Flow patterns rotor-stator

A rotating impeller in a fluid imparts flow and shear to it, the shear resulting from the flow of one portion of the fluid past another. Limiting cases of flow are in the axial or radial directions so that impellers are classified conveniently according to which of these flows is dominant. By reason of reflections from vessel surfaces and obstruction by baffles and other internals, however, flow patterns in most cases are mixed. When a close approach to axial flow is particularly desirable, as for suspension of the solids of a slurry, the impeller may be housed in a draft tube and when radial flow is needed, a shrouded turbine consisting of a rotor and a stator may be employed. 

Another type of gravity-flow, vertical contactor with a rotating axial shaft is the rotating disk contactor developed by the Shell Development Company [R1, R2], shown schematically in Fig. 4.28. It consists of alternate annular stator disks attached to the outer shell and circular rotor disks attached to the rotating shaft. Rotation of the central shaft, at peripheral speeds up to 6 m/s, provides controlled dispersion of the two phases and sets up a toroidal flow pattern within each stator compartment. There are no settling chambers, and the two phases drift past each other in countercurrent flow. 

Because the tooth depth was small compared to the mixer diameter, it was initially believed that the flow field was two dimensional. Figure 8-9 shows mean velocity vectors, resulting from a 2D simulation, in the quadrant closest to the exit pipe. These results are angularly resolved in that the flow field changes as the rotor passes the stator. The direction of rotor rotation is clockwise and an extremely complex flow pattern is revealed in the stator slots and volute. Circulation cells in the stator slots allow reentrainment of volute fluid back into... 

Progression through the mixer is represented diagrammatically in Figure 2.28, which depicts the cross sectional plane of part of the stator with the rotor cavities passing in an anti-clockwise direction. The lands between the cavities are numbered round in a clockwise direction. Both true cross-sectional representation and flow paths are very complex, but this simplified picture gives a good representation of the overall pattern. 

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