Abstract
The previous linear chemical doser design requires that the alum flow be laminar. This is the only way the The linear flow design uses the relationship between laminar flow and major losses in the doser tube. This creates a linear relationship between height of water in the grit chamber and the flow of alum can exist. As the flow rate through a plant is increased,(Linear Chemical Doser). For high plant flow rates, the flow rate of alum will increase as well. As this flow rate increases, so to does the velocity, and thus the Reynolds number. Eventually the flow of alum will become turbulent and the linear relationship will ceases to exist. Tragically, this means we can no longer uses the linear flow orifice meter for large flow ratesbe turbulent. When the flow in the tube is turbulent the linear relationship no longer exists and a nonlinear dose controller is necessary to maintain a constant chemical dose with variations in flowrates.
To get around this issue, it has been determined that the flow rate to height relationship in the entrance tank can be nonlinear so long as the alum has the same nonlinear relationship. For example, if water flows from an orifice in the entrance tank to rapid mix, then alum must flow through a similar orifice, so that they have the same relationship. We decided to achieve this by having the doser consist of a large pipe that moves with the fluctuations of the water in the entrance tank. Since the pipe diameter is so large, major losses can be neglected, and we are essentially moving the location of the orifice up and down, creating different elevation heads.
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