Absurdly simple thermoacoustic-steam "rice" engine – What's going on here?

[Tom Booth]

What mainly got my curiosity going was this video you posted:

https://youtu.be/Lyhylj5kHjw

Looks as though the weight on the diaphragm is about to go through the ceiling!

So many times I've heard people comment that Stirling engines have no power or no torque, can be stopped with a feather, are impractical etc etc which is often observably true

Then I see something like that and wonder what caused that momentary surge of power?

Like the other day, I wish I had the recorder going at the time, but with the various modifications to a little "toy" Stirling and adjusting the timing, the thing was going like mad. I was sticking an ice cream stick into the spokes of the flywheel and that didn't stop it, or even slow it down much, then I got my finger in there by accident and the force with which the flywheel spoke hit my finger really hurt, I was like swearing out loud and shaking my finger,.. and again, the engine didn't miss a beat ..

Up until the displacer came loose.

Anyway, I think the "rice engine" looks like it could have some real potential.

The way I look at it, if an engine can complete three or four or more cycles with some given power output then IT IS completing a full cycle, which, then, in theory, should be sustainable.

But holding a can over a stove burner does not provide enough control to determine what the cause might have been.

Was it the induction type stove ? The distance from the burner? The amount of water? the temperature ? or the acoustic properties, etc. etc.

Without people getting curious about these things and doing a lot of experimenting, we may never know.

I worked in an engine repair shop nearly my whole lifetime since high school and have seen hundreds of IC engines that ran no better than a typical Stirling engine, but there is always a cause and it is "repairable".

A good running engine is a delicate balancing act of a multitude of different variables.

I think the only real advantage an IC engine has over a Stirling is people in the past have worked out all the details of what makes an IC engine run good.

Not as much attention has been given to Stirling engines, having been largely neglected for 200 years.

[Tom Booth]

One thing I think is irrefutable; that is not isothermal expansion.

Resize_20221011_172514_4257.jpg (72.19 KiB) Viewed 3488 times

That is, it seems clear from that image that the balloon is not expanding and lifting the weight, but the momentum of the weight is pulling and stretching the balloon.

[skyofcolorado]

Unfortunately, I don't have access to the full article, and I didn't find it on Sci-Hub. Still, what the abstract describes seems in line with what we're thinking.

It is very interesting..

[skyofcolorado]

The reference section on that paper is a gold mine for anyone researching thermoacoustics.

[tenbitcomb]

Incredible! Thanks for finding that and sharing!

The conclusion of the paper seems to be that a stack that absorbs water does reduce the required temperature difference and that capillary action helps the effect last longer by drawing more water into the stack.

Absorption seems like a minor yet significant effect given that the rice engine still seems to work with glass beads in place of rice. In the latest video by the rice engine guy, he mentioned he's been able to get the engine to run for up to an hour using the glass beads and making the cylinder longer so the temperature gradient is preserved. That's really awesome considering the original rice engine only runs for a handful of minutes, which is what I experienced, and improves the chance that the engine can have a practical purpose.

Yeah, that references section does look like a goldmine!

[Tom Booth]

Absorption seems like a minor yet significant effect given that the rice engine still seems to work with glass beads in place of rice. ...

I'm wondering about the size and shape of the beads vs. the rice.

Also the surface texture.

Somehow, given the speed at which the engine runs, I don't imagine there would be sufficient time for any significant water absorption in a given cycle. But there could be a considerable difference in surface area between the rice and beads, including on a microscopic scale, the glass beads would likely have a much smoother surface than the rice, which could possibly account for the difference.

[skyofcolorado]

I have some 3 angstrom zeolite pellets meant to adsorb water from a gas stream or liquid fuel. About the same form factor as rice. May have to try that. Being basically clay, they should be able to take whatever heat is present.

[Tom Booth]

I have some 3 angstrom zeolite pellets meant to adsorb water from a gas stream or liquid fuel. About the same form factor as rice. May have to try that. Being basically clay, they should be able to take whatever heat is present.

Seems like an excellent choice!

Has similar rice-like desiccant properties, but probably more-so. And relatively inexpensive. And unlike rice, which could get soggy or moldy, if it does absorb water to the point of saturation, it could be dried out in the sun and "reactivated".

[tenbitcomb]

Success! I got this engine to work and it's quite powerful!

https://www.youtube.com/watch?v=Rh4m8mrB2t8

I've found it pretty difficult to start, but once it starts it really goes. It also takes a considerable amount of heat to get going. I'll get to why I think that might be.

Based on what seems true from the literature, I changed some of the parameters of the engine:

- No regenerator stack
- Two cans combined
- Bottom can is the reservoir for the water
- Top can holds the rice and has a bottom with holes drilled in the bottom

Here are my observations:

- The rice is definitely the important part. I haven't tried glass beads or something else ideal yet, but the engine doesn't seem to work without rice. Copper scrubbers in place of the rice didn't work. I tried my idea of using calcium chloride beads and that didn't work, though it caused the diaphragm to pulse every time it precipitated, which was kind of interesting.
- A regenerator is not required, but it may be a good idea. The lack of a regenerator for the engine I made may be one explanation for why the engine struggles to start. I'm thinking maybe a regenerator can surround the outside of the hot end so that it doesn't get corroded by the water like in the original engine.
- The temperature of the "cold" end of the engine doesn't seem to matter that much. You'll notice in my video that I tried to cool the top section by wrapping a wet paper towel around it, and you can see it steaming. I don't really think that made a difference. I ran the engine before without it and it ran at the same intensity.
- The diaphragm somehow remains cool to the touch even when the rest of the top end of the engine is really hot. Latex doesn't conduct heat well to start with, so maybe it protects itself somewhat from the steel can it's attached to. Upon opening the engine after operation, the rice at the top is always cool. The rice not only buffers the cold end from the steam in the hot end but may also be responsible for the temperature gradient.
- Once the engine is running, it can run without building up too much pressure or exploding. In the video, the holes for the top and bottom cans were covered.

I also ran the engine without the diaphragm and pretty easily got it to generate a tone so long as I placed my hand over most of the open end.

https://www.youtube.com/watch?v=DfS4p7YpSeU

This thing seems to be sensitive to tuning, so maybe the engine will run better with the diaphragm if it's tuned for a higher/lower resonance. Without the diaphragm, I got it to generate a tone for a very long time.

[tenbitcomb]

Tom, I missed your message about observing visible water droplets in suspension. That's a really interesting idea. I don't see why it can't be done by at least making the resonator section out of glass. From what I can tell, there usually isn't much visible steam or "fog" above the rice, but sometimes there's a slight vapor condensation that can be seen when the diaphragm is removed after operation. That could be enough to go off of, but I'm sure adding particulate smoke could work so water molecules can grab on. I think this is something I want to try if I can figure out how to get the engine to run reliably. There's got to be something I'm not doing that's preventing the engine from starting. Might simply not be enough water in the reservoir, or the water needs to be added cold so that there's a flash of steam. Unlike the guy in the original video, I'm not injecting the water with a syringe.

I get your skepticism as to whether this is involving any sort of thermoacoustics. Anything I say is really just a guess, and I generally share said skepticism. Some sort of creation of a standing wave is my current hypothesis because that's just what it seems like. This engine either seems to want to run or not. When I've gotten it to run, I did notice a subtle vibration of the free piston (before I jostled it into full motion), but not long before that it didn't even come close to running. No false starts or anything. In the handful of times I've actually managed to get it to run, it was pretty much all or nothing. If there was something else initiating a Stirling cycle or thermal lag, my expectation would be some false starts. To be clear, I'm just guessing! You've been studying heat engines for much longer than I have, so what you think means something. I plan to read some more literature today because even though I *think* I understand this engine better, it's still very mysterious to me. The Stirling cycle clicks with me at this point, as does thermal acoustics and, to a lesser extent, thermal lag, but there's something especially weird about a steam engine that operates entirely sealed with that much heat input but no pressure overload.

[tenbitcomb]

Very nice! The engine does seem to need to be kicked off before it can be sustained with lower power. I've been able to keep mine running indefinitely with a mini butane torch lighter.

Also, I tried swapping out the rice with aquarium gravel and it works quite nicely. I think I'll be using that from now on.

https://www.petsmart.com/fish/decor-gra ... hod=Browse

My engine runs very nicely now. It turned out that the main thing preventing it from starting was the fact I was holding it. I don't have an induction cooktop so I've been mostly holding the engine over a flame, and the fact that I'm holding it affects the frequency it resonates at. It starts immediately once placed on a firm surface.

The size of the cans and the tautness of the balloon play a major role in terms of how easily the engine will start. I find the balloon needs to be kept very taut. I also had an easier time getting the engine to start with a can size similar to the one in the original videos (something like 8.5 cm by 11.3 cm). I'd be curious to try making a piston based variation because that could eliminate some of the variation caused by the balloon. That is if it can even start using a piston.

[Tom Booth]

Some astonishing developments! Really fantastic!

[Tom Booth]

Maybe someone can guess what I'm thinking.

I saw a YouTube video a long time ago, which for some reason, has since been made "private" but was linked to this article: https://www.northumbria.ac.uk/about-us/ ... e-on-mars/

A search for "Leidenfrost engine" however, will turn up a few similar videos. This one for example:

https://youtu.be/0vSPeKPP1T0


This inspired another discussion on the forum and some failed experiments:

viewtopic.php?f=1&t=2667

As previously noted, the video was removed. There wasn't much difference except that if I remember right, something was placed on top of the spinning drop of water, like another ring that was carried along and made to spin.

The point of the thread though was to find some liquid with a lower boiling/condensation temperature

I could not get that to work in any ordinary Stirling engine, but, of course, I was missing the aquarium gravel or whatever condensation medium.

On that thread "sockmonkey" made an insightful comment that might be applicable here:

"As I understand it, getting a phase change gets you more pressure, but it takes longer to change it back down to liquid without a proper condenser."

[Tom Booth]

A variation on the "cloud in a bottle" experiment:

https://youtu.be/msSVQ903T8k

I tried this experiment using some rubbing alcohol (And also a bit of smoke in the bottle).

I found that it was very easy to get a cloud, and the foot pump was not necessary at all Just putting the cap on and squeezing the bottle formed a cloud very easily, much easier and more effective than with water.

I'm not sure if the smoke was necessary, but obviously, the combination of a flammable liquid or fumes and open flame, at the same time, should be avoided.

[Tom Booth]

...but there's something especially weird about a steam engine that operates entirely sealed with that much heat input but no pressure overload.

Yes, it kind of goes contrary to a lot of published information about how heat engines are supposed to operate, by supposedly being heated and then COOLED, requiring a "sink" to remove the heat..

It has been my contention for years, that the cooling (or heat removal) is not needed. The heat is converted to mechanical "work" output, which seems obvious in a way but very weird and hard to think about or accept in another way.

Heat, though following certain general laws of mechanics, like a fluid, is not such; it is energy which may be converted into other forms of energy as it passes from a high to a low level. ... the heat is transformed in passing from hot to cold. If the process of heat transformation were absolutely perfect, no heat at all would arrive at the low level, since all of it would be converted into other forms of energy

- Nikola Tesla (1900)