Forces of attraction and repulsion of gas molecules in a Stirling engine.

[Fool]

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Fool pretending he knows all about things he's pretty obviously never heard of before or he would not be advocating kinetic theory (gases always repel "forever" with no attractive forces or other interaction) as the ultimate reality or other 1820's heat engine theory, long ago rendered obsolete.

There's no pretending with you. You really have zero scientific knowledge. You have gone from an interested ignoramus to a caustic arrogant ignoramus with an extended useless volcabulary. You need to have knowledge of the vocabulary as well as how it scientifically is used. You lack the second part of that.

You are unlikely ever to understand the meaning of 'gases always push'. You will never understand how to use that well known scientifically observable fact. You are just lame, lame lame.

The lame brain named, the lame brain, 'lamebrain'.

Good luck with your lies and misunderstanding. Hope they work for you, or you grow out of your own arrogance and cognitive dissonance.

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[Fool]

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If we assume that each gas molecules is essentially motionless, at least from our macro perspective and is in a state of balance in relation to all other gas molecules, (within the confines of a Stirling engine) poised between attracting and repelling, then how might this change the choices we make as far as how we design our engine?

If solids have the molecules suspended between attraction and repulsion, and liquids are about the same density, then gasses must be greatly further apart, outside the range of balance. Electric fields are unaffected by temperature, so the balance point will at the same radial distance regardless of temperature. Both forces will become zero at a radial distance of 2 or 3 and smaller when even further away.

The fact that gasses expand so much, leaves the molecular forces behind.

Also:

Molecular forces are dependent on electric fields which are way stronger than any of the inherent self induced magnetic fields. IOW, atoms and molecules 'stick' together because of electric forces, not magnetic forces. Magnetic forces have little influence and should be ignored.

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[Tom Booth]

It seems the operation of a Stirling engine is an interplay between the natural attraction of the working fluid molecules and their natural repulsion.

Everything seeks balance or equilibrium.

Compress the gas from its "natural" state of balance and it tries to expand. Expand it beyond its natural state of balance and it wants to contract, much like a spring

Very simple,logical and observably true.

You seem to contradict yourself by saying the gas must be cooled externally in order for it to contract or for it to be compressible.

There are two ways of removing energy so the gas can be more easily compressed. Remove heat or remove work.

Removing work increases efficiency. Removing "waste heat" reduces efficiency.

Why you favor the latter is a bit of a mystery.

[matt brown]

This also explains why an air compressor, putting air into an air tank equalizes with the environment in temperature, but not in pressure.

If a gas were really composed of completely independent molecules that do not interact and if pressure were a function of kinetic energy (temperature) then when the temperature equalized with the ambient temperature then logically it would seem that the pressure would also

The pressure in the tank, then, comes from the mutual repulsive forces of the gas molecules repelling one another because they have been crowded together "too close for comfort" due to their molecular structure and tendency for mutual repulsion at close distances, not their kinetic energy or temperature, zipping around and colliding with the walls of the air tank.

Obviously, you fail to grasp the most basic thermo concept where PV=nRT

[Tom Booth]

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If we assume that each gas molecules is essentially motionless, at least from our macro perspective and is in a state of balance in relation to all other gas molecules, (within the confines of a Stirling engine) poised between attracting and repelling, then how might this change the choices we make as far as how we design our engine?

If solids have the molecules suspended between attraction and repulsion, and liquids are about the same density, then gasses must be greatly further apart, outside the range of balance. Electric fields are unaffected by temperature, so the balance point will at the same radial distance regardless of temperature. Both forces will become zero at a radial distance of 2 or 3 and smaller when even further away.

The fact that gasses expand so much, leaves the molecular forces behind.

Also:

Molecular forces are dependent on electric fields which are way stronger than any of the inherent self induced magnetic fields. IOW, atoms and molecules 'stick' together because of electric forces, not magnetic forces. Magnetic forces have little influence and should be ignored.

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First of all, relating molecular attractive forces to magnetic attraction is clearly an analogy not intended to be takeniterally.

The fact that gasses expand so much, leaves the molecular forces behind.

There are dozens of sources related to the behavior of "real gases" that say otherwise. The forces of attraction between molecules weakens with distance but is basically "infinite" like gravity, if not actually the same force as gravity.

Repulsive molecular forces are limited to overlapping electron clouds, apparently.

All the sources discussing"real gases" talks about how these forces DO have a real measurable influence on pressure in a vesel or container (engine cylinder etc.) at distances relevant to our concerns here. Stirling engines.

Anyone can do a search on "real gas behavior", "Van der Waals forces", etc and compare reality with your nonsensical baseless, irrelevant, outdated, obsolete, opinions.

[Tom Booth]

This also explains why an air compressor, putting air into an air tank equalizes with the environment in temperature, but not in pressure.

If a gas were really composed of completely independent molecules that do not interact and if pressure were a function of kinetic energy (temperature) then when the temperature equalized with the ambient temperature then logically it would seem that the pressure would also

The pressure in the tank, then, comes from the mutual repulsive forces of the gas molecules repelling one another because they have been crowded together "too close for comfort" due to their molecular structure and tendency for mutual repulsion at close distances, not their kinetic energy or temperature, zipping around and colliding with the walls of the air tank.

Obviously, you fail to grasp the most basic thermo concept where PV=nRT

I grasp the concept, but if moles of gas are composed of individual particles that have no volume and do not interact at all then compressing a gas into a smaller volume has no meaning, and logically should have no influence

Without intermolecular forces PV=nRT has no logical basis.

At any rate the ideal gas law is very limited and needs correcting by adding Van der Waals forces in situations involving compression and expansion of gases away from STP.

PV=nRT is like a stopped clock. There are only limited situations where it happens to be correct.

[matt brown]

What is most notable about this is that force might be transmitted through the working fluid without the transmission of any "heat" at all. The "hot' gas can be expanded on the hot side and just transmit "pressure" to the piston, indirectly while the cold side of the engine, for the most part, remains almost entirely cold. There is no need whatsoever for any heat to "travel" through the engine from the hot side to the cold side.

This provides a satisfactory model of gas behavior that explains my experimental results, that indicate the same.

A Stirling engine can operate just fine while transmitting no heat whatsoever through to the supposed "sink".

Here's a little "cartoon" that you should study carefully...

PVT basics.png (15.48 KiB) Viewed 563 times

Note the PVT values for this constant volume heating process where this 300-600k cycle would require heating 40% of the gas to Tmax for only 25% increase in pressure. This is where the whole idea of any ambient LTD dwell scheme falls apart with no way to get enough heat into each cycle with a 'quick jab' of heat or whatever buzz you choose.

Any real output will require a pressure swing and there's very few ways to achieve this. Your continue fantasy of 100% eff is worthless when 100% x zero = zero

[matt brown]

Without intermolecular forces PV=nRT has no logical basis.

At any rate the ideal gas law is very limited and needs correcting by adding Van der Waals forces in situations involving compression and expansion of gases away from STP.

PV=nRT is like a stopped clock. There are only limited situations where it happens to be correct.

That little equation explains a lot of stuff that evaded human comprehension for eons and is chiefly responsible for our current standard of living. It's logical basis is that it works great when not chasing rainbows...

[matt brown]

It seems the operation of a Stirling engine is an interplay between the natural attraction of the working fluid molecules and their natural repulsion.

Everything seeks balance or equilibrium.

Compress the gas from its "natural" state of balance and it tries to expand. Expand it beyond its natural state of balance and it wants to contract, much like a spring

Very simple,logical and observably true.

Expansion does not make a gas want to contract; the gas will remain in an expanded state until effected upon.

You seem to contradict yourself by saying the gas must be cooled externally in order for it to contract or for it to be compressible.

Even when cooled, the gas does not contract, it merely looses pressure due to less kinetic energy. Fool's phase diagrams tell the story...supercritical gas behaves akin ideal gas law, but once in lower two phase region (near condensation point) then things change.

There are two ways of removing energy so the gas can be more easily compressed. Remove heat or remove work.

Removing work increases efficiency. Removing "waste heat" reduces efficiency.

Why you favor the latter is a bit of a mystery.

Compression involves work INPUT so you can't remove work while adding work, duh. Therefore, removing heat is the only option, but this can be done prior compression or during compression.

[Tom Booth]

Wanting a more accurate picture of actual reality is not "chasing rainbows" its called engineering where percussion matters.

PV=nRT provides a rather wild estimate for a generalized, but non-existent "ideal gas".

Real gases subject to swings in temperature and pressure, such as in an engine will deviate from the "ideal" significantly.

[Tom Booth]

...removing heat is the only option,...

James Joule proved otherwise decades ago.

[matt brown]

Wanting a more accurate picture of actual reality is not "chasing rainbows" its called engineering where percussion matters.

PV=nRT provides a rather wild estimate for a generalized, but non-existent "ideal gas".

Real gases subject to swings in temperature and pressure, such as in an engine will deviate from the "ideal" significantly.

Maybe 10% deviation in extreme examples, but zilch for anything we'll encounter (DIY or otherwise). When did any engine deviate from the ideal gas law "significantly" ???

[matt brown]

...removing heat is the only option,...

James Joule proved otherwise decades ago.

I said "Compression involves work INPUT so you can't remove work while adding work, duh. Therefore, removing heat is the only option, but this can be done prior compression or during compression."

[Tom Booth]

...removing heat is the only option,...

James Joule proved otherwise decades ago.

I said "Compression involves work INPUT so you can't remove work while adding work, duh. Therefore, removing heat is the only option, but this can be done prior compression or during compression."

Well, I disagree. "Removing heat" prior to, during or after compression, is not the "only option".

James Joule proved that decades ago.

I know perfectly well what you said.

Instead of removing "heat" it is better to remove "work".

That "compression involves work input" IMO is wrong.

Also "Even when cooled, the gas does not contract" is also wrong.

Taking energy out of a gas as either heat OR work will cause the gas to contract, and as the gas contracts, the engine can perform additional work, as outlined rather eloquently in VincentG's introductory post here:

viewtopic.php?p=24572#p24572

Andrew Hall's video demonstration:

https://youtu.be/SHyke4hUNOs

And my own observations and experiments.

And incidentally, also, dozens of scientific resources that state unequivocally that gas molecules do indeed attract, "contract" or condense. Even in the vacuum of outer space

[VincentG]

The important thing is that the man has traded force for distance. By taking a longer path, the weight was raised without additional perceived force. No different than any other form of mechanical advantage, except that perhaps this example can be extended to thermodynamic work by allowing less force (lower delta T) to do more work.

In this way the lower temperature delta can be used like a lever to increase its effective force. Just like a prybar, the object being acted on must be as rigid as possible to make use of the mechanical advantage. For a gas, this means increasing its density and pressure as much as possible so that a small temperature increase results in a relatively large and useful effect.

As Matt has found, the smaller the delta T, the more efficient a cold connected piston becomes. That combined with much better thermal performance of low temperature materials makes a strong case for LTD engines. The problem of low overall efficiency is that LTD engines are essentially prying against a piece of foam (1bar). A turning point should arise when the low temperature delta is compelled to pry against pressure and energy levels that are "rigid" enough to affect practical work output. The increased pressure levels are allowing us to tap into the baseline internal energy levels of the gas. The same energy that would be contained in the rope but not available to us.

Phillips was obviously attempting this with megabar charge pressures, but maybe just took a wrong turn trying to hammer in more, and more heat instead of focusing on effective temperature delta.

Tom, I think a lot of what you are saying ties into what I was trying to say here. There's a few problems that Matt's latest graphic illustrates well. The cold volume may increase somewhat in pressure when only a partial volume is heated, but it is an overall net negative. The smaller the cold volume, the greater the pressure swing. So the way I see it is that a cold volume can be tolerated, but should be as small as possible.

Luckily the power piston compresses the gas from a large space to a small space, and combined with high enough pressures in this cold space, the partial heating can be much more effective but still not as good as complete heating.

Let's introduce another fictional planet where another engine builder, named Ralph, has just completed his new engine. Ralph's planet is much larger than earth and so has an atmosphere of 100bars, but Ralph and his workload are the same size as us earthlings.

Ralph builds an atmospheric engine like the one in Andrew Halls video. It too needs no flywheel, as it has no effective "compression". The difference is that it makes 100 times more power.

If Ralph shipped his engine back to Tom, here on earth, Tom would witness the engine explode from the internal pressure that Ralph witnessed "contracting" back on his planet.


I'd love to comment on forces of attraction and repulsion of gas molecules, but won't, until I can observe them directly. I can however say I don't doubt for a second that gas could briefly contract more than PV=nRT allows when rapidly cooled at constant volume.