Stirlingengineforum.com

A long time ago I did this experiment, curious to see how much air escaped past the piston when the engine was first heated up.

I had expected a lot. I anticipated the balloon blowing up quite a bit as the air inside the engine got hotter and hotter and the gas expanded more and more until ready to run

Instead, there was virtually nothing. If any air escaped past the piston it was not apparent.


https://youtu.be/iOs3BADFeKI?si=pjx5slRm4Gv8ksnG


I thought it somewhat puzzling as well how flaccid the.ballon remained the entire time while heating the engine and also while running.

I didn't think much more about it, but somehow this was not what I had expected, just now however, I came across this video:


https://youtu.be/zjCKQHdObWQ?si=4iTSNYdPxMO0qhYp


Well, not only was this person way ahead of me in my "high temperature LTD" experiments (the video is from eleven years ago), but if watched to the end, near the conclusion he similarly seals up the power cylinder.

First with the palm of his hand, then as I did, with a balloon stretched over the cylinder.

What I found surprising is that completely sealing the cylinder with the palm of his hand appeared to have no effect whatsoever on how the engine was running, as far as I could tell. Also the balloon when stretched over the cylinder, as in my own experiment remained flaccid.

What puzzles me is that there had been considerable debate on this forum regarding the expansion and especially CONTRACTION of the working fluid. Is it even proper to use the term "contraction"?

The argument being, the gas does not "contract" rather, the piston is "pushed back inward by atmospheric pressure".

So, if that is really the case, if atmospheric pressure is removed,... should the engine continue running unaffected?

Well, OK, so with the cylinder sealed there is then a "buffer pressure". But, the balloon seems to display no "pressure" one way or the other. It does move very slightly.

Either engine though, running on high temperature heat sources, seems to be running with considerable energy and force.

Up until seeing this video, I've somewhat begrudgingly conceded that there is not really any "contraction" of the gas, and have been careful to almost always say "when ATMOSPHERIC PRESSURE pushes the piston back" rather than "when the gas contracts" more to avoid arguments than anything, but I also assumed it to be technically more accurate, if somewhat nit picking and pedantic.

This seems to me like evidence that "contraction" may actually be correct or more accurate.

Certainly REAL gas molecules do have attractive forces that cause them to clump or pull together. Could it be that gas molecules DO exert some "pulling" force on the molecules of solid objects they happen to be adjacent to? Cylinder walls and/or pistons in an engine? Or the inner walls of a 55 gallon drum filled with steam.

In the above videos, it appears to me that the inside "pull" of the "contracting" gas has more influence than outside "atmospheric pressure".

Edit: perhaps the cylinder could be sealed and also equipped with a one way check valve to completely eliminate external or "buffer" pressure, or perhaps the air could be drawn out with a vacuum pump.

Or, what if we were to do the steam condensing in a can experiment, but before the can can cool and collapse, put it inside a vacuum chamber.

Would the "attractive" force of the condensing steam collapse the can without the external atmospheric pressure?

This experiment seems applicable.


Is the egg really being "sucked" into the bottle or is it being "pushed" in by external atmospheric pressure?


https://youtu.be/LyMGEZRq520?feature=shared

What about this:


https://youtu.be/o7aCWFcuKJE?si=yazpa4UjCjZoY6gV


The egg is torn in half.

To me, that seems a bit strange if the egg is only being "pushed" from the outside.

What if we do something like this:

Heat up two milk bottles.

Put the mouths of both bottles together with the hard boiled egg between them.


Which way will the egg go?

Or with no outside atmospheric pressure to push the egg either way, maybe nothing at all will happen. Or will the egg explode? Would it get pulled apparent and 1/2 the egg end up in each bottle?

I really have no idea

I searched to find any such experiment on the internet somewhere, but could find none.

I also tried to find anything about what might happen to a hard boiled egg in a vacuum chamber. Nothing there either.

My illustration shows a sleeve around the top of the bottles and the egg, which could perhaps be some tight fitting rubber tube or something to prevent the atmospheric pressure from infiltrating the space or crack between the two bottles and the egg.

... Or will the egg explode? Would it get pulled apparent and 1/2 the egg end up in each bottle?

Having done lots of vacuum chamber experiments, my guess would be that if it's a good enough vacuum, the water in the egg would boil at room temperature - as water does in a vacuum, and the egg would lose integrity and possibly split in some way until those vapors have been released from the egg to the bottles.

If it's a lesser vacuum, I doubt you would see much unless there was an air pocket in the egg, because as you noted, there's no pressure differential present.

skyofcolorado wrote: ↑Mon Feb 05, 2024 8:24 am

... Or will the egg explode? Would it get pulled apparent and 1/2 the egg end up in each bottle?

Having done lots of vacuum chamber experiments, my guess would be that if it's a good enough vacuum, the water in the egg would boil at room temperature - as water does in a vacuum, and the egg would lose integrity and possibly split in some way until those vapors have been released from the egg to the bottles.

If it's a lesser vacuum, I doubt you would see much unless there was an air pocket in the egg, because as you noted, there's no pressure differential present.

I guess that probably wouldn't answer the question.

From what I've read generally, the universal attractive force, or one of them -gravity? Maybe others? Is, well, universal and INCREASES with distance, which seems odd.

It seems odd that water vapor condenses in a 55 gallon drum when cooled at all, considering how water boils in a vacuum. And why such an apparently sudden and violent "implosion" ? Maybe that is just the 55 gallon drum being so strong, presumably the vacuum forms gradually.

But, "no such thing as a vacuum" just an absence of pressure?

But gravity between all mass everywhere exists or the atmosphere would fly off into space immediately and the planet would break apart into dust. There is attraction.

There is just as much mass in the bottle or 55 gallon drum after condensation, or after cooling and contraction.

Without attractive force there would be no atmospheric pressure. Right?

The force of gravity is what causes the atmosphere to have pressure, from all those air molecules being pulled down and being pulled together by attractive forces.

Based on my extensive vacuum chamber experiments, I would venture to say that in a sufficiently strong vacuum, the water within the egg could reach its boiling point at room temperature. This phenomenon, common in vacuums, might cause the egg to lose its structural integrity, potentially resulting in some form of splitting until the vapors are released into the surrounding bottles.

On the other hand, if the vacuum is less intense, observable effects may be limited unless there's an air pocket within the egg. As you astutely pointed out, the absence of a significant pressure differential could mitigate noticeable changes in this scenario. It's a fascinating interplay of physics, and the outcome may vary based on the vacuum strength and the egg's internal composition.

Or, what if we were to do the steam condensing in a can experiment, but before the can can cool and collapse, put it inside a vacuum chamber.

Would the "attractive" force of the condensing steam collapse the can without the external atmospheric pressure?

No. No collapse if done under vacuum. It would collapse after the vacuum is released.
A study of the combined gas law would go a long ways toward your understanding of what is happening. So far I'm not seeing anything inconsistent with it, at least with the information available. There's a lot that's not stated or known from both your experiments and scenarios, so without those additional details it's hard to say for sure.

If it would help you, design an experiment that I can reproduce and I'll film it in the chamber. It's 28cm deep and 29cm diameter.

Not sure anything would help.

Mostly I'm just puzzling over what seems somewhat inexplicable phenomenon. Or at least, there seems to be some missing piece to the puzzle.

I'm thinking of a piston returning to TDC "by atmospheric pressure" without any apparent means for heat removal.

Similarly, a 55 gallon drum suddenly collapsed when filled with steam, then cooled. How does the steam condense in a vacuum that isn't a vacuum until the steam condenses but if water were to condense it would boil and produce cold steam.

What triggers the drum to collapse?

What triggers the piston (free piston) to suddenly stop and throw itself back to TDC, IMO, more rapidly than it should be possible to cool the gas, especially when the engine is wrapped in insulation.

In the 55 gallon drum, does the steam condense first?

I'm guessing there must be some catalyst that triggers the drum to collapse and the steam to condense simultaneously.

Some quantum field sort of gremlin.

Similarly, a 55 gallon drum suddenly collapsed when filled with steam, then cooled. How does the steam condense in a vacuum that isn't a vacuum until the steam condenses but if water were to condense it would boil and produce cold steam.

The parameters are changing as the event transpires. It starts out as a 55 gal container, but as the steam condenses and a partial vacuum forms (not much of a vacuum is required to start the collapse of a 55 gal drum) the drum volume reduces rapidly as the collapse is happening. The steam continues to condense collapsing the drum further, until an equilibrium is formed between the volume of the drum and the remaining water vapor pressure. In the end, there's no more vacuum, thus no (or very little) cold water vapor.

At no time is there enough of a vacuum to boil water at ambient temperature so this condition never occurs:

but if water were to condense it would boil and produce cold steam

I'm thinking of a piston returning to TDC "by atmospheric pressure" without any apparent means for heat removal.

I think these are two completely and totally unrelated matters, which may be part of the confusion. The power piston in a gamma engine has zero role in heat transfer/removal. Its motion is the result of heat transfer changing the system pressure during the cycle. The power piston and power cylinder could be made of a perfectly insulating aerogel that holds and transfers nearly zero heat energy, and the engine would work the same.

I would imagine the piston in an "acoustic" or whatever kind of engine would be the same since the motion (the traveling wave) is apparently what acts as the "displacer" and the resulting contact of the fluid mass with the hot or cold parts (far removed from the power piston) are what change the system pressure and move the power piston. Didn't you experiment with a wood piston once? Isn't that largely the same idea? What possible (practical) role could a piece of wood have in heat transfer, yet the engine works?

Perhaps in an alpha config the piston might have a role in this because the heat differential is based on the two cylinders being at opposite ends of the flow, but not a gamma or acoustic. At least that's how it registers in my mind anyway, but I don't know if I'd put money on it though.

skyofcolorado wrote: ↑Mon Feb 05, 2024 2:05 pm

Similarly, a 55 gallon drum suddenly collapsed when filled with steam, then cooled. How does the steam condense in a vacuum that isn't a vacuum until the steam condenses but if water were to condense it would boil and produce cold steam.

The parameters are changing as the event transpires. It starts out as a 55 gal container, but as the steam condenses and a partial vacuum forms (not much of a vacuum is required to start the collapse of a 55 gal drum) the drum volume reduces rapidly as the collapse is happening. The steam continues to condense collapsing the drum further, until an equilibrium is formed between the volume of the drum and the remaining water vapor pressure. In the end, there's no more vacuum, thus no (or very little) cold water vapor.

At no time is there enough of a vacuum to boil water at ambient temperature so this condition never occurs:

Well, honestly, that sounds kind of like a rather gradually process, whereas the 55 gallon drum demonstration is popular, I think, mainly for its shock value. The drum implosion is like a gunshot. Blink and you'll miss it. BAM!!?

I was thinking more along the lines of a catalytic transformation, like supercooled water "instantly" changing to ice.


https://youtu.be/Yu6umSB-MsQ?si=-wGhysN78kqCM7xQ


Can't say I have any clear ideas what this guy is talking about about:


https://youtu.be/ITjG4ExFXGs?si=8Um_VUjZnLvM0-Qm


There are some obvious similarities. Sometimes, with the 55 gallon drum and steam, the drum doesn't collapse. A blow from a hammer, though, can start the "chain reaction"


https://youtu.be/0v248ogW-dA?si=h6XYRekcAn-_pWyh


https://youtu.be/vpz9nTXZhnQ?si=yP6XK5-xpIP8jhjk


If it is a chain reaction.


https://youtu.be/gQq8dTFHSWg?si=THDLUkjFw63w957e


Now, to me it looks like the common denominator in all this is that some substance is taken ",over the limit" or beyond its "normal" phase transition parameters. It SHOULD, freeze, or condense or expand or solidify or crystalize or whatever but doesn't. The process is delayed or not all necessary conditions exist or things are happening too fast or whatever.

Supercooled water vapor in clouds can be a danger to airplanes, when the plane itself acts as the catalyst.


https://youtu.be/NgoU8PmhL9c?si=2ExpUx0yM01p323_


My thoughts is that when the working fluid in a Stirling engine is "overexpanded" as the piston moves out towards BDC, the gas is cooled adiabatically to a point beyond where it should really be contracting, but...

The momentum of the piston, the expansion ratio, ... Whatever, the gas is forced to continue to expand until at some point, BAM! The gas suddenly contracts. The piston, "sucked in" by the resulting "vacuum" or pushed back to TDC by "atmospheric pressure", whatever. However anyone wants to look at it.

What strikes me is the suddenness.

The piston is blasted out by hot expanding gas, then all of a sudden it reverses direction and returns all the way back to TDC, in a Lamina Flow, or "Thermal Lag" running "free piston" this can be happening a dozen times per second. Way faster than can be attributed to any normal heat transfer.

Well, honestly, that sounds kind of like a rather gradually process, whereas the 55 gallon drum demonstration is popular, I think, mainly for its shock value. The drum implosion is like a gunshot. Blink and you'll miss it. BAM!!?

A matter of perspective I suppose. I've had a global shutter high-speed video camera for a lot of years, so everything seems like a gradual process once you've seen the more common things we experience around us in sub-milisecond frame sequences.

Add that asset to my offer of a vacuum chamber experiment. As it happens I've never seen the can-crushing experiment in high-speed. If someone else hasn't already filmed it, we could do that if it's sufficiently analogous to the 55gal drum. I know it seems fast, but it probably takes ages on that camera.

This is what I love about physics; the math can be brutally real when the conditions are right. Seems like magic, but in the end it's just math, in this case a phase change and resulting combined gas law equation manifesting a crumpled drum in milliseconds.