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  • 1
    Electronic Resource
    Electronic Resource
    Temperature dependence of one-component permeation through a silicalite-1 membrane (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2203-2214 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The one-component steady-state permeation of gases through a silicalite-1 zeolite composite membrane as a function of the temperature is studied from 190 to 680 K for light hydrocarbons, noble gases, and some inorganic gases. In general, with increasing temperature the permeance shows a maximum followed by a minimum. For gases weakly adsorbed the permeance has only a minimum and for gases strongly adsorbed only a maximum is observed in the permeance. The permeance for various gases, for a feed pressure of 101 kPa, span four orders of magnitude. The lowest permeation is for i-butane at 300 K: a permeance of 0.07 × 10-8 mol. m-2.s-1.Pa-1. The highest value is observed for methane: a permeance of 70 × 10-8 mol. m-2.s-1.Pa-1 at about 240 K. A comparison between the isobars and the temperature dependence of the steady-state permeance, both at 101 kPa, shows that at the temperature where the amount adsorbed vanishes the permeance starts to increase. The temperature dependence of the steady-state fluxes through the silicalite-1 membrane can be described only if two diffusion mechanisms are taken into account. For high occupancies the mass transport can be described by equilibrium adsorption followed by surface diffusion and for low occupancies the mass transport can be described by activated gaseous diffusion. With increasing temperature the mass-transport mechanism shifts from the surface diffusion regime to the activated gaseous diffusion regime. With these two diffusivities modeling results agree well with experimental results for the one-component flux through the silicalite-1 zeolite membrane.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690430907
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  • 2
    Electronic Resource
    Electronic Resource
    Analysis of interface evolution and pattern formation during CVD (1995)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 1926-1943 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Morphological aspects of the evolution of a gas - solid interface during typical CVD processes are presented, as well as a continuum model of CVD growth. A linear stability analysis used determines the effect of reactor conditions on the stability of planar growth. The main focus, however, is numerical solution of governing equations under a wide variety of conditions and with different initial interface shapes as starting point. Simplified solutions under specific deposition conditions and the numerical procedure for solving the complete system of equations are presented. The focuses are on the use of a parametrization that eliminates numerical problems encountered with steep interface gradients and the automatic generation of an adaptive mesh for the domain above the interface. Several examples illustrate the numerical solution procedure. To our knowledge, this is the first attempt to simulate interface evolution during CVD for long deposition times from various initial interface shapes. The simulation revealed several morphological phenomena observed experimentally in previous studies, including the formation of occlusions that contributes to film porosity and was clearly shown by the numerical results. Film uniformity strongly depends on the controlling mechanism of deposition. Severe nonuniformities develop under diffusional limitations, while deposition is very uniform under conditions of kinetics control. Film uniformity could be improved by choosing conditions for which a Damköhler number of deposition, Da, would have the lowest value.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690410810
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  • 3
    Electronic Resource
    Electronic Resource
    Prediction of sedimentation and consolidation of fine tails (1996)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 960-972 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Sedimentation and consolidation of suspensions of fine particles were analyzed by integrating experimental measurement of properties in a centrifuge with a comprehensive numerical model. The yield stress and settling velocity for tailings from tar sands extraction were determined experimentally as a function of the volume fraction of solids. The evaluated state functions were used to simulate batch settling and consolidation, and the results compare well with long-term settling tube tests. This approach is very attractive where gravity sedimentation may take many years, and it allows prediction of the rate of clear water production, total time for sedimentation and consolidation, and the maximum concentration of solids.Scaling of the sedimentation between centrifuge and field conditions is discussed. Conversion of permeability-void ratio relationships from geotechnical experiments to state functions of hindered settling velocity is demonstrated, allowing the use of data derived from a variety of experimental techniques.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690420409
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  • 4
    Electronic Resource
    Electronic Resource
    Kinetics of the CO oxidation by O2 and N2O over Cu-Cr/Al2O3 (1992)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 38 (1992), S. 385-396 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The oxidation of CO by O2 and N2O over an oxidized 10 wt. % Cu-Cr/Al2O3 catalyst (Cu:Cr=1:1) has been studied by temperature-programmed reactivity measurements (400-550 K) over a wide range of partial reactant pressures, including inhibition by CO2. The CO oxidation rate is zeroth-order in oxygen and has orders between 0-1 in CO and N2O, depending on the gas-phase composition. Mechanistic information from literature combined with the kinetic data resulted in the selection of an Eley-Rideal-type of kinetic model without a priori assumptions on rate-determining processes. The model consists of the oxidation of reduced sites by O2 and/or N2O, followed by a reaction with CO, yielding a surface intermediate that releases CO2 in a consecutive step. CO2 inhibits both by reversible adsorption on oxidized and reduces sites, the latter under formation of the surface reaction intermediate. Apart from the surface oxidation by O2, the reaction rates of all assumed elementary processes are of the same order of magnitude and, therefore, determine the overall rate. The surface oxidation by oxygen is about four orders of magnitude larger, which explains the zeroth-order in oxygen and the observation that oxygen first reacts with CO before N2O is able to oxidize CO. The obtained activation energies of the elementary processes agree with values in the literature for corresponding systems.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690380307
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  • 5
    Electronic Resource
    Electronic Resource
    Controlling the morphology of CVD films (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 1032-1045 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The morphology of the gas-solid interface during typical chemical vapor deposition (CVD) processes is investigated. The dynamic behavior of the interface depends on many factors, including local curvature of the film, reactant diffusion, adsorption equilibrium, surface kinetics, and mobility of adatoms. These factors depend on material properties of the system and reactor conditions, such as the deposition temperature and pressure. A 2-D model proposed describes the evolution of the interface in Cartesian coordinates under the influence of stabilizing and destabilizing effects. A linear stability analysis is used to predict under which conditions a planar interface becomes unstable. Stability criteria of a simplified 1-D analysis is not necessarily valid if the real system has more than one dimension. The substrate temperature and reactor pressure are important factors affecting the stability of film growth and thus the morphology of CVD films. An increase in temperature stabilizes planar film growth if the deposition is diffusion-limited, but destabilizes it if the process is reaction-controlled. The reactor pressure has a destabilizing effect on planar film growth during a typical CVD process.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690400614
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  • 6
    Electronic Resource
    Electronic Resource
    High-pressure particulate expansion and minimum bubbling of fine carbon powders (1987)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 33 (1987), S. 1698-1706 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Particulate expansion and minimum bubbling parameters (n, u′t, umB, εmB) are measured for fine carbon powders (dp = 44 and 112 μm) fluidized with synthesis gas (H2/CO = 0.8) at pressures within the range 2,070 〈 P 〈 12,420 kPa in an industrial, pilot-scale fluidized bed. Deviations between minimum bubbling (umB and εmB) and minimum fluidization (umf and εmf) conditions increase with increasing pressure, P. The expansion index, n, decreases with increasing P and always exceeds values recommended by Richardson and Zaki for solid/liquid systems. Particulate bed expansion for the fine powders is well characterized by the equations of Foscolo et al. and Abrahamsen and Geldart. The theory of Foscolo and Gibilaro adequately estimates the onset of bubbling for both powders at all P, provided that experimentally determined values of n and u′t, are applied. For the dp = 112 μm powder, the theory of Foscolo and Gibilaro is applicable with calculated values of ut and experimental values of n.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690331013
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  • 7
    Electronic Resource
    Electronic Resource
    Normal bubbling of fine carbon powders in high-pressure fluidized beds (1988)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 34 (1988), S. 1395-1397 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690340822
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  • 8
    Electronic Resource
    Electronic Resource
    Wake phenomena in a liquid-liquid fluidized bed (1973)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 19 (1973), S. 720-728 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Measurements of the size and rate of shedding of wakes of drops, average drop holdup and velocity of the continuous phase as functions of drop size for kerosene, hexane, and benzene dispersed in water in a liquid-liquid fluidized bed are reported. The average drop size ranged between 3.3 and 4.8 mm. The water velocity was 5.0 to 12.05 cm/s. The average drop hold up was 0.065 to 0.560.The ratio of wake to drop volume was 0.2 to 2.4, and the rate of wake shedding, reported as time of wake transfer units, was 0.7 to 2.4. At low drop holdups, the effect of single drops and groups of drops is dominant. At high drop holdups, the effect of neighboring drops and wakes is dominant. The wake size is correlated with slip velocity and can be calculated from empirical holdup measurements.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690190407
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  • 9
    Electronic Resource
    Electronic Resource
    The mixing of Granular solids in a rotary cylinder (1980)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 26 (1980), S. 928-934 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A model is derived for solids mixing and material transport in a continucus flow rotary dryer or reactor. Detailed analysis of the particle motions in the turnover process provides an opportunity to apply well-known reactor models to several subregions and to relate the overall results to different design geometries and operating conditions. The essential parameters of the model are the number of stages, the volume fractions of mixed flow and plug flow in each stage, the recycle ratio and the bypass ratio.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690260607
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  • 10
    Electronic Resource
    Electronic Resource
    Fully developed viscous flow and heat transfer in curved semicircular sectors (1979)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 478-487 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The Navier-Stokes equation in stream function-vorticity form and the energy equation are solved numerically for a fully developed flow of a Newtonian fluid in coiled circular sectors having zero pitch. Two heat transfer cases are studied: axially uniform heat flux with uniform peripheral temperature and axially uniform temperature with mixed conditions along the periphery. Solutions are presented for curvature ratios in the range of 5 to 30, Prandtl numbers in the range of 0.7 to 100, and Dean numbers up to 300. In all cases studied, the heat transfer performance for the curved tubes was superior to that of a straight tube geometry.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690250313
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