TY - JOUR
T1 - Diagnostic techniques of mixing effectiveness
T2 - the effect of shear and elongation in drop production in mixing tanks
AU - Collias, Dimitris I.
AU - Prud'homme, Robert K.
N1 - Funding Information:
Acknowledgements-We would like to thank Dr. D. Leng of Dow Chemical Company for first suggesting drop breakup as a diagnostic tool and Prof. John Boume for helpful comments on the manuscript. Financial support has come from the National Science Foundation.
PY - 1992
Y1 - 1992
N2 - Results on drop-size distributions produced in mixing tanks using Rushton turbine, anchor and blade impellers are presented. The goal is to assess the relative importance of shear and elongational flows on the drop breakup process. The ratio of the dispersed- to continuous-phase viscosity was varied from 0.08 to 11.9 by varying the viscosity of the dispersed phase. The interfacial tension was varied from 0.00327 to 0.0118 N/m. Correlations of drop diameter as a function of the Weber number, percentage of the organic (dispersed) phase and viscosity ratio of dispersed to continuous phase are presented for the Rushton turbine and blade impeller, and they are valid for Reynolds numbers from 750 to 2700. Shear and elongational flows have different efficiencies in breaking liquid drops: at viscosity ratio of one, shear and elongation contribute equally to breakup but, at a higher viscosity ratio, only elongational flow produces breakup. This allows us to quantify the relative strengths of shear and elongational flows in complex geometries by considering the largest surviving drops. Using drop breakup data, we found that the anchor impeller produced higher elongation rates than the Rushton turbine, and the blade impeller produced the same elongation rates as the Rushton turbine. The anchor impeller was found to produce the smaller sized drops per unit of specific power input; but the Rushton turbine produced the smallest drops when the three impellers are considered at the same rotational speed. Finally, the turbulence intensity factor for the anchor and the blade impellers was found to be 2.9 and 2.0 times that of the Rushton turbine, respectively.
AB - Results on drop-size distributions produced in mixing tanks using Rushton turbine, anchor and blade impellers are presented. The goal is to assess the relative importance of shear and elongational flows on the drop breakup process. The ratio of the dispersed- to continuous-phase viscosity was varied from 0.08 to 11.9 by varying the viscosity of the dispersed phase. The interfacial tension was varied from 0.00327 to 0.0118 N/m. Correlations of drop diameter as a function of the Weber number, percentage of the organic (dispersed) phase and viscosity ratio of dispersed to continuous phase are presented for the Rushton turbine and blade impeller, and they are valid for Reynolds numbers from 750 to 2700. Shear and elongational flows have different efficiencies in breaking liquid drops: at viscosity ratio of one, shear and elongation contribute equally to breakup but, at a higher viscosity ratio, only elongational flow produces breakup. This allows us to quantify the relative strengths of shear and elongational flows in complex geometries by considering the largest surviving drops. Using drop breakup data, we found that the anchor impeller produced higher elongation rates than the Rushton turbine, and the blade impeller produced the same elongation rates as the Rushton turbine. The anchor impeller was found to produce the smaller sized drops per unit of specific power input; but the Rushton turbine produced the smallest drops when the three impellers are considered at the same rotational speed. Finally, the turbulence intensity factor for the anchor and the blade impellers was found to be 2.9 and 2.0 times that of the Rushton turbine, respectively.
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U2 - 10.1016/0009-2509(92)80285-K
DO - 10.1016/0009-2509(92)80285-K
M3 - Article
AN - SCOPUS:0026852955
SN - 0009-2509
VL - 47
SP - 1401
EP - 1410
JO - Chemical Engineering Science
JF - Chemical Engineering Science
IS - 6
ER -