Summary:

.) Would you purchase an ultrasonic kit?

.) Kit quick sketch

.) Making (and holding) a bubble underwater is a hard problem

Would you purchase a kit?

My goal for the project was to have a system for exploring the Haber process, which I now have.

The specs and design files are in the repository, but the project isn't trivial. There's some expertise needed in assembling the electronics, designing and tuning the horn, and setting up the system. Also, a builder would have to make a PCB and purchase components in single quantity from several vendors.

I was wondering if there's any interest in a kit. I could purchase parts in batch quantities and parcel them out for people to assemble. The kit (listed below) would include a PCB, all components, a transducer, aluminum stock for a horn, and a pre-programmed Nano. The cost would be about $200, which is 4x the cost of materials.

This is not something I'm planning to do. Sales and marketing is tedious, and I'd much rather be doing experiments and building things.

...but if there's enough interest I might be convinced.

If you would probably purchase a kit 6 months from now for $200, please leave a response below. I'll decide based on the number of responses.

Kit quick sketch

A "quick sketch" of what I think would go into the kit. The specifics aren't important (to answer the question), it's just to get a feel for the amount of interest.

The kit would contain:

• A PCB
• All components
• A pre-programmed Arduino Nano
• The SMPS power transformer
• One transducer
• One 4" length of aluminum rod

The user would need to:

• Supply a project enclosure
• Supply a power supply
• Make mounting hardware (lasercut acrylic pieces)
• Turn the rod into a horn, depending on the application
• Assemble the PCB

As an alternate kit, levitation doesn't require a horn or tuning. A kit demonstrating ultrasonic levitation would include everything you need, including mounting hardware and power supply, for about the same price (4x the material cost.)

Making (and holding) a bubble underwater is a hard problem

Generating and holding bubbles underwater at the end of a tube is hard, due to the dynamics of surface tension.

Suppose you are holding a large bubble and a small bubble at the ends of a connected tube, by pinching the tubes shut.

Which of the following happens when you stop pinching the tubes and allow the pressure to equalize?

1. The large bubble gets smaller, the small one gets bigger
2. The large bubble gets bigger, the small one gets smaller
3. The bubbles stay the same

As it happens, the force due to surface tension is in inverse proportion to the radius, which means that the smaller bubble has a higher pressure (on the inside) than the bigger bubble. The small bubble will contract while the bigger one expands.

Next consider a tube immersed in water.

The small surface area across the end of the tube requires a high pressure to start a bubble.

If the volume of the tube is large relative to the volume of the bubble, then pushing out the bubble will not appreciably change the tube pressure. The tube air is effectively at constant pressure.

Since a bigger bubble requires less pressure, the constant pressure in the tube tends to overinflate the bubble, eventually causing it to break off and float away. If the pressure is high enough to start a bubble, it's high enough to inflate and eject a bubble.

So to hold a bubble at the end of a tube, you need to immediately back off on the pressure once the bubble starts to form. This is hard for a human, and pretty much impossible for a computer.

...so I need another method of generating and holding bubbles under water.

I've got some ideas to try.

Maybe I don't need to actually *hold* the bubble in place, maybe I can break off a bubble and let it float up into the cavitation focal point. Maybe I can "catch" the bubble on a plate or something. Maybe I can generate the bubble with the tube pointing down instead of up.

Yep - this is science. Keep trying things until you get something that works.

(Also, ordered syringe tips of various sizes to see if I can adjust the bubble size.)