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Figure 12. Reynolds Number Effect on Pressure Coefficient Drop
By changing the inlet velocity, the The effect of having different Reynolds numbers was analyzed. A normal flow rate has the Reynolds number on the pressure coefficient drop was analyzed. This was done by changing the inlet velocity which initially produces a Reynolds number of 10,000. From figure 12, it can be seen that the value of the pressure coefficient drop 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 implies that the design of the flocculator should not be altered by the inlet flow rate. 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
By adjusting The effect of the clearance height , the effect on the pressure coefficient drop was also analyzed. It can be seen that the pressure coefficient drop is independent of the change in clearance height as long as after the clearance height is greater than a certain critical value. Figure 13 shows that after a critical value of 1, the pressure coefficient drop is constant. This phenomena can be explained using figure 5. Figure 5 shows the clearance height of by looking at figure 14 below. Figure 14 shows the turbulent dissipation rate for clearance heights of 0.1 and 0.15 m. However, from 0.1 m onward, the flow is mostly stagnant in the flocculator. This mean It can be observed that the length of high dissipation rate is equal for both reactors. This means that 0.1 m is needed for the flow to navigate through the turn and after this point onward, there is not much activity happening. Clearance height of the clearance height after which a stagnant fluid starts to form at the bottom. A similar argument can be made for the values of maximum velocity . A clearance height less than 0.1 m gave results in a higher pressure coefficient drop as it created a constriction of flow and the frictional loss was increased. With this result, it is creates an 'unnatural' constriction to the flow increasing frictional losses. It is therefore recommended for the design team that the clearance height must be at least the same of bigger than as the baffle width to produce predictable pressure coefficient drop. . The correlation between pressure coefficient drop and maximum velocity should also be noted.
Figure 14. Comparison of Turbulent Dissipation Rate for Clearance height of 0.1 m and 0.15 m
To Figure 14 above further validate that the result is validates that results are not sensitive to the change in clearance height, the contours . Contours of turbulence dissipation rate for clearance heights of clearance height 0.1 m and 0.15 m was were compared. The result showed These results show that the region of active turbulent dissipation was is the same for both reactors, about two times the length of baffle spacing. With this result, it is concluded that the design team has the freedom of choosing clearance height according to their design constraint and not theoretical constraint as long as the clearance height is greater than the baffle spacing.
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Figure 14. Effect of Figure 14. Effect of Turbulence Model on Pressure Coefficient Drop
Pressure coefficient drop was least in the K-ε model and the most in the K-ω model.
Figure 15. Contours of Velocity Magnitude for Different Turbulence ModelModels
As figure 15 depicts the standard K-ε has the smallest region of high and low velocity region. This explain why it has the lowest pressure coefficient drop. K-ω has the biggest region of high and low velocity. K-ω has highest pressure coefficient drop.velocities, shown in red and blue respectively. This explains why it has the lowest pressure coefficient drop. The K-ω model has the biggest region of high and low velocities therefore having larger pressure coefficient drops.
However, as it can be observed from the transparent demo plant, the recirculation area is only the length of one or two baffle widths. This is contrary to the excessively large blue/red regions predicted by the k-e realizable, and k-w models. Therefore it was concluded that the standard k-e model best simulates the turn.
4. Conclusions
1. An area of recirculation occurs near the center wall immediately after the turn
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4. Most of the energy dissipation occurs in the region after the turn over a distance of about two baffle widthwidths
5. The pressure coefficient drop is insensitive to the Reynolds number for a large range of inlet velocities
6. About A mesh with 20,000 mesh elements is sufficient to obtain accurate modeling results
7. Different turbulence model resulted in fairly different results
8. The standard k-e model best simulates the turn
6. Future Research
1. Measure Gtheta value from FLUENT
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During the course of this project, we received invaluable advice and direction from DrProf. Monroe Weber-Shirk, whose direction leadership of the AguaClara team project spurred this research and technical investigation. All questions we had were directed towards Dr. Rajesh Bhaskaran, his expertise and academic guidance kept us on schedule and on task. We would also like to thank Prof. Brian Kirby for elucidating some technical aspects we encountered. For their help, we are grateful.
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