Break-up of flocs in contraction and swirling flows

The break-up of ferric hydroxide flocs was observed by optical methods in a contraction and a swirling flow. The corresponding flow fields were produced by pumping water through two pipes of different diameter, which were either kept stationary or rotated around the axis of symmetry. Digital image analysis was applied to obtain data on the orientation and deformation of the flocs. It was found that flocs were broken apart by both flow fields before they passed the orifice. Based on a simplified model the rupture forces were estimated to be on the order of 0.1 N m−2.