorption isotherms were derived and the unknown experimental equilibrium constants were determined. These equilibrium models were able to correlate the experimental data well and explained the peculiarities in the obtained experimental adsorption isotherms.
Liquid–liquid extraction with chemical reaction in a novel impinging‐jets reactor
Authors: Dehkordi Asghar Molaei 
Published: April 2004

AbstractThe theory of mass transfer accompanied by chemical reaction for the pseudo‐first‐order heterogeneous liquid–liquid reactions was used to measure the effective interfacial area in a novel two‐impinging‐jets reactor (TIJR), which is characterized by a small reactor volume equipped with two simple nozzles directed toward each other. Aqueous and organic streams were jetted through the nozzles into rotating and stationary disks, resulting in a highly turbulent mixture of aqueous and organic phases. Experiments were also conducted on the physical extraction of n‐Butyl formate into distilled water to measure the overall volumetric mass‐transfer coefficients. Due to both the impinging process and high rate shear forces acting on the phases, the overall volumetric mass‐transfer coefficients and volumetric extraction rates obtained by the physical and chemical method, respectively, increased dramatically compared to those obtained by conventional reaction systems and an air‐driven two‐impinging‐streams reactor developed by the present author. The enhancing effect of impinging jets on the conversion of aqueous NaOH solution was tested by another nonimpinging‐jets reactor.
Real‐time, nonlinear control of a constrained, nonminimum‐phase process
Authors: Kanter Joshua M. , Seider Warren D. , Soroush Masoud 
Published: April 2004

AbstractThis article presents the first real‐time implementation of a recently‐developed model‐based control method on a pilot‐scale, multivariable, liquid‐level process that exhibits inverse response and whose actuators can be saturated. Issues in real‐time implementation of the control method are discussed, as well as a controller tuning procedure. Two model‐based controllers are implemented: one is derived using the process outputs; the other is derived using auxiliary outputs. Servo and regulatory responses presented show the differences in the performance of the two controllers. In real time, one of the model‐based controllers eliminates inverse response in one controlled output at the expense of yielding a larger inverse response in the other controlled output. This inverse‐response elimination is a real‐time validation of the linear and nonlinear theoretical results reported in the systems literature.
Multiple plant heat integration in a total site
Authors: Bagajewicz Miguel , Rodera Hernán 
Published: April 2004

AbstractHeat integration across plants can be accomplished either directly using process streams or indirectly using intermediate fluids. Extensions to many plants of LP and MILP models previously developed for the two‐plant case are presented. The targeting procedure first identifies the maximum possible savings for the whole system, and, subsequently, the minimum number of connections between the two‐plant combinations required to obtain maximum savings is established. The location of intermediate fluid circuits to indirectly integrate the system is then found. Alternative solutions exist, which allow flexibility when the design of a multipurpose heat exchanger network is pursued. Finally, the optimal location of the circuits for cases of restricted operation is discussed.
Kinetic model for the pyrolysis of polysiloxane polymers to ceramic composites
Authors: Plawsky Joel L. , Wang Feng , Gill William N. 
Published: April 2004

AbstractA model describing the pyrolysis of an organo‐silicate polymer (Blackglas polymer) to form a silicon oxycarbide glass was developed based on the known chemistry and architecture of the polysiloxane precursor. The objectives were to develop a plausible reaction pathway to explain the pyrolysis process, rate, and product spectrum, and to study the effect of various heating protocols on the pyrolysis process. The model successfully predicted the evolution rates of the major gases as a function of process temperature and the overall pressures reached during the process. The effects of various heating protocols on the outgassing kinetics were studied to develop an optimum protocol for a rapid pyrolysis process that gives a composite with desirable mechanical properties. Overall, the model appears to capture the essential characteristics of the process and is in good agreement with experimental results.
COSMOSPACE: Alternative to conventional activity‐coefficient models
Authors: Klamt Andreas , Krooshof Gerard J. P. , Taylor Ross 
Published: April 2004

AbstractAn analytical solution, COSMOSPACE, to the statistical thermodynamics of a model of pairwise interacting surfaces, is presented. This solution was initially developed for the a priori prediction model COSMO‐RS in an implicit form. A comparison of COSMOSPACE with UNIQUAC and with the quasi‐chemical theory of Guggenheim reveals the conditions under which the models yield similar results and when they differ very considerably. It is shown that COSMOSPACE is in extremely good agreement with Monte‐Carlo simulations for some lattice fluids (where UNIQUAC is particularly poor). The ability of COSMOSPACE to provide good fits to experimental data is shown for three binary mixtures including ethanol‐cyclohexane, where UNIQUAC incorrectly predicts a liquid–liquid phase separation.
Thermal conversion of biomass: Comprehensive reactor and particle modeling
Authors: Wurzenberger Johann C. , Wallner Susanne , Raupenstrauch Harald , Khinast Johannes G. 
Published: April 2004

AbstractThermal conversion of biomass is often carried out in packed‐bed furnaces. Optimization of thermal efficiency and furnace emissions is an important goal, which requires accurate understanding of all physical and chemical effects in the reactor. A combined transient single particle and fuel‐bed model is presented. The fuel‐bed model is discretized, and a representative particle is chosen and discretized in a radial direction at each grid point. Mass, momentum and energy balances are solved for the entire system. Drying is modeled using an equilibrium approach, and primary pyrolysis is described by independent parallel‐reactions. Secondary tar cracking, homogeneous gas reactions, and heterogeneous char reactions are modeled using kinetic data from literature. Simulations validated for single particles agree well with experimental studies. Simulation results for the combustion of a biomass bed are presented for one set of furnace conditions.
Enhancement of the methane storage on activated carbon by preadsorbed water
Authors: Zhou Li , Sun Yan , Zhou Yaping 
Published: April 2004

AbstractThe enhancement effect of preadsorbed water on methane storage on activated carbon was experimentally proven. Adsorption isotherms of methane on dry and wet activated carbon with different water content were measured at 275–283 K and pressures up to 11 MPa. A sudden change in the methane uptake mechanism that was indicated by the inflection point of isotherms was observed. The measured amount adsorbed always decreased with the increasing water content of carbon before the inflection point. However, a step rise in the isotherm to as much as 63.3% was observed when the pressure reached the inflexion point locating at 4–5 MPa. The significant enhancement of water on the methane‐storage capacity of activated carbon is expected to considerably improve the adsorbed natural gas (ANG) technology.