bluuebunny/crossref_metadata_2025_split huggingface dataset:
Parameters affecting fluid dispersion in a continuous oscillatory baffled tube
Authors: Ni Xiongwei , Pereira Nitin E. 
Published: April 2004

AbstractExperimental measurements on the axial dispersion of fluid in an oscillatory baffled tube that is operated continuously were studied. Two models, the continuous stirred tank with feedback and the plug flow with axial dispersion, were used to analyze the residence‐time distributions and determine the axial dispersion for this system. The effect of the density of tracer solution, the tracer injection position, and the tracer injection time on the axial dispersion was explored. It was found that the axial dispersion was sensitive to the changes in the density of tracer solution, but insensitive to the tracer injection position and injection time. A correlation linking the axial dispersion with the energy dissipation in the system both in the absence and presence of fluid oscillation was established. The Isotropic Turbulence Theory was applied, and for the first time the mixing length in the system was evaluated and compared with that of other devices.
On‐line data compression and error analysis using wavelet technology
Authors: Misra Manish , Qin S. Joe , Kumar Shailesh , Seemann Dick 
Published: April 2004

AbstractWavelet representation of a signal is efficient for process data compression. An on‐line compression algorithm based on Haar wavelets is proposed here. As a new data point arrives, the algorithm computes all the approximation coefficients and updates the multiresolution tree before it prepares to receive the next data point. An efficient bookkeeping and indexing scheme improves compression ratio more significantly than batch‐mode wavelet compression. Reconstruction algorithms and historian format for this bookkeeping are developed. Various analytical results on the bounds on compression ratio and sum of the square error that can be achieved using this algorithm are derived. Experimental evaluation over two sets of plant data shows that wavelet compression is superior to conventional interpolative methods (such as boxcar, backward slope, and SLIM3) in terms of quality of compression measured both in time and frequency domain and that the proposed on‐line wavelet compression algorithm performs better than the batch‐mode wavelet compression algorithm due to the efficient indexing and bookkeeping scheme. The on‐line algorithm combines the high quality of compression of wavelet‐based methods and on‐line implementation of interpolative compression algorithms at the same time.
Improving dual composition control in continuous distillation by a novel column design
Authors: Barolo Massimiliano , Papini Claudio A. 
Published: April 2004

AbstractHow a novel design of continuous distillation columns may impact the performance of conventional controllers when it is required to accurately control the purity of both products in a binary separation is analyzed. The proposed column layout is characterized by the presence of a middle vessel, to which two streams are fed: the liquid flow coming from the rectifying section and the feed to be separated. The actual liquid flow to the column is determined by the middle‐vessel level controller. For different control configurations and conventional proportional‐integral control, it is shown that using a middle‐vessel column provides a way to reduce the interaction between the composition loops, in such a way that the control performance of middle‐vessel columns may be made remarkably superior to that of the conventional columns. The results obtained are supported by a theoretical analysis based on the frequency‐dependent relative gain array tool.
Equations of state for the calculation of fluid‐phase equilibria
Authors: Wei Ya Song , Sadus Richard J. 
Published: April 2004

AbstractProgress in developing equations of state for the calculation of fluid‐phase equilibria is reviewed. There are many alternative equations of state capable of calculating the phase equilibria of a diverse range of fluids. A wide range of equations of state from cubic equations for simple molecules to theoretically‐based equations for molecular chains is considered. An overview is also given of work on mixing rules that are used to apply equations of state to mixtures. Historically, the development of equations of state has been largely empirical. However, equations of state are being formulated increasingly with the benefit of greater theoretical insights. It is now quite common to use molecular simulation data to test the theoretical basis of equations of state. Many of these theoretically‐based equations are capable of providing reliable calculations, particularly for large molecules.
Molecular thermodynamics of asphaltene precipitation in reservoir fluids
Authors: Wu Jianzhong , Prausnitz John M. , Firoozabadi Abbas 
Published: April 2004

AbstractA previously described molecular‐thermodynamic framework, based on colloid theory, is used to correlate experimental asphaltene‐precipitation data at high‐temperature and pressure conditions. In this framework, asphaltenes and resins are represented by pseudopure components, and all other components in a crude oil are presented by a continuous medium that affects van der Waals attractions among asphaltene and resin molecules. Model parameters are evaluated systematically from average properties of asphaltenes and resins in crude oils, and from dispersion‐force properties of the oil medium. Given the composition of the medium, and asphaltene and resin concentrations, the molecular‐thermodynamic model described here can be used to identify the onset of asphaltene precipitation, and the total amount of precipitation at the given operation conditions. Calculated results for the effects of oil composition and pressure on asphaltene precipitation are in good agreement with at least some experimental measurements for four reservoir fluids, including Texaco, Shell, Weyburn, and North‐Sea crude oils.
Characterization of differential ebulliometers for measuring activity coefficients
Authors: Raal J. David 
Published: April 2004

AbstractDifferential ebulliometry is a powerful and rapid procedure for obtaining infinitely dilute activity coefficients with potentially very good accuracy. Tedious degassing procedures are not necessary, as in a static method, and from only a few measurements full system phase behavior can be evaluated. The principal problem, precise evaluation of the equilibrium liquid composition from the known composition of a prepared solution charged to the apparatus, is well known but has so far defied adequate resolution. A system of exact self‐consistent equations was developed for the characterization of an ebulliometer through a dimensionless ebulliometer constant. Evaluation of this constant from typical data and its subsequent use are illustrated for a system of known phase equilibrium behavior. Remarkably, the equations permit evaluation of the effective “static” holdups in various parts of the equipment without any volume measurements. Since one equation is redundant to the main purpose, it can be used for a consistency check of measured and calculated data. The equations also furnish a guide for the operation of ebulliometers.
Coalescence in polymer blends during shearing
Authors: Lyu Su‐Ping , Bates Frank S. , Macosko Christopher W. 
Published: April 2004

AbstractControl of coalescence is a critical factor in preparing polymer blends with specific morphologies. Coalescence was studied as a function of shear rate, volume fraction, viscosity ratio, and amount of block copolymer in a model system comprising polystyrene (PS) and high density polyethylene (HDPE). Small drops of HDPE (∼2 μm) were initially developed by shearing at 10 s−1 in a cup‐cone shear cell for 20 min. The shear rate γ˙ was then decreased to between 0.1 and 2.5 s−1, and the state of coalescence was determined after quenching samples following specified periods of steady shearing. The PS portions of quenched samples were dissolved in chloroform, and the HDPE particles filtered from the suspension. These particles were imaged by scanning electron microscopy, which showed a sharp increase in the volume‐average particle diameter at specific times that depend on shear rate volume fraction, and viscosity ratio. Little change was observed in the number average diameter (Dn) at low shear rates up to a total strain of 360. At higher shear rates, however, Dn significantly increased. Interestingly, adding small amounts of block copolymer to the blends significantly suppressed coalescence. These results are discussed in terms of particle trajectory and deformation during flow.
Influence of geometry and angular velocity on performance of a rotating disk filter
Authors: Bouzerar Roger , Jaffrin Michel Y. , Ding Luhui , Paullier Patrick 
Published: April 2004

AbstractThe influence of internal geometry and angular velocity on the performance of a rotating‐disk filtration device is described. This module consists of a disk rotating at speeds up to 2,000 rpm inside a cylindrical housing equipped with a fixed flat membrane. The test fluid was a calcium carbonate suspension (4.7‐μm mean particle diameter), and the membranes were in nylon (0.2‐μm mean pore diameter) and PVDF (0.1 and 0.18 μm). The shear stress on the stationary membrane in the laminar boundary‐layer regime was estimated from a similarity solution, and in the turbulent regime from the friction coefficient for a flat plate. Several inlet and outlet configurations were tested. The permeate flux was independent of the axial gap (disk to membrane), but increased when the radial gap (from disk to housing) was raised from 2 to 5 mm. The inviscid fluid core in the axial gap was observed to rotate at 42% of angular velocity with a smooth disk. This factor rose to 64% when the disk was equipped with small vanes. Fouling was limited to the central part of the membrane at 1,500 rpm and disappeared completely for a disk equipped with vanes. Permeate fluxes were consistently much higher than in classic cross‐flow filtration.
Performance assessment of cascade control loops
Authors: Ko Byung‐Su , Edgar Thomas F. 
Published: April 2004

AbstractThe minimum variance control law for a cascade control system is derived for two cases: the primary process has stable and unstable inverses. The expression for the primary output variable under the minimum variance cascade control is shown to be feedback‐invariant. An estimate of the minimum achievable variance in a cascade control loop can be obtained via multivariate time‐series modeling of the primary and secondary measurements collected under normal operation. The utility of the proposed performance assessment method is demonstrated using simulated and industrial data.
Systematic estimation of state noise statistics for extended Kalman filters
Authors: Valappil Jaleel , Georgakis Christos 
Published: April 2004

AbstractThe successful application of model‐based control depends on the information about the states of the dynamic system. State‐estimation methods, like extended Kalman filters (EKF), are useful for obtaining reliable estimates of the states from a limited number of measurements. They also can handle the model uncertainties and the effect of unmeasured disturbances. The main issue in applying EKF remains that one needs to specify the confidence in the model in terms of process noise covariance matrix. The information about the model uncertainties can effectively and systematically calculate the process noise covariance matrix for an EKF. Two systematic approaches are used for this calculation. The first is based on a Taylor series expansion of the nonlinear equations around the nominal parameter values, while the second accounts for the nonlinear dependence of the system on the fitted parameters by Monte Carlo simulations that can easily be performed on‐line. The value of the process noise covariance matrix obtained is not limited to a diagonal form and depends on the current state of the dynamic system. Thus the a‐priori information regarding the uncertainty in the model is utilized and the need for extensive tuning of the EKF is eliminated. The application of these techniques to example processes is also discussed. The accuracy of this methodology is compared very favorably with the traditional methods of trial‐and‐error tuning of EKF.
Internal model control design for transition control
Authors: Chiu Min‐Sen , Cui Shan , Wang Qing‐Guo 
Published: April 2004

AbstractThe problem of controlling processes with a wide range of operating conditions is addressed. The process dynamics is represented by the weighted‐sum of the linear model by using model validity functions. By treating the validity functions as uncertainties in the system, an internal model control (IMC) design strategy is developed for a particular class of nonlinear systems. Robust stability analysis under mixed time‐varying and time‐invariant uncertainties is presented. Simulation results confirm that the proposed IMC design method is indeed superior to its conventional counterpart.
Microbial competition: Study of global branching phenomena
Authors: Ajbar Abdelhamid , Alhumazi Khalid 
Published: April 2004

AbstractThe stability characteristics of a bioreactor with cell recycle involving the competition between microbial cultures are investigated. The unstructured model, based on Andrew's inhibitory kinetics, involves the pure and simple competition between two microorganisms for a single pollutant. The singularity theory used for this study allows an in‐depth analysis of both the static and dynamic bifurcation mechanisms occurring in the system. The hysteresis with five solutions is the highest singularity the system can exhibit. With inhibitory kinetic expressions, the model can also predict self‐sustained oscillations for a wide range of parameters. The analysis of clean feed conditions shows that the model cannot exhibit periodic behavior regardless of the growth kinetics model. Analytical criteria are also derived for the coexistence of the competing cultures and for the prevention of wash‐out conditions. The stability characteristics for Monod kinetics, derived as a limiting case of the inhibitory kinetic expressions, are incorporated in the general framework offered by the singularity theory.
Kinetic mechanism reduction based on an integer programming approach
Authors: Androulakis Ioannis P. 
Published: April 2004

AbstractAn approach toward kinetic mechanism reduction, both in terms of reactions and species, is discussed. The driving force of the approach is to derive reduced kinetic models while maintaining the structural integrity of the detailed mechanisms. The mechanism reduction problem is defined as an integer optimization problem with binary variables denoting the existence/nonexistence of reactions or species. A Branch & Bound framework is implemented for the solution of the resulting mathematical programming problem. Several examples, utilizing a variety of kinetic networks, are presented and the results are analyzed.
Engineering design method for cavitational reactors: I. Sonochemical reactors
Authors: Gogate Parag R. , Pandit Aniruddha B. 
Published: April 2004

AbstractHigh pressures and temperatures generated during the cavitation process are now considered responsible for the observed physical and chemical transformations using ultrasound irradiation. Effects of various operating parameters reported here include the frequency, the intensity of ultrasound, and the initial nuclei sizes on the bubble dynamics, and hence the magnitude of pressure generated. Rigorous solutions of the Rayleigh‐Plesset equation require considerable numerical skills and the results obtained depend on various assumptions. The Rayleigh‐Plesset equation was solved numerically, and the results have been empirically correlated using easily measurable global parameters in a sonochemical reactor. Liquid‐phase compressibility effects were also considered. These considerations resulted in a criterion for critical ultrasound intensity, which if not considered properly can lead to overdesign or underdesign. A sound heuristic correlation, developed for the prediction of the pressure pulse generated as a function of initial nuclei sizes, frequency, and intensity of ultrasound, is valid not only over the entire range of operating parameters commonly used but also in the design procedure of sonochemical reactors with great confidence.
Screening multiphase reactors for nonisothermal multiple reactions
Authors: Kelkar Vaibhav V. , Ng Ka M. 
Published: April 2004

AbstractA screening procedure developed synthesizes a multiphase reactor and the accompanying heat‐transfer devices desired for a given reaction scheme. It is an extension of a procedure, previously described for isothermal systems with a single reaction to multiple reactions involving heat effects. The three key elements to this approach include a generic reactor model, an accompanying sensitivity model, and a knowledge base consisting of heuristics, as well as correlations on hydrodynamics, heat, and mass transport. The generic reactor model is extended to include various topologies and reactor constituent parts for heat and mass transfer. The sensitivity model quantifies the potential impact of various reactor parameters on reactor performance. The knowledge base is expanded to tackle multiple, nonisothermal reactions. In this procedure, reactor attributes and constituent parts are aggregated to form a reactor for the specific reaction under consideration. It is especially useful at the early stage of process development, when there is a great deal of uncertainty regarding reaction kinetics, and potential limitations of heat and mass transfer.
Evolution of primary and aggregate particle‐size distributions by coagulation and sintering
Authors: Tsantilis Stavros , Pratsinis Sotiris E. 
Published: April 2004

AbstractA sectional model for aggregate aerosol dynamics accounting for gas‐phase chemical reaction, coagulation, and sintering at nonisothermal conditions is presented. The aggregate structure was considered by the implementation of a constant mass fractal dimension on the aggregate collision diameter and an average, but variable, aggregate area within a given volume section. The model showed separately the evolution of the size distribution of the primary and aggregate particles. Model predictions with respect to average primary particle diameters and aggregate particle‐size distributions were evaluated by comparing with experimental data for synthesis of titania by TiCl4 oxidation in a furnace aerosol flow reactor. The effects from sintering time and mass fractal dimension are also discussed.
Thermodynamic micellization model for asphaltene precipitation inhibition
Authors: Pan Huanquan , Firoozabadi Abbas 
Published: April 2004

AbstractAromatic solvents and oil‐soluble amphiphiles are recognized as asphaltene precipitation inhibitors in oil production and transportation. In the absence of the model describing the effect of these inhibitors on asphaltene precipitation from crudes, proposed is a thermodynamic micellization model explaining the inhibition mechanism for both aromatic solvents and oil‐soluble amphiphiles. The model shows that aromatic solvents are concentrated in the micellar shell, and the interfacial tension between the asphaltene micellar core and shell is reduced as the micelles becomes stabler. A crude, mixed with a small amount of an oil‐soluble amphiphile, achieves a high micellar stability. The amphiphiles behave like resin species of the crude and coadsorb onto the micellar core with resins. The adsorption enthalpy of an amphiphile onto the micellar core is much higher than that of the resin and, therefore, amphiphiles can be very effective inhibitors. The results suggest that the adsorption enthalpy data can be used to screen the amphiphiles for asphaltene precipitation inhibition. For a given oil‐soluble amphiphile, this model can predict the amount of the amphiphile required to inhibit the precipitation.
Numerical investigation of gas‐driven flow in 2‐D bubble columns
Authors: Pan Y. , Dudukovic M. P. , Chang M. 
Published: April 2004

AbstractGas‐liquid bubbly flow in 2‐D bubble columns was studied by numerical simulation. A Eulerian‐Eulerian two‐fluid model used describes the time‐dependent motion of liquid driven by small, spherical gas bubbles injected at the bottom of the columns. Such equations, numerically implemented in this work, were derived by Zhang and Prosperetti. A distinctive feature of this method is the derivation of the disperse‐phase momentum equation by averaging the particle (here, the bubble) equation of motion directly, not the macroscopic equation for the particle phase. Both the time‐averaged quantities and dynamic characteristics of the macroscopic coherent structures agree with the experimental data of Lin et al. and Mudde et al. The comparison of simulated results with data demonstrates that this physical model and numerical approach can provide the key features of the time‐dependent behavior of dispersed bubbly flows qualitatively with reasonable quantitative accuracy. Effects of the number of injectors, magnitude of bubble‐induced viscosity, and various parameters in the interphase momentum exchange were also studied by simulating various cases and comparing with measurements. The applicability of different boundary conditions and the sensitivity to the mesh system used are also examined.
Molecular tagging velocimetry characterization of rapid KDP crystal growth
Authors: Maynes D. 
Published: April 2004

AbstractMeasurements of the tangential and axial velocities near the prism faces of a rotating mock crystal mounted on a rotating platform are presented. These measurements were made using molecular tagging velocimetry and are significant to the rapid growth of KDP crystals because they provide a description of the flow field and the evolution of the relative tangential and axial velocities near the prism faces and in the bulk flow region. These data represent the first measurements of fluid velocities around rotating crystal geometries, and thus provide a benchmark for future computer simulations of the crystal growth process at higher Re than previously obtainable. The measurements provide a temporal and spatial description of the evolving velocity field in the vicinity of a rotating crystal. Rotational conditions and locations on the prism faces where low shear rates are likely to occur, based on the measurements presented, are discussed qualitatively.
Hydrodynamics of slug flow applied to cross‐flow filtration in narrow tubes
Authors: Mercier‐Bonin Muriel , Maranges Claude , Lafforgue Christine , Fonade Christian , Line Alain 
Published: April 2004

AbstractThis article focuses on the characterization of slug‐flow hydrodynamics in two sizes of tubular membrane diameters (6 and 15 mm) to quantify the main mechanical phenomena involved in the limitation of particle fouling during cross‐flow filtration of suspensions. By using a conductance probe technique, the flow structure was accurately identified for two geometries, and noticeable differences were observed in terms of void fractions, velocities and lengths of Taylor bubbles, and liquid slugs. This characterization allowed some data to be theoretically estimated (wall shear stress, “falling” film velocity, film thickness) thanks to the application of a phenomenological model initially developed for oil pipes. The results obtained in a 15‐mm tube showed that the ultrafiltration flux improvement, experimentally achieved with bentonite and yeast suspensions, was partly due to the increase in the wall shear stress, induced by continuous gas sparging inside the tubular filtration module. Other hydrodynamic phenomena linked to the quasi‐periodic succession of Taylor bubbles and liquid slugs were also involved in the control of the particle entrainment: intermittency frequency, reversal of the wall shear stress, instantaneous pressure variations in the long bubble wake with a higher level of turbulence, and an enhanced local mixing.