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In addition to these designs, we also tested for the three limiting parameters of foam formation from water jets.
Figure: Setup testing parameters for foam formation
For this experiment, dial soap mixed in water, pump, flow accumulator, water tank and water container were used in order to create water jets.
Three parameters were investigated to study foam formation:
1) Average velocity of jets
2) Type of surface
3) Length the water travels down the incline plane
The velocity of the jets in our experiment was increased by increasing the flow coming from the pump, which substituted for increasing the head in the actual plants. In the first run, the jets fall onto the accumulated water on the tank, then a plane was used to catch the water jets before falling into the tank. The plane was placed at different distances and angles to observe the change in bubble formation. You can find the summary of this experiment at the Experimental Method for Limiting Parameters of Foam Formation from Water Jets page
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 had discovered that a bucket inserted into the LFOM below the orifices could catch the jets before they hit the water, the bucket theory would 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. Also, we used MathCAD to determine the size of the orifice needed in the bottom of the bucket to maintain the plant flow rate. We determined that the orifice would have to have a 4.5cm radius, which was far too large for our buckets. The MathCAD calculations eliminated both the bucket theory and the bucket with a hole theory as possible solutions. The MathCAD files are attached.
(Please document equations used and summarize results obtained on the wiki as well)
Jet Distance Calcs 7-13-09.xmcd
CDC_Retrofit_Designs.xmcd
Testing
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. (You need to put this as a separate page and list separate experiments on different pages)
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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. (You need to compare it to the sizes in AguaClara plants as well as parameters in AguaClara plants)
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. (When explaining these results, how are these helpful to the dimensions in an AguaClara plant at 6". If they are helpful, talk about how you would scale this.)
The Vertical Plane and "Pipe within the LFOM" tests and results can be found at the vertical plane page and the "pipe within a pipe" page.
Results and Discussion
We We were able to document results for each variation of the designs visually with photographs and short movies on cameras, see the gallery below to view the photos.
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Testing for Three Limiting Parameters of Foam Formation from Water Jets
The experiment affirmed that the velocity of the jet, its length, and the type of surface it impacts are all limiting parameters. By observing the water jet at different flow rates it was determined that the length of the jet is dependent on the velocity of the jet. At low flow rates the length of the jet is shorter than at higher flow rates. As seen in Figure 1, the length of the jet refers to the part of the jet where the water surface is turbulence-free and thus appears smooth and transparent. It is when the surface of the jet becomes sufficiently turbulent that air is entrained as the symmetry of the jet breaks during free fall. When a jet hits the water surface a void forms in the water and from the tip of this void an air bubble is pinched off as demonstrated in the attached scientific paper: The entrainment of air by water jet impinging on a free surface. Therefore, when the water jet hit a solid smooth surface there was no foam formation.
Conclusions
Conclusions
At the end of all of our testing, we found that inserting a vertical plane into the LFOM would not effectively reduce the bubble formation enough to solve the problem. However, we did determine 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. This would translate to about a 10cm-diameter pipe in the AguaClara plant at Cuatro Comunidades. Hopefully this design change can be easily executed in the AguaClara plants in Honduras to fix the foam problem. (This only works for a 7.5" I.D. LFOM. You cannot make this conclusion for the AguaClara plant. What about the inclined plane? Does this work??)