Abstract
The previous chemical doser design requires that the alum flow be laminar. This is the only way the linear relationship between height of water and flow of alum can exist. As the flow rate through a plant is increased, 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 rates.
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.
Since the focus of the CDC team was shifted to design, this aspect of the project has been put on hold temporarily.