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Much of the focus of our design work has been on the alum doser. Originally, we planned to use the alum doser to dose untreated water at an appropriate level using a mere "hole-in-the-bucket" situation with a float valve to maintain a constant water level and thus maintain constant head. Yet we discovered that this design required a bottom orifice with a diameter of less than 3 mm. These calculations can be seen in the Alum Doser MathCAD file.
The problem with small orifices (with diameters below 3 mm) is that clogging occurs very easily. Thus, we needed designs that incorporated large amounts of head loss in the system to allow for the use of a larger orifice size.
Hence, we proposed We propose three alternative designs for incorporating the this alum doser into our system:
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Unfortunately, we realized that non none of these proposed designs work well with our unit constraints. In order for the alum doser to dose the untreated water at an appropriate level using a mere "hole-in-the-bucket" situation, a bottom orifice of less than 3 mm is needed. These calculations can be seen in the Alum Doser MathCAD filegenerate enough head loss to dose with small amounts. For example, in order for the the spiral tubing design to successfully work, a extra tubing length of around 8 meters is needed. This is not feasible considered our desire to have a small overall filtration unit. Hence, we need to look into other viable options for the design of the alum doser (which will be a model for the required chlorine doser as well).
As of currently, we are re-considerig the use of a float value to monitor the surface level of the alum solution. This should make dosing less variable and may help find a better solution to the orifice problem. Originally, we eliminated this design because we did not want to include small, hard-to-fabricate components into the design. Yet, this seems like the only potentially successful option at the moment.