摘要:

AbstractA computational study of steady, developing flow of gas‐particle suspensions in a vertical riser has been carried out, using a model based on kinetic theory of granular materials, to understand the role of inlet configuration on the pattern of flow development. Three inlet configurations—uniform inlet, core‐annulus flow at the inlet and circumferential injection of secondary gas—were examined. It is found that the inlet configuration can have a profound impact on the rate of segregation of particles to the wall and the internal recirculation. Circumferential injection of gas has a favorable effect on the flow in the sense that it can decrease the extent of internal recirc

ISSN:0001-1541    

DOI:10.1002/aic.690390402

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractAn experimental study of the deformation of gas bubbles in viscous Newtonian liquids subjected to simple shear flow has been undertaken as a first step toward understanding bubble dynamics in polymer processing. Measurements of the shape, interfacial area, and volume of air bubbles suspended in the gap between two coaxial, counterrotating cylinders are presented and discussed as function of capillary number. At high capillary numbers (high deformations), the experiments confirm the theoretical model of Hinch and Acrivos.

ISSN:0001-1541    

DOI:10.1002/aic.690390403

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThis article shows the settling behaviors of flocculated, magnetic and nonmagnetic iron oxide suspensions. It is unique, since in the literature on settling of model submicron flocculated particulate suspensions there is no direct visualization of the structures and how they change during settling. Channeling, cracking, and a novel collapse phenomenon were detected during settling. Causes were investigated using lapse videorecording for side and top views. The effect of air bubbles was shown to contribute to the accelerated settling of the suspension by creating channels that conduct oil to the settling front. Settling heights were recorded for long periods of time (up to a year) for iron oxide suspensions of different concentrations. Decreasing tube diameters delayed settling, and magnetic interparticle forces produced smaller final settling heights. The effect of magnetic forces was interpreted in terms of a floc model. The model finds magnetic flocs 1.3 to 1.4 times denser than their nonmagnetic analogs. Finally, a mechanism is put forth to interpret the settling behavior observed.

ISSN:0001-1541    

DOI:10.1002/aic.690390404

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractA modified sieve (that is, T‐By) tray uses a system of weirs and risers to approximate liquid plug flow over a cross‐flow, circular‐section tray. Vapor‐liquid contact is improved using a system of curtain‐pattern vapor holes and intermediate weirs to form cells across the tray that promote liquid mixing into discrete, wellmixed pools and stabilize froth. A theoretical model is used to analyze experimental data, guide tray design, and suggest new strategies for improving performance. These results indicate that tray efficiencies and stabilities can be increased without capacity losses. Pressure drop can also be manipulated to enhance pe

ISSN:0001-1541    

DOI:10.1002/aic.690390405

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractUnlike the traditionally fixed recipes in batch process operation, flexible recipes allow the adjustment of some of its relevant recipe items. These adjustments can either be predefined in cases of planned experimentation, or suggested by a formal process optimization or control algorithm on the basis of actual information. In both the response surface methodology and the simplex evolutionary operation (EVOP), some well‐known methods for empirical model building and process optimization, flexible recipes are involved. Another application of flexible recipes arises in a feedforward quality control strategy of batch processes when variations in market or process conditions are known a priori. The experimental results of these strategies are presented for the batchwise production of benzylalcohol on a pilotplant scale. Experiments have been performed to obtain a reliable model of the yield. On the basis of this model, better process conditions have been suggested, which substantially deviate from the final simplex resulted from experiments within simplex EVOP. Finally, an adaptive feedforward control strategy has been applied for a priori known disturbances in the process input

ISSN:0001-1541    

DOI:10.1002/aic.690390406

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractA nonlinear model‐predictive control strategy is developed to maintain the superior‐to‐steady‐state performance of a periodically forced chemical reactor. The performance of the predictive controller is investigated in the presence of measurement disturbances and parametric uncertainty. It is also shown that statistically inferred input‐output models can be a substitute whenever detailed fundamental models are not available. A nonlinear autoregressive polynomial model based on observed plant data is built and incorporated into the control scheme. The catalytic oxidation of ethylene in a periodically‐forced, continuous stirred‐tank reactor is considered as

ISSN:0001-1541    

DOI:10.1002/aic.690390407

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractA model based on kinetic theory is derived for surface diffusion of multilayer adsorbed species on a homogeneous surface. A simple solution is obtained for expressing the concentration dependence of surface diffusivity. For monolayer adsorbate, the solution is reduced to the classical HIO model. This solution, in principle, requires no fitting parameters and is capable of predicting the unique concentration dependent behavior exhibited by multilayer surface diffusion, where the diffusivity first increases with surface concentration to a maximum followed by a decrease. Seventeen sets of experimental data from the literature are used to test the model, with fair results. It is also shown that heats of adsorption can be calculated from multilayer surface diffusivity data by using this model.

ISSN:0001-1541    

DOI:10.1002/aic.690390408

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe hydroisomerization of n‐heptane has been used as a model to study the acidmetal balance requirements for Pt/zeolite catalysts. Experiments were carried out using physical mixtures of zeolite beta and Pt/Al2O3particles, in which the level of the metal‐containing component was varied to change the acid‐metal balance. Selectivity, in terms of cracking vs. isomerization, varies significantly with the metal loading up to a point beyond which the degree of paraffin isomerization is independent of metal loading. These results are interpreted in terms of a simple dualsite model based on a classical theory of polyfunctional catalysis, first advanced by Weisz (1962). The model is also used to show how an imbalance in hydrogenation and acid functions can even alter the apparent reaction network of the observable chemical species in the s

ISSN:0001-1541    

DOI:10.1002/aic.690390409

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractAn experimental study has been performed of the reactions occurring when the reactive particles of calcium oxide are exposed to sulfur dioxide bearing flue gas. Using a differential, fixed‐bed reactor, kinetic measurements have been made in the temperature range of 170 and 580°C. A relatively simple correlation based on the amassed data has been proposed. This correlation allows the estimation of the reaction rate as a function of temperature, conversion of the solids and concentration of sulfur dioxide in the gas phase. The proposed rate law equation makes it possible to predict in a straightforward manner the rate of sorption which would be required to design the performance of a desulfurization un

ISSN:0001-1541    

DOI:10.1002/aic.690390410

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY

摘要:

AbstractThe solubility and diffusion coefficients of low‐molecular‐weight penetrants in a polymeric stationary phase were determined by use of inverse gas chromatography (IGC). Previously reported applications of packed‐column IGC to the measurement of the stationary‐phase diffusion coefficient have been carried out via the van Deemter approach. We present here a new mathematical model to describe the chromatographic process in packed columns. A moment analysis procedure was developed from this model to analyze the chromatographic peaks eluting from packed columns. The first moment (mean retention time) is determined to depend only on the equilibrium partition coefficient, whereas the second moment (variance) is related to both the thermodynamic and transport properties of the polymer‐solute system. The validity of the technique was demonstrated by measuring the diffusivity and solubility of toluene and benzene in polystyrene above the glass transition temperature of the polymer. Free‐volume theory was used to interpret and correlate the diffusivity data obtained at infinite dilution of the solute. One can use the results obtained at infinite dilution to predict reliably via the free‐volume theory the concentration and temperature dependence of polymer‐solvent diffusi

ISSN:0001-1541    

DOI:10.1002/aic.690390411

出版商:American Institute of Chemical Engineers    

年代:1993

数据来源: WILEY