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Contours of strain rate show high velocity gradients around the turn. There are also high strain rates in at the boundary layer layers near the wall. It is postulated that flocculation is directly proportional to the strain rate.
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Figure 10 shows that the y+ values were less than 5. According to FLUENT documentation "the mesh should be made either coarse or fine enough to prevent the wall-adjacent cells from being placed in the buffer layer (y+ = 5~30)". Since the y+ from the model was consistently less than five (inside in the viscous sublayer) the turbulence near the walls was resolved properly.
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Figure 11 shows the pressure coefficient drop over one turn for different mesh densities. In general, finer meshes provide more accurate results. However, as the mesh was refined the pressure drop remained constant as can be seen in figure 11. Hence, it was concluded that results were not sensitive to mesh density and the coarse mesh was sufficient.
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By changing the inlet velocity a range of , the effect of having different Reynolds numbers were was analyzed. The A normal flow rate has a Reynolds number of 10,000. From figure 12, it is can be seen that the value of the pressure coefficient drop changes only a little with has a small change when compared to big changes in Reynolds number. In other words, the pressure coefficient drop is not sensitive to the Reynolds number at the inlet. This is a good thing because in implies that the design of the flocculator , should not be altered by the inlet flow rate can be neglected. This is to say that one flocculator design can be used for different flow rates.
Figure 13. Clearance Height Effect on Pressure Coefficient Drop and Maximum Velocity
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