I wouldn’t have thought it was that low. I just saw a chinese patent for new linear motor… I probably should have looked at it. Apparently there is some other tech though. I don’t know how well this works with concentrated power with the standing waves in the TAEG.
Researchers have developed ultrathin polyacrylonitrile (PAN) nanofiber membranes that can convert ambient noise into significant levels of electrical energy, with a device generating up to 58 V and 12 µA under common noise conditions (117dB)
A small device (3x4 cm²) can generate a peak voltage output of 58 V under 117 dB sound (e.g., from a noisy workshop or traffic), which is sufficient to directly power commercial electronic devices like LEDs without needing pre-accumulation in a battery.
Enhanced Versions: Blending PAN with polyvinylidene fluoride (PVDF) in a single-layer membrane has produced even higher outputs, with peak voltages reaching over 94 V and a high energy conversion efficiency of 25.6%.
If I’m remembering right, 117 dB is 100 times the sound power of the OSHA 8 hour exposure limit. It may only be 10 times; I can’t remember if acoustic dB is based on sound pressure or sound power (it’s too late for serious thought). Pretty serious noise either way. 700 microwatts isn’t much power. It might light an LED, but it won’t be very bright. It’s interesting research, but it won’t charge your flashlight.
Speakers convert current in the voice coil into mechanical motion with pretty good efficiency. Moving air with the speaker cone has low efficiency, in part because the pressure wave goes everywhere, the mass of air being moved is very low compared to speaker coil. It’s like pushing on a string.
Stirling engines, including thermoacoustic ones… have high pressure gas in them so that the mass of the working gas in a given volume is much higher that standard air pressure and that makes pushing it around more efficient. The gas itself is confined to the engine vessel so the pressure waves never escape and with proper tuning they don’t fight themselves.
The whole idea of thermoacoustic generators is that the pressure waves remain coherent (lined up) and the pressure wave is tuned, like an organ pipe, so that its wave length lines up with the physical dimensions of the engine. That causes certain parts of the pressure wave to stay in the same physical place, a so called “standing wave”, and both simplifies the engine and allows the engine to better extract power.
To give an instinct… most stirling engines have two mechanisms operating: one piston to shuttle gas between hot and cold and one piston to extract work (power) from overall expansion and contraction of the working gas. A thermoacoustic stirling engine uses the properties of a standing wave to shuttle gases around and so it can get away with just one pistol, the piston that extracts power.
It is also reversible similar to stirling, so you can input power and get a hot and cold effect.
The pressure which is increased is another reason why they like to use speakers as they are sealed already.
in the super high efficiency ones they use helium as the gas, which is expensive. I wonder what the efficiency loss is with say with argon which is another (more or less) unreactive noble gas and is cheaper.
The highest efficiency gas is hydrogen, then helium and then I suppose argon. It’s the mass per molecule of gas that counts. Hydrogen has a mess of practical problems but scientifically it’s the best.
They were using helium because it is a noble gas, thus inert( technically slightly reactive) plus it is a light molecule. Helium and Argon are the next two noble gases… you could have like nitrogen,oxygen, flourine and chlorine that are lighter then argon.
I thought they told me I could get argon at airgas. but I can get oxygen and helium there as well.
Helium is not a problem. It is readily available on the market as helium for fancy baloons filling. The price is quite different per volume and packaging/pressure, but on average the price is around $100 per cubic meter. Which is not very much comparing to the rest of the engine and price of the electricity generated
Nitrogen bonds to itself… so that’s double the mass; same with oxygen, fluorine and chlorine. At least Nitrogen (N2) is super inert, but Argon is even better. Helium should be relatively easy to get too but the party store stuff is not pure at all. Regardless… it leaks slowly through steel.
I would be shocked if Airgas didn’t have argon. They chill regular atmospheric air to liquidify most of it and pull out the parts which includes a decent amount of argon. If they have nitrogen and oxygen from that process… they will have argon. Plus it’s a common welding gas…
I guess it doesnt matter helium isnt as expensive as it was the last time I looked which was like 10 years ago. It is only marginally more then argon as near as I can tell. However, the tanks are expensive as always. I was really just planning on using compressed air because that is cheaper.
Airgas has pretty much everything because they supply industry, medical and research. They have 5 grades of helium. and high pressure, low pressure and liquid (I guess you use it to supercool magnets for like MRI’s.)
If you use air, be careful with any lubricants. Compressed air allows for combustion of extremely “lean” fuel mixtures, even stray oil or dry graphite. Compressed nitrogen is safer on that score.
There is a diagram of efficiency dependency on gas composition in the second paper I have posted here eralier. It shows that even 80% helium has double efficiency than pure argon. I read another study comparing different gases. Air and its components work quite the same way.
See that in the paper. Low projected efficiencies regardless but helium is MUCH better. Interesting.
Maybe the high cycle frequencies that acoustic Stirling engines allow make them more sensitive to the working gas characteristics. I don’t recall the penalty for argon/nitrogen/air being as high for traditional stirling engines. The paper basically says use helium or quit. Chart below from that paper shows efficiencies at two levels of working gas pressure based on gas mix. Related 2MPa is ~20 atmospheres or ~300PSI. 3Pa is 50% higher of course. Non-trivial pressures for steel especially on that hot side! And efficiency goes up sharply with pressure.
The mole fraction portion is 100% argon at 0 and 100% helium at 1.
with a constant drive ratio of .04. which is a little confusing because the drive ratio at .06 the efficiency jumped from like 3.8 to 5.5 at 3 mpa according to figure 6.
Then their assumption is that the speed of sound is the ideal speed because it would carry the most energy. They say a low prandt number is the best, then they say plus the highest speed of sound is the most efficient, and the lowest prandt number is around .7 moles according to Figure 10 and the 100% of either gas has the highest prandt number. Then they say the speed makes up for high prandt number because of the speed of sound is faster in helium.
It reminds me of the high rpm vs low rpm engine debates for HP to some extent. And turbines had issues because we didn’t have bearings that could handle the higher rpms.
They are also saying thermal efficiency which isn’t the same as Carnot efficiency.
It is an interesting paper and the information is useful, I just don’t think it is the whole picture.
What I do see as a main drawback of TAEG is a fact that most of losses are caused by internal irreversibilities which are not convertible into usefull work.
E.g. even very poorly working steam turbine could supply exhaust steam into steam condensing heater and thus recover most of the heat addes to the cycle. ICE could do the same with block cooling and exhaust heat recovery.
Even if your fuel(wood) is virtually of zero price, one should not destroy energy in such a useless way.
Keep going. take your condensing heater, you are just removing heat, now where does that heat go? How do you get rid of that heat? Can you make something useful with it? What technology works with low-grade heat to remove it from a system by converting it to another form of energy?
Oh, I never think about such big thing like a power station and district heating. I always considered utility for family house or small company or workshop.
That is fair. I wasn’t looking to replace a generator. I originally looked at it as a way too cool the attic in the summer about 20 years ago. The attic gets hot and pushes the heat down through the house.
