ISSN:0001-1541    

DOI:10.1002/aic.690430102

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractEffects of elongation on the radiation heat transport down a spheroidal cavity, located in a conducting solid with a diffusely reflecting cavity–solid interface, are examined. An effective conductivity λeand a void radiation conductivity λrare obtained as a function of cavity eccentricity α; and surface emissivity ε. To facilitate the calculations and produce readily applicable equations, a rigorous variational principle is used. Exact solutions are generated in the neighborhood of the spherical cavity (α2→ 0) for any ε>0, a long needle‐shaped void (α2→ 1) for any ε>0, and a perfect reflector (ε → 0) for arbitrary elongation (0 ≤α2≤ 1). Significant differences arising from the shape change are observed. The α2→ 0 edge demonstrates a linear increase in λrwith ε. At the opposite edge α2→ 1 and positive ε, λris a horizontal line independent of ε, much like the long cylinder, whose conductivity is a factor of 32/(9π) (= 1.13) larger. In the neighborhood of ε 0, λris always zero for any 0 ≤ α2≤ 1. The emissivity slope for ε → 0 starts from unity at α2= 0 and increases monotonically with elongation to a singularit

ISSN:0001-1541    

DOI:10.1002/aic.690430103

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractIn most industrial gas‐phase polyethylene reactors, heat is removed by cooling the recycle gas stream in an external heat exchanger, where a portion of the vapor is condensed. The condensate evaporates in the reactor to absorb heat released by polymerization reactions, thereby increasing the production capacity of the unit. Nonequilibrium methods of multicomponent condensation are applied to develop a 1‐D model to simulate the cooling unit of an industrial polyethylene reactor system operated in partial condensing mode. Finite difference approximations are used to convert the resulting set of differential equations to algebraic equations. A practical method of solving the equations is to combine the rapid local convergence of Newton's method with a globally convergent strategy. Correlation methods for estimating local heat‐transfer coefficients in the liquid film layer are discussed. Butterworth's method for shear‐stress‐controlled condensate flow gives reasonable agreement between simulation results and industrial data, while Chen et al.'s method can better describe the transition process of condensate flow from laminar to turbu

ISSN:0001-1541    

DOI:10.1002/aic.690430104

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractDiffusion coefficients measured by holographic interferometry are presented for two globular proteins and three nonionic surfactant species in agarose gels. The cloud points for the surfactants in agarose solutions are also given. In all cases, rates of diffusion in the gel are smaller than those in bulk solution, with the hindering effect of the gel increasing both with increasing gel concentration and with increasing solute size. It is shown that the diffusion rate of the surfactant micelles is very similar to that of proteins having similar hydrodynamic radii; it would therefore appear that the size and shape of the micelles in the solution and gel phases are similar. In addition, the measured rates of hindered diffusion agree very well with rates predicted by a rigorous hydrodynamic theory in which the solutes are modeled as hard spheres and the gel fibers are modeled as straight, cylindrical fibers. Hence, for the range of conditions considered, rates of hindered diffusion for both the globular proteins and the micellar species are determined primarily by hard‐sphere hydrodynamic and steric interactions between the solute and the gel matri

ISSN:0001-1541    

DOI:10.1002/aic.690430105

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractEquations were derived that describe the dynamics of cake growth in cake filtration, and methods for their solutions were developed. In deriving the equations, the moving boundary nature of the cake formation process and the effect of fine particle retention were considered. It was shown that fine particle retention may contribute significantly to the decrease of cake permeability and thus alters the performance of cake filtration even if the amount of fine particles involved is small. Through numerical examples, it was also demonstrated that fine particle retention in filter cakes may cause serious errors in determining the constitutive relationships from filter test data.

ISSN:0001-1541    

DOI:10.1002/aic.690430106

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractFundamental characteristics of liquid–solid fluidization at high pressures (up to 21 MPa) and moderate temperatures (up to 89°C) are investigated. Properties under study include minimum fluidization velocity (umf), bed voidage at minimum fluidization, and bed expansion. Devices for in‐situ measurements of physical properties of the liquid in the bed are developed, and measurements are carried out to quantify the pressure and temperature effects on the fluidization behavior. The results indicate that under high pressures and moderate temperatures, liquid–solid fluidization behavior is affected significantly by the variation of liquid density and viscosity with pressure. As the pressure increases, the liquid viscosity and density increase, yielding an increased drag force and buoyancy force on the particles, and hence a decreasing umfand an increasing bed expansion for a given liquid flow rate. An increase in temperature has an opposite effect on the physical properties of the liquid, increasing umfand decreasing the bed expansion for a given liquid flow rate. Various correlations proposed in the literature for umfand bed expansion, including those by Richardson and Zaki (1954) and Chitester et al. (1984), are applicable to high‐pressure and high‐temperature conditions when proper account is made of the liquid physical properties under bed operating

ISSN:0001-1541    

DOI:10.1002/aic.690430107

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractAsymptotic power series solutions for the mass‐transfer enhancement factor for absorption of a gas component into a liquid where it undergoes irreversible instantaneous chemical reaction(s) with one and two liquid‐phase reactants are developed in this work. The Padé technique is used to extend the region of applicability (accelerate the convergence) of the four‐term asymptotic power series solutions. The resulting modified asymptotic expressions for the enhancement factor show excellent accuracy over a wide range and can be used to predict enhancement factors as low as 2 with an error of about 5% compared to the exact numerical solution. Predictions of these new asymptotic solutions are compared with experimental absorption data for H2S absorption into aqueous methyldiethanolamine and H2S absorption into aqueous mixtures of methyldiethanolamine and diethanolamine obtained in a laminar‐jet absorber. The absolute mean deviations of the predictions from the experimental absorption data for the single and mixed amine solutions were 4.6% and 2.4%, resp

ISSN:0001-1541    

DOI:10.1002/aic.690430108

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractIn many instances of practical interest, countercurrent adsorption separations operate on feed streams containing not only the components to be separated but also some desorbent. Criteria for the optimal and robust design and operation of these units are developed by extending previous treatments developed for desorbent‐free feedstreams. The effect of the presence of some desorbent (weak, intermediate, or strong) on the location and robustness of the region of complete separation in the operating parameter space is discusse

ISSN:0001-1541    

DOI:10.1002/aic.690430109

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractIon‐exchange processes involving weak electrolytes are influenced strongly by the pH via the occurrence of association/dissociation equilibria. This influence was investigated quantitatively through binary displacement experiments with different electrolytes to gain better insight in the role of the pH and to test a fixed‐bed ion‐exchange model used for the description of multicomponent processes. The two major factors determining the ion‐exchange behavior of weak electrolytes are the actual exchange of counterions and the sorption of neutral species. The sorption of neutral species resulted in concentration fluctuations superimposed on the normal ion‐exchange profiles, whereas pH fluctuations inherent to ion‐exchange processes in general also influenced concentration through modified ionic fractions. The relative importance of these contributions is determined by the magnitude of parameters such as resin capacity, distribution coefficients of neutral species, and selectivities of ions, as well as by operating conditions such as concentrations of

ISSN:0001-1541    

DOI:10.1002/aic.690430110

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractLarge, high‐quality, single crystals of pure‐silica ferrierite are synthesized, and the structure is described. Selected individual crystals (approximately 600 μm X 500 μm X 20 μm) are mounted in a membrane configuration so that only the 10‐membered‐ring channels (5.4 Å X 5.4 Å X 4.2 Å) or the 8‐membered‐ring channels (4.6 Å X 3.7 Å X 3.0 Å) are accessible for gas‐molecule permeation. The first examples of transport exclusively through 8‐ or 10‐membered‐ring channel systems are reported and obtained through crystal orientation in the membrane. A series. of adsorption experiments are conducted to help select suitable probe molecules and evaluate the role of adsorption in the permeation process for single‐crystal membranes. Methane, n‐butane, isobutane and nitrogen probe molecules are used to study intracrystalline sorption and transport effects for different crystal orientations, pressures and temperatures. Both pure‐gas selectivities and mixed‐gas separation factors are reported. A mixed‐gas separation factor of n‐butane/isobutane = 116 for the 10‐membered‐ring orientation of the crystal at 383 K and a transmembrane pressure difference of 1.01 X 105Pa are found using this technique. In addition, molecular sieving is observed for the 8‐membered‐ring orientation of the crystal since methane, but not butane, tr

ISSN:0001-1541    

DOI:10.1002/aic.690430111

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY