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To extend the current 2D CFD models of flocculation tank in to 3D , will greatly enhance our understanding of the fluid dynamics inside the flocculation tank. In this report, four sets of preliminary 3D computational simulations were presented and discussed: first on investigating the difficulty of 3D models in converging to satisfactory residual; and then on comparing the validity of 2D and 3D models by running 3D simulations with the model on which 2D assumptions were imposed.
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Results are shown in Figure 1 and Figure 2 below. Figure 3 indicates the plane where the contour in Figure 2 were drawn, in grey.
a. Case 1
b. Case 2a
c. Case 2b
d. Case 3
Figure 1 Plots of residuals as a function of iteration steps 
a. Case 2a
b. Case 2b
Figure 2 Contours of energy dissipation rate showing the effects of turbulence intensity and hydraulic diameters, drawn on the same scale
Figure 3 The plan where the contours were drawn, in grey
Observations:
- Case 1 converged to 10^-3 within 300 iteration steps;
- Case 2a converged to 10^-3 within 300 iteration steps, stopped converging after 500 steps and started fluctuating after 1000 steps;
- Case 2a converged to 10^-3 within 200 iteration steps, stopped converging after 1000 steps and started fluctuating after 1000 steps;
- Case 3 converged to 10^-9 with 1st order solver and then to 10^-6 with second order solver within altogether 8000 iteration steps.
- There was no observable significance difference in the results between different turbulence intensity and hydraulic diameters at the inlet, except for less turbulent flow had lower minimum energy dissipation rate at the entrance region.
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