cloak.toggle.exclusive=false

It was recently noticed by our team that after the loading state had switched to the settling state, a slow but seemingly never-ending recirculation of particles was occurring in the settling column. This recirculation is affecting our settling data, and maybe the important clue into why we haven't been seeing "great" settling curves as we would have expected in our results. To rid our setup of this recirculation problem will give us more accurate results.

It was hypothesized that this could have been a result of the elbow connections, the change in diameter tubing from the flocculator to the settling column, the valve shutoff, upflow versus downflow through the column, heat induced currents from the turbidimeter lamp, or the abrupt stopping of the pumps in the transition of states. All of these ideas were put to the test in simple visual experiments.

Several visual experiments were conducted to determine what the actual cause of the reciruclation was from. First, we conducted experiments changing the pump control shutoff, then we experimented with the changing diameter of the elbow to the column, and lastly, we experimented with the heat factor.

First, the pump control shutoff was removed from the beginning of the settle state to a new state before settle state. This allowed for the pumps to be shutoff seconds before the valves were shutoff. Different times between the two shutoff points were experimented with, but each time, at the time of the valve shutoff, a jerk in motion would seem to cause a recirculation in flow. Perhaps we need to not shutoff the valve in order to prevent this recirculation.

Monroe programmed a new variable in Process Controller to ramp down the pump controls to zero instead of abruptly switching from a high pump control value to zero (shutoff) automatically. We installed this ramp down function in Process Controller and tested it on our apparatus. The ramp down would bring the flow down to an easier flow. We tried this new function with both a downward flowing and upward flowing column to detect any differences.

After careful observation, it was concluded that the recirculation was occurring even without the valve shutoff (about 20-30 seconds into settling state) and it maybe from either the pump shutoff causing a "push/pull" in the water (even though the pump is being ramped down, there is still a slight pressure change when the pump is completely shutoff) or from the diameter change from the flocculator tube to the settling column causing eddies of turbulence in the top of the column.

Another possible source of recirculation in the settling column is the elbow connections. The settling column is bounded by both an elbow connection coming into the column and going out of the column. Not only do these connections cause a sharp turn in flow, but there is a diameter change between the elbow and the column. The change in diameter could be causing preferential flow in the column, therefore, a recirculation current.

In order to alleviate the possibility of recirculation due to the change in diameters, a bunch of plastic drinking straws were cut to 2.5 inches and placed in the upper portion of the settling column where the column attaches to the elbow connection. This, the team thought, would help to reduce the preferential flow pattern that could be caused by the change in diameter. After placing the straws into the settling column, we observed that the recirculation currents were reduced. It is important to note for the next experiment that the majority of these elbow experiments were conducted with the settling column outside the turbidimeter.

Next, it was hypothesized that the heat produced from the IR lightbulb in the turbidimeter may be causing the recirculation. Comparison experiments were conducted with the settling column outside the turbidimeter, where heat from the lamp would not be an issue, and inside the turbidimeter, where the heat could have an affect on the column. When the column was placed outside the turbidimeter, no recirculation was occurring. However, experiment conducted when the column was inside the turbidimeter, recirculation currents were clearly visible.

In order to ensure that heat may be the determining factor, the team wanted to test whether another type of heat source would cause recirculation. The settling column was placed outside the turbidimeter but when the experiment came to the settling state, a team member wrapped their hand around one part of the column to provide a heat source. Once again, recirculation was visible and the team determined that heat was definitely the major contributing source to recirculation in the settling column.

While the recirculation problem in the settling column was finally treated by removing the heat source from the column, the team believes that the problem could have been caused by several different sources and the culmination of all of these experiments probably helped in solving the recirculation currents.

To remove the heat source, the team is working with HF Scientific to replace the IR lamp with a non-heat producing LED lamp. Additionally, the team has replaced the elbow connections with straight connections. In order to be able to use these straight connections, the team needs to figure out a way to stop the flow traveling into the settling column after the settle state has begun, in order to prevent watching the settling of a long vertical tube besides just the sample in the settling column. By introducing a slanted tube with a simple trap before the tube inlet, the team has managed to collect settling flocs from the top of the board during no-flow state.

Also, the team will determine whether or not the straws are helping to reduce the recirculation problem even after the straight connections have been added and the heat source is removed, or if they are unnecessary.