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Concluding, we need to select the component that will be used for the metering orifices in AguaClara plants. Once we determine and fabricate our orifices, we can then begin to quantify accuracy and surface tension issues.
Once a final decision has been made as to what material will be used for fabricating the orifice, the dosing scale will need to be developed. Again, because surface tension is directly related to material finish, fluid flow through a drilled PVC orifice is apt to behave quite differently than a laser pierced ruby. Fall 2009 developed a dual-scale, dual-orifice system. (link Mathcad file) This scale does not accommodate surface tension in anyway and therefore fails at low plant flow rates and low dosing concentration. Spring 2010 attempted to solve this problem with the development of the triple-scale, triple-orifice (link Mathcad file) This scale works well for all concentration ranges by starting the scale farther from the pivot point. However, at 50% plant flow rate, the head-loss through the plant is only 10 cm. We could easily enter the range where surface tension (depending of the material selected for the orifice) restricts flow at low concentrations of alum. The Summer 2010 team attempted to correct this by moving the float during periods of low flow so that a 4:1 relationship exists between plant flow and dose height. (link Mathcad file) . This solution maintains the dual-scale but does incorporate triple-orifice and requires an additional action from the operator.
One of the above listed scales or newly developed scale needs to be selected then coding developed so the Automated Design Tool can generate the scale template need for the CDC.