摘要:

AbstractProcessing of ceramics is reviewed from a broad perspective, with emphasis on the predominant powder‐based methods, but with considerable attention to other methods. Major stages of the powder process, from preparation, modification, and handling, to sintering or pressure densification (or postdensification) are discussed. Nonpowder‐based methods, such as chemical vapor deposition, melt, and polymer pyrolysis processing, are also presented. Processing of ceramic composites is reviewed, noting the shifts in processing technology this entails. Practical aspects, such as part size, shape, volume, and the costs of various processes are also addres

ISSN:0001-1541    

DOI:10.1002/aic.690360402

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractThe effect of mixing intensity (power input) on the precipitation/crystallization of barium sulfate in a two‐feedstream (sodium sulfate, barium chloride) continuous stirred‐tank crystallizer with mixed product removal was investigated through experiments and companion mathematical models. Crystal growth rate and nucleation rate were very sensitive to mixing intensity, with growth rate increasing eightfold and nucleation rate decreasing 100‐fold as power input per unit mass was increased from 0.001 to 0.73 m2/s3(0 to 1,200 rpm stirrer speed). Experimental results at high feed concentration were accurately described by a model accounting for homogeneous nucleation and kinetic growth of particles as well as turbulent mass transfer to particles and turbulent micromixing of feedstreams. The principal mixing effect was due to particle mass transfer, not micromixing. Experiments at low feed concentration were more difficult to model because of a more complex nucleation mechanism and altered particle morph

ISSN:0001-1541    

DOI:10.1002/aic.690360403

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractDetailed knowledge of solids circulation, bubble motion, and frequencies of porosity oscillations is needed for a better understanding of tube erosion in fluidized bed combustors. A predictive two‐phase flow model was derived starting with the Boltzman equation for velocity distribution of particles. The model is a generalization of the Navier‐Stokes equations of the type proposed by R. Jackson, except that the solids viscosities and stresses are computed by simultaneously solving a fluctuating energy equation for the particulate phase. The model predictions agree with time‐averaged and instantaneous porosities measured in two‐dimensional fluidized beds. Observed flow patterns and bubbles were also pr

ISSN:0001-1541    

DOI:10.1002/aic.690360404

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractRecent theoretical results (Japas and Levelt Sengers, 1989) for the temperature dependence of Henry's constant near the solvent's critical point are used to obtain a linear expression which, for aqueous solutions of nonpolar gases, fits experimental Henry's constant data at temperatures from water's critical point down to roughly the normal boiling point. A small correction with only one additional adjustable parameter extends the correlation to 0°C. The final result is a three‐parameter correlation, covering the entire range of temperatures, which fits the available data as well as or better than existing four‐parameter empirical expressions and better than a recently proposed three‐parameter expression. Since the correct near‐critical behavior is built in, the new correlation should be especially useful for estimating Henry's constants in systems where little or no data exist at high temperatures. Fitted parameters are given for ten nonpolar gases in H2O and six nonpolar gase

ISSN:0001-1541    

DOI:10.1002/aic.690360405

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractNuclear magnetic resonance flow imaging (MRFI) was used to measure fluid flow noninvasively in the extracapillary space (ECS) of a hollow‐fiber bioreactor without cells. Agreement between these axial flow measurements in a single hollow‐fiber module and predicted axial velocity contour plots at various image planes along the path length was good.Flow in a solid‐wall tube (phantom) was first used to calibrate pixel intensities with axial velocities. Flow images at several locations along the permeable hollow fiber length were then obtained in order to observe the well‐known leakage or Starling flow in the ECS. These quantitative spatially dependent velocity measurements were then compared to theoretically derived velocities obtained from a solution of Poisson's equation with a constant pressure gradient and no slip at the solid surfaces. A mathematical transformation was used to simplify the numerical methods. Leakage flow through the ECS of a multifiber bioreactor (40 fibers) was also measured by MRFI, illustrating the applicability of this method for optimizing operational procedures and design of membrane bioreactors and filtration

ISSN:0001-1541    

DOI:10.1002/aic.690360406

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractThe diffusion of 1,3,5 tri‐tert‐butylbenzene (TTB) into cylindrical γ‐alumina extrudates of varying micropore diameter and macropore volume has been studied by NMR spectroscopy. The proton NMR signal of the methyl proton of TTB in the micropores of the alumina extrudate was found to be well resolved and shifted upfield relative to that in the bulk liquid by 0.55 ppm. The area under the shifted peak is proportional to the liquid concentration of TTB in the micropores. The change in the intensity of this peak as a function of time and measurements of the amount of TTB absorbed on the surface alumina at equilibrium were used to calculate the effective diffusivity of TTB in each extrudate. Measured values of the effective diffusivity are in reasonable agreement with predictions using correlations in the literature. These observations suggest a new method for measuring the liquid‐phase effective diffusivity in porous m

ISSN:0001-1541    

DOI:10.1002/aic.690360407

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractMany recent attempts to use expert systems for process fault diagnosis have included information derived from deep knowledge. This information is generally implemented as a rule‐based expert system. Drawbacks of this architecture are a lack of generality, poor handling of novel situations, and a lack of transparency. An algorithm called the diagnostic model processor is introduced; it uses the satisfaction of model equations from process plants to arrive at the most likely fault condition. The method is generalized by the process model and diagnostic methodology being separated. The architecture addresses each of the shortcomings discussed. Experiments show that the methodology is capable of correctly identifying fault situations. Furthermore, information is derived from an a priori analysis technique, which is used to show the degree to which different faults can be discriminated based on the model equations available. The results of this analysis add further insight into the diagnoses provided by the diagnostic model processo

ISSN:0001-1541    

DOI:10.1002/aic.690360408

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractFeedforward control has the theoretical potential for perfect control; therefore, research to simplify and improve the use of such a control strategy for possible industrial applications has potential value. A general model for simulation of controlled distillation columns is used to reproduce operating trends of some monitored variables for an industrial column. Comparisons between simulated and operating data show a general good agreement.When a rigorous model is available and can be proved reliable for practical purposes, the design of feedforward control schemes becomes viable and can be incorporated in the more conventional approach. A specific industrial example shows the practical implementation problems and the real economic value of a feedforward control strategy to optimize the process behavior. In particular, the feedforward control action can reduce the inherent error from changes in feed composition when a basic feedback control structure is used to infer composition.

ISSN:0001-1541    

DOI:10.1002/aic.690360409

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractBlade coating is the most common method of coating paper, and it is applied in coating magnetic suspensions and adhesives. Typically, the blade's upstream edge is clamped into a rigid holder so that the blade and substrate form a converging wedge. The translating substrate drags liquid into the wedge, where liquid forces develop and deflect the elastic blade, but it is loaded externally to counteract the deflection. Liquid dragged past the blade and thus the coating thickness depend on the elastohydrodynamic interaction among blade, liquid, and loading. Shell theory and lubrication flow theory describe the interaction by means of differential equations that are shown to be equivalent to Saita and Scriven's (1985) earlier formulation but that lead to a computationally more efficient analysis. Predictions computed agree with those of the earlier formulation and with experiments. Moreover, the new predictions illustrate effects of normal force loading and broaden the theory of blade coating.

ISSN:0001-1541    

DOI:10.1002/aic.690360410

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY

摘要:

AbstractIn 1954, G. I. Taylor derived an expression for an apparent axial dispersion coefficient for mass transfer in turbulent flow under the assumption of no mass transport between the tube wall and the fluid inside the tube. Taylor's expression has been verified in a number of experimental efforts for both mass and heat transfer.This work extends the results of Taylor to the case where there is a significant transport of heat from the tube wall to the fluid in the tube, such as in a double‐pipe heat exchanger. Using an analysis similar to Taylor's, it is shown that the apparent axial dispersion coefficient is about one order of magnitude larger when a large radial gradient is present. Experimental data on a double‐pipe heat exchanger show significantly improved correspondence with a dispersion‐based model of the system when the larger dispersion coefficients are

ISSN:0001-1541    

DOI:10.1002/aic.690360411

出版商:American Institute of Chemical Engineers    

年代:1990

数据来源: WILEY