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Pipe Diameter
The effluent launderer launder will span the length of the tank at the about 4in off of center of the widthtank. The launderer launder is placed 20cm beneath the top of the water level, which is taken from a constant in the launderer MathCAD equations2in beneath the water level, this value was chosen to be close to the surface of the water and while allowing a few inches for water height variation. The diameter of the effluent launderer was calculated by iterating through pipe diameters to find the diameter pipe that matched up with the flow rate. The diameter was selected based on the following equation:
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The best pipe diameter is 2 inches. The number of orifice holes in the pipe is equal the the length of the tank divided by the lamina spacing. We used a lamina spacing of 2.5cm, which is what would have been used for our plant if we had enough height to use them. Therefore, the total number of orifices is 45was chosen so that the hole diameter would match up with a drill bit size while still giving the proper about of head. This head loss was defined to be about 20 times the water height over the accessory outlet weir. The goal was to make this height change insignificant with respect to head out of the sedimentation tank. The head out of the sedimentation tank needed to be the dominating head value to ensure that flow through the sedimentation tank is always uniform and steady. The total number of orifices was found to be 15.
Orifice Diameter
The diameter of the orifices was calculated by finding the necessary area of the orifice based on the head at the launder, the minor loss of the orifice, and the flow rate through the orifice (plant flow rate divided by number of orifices). The equation to find the area is found below. With the area, the diameter of the orifice can easily be calculated by solving the area of a circle for the diameter. The minor loss coefficient of an orifice is 0.6263, and the head, h, is equal to the height of the sed tank minus head loss through the launder minus the velocity head through the orifice. The diameter of each orifice was figured out to be .285 cm3/16". This value was rounded to the next smallest drill bit size.
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The head loss due to the orifice ends up being an important parameter because it affects how much water goes into the sedimentation tank, and how much bypasses it. We decided that we want a head loss of an order of magnitude or about 20 times greater than the headloss in the weir at the end of the floc tank because this will minimize the effects if the flow through the floc tank changes. This will be explained further below.
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