摘要:

AbstractA fractionation method for fine‐particle suspensions using resonant ultrasonic fields coordinated with bidirectional fluid flow fields is described. The basis for the separation is differences in the speed of response of particles to the imposition of a resonant acoustic field. As such, the method is sensitive to the particle size and the acoustic contrast between the solid particles and their suspending fluid. Both batch and continuous fractionation processes can be developed from a two‐step acoustic‐flow cycle. An analytical model was constructed from equations that describe the trajectories of particles as they respond to the acoustic and flow fields. Model predictions indicate how the fractionation can be controlled through choice of cycle parameters. The method was implemented experimentally. Results for the fractionation of 325‐mesh polystyrene spheres indicate that sharp fractionations can be achieved. The experimental results are generally in agreement with the model pred

ISSN:0001-1541    

DOI:10.1002/aic.690390202

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractRheological behavior of moderately concentrated (up to 35 vol. %) suspensions or slurries prepared with non‐Newtonian carrier fluids is investigated. Extensive experimental data on the Poiseuille slit flow of suspensions of sand in Hydroxypropyl Guar (HPG) solutions are presented. Flow data are gathered by pumping various non‐Newtonian slurries into a unique, 8 ft (2.4 m) tall vertical apparatus, with great care taken to calibrate the instrument and to avoid settling difficulties. Investigated are the effects of polymer concentration, solids concentration, test temperature, and shear rate on the rheological properties of slurries. The rheological behavior of HPG solutions and HPG suspensions is characterized by a pseudoplastic power law non‐Newtonian fluid model over a shear rate range of 30 to 500 s−1. The correlations for predicting the relative slurry viscosity for HPG fluids are presented. Substantial increase in viscosity of these non‐Newtonian fluids is observed, and they are found to be a strong function of polymer concentration, shear rate, test temperature, and particle concentration. Results of this investigation are also compared with those available for Newtonian and non‐Newtonian

ISSN:0001-1541    

DOI:10.1002/aic.690390203

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractA simple statistical‐mechanical theory, known as the random‐phase approximation, is applied to study liquid‐liquid phase separations in solutions of globular proteins. Phase separation may be induced by addition of nonionic polymer or/and ordinary electrolytes. In this analysis, the osmotic‐attraction mechanism, whereby the depletion of “solvent” particles between two proteins causes an attractive force, is primarily responsible for phase separation. For one‐component models of protein solutions, the theory yields simple algebraic expressions for the equation of state and for the chemical potential of the protein. This analytical theory describes the observed solubility behavior of proteins, including the effect of protein and polymer size, protein charge and concentration, and concentration of simple

ISSN:0001-1541    

DOI:10.1002/aic.690390204

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractLiquid circulation and a finite entrance zone are accounted for in modeling gas absorption into cocurrent flows of pure oxygen and CMC solutions. The new models lead to a Taylor‐like correction factor to account for circulation in both absorption and transient dispersion experiments. Steady‐state experiments for viscosities of 1, 12, 25 and 50 mPa·s were conducted by measuring dissolved gas concentration profiles along the column axis. Liquid mixing experiments were performed using the transient acid‐base neutralization method, leading to measured values of axial dispersion coefficients which depended on viscosity to the power 0.75. Measurements suggest that circulation was minuscule owing to uniform gas injection by Flexisparger in the present

ISSN:0001-1541    

DOI:10.1002/aic.690390205

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe addition of cosolvents to supercritical fluid (SCF) solvents can have large effects on solubilities, giving engineers the ability to tailor loadings and selectivities of solutes for difficult separations. It is necessary to have a better understanding of the special intermolecular interactions that occur in SCF solutions to predict the effects of cosolvents. We use a SCF chromatographic technique to acquire a database of cosolvent effects for a variety of cosolvents and solutes; examination of the cosolvent effects shows evidence of hydrogen bonding, charge transfer complex formation, and dipole‐dipole coupling between solute and cosolvent molecules. SCF solvents, carbon dioxide, ethane, and fluoroform, are compared, and then the use of the chromatograph to measure solubilities is discusse

ISSN:0001-1541    

DOI:10.1002/aic.690390206

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractIn this article, we present a model to describe sorption kinetics of gaseous adsorbates onto bidispersed heterogeneous microporous particles. This model describes adsorption and desorption of gaseous adsorbates with allowance for the energy distribution of adsorption site for both equilibrium isotherm and diffusion of the adsorbed species. The adsorbed species of all energy level diffuse in two directions inside the particle. One direction is the direction along the particle coordinate while the other is the direction perpendicular to the particle coordinate (that is, the direction into the grain of the solid). This model is more fundamental than models previously proposed by Do and coworkers. Effects of energy distribution on the adsorption and desorption dynamics are investigated. Extensive experimental analysis of adsorption and desorption dynamics of ethane and propane onto Ajax activated carbon are carried out to validate this theory.

ISSN:0001-1541    

DOI:10.1002/aic.690390207

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThis article discusses the existing linear model predictive control concepts in a unified theoretical framework based on a stabilizing, infinite horizon, linear quadratic regulator. In order to represent unstable as well as stable multivariable systems, the standard state‐space formulation is used for the plant model. The incorporation of a nominally stabilizing constrained regulator eliminates the current requirement of tuning for nominal stability. Output feedback is addressed in the well‐established framework of the linear quadratic state‐estimation problem. This framework allows the flexibility to handle nonsquare systems, noisy inputs and outputs, and nonzero input, output, and state disturbances. This formulation subsumes the integral control schemes designed to remove steady‐state offset currently in industrial use. The online implementation of the controller requires the solution of a standard quadratic program that is no more computationally intensive than existing alg

ISSN:0001-1541    

DOI:10.1002/aic.690390208

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractNonlinear kinetics in multicomponent mixtures are best described in terms of continuous distribution functions. The quasilinearization procedure that we introduced in 1988 for “uniform” kinetics does not carry over to problems where second‐order derivatives appear, as in all cases where diffusion phenomena are of importance. We analyze a simple diffusion‐reaction problem in a porous catalyst, by making use of a perturbation technique. The general conclusions reached from this specific problem can be generalized to a wider class of diffusion‐reaction problems in complex

ISSN:0001-1541    

DOI:10.1002/aic.690390209

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractIon bombardment of solid surfaces produces a number of changes in the nearsurface region. The surface is etched by ejection of material by momentum exchange. The surface concentrations of the components of a multicomponent solid, such as an alloy, are altered by preferential sputtering. Finally, the incident ions penetrate a distance into the solid, producing a damaged region referred to as the “altered layer” in which diffusion is enhanced relative to that in the unaltered bulk. Previous models have not explicitly accounted for the ion penetration depth and the discontinuity of solid diffusivities at this boundary. We demonstrate that this problem is directly analogous to that of a plug‐flow reactor with axial dispersion, and solve for steady‐state and transient concentration profiles in a binary solid, taking into account the different values of the “Peclet number” appropriate for the two regions, the altered layer and the unaltered bulk o

ISSN:0001-1541    

DOI:10.1002/aic.690390210

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractA phenomenological, pore‐scale, hydrodynamic model is developed for representation of the uniform, cocurrent, two‐phase flow in the low interaction regime in trickle bed reactors. Comparison of model predictions with numerous pressure drop and liquid holdup data reveals that phase interaction terms are negligible which results in a simplified model with no adjustable parameters. This model yields improved pressure drop and liquid holdup estimates for the low interaction regime. In addition, a criterion for the prediction of the trickle to pulsing flow regime transition is developed based on Kapitza's (1945) work on laminar film stability. This criterion compares favorably to data and to some other existing models for prediction of the trickle to pulsing flow regime transit

ISSN:0001-1541    

DOI:10.1002/aic.690390211

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY