Experimental Method for Limiting Parameters of Foam Formation from Water Jets

Surface foam is formed at the end of the rapid mix in AguaClara plants. It was observed in pilot plant (Here at Cornell) that the freefall of water jets from the LFOM resulted bubble formation due to aeration in the water. This experiment was set in order to study the relationship between the freefall jets and foam formation under different parameters.
Three parameters were investigated to study foam formation:
        1) Average velocity of jets (assuming the jets from the Orifices joined before hitting the surface of the water below the LFOM)

        2) Type of surface (the surface, which the jets hit, a plane or water)

        3) Length the water travels down the incline plane(jets after hitting incline plane)

For this experiment, dial soap mixed in water, a pump, a flow accumulator, a water tank and a water container were used in order to create water jets that similar to those found in the LFOM.

Figure: Setup testing parameters for foam formation

Testing for Three Limiting Parameters of Foam Formation from Water Jets

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.  

This experiment was videotaped to document it fully. A copy of the video it attached to this page.
Water Jets Parameters Experiment.mov

Results and Discussion

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. 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 and explained in the attached scientific paper: The entrainment of air by water jet impinging on a free surface by Wee King Soh et al. Therefore, when the water jet hit a solid smooth surface there was no foam formation.

In conclusion, the experiment affirmed that the velocity of the jet, its length, and the type of surface it impacts are all limiting parameters. Given the complexity of water jet fluid dynamics though it is recommended that all AguaClara switch to a non-linear chemical dose controller and thus eliminate the need for a retrofit design for the LFOM.