Number of strings for orifice area and water height

[MadelineGarell]

For an orifice area of 1cm^2 and a water height of 5cm and a flowrate of 10 microliters/s on 1 string we found that the number of strings needed is 614. And if there is 5mm spacing between strings arranged in a square grid, the side length of the reactor is 12cm.

[monroews]

Great! This suggests that we need to get 614 strings lined up in a way that allows a spray from a single stream of water to divide between them equally. We still have the option of using intermittent spraying if needed.

It would also be cool if the velocity through the orifice were high enough so that biofilms didn't grow. I don't know if that velocity is a number that is available in the literature.

You used a rather large orifice. Now use an orifice that is 5 mm in diameter. That will be a much smaller flow rate. But it is possible that a 5 mm diameter orifice with low head won't produce enough flow to create a good spray pattern when hitting a deflector. I suggest you experiment with this in the sink and see what flow rate and height is required to get a good spray pattern. I realize this is very subjective. This simple observation gives us a place to start and then we will need to build an apparatus where we can test some of these ideas.

[Emily-Wood]

We made a mistake on the original calculation from 6/5/19, so please ignore those numbers. Redoing the calculation with an orifice diameter of 5 mm, a flow rate of 10 microliters/seconds per string, and a water height of 15 cm (this height was experimentally determined to produce a better spray pattern than the original 5 cm height), a total number of 2087 strings would be needed. If the strings are arranged in a square with 5 mm spacing, the square would have a side length of 22.84 cm.

Using the laboratory faucet, a flow rate of 0.116 L/s with an orifice diameter of 4-5 mm on a thin PVC sheet produced a wide and even spray pattern that seems like it would work very well as a distribution system. This flow rate corresponds to 11,596 strings. If aligned in a square with 5 mm spacing, this square would have a side length of 53.8 cm long. This distance is reasonable, as the water spray from the sink easily reached this length.

Using the orifice equation with these numbers (Orifice diameter = 5 mm and total flow rate = 0.116 L/s for 11596 strings), the optimal water height would be 4.63 m. However, if you widen the orifice diameter to 1 cm, the optimal water height drops to 0.2894 m.

We decided to briefly test out this idea by gluing a PVC pipe to a small piece of PVC sheet and drilling a hole in the bottom, effectively making a tall bucket. With an 1 cm diameter orifice and a water height of 29 cm, the spray pattern was similar to that produce by the sink, but the water droplets were slightly less even in size and location. The experiment was not great as it was difficult to maintain the water height at 29 cm. Even so, these dimensions seemed to be a good baseline and starting point for future testing and refinement.

[monroews]

This is great. The 12,000 strings seems like a challenge. I suggest that one goal could be to see if you can get good spray of water using an even lower flow rate. Once you've found the lowest flow rate that can work (play with flow and with velocity by adjusting the fall height of the jet) then we might consider an intermittent flow of water to further reduce the minimum number of strings for one jet of water.