Experimental Method for Retrofit Designs

Once our team figured out the cause of the foam forming in AguaClara plants in operation in Honduras (put link citing causes), we set about designing retrofits for these plants. Our team came up with four different designs to test:
-the "pipe within the LFOM"
-the vertical/inclined plane
-the "teacup" theory, using an overflowing bucket to catch the falling water
-a variation on the teacup theory, using a bucket with an orifice in the bottom

See the retrofit designs page for visuals of each theory.

Our first goal was to narrow down from 4 different designs to our top choice to facilitate and expedite lab testing.

Calculations

As a team, we worked in MathCAD to calculate the distance that the jets of water coming into the LFOM would travel inside the LFOM. If we discover that a bucket inserted into the LFOM below the orifices can catch the jets before they hit the water, the bucket theory will be a viable option. We determined that all but the top three jets of water would in fact hit the far wall of the LFOM before reaching any size bucket that we could place in the LFOM. This eliminated both the teacup theory and the variation on that theory as possible solutions. The MathCAD file is attached. (what was the purpose of doing this?)

After eliminating both bucket theories, we decided that testing the last two designs in a lab would not be difficult and would give more realistic, tangible results than our calculations.

Testing

We used the pilot plant to test our retrofit design in an environment that replicated the actual plants as closely as possible. We set the flow rate of the pilot plant at about 150L/min, which, coupled with the 7.5cm-diameter LFOM, would be roughly comparable to the 400L/min, 15cm diameter LFOM in the plant at Cuatro Comunidades.

The first design we tested was the vertical/inclined plane. We used a 5cm-wide, 60cm-long steel plate to test the effectiveness of this plan to reduce water aeration. We were looking at the amount of bubbles formed under the LFOM to determine results, and documented them photographically.

Next, we used various-sized pipes inserted within the LFOM to test the "pipe within the LFOM" theory. First, we tested a 3cm-diameter pipe by inserting it vertically into the 7.5cm-inner diameter LFOM. Second, we tested a 5cm pipe, and noticed that it produced a reduction of bubbles. After leaving the 5cm pipe in the LFOM for 5 minutes to ensure no overflow, we moved to test the 6cm pipe. This pipe also showed signs of reducing the amount of bubbles, so we left it in for 5 minutes as well to determine if it would overflow, which it eventually did.

Results and Discussion

Vertical/Incline Planes

Unfortunately, we determined visually that there was very little, if any, change in the amount of bubbles formed before and after inserting the steel plate into the LFOM. Even at various angles of inclination, the amount of bubbles formed was the same. We believe it was ineffective for two reasons. First, the spread of orifices wraps around the pipe far enough that the jets of water at the edge do not touch the steel plate. Second, the water jets are flowing fast enough that the water simply ricochets off the steel plate, instead of running down the plate as intended. See the gallery of photos below for photos illustrating our results.

"Pipe within the LFOM"

With our initial test of the 3cm pipe, there was no noticeable change in the amount of bubbles formed under the LFOM. For the 5cm-diameter pipe we found a drastic reduction in the amount of bubbles formed under the LFOM. Keeping the pipe in for 5 minutes showed no signs of overflowing the LFOM or even raising the water level, so we can assume that 5cm is a possible solution. Finally, we tested a 6cm pipe for 5 minutes in the LFOM. We noticed that the water level outside the LFOM rose slowly throughout the 5 minutes until the water flowed over the top of the LFOM. This clearly meant that the 6cm pipe was too big, and was causing a backup of water within the LFOM. (attach mathcad sheet here)

We were able to document results for each variation of the designs visually with photographs and short movies on cameras.

At the end of all of our testing, we determined that inserting a 5cm-diameter pipe would effectively reduce the amount of bubbles produced by the LFOM, while not constricting the overall plant flow rate.