Thermoacoustic electric generation at high frequency?

The goal: cheap, easy(ish) electricity.

The power source: concentrated sunlight or fire.

The question: Has anyone here made them self one of these? :
a thermoacoustic electric generator which runs at high frequency.

I'm not talking about a sterling engine at least not exactly. Rather I'm looking to make something that resonates much faster and could be harnessed with a voicecoil or a piezo electric transducer. This has been done by grad students and researchers but I haven't seen any built by the DIY crowd.
There are some startups around who tout this method because it is more efficient than a sterling engine and easier to build because there are essentially no moving parts or sliding seals.

The higher frequency seems to be the tipping point in efficiency because there is less gas moving but moving with the same energy:
"Minimizing the flow velocity of the gas overcomes viscous losses inside the regenerator, whose tiny pores allow heat to move between gas and solid most efficiently." http://www.americanscientist.org/issues/feature/the-power-of-sound/5

I'm thinking of making something with common materials: a loop of steel pipe and speakers or a bunch of piezo buzzers and a bike tire valve to add compressed air (for higher frequency oscillation).

Can anyone lend the voice of experience for us?

Here's some reference material:
In greater depth: http://www.americanscientist.org/issues/feature/the-power-of-sound/

And there's a good explanatory video out of Europe but I can't find it now.

Key words for 'bots: TAPEC ECN TAP (Thermo Acoustic power) SCORE (Stove for Cooking,
Refrigeration and Electricity)

drewyou4 years ago
Hi All, Yes I have built several of these. I don't yet have an instructable for it but I have a couple of videos up. I am planning on making an instructable but won't have time for a bit. The engine I made is a traveling wave type thermoacoustic engine. Theoretically this can be much more efficient than a standing wave engine. The design is based on Ivan Rodriguez's thesis. I have also made a symmetrical, double heat exchanger engine which operates at a lower heat difference. They are both made out of standard copper plumbing fittings. There are a couple specialty items. small mesh copper screen, and a short section of mild steel tube (electrical conduit that has had the galvanized coating removed. The device uses a piezo microphone to generate a current. Not much, One has to build a pressure vessel system and design heat exchangers carefully to produce viable power density. The videos of my designs are here:




This last one shows the inside parts. Not much at all to these machines, but they can be a little tricky. Took me a year or so of tinkering to understand them. Good luck.
adrian874 years ago
If you want easy(ish) electricity generation, I wouldn't recommend this type of project. I have a B.S. in physics and think this type of device is a little intimidating to build. While it looks pretty simple in terms of the material requirements (tube, cotton ball or glass mesh, cotton mesh, piezo element) and it doesn't have moving parts, the principles of operation are based on resonance which requires relatively precise cutting/position of the pieces to maximize efficiency.

If you don't mind reading a few technical papers though, just search on Google Scholar for Orest Symko. He is a professor at University of Utah, I had a chance to meet him once at a physics club regional meeting. He's been working on this type of electrical generator for over a decade and came up with a fairly practical mid-audio to ultrasonic version that can be made for cheap and can produce 1W+ of power from a cigarette lighter heating one end of the engine. I have yet to figure out the exact engineering specs of his device though, and that's the "catch" of this. I'll have to go through a few calculations based on the experimental data he provides in his patents - surprisingly enough, he's quite forthcoming about several optimizing strategies and particular materials he used that wouldn't be critical to getting the patent accepted, so much of the specifics are already there. It's just the dimensions that aren't mentioned, and a few other things like the technique for fabricating 2-piece piezo elements with the brass shim. Maybe one day I'll get around to making my own, but as of yet I haven't seen anyone else post the specifics of engineering one of these that would actually be helpful in construction - just lots of physics windbags talking about how to optimize the design.
snotty (author)  adrian874 years ago

Thank your for these insights! I agree there are all sorts of windbags :)

Regarding optimization though, while I agree efficiency is nice, many of my friends have wood stoves that generate zero electricity. When you're off-grid sometimes something is better than nothing :)

Please keep us posted as you experiment.

Best wishes
gabdab4 years ago
much later on ..
I am interested in thermoacoustic refrigeration as a diyer as well and thinking about checking for some patents .
I am not aware of any 'instructable' available for this topic today.