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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Adsorption 2 (1996), S. 9-21 
    ISSN: 1572-8757
    Keywords: nanopores ; zeolites ; Monte Carlo simulations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract A Grand Canonical Monte Carlo simulation method is used to determine the adsorption isotherms, interaction energies, entropies, and density distribution of a Lennard-Jones fluid adsorbed in smooth-walled nanopores of varying size and shape. We specifically include very crowded pores, where packing effects are important. Differences in the isotherms of slit, cylindrical, and spherical nanopores of varying sizes can be explained in terms of the adsorbate-adsorbate interaction energy, the adsorbate-pore interaction energy, and the density profiles, which influence the balance between the former and the latter energy contributions. The expectation from low loading studies that the most energetically favorable adsorbate-pore interactions maximize adsorption is not borne out at intermediate and higher loadings. Instead, the relationships between adsorbed amounts and pore size and shape are found to be strong functions of the depth and steepness of the external potential, the extent to which adsorbate-adsorbate repulsion establishes short range fluid order, and the accessible pore volume. This study has implications for high pore density processes in nanoporous materials, such as zeolite catalysis, separations, and templating in zeolite synthesis.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 2274-2281 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: In this work the experimental observations are explained with the aid of a simple air-entrapment model based on the concept of two levels of porosity of fiber mats. A simple model that includes liquid bypassing with initial air trapping, subsequent capillary invasion of regular fiber bundles with air compression, and finally mobilization is proposed to explain air-entrapment phenomena. The simple model successfully rationalizes the observed air trapping and compression during initial liquid-fiber contact. An empirical equation for the mobilization efficiency is adapted to the model to estimate void content. The velocity dependence of the trapped void content predicted by the model is in good agreement with observations.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 925-934 
    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 new adsorption model is developed for small molecules in zeolites whose form is based on features revealed by molecular simulation. Adsorption is assumed to occur onto a 3-D polyhedral lattice, and both the energy and entropy of the lattice sites are accounted for using a statistical mechanics approach. Energetic interactions are described by an Ising model with both 2- and multibody nearest-neighbor in-teractions. Entropic interactions are included by an adsorption site volume term which accounts for the loss of traslational freedom associated with lattice crowding.The model is applied to a system of small molecules (xenon, methane) adsorbed in idealized zeolite NaA, where adsorption has been shown by computer simulation to occur on finite, cuboctahedral lattices (Van Tassel et al., 1992). The model quantitavely predicts the simulated isotherm over the entire pressure range. Comparison is made with a Langmuir model and a van der Waals gas model which, although valid at low pressures, fail at high pressures due to overestimation of translational entropy and inaccurate portrayal of sorbate-sorbate interaction energy.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 2261-2273 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Wetting of glass fibers was visualized using an oil with the same refractive index. With both a video-enhanced microscope and a high-magnification video camera we followed the flow front and qualitatively measured the entrapped air bubbles by image analysis. Due to different permeabilities between the fiber mats and bundles, air bubbles are entrapped. Two major kinds of air bubbles are observed: small cylindrical micro voids between fiber filaments (inside fiber bundles) and spherical macro voids outside fiber bundles. These air bubbles can be described by three major mechanisms initial liquid bypassing/air trapping, later capillary invasion of disordered fiber bundles, and air bubble mobilization. Both random and unidirectional fiber mats were used in this study. Vacuum as well as different fluid viscosities and surface tensions were also investigated, which led us to guidelines of optimum processing parameters of fiber wetting for resin transfer molding and structural reaction injection molding. They are low viscosity, vacuum, high mold temperature, and high pressure.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
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