Page History

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A flow rate of 114 L/min was the closest flow rate to the target flow rate of 120 L/min that could be achieved. The residence time of the tube settlers was found to be 7.6 min, and the residence time of the flocculator was 18 min. In order to ensure that our measurement of the residence time of the flocculator was correct a test was run. This test consisted of turning off the alum and waiting till there was little or no floc formation. Then the alum was turned on and when there was observable floc it was timed to see how long it took to reach the end of the flocculator. When this measurement was done it was discovered that the residence time of the flocculator was about 35 min. This value was the value that was used in Process Controller. This and other evidence discussed in Data collection and troubleshooting below helped us to conclude that that was short circuiting of water in the flocculator. This evidence was used to make further adjustments to the tank, also discussed in detail in Data collection and troubleshooting.
At the beginning of the summer there were some minor adjustments made to the flocculator. The first is that the baffles at the end of the first section appeared to be rising up and away from the bottom of the flocculator causing baffle skipping. There was also some concern that water might be flowing under the dividers from the first section to the third section. To fix both these problems sand was added to the bottom of the flocculator at a thickness of about 5 cm.
The module in the last section of the flocculator also seemed to be drifting towards the end of the section. This was due to the force acting on the baffles causing them to drift with the flow. The force is due to the water level on either side of the baffle being slightly different due to head loss. This causes the pressure on one side of the baffle to be slightly higher at each point on the baffle than on the other side creating a force over the entire area of the baffle. The pressure on each baffle is translated through the PVC connector pipes from one baffle to another, until the last baffle and the final connector pipes are carrying the entire force. A MathCAD file labeled "Force on baffles" was created to assist with this calculation. Equations for head loss were used to find the head loss over just one section. It was found that there should be a head loss of 3.8 cm over each section. With this information, equations listed below were used to find the total force on each section and then the force each connector pipe would have to support.

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