Stirling Engine & Heat Pump

[Tom Booth]

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One of these days you will understand that using the term "contract" for gas in an engine is just plain wrong. ...

Seems perfectly reasonable to me:

Dictionary definition:

contraction noun (REDUCTION)

the fact of something becoming smaller or shorter:

Cold causes contraction of the metal.

https://dictionary.cambridge.org/us/dic ... ontraction

The volume of the gas is reduced. "becomes smaller".

Fool wrote: "You lament over a trivial difference".

LOL.. a bit like the pot calling the kettle black. Your constant agonizing and hair splitting over the use of common English is part of your mental derangement that makes you a repugnant "troll'.

[Fool]

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Yes. In a misleading colloquial sense. Where is you link that states gas pulls a container in.

You are misleading yourself to prove a semantic. The science I'm talking about is better described by compression, or crushing force from outside, making the container smaller.

When someone misleadingly says, 'When gas cools, it contracts.', what they really mean is, 'Even when cooled, absolute gas pressure is always still positive, it is lower if the outside pressure doesn't make the container smaller. '.

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[Tom Booth]

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...Where is you link that states gas pulls a container in.
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I'm not sure why I need to provide a link to something I don't think I ever said. Looks like more straw manning and misrepresentations on your part.

I may have speculated about some such possibility at some time. So show the context.

If gas molecules have attractive forces between each other and also between each other and the container walls, why not?

I wouldn't rule it out, but that is not my position.

I've said over and over that the attractive and repulsive molecular forces usually balance each other unless the equilibrium is upset by adding heat or by a reduction in temperature.

The reduction in temperature could be by heat removal by conduction, radiation etc. OR by the gas doing "work".

Either way, the result is that the gas "contracts".

I've also said many times, you can view that as the gas literally "contracting" or being reduced in volume by outside atmospheric pressure.

The observable result is the same regardless of how the description of the process is worded.

[Fool]

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Nature is the same regardless of what we call it. What we call it can muddle our understanding. Smell instead of aroma or fragrance. Oh my! Colloquialisms have their places but clearness of scientific descriptions, have their places too.

You are arguing for the right to be misleading, obfuscation. You are not clearing up the understanding of nature.

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[Tom Booth]

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Nature is the same regardless of what we call it. What we call it can muddle our understanding. Smell instead of aroma or fragrance. Oh my! Colloquialisms have their places but clearness of scientific descriptions, have their places too.

You are arguing for the right to be misleading, obfuscation. You are not clearing up the understanding of nature.

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IMO, you are just full of yourself and prejudiced by your own beliefs and opinions regarding what you THINK "nature" is doing.

You are so insecure, you can't stand anyone using what you consider the 'wrong" or "incorrect" wording.

IMO the gas/water vapor or steam in a 55 gallon drum will "contract" or condense into a liquid leaving a vacuum BEFORE the drum implodes.

That does not mean the gas "pulls" anything necessarily.

There is nothing whatsoever "wrong" with stating that a gas "contracts" before, or as it phase changes into a liquid.

You have been acting like a fanatical enforcement officer obsessed with "correcting" other people's use of words because you've been educated/brainwashed by the "ideal gas" and kinetic theory of gas behavior, which are, at best, incomplete, misleading and erroneous mathematical simplifications, once, a long time ago, believed to be literally true but now known to have been superseded by more advanced understanding.

Gases DO have forces of attraction. Will draw together, even in a vacuum.

If they do not, then how did planets and stars ever form in the vacuum of space?

Not from the mass of planets that did not exist before they formed in the first place.

Without attractive molecular forces the universe, Sun, moon and earth and the atmosphere we breath would not exist.

Your assertion that gases in a vacuum will expand forever and never attract is illogical nonsense.

[Fool]

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Your insistence has taken this far beyond simple semantic differences. Bringing gravitational forces strawman like in on the discussion still doesn't explain your misunderstanding of the principle of escape velocity. Not all molecules have escaped velocity. In thermodynamics it is related to temperature and pressure. Higher temperatures and pressures have higher speeds and more bouncing. A gas released to space above a certain pressure and temperature will have a molecular escape velocity that is above all relevant masses. If far enough away, that temperature and pressure, velocity, would be very close to zeros.

Gases condensed, "contracted" [Sic], into planets because their density, mass, temperature, and pressure, their velocity, is below the escape velocity of their own mutual gravitational attraction mass and distance.

Gravitational attraction is way weaker, but doesn't drop off as fast (1/r^2), as inter molecular attraction. It's not the same force. It has little, negligible, affect on the gas in a Stirling Engine.

The following topic, IMHO is the blind leading the blind through a round room trying to find a corner. You mention the notion of vacuum or gas pulling many times. It is not the only place you ignorantly mislead and swamp out the discussions.

viewtopic.php?t=5610&hilit=Egg&start=15

Please realize the negative pressure being discussed, only applies to liquids. Thinking about 'surface tension' or 'capillary action' might be helpful. I'm not going to waste my time thinking about how liquids behave when engineering gas phase heat engines. Nor gravitational effects.

To make a volume of gas smaller, something must force it smaller. It is a battle against the ever present gas pressure, however small that pressure may be. Doing so puts energy into the gas, a temperature rise. That energy increases pressure and required back work. It can be removed as heat by temperature difference cooling. That necessitates rejection of heat to a cold plate.


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[Fool]

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This would be a lot easier if you'd do some research on gasses never pulling. Never negative gas pressure. Filling the container. Etc. It would be better than defiantly proving your misdirections over and over again. Lowest pressure in an Earth lab vacuum. Lowest pressure on the moon. Lowest pressure in space. See if any are negative absolute gas pressure. If nothing else, measure a few. Look up how really low pressures are measured.

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[Tom Booth]

It looks like I made reference to a Veritasium video that mentioned "negative pressure", and said It went further than how I would use the term; as "relative pressure" below atmosphere.

You seem to be ranting incoherently and grasping at straws.

As I said many times before, it is obvious, experimentally, that the piston in a Stirling engine returns to TDC without any apparent active (conductive) heat removal but only energy removal in the form of "work" output. (Conversion of heat to mechanical motion).

The question of molecular attraction is irrelevant. You can explain the observation without it by atmospheric pressure and say the gas simply has less kinetic energy after doing work. That does not change the observation that the engine continues running with the cold side insulated so heat cannot escape, or that the uninsulated side gets colder than ambient even after hours of continued operation on near boiling hot water.or steam.

The molecular attraction theory is not necessary, but molecular attraction does exist, it does have an influence, as shown in the video experiment with the balloons in liquid nitrogen "contracting" more than can be explained by a reduction in kinetic energy alone.

You are simply ignoring clear experimental evidence.

Without molecular attraction causing the air in the balloon to "contract", the balloon would only shrink down to 1/4 it's original size due to a reduction in temperature/kinetic energy and atmospheric pressure.

https://youtu.be/MNL7VzG8OGc

You are the one ignoring science.

[Fool]

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You are the one that fails to understand the science that I am reciting. The balloon shrinks more because it has less molecules in it that are in the gaseous state. As Matt said it is a phase change to liquid. Yes. It liquefies because of molecular attractions, and speeds that are slow enough for capture, and external pressures that force the gas molecules close enough. Not 'contraction'.

Classical science covers that in steam tables and phase diagrams. When you learn how they work you will understand this better.

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[Tom Booth]

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You are the one that fails to understand the science that I am reciting. The balloon shrinks more because it has less molecules in it that are in the gaseous state. As Matt said it is a phase change to liquid. Yes. It liquefies because of molecular attractions, and speeds that are slow enough for capture, and external pressures that force the gas molecules close enough. Not 'contraction'.

Classical science covers that in steam tables and phase diagrams. When you learn how they work you will understand this better.

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Liquid air boils at about the same temperature as liquid nitrogen.


Liquifying air with liquid nitrogen would be like trying to condense steam with boiling water. Very unlikely to be completely successful. You might condense some oxygen.

Be that as it may, an "ideal gas" remains a gas down to 0°K.

So now you agree that air could liquify in a Stirling engine?

I've seen quite a few examples of Stirling engine running on liquid nitrogen so it seems relevant.

Here is a Stirling engine running on a dewar of liquid nitrogen.

Stirling engine running on liquid nitrogen

Compress_20241030_032918_8974.jpg (38.4 KiB) Viewed 938 times

https://youtu.be/KFRlFj9p9V0

[Fool]

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Liquifying air with liquid nitrogen would be like trying to condense steam with boiling water.

Good point. The volume, pressure, temperature, responses for a real gas differs more so as the temperature and pressure near the boiling point, even before any liquefaction starts. As seen on phase diagrams and in steam tables.

So now you agree that air could liquify in a Stirling engine?

Not from purely expansion. Unless it is compressed and cooled first. Expansion without cooling just leaves the gas molecules further apart. Less dense and colder. The boiling point drops as well. Cooling off to liquify a gas, is the principle of the cold finger. The escaping colder gas cools the arriving compressed gas before expanding and cooling to continue the cycle.

Those, running on liquid nitrogen demonstrations, sort of, dispell the cold plate colder than the sink theory. Otherwise, the gas in the engine would all condense out, almost immediately stopping the engine. Hmmmm.

I wonder what would happen if run on liquid neon? Neon boils well below nitrogen. Liquid argon boils above liquid nitrogen, but the internal gas could easily be replaced by argon and then tested with liquid nitrogen.

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[Tom Booth]

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Liquifying air with liquid nitrogen would be like trying to condense steam with boiling water.

Good point. The volume, pressure, temperature, responses for a real gas differs more so as the temperature and pressure near the boiling point, even before any liquefaction starts. As seen on phase diagrams and in steam tables.

So now you agree that air could liquify in a Stirling engine?

Not from purely expansion. Unless it is compressed and cooled first. Expansion without cooling just leaves the gas molecules further apart. ...

Cooling (drop in temperature) takes place due to external "shaft work" output during expansion.

[Fool]

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That is not true. All that is needed is a movable wall, or piston. No shaft output needed. And yes the temperature drop is from an adiabatic process. No cooling from a temperature difference needed. But at the same time density decreases. The molecules spend even more time further away. Also at the same time the boiling temperature decreases. Won't liquify, unless much colder.

The few adiabatic lines that travel into the liquid-vapor dome on a T-S diagram, never hit the all liquid line. The adiabatic lines starting as liquid before expansion, start boiling when hitting that line, turning to gas.

The gaseous lines that hit the vapor dome start at 300K and 75 bars. Well out of the range of liquefaction in any of our engines from expansion only. It helps to study and understand these charts.

Throttling_in_Ts_diagram_01.jpg (130.2 KiB) Viewed 837 times

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[Fool]

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viewtopic.php?t=370


https://en.m.wikipedia.org/wiki/Liquid_nitrogen_engine

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[Tom Booth]

Cooling (drop in temperature) takes place due to external "shaft work" output during expansion.

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That is not true. All that is needed is a movable wall, or piston. No shaft output needed. And yes the temperature drop is from an adiabatic process. No cooling from a temperature difference needed. But at the same time density decreases. The molecules spend even more time further away. ...

Conservation of energy.

Where do you think the energy to do external work, such as driving a generator comes from?

Magic? Out of thin air?

No, it comes from the energy in the working fluid resulting in a drop in temperature.

You've displayed a persistent ignorance and denial of this rather simple principle, but it is taken advantage of in an industrial scale every day for liquifying gases all around the world.