The O/A ratio of the phases in a mixer has a
significant effect on entrainment as shown in Figures 1 and 2. With organic
continuous dispersions, aqueous entrainment in the organic phase increases
considerably at O/A ratios greater than 1.5:1. Organic entrainment in the
aqueous phase is very low for organic continuous dispersions and is not
dependent on the O/A ratio in the mixer.
For aqueous continuous dispersions, organic
entrainment in the aqueous phase increases sharply at O/A ratios of less than
1:1, and aqueous entrainment is lowest between O/A ratios of 1:1 to 2:1.
Therefore, the optimum O/A for both organic and aqueous continuous dispersions
is between 1:1 to 1.5:1.
The O/A ratio of the phases in a mixer can be
maintained between 1:1 to 1.5:1 by recycling either the organic or aqueous
phase from the settler to its mixer. Another important reason for maintaining
the optimum O/A ratio is to improve the mass transfer rate and stage
efficiency. At the optimum O/A ratio the rate of coalescence and re-dispersion
of the dispersed phase is enhanced.