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FIGURE 10.17 Flow field behind impeller blades (pitched blade turbine) (from Ranade et al., 2001a).

since two impeller streams merge and form two large ring vortices. The third stable flow pattern was named 'diverging flow' (Fig. 10.21c) and was observed for smaller bottom clearance at the lower impeller (C1 = 0.15T, C2 = 0.5T, C3 = 0.35T). In this case, the lower impeller stream is directed towards the vessel bottom. This results in the lower impeller producing one large ring vortex while the upper impeller generates the usual well-defined two ring vortices.

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