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Sizing refers to both the CD design in MathCAD and the proper scaling for the plant. The MathCAD sheet that can be used to design a CD is attached to the main chemical doser wiki page. The main constraint used in designing a CD is the for it to deliver enough chemical (mg chemical per L plant flow rate) for the maximum plant requirement while making sure that the flow controller is not going to exceed the turbulent transition flow rate. The CD is designed to operate with the LFOM with a maximum head loss of 20 cm, and a lever arm length of 35 cm as requested in Tamara. The constraints are input to the MathCAD sheet to find a combination of FC outflow tubing length and inner diameter that matches the plant chemical dosing needs.
In Tamara the CD lever arm can be no longer than 37 cm (on the outer side of the pivot) because of the layout of the plant. AguaClara Engineers in Honduras asked that the CD stick out no farther than the rapid mix pipe so as to not interfere with the walkway that plant operators use between the entrance and exit tanks. The CD for Tamara has been designed to require a lever arm with 35 cm of length out from the pivot.
Another scaling issue that needs to be addressed before installation is the vertical relationships between the FC and the chemical stock tanks. The FC fill line cannot be located above the level of the stock tank exit, or else the FC will not maintain a constant head.
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