Stirlingengineforum.com

I think this is one of the most telling videos.


https://youtu.be/ugk819GQ6Z0?si=IXwV5F6J_eumSuFS


There was a lot of debate earlier. Would conducting heat away faster in the condensation section (with the rice or beads or pebbles or whatever) help the engine to run better.

Of course, I was arguing that the heatt is "removed" as a result of conversion to Work, so no, using a copper tube instead of a tin can would just take away the heat the engine needs to run. Better to do the opposite and make the condensation chamber out of ceramic or PVC pipe or something non-heat conducting.

In the above TNT video he does just that, and the engine is able to start and run with less heat input.

He also tries using a fluid with a lower phase change temperature, and so runs the engine on the heat from just some hot water.

When a theory can lead to some predicted experimental results and the outcome of the experiment is positive, that tends to lend credence to the theory.

If different fluids with different phase change temperatures are used, the engine runs near to that temperature.

What might constitute "proof" I don't know. But IMO the preponderance of evidence seems to support the phase change / evaporation, condensation theory

In this video be suggests that by using copper bb's instead of glass beads he has improved or increased cooling efficiency.


https://youtu.be/qYkPTjfnawo?si=8mK1M49S45dr2OuW


I don't really see a clear before/after comparison as with the TNT video where using a ceramic cylinder pretty clearly leads to a more efficient engine able to run with less heat input.

I think we can all be guilty at times of trying to promote or advance our own "pet theories" and loose objectivity, tending to see what we want to see.

Another thing that occurs to me, which I have found rather perplexing, that I think also favors the phase change theory, is the fact that what would normally constitute enormous volumes of "dead air space" in these "wet' engines seems to have no detrimental influence.

People seem to be able to build these engines as big as they care to, stacking empty cans one on top of the other.

Normal atmospheric air does not have the expansion and contraction ratio or capability where someone could simply add on an extra soup can of AIR volume and expect that the engine would still run.

There is no problem with "dead air space" in these engines, because there is no longer any air!

The air has been entirely displaced by phase change fluid, steam or alcohol vapors or whatever is used. It almost seems as though the more volume the better, doubling the volume only amounts to another drop of water, more or less that needs to undergo phase change. Stacking up cans on top of cans in such a way would be fatal to the operation of any normal "hot air" engine.

The original "rice engine" had everything closely compacted in one can:


https://youtu.be/WwvOM8Sfzts


Later versions add a spacer in the bottom to keep the steel wool out of the water, then a second can is added, and then even a third entirely empty can.

But listen and follow carefully what he says in this video:


https://youtu.be/IEPiTa9XJAw?si=QqdQddgrRTE6YInX


With the taller engine, with only one pinhole near the bottom he got inconsistent performance due to varying amounts of air trapped in the upper chambers.

When he made another pinhole in the top so the rising steam could escape out the top and displace ALL the air in all the chambers, the taller engine ran great and consistently and even became self starting.

If that isn't "proof" I don't know what is.

tenbitcomb wrote: ↑Sun Oct 23, 2022 9:49 am I had some modest success with a diaphragm made of parchment paper. Sounds just like a two-stroke!

https://www.youtube.com/watch?v=T_-j91E6CCQ

This is very interesting for a couple of reasons.

1. Parchment paper is very fragile and easily torn. Remarkable how such rapid and forceful pressure variations stop short of tearing the paper.

2. Parchment paper has no (or very negligible, if any at all) elasticity.

So, the stretching of the rubber "piston" when using a balloon, likely, has little or no influence in "compressing" or helping to compress the working fluid (saturated vapor?).

This is similar to a Stirling engine operating "without a flywheel", so there is no stored energy in an external revolving mass to put energy back in to "compress" the gas or in this case water vapor. It is oscillating, or expanding and contracting "on its own" so to speak.

Again, parchment has no elasticity, yet it works for this application, so, perhaps the balloon could be replaced by something like a somewhat loose fitting but non-elastic rubberized tarp or relatively inelastic rubber roll roofing material.

Also interesting from the previous video, the force and/or power of these engines is controllable by the proportion of water vapor to air, or the ratio of water vapor to air.

The higher the percentage of pure "saturated vapor" the more complete the condensation/contraction, evaporation/expansion so the more rapid and violent the response, to the point of potential catastrophic failure.

A couple things I think can be concluded from these "facts"? If true.

We are probably not limited to using small balloons but could make larger engines based on the evaporation/condensation of a saturated vapor using other covering materials. Perhaps even something like kitchen plastic wrap draped almost loosely over a coffee can.

Or, Super-Size-It using an open top 55 gallon drum covered with a thin plastic tarp.

In essence I think the saturated vapor as working fluid is similar to a self contained undulating blob of jelly. The oscillations are self limiting, so the parchment paper, or even what would normally be a very weak and fragile balloon can be used as a power piston without rupturing.

BTW, I was mistaken regarding the 800:1 expansion ratio. I think that is the expansion ratio of liquid air.

Water is a little more than double that. 1700:1

I think in essence this is the same thing as cavitation but since it is a saturated vapor there is no surrounding medium.

This is a slow motion video of cavitation bubbles appearing and disappearing. They are being formed by simply hitting a tube filled with water with a hammer.


https://youtu.be/00yPu18B39I?si=yzQPb6z2hgQ2vp6f


Anyway, if we can understand the phenomena, it can be controlled and possibly made useful or even scaled up a bit.

Though really, it need not be scaled up much if at all, possibly it could even be scaled down. Something like a very small but powerful pocket generator.

Or maybe a solar powered generator 55 gallon drum size to power a home.

This is interesting.

I was just discussing this with my wife and she asked about the parchment paper, what is it anyway?

I had no idea really. So I looked it up:

What is Parchment Paper?

Parchment paper is essentially paper that's been coated in a layer of silicone, which is what gives it its superb nonstick quality. The silicone coating also makes it heat-resistant as well as water-resistant. In addition, it helps to regulate temperature and ensure even heating during baking.

https://www.foodnetwork.com/recipes/pac ... -paper-101

Well that's something I didn't know.

Basically a very thin silicone oven mat on a paper or cotton fiber substrate.

Maybe a bit tougher and a little more elastic than I thought. Usually I only see it after it comes out of the oven with some cookies. By then it is quite brittle.

I have a suspicion.

laser-induced cavitation bubbles can grow up to several millimeters in diameter and last for several hundreds of microseconds

https://opg.optica.org/oe/fulltext.cfm? ... &id=431250

Well, what's "several" exactly ?

...this device can generate oscillating cavitation bubbles up to a maximum radius of 14 mm by adjusting the available discharge energy

https://pubs.aip.org/aip/rsi/article-ab ... ion-bubble


So, let's say that a drop or molecule or whatever of water vapor has a maximum "reach" or capacity for expansion and contraction of about 14 millimeters (or slightly more than 1/2 inch) maximum.


This seems to corelate with the size of the glass beads, aquarium pebbles or whatever people have generally found to work effectively as condensation medium.

So my thought is, this process of expansion and contraction or condensation and evaporation is not happening at the bottom of the can where heat is applied. That is just the initial source of water vapor to fill the can and fill the voids between all the beads or pebbles or rice granules or whatever.

So the expansion or "cavitation bubbles" need no more than about 1/2 inch of space to do their thing.

Likely, in these engines the "bubble" size is considerably less than the maximum for electrically induced bubbles, but that isn't particularly relevant to the theory.

In other words, the condensing water vapor likely does not need to accumulate and drip back down to the bottom to again evaporate.

I think this is more a pressure induced phenomenon.

There is a "cloud" of water vapor in the spaces or voids between all the pebbles or beads. The vapor needs something within its "reach" or close proximity on which to condense and from which it can then evaporate, maybe 10X/second.

There isn't time for water to accumulate and drip back down to the bottom. These "cavitation bubbles" are forming in a kind of cloud or matrix in the spaces between the pebbles. Only, there are no actual "bubbles" as this is taking place within a virtual vacuum or saturated vapor

What a "saturated vapor" means is that the vapor pressure and liquid water are at an equilibrium so that condensation is just as likely as evaporation.

It therefore only takes a very slight change in temperature and/or pressure to tip the scale one way or the other or both in a continuous oscillation.

Now I'm wondering if,... and thinking I might like to try building, one of these "rice engines" with the top can turned sideways and driving a flywheel with a generator.

Mostly because it's next to impossible to find any kind of affordable linear generator, whereas rotating generators and alternators are plentiful and cheap.

Maybe something like this:


I'm not even sure it is necessary to have the boiler section upright or vertical, but seems the most sensible and expedient arrangement at the moment

Alternatively the piston could also be left upright with some kind of walking beam type arrangement to drive the flywheel/generator.

But mostly I'm just wondering about the dynamics of the expansion and contraction.

Could it drive a flywheel at all?

Most "free piston" or thermoacoustic type linear engines will run with or without a flywheel. Somehow the expansion and contraction cycle adjusts to the circumstances and the load.

I suspect it would be the same with one of these "rice" engines, though AFAIK it hasn't been tried as yet.

55 gallon drum over a campfire version:

I searched through the thread as well as the whole message board and it seems this is a fairly recent video that was not previously posted, though watching it, I recognize parts I've seen before, so I believe it is a compilation of previous video highlights, put together to make a new video:

https://youtu.be/696hUdcrDMQ?si=ZkXvXyQNRzewgjYX

Interesting that with the ceramic section in the middle the engine doesn't need a pin hole as a pressure release valve and is also self starting.

He says he will be adding a linear generator and making another video. The above video was 5 months ago, according to the heading data, so perhaps that has already been posted, so I'll have a look.

Looks like the generator video was already posted here a year ago, link to earlier post:

viewtopic.php?p=18440#p18440

Generally speaking, pretty much all accounts or theories assume either some kind of "thermoacoustic" process or if a condensation/evaporation cycle is admitted the theory is that the condensation medium acts as a kind of regenerator to absorb heat to cool the working fluid, heat being transfered to the outer walls and to the air.

The fact that a ceramic section seems to improve performance, allowing the engine to run without a relief valve to let out excess hot steam and become self Starting seems to contradict the cooling condensation medium theory.

Another fact that seems to contradict the idea that the medium needs to absorb heat or be cold and able to transfer heat or have a high heat capacity, is that this is a "rice" engine.

The original, and arguably best condensation medium is rice. At least it works, and works well.

I don't believe rice has any great heat absorbing capacity or heat conductivity or heat transfer capabilities.

IMO it would be preferable that the condensation material be something non-heat conducting. Glass beads are known to work and glass is not highly heat conductive. Perhaps plastic or ceramic would work effectively.

IMO the temperature difference is, and should be due to the pressure alterations and energy transfer to work output rather than heat transfer to the outside ambient "sink".

Anyway, I'm trying to wrap up some rather pressing home improvement type projects that have been occupying most of my time of late, so may be able to carry out some, or all of the several rice engine experiments I've had in mind to try for some time.

First, I'll probably just start with a basic, easy to put together engine that has already been proven to work.

Personally I don't know as there is any other DIY heat engine that is cheaper or easier to build, works more reliably or puts out more power for the time and money invested.

Why bother with anything else?

It has the potential for being completely sealed, self starting and perhaps nearly maintenance free.

Cheap and easy to build with demonstrable power output.

Is there a down side?

I'm pretty sure this one has not been posted here yet:


https://youtu.be/g9JkmS18u1I?si=WdMqxZE43Y3Fb-Zl


Amazing a plastic laundry bottle top works for this, and the plastic doesn't melt.

Also, like the ceramic, non-heat, or very low heat conductivity above the boiler. Rice and plastic couldn't provide much of an effective heat sink, but it runs! Maybe because the rice is absorbent as has been suggested previously, so it would be interesting to see if such a plastic body "rice" engine could also work with a non-absorbent "condensation" medium.

Or is it a regenerator? Or thermal resonator? Or... Quantum heat teleportation doorway.

The heat has to be going somewhere right?

One thing I think is interesting is when he dumps out the rice, he comments on how hot it is.

In this TNT video, about half way through the video he dumps out the aquarium gravel, after some minutes of dialogue and the gravel is still steaming hot.


https://youtu.be/696hUdcrDMQ?si=po-u6G4IXAD2jt9t

Now in theory, or some have theorized, or assumed that the steam is cooling and condensing and dripping back down to the bottom of the can to be reheated to a boil and vaporized again.

I think it may be more likely that the phase change is primarily taking place very rapidly in situ, condensing and evaporating right within the gravel due to more ubiquitous changes in temperature and pressure rather than there being much, if any of a heat gradient.

Much like the "cloud in a bottle" the condensation or "cloud" appears and disappears "everywhere" throughout the entire air space within the bottle, or at least wherever there is a smoke particle (or gravel or rice or whatever) for nucleation.

One good thing about being able to use plastic or other nonmetallic material for the upper engine body is that it does not interfere with the linear generator.

With a metal can the magnet can be attracted to the metal resulting in a reduction in power output.

Another indicator that I think suggests support for the theory of a phase change taking place throughout the rice or gravel rather than it being limited to a gradient is Robert Murray-Smith's observations in the above TnT-Omnibus video that the amplitude (he calls it "frequency" but his hand gesture indicates amplitude) of the diaphragm piston corresponds with the depth of the gravel
He says "the frequency depends on the depth".

A little gravel produces a shallow high frequency motion. More gravel, filling the whole can with gravel produces a deeper lower frequency oscillation.

To me, that indicates that the more volume of material to provide points for nucleation for the steam to condense onto and evaporate from, the greater the expansion ratio, the higher the amplitude and the lower the frequency.

It should then be possible to "tune" the engine by adjusting the depth of the gravel to produce a throw appropriate for the weight of the flywheel, if a crankshaft and flywheel were added.

I think in many cases it could be more practical to have a mechanical or rotary output, either to have the engine do mechanical work directly or to drive a rotary generator. Not necessarily because rotary generators are "better" or more efficient,, just that they are, at this time, cheaper, and easier to obtain.

Personally, I've been buying up used.electric generators with inoperative engines when I can find them, selling for practically nothing, in anticipation of being able to convert the engines to Ringbom, using the existing piston and cylinder or drive the generator unit with a whole new Stirling engine built from a 55 gallon drum or whatever if going big is necessary.

Anyway, rotary motors and generators are everywhere. Probably for a linear generator it would have to be fabricated from scratch, or would be prohibitively expensive, or limited to a low power coil and magnet out of a "shake" flashlight or something.

I had anticipated much of this here on the forum all the way back in 2006:

viewtopic.php?p=174#p174

I can't say where or on what forum I read about adding a little water and smoke in a Stirling engine, but I read recently that apparently the observation was first made by William Beale, inventor of the free piston engine.

Back then I received a lot of push back mentioning that. "Don't ever put water in the engine!", was the general response.

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.

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

The reference cited is:

WalkerG.
Stirling cycle cooling engine with two-phase, two-component working fluid
Cryogenics
(1974)