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Water Science & Technology Vol 43 No 8 pp 167–173 © IWA Publishing 2001 Small scale model for CFD validation in DAF applicationJ Hague*, CT Ta**, MJ Biggs*** and JA Sattary*****
Thames Water Group Research and Development, Kempton Park R&D Centre,
Feltham Hill Road, Hanworth, TW13 6XH, UK
Department of Chemical and Process Engineering, University of Surrey,
Guildford GU2 5XH, UK
ABSTRACT A laboratory model is used to measure the generic flow patterns in dissolved air flotation (DAF). The Perspex model used in this study allows the use of laser Doppler velocimetry (LDV), a non-invasive, high-resolution (  2 mm s+1) laser technique of flow velocity
measurement. Measurement of flow velocity in the single-phase situation
was first carried out. Air-saturated water was then supplied to the tank and
measurements of bubble velocity in the two-phase system were made. Vertical
flow re-circulation was observed in the flotation zone. In the bottom of
the flotation zone (near the riser) secondary flow re-circulation was
observed, but only in the two-phase system. Another phenomenon was the
apparent movement of flow across the tank width, which may be due to
lateral dispersion of the bubble cloud. Data from preliminary
computational fluid dynamics (CFD) models were compared against this
measured data in the case of the single-phase system. The CFD model
incorporating a k-e model of turbulence was found to give closer agreement with the measured data than the corresponding laminar flow model. The
measured velocity data will be used to verify two-phase computational
fluid dynamics (CFD) models of DAF.
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