摘要:

AbstractAn assumption commonly, but by no means universally, made in the stability analysis of the homogeneously fluidized state is that the pressure field may be well approximated by its gravitational component alone. This assumption is critically examined: the results indicate that it is valid for most cases of practical interest but can lead to significant discrepancies for liquid fluidization of low‐density particle

ISSN:0001-1541    

DOI:10.1002/aic.690351202

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe model of uniform nonlinear kinetics recently developed for the continuous description of a multicomponent mixture reacting in a batch or plug flow reactor (Astarita, 1989) is applied to the analysis of a continuous stirred tank reactor (CSTR). It is shown that most of the equations can be solved in general, independently of the specific kinetic mechanism. Some specific mechanisms are discussed. The difference between the behavior in a plug flow reactor (PFR) and a CSTR turns out to be quite dissimilar from what one would expect by considering the single‐component cas

ISSN:0001-1541    

DOI:10.1002/aic.690351203

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractMany industrial proceses require the circulation of particles between reacting fluidized compartments at a stable, but flexible rate, so that the processes can be operated at different solids rates. In order to understand the phenomena involved in the circulation and its control, circulation of sand particles has been studied through a new experimental approach, using an open‐loop two compartment circulating system.Experimental results show that the control of the circulation rate depends on three phenomena: the vertical resisting force in the fluidized compartments, the contraction of flow in the communication zone, and the bypass of gas between the compartments. For industrial purposes, the first appears to be predominant in the control of the solids rate. The second ensures neither the strict control of this rate nor the required flexibility. The link between the gas bypass and the circulation phenomena is explained and recommendations for the design and operation of circulating systems are give

ISSN:0001-1541    

DOI:10.1002/aic.690351204

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractA Monte Carlo (MC) technique involving explicit calculation of molecular trajectories in fibrous media is used to obtain effective transport coefficients in the Knudsen regime of gas diffusion. A fully penetrable cylinders (FPC) model is used to represent a fibrous substrate during the course of densification, as in composite fabrication processes such as chemical vapor infiltration (CVI). The calculated Knudsen permeabilities are in excellent agreement with available data. Accessible porosities are computed as a function of total porosity and are shown to depend on the fiber number density. The nonfiber phase is shown to percolate at ϕ ≈ 0.095, but the threshold is sensitive to the boundary conditions employ

ISSN:0001-1541    

DOI:10.1002/aic.690351205

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractA previously developed method (Sotirchos and Burganos, 1988) for studying isobaric multicomponent diffusion in a class of capillary networks is extended for application to the problem of convection and diffusion of gaseous mixtures in porous media. The method is used to develop flux models for nonisobaric transport in capillary structures, which are then compared with corresponding “three‐parameter” dustygas models. Results for discrete and continuous pore size distributions show that the predictions of the developed flux models depend strongly, both qualitatively, and quantitatively, on the procedure used to average the dusty‐gas model equations for a single pore over the pore‐size dis

ISSN:0001-1541    

DOI:10.1002/aic.690351206

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractA computer simulation of turbulent flow in a channel is used to detect flow patterns related to the production of Reynolds stress. It is found that quadrant 2 and quadrant 4 events possess a streaky structure in the viscous wall region and that these events can be best understood by examining the velocity field in they‐zplane. Large turbulence production in the viscous wall region is found to occur in updrafts and downdrafts associated with closed eddies. These eddies, on average, have a spanwise dimension of 50 wall units and a streamwise dimension of 400–450 wall units. They are often seen to originate from small attached eddies at the w

ISSN:0001-1541    

DOI:10.1002/aic.690351207

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractA model is developed describing consecutive gas‐solid reactions occurring in porous media. The model calls for independently measurable parameters and predicts two maxima in the reaction rate at intermediate conversions. The low temperature (350°C) reduction of hematite to iron in a hydrogen‐nitrogen atmosphere was used to test the model. The experimental data confirmed the expected rate maxima. The conversion predictions are very close to the data for conversions below 30%, but are systematically somewhat lower than the experimental values for higher levels of conversion. An explanation for the discrepancy is offered in terms of the description of the pore struc

ISSN:0001-1541    

DOI:10.1002/aic.690351208

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractA study was made of phenol degradation by bacteria immobilized onto particles of calcined diatomaceous earth in a draft‐tube, three‐phase fluidized‐bed reactor.A mathematical model is used to describe simultaneous diffusion and reaction of oxygen and phenol in the reactor. Kinetic parameters for the growth of nonsupported cells were obtained in batch and chemostat experiments. Liquid‐solid mass transfer coefficients were determined experimentally and showed good agreement with literature values for conventional three‐phase fluidized beds. Experimental steady‐state degradation data were used to calculate biofilm substrate diffusivities. These were found to decrease as the biofilm density increased.The transition from phenol to oxygen‐limiting biofilm kinetics predicted by the model was shown to exist experimentally. A critical ratio of phenol/dissolved oxygen concentration was found at which this transition occurred. This provides a criterion for establishing whether increased aeration will increase the volumetric deg

ISSN:0001-1541    

DOI:10.1002/aic.690351209

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractThe ability of knowledge‐based expert systems to facilitate the automation of difficult problems in process engineering that require symbolic reasoning and an efficient manipulation of diverse knowledge has generated considerable interest recently. Rapid deployment of these systems, however, has been difficult because of the tedious nature of knowledge acquisition, the inability of the system to learn or dynamically improve its performance, and the unpredictability of the system outside its domain of expertise.This paper proposes a neural‐network‐based methodology for providing a potential solution to the preceding problems in the area of process fault diagnosis. The potential of this approach is demonstrated with the aid of an oil refinery case study of the fluidized catalytic cracking process. The neural‐network‐based system successfully diagnoses the faults it is trained upon. It is able to generalize its knowledge to successfully diagnose novel fault combinations it is not explicitly trained upon. Furthermore, the network can also handle incomplete and uncertain data. In addition, this approach is compared with the knowledge‐bas

ISSN:0001-1541    

DOI:10.1002/aic.690351210

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY

摘要:

AbstractCeramic particle formation processes have been studied using SiO2as a model compound. Silica particles have been synthesized in a counterpropagating diffusion flame reactor, in whichin‐situmeasurements of particle size and number density have been made. In addition, the time‐temperature history of the particle field has been calculated from a flame simulation. Numerical simulations using moment and sectional methods for particle formation have been applied and compared to the experimental measurements. The simulations for the particle formation assume a kinetically‐constrained approach, allowing a simple representation of nucleation, surface growth and coagulation. The results suggest that, if the source rates are known well enough, particle formation of low vapor pressure species can be predicted. Both models do well in predicting the gross features of particle formation (number density and mean particle size), although the moment solution does a poor job of predicting the polydispersity effects during periods of high monomer generation

ISSN:0001-1541    

DOI:10.1002/aic.690351211

出版商:American Institute of Chemical Engineers    

年代:1989

数据来源: WILEY