Effects of internal geometry on hydrodynamics of dissolved air flotation (DAF) tank: An experimental study using particle image velocimetry (PIV)

Abstract

The hydrodynamics of flotation tanks significantly affect the removal efficiency of dissolved air flotation (DAF) systems. In the present study, for the first time, particle image velocimetry (PIV) was used to provide a fully detailed map of the velocity field in the contact and separation zones of a real scale DAF system under the influence of different internal geometries. The observed flow patterns indicated that flow circulations occur in the upper part of the contact zone, and as the height of the inlet baffle increased, the flow circulations became more intense. Additionally, as the inlet baffle was inclined, the flow inside the contact zone deviated from the plug flow. The outlet baffle contributed to the formation of a large rotational flow in the separation zone, and the shape of the rotational flow was a function of inlet baffles’ height. The range of the measured velocities of microbubbles in this study varied between 0–64 mm/s in the contact zone which was greater than the estimated rising velocities by Stoke’s law (1.37–17.82 mm/s). The velocities of microbubbles were also measured in the separation zone which varied between 0–25 mm/s. For the same internal geometry and flow conditions, the hydrodynamics of the flow without microbubbles (single phase flow) was also investigated. Results showed that the velocity of microbubbles was higher than single-phase flow (varied between 0 and 38 mm/s). Moreover, it appears that the buoyancy of microbubbles enhances the formation of rotational flows inside the separation zone.