bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical simulation of intense reaction propagation in multiphase systems
Authors: Pape Ronald , Gidaspow Dimitri 
Published: April 2004

AbstractA numerical model was evaluated including Arrhenius reaction kinetics to simulate multiphase flows with intense reactions and severe property gradients. Although these problems are common in chemical engineering, such an extreme case as detonation propagation in a dispersed particulate flow was investigated. The model was evaluated with respect to the form of the conservation relations being simulated, frame invariance verification, constitutive relations, numerical stability, numerical diffusion, and model verification using available experimental results and equilibrium thermochemical predictions. The model was adequate with respect to numerical issues of particular concern such as stability and numerical diffusion. To simulate experimental results realistically, Arrhenius reaction kinetics alone were insufficient. When considering important physical mechanisms in the reaction modeling based on single particle heat transfer, the multiphase model simulates experimental results realistically.
Electrochemical membrane flue‐gas desulfurization: K2SO4/V2O5 electrolyte
Authors: Schmidt Douglas S. , Winnick Jack 
Published: April 2004

AbstractThe viability of a new electrolyte was demonstrated in the bench‐scale electrochemical removal of SOx from flue‐gas streams at high temperatures. At current densities up to 20 A/m2, approximately 99% current efficiciency was achieved when removing 90% of inlet SOx at 480°C. As current densities increased to 100 A/m2, current efficiencies were 64% at 480°C and 73% at 520°C. While species present in this K2SO4/V2O5 molten salt are not well understood, a simple mechanism was used to develop a model to describe the observed removal results. This model was then used to predict preliminary economic viability of this system based on known electrochemical technology.
Complete separation conditions for a local equilibrium TCC adsorption unit
Authors: Chiang Anthony S. T. 
Published: April 2004

AbstractA new technique presented can offer analytical solutions for the local equilibrium true countercurrent model to study the simulated moving‐bed (SMB) separation process. This equilibrium theory could be vey useful for predicting both optimal and robust operation conditions for the SMB separation process, if the results can be easily calculated. However, analytical solution was available only in the limiting case of binary separation. With this analytical solution for multicomponent systems, the application of equilibrium theory will be more practical. While developing these solutions, a new way of applying the well‐known ω‐transformation to nonlinear adsorption system was conceived. This approach may have broader applications than are presented here.
Wavelet‐based modulation in control‐relevant process identification
Authors: Carrier John F. , Stephanopoulos George 
Published: April 2004

AbstractThe identification of models from operating data for process controller design requires that the information from the process be extracted in pieces that are localized in both time and frequency. Such an extraction process would allow the separation of valuable signal information from the effects of nonstationary disturbances and noise. The wavelet transform provides an efficient approach for such a decomposition, which is organized in a multiscale, hierarchical fashion. By using the method of modulating functions in conjunction with the wavelet decomposition, it is demonstrated that recursive state‐space models, which are multiscale in character and suitable for the design of model‐predictive controllers, may be readily constructed with lower levels of modeling error than yielded by traditional techniques. The method is especially suitable for the identification of time‐varying and nonlinear models, where the nonlinear process is represented by a set of linear models. The multiscale character of the wavelet basis makes it particularly suitable for multirate, multivariable processes. A series of examples illustrates various aspects of the proposed approach and its inherent advantages.
Safety verification using a hybrid knowledge‐based mathematical programming framework
Authors: Srinivasan R. , Dimitriadis V. D. , Shah N. , Venkatasubramanian V. 
Published: April 2004

AbstractHazard and operability analysis (HAZOP) is widely used to perform hazards analysis of chemical plants. It is labor‐ and knowledge‐intensive and could benefit from automation. Toward that goal, a knowledge‐based framework for automating HAZOP analysis (HAZOPExpert) was proposed. Recently, Dimitriadis et al. proposed a quantitative model‐based approach that uses a dynamic model of the plant and a description of process disturbances and parameters for hazard eualuation. These two different approaches have their own merits and demerits. The qualitative analysis performed by HAZOPExpert is thorough and computationally efficient, but can lead to ambiguous conclusions. The quantitative approach can perform an exact analysis without ambiguities, but a complete analysis can be computationally prohibitive. Thus, these two frameworks appear to complement each other. This article presents an integrated approach for hazard identification and evaluation, which overcomes the shortcomings of purely qualitative and quantitative methods. In the integrated framework, the overall features of a particular hazardous scenario are extracted by inexpensive qualitative analyses. If necessary, a detailed quantitative analysis is then performed, and that too only on those parts of the plant identified by the qualitative analysis as hazardous. The results of this framework are compared to those of purely qualitative reasoning using an industrial case study.
Miscibilization of reactive polymers during early‐stage spinodal decomposition
Authors: Yashin Victor V. , Spontak Richard J. 
Published: April 2004

AbstractReactive compatibilization constitutes an important method by which to control the size scale of phase separation in immiscible polymer blends. If a polymer pair exhibits a miscibility window at experimentally accessible temperatures, then reactive chain coupling can also be used to enhance the miscibility of the blend during spinodal decomposition in the biphasic region. We consider here the simultaneous phase separation and chemical reaction of A and B homopolymer blends in which end‐functionalized A chains react with a variety of functionalized B chains to form either AB diblock, ABA triblock, or n‐armed B‐g‐A graft copolymers. Analytical expressions for the structure factors and Onsager kinetic coefficients are developed for each of these copolymer architectures in the kinetically controlled mean‐field limit of early‐stage spinodal decomposition. Multifunctional conversion‐architecture‐phase stability (CAPS) diagrams are introduced to facilitate comparison of the effect of copolymer architecture on reaction‐driven blend miscibilization.
Morphology development in shear flows of straight and folded molten fibers
Authors: Zhang D. F. , Zumbrunnen D. A. , Liu Y. H. 
Published: April 2004

AbstractThe morphological evolution of straight and folded molten fibers in shear flows was systematically investigated. Shear flows represent local flow conditions within actual batch mixers and extruders. Folded fibers were of interest, since folding may occur during melt processing and since folded fibers resemble portions of more complex extended structures arising in polymer blends. A general, three‐dimensional numerical model of the time‐dependent fluid flows within the molten‐fiber phase and major‐phase fluid was developed. Interactions between both fluids via fully dynamical, three‐dimensional interfaces were considered. The relation of morphological changes in the fibers to the flow field for specified interfacial tensions and viscosity ratios are presented.
Comparison of converging and diverging radial flow for measuring cell adhesion
Authors: Goldstein Aaron S. , DiMilla Paul A. 
Published: April 2004

AbstractRadial flow between parallel surfaces produces a spatially dependent wall shear stress that permits investigation of cell adhesion for a range of shear simultaneously. The maximum for this range is limited by accurate prediction of fluid mechanics at small radial positions. Numerical and analytical models for predicting fluid mechanics demonstrate that corner and inertial effects at small radial positions are not only significant but differ with the direction of flow (i.e., converging vs. diverging). For diverging flow from an axially oriented inlet, the recirculation zone downstream of the corner disturbs streamlines at small radial positions. With converging flow this recirculation zone is confined to the axially oriented outlet. Also, inertia contributes positively for converging flow, enhancing the magnitude of shear stress, but negatively for diverging flow. Experiments with cells support the validity of this analysis: the strength of cell adhesion does not vary with direction or magnitude of flow.
Quick analysis of enantioselectivity by a chromatographic reactor
Authors: Wu Jau‐Yann 
Published: April 2004

AbstractThe transient behavior of enzyme‐catalyzed reaction in a proposed chromatographic reactor was investigated, and application of the technique to evaluate the capability of the enzyme in the process of kinetic resolution was developed. The theoretical result reveals that the enantioselectivity of the enzyme can be obtained directly from the amount of substrates eluted without any further treatment if a large amount of enzyme is provided. Because of its simplicity in operation and data analysis yet without any adverse consequences induced by enzyme deactivation, the technique presented can facilitate the development of an optimal condition for enzymatic kinetic resolution.
Simulation of structural phenomena in mixed‐particle fluidized beds
Authors: Seibert Kevin D. , Burns Mark A. 
Published: April 2004

AbstractA statistical mechanical simulation was developed and used to predict the macroscopic and microscopic behavior of fluidized beds. In particular, the model was used to study structural phenomena in liquid fluidized beds that contain a distribution of particle sizes and/or densities. Bed structural phenomena, such as density‐based and size‐based segregation, classification, expansion, inversion, and solids dispersion have all been successfully simulated. Experimental data for the segregation of glass beads of different sizes and different densities agree well with predictions made from the simulation (without adjustable parameters). Classification and dispersion simulations also show good agreement with experimental data.
Modeling strategies for enantiomers separation by SMB chromatography
Authors: Pais Luís S. , Loureiro José M. , Rodrigues Alírio E. 
Published: April 2004

AbstractModeling strategies for simulated moving bed adsorbers were studied to compare the simulated moving bed model (SMB) that considers the real shift of the injection and collection points to the true moving bed approach (TMB) that considers liquid and solid flow in opposite directions. The prediction of these two models is compared in terms of steady‐state performance, steady‐state internal concentration profiles, and transient behavior of the extract and raffinate purities. The influence of the degree of subdivision of the bed in the SMB model predictions is also analyzed and compared with the TMB performance. Model results are compared with experimental results obtained for the chromatographic separation of binaphthol enantiomers.
Emulsion‐liquid‐membrane extraction of copper using a hollow‐fiber contactor
Authors: Hu Shih‐Yao B. , Wiencek John M. 
Published: April 2004

AbstractA novel extraction technique using an emulsion liquid membrane within a hollow‐fiber contactor was developed and utilized to extract copper using LIX 84 extractant. Emulsion liquid membranes are capable of extracting metals from dilute waste streams to levels much below those possible by equilibrium‐limited solvent extraction. Utilizing an emulsion liquid membrane within a hollow‐fiber contactor retains the advantages of emulsion‐liquid‐membrane extraction, namely, simultaneous extraction and stripping, while eliminating problems encountered in dispersive contacting methods, such as swelling and leakage of the liquid membrane. Mathematical models for extraction in hollow‐fiber contactors were developed. The models satisfactorily predict the outcome of both simple solvent extraction and emulsion‐liquid‐membrane extraction of copper by LIX 84 in a hollow‐fiber contactor over a wide range of conditions. Emulsion‐liquid‐membrane extraction performs exceptionally well when the extraction is close to equilibrium limit. It is also capable of extracting a solute from very dilute solutions. Stability of the liquid membrane is not crucial when used in hollow‐fiber contactors; the surfactant in liquid membrane can be reduced or even eliminated without severely impairing the performance.
Solvation effect on kinetic rate constant of reactions in supercritical solvents
Authors: Chialvo A. A. , Cummings P. T. , Kalyuzhnyi Yu. V. 
Published: April 2004

AbstractA statistical mechanical analysis of the solvation effects on the kinetic rate constants of reactions in near and supercritical solvents is presented to understand the experimental findings regarding the thermodynamic pressure effects. This is an extension of the solvation formalism of Chialvo and Cummings to the analysis of the microscopic basis for the macroscopic pressure and temperature effects on the kinetic rate constants of reactions conducted in the compressible region of the solvent phase diagram. This analysis is illustrated with integral equations calculations involving Lennard–Jones infinitely dilute quaternary systems to describe the species in solution during the reaction of triplet benzophenone (3BP) with a cosolvent (either O2 or 1,4‐cyclohexadiene) in supercritical CO2 along the supercritical isotherms Tr = 1.01 and 1.06. The role of the species molecular asymmetries and consequently their solvation behavior in determining the thermodynamic pressure and temperature effects on the kinetic rate constant of reactions at near‐critical conditions are discussed.
Differential pressure sticking of drill string
Authors: Sherwood J. D. 
Published: April 2004

AbstractThe frictional forces acting on a drill string in a borehole can be large if the drill string is embedded in a pastelike filter cake formed at the borehole wall by the drilling fluid. In extreme conditions, the drill string can become stuck, leading to expensive delays in the drilling process. The hydraulic pressure within the wellbore is usually higher than the pore pressure within the rock. This excess pressure is responsible both for the growth of the filter cake, and for the normal force that can hold the drill string against the borehole wall. We obtain estimates of the normal and frictional forces acting on the drill string, based on an analysis of the pressure and concentration profile within the filter cake. The forces can be minimized by ensuring that the cake is highly compressible, so that the bulk of the pressure drop between the borehole and porous rock occurs across a thin boundary layer at the base of the cake. The forces acting on a sphere (rather than a cylindrical drill string) are also modeled, and are compared against experiment. The predicted fictional force is smaller than observed experimentally, but the predicted t3/4 growth of the force with time t agrees with experiment.
Polymer cross‐linking in post‐gel region for continuous and batch reactors
Authors: Cozewith C. , Teymour F. 
Published: April 2004

AbstractTetrafunctional chain coupling of polymers is an important process for introducing long‐chain branching to modify flow behavior and for forming cross‐linked networks. Reactor modeling for polymers branched beyond the gel point is a difficult problem because of the divergence of the moments of the MWD to infinity. A newly developed technique, numerical fractionation, based on the method of moments is applied to modeling chain coupling (cross‐linking) kinetics in continuous flow stirred tank (CFST) and batch reactors. The resulting model is applicable from 0 to 100% gelation and predicts the amount of sol fraction and its molecular weight and MWD as a function of operating conditions. This technique is easier to apply to reactor simulation than others for calculating properties of polymers in the post‐gel region. An examination of CFSR dynamics during reactor startup indicates a wide range of behavior depending on the critical residence time for gel formation. At residence times close to the critical, long times are needed to reach steady state, but at residence times much greater than the critical, the reactor can reach steady state in less than three turnovers. For both the batch and CFST reactors, polymer properties are determined by only two parameters: initial polymer MWD and reduced reaction time or reduced residence time. Consequently, at a given sol fraction, the molecular weight and MWD of the sol polymer are fixed. Narrowing the initial polymer MWD increases the amount of gel present at a given reaction time. Considerable differences are shown in the rate of the chain coupling reaction and properties of the sol phase between the two reactor types.
Thermodynamic properties prediction of vinyl acetate systems at high pressures
Authors: Prasad B. G. Shiva , Woollatt Derek 
Published: April 2004

AbstractVinyl acetate (a polar compound) has become a key ingredient in many industrial and consumer products. However, very little is known about its thermodynamic properties. This article presents a simple modification of Wu and Stiel's (1985) method (originally) developed for predicting thermodynamic properties of polar compounds up to Pr = (10) for extending its range of applicability to very high pressures of the order of Pr = 80. The predictions show good agreement with the experimental data for specific volume in the case of vinyl acetate, and specific volume, enthalpy and entropy for mixtures of ethylene and vinyl acetate for compositions up to 50 wt. % of vinyl acetate. Further validation for other polar systems would determine if this method is applicable to polar compounds in general.
Comparison of models on the prediction of binary equilibrium data of activated carbons
Authors: Ahmadpour A. , Wang K. , Do D. D. 
Published: April 2004

AbstractA pure‐component equilibrium adsorption isotherm of methane, ethane, propane, and CO2 at different temperatures and the binary adsorption data of methane with the other three species measured at 500 torr (66.7 kPa) and temperatures of 273 K and 303 K are presented and discussed. These measurements were carried out on three nutshell‐derived KOH chemically activated carbon (AC) samples and one commercial activated carbon. The binary adsorption data of another commercial AC (Nuxit‐al) from the literature are also used for comparison purposes. The single and binary experimental data were applied to six models: IAST, loading‐dependent isosteric heat, micropore‐size distribution (MPSD), energy distribution (ED), extended Langmuir, and extended Sips models. The models were found to describe the experimental data of the commercial ACs with a reasonably good accuracy, but only the model assuming isosteric heat as a function of loading could reasonably predict the data of KOH chemically activated carbons.
Liquid jet‐array cooling modules for high heat fluxes
Authors: Oh Chang H. , Lienhard V John H. , Younis Hesham F. , Dahbura Rudy S. , Michels Dirk 
Published: April 2004

AbstractLiquid jet‐array cooling modules had been designed for operation at very high heat fluxes and were used to remove fluxes as high as 17 MW/m2. Experimental results, numerical studies, and thermal stress analyses are reported. Modules having actively cooled areas of 10 cm2 were developed. Cooling is provided by an away of small‐diameter water jets operating at speeds of 47 m/s. These jets impinge on the rear side of a 2‐to 4‐mm‐thick metallic faceplate from which the heat load is absorbed. Cooling is entirely convective without boiling. The behavior of cooling jet arrays is summarized, including numerical simulations for our specific cases. Finite‐element studies of the stresses in candidate faceplate materials are described for typical thermal and mechanical conditions. A thin‐film high‐flax resistance heater provides the heat load for testing module prototypes. The thermal resistances of the system are quantified experimentally and incorporated in our numerical model. The dominant thermal resistance is associated with the heating element. The modules are believed to be serviceable to fluxes above 20 MW/m2, although dificulties with the heating element prevented this level from being reached.
Olefin/paraffin separations by adsorption: π‐Complexation vs. kinetic separation
Authors: Rege Salil U. , Padin Joel , Yang Ralph T. 
Published: April 2004

AbstractMonolayer dispersed AgNO3 on silica gel was prepared by thermal dispersion. This sorbent exhibited superior adsorption properties for olefin/parafin separations by selective adsorption of olefins through π‐complexation. This sorbent, along with Ag+ ion‐exchanged resin, was subjected to simulation studies for olefin/parafin separations by pressure‐swing adsorption. Kinetic separations (due to differences in olefin/parafin diffusivities) using zeolite 4A and molecular‐sieve carbon were also studied, Using 50/50 mixtures of C2 H4/C2 H6 and C3H6/C3H8, separations using these sorbents were compared directly based on olefin product purity, recoveiy, and throughput. The monolayer AgNO3/SiO2 sorbent showed superior separation results for C3H4/C3H8, and the Ag+‐exchanged resin showed best results for C2H4/C2H6. In both cases, over 99% product purities could be obtained at reasonably high recoveries and throughputs. For C3H6/C3H6 separation on AgNO3/SiO2, multiplicity of cyclic steady states were observed within certain regions of feed and purge velocities. within these regions, two stable cyclic steady states were reached starting ffom different initial‐bed conditions while all operating conditions were identical.
Lumen mass transfer in hollow‐fiber membrane processes with nonlinear boundary conditions
Authors: Qin Yingjie , Cabral Joaquim M. S. 
Published: April 2004

AbstractHollow‐fiber membrane separation or reaction processes, with a nonlinear boundary condition at the lumen interface, are analyzed numerically. Sixteen different nonlinear boundaly conditions in the literature were simplified to four dimensionless boundary conditions, in which only two parameters are needed to incorporate the effect on mass transport of membrane and shell resistances, lumen inlet Concentration, shell concentration, phase and/or chemical equilibria, and interface reaction kinetics. The lumen mass‐transfer coefjicients were obtained by solving the continuity mass‐conservation equation with the corresponding boundary conditions. The calculated results demonstrate that the lumen mass‐transfer coefjicient is a function of lumen‐inlet concentration and shell concentration, as opposed to the case when a linear boundary condition occurs at the lumen interface. By using the empirical correlations of the lumen local mass‐transfer coefjicient, an ordina ry differential equation substituting a partial differential equation can be applied to obtain the lumen dimensionless mixed‐cup concentration with an absolute error of less than 0.005 in most cases, thus making it possible to design and evaluate the hollow‐fiber membrane separation or reaction processes.