ANC CONTROL

Design 2010

Introduction

The Spring 2010 ANC Control team inherited the original apparatus used by the Fall 2009 team. The original design of the apparatus was giraffe-like in shape, with two 1" pipes connected at a 45 degree angle. See Figure 1.

Figure 1

Spring 2010 Design

In order to address the initial failure hypotheses and provide an easy way to feed lime, the team chose to redesign the apparatus. By adding a vertical column to the top half of the reactor which is open to the atmosphere at the top, we can now simply pour lime in while the apparatus is running. Because the water in the upper vertical column is still, lime settles down and joins the fluidized bed in the lower segment.

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. See Figures 2 and 3 .
Figure 2depict the two apparatuses constructed by the Spring 2010 ANC Control Team.




Figure 3

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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