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

[Tom Booth]

So it has been demonstrated this engine will run on methanol, which has a boiling/condensation point about 60° lower than water (148.5).

What if we go with some liquid with a boiling point that is lower yet ?

What about some refrigerant type fluid with a boiling point at or below ambient ?

https://youtu.be/qTDtyFaAZy8

Methylene Chloride normally boils at about 103° F but as a saturated vapor under partial vacuum. Just body temperature is enough.

Getting closer.

A Christmas light has no piston or movable membrane, so the vapor has nowhere to expand to, but what if it did?

[Tom Booth]

A couple more videos I don't think we have seen here.

I was wondering if copper BB's (copper coated I think these days) would work for this.

https://youtu.be/qYkPTjfnawo

https://youtube.com/shorts/E9xB6XF9LPo?feature=share

[Tom Booth]

The comments associated with this video are interesting, saying that the engine can hold a large reservoir of water that acts as a heat battery and that it will run for several minutes ("3 to 5 minutes") after being removed from the heat.

https://youtu.be/FyvXBbuNc6g

[tibsim]

Since I have too much work to do and I don't know when I can try it, I'm sharing now this idea :

I'm moving from YouTube to Odysse:
https://odysee.com/@Tibsim:9

[tibsim]

[tibsim]

If you simply do not put water or alcohol in the "rice" machine, but rather a mixture of water and alcohol in a ratio of say 50-50%, then the water will work in the lower layer of the "rice" , and the alcohol in the upper one. Overall, the difference in temperature between the cold side and the hot side of the machine will be greater. What do you think?

[VincentG]

It seems to me that the main problem with these types of engines is that the delta T is not nearly fully realized by the working gas. So any attempt like this to fix that issue sounds like a good idea.

There might also be an interesting effect with the addition of a gas molecule of different size.

[tibsim]

Theoretically, the 96-4% water-ethanol mixture is the azeotropic mixture. When the alcohol and water do not separate during distillation, and they condense at the same temperature. So far I haven't found a table for it, about how things work for eg 50-50 mix ratio and the ChatGPT writes nonsense. I don't have access to any such tables...

[tibsim]

Hi VincentG! Our biggest problem is that we cannot build overpressure engine in the kitchen. Air is too rare at atmospheric pressure, and steam has too small a delta. The superheated steam is also at the same atmospheric pressure as atmospheric air. If we could increase the delta by using wet steam, it would be possible to improve it at atmospheric pressure. This can still only have a maximum efficiency of 6%...

[tibsim]

In theory, it might be possible to make a usable atmospheric pressure machine with acetone, but it is flammable and not very healthy, and you have to calculate with these... But I'm even dumber when it comes to chemistry...

[tibsim]

It could improve the steam thermoacoustic engine if we used a thinner piston (maybe with flywheel) instead of a diaphragm to achieve a greater compression difference (and delta-T)? Of course you have to try it, I'm just working so much lately that I don't have the opportunity... What do you think?

[Tom Booth]

Behind a paywall, but the "highlights" alone are worth some time spent reading and pondering:

"This demonstrates the promising potential of the evaporative Stirling engine for ultra-low-grade heat recovery."

A few snippets from the snippets: (Full PDF about $40)

Emphasis (bold text) added to passages of particular significance, IMO. Or skip straight to the source: https://www.sciencedirect.com/science/a ... 422300676X

Energy
Volume 273, 15 June 2023, 127282

Revisiting the evaporative Stirling engine: The mechanism and a case study via thermoacoustic theory

Rui Yang a, Junxiang Wang a b, Ercang Luo a b

Highlights...

Phase change reduces the temperature difference and increases the specific power of the engine.
...

Abstract
In this work, a new explanation on an old idea to enhance the Stirling engine, i.e., the evaporative (two-phase two-component) Stirling engine, has been provided through thermoacoustic theory. In such a system, the periodical evaporation and condensation of an evaporative species is incorporated into the classical Stirling cycle ....

The main reason for the improvement is the enhanced thermoacoustic conversion by the phase change of the evaporative species...

... This demonstrates the promising potential of the evaporative Stirling engine for ultra-low-grade heat recovery.

... there is an old idea to increase the specific power of the Stirling system: the evaporative Stirling engine... a two-component mixture as the working fluid, ...that undergoes reciprocating evaporation and condensation (such as water). During operation, the phase change of the evaporative species enhances the amplitudes of compression and expansion of the cycle, thus increases the specific output power of the engine...

This idea seems to be a result of serendipity. According to a personal communication mentioned in Walker and Agbi [3], Prof. W. Beale observed a significant increase in pressure amplitude after a few drops of water were added into a Stirling engine—The oscillation was so strong and became a catastrophe to the relatively fragile system. This enhancement was not expected, because he had meant to use the water for improving sealing. ...

...Iwasaki and Hirata [12] developed a small-scale Stirling engine with freon-air mixture as the working fluid. The engine was able to work with a temperature difference of only 85
, and the heat transfer coefficient at the wall of the heat exchanger could be improved by a factor of 10. ...

However, the evaporative Stirling engine has rarely been mentioned after 1990s due to the slow progress in experiments,...The main reason accounting for the standstill is the neglect of the role of the regenerator during the conversion. In the classical Stirling analysis, the regenerator is just a place to temporarily store heat, rather than where the energy conversion occurs. Understandably, following the classical Stirling engines, the metal-mesh screen was used in the evaporative engines as the regenerator [12], [13], [15]. However, the metal-mesh screen cannot sustain continuous evaporation/condensation from/onto the regenerator... Further, the condensed liquid might block the narrow and zigzag passages of the overlapped screens. Therefore, the improper choice of the regenerator forbade the evaporative engines to be efficient [12], [13], [15].
...

To date, the mechanism of the evaporative Stirling engine remains unclear, and the extent to which the Stirling engine can be enhanced by the phase change of an evaporative species has yet to be studied. Encouraged by the progress in the wet thermoacoustics and the essential similarities between thermoacoustic and Stirling cycles, herein, the almost forgotten idea of the evaporative Stirling engine has been revisited. ...

... Our results illustrate that the evaporative Stirling engine exhibits a high specific power while driven by a small temperature difference under a low mean pressure.

https://www.sciencedirect.com/science/a ... 422300676X

[Tom Booth]

It seems to me that the main problem with these types of engines is that the delta T is not nearly fully realized by the working gas. So any attempt like this to fix that issue sounds like a good idea.
...

Hi VincentG!

...and steam has too small a delta. The superheated steam is also at the same atmospheric pressure as atmospheric air. If we could increase the delta by using wet steam, it would be possible to improve it at atmospheric pressure. This can still only have a maximum efficiency of 6%...

I think you guys need to forget "Carnot efficiency".

This is a whole new ballgame IMO.

All the evidence indicates that these "wet" engines ACTUALLY DO produce MORE power at rediculously low temperature differentials. That is the nature of and the advantage of phase change. A HUGE expansion and contraction ratio by just going slightly above and slightly below the phase transition temperature.

This makes theoretical efficiency based on ∆T obsolete. Really obsolete, as if it wasn't all bogus in the first place.

[VincentG]

That was based on my misunderstanding of the cycle perhaps. I was only considering the "steam" as just being hot water vapor being used to warm the gas. If there is a phase change each cycle than sure the temperature doesn't matter so much. But is there any proof that is what's happening?

[Tom Booth]

That was based on my misunderstanding of the cycle perhaps. I was only considering the "steam" as just being hot water vapor being used to warm the gas. If there is a phase change each cycle than sure the temperature doesn't matter so much. But is there any proof that is what's happening?

That seems feasible.

I may be wrong, and I'm always happy to entertain as many different theories as possible.

Logically though, water when heated and transformed into steam expands, or increases in volume about 800 times. So, IMO, as soon as the steam begins to form it would almost immediately displace all the air.

Watching this video, the engine starts up almost immediately.

Has all the air been displaced that quickly? I'm not sure.

I suspect the engine may have already been heated previous to the start of the video. Almost immediately steam can be seen streaming from the pinhole, or both pinholes, sputtering like a teakettle. I think the engine was likely already hot and had been running before the start of the video. Just speculation, but I haven't ever seen a stove, or water reach a boil so quickly before.


https://youtu.be/Lyhylj5kHjw?si=DAIAPeYX2aJujbwG


As Sherlock Holmes would say: When you've eliminated all the other alternatives, whatever remains, must be the truth.

So, could the steam be used to warm a gas that is no longer there? IMO, it doesn't look like it to me. At least not by the time the engine reaches its full potential and is running wildly.

The more water squirted in, the more steam, the less air, the stronger the engine runs, until it's practically flying out of his hand.

So, if it IS an evaporation and condensation of steam and only steam, there is still the issue of what causes the cooling/condensation and contraction?

There are at least two theories to grapple with there as well.

As far as the question at hand, would a greater ∆T produce yet more power?

I suppose, maybe. But these "Rice Engines" display as much power as anything else I've ever seen to the point of the engine nearly flying apart and at a greatly reduced ∆T.

I just fail to see how an insufficient temperature difference constitutes an actual problem It seems more like a huge advantage. More power from lower grade heat. Even moreso if a fluid with a lower boiling point is used.