ANC CONTROL

Design 2010

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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

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Spring 2010

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Design

In order to address the Hypothesis and also to increase the ease with which the lime is fedinitial 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 apparatus, the operator now has access to simply pour the lime in. As the lime travels down the vertical column, the particles will settle in the lower part of the apparatus and/or flow into the diagonal piece, but then settle out before leaving in the effluentthe 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 address the other improve the reactor's performance and address some hypotheses, the team decided to build two apparatuses: one with all 1" tubes, one with 1" vertical columns and 2" diagonal tubingbuilt an additional apparatus with an upper slanted segment of 2" diameter instead of 1". By doubling the diameter of the tubing, it divided the flow rate through the diagonal portion by the design reduces the upflow velocity in that segment by a factor of four. This allowed allows for a lower capture velocity, which attempts to address addresses the issue of lime being lost out with the effluent and allows higher flow rates. See Figures 2 and 3.

Figure 2

Figure 3

Siphon Problem

In designing the new apparatuses, the team made the vertical column taller than the diagonal column to ensure that water would flow out the diagonal column. It was determined that the head loss through the fixtures at the end of the diagonal column would be negligible. However, when the team began running experiments a problem was discoveredthe 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 was is a candy-cane shaped piece that the water flowed through - this was in order to have the water pass over flows through which backs up the flow enough that the pH probe properly can be immersed (see Figure 4). However, because this resulted in a dip of the height of the water, and the water filled up the tube, the atmospheric pressure at the top of the water in the tube forced the water in the vertical column to drop to its same height 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).

Figure 4

Figure 5

The team attempted to correct this problem by sealing the top of the vertical column with a cap. This would result in It was hoped that this would create a vacuum in above the area about the water level and would allow the water in the column to remain vertical column and hold that surface at a constant height elevation (see Figure 6). However, it was not possible to fully seal the cap and having an open vertical column to pour lime directly into was part of the design's attractivenessthe cap would not seal well enough to solve the problem, and the solution meant that the reactor would be drained each time the cap was removed for lime feeding.

Figure 6

The team instead chose to alter

Instead, the team altered the design by opening the very top of the diagonal column to atmospheric pressure. Doing so allowed for open channel flow in the tube and allowed the height of the water in the vertical column to remain constant, matching the height of the water level in the diagonal column. (See Figure 7)

Figure 7