摘要:

AbstractThere exists a narrow operating window in bubble columns where the motion is so gentle that the normally dominating forces of coalescence and breakup no longer define the bubble size, hence formation dynamics must control. Elementary force balances are presented to predict bubble size, which compares favorably with experimental data and is shown to be applicable to both rigid and flexible spargers. The main focus is on the prediction and performance of a small‐holed flexisparger, for which it is proved that the gas momentum term is highly significant. Also, it is shown that the intermediate drag law is more appropriate than Stokes for forming bubble

ISSN:0001-1541    

DOI:10.1002/aic.690370202

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractNonequilibrium diffusion behavior in nonionic and ionic surfactant microemulsion systems has been studied experimentally using the open‐ended capillary method. Experimental results for these systems have been compared with a drop theory of diffusion for microemulsions under conditions where large concentration and electrostatic gradients exist. The results show good agreement in concentration profiles between theory and experiment for the microemulsion components—water, benzene, and phenol. Furthermore, under certain conditions the theory predicts that over a limited time interval phenol will diffuse from low‐concentration regions to regions of higher concentration. This phenomenon has been obs

ISSN:0001-1541    

DOI:10.1002/aic.690370203

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractExperimental measurements of the crystal‐size distribution (CSD) clearly indicate a pronounced difference in the dynamic behavior of a 20‐ and 970‐L continuous crystallizer that produces ammonium sulfate. The difference in their circulation time offers a probable explanation for this phenomenon. It causes different supersaturation profiles in the two crystallizers, which leads to internal fines dissolution in the large crystallizer. This contributes to the observed oscillations in the 970‐L crystallizer as opposed to the first‐order responses in the 20‐L crystallizer. To numerically study the effect of the supersaturation profile a dynamic model, from which the MSMPR (mixed suspension mixed product removal) assumption is omitted, is developed. Calculated supersaturation profiles differ considerably for the 20‐L, the 970‐L and an imaginary 50,000‐L continuous evaporative crystallizer. Coincident with changes in the supersaturation profiles, the numerical solution of the model indicates the tendency of large crystallizers to oscillate and supports this sugg

ISSN:0001-1541    

DOI:10.1002/aic.690370204

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractA generalized linear dynamic model or singular model, for which the standard state space representation and the Kalman filtering cannot be applied, is used to develop a new algorithm to solve the linear dynamic material balance problem. This algorithm is based on the method developed in the steady‐state case and leads to a recursive scheme, which is very useful in real‐time processing. It reduces the computational problem such as singularities and round‐off errors that may occur in complex systems. Convergence conditions are given and verified for the dynamic material balance

ISSN:0001-1541    

DOI:10.1002/aic.690370205

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractA single‐pellet reactor has been used to investigate the impact of partial external wetting on catalyst performance in a multiphase reaction system. The novel design simulates the local environment within a trickle‐bed reactor, and permits the direct measurement of the degree of wetting under reaction conditions. Experimental data of the hydrogenation of α‐methylstyrene (AMS) over a Pd/Al2O3pellet provide unequivocal evidence of effectiveness enhancement by partial wetting, a predicted single‐pellet phenomenon (e.g., Harold and Ng, 1987; Funk et al., 1988, 1989). The overall reaction rate is an increasing (decreasing) function of the degree of wetting if the overall limiting reactant is more effectively supplied through the wetted (nonwetted) part of the surface. A maximum in the reaction rate can occur at an intermediate degree of wetting, signaling a transition from an overall AMS‐limited to hydrogen‐limited reaction. The dependence of the degree of wetting on the liquid flow rate for low reaction rates is consistent with a simple rivulet flow model. At higher reaction rates the degree of wetting decreases, with all other conditions fixed. Possible mechanisms for this interesting link between the degree of wetting and reaction a

ISSN:0001-1541    

DOI:10.1002/aic.690370206

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractAn equation‐of‐state‐based sorption isotherm is developed and used in modeling isothermal supercritical fluid desorption in fixed beds. The conventional fixed‐bed desorber model when coupled with density‐dependent sorption isotherm predicts the temperature, pressure, and density effects on desorber dynamics and regeneration efficiencies that are experimentally observed in supercritical fluid regeneration of fixed beds.Experimentally observed phenomena such as the presence of pressure‐dependent optimal regeneration temperature, high‐pressure‐favored regeneration, and the reversal of temperature dependence of sorption isotherm—which formerly were attributed to supercritical fluid density and viscosity, and to the endothermicity of sorption isotherm—were fully predicted and explained in terms of a density‐dependent sorption isotherm.The proposed method also promises prediction of regeneration efficiencies in cosolvent‐aided supercr

ISSN:0001-1541    

DOI:10.1002/aic.690370207

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractThree parametric sensitivity criteria were examined for application to a pseudohomogeneous tubular reactor system, in which both methanol dehydration (exothermic) and methanol dissociation (endothermic) were catalyzed. The addition of the endothermic reaction was shown to lead to a desensitized reactor. It was illustrated, however, that the relative activities of the two catalysts should be somewhat similar to maintain the overall conversion of the resulting reactor for a given residence time.The three criteria investigated tended to disagree with one another more, as the system was made less sensitive by the addition of more endothermic catalyst. A potential application of the resulting nonsensitive reactor design would be in methanol‐fueled vehicle

ISSN:0001-1541    

DOI:10.1002/aic.690370208

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractNonlinear principal component analysis is a novel technique for multivariate data analysis, similar to the well‐known method of principal component analysis. NLPCA, like PCA, is used to identify and remove correlations among problem variables as an aid to dimensionality reduction, visualization, and exploratory data analysis. While PCA identifies only linear correlations between variables, NLPCA uncovers both linear and nonlinear correlations, without restriction on the character of the nonlinearities present in the data. NLPCA operates by training a feedforward neural network to perform the identity mapping, where the network inputs are reproduced at the output layer. The network contains an internal “bottleneck” layer (containing fewer nodes than input or output layers), which forces the network to develop a compact representation of the input data, and two additional hidden layers. The NLPCA method is demonstrated using time‐dependent, simulated batch reaction data. Results show that NLPCA successfully reduces dimensionality and produces a feature space map resembling the actual distribution of the underlying system par

ISSN:0001-1541    

DOI:10.1002/aic.690370209

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractA new computational procedure based on the finite difference methods is developed to solve the coupled partial differential equations describing nonisothermal and nonequilibrium sorption of multiple adsorbate systems on a fixed bed that contains bidispersed pellets. In this numerical method, a solution‐adaptive gridding technique (SAG) is applied in combination with a four‐point quadratic upstream differencing scheme to satisfactorily resolve very sharp concentration and temperature variations occurring in the case of small dispersing effects. Furthermore, the method resorts to a noniterative implicit procedure for solving the coupling between the column transport equations and the adsorption kinetics inside the pellets, which may be particularly efficient when the particle kinetics equations are highly stiff.The numerical model will be tested for one‐, two‐ and three‐transition systems. The results are compared to available analytical and equilibrium theory

ISSN:0001-1541    

DOI:10.1002/aic.690370210

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractThe utility of the Hammerstein model, which is composed of a static nonlinear element in series with a linear dynamic part, was investigated to represent the dynamics of nonlinear chemical processes. Different methods to identify the parameters of Hammerstein models were tested. The methods were applied to the identification of simulated distillation columns and to an experimental heat exchanger process. The results show that the dynamics of such processes can be better represented by Hammerstein‐type models than by linear model

ISSN:0001-1541    

DOI:10.1002/aic.690370211

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY