LIQUID DISPERSION MECHANISMS IN AGITATED TANKS: PART II. STRAIGHT BLADE AND DISC STYLE TURBINES

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Abstract
The dispersion of oil in water in an agitated vessel was studied for two types of radial discharge impellers, straight blade and disc style turbines. Two different dispersion mechanisms, ligament stretching and turbulent fragmentation, were observed to occur in the vortex systems of the impeller discharge. Although these two dispersion mechanisms were similar to pitched blade turbine performance, differences in the velocity magnitudes and vortex interactions were observed with the radial flow impellers. The ligament stretching mechanism was observed between the vortex formation regime and the transition to the fragmentation regime. The turbulent fragmentation mechanism was observed only in highly turbulent flow. Blade thickness was found to influence the ligament stretching mechanism. A thin blade on the straight blade turbine created higher vortex velocities and smaller drop sizes than a thick blade for the same tip speed and processing time. The consequences of this blade thickness effect could be significant when laboratory data are used to design large process equipment for liquid-liquid dispersion.

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