摘要:

AbstractThin polymer coatings produced from water‐ and organic‐solvent‐based precursor liquids are ubiquitous components of industrial and consumer products. Design and optimization of dryers for these coatings require accurate predictions of their drying rates. Accurate drying predictions for many polymer/solvent coatings require a satisfactory description of the polymer/solvent mutual diffusion coefficients. A method is proposed ot determine a satisfactory description of the diffusion coefficients by effective free‐volume theory parameters. The effective parameters are determined from gravimetric data measured in a bench‐scale drying apparatus. The application of the method to a poly(vinyl acetate)/toluene solution shows that the effective free‐volume parameters give diffusion coefficients that agree with published data. The method is also applied to a rubber‐based adhesive in industrial‐grade heptane by treating the complex adhesive as a pseudobinary solution. For both systems, the effective parameters lead to quantitatively accurate drying predictions in a p

ISSN:0001-1541    

DOI:10.1002/aic.690430802

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractExplicit algebraic scalar‐flux models that are valid for three‐dimensional turbulent flows are derived from a hierarchy of second‐order moment closures. The mathematical procedure is based on the Cayley–Hamilton theorem and is an extension of the scheme developed by Taulbee. Several closures for the pressure–scalar gradient correlations are considered and explicit algebraic relations are provided for the velocity–scalar correlations in both nonreacting and reacting flows. In the latter, the role of the Damköhler number is exhibited in isothermal turbulent flows with nonpremixed reactants. The relationship between these closures and traditional models based on the linear gradientdiffusion approximation is theoretically established. The results of model predictions are assessed by comparison with available laboratory data in turbule

ISSN:0001-1541    

DOI:10.1002/aic.690430803

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractRecent experimental validation of theoretical and numerical predictions regarding scalar variance decay in a pipe have revealed that the traditional plug‐flow reactor picture of pipe flow omits key physical mechanisms. In particular, the far‐field decay exhibits a power law rather than exponential decay. These observations are examined by performing a set of experiments where the manner in which the scalar constituents are introduced into the pipe is varied. Significant differences are noted in the behavior of the variance decay until the very far field is reached, where an invariant power‐law form em

ISSN:0001-1541    

DOI:10.1002/aic.690430804

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractThe velocity of rise and the drag of a single vapor bubble collapsing in another immiscible liquid were measured experimentally. During the process of collapse, the dispersed‐phase vapor bubble was transformed to a two‐phase bubble with condensate accumulating at the rear of the two‐phase bubble and vapor at its top. Such a configuration of a two‐phse bubble is commonly known as a drobble. Experimental data for the six pairs of liquids covered a range of drobble (two‐phase bubble) Reynolds numbers from 0.003 to 3,000. Two regimes of drobble movement were encountered. In the first regime (Re<100), the drobble maintained its sphericity, and the observed drag was less than the solid‐sphere drag predicted by the established solid sphere or Hadamard et al. fluid‐sphere drag models. In the second regime, the drobble was deformed and oscillated; the observed drag departed suddenly from predictions of spherical models and increased with increasing Reynolds numbers. The critical Reynolds number covered a range from 100 to 1,000. Empirical models for drobble velocity and drag coefficien

ISSN:0001-1541    

DOI:10.1002/aic.690430805

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractThe use of optical fibers in a fluorescence–detection scheme permits the accurate determination of the radial distribution of the transit time, the column efficiency, and the analyte concentration at the exit of a chromatographic axial–compression column (50 mmID). The results obtained demonstrate that the column is not homogeneous, but suggest a nearly cylindrical distribution of the packing density. The average velocity close to the column wall is 7% lower than along its axis and the HETP 25% higher. The lack of homogeneity of the column packing is another source of band broadening not taken into account in chromatography so far. It causes the apparent HETP derived from the conventional elution chromatogram recorded on the bulk eluent to be larger than the local HETP and the band profile to be unsymmetrical with a slight tail reminiscent of kinetic tail

ISSN:0001-1541    

DOI:10.1002/aic.690430806

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractHollow‐fiber membrane processes with a constant external resistance having a constant or variable shell concentration resulting from an operational mode of cocurrent or countercurrent are studied. By solving numerically the continuity mass‐conservation equation with the corresponding boundary conditions, the lumen laminar mass‐transfer coefficients for both cases are correlated. The correlations greatly improve the calculating accuracy of the overall mass‐transfer coefficient and can be used to obtain the lumen mixed‐cup concentration by an algebraic equation substituting the partial differential equation. A separation factor m' is introduced to characterize the effect of the operational mode. Calculation results demonstrate that the lumen mass‐transfer coefficient is independent of the real lumen and shell concentrations, but it is greatly influenced by m'. The countercurrent mode, compared to the cocurrent mode, provides not only a higher mean driving force, but a higher lumen mass‐transfer coefficient. This conclusion is novel and valid for the tube‐shell heat or mass‐transfer processes and is supported by the experimental data in the literature and our gas membrane separ

ISSN:0001-1541    

DOI:10.1002/aic.690430807

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

ISSN:0001-1541    

DOI:10.1002/aic.690430808

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractSheet and film processes pose a challenging identification and control problem due to high complexity, poor conditioning, and limited input–output data. The interaction between model accuracy and closed‐loop performance is explored for sheet and film processes using a model decomposition in terms of two static orthogonal matrices in series with a diagonal transfer‐function matrix. It is shown that the accuracy of the diagonal elements of the transfer‐function matrix directly specifies the closed‐loop performance achievable by a model‐based controller. This motivates the development of a combined identification and control procedure in which the controller is designed to be robust to model inaccuracies quantified during identification. The resulting controller is compared to an industrially accepted controller design method for two examples, including a simulated blown‐film process. Based on the theoretical results and simulations, it was concluded that the poor performance often reported for existing industrial sheet and film process‐control systems is likely due to signs of the model gains being incorre

ISSN:0001-1541    

DOI:10.1002/aic.690430809

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractIndustrial continuous processes may have a large number of process variables and are usually operated for extended periods at fixed operating points under closed‐loop control, yielding process measurements that are autocorrelated, cross‐correlated, and collinear. A statistical process monitoring (SPM) method based on multivariate statistics and system theory is introduced to monitor the variability of such processes. The statistical model that describes the in‐control variability is based on a canonical‐variate (CV) state‐space model that is an equivalent representation of a vector autoregressive moving‐average time‐series model. The CV state variables obtained from the state‐space model are linear combinations of the past process measurements that explain the variability of the future measurements the most. Because of this distinctive feature, the CV state variables are regarded as the principal dynamic directions A T2statistic based on the CV state variables is used for developing an SPM procedure. Simple examples based on simulated data and an experimental application based on a high‐temperature short‐time milk pasteurization process illustrate advantages of the

ISSN:0001-1541    

DOI:10.1002/aic.690430810

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractThe problem of simultaneous control of composition and molecular weight of copolymers produced in semicontinuous emulsion polymerization is addressed. A first‐principles model of emulsion copolymerization is used to produce optimal open‐loop policies, which are then experimentally tested on the system methyl methacrylate/vinyl acetate. In contrast to earlier work in the control of semicontinuous emulsion copolymerization, the control problem addressed has multiple inputs and multiple outputs, and the experimental application is free of empirical correlations and performed on an unseeded system. Optimal open‐loop policies are calculated efficiently by optimizing properties of the instantaneous polymer being formed. The experimental results confirm the feasibility of these techniques. A model‐predictive control scheme, in which optimal policies are recomputed on‐line to account for disturbances, is proposed. The scheme, which exploits the advantages of the efficient calculation of optimal policies, is tested by simulation showing good pe

ISSN:0001-1541    

DOI:10.1002/aic.690430811

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY