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Fixed Beds (fixed + bed)

Distribution by Scientific Domains
Chemistry100%

Terms modified by Fixed Beds

  • fixed bed reactor
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    Selected Abstracts

    Pore-scale simulations of unsteady flow and heat transfer in tubular fixed beds

    AICHE JOURNAL, Issue 4 2009
    P. Magnico
    Abstract Small tube-to-particle-diameter ratio induces a radial heterogeneity in tubular fixed beds on the particle scale. In this complex topology, theoretical models fail to predict wall-to-fluid heat transfer. In order to be more realistic, a deterministic Bennett method is first used to synthesize two packings with a tube-to-sphere-diameter ratio of 5.96 and 7.8, containing 236 and 620 spheres, respectively. In a second step, unsteady velocity and temperature fields are computed by CFD. In the range of Reynolds number lying between 80 and 160, hydrodynamic results are validated with experimental data. The thermal disequilibrium in the near-wall region is described in detail. Several pseudo-homogeneous models are compared to the numerical simulations. The radial and axial profiles of temperature show a clear agreement with the model of Schlünder's research group and the model of Martin and Nilles. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

    Effect of chemical heterogeneity on adsorbed solute dispersion at column scale

    AICHE JOURNAL, Issue 4 2008
    Safia Semra
    Abstract Chemical heterogeneity seems to be responsible for spreading increase of adsorbed solute breakthrough curves. Adsorption in fixed beds assumes chemically homogeneous media. However, this is not always true, in particular when natural sands or mixed adsorbent filters are used in drinking water purification. Neglecting eventual effect of chemical heterogeneity may engender false modeling bases. So, considering homogeneous grain size distribution, the effect of chemical heterogeneity on global dispersion in porous media has been investigated experimentally in this article at column scale. Breakthroughs of adsorbed solute showed a visible effect of chemical heterogeneity on solute global dispersion increasing. The more heterogeneous the medium, the more spread the adsorbed solute breakthrough. Reduced variance showed a linear variation with the chemical heterogeneity scale at closely constant media global capacity. A pseudo-homogeneous model has been developed to simulate experimental data by increasing dispersion parameter. © 2008 American Institute of Chemical Engineers AIChE J, 2008 [source]

    Multicomponent mass transport model for the sorption of metal ions on bone char

    AICHE JOURNAL, Issue 9 2004
    Danny C. K. Ko
    Abstract The sorption of binary mixtures of copper/cadmium and copper/zinc ions onto bone char was studied in fixed beds. The effects of solution flow rate, initial dye concentration, and bone char particle size range were investigated. A mass transport model based on film-surface diffusion and the IAS model for the equilibrium relationship was used to develop theoretical fixed-bed breakthrough curves. The model incorporates the Sips isotherm for the first time in fixed-bed predictions, since this isotherm gives an excellent correlation of the experimental equilibrium data. The model was used to determine the optimum surface diffusivities as 7.37 × 10,10 and 2.73 × 10,9 cm2/s for copper and cadmium in the Cu/Cd system; and 1.61 × 10,9 and 2.43 × 10,9 cm2/s for copper and zinc in the Cu/Zn system. © 2004 American Institute of Chemical Engineers AIChE J, 50: 2130,2141, 2004 [source]

    Activated Carbon Adsorbent for the Aqueous Phase Adsorption of Amoxicillin in a Fixed Bed

    CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 4 2010
    N. J. R. Ornelas
    Abstract Equilibrium constant and mass transfer parameters are needed for the study of amoxicillin separation in any process involving adsorption in fixed beds. In this work, the adsorption of amoxicillin and 6-aminopenillanic acid in aqueous solution on activated carbon were studied using static adsorption tests. The adsorption capacity was found to be strongly dependent on the pH of the aqueous phase. The adsorption constants, overall mass transfer coefficients, and axial dispersion coefficients for amoxicillin and 6-aminopenillanic acid were determined, by moment analysis, from a series of step tests in a fixed bed packed with activated carbon. The total bed voidage and axial dispersion coefficient were estimated from blue dextran pulse test data at different flow rates. The results show that adsorption intensity increased with increasing temperature. Furthermore, the increasing trend of HETP with velocity suggests that axial dispersion and mass transfer resistance control the column efficiency. [source]

    Axial Dispersion and Wall Effects in Narrow Fixed Bed Reactors: A Comparative Study Based on RTD and NMR Measurements

    CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 8 2004
    D. Tang
    Abstract Axial dispersion and wall effects in narrow fixed beds with aspect ratios < 10 were investigated, both by classical methods and by NMR imaging. The residence time distribution (RTD) in the center and at the wall was measured, system water/NaCl-solution as tracer, and subsequently compared with radial velocity profiles based on NMR imaging. The influence of the aspect ratio and Rep on dispersion and on the degree of non-uniformity of the velocity profile was studied. The NMR results are consistent with the RTD and also with literature data of numerical simulations. For low aspect ratios, dispersion/wall effects have a strong influence on the reactor behavior, above all, in cases where a low effluent concentration is essential, as proven by breakthrough experiments with the reaction of H2S with ZnO. [source]

    Comparison of Fixed and Fluidized Activated Carbon Beds for Removal of Organic Vapors

    CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 7 2004
    I.E. Agranovski
    Abstract Activated carbons are commonly used for removal of organic vapors from exhaust air streams. Two configurations, including fixed and fluidized carbon beds are usually employed in industry to meet various requirements of the industrial process which is being used. This paper investigates the performance of such configurations and provides a comparative analysis. It was found that for thin carbon layers, the fixed bed performs more efficiently with the difference exceeding 15,% for the layers with the thickness less than 15,mm. This difference is decreasing with increase of the layer thickness and becomes less than 5,% for the beds thicker than 100,mm. Considering various advantages of the fluidized beds over fixed beds, including lower resistance to the gas flow, excellent gas distribution and minimal possibility of clogging in case of existence of alien particles in the gas, they are recommended for use with the minimal thickness of the layer to be larger than 100,mm. [source]