The Eulerian-Eulerian approach is used to simulate the two phase flow of air and water in a dissolved air flotation (DAF) tank. Unsteady simulation is adopted to obtain the quasi-steady result. The two dimensional model cannot capture the three dimensional feature of flow pattern in the tank. The three dimensional model reproduces the stratification structure observed in the experiment and obtains the satisfactory volume fraction of air bubbles in the separation zone. To account for the turbulence effect, four two-equation turbulence models are evaluated. Although all turbulence models capture the stratification structure in the separation zone, the re-normalization group theory (RNG) k-ɛ model obtains the best agreement with the experimental data. The effect of bubble diameter on the performance of DAF tank is simulated. Small air bubbles can form a big range of high volume fraction of air bubbles, which helps to remove the suspended matters.

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