On the structure of turbulent liquid—liquid dispersed flows in an agitated vessel
The structure and stability of dispersed liquid—liquid flow have been studied in a stirred vessel under semi-batch (wash-out) and batch conditions. Four aqueous-organic systems were used with the density and viscosity of the organic phase close to and straddling the values for water. A recently deve...
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Published in | Chemical engineering science Vol. 49; no. 20; pp. 3485 - 3498 |
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Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
Oxford
Elsevier Ltd
1994
Elsevier |
Subjects | |
Online Access | Get full text |
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Summary: | The structure and stability of dispersed liquid—liquid flow have been studied in a stirred vessel under semi-batch (wash-out) and batch conditions. Four aqueous-organic systems were used with the density and viscosity of the organic phase close to and straddling the values for water. A recently developed video technique was employed, capable of giving sharp images of the dispersed phase droplets down to 25 μm. In the wash-out system, the dispersed phase fraction was increased from zero continuously until phase inversion occurred; and in the batch case, concentration from 0.05 in steps of 0.1 volume phase fraction up to phase inversion were used. In all cases, for water-in-oil dispersions above ∼ 0.25 volume fraction up to inversion, droplets of oil were found in the drops of water, and within a few seconds of phase inversion, such a structure disappeared. Conversely, for all fractions of oil-in-water, droplets-in-drops were not observed; but, in less than a second, following inversion, droplets of oil in drops of water formed. These findings are used to explain qualitatively: (i) the larger drop sizes found in water-in-oil dispersions at the same concentrations compared to those in oil-in-water ones under equivalent hydrodynamic conditions; (ii) the lower concentration in water-in-oil systems at which phase inversion occurs compared to oil-in-water systems; (iii) the presence of a delay time with water-in-oil inverting to oil-in-water compared to the absence of a delay time in the reverse case. It would appear that the general fluid dynamic treatment of such systems which only utilises the two-phase densities and viscosities and the symmetrical property, interfacial tension, is unable to account for these observations. |
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ISSN: | 0009-2509 1873-4405 |
DOI: | 10.1016/S0009-2509(94)85027-5 |