Author(s): L. Jonsson
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Keywords: No Keywords
Abstract: This paper deals with experimental studies of the flow structure in a Dissolved Air Flotation (DAF) pilot plant tank. Mapping of the water velocities using an Acoustic Doppler Velocimeter showed that basically three different flow structures occurred depending on the hydraulic load and the dispersion load – a large clockwise rotating flow with no density effects, a stratified flow situation and finally a “short-circuit” flow. It is only the stratified flow which provides good separation results. The transition from the rotating flow to the stratified flow was studied and it was found that the transition occurred for a dispersion flow of about 4 % of the hydraulic load irrespective of the hydraulic load for a certain load range. A new method for measuring the bubble size distributions in the tank was investigated using a light blocking particle counter. The output from the counter was interpreted in terms of an assumption of total reflection of the impinging light rays on a bubble. Initial measurements showed that bubble sizes peaked at 40-50 μm and that the peak diminished with increasing depth which could be expected for the stratified condition.
Year: 2009