A multiphase CFD model of DAF process

• Published in: Water Science & Technology Vol. 43; no. 8; pp. 153 - 157
• Main Authors: TA, C. T, BECKLEY, J, EADES, A
• Format: Conference Proceeding Journal Article
• Language: English
• Published: Oxford Pergamon Press 01.01.2001; IWA Publishing
• Subjects: Air; Air bubbles; Applied sciences; Computational fluid dynamics; Concentration (composition); Doppler sonar; Drinking water and swimming-pool water. Desalination; Exact sciences and technology; Flocculation; Flotation; Flow visualization; General purification processes; Models, Theoretical; Multiphase; Particle Size; Pollution; Removal; Simulation; Solubility; Tank geometry; Three dimensional flow; Underwater; Underwater cameras; Velocimetry; Velocity measurement; Volume transport; Wastewaters; Water; Water flow; Water Purification - methods; Water treatment and pollution; Weirs; Drinking water treatment; Flotation; Computational fluid dynamics; Dissolved gas; Physicochemical purification; Air; Waste water purification; Modeling
• ISBN: 1900222817; 9781900222815
• ISSN: 0273-1223; 1996-9732
• DOI: 10.2166/wst.2001.0488

A Eulerian-Eulerian multiphase CFD model is employed for the air/water flow. A 3D structure grid is used to incorporate the air nozzle and tank geometry. The fixed frictionless wall boundary approximating the free surface acts as a sink to allow the air bubbles to escape. The air/water volume fraction in the flotation tank is evaluated to determine the effective air/water fluid density. The floc particle is then introduced and is tracked in the air/water fluid using a disperse Lagrangean model. Fate of these flocs depends on their sizes and density. Flocs therefore can either escape through the top water surface, settles in the main tank or breakthrough under the outlet weir. The CFD model is developed for a full scale DAF tank to predict the flow dynamic, particle removal and settled solid profile. The general flow pattern is compared with flow visualisation using the underwater camera. Comparison of average fluid velocities is carried out using acoustic Doppler velocimetry ADV measurement.