bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bubble growth in a viscous liquid in a simple shear flow
Authors: Favelukis Moshe , Tadmor Zehev , Semiat Raphael 
Published: April 2004

AbstractThe nucleation and growth of a bubble in a Newtonian liquid in simple shear and creeping flow were studied experimentally in a Couette apparatus operating under vacuum. A low molecular weight polyisobutylene was chosen as a typical high‐viscosity Newtonian liquid. The volatile solvent in our experiments was simulated by air, and the formed or growing bubbles were photographed under shear. The experimental foaming results indicate that vacuum (at a level of supersaturation conditions) is not sufficient to boil a viscous solution, even in the presence of bubbles (nucleation sites), as shear also has to be applied. Furthermore, there is probably a critical shear rate (or stress) at which boiling appears. Bubble growth experimental results indicate that the growth rate of a slender bubble increases as the shear rate increases and as the pressure decreases. The experimental results agree well with theoretical models developed by Lee and Biesenberger (for bubble nucleation) and by the authors (for bubble growth).
Equilibria and dynamics for mixed vapors of BTX in an activated carbon bed
Authors: Yun Jeong‐Ho , Choi Dae‐Ki , Kim Sung‐Hyun 
Published: April 2004

AbstractExperimental and theoretical studies were made on the adsorption of benzene, toluene, p‐xylene, and their binary and ternary mixtures by activated carbon in an isothermal condition of 303 K. Experimental isotherms for pure components were measured by two kinds of experimental techniques: the static volumetric method and breakthrough data analysis. Breakthrough data analysis shows that both the extended Langmuir equation and the ideal adsorbed solution theory could explain mixture isotherm data with good accuracy. In addition, a mathematical model was developed to simulate the column dynamics of pure and mixed‐vapor adsorption systems. To represent the mass‐transfer rate inside the adsorbent particle, the linear driving‐force approximation model was applied. By optimizing the pure‐ and the binary‐component breakthrough curve data with a dynamic model, an empirical correlation was proposed to represent the overall mass‐transfer rates for the BTX vapor‐activated carbon system. Results with this correlation, which is a function of the partial pressures for each adsorbate and interstitial bulk fluid velocities, showed that the prediction agrees well with the experimental data of ternary breakthrough curves.
Adsorption equilibrium of α‐amylase in aqueous solutions
Authors: Bautista L. Fernando , Martínez Mercedes , Aracil José 
Published: April 2004

AbstractThe influence of pH, ionic strength and temperature on the equilibrium of adsorption of α‐amylase from Aspergillus oryzae on a hydrophobic (Duolite XAD‐761) and an anion‐exchange (Duolite A‐568) polymer‐based adsorbent was studied by moment analysis of the chromatographic peak responses in HPLC. The adsorption isotherms were also measured in batch experiments at different temperatures. Both systems show a nonlinear equilibrium within the concentration range studied, and the results were fitted to both the Langmuir and Freundlich equations. Enthalpies and entropies of adsorption were estimated from the equilibrium adsorption constant obtained both by moment analysis and by the limit region of the Langmuir isotherm corresponding to Henry´s law. The results show that the process of adsorption of α‐amylase on the hydrophobic resin was exothermic, while the anion exchange process is endothermic.
Thermodynamic approach to the structural stability of process plants
Authors: Hangos Katalin M. , Alonso Antonio A. , Perkins John D. , Ydstie B. Erik 
Published: April 2004

AbstractA thermodynamic approach for analyzing the structural stability of process plants is presented. The results are connected with a theory of systems described by dynamic conservation balances using a potential for stability analysis that generalizes the availability/exergy. This theory is used to show that interconnected systems with no source terms and Kirchhoff convection are structurally asymptotically stable. The approach is applicable for systems where only Kirchhoff convective transport and transfer processes with equilibrium take place. Systems with constant mass holdup in every balancing volume satisfy the condition of Kirchhoff convection. The general results are illustrated in examples of practical importance including heat exchanger networks, multicomponent flash, and multicomponent distillation with constant molar flows.
Optimal location of vertical wells: Decomposition approach
Authors: Ierapetritou M. G. , Floudas C. A. , Vasantharajan S. , Cullick A. S. 
Published: April 2004

AbstractThe generation of a reservoir development plan with well locations, given a reservoir property map and a set of infrastructure constraints, represents a very challenging problem. The problem of selecting the optimal vertical well locations was formulated with 3‐D information as a MILP problem where the binary variables correspond to the decisions of well locations and vertical well completions. A novel decomposition‐based solution procedure is proposed to address real fields characterized by 60,000 grid points. The approach is based on the ideas of refining the feasible set of candidate well locations by applying quality cut constraints. For the solution of the subproblems required at each iteration, a model reformulation was then suggested that enables the efficient determination of the optimal well locations. Two industrial case studies are considered to illustrate the applicability of the proposed procedure to realistic large‐scale problems.
Model reduction for chemical kinetics: An optimization approach
Authors: Petzold Linda , Zhu Wenjie 
Published: April 2004

AbstractThe kinetics of a detailed chemically reacting system can potentially be very complex. Although the chemist may be interested in only a few species, the reaction model almost always involves a much larger number of species. Some of those species are radicals, which are very reactive species and can be important intermediaries in the reaction scheme. A large number of elementary reactions can occur among the species; some of these reactions are fast and some are slow. The aim of simplified kinetics modeling is to derive the simplest reaction system which retains the essential features of the full system. An optimization‐based method for reduction of the number of species and reactions in chemical kinetics models is described. Numerical results for several reaction mechanisms illustrate the potential of this approach.
Interfacial tension reduction and coalescence suppression in compatibilized polymer blends
Authors: Lepers Jean‐Christophe , Favis Basil D. 
Published: April 2004

AbstractThis work examines the influence of well‐defined diblock copolymers on the interfacial tension and morphology of an immiscible polymer blend. The system studied is a blend of 80% polystyrene and 20% ethylene propylene copolymer compatibilized by diblock copolymers of poly(styrene‐hydrogenated butadiene). The diblocks differed in that one contained 53% styrene (symmetric diblock) and the other 30% styrene(asymmetric diblock). The interfacial tension was performed using the breaking‐thread technique, and the results were compared to both the theoretical predictions of Noolandi and Hong, and Leibler. The morphology was tracked using an emulsification curve, comparison of which with the interfacial tension results made it possible to estimate the relative role of interfacial tension and coalescence reduction in particle‐size reduction phenomena.
Modeling of multicomponent drying of polymer films
Authors: Alsoy Sacide , Duda J. Larry 
Published: April 2004

AbstractThe drying of volatile solvents from a coated film is a complicated process since it involves simultaneous heat and mass transfer controlled by complex transport and thermodynamic behavior of polymer solutions. In this work, a model is developed to describe the drying behavior of multicomponent polymer solutions deposited on the impermeable substrate. A key component of the model is incorporation of multicomponent diffusion coefficients that consist of thermodynamic factors and self‐diffusivities. Vrentas‐Duda free‐volume theory was used for predicting concentration and temperature dependency of self‐diffusion coefficients. Drying processes in ovens with different zones in which temperature, velocity, and/or partial pressure of each solvent vary from zone to zone are considered. The predictions from the models provide detailed information about the relative importance of internal and external resistances to drying, effect of operating conditions, effect of the multiple‐zone approach, as well as sensitivity of all physical properties on the drying rate. The validity of the model was confirmed by comparing predictions with the drying data available in the literature and the data collected in our laboratories. The experimental data and the simulation results are in good agreement.
Surfactant and viscoelastic effects on drop deformation in 2‐D extensional flow
Authors: Tretheway Derek C. , Leal L. Gary 
Published: April 2004

AbstractThe deformation and breakup of polymeric drops suspended in an immiscible Newtonian fluid are examined for planar extensional flow in a computer controlled four roll mill are examined. Previous work from this lab with aqueous polymeric drops showed an increase in the degree of deformation compared to Newtonian drops, and two distinct breakup mechanisms, tip streaming, and tip streaming with stretch. This led to the conclusion that breakup for non‐Newtonian drops occurred at a lower capillary number and by a distinctly different mechanism than for a Newtonian drop with a similar ratio of internal to external viscosity. This conclusion was puzzling, because numerical computations with the Chilcott‐Rallison model showed that the influence of viscoelasticity for that model was to decrease the degree of deformation rather than increasing it. In this work, the results for aqueous polymer solutions are compared with results for ethylene glycol polymer solutions. The results suggest that tip streaming and tip streaming with stretch in the original experiments resulted from an undetected surfactant effect, which acts to produce a more pointed drop shape that destabilizes the drop to tip streaming. Viscoelasticity, on the other hand, acts to decrease the deformation of polymeric drops at a given capillary number and increases the critical capillary number, as predicted numerically, when compared to Newtonian drops with an equivalent viscosity ratio.
Measurements of solid concentration in a downward vertical gas–solid flow
Authors: Schiewe T. , Wirth K. E. , Molerus O. , Tuzla K. , Sharma A. K. , Chen J. C. 
Published: April 2004

AbstractNew results from experiments performed in a 15‐cm‐diameter downflow fast‐fluidized bed are presented. Tests were conducted at room temperature and near atmospheric pressure, with 125‐μm glass beads. Superficial gas velocities range from 0 to 6.6 m/s. Two different measurement techniques—gamma‐absorption tomography and capacitance sensing—were applied to the gas–solids flow in the downer tube. The average local solid fractions from both measurement techniques are compared for various operating conditions of the gas–solid flow. In general, good agreement was obtained between the solid concentration measurements from both measurement techniques. It is demonstrated that combined use of both measurement techniques offers the best chance to get time‐average information about the concentration distribution over the whole cross section.
Binary permeation through a silicalite‐1 membrane
Authors: van den Broeke Leo J. P. , Bakker Wridzer J. W. , Kapteijn Freek , Moulijn Jacob A. 
Published: April 2004

AbstractPermeation of binary gaseous mixtures through a silicalite‐1 membrane was studied. Results are reported for the fluxes and separation factors as a function of the feed composition, the pressure and the temperature. For the various cases a comparison is made between the binary and the single‐component permeation behavior. For the permeation of the mixtures the stronger adsorbed component is little affected by the presence of the weaker adsorbed component. On the other hand, for the weaker adsorbed component a clear reduction in the flux is observed. As a consequence, the separation factor for mixtures differs considerably from the so‐called ideal separation factor, which is the ratio of the one‐component permeances. As expected, the separation factor depends on the temperature. The separation factor is also a function of the composition and the feed pressure. This means that the binary equilibrium adsorption cannot be described with the extended Langmuir model. Binary permeation and separation behavior is described using the ideal adsorption solution theory for equilibrium adsorption.
Impact of gas composition on natural gas storage by adsorption
Authors: Mota José P. B. 
Published: April 2004

AbstractAdsorption storage is the most promising low‐pressure alternative for storing natural gas, but some operational difficulties hinder the success of this technology. From a modeling perspective, this article addresses the impact of gas composition on the cyclic behavior of adsorptive natural gas storage systems. The cyclic operation of an onboard storage reservoir is modeled as a series of consecutive two‐step processes, each consisting of charge with a fixed composition gas mixture followed by discharge at constant molar flow rate. Special attention is given to the composition and calorific value of the gas delivered by the storage system and to performance quantifiers that measure net deliverable capacity as a function of cycle number. Evidence of a cyclic steady state is given, and the numerical results are compared with experimental measurements. The results show the need for identifying and evaluating economical means of removing the higher molecular‐weight hydrocarbons and other highly adsorbed species from the gas stream before charging the storage reservoir.
Optimal synthesis of refrigeration cycles and selection of refrigerants
Authors: Vaidyaraman Shankar , Maranas Costas D. 
Published: April 2004

AbstractThe optimal synthesis of the refrigeration configuration and the selection of the best refrigerants that satisfy a set of process cooling duties at different temperatures is addressed. This approach simultaneously selects refrigerants and synthesizes refrigeration structures by minimizing a weighted sum of investment and operating costs. A superstructure representation considers the majority of refrigeration cycle features encountered in real complex multistage refrigeration cycles such as economizers, multiple refrigerants, and heat integration. A novel theoretical treatment of modeling representations and algorithmic improvements is introduced. Results, for example, involving multiple refrigerants, cooling loads, and heat sinks are obtained. Complex, nonintuitive topologies typically emerge as the optimal refrigeration configurations that are better than those obtained when refrigeration synthesis is performed after refrigerant selection.
Structural design for on‐line process optimization: I. Dynamic economics of MPC
Authors: Loeblein C. , Perkins J. D. 
Published: April 2004

AbstractThe structural design of integrated online process optimization and regulatory control systems based on an economic analysis of different structures is addressed. The regulatory control layer is assumed to be implemented using model predictive control (MPC) techniques. An approach to the analysis of the dynamic economics of MPC is presented which uses the state‐space formulation as the plant model. Output feedback is performed in the framework of linear quadratic filtering theory using a Kalman filter. Using the unconstrained model predictive control law, the variance of the constrained variables of the closed‐loop system subject to stochastic disturbances is analyzed. Based on the variance of the constrained variables, the amount of necessary backoff from the constraints due to regulatory disturbances is calculated and the dynamic economics are established. The dynamic economics of the model predictive regulatory control system are incorporated into the method of the average deviation from optimum analyzing the economic performance of an online optimization system. Thus, different structures of the integrated system of online optimization and MPC‐based regulatory control can be analyzed in terms of their economic performance, and the necessary structural design decisions can be taken.
On‐line multiscale filtering of random and gross errors without process models
Authors: Nounou Mohamed N. , Bakshi Bhavik R. 
Published: April 2004

AbstractData Rectification by univariate filtering is popular for processes lacking an accurate model. Linear filters are most popular for online filtering; however, they are single‐scale best suited for rectifying data containing features and noise that are at the same resolution in time and frequency. Consequently, for multiscale data, linear filters are forced to trade off the extent of noise removal with the accuracy of the features retained. In contrast, nonlinear filtering methods, such as FMH and wavelet thresholding, are multiscale, but they cannot be used for online rectification. A technique is presented for online nonlinear filtering based on wavelet thresholding. OLMS rectification applies wavelet thresholding to data in a moving window of dyadic length to remove random errors. Gross errors are removed by combining wavelet thresholding with multiscale median filtering. Theoretical analysis shows that OLMS rectification using Haar wavelets subsumes mean filters of dyadic length, while rectification with smoother boundary corrected wavelets is analogous to adaptive exponential smoothing. If the rectified measurements are not needed online, the quality of rectification can be further improved by averaging the rectified signals in each window, overcoming the boundary effects encountered in TI rectification. Synthetic and industrial data show the benefits of the online multiscale and boundary corrected translation invariant rectification methods.
Chemo‐mechanical interaction in solid‐solid reactions
Authors: Bielenberg J. R. , Viljoen Hendrik J. 
Published: April 2004

AbstractDeflagrations of solid reactants have been widely studied in the context of self‐propagating high‐temperature synthesis. Propagating velocities of the order of sound speed or faster have not been contemplated, due to the belief that the processes determining thermal conduction and diffusion cannot support those rates. Experiments, by Enikolopyan, Gogulya and others, however, disproved those notions. A model for solid‐solid reactions, which describe deflagration and detonation, is presented. The activation energy is large and the system requires significant preheating before ignition occurs. Based on experimental observations, the activation energy of a compressed system is lowered by the amount of elastic work done during compression. This phenomenon is included in the model. Ignition by impact and external thermal sources are investigated, and detonations develop only in the case of impact initiation. Interactions between the shock front and the reaction front are also investigated.
Advanced model for turbulent gas–solid flow and reaction in FCC riser reactors
Authors: Gao Jinsen , Xu Chunming , Lin Shixiong , Yang Guanghua , Guo Yincheng 
Published: April 2004

AbstractA 3‐D two‐phase flow‐reaction model was developed for predicting the performance of FCC riser reactors. This model combines two‐phase turbulent flow with 13‐lump reaction kinetics. The simulated results show that the gas–particulate turbulent reacting flow regime in the riser reactor is extremely complex, especially at the feed inlet zone of the riser reactor. The distributions of velocities, temperature, and yields are not homogeneous in the riser reactor. The model predictions were used as a design tool for operational case studies. The optimum yields of desirable FCC products, gasoline and light fuel oil were achieved at a critical riser height that is less than 10 m above the feed inlet. Beyond the critical riser height, excessive cracking reactions resulted in the increased yields of by‐products, cracking gas and coke, at the expense of desirable products. Model simulations carried out to determine the parametric effects on product yields suggest that injection of water as a reaction‐terminating medium above the critical riser height can be an effective option for optimizing the yields of desirable products.
Laminar and turbulent shear‐induced flocculation of fractal aggregates
Authors: Flesch Jürgen C. , Spicer Patrick T. , Pratsinis Sotiris E. 
Published: April 2004

AbstractA population balance model is used to model simultaneous coagulation and fragmentation in turbulent shear. The fractal‐like aggregate structure is quantified using a mass fractal dimension, Df = 2.05, derived from light‐scattering measurements and is incorporated into the model using appropriate kinetic expressions. In addition, fluid viscous effects on aggregate collisions are taken into account using existing theories on viscous retardation. Flocculation experiments of a polystyrene particle/Al(OH)3/water system in a stirred tank are compared to the model results. Good agreement is found for both average‐size evolution and steady‐state size distribution using only one fitting parameter and assuming binary breakage. The average polystyrene‐Al(OH)3 aggregate size initially increases before reaching a constant steady‐state value during coagulation–fragmentation in a stirred tank. Increasing the applied shear rate increases the coagulation and fragmentation rates, decreasing the steady‐state average aggregate size, and the time lag before steady state. The model developed in this work is applied to laminar shear data from the literature, showing excellent agreement.
Improvement of SRK equation of state for vapor‐liquid equilibria of petroleum fluids
Authors: Wang Li‐Sheng , Gmehling Jürgen 
Published: April 2004

AbstractTo improve the SRK equation of state for the calculation of vapor‐liquid equilibria of petroleum fluids, the parameters of the Mathias‐Copeman α‐function were refitted to a large number of experimental vapor‐pressure data (15,311 data points) stored in the Dortmund Data Bank with a particular view to improving the accuracy of the vapor‐pressure correlation in the low pressure range. Using the new parameters, vapor‐liquid equilibria were calculated using two different mixing rules: the group contribution mixing rule for the mixture parameters a of the SRK EOS; the conventional mixing rules for the mixture parameters a and b of the SRK EOS together with a characterization method developed on the basis of existing empirical correlations for the properties of plus fractions of undefined mixtures. The results show that the accuracy for crude oil and natural gas mixtures can be improved by refitting the SRK EOS parameters.
Generalized Doi–Ohta model for multiphase flow developed via generic
Authors: Wagner Norman J. , Öttinger Hans Christian , Edwards Brian J. 
Published: April 2004

AbstractThe model of Doi and Ohta for multiphase flow is developed and analyzed from a thermodynamic perspective using the general equation for the nonequilibrium reversible irreversible coupling (GENERIC) formalism. A procedure for obtaining a set of “thermodynamically consistent” transport equations is illustrated. The results demonstrate that the Doi–Ohta model is thermodynamically consistent and is thus a valid set of transport equations for multiphase flow. A modification of the original model is proposed to enable comparison with exact theories and validation with published simulation results, for which reasonable agreement is achieved. Extensions for more complex cases are derived within the GENERIC framework. The derivation demonstrates the ability of the GENERIC formalism to improve the theoretical basis of models for transport in complex fluids.