摘要:

AbstractOscillations of a conducting drop immersed in a dielectric fluid in an alternating electric field were modeled to understand the enhancement of transport processes by the electric field. Numerical solutions for oscillation amplitude, velocity distribution, resonant frequency and streamlines were obtained. The effects of viscosity and density on the resonant frequency and the velocity distribution were investigated. It was found that the resonant frequency of viscous fluids was always smaller than the free oscillation frequency of the same droplet. The predicted scanning frequency response curve and the streamlines agree well with the experimental observations.

ISSN:0001-1541    

DOI:10.1002/aic.690371102

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractRandom pore models have been successful in interpreting a wide range of experimental observations in gas‐solid reactions; however, their applicability has been limited to cases where the entire porous structure is initially accessible to reacting gases. In many practical cases, porous solids contain significant void regions that are initially inaccessible to gaseous reactants, but become accessible in the course of the reaction. A conceptual and mathematical model is developed here that accounts for the existence of this hidden porosity. It uses the same representation of the porous network as was developed in the earlier random pore models, but introduces physically meaningful expressions for the discovery of hidden pores, and the subsequent growth of the discovered pores. The modified model calls for only one additional parameter, the initial volume fraction of hidden porosity in the total volume. It is demonstrated computationally that neglecting hidden porosity can lead to serious underestimations of conversion and reaction rate

ISSN:0001-1541    

DOI:10.1002/aic.690371103

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractA family of alkyl‐substituted polycyclic aromatic hydrocarbons was pyrolyzed in microbatch reactors at temperatures between 350°C and 425°C. A general pyrolysis network was deduced for these compounds, and it comprised two major and one minor parallel pathways. The first major pathway resulted in products analogous to the major products observed from alkylbenzene pyrolysis. The second major pathway led to products via the cleavage of the strong aryl‐alkyl CC bond. The third pathway led to small amounts of products, presumably through cyclization and condensation reactions. The relative importance of the two major pathways varied for the different compounds. The rates of aryl‐alkyl bond cleavage differed for the different compounds, and these rates were quantitatively related to the compounds' localization energies through Dewar reactivit

ISSN:0001-1541    

DOI:10.1002/aic.690371104

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractInjecting an acidic aqueous solution into a carbonate‐rich permeable medium can cause the formation of a mobile gas phase through mineral dissolution. The flowing gas can cause significant changes in mineral identities through interaction with the initially present mineral and aqueous species. We have developed a solution to such transport problems based on a finite difference implicit‐pressure/explicit‐saturation formulation for two‐phase flow, using the local equilibrium assumption as calculated with the Villars‐Cruise‐Smith stoichiometric chemical equilibrium algorithm.We illustrate the changes that occur to a calcite/iron (II) hydroxide medium upon injection of hydrochloric acid and the stripping of hydrogen sulfide gas from carbon dioxide gas injected into a siderite‐rich medium. The examples demonstrate that the formation and/or presence of a gas phase can alter resident minerals and that minerals can remove impurities fro

ISSN:0001-1541    

DOI:10.1002/aic.690371105

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractGeneric model control (GMC) takes care of parametric mismatch for underdamped, closed‐loop specification, whereas robust generic model control (RGMC) can handle parametric mismatch for any closed‐loop specification. But, neither GMC nor RGMC is capable of compensating for structural mismatch. In this study, adaptive GMC(AGMC) and adaptive RGMC (ARGMC) structures are proposed, and their effectiveness over GMC and RGMC is demonstrated with several examples. AGMC exhibits better performance over ARGMC, GMC, and RGMC in all the cases of no process/model mismatch, parametric mismatch as well as structural mismatch.Distillation adaptive generic model control (DAGMC) structure is also proposed for dual composition control of distillation. Since embedding of distillation state‐space model in the basic GMC law is practically impossible, linear and nonlinear models are proposed with adaptation using distillation process data, and DAGMC is applied to two typical nontrivial distillation units. Nonlinear DAGMC exhibited better performance over linear

ISSN:0001-1541    

DOI:10.1002/aic.690371106

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractThe two‐dimensional channel structure of clinoptilolite has been altered systematically by ion exchange to study the effects of cation type, size, location, and distribution on the diffusion of N2and CH4probe molecules. Concentration‐dependent diffusion time constants (D/L2) were determined from gravimetric uptake measurements for fully‐exchanged K+, Na+, and H+clinoptilolites, and highly‐exchanged Ca2+(89%) and Mg2+(72%) clinoptilolites. Both plane sheet and parallel channel diffusion models were developed from the one‐dimensional plane sheet diffusion equation and fit to the uptake data. Resulting values of D/L2varied by a factor of more than 1,000 for both N2and CH4, while kinetic selectivity spanned nearly two orders of magnitude for this group of modified clinoptilolites. Achieving this range in performance for the difficult N2/CH4separation demonstrates the excellent potential for tailoring clinoptilolite by cation manipulation for the kinetic separation of other gas

ISSN:0001-1541    

DOI:10.1002/aic.690371107

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractA new configuration of a membrane reactor‐separator for homogeneous catalysis is described that is designed not only to encapsulate the catalyst solution, but to simultaneously separate the product from reactant. It is composed of a porous support layer that is impregnated partially or completely with the liquid‐phase catalyst and is sandwiched between two different membranes. Membrane 1 is readily permeable to the reactant but not to the product, whereas membrane 2 allows free permeation of both the reactant and the product while encapsulating the catalyst solution. The performance of a differential stirred‐cell membrane reactor‐separator was theoretically investigated for the case of a first‐order irreversible reaction. The extent of product separation was studied as a function of membrane permselectivity for reactant and product, the difference in resistance of membrane and catalyst layer, liquid loading of the catalyst layer, and the sweep fluid flow rate. The efficacy of the device was experimentally demonstrated using ethylene hydroformylation with hydridocarbonyltris (triphenyl phosphine) Rh(I) catalyst dissolved in dioctyl phthalat

ISSN:0001-1541    

DOI:10.1002/aic.690371108

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractThe effects of taper on the steady‐state expansion characteristics of a homogeneous fluidized bed are examined theoretically and experimentally. It is shown that secondary factors that might be thought to influence the expansion (fluid accelerational effects including added mass and particle phase elasticity) are unlikely to be of significance in practical situation

ISSN:0001-1541    

DOI:10.1002/aic.690371109

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractA numerical model describing performance of a liquid‐liquid spray column heat exchanger is developed. The model is for a disperse packed column operating in steady state. The fundamental equations for the continuous and distributed phases are developed in Eulerian and Lagrangian forms, respectively. The model predicts simultaneously the volume fraction, velocity, and temperature for each phase. Energy and momentum are exchanged between phases through source variables. Empiricism in the model is limited to the specification of droplet drag coefficient and Nusselt number correlations which are utilized to calculate momentum and energy source terms. Application of the computer model to column operation yields predictions that compare closely with experimental result

ISSN:0001-1541    

DOI:10.1002/aic.690371110

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY

摘要:

AbstractDissolved carbon dioxide and bicarbonate ions in fermentation broths can (independently) inhibit or promote microbial growth and productivity. In research facilities with a large number of fermenters, dissolved carbon dioxide sensors tend not to be used, and as a result this variable will generally go unmonitored, making the meaningful analysis of data more difficult. For aerobic fermentations, mass transfer of carbon dioxide can be described in an analogous way to oxygen transfer. The mass transfer coefficient for carbon dioxide is 0.89 times that for oxygen. The maximum dissolved carbon dioxide concentration as a function of exit gas composition is compared with the concentration obtained by assuming equilibrium between the broth and exit gas. The difference between these two concentrations is typically 20–40% of the equilibrium concentration. In large fermenters, a degree of plug flow behavior in the gas and the generally lower specific aeration rates will serve to produce a better approach to equilibrium than for research fermenter

ISSN:0001-1541    

DOI:10.1002/aic.690371111

出版商:American Institute of Chemical Engineers    

年代:1991

数据来源: WILEY