Project

Prototype 1

Materials:

Acrylic tubing (circular)
water bucket[
one pump
two transducers
3D printed parts

Description

Prototype 2

Materials:

40kHz transducer
Acrylic square tubing ( OD: 1/2 in / ID: 0.37 in)
Electrical tape
Clear silicone waterproof sealant
water bucket
two pumps
Metalpiece
3D printed parts

Description:

Improvement from Prototype 1:
- Using square tubing so the ultrasoundwaves bounce straight back to the top to form standing waves.
- Using one 40kHz transducer with a metalpiece on the other side of the tube to reflect the soundwaves.
- two pumps for mixing up the water and making sure the MPs goes into the system instead of just floating on the surface.
- uses surfactants to reduce MP adhersion.
Observation:
- Transducer has minimal effect on the MPs.
- MPs tend to stick on the tubing, transducere reduce adhersion to some extent.
- MPs flow to the other end that splits to two pipes, with the top one going to polluted container and the other one going to the clean container.
Problem:
- Transducer is producing minimal effect for filtration; filtration in this system is done by buoyancy of MPs (keeping the MPs on the upperhalf of the tube to be filtered out by the upper end of the split) instead of transducers concentrating the MPs to nodes. Therefore we pass this prototype.

Challenges

Finding the Right Frequency

Different sizes of microplastics require different frequencies of standing waves. The smaller the size of the MPs, the higher frequency required. We need to test different frequencies for the 600 μm MPs we have to see which frequency can influence these MPs.

Limitations on Transducers

All transducers are limited to a certain range of frequencies. For the transducers typically found in the commercial market, they go up to about 40kHz. Previous studies concluded that for MPs the size of 486μm require a frequency of 1.58MHz to concentrate effectively. This means that we need to find special transducers for this project. We ended up buying a piezo ceramic disc and made the transducers ourselves because those high-frequency transducers are not commonly found in commerical markets but more in companies that provide customization services for university lab equipments.

Adhesion of MPs

Because polyethylene(PE), the type of MPs we used, is hydrophobic, they tend to stick together or stick onto the surface of the tubes. Therefore, we need a surfactant to make sure they flow smoothly with the water instead of clogging up the piping. The surfactant we used is soap. We dropped a few drops of dishsoap into the polluted water, and the adhersion problem seems to be reduced.

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