bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chromatographic study of alkanes in silicalite: Equilibrium properties
Authors: Hufton Jeffrey R. , Danner Ronald P. 
Published: June 2004

AbstractVariations of perturbation chromatography were used to measure Henry's constants and equilibrium isotherms of various gases on silicalite. Three different adsorbent samples were analyzed (commercial powder and extruded pellets, and laboratory‐synthesized crystals), and no discernable differences among the measured parameters were noted. Henry's constants for the linear alkanes were determined from isobaric and nonisobaric chromatography experiments. They were correlated successfully with temperature and the number of carbon atoms per adsorbate molecule. Isotherms were measured from concentration pulse or tracer/concentration pulse chromatography techniques. The Flory‐Huggins version of the vacancy solution model was used to correlate pure gas isotherms and predict binary behavior successfully.
Model‐independent algorithms for time‐optimal control of chemical processes
Authors: Lin Yeong‐Iuan , Beard John N. , Melsheimer Stephen S. 
Published: June 2004

AbstractThe new time‐optimal control algorithms presented do not require a‐priori knowledge of the process dynamics. They are applicable to systems that can be described by a second‐order (or first‐order) plus deadtime model and generate a dynamic model as a byproduct. Simulations presented illustrate the use of these algorithms in time‐optimal control and the process models obtained. The algorithms are robust with respect to the measurement noise often encountered in real chemical processes and are inherently adaptive to changes in the process dynamics with time. An experimental application to the heatup of a laboratory fiber spinning apparatus is presented.Since these time‐optimal control algorithms are easy to apply and give rapid, smooth responses, they will be of value even when obtaining minimum‐time response is not a critical issue. Such applications include startup of continuous and batch processes. Moreover, they can be used to determine first‐ or second‐order process models (as appropriate) from open‐loop step response data without actually implementing time‐optimal control.
Advanced modeling of fluid catalytic cracking riser‐type reactors
Authors: Theologos K. N. , Markatos N. C. 
Published: June 2004

AbstractA mathematical model is developed that predicts three‐dimensional, two‐phaseflow, heat transfer and reaction inside catalytic cracking riser‐type reactors. The model consists of the full set of partial‐differential equations that describe the conservation of mass, momentum, energy and chemical species for both phases in the reactor, coupled with empirical correlations concerning interphase friction, interphase heat‐transfer and fluid‐to‐wall frictional forces. The cracking reaction is simulated by a simple three‐lump kinetic model, but more realistic kinetic models can be easily included. The model can predict the most important engineering aspects of a riser reactor including pressure drop, catalyst holdup, interphase slip velocity, catalyst acceleration zone, choking behavior and temperature distribution in both phases, and yields distribution all over the reactor. It can also predict other complex engineering three‐dimensional, two‐phase problems realistically using computational fluid dynamics techniques.
A pore‐level scenario for the development of mixed wettability in oil reservoirs
Authors: Kovscek A. R. , Wong H. , Radke C. J. 
Published: June 2004

AbstractUnderstanding the role of thin films in porous media is vital to elucidate wettability at the pore level. The type and thickness of films coating pore walls determine reservoir wettability and whether or not reservoir rock can be altered from its initial state of wettability. Pore shape, especially pore wall curvature, is important in determining wetting‐film thicknesses. Yet, pore shape and physics of thin wetting films are generally neglected in flow models in porous rocks. Thin‐film forces incorporated into a collection of star‐shaped capillary tubes model describe the geological development of mixed wettability in reservoir rock. Here, mixed wettability refers to continuous and distinct oil and water‐wetting surfaces coexisting in the porous medium. This model emphasizes the remarkable role of thin films.New pore‐level fluid configurations arise that are quite unexpected. For example, efficient water displacement of oil (low residual oil saturation) characteristic of mixed‐wettability porous media is ascribed to interconnected oil lenses or rivulets which bridge the walls adjacent to pore corners. Predicted residual oil saturations are approximately 35% less in mixed‐wet rock than in completely water‐wet rock. Calculated capillary pressure curves mimic those of mixed‐wet porous media in the primary drainage of water, imbibition of water, and secondary drainage modes. Amott‐Harvey indices range from −0.18 to 0.36 also in good agreement with experimental values (Morrow et al., 1986; Jadhunandan and Morrow, 1991).
The propagation of surface waves in flow down an oscillating inclined plane
Authors: Weinstein Steven J. , Baumlin Jean‐Marie , Servant Jeanne 
Published: June 2004

AbstractThe propagation of surface waves is investigated theoretically and experimentally for the case of a single layer of viscous liquid flowing down an inclined plane, where the plane is oscillating in the flow direction. This work focuses on the linearized wavemaker problem, where the oscillations create waves which are small perturbations from the undisturbed flow. Downstream from the entrance region to the incline where the fluid is introduced, the undisturbed interface is parallel to the incline surface, and theory predicts that oscillations do not interact with waves that travel along the free surface. These waves grow as if there were no oscillation at all, and their propagation is governed by a dispersion relation between frequency, wavelength, and wave growth for single layer flow down a nonoscillating inclined plane. The entrance region to the incline is therefore responsible for exciting the various wave frequencies which are observed down the incline, as well as the initial amplitude of these waves. Experiments performed verify that waves propagate as predicted. Theory indicates that these conclusions are valid when the oscillations are perpendicular to the incline, as well as for the case of multiple stacked layers.
Approximate simulation of CO2 and H2s absorption into aqueous alkanolamines
Authors: Glasscock David A. , Rochelle Gary T. 
Published: June 2004

AbstractRigorous and approximate methods are compared for the simulation of CO2 absorption into aqueous alkanolamine mixtures of methyldiethanolamine and diethanolamine. In addition, data for the mixtures containing monoethanolamine and the simultaneous absorption of CO2 and H2S are presented. For the rigorous approach, the simplified eddy diffusivity theory is used to simulate the liquid‐phase hydrodynamic characteristics. The approximation methods examined are the pseudo‐first‐order approximation, the interpolation approximation of Wellek et al. (1978), the algebraic combined flux (ACFLUX) approximation and the modified combined flux (MCFLUX) approximation. The latter approximation utilizes the reaction zone concept to determine the kinetic preference of the absorbing gas at the gas‐liquid interface. Under the range of conditions studied, the MCFLUX approximation predicts very accurately the CO2 and H2S flux rates in mixed amine systems, as compared with the rigorous solution of the differential equations.
Saturation gradients in drainage of porous media: NMR imaging measurements
Authors: Fordham E. J. , Hall L. D. , Ramakrishnan T. S. , Sharpe M. R. , Hall C. 
Published: June 2004

AbstractA steady‐state method recently proposed for measuring two‐phase flow properties of a porous medium is supplemented by NMR imaging for measuring the saturation gradients which are allowed to persist in the specimen. The method relies on a strong capillary end effect which is assumed to be enforced by an outlet capillary pressure boundary condition, but direct verification of this has not hitherto been available. For constant flow rates, incremented stepwise, steady‐state profiles of hydrocarbon saturation Soare obtained which agree with predictions that they be monotonic, nonintersecting, and convex.Using D2O for the aqueous phase allows unambiguous detection of hydrocarbon by NMR, and imaging measurements of transverse relaxation time T2were included in the protocol. T2shows a dependence on Sowhich is mild but not negligible for quantitative NMR imaging.
Model for describing activity coefficients in mixed electrolyte aqueous solutions
Authors: Lu Xiao‐hua , Maurer G. 
Published: June 2004

AbstractMost models for describing activity coefficients in ionic solutions are only appropriate for single aqueous electrolyte solutions. Extensions to mixed electrolyte solutions are rarely found and are often unreliable, especially at higher electrolyte concentrations. A new model is developed by combining ionic solvation equilibria and physical interaction forces. It is shown that by using the parameters correlated from single electrolyte aqueous systems, the activity coefficients in mixed electrolyte aqueous solutions can be accurately predicted up to the solubility limit, for example, at very high ionic strength.
Dynamic process modeling with recurrent neural networks
Authors: You Yong , Nikolaou Michael 
Published: June 2004

AbstractA method of nonhlinear static and dynamic process modeling via recurrent neural networks (RNNs) is studied. An RNN model is a set of coupled nonlinear ordinary differential equations in continuous time domain with nonlinear dynamic node characteristics as well as both feedforward and feedback connections. For such networks, each physical input to a system corresponds to exactly one input to the network. The system's dynamics are captured by the internal structure of the network. The structure of RNN models may be more natural and attractive than that of feedforward neural network models, but computation time for training is longer. Our simulation results show that RNNs can learn both steady‐state relationships and process dynamics of continuous and batch, single‐input/single‐output and multiinput/multioutput systems in a simple and direct manner. Training of RNNs shows only small degradation in the presence of noise in the training data. Thus, RNNs constitute a feasible alternative to layered feedforward back propagation neural networks in steady‐state and dynamic process modeling and model‐based control.
Parametric sensitivity study of a CFD‐based coal combustion model
Authors: Smith Joseph D. , Smith Philip J. , Hill Scott C. 
Published: June 2004

AbstractParametric sensitivity of a two‐dimensional pulverized‐fuel (PF) combustion model is studied extensively for the effect of parametric uncertainty on model predictions. Results show that error in coal devolatilization/oxidation parameters has the dominant effect on predicted burnout, NOx formation, local gas temperature, and coal‐gas mixture fraction. Uncertainty in the turbulent particle dispersion parameters appears to have a secondary effect, while error in the particle‐gas radiation parameters has little impact on model predictions. Regions of the computational domain exhibiting sensitivity to specific parameters are identified. Specific parameter sensitivity implies the relative importance of various mechanisms in the overall process. Turbulent particle dispersion seems to be important early in the reactor with kinetic processes dominating at and following the predicted ignition point. Radiation appears to be of minor importance. These results indicate the need for a better method of predicting the overall volatiles yield and further understanding of the devolatilization/oxidation mechanism and its role in the overall PF combustion process. The study provides fundamental direction for future comprehensive model development and focuses on experimental work to better quantify critical input parameters.
Pipeline flow of unstable and surfactant‐stabilized emulsions
Authors: Pal Rajinder 
Published: June 2004

AbstractThe literature available on pipeline flow behavior of emulsions is reviewed critically. New results concerning the laminar and turbulent flow behaviors of unstable (without any added surfactant) and surfactant‐stabilized water‐in‐oil emulsions are presented. The unstable emulsions exhibit drag reduction behavior in turbulent flow; the measured friction factors fall well below the values expected on the basis of the laminar flow properties. Unstable water‐in‐oil emulsions exhibit much stronger drag reduction activity than the unstable oil‐in‐water emulsions. The drag reduction activity diminishes (in some cases vanishes completely) upon the addition of a surfactant to the system.
Design and performance of a simulated countercurrent moving‐bed separator
Authors: Fish Barry B. , Carr Robert W. , Aris Rutherford 
Published: June 2004

AbstractThe design, construction and isothermal (298 K) operation of a continuous flow simulated countercurrent moving‐bed chromatographic separator for the gas‐solid separation of binary mixtures is reported. It consists of only four packed columns, with countercurrency simulated by advancing the feedpoint from column to column in the direction of gas flow. The separated components have periodic concentration profiles, with a duty cycle that depends on operating parameters, and concentrations greater than in the feed stream. Test mixtures of propylene and dimethyl ether, which have retention times differing by a factor of 2 on the 60/80 mesh Chromosorb 101 packing, were successfully separated. Optimum feed advancement intervals and maximum product purity were experimentally determined as a function of feed rate. At low feed rates, when the adsorption isotherm is nearly linear, dimethyl ether was nearly completely separated from propylene, but propylene was found to contain varying amounts of dimethyl ether due to the effects of a nonlinear isotherm and heterogeneous adsorption.
Constrained predictive control using orthogonal expansions
Authors: Finn Cory K. , Wahlberg Bo , Ydstie B. Erik 
Published: June 2004

AbstractIn this article, we approximate bounded operators by orthogonal expansion. The rate of convergence depends on the choice of basis functions. Markov‐Laguerre functions give rapid convergence for open‐loop stable systems with long delay. The Markov‐Kautz model can be used for lightly damped systems, and a more general orthogonal expansion is developed for modeling multivariable systems with widely scattered poles. The finite impulse response model is a special case of these models. A‐priori knowledge about dominant time constants, time delay and oscillatory modes is used to reduce the model complexity and to improve conditioning of the parameter estimation algorithm. Algorithms for predictive control are developed, as well as conditions for constraint compatibility, closed‐loop stability and constraint satisfaction for the ideal case. An H∞‐like design technique proposed guarantees robust stability in the presence of input constraints; output constraints may give “chatter.” A chatter‐free algorithm is proposed.
Rate type equations for the diffusion in polymers: Thermodynamic constraints
Authors: Doghieri Ferruccio , Roda Giovanni Camera , Sarti Giulio C. 
Published: June 2004

AbstractConditions imposed by the second law of thermodynamics on viscoelastic rate type constitutive equations for the diffusive mass flux are considered. The analysis of three different rate type models proposed in the literature points out that presently physically unrealistic predictions are possible in desorption processes. The thermodynamic analysis of such models, based on the entropy inequality and on the stability requirement of the equilibrium states, leads to precise relationships among relaxation times, diffusion coefficients, and entropy equations of state. In particular, the analysis shows that relaxation times and diffusion coefficients cannot be simply constant numbers. When the thermodynamic constraints imposed on the constitutive equations are introduced, the models do not show physically unrealistic behaviors any more; Fickian diffusion close to the pure penetrant or pure polymer regions is also recovered. Finally, it is shown that the stability requirement for the equilibrium states may introduce very rigid requirements for the model feasibility, well beyond what appears explicitly from the kinetic equations alone.
Direct simulation of turbulent particle transport in electrostatic precipitators
Authors: Soldati Alfredo , Andreussi Paolo , Banerjee Sanjoy 
Published: June 2004

AbstractThe dispersion of particles in turbulent duct flow under the influence of electrostatic fields is studied using direct numerical simulation. In this new approach, particles are moved in the temporally and spatially varying turbulent flow field under the influence of electrostatic and gravitational body forces, as well as fluid dynamic drag. The simulations agree well with previously performed experiments (done in geometries typical of wire‐plate and plate‐plate electrostatic precipitators) not only in the overall collection efficiency of particles, but in particle concentration profiles at various axial locations in the flow direction. This gives confidence in the technique that may be used to study different precipitator geometries and flow field configurations, supplementing costly and difficult experiments. Furthermore, information is obtained at a much more detailed level than is possible via experiments, allowing insights into the mechanisms dominating particle collection.
Optimal estimation of cell movement indices from the statistical analysis of cell tracking data
Authors: Dickinson Richard B. , Tranquillo Robert T. 
Published: June 2004

AbstractActive cell migration is essential in many physiological processes and in the function of some bioartificial tissues. Therefore, several investigators have recently attempted to quantitatively characterize random cell movement on isotropic substrata in vitro. A popular approach is to fit a theoretical expression for mean‐squared cell displacement deriving from correlated random walk models to cell tracking data, yielding three objective cell movement indices: root‐mean‐squared speed, directional persistence time, and random motility coefficient (analogous to a molecular diffusion coefficient). The data are obtained typically by averaging cell displacements over a cell track composed of cell positions measured at equal time increments and frequently by further pooling such displacement data from tracks of different cells from the same population. We identify pitfalls introduced if an ordinary nonlinear least‐squares regression analysis is used to fit the theoretical expression to the data as is commonly done and propose a generalized least‐squares regression analysis as a remedy. This method estimates the cell movement indices and associated uncertainties much more accurately. It also predicts the precision of the indices based on their assumed true values and provides a means to address such issues as optimal sampling methods for data acquisition from cell tracks and handling errors associated with measuring cell position.
Strategies for equilibrium‐stage separation calculations on parallel computers
Authors: O'Neill Alfred J. , Kaiser Daniel J. , Stadtherr Mark A. 
Published: June 2004

AbstractWhen multicomponent, multistage separation problems are solved on parallel computers by successive linearization methods, the solution of a large sparse linear equation system becomes a computational bottleneck, since other parts of the calculation are more easily parallelized. When the standard problem formulation is used, this system has a block‐tridiagonal form. It is shown how this structure can be used in parallelizing the sparse matrix computation. By reformulating the problem so that it has a bordered‐block‐bidiagonal superstructure, it can be made even more amenable to parallezation. These strategies permit the use of a two‐level hierarchy of parallelism that provides substantial improvements in computational performance on parallel machines.
Tubular reactors for emulsion polymerization: II. Model comparisons with experiments
Authors: Paquet D. A. , Ray W. H. 
Published: June 2004

AbstractA dynamic model for emulsion polymerization in a tubular reactor has been developed and compared with experimental data. The model uses an axial dispersion coefficient to fit experimentally measured residence time distributions and to represent axial mixing during reaction. Very general emulsion polymerization kinetics are assumed so that a wide range of monomers and operating conditions can be handled. Orthogonal collocation on finite elements was chosen as the numerical solution technique. Comparisons show good agreement between model and experiments for two different monomers.
Hydrodynamic behavior of circulating fluidized bed with polymeric particles
Authors: Jiang Peijun , Bi Hsiaotao , Liang Shu‐Chien , Fan Liang‐Shih 
Published: June 2004

AbstractA systematic study conducted explores the hydrodynamics of a circulating fluidized bed with polymeric particles employing polyethylene resins with a particle density of 660 kg/m3 and size ranging from 90 to 500 μm. The study indicates that polyethylene resins can be fluidized smoothly in the fast fluidization regime. However, the operating range of the fast fluidization regime for these particles is smaller than that for FCC particles. The deviation of the fluidization behavior of polyethylene particles from that of common Group‐A particles is explained considering the interparticle forces. Experiments with fine polyethylene particles are also conducted with coarse particles added in a circulating fluidized bed. Axial profiles of solid holdups in a bed with and without coarse particles, as well as overall fine particle holdup, are studied. The results show a significantly wider operating range of the fast fluidization regime and enhancement of fine particle holdups in a bed with the presence of coarse particles. For comparison, fluidization with FCC particles is also conducted. A mechanistic model considering particle‐particle collision is proposed. The model accounts for the momentum exchange rate between a coarse particle and a cloud of fine particles, which explains the enhancement of fine particle holdups observed experimentally.
Turbulent gas‐particle flow in vertical risers
Authors: Dasgupta Sanjay , Jackson Roy , Sundaresan Sankaran 
Published: June 2004

AbstractMany experimental studies on the cross‐sectional distribution of particles in vertical risers have revealed marked segregation of particles. These flows are inherently unsteady with large fluctuations in suspension density. In this article, we have analyzed the time‐smoothed equations for the motion of dense suspensions to demonstrate the role of these fluctuations on the occurrence of segregation. It is shown that the particles will congregate in regions where the kinetic energy of fluctuations associated with the particles is small. In the context of transport of small particles such as FCC, a simplified model based on the mixture velocity can be constructed. A speculative K‐ϵ model based on this velocity is analyzed to illustrate the extent of segregation of particles afforded by unsteady fluctuations.