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First, a control experiment, using water, was performed to allow us to see normal pressure readings without any clog being present. These pressure readings will serve as a basis for comparison when we begin to run alum through our system. The pressure results from pressure sensor 1 can be seen in the following graph below.
Graph 1: Pressure readings for the control experiment using water
Next, alum was used in order to determine the time it would take for a clog to form in our .1 cm orifice. The experiment was run for four days but the most conclusive data was seen within the first hours. The pressure readings, from pressure sensor 1, from Figure 1, are shown in Graph 2 below.
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Graph 2: Pressure sensor 1 readings using alum
The first experiment using an alum solution ran continuously for four days. From the data, a 1 cm change in pressure was observed about 2.4 hours after the experiment began. Other fluctuations in pressure were observed throughout the remaining time, but they were deemed negligible. The blip seem in day four is a result of flow rate measurements made by the team.
Conclusions
As can be seen from the graph there is a large spike in the pressure readings about 4 hours after beginning the test. The pressure sensor reads a higher and higher pressure, due to the clogging orifice, until the it builds up enough to "blow out" the clog.
Possible sources of error
The elevated pressure, shown in Graph 2, seems indicative of a clog, but the spike was not repeated at all for the remainder of the experiment. If the clog was "blown out" due to the increase in pressure then it should simply reform after another 4 hour time span, forming a clogging cycle. Yet this cycle of perpetual clogging and clearing of the orifice was not observed. This seems strange and might indicate erroneous pressure readings for the spike.
Conclusions/future work
The .1 cm orifice appeared to clog after 4 hours, indicating that a larger dosing orifice might need to be used.
Since lab grade alum was utilized in this experiment and a clog was still present,the presence of foreign material, might not be the main cause of the clogs present in the Honduran plants. An inline strainer would still be recommended for future dosing systems, yet it should be noted that this won't eliminate the occurrence of clogsFor the first run, it appears that the orifice clogged after 2.4 hours. The clog was pushed through the orifice by a one cm increase in pressure. No other clogs were observed.