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The vertical column addressed the issue of feeding the lime but in order to improve the reactor's performance and address some hypotheses, the team built an additional apparatus with an upper slanted segment of 2" diameter instead of 1". By doubling the diameter of the tubing, the design reduces the upflow velocity in that segment by a factor of four. This allows for a lower capture velocity, which addresses the issue of lime being lost with the effluent and allows higher flow rates. Figures 2 and 3 depict the two apparatuses constructed by the Spring 2010 ANC Control Team.
Figure 3
Figure 2
The redesigned apparatus took the original apparatus and added a vertical 1" column by which lime is to be fed.
Figure 3
A second apparatus was built with an almost identical design, only 2" columns for the upper half of the apparatus were implemented.
Siphon Problem
In designing the new apparatuses, the team made the vertical column taller than the diagonal column to ensure that the former, which is open to the atmosphere, would not overflow when water was pumped through. However, the team discovered a problem when it began running experiments. At the end of the effluent tube, there is a candy-cane shaped piece that the water flows through which backs up the flow enough that the pH probe can be immersed (see Figure 4). This creates a free surface open to the atmosphere at the elevation of the sink. Basically, the only other free surface in the system exposed to atmospheric pressure is the water in the vertical feeding tube, which should be at a much higher elevation. This creates a siphon which drains the reactor to the elevation of the pH probe. (see Figure 5).
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