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Some consequences for turbulent mixing of fine-scale intermittency

✍ Scribed by J. Baldyga; J.R. Bourne


Publisher
Elsevier Science
Year
1992
Tongue
English
Weight
625 KB
Volume
47
Category
Article
ISSN
0009-2509

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✦ Synopsis


Even in homogeneous turbulence, energy dissipatisn does not occur uniformly at a constant rate, but the fine-scale structure is intermittent and spotty. Equations traditihnally used to calculate the rate of micromixing and the maximum stable drop size in a dispersion take no account of intermittency. Its effect should be to decrease both these quantities, relative to the values predicted by available equations. When scaling-up, intermittency modifies the fine-scale turbulence even when the power per unit volume is held constant. The oversimplified &model was employed to approximately quantify these effects. Correction factors for the traditional equations used for micromixing and drop dispersion were-easily derived from the fl-model. The iine structure is not space-filling, but has a fractal dimension c 3, so that the correction factors deviate from unity. Examples of such corrections arc given for micromixing and drop dispersion as well as for the scale-up of these operations. For dispersing drops having negligible viscosities the B-model predicts an exponent on the Weher number of -0.65, whereas a recent and extensive correlation of measurements gives -0.66. It is sugggested that more attention should be given to the influence of intermittency on certain chemical engineering operations.


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