Analysis of the flow agitated by disc impellers with pitched blades

Abstract

In this study we are concerned with the flow in a tank stirred by disc impellers with pitched blades. A mathematical method, based on multiframe of reference and unstructured grid technology, was employed in the flow simulation. It was learned from the study by Tsui et al. [12] that for a pitched-blade impeller, which does not include the disc, the flow pattern in the agitated tank is transformed from the axial type to the radial type at a particular angle when the blade angle is increased. A similar phenomenon was observed in the present study. However, in contrast to the results of Tsui et al., the change of flow pattern brings about a sharp decrease in power requirement and a jump in pumping capacity. The cause of the difference is related to the disc which obstructs the fluid when it flows in the axial direction at low blade angles and makes it flow smoothly in the radial direction along the disc at high blade angles. It was shown in the results that the transition angle is increased when the impeller size, the disc size as well as the off-bottom clearance are reduced.