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The experimental setup accurately mimics the conditions in the non-linear dose controller without incorporating the additional hassles of a large stock tank, constant head tank and entrance tank. The water circulates through a peristaltic pump to a small one liter reservoir intended to steady the pulsing input from the pump. The reservoir is connected to a tee, which connects a pressure sensor to the system just before the orifice. Water then drips through the smallest orifice, 0.1 cm diameter, into another one liter reservoir. The reservoir is connected to the pump, creating a closed system. The pump will be set to pump water at the same rate as the water flows through the orifice to maintain steady-state operation. The experiment will first be run with deionized water as a control. Then it will be run with the maximum concentration of alum to be used in a plant, 125 g/L. As the experiment runs, Process Controller will record the pressure directly upstream of the orifice. If the orifice clogs, the pressure will increase significantly and Process Controller will turn off the pump to prevent any damage.
Results
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.
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 day but the most conclusive data was seen within the first hours. The pressure readings which pressure sensor 1, as seen in Figure 1, are shown in the Graph 2 below.
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
For 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.