Direct determination of energy dissipation in stirred vessels with two-point LDA

Authors

  • A. Ducci,

    1. Experimental and Computational Laboratory for the Analysis of Turbulence (ECLAT), Department of Mechanical Engineering, King's College London, Strand, London, WC2R 2LS, U.K.
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  • M. Yianneskis

    Corresponding author
    1. Experimental and Computational Laboratory for the Analysis of Turbulence (ECLAT), Department of Mechanical Engineering, King's College London, Strand, London, WC2R 2LS, U.K.
    • Experimental and Computational Laboratory for the Analysis of Turbulence (ECLAT), Department of Mechanical Engineering, King's College London, Strand, London, WC2R 2LS, U.K.
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Abstract

The ensemble-averaged kinetic energy viscous dissipation rate was determined with a multipoint LDA technique in a vessel stirred by a Rushton turbine. Nine out of the total of 12 mean squared velocity gradients constituting the dissipation rate were directly measured in the impeller stream, and the deviation of the flow from local isotropy was investigated. The dissipation rate normalized with N3D2, where N and D are the impeller rotational speed and the impeller diameter, respectively, was found to be approximately constant for Reynolds numbers of 20,000–40,000, whereas the fluctuating gradients were found to vary significantly, by up to three times the ensemble-averaged values, with blade angular position. The ensemble-averaged dissipation rate values were also assessed through a local turbulence kinetic energy balance. © 2005 American Institute of Chemical Engineers AIChE J, 2005

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