摘要:

AbstractThe structure of thin, wavy falling films was studied to evaluate whether the random‐appearing wave structure is a result of deterministic chaos or a purely stochastic process. The time‐varying film thickness was obtained at different spatial locations near the point of wave inception for flow rates in the range of Re=3–10. Under all conditions the wave structure was aperiodic in nature and displayed none of the known transitions to chaos. However, the power spectra followed an exponential decay law at high frequencies that is characteristic of chaotic systems. The estimated attractor dimension, used to characterize the complexity of a chaotic system, was much higher than those of known model chaotic systems. It is demonstrated that these high values could be explained due to small levels of noise present in experimental situations. Since experimental data are seldom noise free, a basic limitation in applying these methods to experimental measurements is demonst

ISSN:0001-1541    

DOI:10.1002/aic.690370402

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractThe development of a concentration gradient along the vertical axis of a column of quiescent solution is explained within the framework of nonequilibrium thermodynamics. The formulae derived enabled us to determine explicitly the concentration difference between two vertical levels in a liquid column and specific conditions under which the concentration profile is at equilibrium. The concept of solute cluster formation in a supersaturated solution is consistent with the presented theory although the theory itself does not provide any direct or indirect proof of the occurrence of clustering.

ISSN:0001-1541    

DOI:10.1002/aic.690370403

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractSimple distillation columns with ideal vapor‐liquid equilibrium may display multiple steady‐state solutions. Two fundamentally different sources for the multiplicity are presented. Both bring about the unexpected result that increasing reflux makes separation worse in the top part of the column. It corresponds to an unstable operating point.The first type of multiplicity is found for columns with mass or volume inputs (e.g., mass reflux and molar boilup). Even for constant molar flows, the transformation from the actual input units to molar units may become singular (corresponding to a pitchfork bifurcation point), resulting in multiple steady‐state solutions. The results are highly relevant in practice, as industrial columns usually have inputs on a mass or volume basis. The second type for specifications on a molar basis (e.g., molar reflux and molar boilup) depends on the presence of an energy balance in the model. The multiplicity is caused by interactions between flows and compositions in the c

ISSN:0001-1541    

DOI:10.1002/aic.690370404

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractThe enhanced dispersion resulting from solute exchange between phases was investigated experimentally for the case of a long, cylindrical capillary tube, in which a stationary absorbing phase formed a thin annular film around a flowing fluid. Solute diffusion into the stationary phase was analyzed in detail to accurately determine the coupling of film diffusion and hydrodynamic effects. The experimental results and analyses showed an increase in dispersion relative to the usual Taylor effect. The increased dispersion was a function of the relative partitioning of solute between phases and was in quantitative agreement with predictions from previously published theoretical studies.

ISSN:0001-1541    

DOI:10.1002/aic.690370405

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractThis work concerns general multiple‐input/multiple‐output (MIMO) nonlinear systems with nonsingular characteristic matrix. For these systems, the problem of inversion is revisited and explicit formulas are derived for the full‐order and the reduced inverse system. The reduced inverse naturally leads to an explicit calculation of the unforced zero dynamics of the system and the definition of a concept of forced zero dynamics. These concepts generalize the notion of transmission zeros for MIMO linear systems in a nonlinear setting. Chemical engineering examples are given to illustrate the calculation of zero dynamics. Input/output linearization is then interpreted as canceling the forced zero dynamics of the system, and precise internal stability conditions are derived for the closed‐loop

ISSN:0001-1541    

DOI:10.1002/aic.690370406

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractThe heat transfer to, and the resultant evaporation of, drops of a volatile liquid sprayed upward in an immiscible liquid flowing down in a vertical column are analyzed to enable calculation of the volumetric heat transfer coefficient in the column. For this analysis, a model is contrived that assumes no nucleation delay in initially monodispersed drops and a heat transfer to each of the drops, with simultaneous evaporation, that can be approximated by an empirical correlation for heat transfer to an isolated drop evaporating in a quiescent, sufficiently extended medium. The expression obtained for the volumetric heat transfer coefficient is used to predict its values under some particular column operating conditions, which are then compared with relevant experimental data found in the literature.

ISSN:0001-1541    

DOI:10.1002/aic.690370407

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractThe interstitial pressure buildup and the internal stresses on the skeleton of a cylindrical green body during burnout are analyzed numerically. The intrinsic kinetics of pyrolysis is coupled with the Carman‐Kozeny equation or the slip‐flow model of Wakao and Smith to evaluate the pressure distribution. The stress distributions before failure are estimated from elasticity theory. The stresses are tensile, and their maxima are located at the center of the cylinder. The tangential stress is larger than the radial stress. The effects of green body size, specific surface area, and pressurized atmosphere are discussed. The approximate solution is accurate for small green bodies. The pressurized atmosphere reduces the interstitial pressure and the internal stresses effectiv

ISSN:0001-1541    

DOI:10.1002/aic.690370408

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractA versatile reaction‐separation (VERSE) model was developed to quantitatively simulate the behavior of chromatographic separations coupled with reactions. Detailed mass transfer and reaction mechanisms are considered. Aggregation data of myoglobin and β‐lactoglobulin A verified the model. The effects of concentration, equilibrium distribution, reaction rate, convection rate, particle radius, and relative affinity are shown for a dimerizing system. When the aggregation rate is relatively slow compared with convection and mass transfer rates, the individual forms behave as separate species in frontal, elution, and displacement chromatography. For rapid aggregation rates, the individual forms behave as a single component with an average affinity. The wave asymmetry and increased spreading due to aggregation depend on relative affinity differences. Serious error may result if aggregation is overlooked in parameter estimation using frontal or pulse analysis. The dimensionless group principles developed here are useful in scaling and predicting when peak or wave splitting or merging will occur in reaction chromatography sys

ISSN:0001-1541    

DOI:10.1002/aic.690370409

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractDeep knowledge about process behaviors plays an important role in the diagnosis of chemical processes. Cause‐and‐effect reasoning using deep knowledge is useful especially for interacting malfunctions. This work explores the integration of deep knowledge into task‐specific, knowledge‐based architectures for resolving interacting multiple malfunctions and presents a novel methodology called diagnostically focused simulation (DFS). Invoked in an auxiliary manner, DFS uses deep knowledge and performs qualitative simulation in a highly constrained manner. The close integration with other problem solvers is an evolutionary approach to using qualitative simulation in diagnosis and manages a normally computationally‐explosive procedure. Diagnostic results from the compiled problem solver provide a situation‐specific assessment of the chemical process, identify possible malfunction scenarios, and focus on appropriate levels of process detail. DFS effectively demonstrates a balance between run‐time simulation and compiled problem solving

ISSN:0001-1541    

DOI:10.1002/aic.690370410

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractWe have shown that ionomeric membranes of perfluorosulfonic acid (PFSA) polymer allow selective pervaporation of polar organic compounds from their azeotropic mixtures with less polar compounds. A composite membrane of a thin PFSA polymer film, cast on a porous Teflon support, provided desirable permeant fluxes with good selectivity. Model binary azeotropes, composed of alcohols and hydrocarbons, were separated with total pervaporation fluxes of up to 9.5 kg/h·m2using a stirred membrane permeation cell, the product side of which was exposed to vacuum. Fluxes increased with increasing alcohol content of the feed and with temperature. But the selectivity of the more permeating component remained reasonably constant around the azeotropic point and also over the range of temperature used in the study (25–55°C). Total pervaporation fluxes depended little on downstream pressure up to 6.66 kPa (50 torr). These separation data were explained by a mathematical model based on a solution‐diffusion mech

ISSN:0001-1541    

DOI:10.1002/aic.690370411

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY