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  • Chemical Engineering  (129)
  • Lunar and Planetary Science and Exploration
  • Wiley-Blackwell  (129)
  • 11
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 39 (1993), S. 1581-1591 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Lagrangian statistics are explored as a means of describing the transport of solids in a turbulently flowing liquid. The essential feature of the approach is to represent the concentration field as resulting from a distribution of sources of particles. It is argued that this provides a better framework to understand the physics than the Eulerian analysis currently being used. Fully developed concentration fields are calculated, using the assumptions of homogeneous turbulence and plug flow. It is found that the configuration of solids and the suspended load depend primarily on the ratio of the settling velocity to the friction velocity, which is a measure of the relative importance of turbulence and of settling in depositing particles. The analysis emphasizes the need for a better understanding of the mechanism and the rate of entrainment of particles into a turbulently flowing liquid.
    Additional Material: 8 Ill.
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  • 12
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 39 (1993), S. 1741-1753 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Experiments were conducted with air-water flow in a horizontal 0.095-m pipeline at atmospheric pressure to examine the mechanism by which slugs form in a stratified flow. A specially designed entrance box was used to avoid disturbances. In these experiments, at superficial gas velocities less than 3 m/s, the slugs are found to evolve from waves, with a length of about 0.085 m, that are generated by a Jeffreys mechanism. These waves grow in height and eventually double in wavelength by a nonlinear resonance mechanism. Depending on the height of the liquid, the growth can lead to a breaking wave or to a wave that fills the whole pipe cross section. At superficial gas velocities equal to or greater than 4 m/s capillary-gravity waves with a wide range of lengths are generated by a linear Kelvin-Helmholtz mechanism. These rapidly evolve into long waves outside the range of linear instability. If the liquid height is large enough, these waves can form slugs through a nonlinear Kelvin-Helmholtz instability that is aided by wave coalescence.
    Additional Material: 21 Ill.
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  • 13
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 301-318 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Experiments conducted quantify the macroscopic hydrodynamic characteristics of various scale 2-D bubble columns, which include dispersed and coalesced bubble regimes characterized by two flow conditions (4- and 3-region flow) with coherent flow structures. Hydrodynamic behavior is analyzed based on flow visualization and a particle image velocimetry (PIV) system. Columns operated in the 4-region flow condition comprise descending, vortical, fast bubble and central plume regions. The fast bubble flow region moves in a wavelike manner, and thus the flow in the vicinity of this region is characterized macroscopically in terms of wave properties. In columns greater than 20 cm in width, the transition from the dispersed bubble flow regime to the 4- and then to 3-region flow in the coalesced bubble regime occurs progressively with gas velocities at 1 and 3 cm/s, respectively. The demarcation of flow regimes is directly related to measurable coherent flow structures. The instantaneous and time-averaged liquid velocity and holdup profiles provided by the PIV system are presented in light of the macroscopic flow structure in various 2-D bubble columns. Numerical simulations demonstrate that the volume of fluid method can provide the time-dependent behavior of dispersed bubbling flows and account for the coupling effects of pressure field and the liquid velocity on the bubble motion. Comparison of computational results with PIV results for two different bubble injector arrangements is satisfactory.
    Additional Material: 27 Ill.
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  • 14
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 35 (1989), S. 1962-1974 
    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 computer simulation of turbulent flow in a channel is used to detect flow patterns related to the production of Reynolds stress. It is found that quadrant 2 and quadrant 4 events possess a streaky structure in the viscous wall region and that these events can be best understood by examining the velocity field in the y-z plane. Large turbulence production in the viscous wall region is found to occur in updrafts and downdrafts associated with closed eddies. These eddies, on average, have a spanwise dimension of 50 wall units and a streamwise dimension of 400-450 wall units. They are often seen to originate from small attached eddies at the wall.
    Additional Material: 18 Ill.
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  • 15
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 31 (1985), S. 895-902 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: New measurements are presented for film height and pressure drop for vertical gas-liquid annular flows. Improved methods for predicting the film height and interfacial friction factor are developed for situations in which the liquid film flow rate is known.
    Additional Material: 13 Ill.
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  • 16
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 33 (1987), S. 1481-1495 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Optimal linear-quadratic (LQ) controller design is usually associated with state space techniques. However, when one has measurements of the outputs to be controlled, there are many advantages to designing these LQ controllers using input-output transfer function models. The design procedure leads to a discrete equivalent of the Wiener-Hopf equation, which can be solved using a spectral factorization approach.In this paper the design procedure is presented and various interpretations of the resulting controllers are discussed. In particular, the controllers are shown to be of the internal model controller (IMC) form, and the Wiener-Hopf procedure is shown to be a powerful way of selecting approximate model inverses and filters that yield good performance and robustness characteristics. The approach treats the problem of simultaneous disturbance rejection and set-point tracking, and it easily handles nonsquare systems.The design approach, its performance/robustness trade-offs, and the structure of the resulting controllers are demonstrated using models for several processes, including a two-input/one-output sheet forming process, a (3 × 3) multivariable level control problem, and a (2 × 2) multivariable catalytic reactor.
    Additional Material: 10 Ill.
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  • 17
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 34 (1988), S. 610-617 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An experimental study was made of tracer dispersion in bidisperse sintered glass materials prepared from mixtures of two sizes of beads with mean diameters of 325 and 95 μm. The equivalent dispersion coefficient increases by a factor of 30 when the porosity decreases from 30 to 12%; this variation is similar to that measured in monodisperse samples. The variation of dispersion can be characterized by the ratio R = ℓd/L1 where ℓd is a length scale deduced from the equivalent dispersion coefficient and L1 is obtained from conductivity and permeability measurements. It is shown that the increase of ℓd/L1 correlates with the loss of porosity during the sintering process. Lightly sintered samples with a percentage of small beads around the minimum of porosity display a nearly Gaussian behavior, with a dispersion coefficient close to that obtained in homogeneous equivalent mixtures. This result is in contrast with very large anomalies observed by other authors. These results imply that dispersion in consolidated samples is sensitive to large-scale inhomogeneities of the materials rather than to their detailed structure.
    Additional Material: 6 Ill.
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  • 18
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 31 (1985), S. 1263-1274 
    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 combustion retorting of oil shale is analyzed. By using coordinate systems moving at the same velocity as reaction zones, a model is obtained for the fully developed thermal wave which would exist after the wave has progressed a sufficient distance into the bed. Of particular interest is the interpretation of oil yield in terms of the structure of the wave and of operating variables.
    Additional Material: 6 Ill.
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  • 19
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 32 (1986), S. 1108-1115 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Numerical solutions to the unaveraged mass balance equation for the case of a flat mobile interface reveal that both high- and low-frequency velocity fluctuations can contribute to mass transfer. This is in contrast to transport to a solid boundary where only low-frequency fluctuations, normal to the wall, are important. The average mass transfer coefficient is found to depend on Schmidt number to the -0.5 power, in agreement with classical theories. It is related to the velocity field in the liquid primarily through the mean-square value of the gradient of normal velocity fluctuations at the interface.
    Additional Material: 6 Ill.
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  • 20
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 31 (1985), S. 1069-1076 
    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 surface dynamics of pendant aqueous droplets forming at a submerged nozzle in an immiscible organic solvent have been studied using a novel laser-activated photochromic tracer technique. This enabled a small element of surface to be labeled so that its subsequent history could be recorded photographically.Results for aqueous droplets forming in toluene in the absence of any mass transfer indicated only a slow interfacial circulation from the front to the rear, and there was no indication of any surface renewal as a result of hydrodynamic flow even at nozzle Reynolds numbers as high as 300. By contrast, the introduction of any one of a number of organic solutes into the toluene phase led to sporadic Marangoni-type interfacial disturbances, which in turn resulted in rapid replacement of elements of the droplet surface. It is proposed that renewal of the droplet surface is dependent on solute diffusion in the present instance and that the processes of surface renewal and mass transfer are likely to be interactive.
    Additional Material: 6 Ill.
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