bluuebunny/crossref_metadata_2025_split huggingface dataset:
Chaotic mixing of shear‐thinning fluids
Authors: Niederkorn Thomas C. , Ottino Julio M. 
Published: June 2004

AbstractThis article investigates the effect of shear‐thinning viscosity on chaotic mixing when the kinematics first begin to deviate from Newtonian flow. Computations are done for a 2‐D, time‐periodic flow between eccentric cylinders. The effectiveness of mixing is analyzed by examining the asymptotic coverage of a passive tracer, character and location of periodic points, and the rate of stretching of fluid elements. Small variations in the velocity field associated with non‐Newtonian kinematics produce large effects in the chaotic advection of a passive tracer. The stretching rate remains exponential, but with a long time constant as the shear‐thinning effect increases, often resulting in the birth of new periodic islands and a decrease in the asymptotic coverage of the tracer. Exceptions to these observations are possible: both the stretching rate and the asymptotic coverage might increase as shear thinning increases. Results also indicate that suitable manipulation of operating conditions can produce shear‐thinning flows which mix as well as Newtonian flows. Since significant effects are observed with less than a 4% difference in the velocity fields, the assumption of Newtonian kinematics can lead to large errors in the design and operation of process mixing equipment for non‐Newtonian fluids.
Multicomponent separation using a column‐switching chromatographic method
Authors: Ching C. B. , Chu K. H. , Hidajat K. 
Published: June 2004

AbstractA cyclic chromatographic process based on the method of column switching was used to separate a three‐component carbohydrate mixture. It permits continuous introduction of the feed and is designed to produce higher product concentration compared to a normal elution cyclic process. A fixed‐bed model incorporating axial dispersion and a linear driving force for mass transfer was successfully used to estimate optimum operating conditions (switch times and fluid‐flow rates). Its experimental setup can be easily constructed by modifying the apparatus of a simulated countercurrent process since both systems comprise segmented columns equipped with on‐off valves for fluid‐flow control. This allows one to conduct either multicomponent separation based on elution operation or binary separation based on countercurrent operation using essentially the same set of experimental apparatus with minor modification.
Video technique for measuring dynamics of liquid‐liquid dispersion during phase inversion
Authors: Pacek A. W. , Moore I. P. T. , Nienow A. W. , Calabrese R. V. 
Published: June 2004

AbstractStudies on the dynamics of phase inversion available offer limited information due to the difficulty of following the transient mean and drop‐size distribution. A new technique developed provides such data. A stereo microscope with a very shallow depth of field attached to a video camera gives sharp images of droplets in intensely‐agitated, immiscible liquid dispersions by using a Strobotach pulsing at the camera framing rate. Droplets from 40 μm upward at concentrations up to 70% by volume dispersed phase can be measured accurately. Droplets of continuous organic phase in aqueous drops can be seen. The pictures can be analyzed semiautomatically using a computer and in‐house software to give, using a variety of discretizations, cumulative and frequency distributions to any base and any mean size. Means and distributions are a function of time for phase inversions generated in three ways. The technique gives a powerful tool for understanding fast, complex dispersion processes.
Experimental study and parameterization of gas absorption by water drops
Authors: Amokrane H. , Saboni A. , Caussade B. 
Published: June 2004

AbstractLiquid‐phase mass‐transfer coefficients are determined for the absorption of sulfur dioxide by water drops larger than 1.1 mm in dia. A local model based on the large eddy interfacial model proposed by Fortescue and Pearson (1967) is obtained by the characteristic interfacial scaling. In particular, the agitation process of the liquid phase in the interfacial region is characterized by the interfacial liquid friction velocity. Experiments of sulfur dioxide absorption and desorption from large individually free‐falling water drops are also carried out in a 5‐m rain shaft under various environmental conditions. These experimental results agree well with those from the local model characterizing the interfacial process in water drops greater than 1.1 mm in dia.
Local effective diffusivity in a pellet deactivated by multilayer coking
Authors: Lee Hong H. 
Published: June 2004

AbstractA relationship is developed for the change in local effective diffusivity with coking using the models available for effective diffusivity. When this relationship is combined with the earlier multilayer kinetic model, the local effective diffusivity becomes dependent solely on the fraction of catalyst deactivated. Experimental procedures developed determine the relationship for the local effective diffusivity. These results provide a framework for a consistent and systematic treatment of the complex deactivation‐diffusion problem caused by coking and coke growth. Unique aspects of coking are accounted for through the fraction of catalyst deactivated, which is the basic quantity for catalytic activity, rather than the coke content.
Dynamic simulation and nonlinear‐model‐based product quality control of a crude tower
Authors: Chung Chang‐Bock , Riggs James B. 
Published: June 2004

AbstractThe dynamic stagewise adiabatic flash algorithm is applied to the dynamic simulation of a crude column. This algorithm is based on the implicit integration of the model equations of each stage and the explicit combination of the stage models to form the column model. Stable, efficient integration for the crude column model is observed with simulation CPU requirements that are 20 times faster than real time using a 50 MHz 486 P.C. Specific dynamic of a crude column are identified such as one‐way interaction and inverse action. The dynamic crude column model is used to study product quality control of a crude column using nonlinear‐process‐model‐based control (PMBC) which was tested using two different steady‐state controller models for setpoint tracking and disturbance rejection. Both nonlinear PMBC controllers show good control performance, but are limited by the inherent inverse action of the crude column. Control results for a set of single‐loop PI controllers is also presented as a point of reference.
Impact of process design on the multiplicity behavior of a jacketed exothermic CSTR
Authors: Russo Louis P. , Bequette B. Wayne 
Published: June 2004

AbstractResearch on exothermic reactor operation has been based mostly on the classic two‐state continuous stirred tank reactor model, implicitly assuming that the cooling jacket temperature dynamics are negligible. In this case, the cooling jacket temperature is the manipulated input instead of the cooling jacket flow rate for feedback control of reactor temperature. Adding a cooling jacket energy balance results in much more complex behavior than a simple lag effect. A stabilizing inner‐loop cascade controller is assumed in the two‐state CSTR model, because the three‐state model incorporating cooling jacket temperature dynamics may be open‐loop unstable when the two‐state model is open‐loop stable. The influence of design parameters on the multiplicity behavior of a three‐state model is considered. Elementary catastrophe theory is used to study the effect of process parameters such as the cooling jacket flow rate, heat‐transfer coefficient, heat of reaction, and cooling jacket feed temperature on the steady‐state multiplicity of the three‐state model. This multiplicity analysis is particularly relevant for control because the primary bifurcation parameter is the cooling jacket flow rate, the manipulated input for feedback control in the three‐state model. This multiplicity analysis guides improvements in process design and/or operation to eliminate difficult operating regions associated with steady‐state multiplicities; the presence of multiple steady states results in safety and operation problems due to ignition/extinction phenomena. Reactor scale‐up affects the presence of these infeasible reactor operating regions. Certain design parameter changes that remove multiplicities in the two‐state model cannot remove multiplicities in the three‐state model.
Hydrogen ion activities and species distribution in mixed metal sulfate aqueous systems
Authors: Filippou Dimitrios , Demopoulos George P. , Papangelakis Vladimiros G. 
Published: June 2004

AbstractThe activity of the hydrogen ion (H+) is estimated in sulfuric acid aqueous solutions of concentrations 0.25 to 2.0 mol.L−1 at temperatures 298 to 373 K (25 to 100°C). This is done by following an existing “extended Debye‐Hückel” equation, which was originally developed only for the case of pure H2SO4 solutions at ambient temperature. The same equation is applied for the evaluation of the activity of H+ in mixed metal sulfate solutions, particularly for the aqueous system H2SO4‐ZnSO4‐FeSO4‐Fe2(SO4)3. The estimation of the activity of H+ by this method requires the knowledge of the molality of free H+ ions and the true ionic strength (in molal scale). Consequently, an algorithm is advanced for the calculation of species concentrations in such mixed solutions. Estimated pH values agree very well with experimentally measured ones.
Effect of solute‐solute correlations on rapid reactions in supercritical fluids
Authors: Ganapathy Shankar , O'Brien James A. , Randolph Theodore W. 
Published: June 2004

AbstractBrownian and molecular dynamics simulations are used to study rapid bimolecular reactions at near‐infinite dilution in near‐critical and supercritical fluids. We probe the dynamics of both nonreactive and reactive collisions and measure rate constants for reaction and collision. Collision rate constants are nearly independent of bulk solvent density, but affected by local solute‐solute density enhancements at a given density: their magnitudes depend on the length scale for molecular encounters (cybotactic radius) in the reaction through the equilibrium solute‐solute radial distribution function. In contrast, reaction rate constants asymptotically approach the gas‐kinetic limit at low densities and the Smoluchowski liquid‐like limit at high densities. They also display the same radial dependence as collision rate constants at lower densities and a direct dependence on the cybotactic radius at higher densities (as in the Smoluchowski theory). Their behavior is explained in terms of a transition from a collision‐limited regime at low densities to a diffusion‐limited regime at higher densities. The transition between these regimes depends on the cybotactic radius and the density of the system, the interplay of which causes shifts in the transition region which depend not only on the properties of the near‐critical solvent: they differ for different reactions, even at the same solvent density. This explains some of the apparent inconsistencies among previous experimental and computational studies of reactions in supercritical fluid media.
Henry's law and synergism in dilute near‐critical solutions: Theory and simulation
Authors: Munoz F. , Li T. W. , Chimowitz E. H. 
Published: June 2004

AbstractAn asymptotic analysis based on Taylor series expansions is used for first‐order correction terms to the Henry's law approximation to describe solvation phenomena in multiple solute‐multiple solvent systems. The magnitude of these correction terms in solvent systems very near their critical points is of particular concern, as shown in model fluid calculations with the aid of integral equation theory. The results clearly demonstrate that close proximity to the critical point in pure and mixed solvent systems causes the Henry's law approximation to show large errors in predicting solubilities, especially near the critical azeotrope of a mixed solvent system. Theoretical results also show that cross solubility enhancements in a two solutesupercritical solvent system cause cooperative synergism (both solute solubilities are increased relative to the corresponding single solute situations) or reverse synergism (both depressed relative to the single solute situation). It appears to be consistent with the available data. In computer simulations, the solute's infinitely dilute reference state is often used as a basis for describing solute thermodynamic behavior. These simulations are best achieved in the canonical ensemble because of the weak composition dependence of free energies in terms of characteristic variables of this ensemble.
Analysis of bacterial migration: II. Studies with multiple attractant gradients
Authors: Strauss Ian , Frymier Paul D. , Hahn Christopher M. , Ford Roseanne M. 
Published: June 2004

AbstractMany motile bacteria exhibit chemotaxis, the ability to bias their random motion to ward or away from increasing concentrations of chemical substances which benefit or inhibit their survival, respectively. Since bacteria encounter numerous chemical concentration gradients simulatneously in natural surroundings, it is necessary to know quantitatively how a bacterial population responds in the presence of more than one chemical stimulus to develop predictive mathematical models describing bacterial migration in natural systems. This work evaluates three hypothetical models describing the integration of chemical signals from multiple stimuli: high sensitivity, maximum signal, and simple additivity. An expression for the tumbling probability for individual stimuli (Brown and Berg, 1974) is modified according to the proposed models and incorporated into the cell balance equation for a 1‐D attractant gradient (Ford and Cummings, 1992). Random motility and chemotactic sensitivity coefficients, required input parameters for the model, are measured for single stimulus responses. Theoretical predictions with the three signal integration models are compared to the net chemotactic response of Escherichia coli to co‐ and antidirectional gradients of D‐fucose and α‐methylaspartate in the stopped‐flow diffusion chamber assay. Results eliminate the high‐sensitivity model and favor the simple additivity over the maximum signal. None of the simple models, however, accurately predict the observed behavior, suggesting a more complex model with more steps in the signal processing mechanism is required to predict responses to multiple stimuli.
Mass and heat transfer in crushed oil shale
Authors: Carley James F. , Ott Linda L. , Swecker Jeanne L. 
Published: June 2004

AbstractStudies of heat and mass transfer in packed beds, which disagree substantially in their findings, have nearly all been done with beds of regular particles of uniform size, whereas oil‐shale retorting involves particles of diverse irregular shapes and sizes. We, in 349 runs, measured mass‐transfer rates from naphthalene particles buried in packed beds by passing through air at room temperature. An exact analogy between convection of heat and mass makes it possible to infer heat‐transfer coefficients from measured mass‐trans‐fer coefficients and fluid properties. Some beds consisted of spheres, naphthalene and inert, of the same, contrasting or distributed sizes. In some runs, naphthalene spheres were buried in beds of crushed shale, some in narrow screen ranges and others with a wide size range. In others, naphthalene lozenges of different shapes were buried in beds of crushed shale in various bed axis orientations. This technique permits calculation of the mass‐transfer coefficient for each active particle in the bed rather than, as in most past studies, for the bed as a whole.The data are analyzed by the traditional correlation of Colburn jD vs. Reynolds number and by multiple regression of the mass‐transfer coefficient on air rate, sizes of active and inert particles, void fraction, and temperature. Principal findings are: local Reynolds number should be based on the active‐particle size, not the average for the whole bed; differences between shallow and deep beds are not appreciable; mass transfer is 26% faster for spheres and lozenges buried in shale than in all‐sphere beds; orientation of lozenges in shale beds has little or no effect on mass‐transfer rate; and for mass or heat transfer in shale beds, log(j·ϵ) = − 0.0747 − 0.6344logNRe + 0.0592log2 NRe.
The effect of gravity degradation on low‐speed centrifuge capillary pressure data
Authors: Chen Zhigang Andy , Ruth Douglas W. 
Published: June 2004

AbstractThe gravity degradation effect has been identified as a significant physical problem in using centrifuge techniques for determining capillary pressure curves. In 1992, the authors characterized the effect by an angle; however, such an evaluation is simplistic. Here, a new model is constructed to characterize the effect quantitatively. The results with simulated data sets show that there exists a pronounced effect of gravitation on the horizontal centrifugal field in low‐speed experiments (≤ 500 rpm on a standard Beckman centrifuge). Gravity affects the production history for some samples, which leads to inaccurate interpretations of capillary pressure information near the threshold pressure.
New sorbents for olefin/paraffin separations by adsorption via π ‐complexation
Authors: Yang R. T. , Kikkinides E. S. 
Published: June 2004

AbstractNew adsorbents for olefin/paraffin separation are synthesized by effective dispersion of Ag(I) and Cu(I) cations on substrates with hydrocarbon‐phobic surfaces. These cations bind olefin molecules by a π‐complexation bond, a weak chemical bond. Ethane/ethylene and propane/propylene separations are considered. Cation exchange resins and CuCl/γ‐Al2O3 are effective substrates. On the Ag(I) resin at 25°C and 1 atm, the equilibrium adsorption ratio for C2H4/C2H6 = 9.2 and C2H4 capacity = 1.15 mmol/g; the corresponding values for C3H6/C3H8 = 10.4 and C3H6 capacity = 1.29 mmol/g. The CuCl/γ‐Al2O3 sorbent shows equally promising results. The sorption rates are pore‐diffusion‐controlled and rapid. The olefin selectivity; capacity, and rates are much higher than all previous attempts and are suitable for applications in cyclic adsorption processes.The equilibrium data are correlated with an isotherm equation that accounts for both physical adsorption and π‐complexation with energy heterogeneity, using only two true fitting parameters. Molecular orbital calculations using a C6H5SO substrate indicate that the π‐complexation bond is contributed mainly by the donation of olefin π‐bond electrons to the empty s‐orbital of the metal, while the d‐π* back donation contributes only 16%. Moreover, the relative order of the heats of adsorption is correctly predicted.
Agglomeration during precipitation: I. Tracer crystals for Al(OH)3 precipitation
Authors: Ilievski D. , White E. T. 
Published: June 2004

AbstractTracer crystals are developed to study the agglomeration, growth and residence time behavior of gibbsite crystals, an industrially important polymorph of Al(OH)3, in continuous and batch precipitation. Satisfactory tracer crystals contain detectable amounts of Zn and have the crystal structure of gibbsite. The tracer crystals behave in the same manner during precipitation as the nontracer Al(OH)3 crystals. The application of the tracer crystals for investigating, both batch and continuous, seeded Al(OH)3 precipitation is demonstrated. The tracer experiments provide information on the growth and agglomeration kinetics of different size fractions. The tracers are a useful tool for the quantitative investigation of solid‐phase residence time distributions within a crystallizer.
Dynamic modeling of suspension crystallizers, using experimental data
Authors: Eek Rob A. , Dijkstra Sjoerd , Van Rosmalen Gerda M. 
Published: June 2004

AbstractA model for the dynamics of a single‐stage suspension crystallizer is developed, which serves as a basis for process analysis and the design of controllers. A population balance for the dynamics of the crystal size distribution (CSD) with mass and heat balances is described, as well as empirical relations for the separation efficiency of classified particle removal systems, the initial CSD, and the crystallization kinetics. A continuous pilot crystallizer is used that is equipped with a separator and dissolver for fine crystals and a CSD sensor based on forward light scattering. The process and sensor are modeled separately. The sensor model is based on Fraunhofer light scattering theory assuming rectangular‐shaped particles. CSD dynamics data are obtained from startup experiments with the pilot plant at different process conditions. Experimental process data show a strong effect of fines and the slurry retention time on the CSD dynamics. A nonlinear parameter estimation procedure determines the empirical parameters directly from raw sensor data. The model fits accurately to the measured data. Evidence is found for the existence of a population of slow growing crystals with a growth rate approximately ten times lower than the fast growing crystals. A strong correlation is found between the total surface area of crystals with a size larger than 600 μm and the nucleation rate.
Feedback control of nonlinear differential‐algebraic‐equation systems
Authors: Kumar Aditya , Daoutidis Prodromos 
Published: June 2004

AbstractThe output feedback control problem is addressed for a class of nonlinear multivariable high‐index differential‐algebraic‐equation systems in semiexplicit form. Initially, an algorithmic procedure is developed and used to derive an equivalent state‐space relization of the constrained system. An output feedback synthesis problem is then formulated on the basis of the derived state‐space realization and solved through the combination of state feedback and appropriate state observers. The developed methodology is applied to a two‐phase reactor, and its performance and robustness characteristics are evaluated through simulations.
Glucose hydrolysis and oxidation in supercritical water
Authors: Holgate H. Richard , Meyer Jerry C. , Tester Jefferson W. 
Published: June 2004

AbstractGlucose hydrolysis and oxidation occurred rapidly in supercritical water at 246 bar and at 425 to 600°C. A diverse set of products, present in the liquid‐phase reactor effluent and also subject to hydrolysis, was formed. At 600°C and a 6‐s reactor residence time, glucose is completely gasified, even in the absence of oxygen. In the presence of oxygen, destruction of liquid‐phase products is enhanced, with none found above 550°C at a 6‐s reactor residence time. Major products formed wee acetic acid, acetonylacetone, propenoic acid, and acetaldehyde in the liquid phase, and carbon monoxide, carbon dioxide, methane, ethane, ethylene, and hydrogen in the gas phase. Methane and hydrogen were present among the products at temperatures up to 600°C for reactor residence times of 6 s.
Novel method for noncontact measurement of particle temperatures
Authors: Wagenaar B. M. , Meijer R. , Kuipers J. A. M. , van Swaaij W. P. M. 
Published: June 2004

AbstractA nonintrusive temperature measurement technique is developed for noncontact measurement of the temperature of single particles with < 200 μm dia. It is based on the temperature dependence of the fluorescence spectrum resulting from irradiation of a certain phosphor mixture with UV light by applying a mixture of two phosphors with fluorescence colors (blue and green) and a color shift from green to blue (with temperature increase from 20 to 280°C). An experimental setup is described for temperature measurement of particles based on the fluorescence color, together with the calibration of this system. The fluoroptic technique is applied to measure the temperature decrease of hot particles flowing down a cold chute. The measurements agree very well with thermocouple measurements. This novel technique can be applied to nonintrusive measurement of particle temperatures in (dense) multiparticle systems as encountered in packed and fluidized beds.