摘要:

AbstractPulsed magnetic field gradient stimulated echo NMR measurements are performed for diffusion and flow of an aqueous phase both within a sample of packed spherical beads and within a 25% porosity Fontainebleau sandstone. The stimulated echo dependence on the gradient pulse area q is used to derive the displacement probability distributions PΔ(X) for fixed observation times Δ. The shape of PΔ(X) as a function of Δ is simulated for computer‐generated porous media, and a good agreement is obtained between the experimental NMR data and the simula

ISSN:0001-1541    

DOI:10.1002/aic.690430702

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractMicrowave thawing of materials, which melt over a finite temperature range, are analyzed using the effective heat capacity method. The state of the material, solid, liquid or mush is deduced from the equilibrium liquid volume fraction vs. temperature relationship for the substance, and the microwave power is calculated from Maxwell's equations. Using Galerkin finite elements, the microwave power, temperature and liquid volume fractions were obtained for microwave thawing of tylose slabs. Thawing progresses from the inside and/or outside depending on the slab thickness. For slabs ⩾ 5 cm, thawing progresses predominantly from the surface of the sample. Resonances, during which the microwave power absorption is high, causes the 2‐cm slab to thaw quicker than 1‐cm slabs. A power law for the thawing time vs. sample thickness yields an exponent of 1.56 for microwave thawing and 2 for conventional thawing. To control the temperature rise in the liquid regions, simulations were carried out with an on‐off control on the microwave power. On‐off control results in greater power savings for thic

ISSN:0001-1541    

DOI:10.1002/aic.690430703

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractIn gas–liquid flows through tee junctions, because of the difference in inertia between the phases, the flowing mass fractions for an individual phase at the outlet sides differ from those at the inlet. This phase separation is an important consideration in delivering fluids and energy through pipe networks in the power and process industry. In this work, air–water and steam–water flows through branching and impacting tee junctions are considered. Under certain conditions (when the volumetric fraction of the liquid drops does not change appreciably and their bulk density is much higher than the gas density, and when the flow rates and/or the gas volumetric fraction are high), these flows can be approximated as irrotational flows of incompressible, inviscid fluids and are amenable to potential flow methods, for example, conformal mapping. For the general case of gas–liquid flows through a branching or impacting tee, a CFD code is utilized to conduct transient flow simulations. Predictions of phase separation for both types of tee junction agree well with experiment

ISSN:0001-1541    

DOI:10.1002/aic.690430704

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractIn this study back‐propagation, feed‐forward neural networks are applied to estimate mass‐transfer parameters in fast fluidized beds of fine solids. These networks are trained to predict mass‐transfer rates using measurements of the sublimation rate of coarse naphthalene balls in fast fluidized beds of fine glass beads at several solid‐to‐gas mass flow rates within the relevant superficial gas‐velocity range. When tested to predict the effective diffusivities from a coarse particle to the bulk of the fast bed of fine solids, trained neural networks calculated the Sherwood number with high accuracy. It is demonstrated that back‐propagation, feed‐forward neural networks provide a more accurate correlation for the mass‐transfer coefficient compared to those obtained by the currently us

ISSN:0001-1541    

DOI:10.1002/aic.690430705

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractPore fractal objects are expected to be optimal catalysts, since material is supplied to the narrower pores, which are also shorter through the larger pores where diffusion resistance is smaller. To demonstrate this, diffusion and reaction were simulated on Sierpinski‐gasket‐type fractal objects and on the corresponding nonfractal uniform‐pore structures of the same size, porosity and reactive area. Positive order reactions limited by Knudsen diffusion were shown to exhibit larger rates in fractal than in uniform‐pore objects. Fractal catalysts also exhibited a new intermediate domain in which the rate depends only weakly on the kinetics parameters. In nonmonotomic kinetics the branching point (bifurcation point) was extremely sensitive to the pore st

ISSN:0001-1541    

DOI:10.1002/aic.690430706

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractThe shear and compressive properties of aggregated alumina particles are determined as functions of volume fraction and the strength of the interparticle attraction. Over a range of volume fractions, yield stresses, τy, elastic moduli, the strain delimiting the extent of the linear elastic response, and compressive yield stress, Py, are well described by power‐law functions of volume fraction, while the role of interparticle attractions can be accounted for by expressing these mechanical properties as (ϕ/ϕg− 1)n, where ϕgcaptures the strength of particle attractions and n the microstructure. The links between compressive and shear properties are well described by linear elastic models where the Pyand τyare a function of Poisson's ratio which, for the suspensions investigated, has a value n

ISSN:0001-1541    

DOI:10.1002/aic.690430707

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractAn electrochemically modulated complexation (EMC) process was designed to selectively extract and concentrate ethylene from a feed‐phase mixture with ethane. Unlike previous EMC processes, where the separation was based on equilibrium solubility differences, this separation was based on differences in the rate of complexing with copper(I) solution between the two gases. The EMC process employed flowthrough electrolysis cells that electrochemically modulate aqueous‐phase copper chlorides between high, copper(I), and low, copper(II), affinity states. The liquid phase in the high affinity form contracts a feed gas phase in a hollow‐fiber membrane module for selective extraction and contacts the receiving gas phase in the low affinity form for concentration. Experimental results and modeling of the process are rep

ISSN:0001-1541    

DOI:10.1002/aic.690430708

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractCylindrical internal reflectance infrared spectroscopy (CIR‐FTIR) was used for the determination of the transport properties of hydrocarbons in zeolite L at high temperatures and pressures. This was the first time that the intracrystalline diffusivity of hydrocarbons in microporous media could be determined under supercritical conditions by using a dynamic technique. The study investigated the self‐diffusion of n‐heptane, the counterdiffusion of n‐hexane and 1‐hexene, and the codiffusion of n‐heptane and pyxlene in zeolite L under subcritical and supercritical conditions. The diffusion time constants obtained for the single and binary systems showed that the diffusion within the pore was reduced significantly under supercritical conditions (i.e., liquidlike behavior) as the hydrocarbon density within the pore wa

ISSN:0001-1541    

DOI:10.1002/aic.690430709

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractThe magnitude and direction of the ultrasonic radiation forces that act on individual particles in a standing‐wave field were determined using a microscope‐based imaging system. The forces are calculated from measured particle velocities assuming that the drag force, given by Stokes' law, is exactly counterbalanced by the imposed ultrasonic forces. The axial primary radiation force was found to vary sinusoidally with axial position and to be proportional to the local acoustic energy density, as predicted by theory. The magnitude of the transverse primary force was determined by two independent methods to be about 100‐fold weaker than the axial force. Separation concepts exploiting the transverse force for cell retention have been successful despite the great disparity in magnitude between the axial and transvers‐force components. This may be explained by the reduced hydrodynamic forces on aggregated particles in transverse flow due to their alignment in the soun

ISSN:0001-1541    

DOI:10.1002/aic.690430710

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY

摘要:

AbstractA systematic method is presented to synthesize reactive crystallization processes. It shows how to selectively crystallize a desired solid product(s) after a reaction step and how to use compound formation to effect separation of a mixture. The method is based on the generation of phase diagrams with liquid‐phase reactions. Using transformed coordinates, systems with three or fewer degrees of freedom can be conveniently analyzed, regardless of the number of components and reactions. Features of the solid–liquid phase diagram that are relevant to process synthesis are identified. The method is illustrated with systems with multiple components, complex reactions, and multiple pha

ISSN:0001-1541    

DOI:10.1002/aic.690430711

出版商:American Institute of Chemical Engineers    

年代:1997

数据来源: WILEY