The inversion temperature of gas and its role in hot air engines

[VincentG]

The following excerpt is from https://en.wikipedia.org/wiki/Joule%E2% ... n%20effect.

Helium and hydrogen are two gases whose Joule–Thomson inversion temperatures at a pressure of one atmosphere are very low (e.g., about 40 K, −233 °C for helium). Thus, helium and hydrogen warm when expanded at constant enthalpy at typical room temperatures. On the other hand, nitrogen and oxygen, the two most abundant gases in air, have inversion temperatures of 621 K (348 °C) and 764 K (491 °C) respectively: these gases can be cooled from room temperature by the Joule–Thomson effect.[1][11]

This is from https://en.wikipedia.org/wiki/Inversion_temperature

The inversion temperature in thermodynamics and cryogenics is the critical temperature below which a non-ideal gas (all gases in reality) that is expanding at constant enthalpy will experience a temperature decrease, and above which will experience a temperature increase. This temperature change is known as the Joule–Thomson effect, and is exploited in the liquefaction of gases. Inversion temperature depends on the nature of the gas.

Besides explaining why power gains from helium and hydrogen can be so significant, this also explains model HTD engines. This thread documented the low displacer chamber effectiveness of these models. viewtopic.php?t=5638&hilit=toys

Despite the lack in chamber performance, huge heat input and almost non-existent cooling, these things offer an impressive show. The hot end easily reaches the inversion temperature of at least nitrogen. This should be a significant advantage even if it's only being partly utilized in these models.

It seems that for real gasses, the increased heat (read kinetic) energy eventually manifests itself at high enough temperatures, likely when the inertia of the gas molecules from heat energy is enough to start overcoming intermolecular attractive forces. Then perhaps more molecules are available to impart their energy at any one given time. So perhaps no actual change to internal energy levels, just an increase in readily available energy. Like R.A.M but R.A.E (random access energy) lol.

What does this mean for hot air engines? At worst this all wrong, but at best a potential increase in classical efficiency if gamed well.

For the low tech engine, it's hard to maintain a hot end that is entirely above the inversion temperature. But if only a select area of the hot end can maintain well above the inversion temperature, it should have large benefits to the propagation of heat and pressure throughout, as well as potentially more complete utilization of heat for an adiabatic process exhausting to Earth's atmosphere.

[Fool]

Isn't the inversion temperature only relevant to the Joule-Thomson expansion effect? So it would not have any relevance for expansion with work, as in our engines?

Don't helium, hydrogen, nitrogen, and all, cool when expanded using a piston or turbine, no matter what the temperature or pressure? PV=nRT?

Didn't they test for that when developing those theories?

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[VincentG]

Isn't the inversion temperature only relevant to the Joule-Thomson expansion effect? So it would not have any relevance for expansion with work, as in our engines?

Don't helium, hydrogen, nitrogen, and all, cool when expanded using a piston or turbine, no matter what the temperature or pressure? PV=nRT?

Didn't they test for that when developing those theories?

-What is the difference between the J-T effect and the displacer chamber allowing pressurized hot air above the inversion temperature to expand through a small conduit into a separate volume while the power piston is dwelling at TDC? I don't see any work being done at this point in the cycle.

-I don't know.

-Yes, it seems this is why a distinction is drawn between ideal gases and real gases.

[Tom Booth]

From what I remember reading somewhere, the modern understanding of the Joule-Thomson effect is that it has to do with "work" resulting from the gas's own molecular attraction and repulsion.

Think of helium and hydrogen at normal "room temperature" as spring loaded. The helium molecules repellent each other. So when released from confinement and allowed to expand freely helium molecules fly apart like compressed springs.

Most other gases have a stronger attraction to each other so when allowed to, or when forced to expand, it is in opposition to the attractive force.

So usually an expanding gas does "work" against the mutual attractive force but helium and hydrogen are worked on, receiving additional kinetic energy from mutual repulsion.

So that is why helium, free to expand will go right up to the upper atmosphere and is very light because the helium molecules repel each other. Other gases are heavier due to being more dense because they more strongly attract each other

Gas molecules act as though they are attached together by springs. The springs can be compressed or stretched.

The "relaxed" spring state, where the attractive and repulsive forces are balanced is the inversion temperature.

Not that I really know what I'm talking about , but that's more or less how I've come to think of it

At any rate, the Joule-Thomson effect is generally not very strong and is just a kind of subset of gas "doing work".

Gas doing real work, such as driving a load on an engine produces a much greater work output and therefore a much greater cooling effect or loss of kinetic energy rendering Joule-Thompson negligible, I think.

Not that the idea of taking some advantage of it isn't worth exploring.

I would assume most info relating to Joule-Thomson is for ordinary temperatures and pressures and the effect is generally slight. I'm not so sure at high pressures and temperatures or other extreme conditions.

[Tom Booth]

So, if you heat a gas to the inversion temperature, add a little more heat and expansion will be assisted by the gases molecular repulsion.

Cooling it below the inversion temperature will assist compression due to the gases own molecular attraction.

Maybe?

[VincentG]

So, if you heat a gas to the inversion temperature, add a little more heat and expansion will be assisted by the gases molecular repulsion.

Cooling it below the inversion temperature will assist compression due to the gases own molecular attraction.

Maybe?

That's the theory. I think I have a way to test this directly and experimentally but don't think it's worth the time for me. The proof would be in an engine running at greater than expected efficiency.

[Tom Booth]

So, if you heat a gas to the inversion temperature, add a little more heat and expansion will be assisted by the gases molecular repulsion.

Cooling it below the inversion temperature will assist compression due to the gases own molecular attraction.

Maybe?

That's the theory. I think I have a way to test this directly and experimentally but don't think it's worth the time for me. The proof would be in an engine running at greater than expected efficiency.

Not sure, but perhaps when an engine reaches "operating temperature" it is because it has reached the inversion temperature of some one or another constituent of the air or working fluid?

Possibly a mixed gas like air would have an "average" inversion temperature, but I don't know if it works that way, but mixtures of liquids do, at least sometimes. A mix of water and alcohol will have a boiling point between that of the two pure liquids.

Not much information on the subject that I know of, but could be a fruitful area for some experimentation, perhaps.

[VincentG]

Not sure, but perhaps when an engine reaches "operating temperature" it is because it has reached the inversion temperature of some one or another constituent of the air or working fluid?

Possibly a mixed gas like air would have an "average" inversion temperature, but I don't know if it works that way, but mixtures of liquids do, at least sometimes. A mix of water and alcohol will have a boiling point between that of the two pure liquids.

Not much information on the subject that I know of, but could be a fruitful area for some experimentation, perhaps.

Very well said Tom. The inversion temperature of argon is a very low 425k. It makes up less than 1% of air but it, especially in higher concentrations, could greatly aid the rate of heat transfer and effective expansion characteristics.

[Fool]

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What is the difference between the J-T effect and the displacer chamber allowing pressurized hot air above the inversion temperature to expand through a small conduit into a separate volume while the power piston is dwelling at TDC? I don't see any work being done at this point in the cycle.

I suppose there is some J-T effect in that area. My guess is it will be nothing more than hysteresis losses no matter how it is 'gamed', or at best a negligible but negative effect.

Putting energy into a gas to increase the pressure, displacer motion, throttle it with friction, get less energy out than went in. Put more in to get a bigger effect, get less out per in.

Gas cools entering expansion chamber, irreversible loss of added energy. Leaves; less, plus less for expansion.

Gas entering expansion chamber heats as it enters, increase in energy, but lower pressure for pushing piston. Leaves; less energy, plus less energy, plus a little bit of energy back.

The throttling process inside an engine is tantamount to windage. Put more energy in, and remove it irreversibly by friction, to have a lower pressure to drive a piston. I'm not exactly sure what you expect to gain from friction?

The J-T effect relies on there being a pressure difference from throttling. Throttling is an irreversible friction device. The higher the effect, the greater the pressure difference must be. Ultimately the pressure will be so low it will be below atmospheric. This is killer windage.

It is similar to putting work into adiabatic temperature rise, to get more work out, but you only get a maximum amount more out as you put in, zero-zero, minus the windage for the cycle. This is a, sort of, reversible process, equal in and out. Now you are talking about doing it with an irreversible expansion before the usual reversible expansion process.

It sounds similar to using the piston cylinder friction to heat the gas and get a better expansion. Also, don't forget to figure in hot cylinder compression.

The problem is how to draw system boundaries so that easy equations can be used to model it for each subsystem, and then add them all up. Matt has been trying to break it up into finite elements of equal moles. He is doing it a lot by hand with large elements. The number of elements needs to be significantly increased and entered into a computer for simulation.

The displacer, and chamber, has three distinct parts/systems. The hot side. The cold side, and the regenerator. Add a expansion cylinder and interconnecting tube and it becomes five. All must be entered into the model. They all have a transfer of mass and interact with each other. A perplexingly difficult modeling process. Probably well beyond the hobby engines being explored here.


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[Tom Booth]

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What is the difference between the J-T effect and the displacer chamber allowing pressurized hot air above the inversion temperature to expand through a small conduit into a separate volume while the power piston is dwelling at TDC? I don't see any work being done at this point in the cycle.

...nothing more than hysteresis losses no matter how it is 'gamed', or at best a negligible but negative effect.

...throttle it with friction, get less energy out than went in. ...less out per in.

...irreversible loss of added energy. Leaves; less, plus less for expansion.

...lower pressure for pushing piston. Leaves; less energy, plus less energy,...

The throttling process inside an engine is tantamount to windage. Put more energy in, and remove it irreversibly by friction, to have a lower pressure to drive a piston. I'm not exactly sure what you expect to gain from friction?

...Throttling is an irreversible friction device. ...Ultimately the pressure will be so low it will be below atmospheric. This is killer windage.

.. zero-zero, minus the windage for the cycle...

... A perplexingly difficult modeling process. Probably well beyond the hobby engines being explored here.

Chronic negativity and advice based on ignorance and misinformation.

JT effect has nothing to do with friction and does not produce any mechanical friction.

At least "fool" is picking on someone else for a change. Congratulations VincentG you must be on to something.

[VincentG]

At least "fool" is picking on someone else for a change. Congratulations VincentG you must be on to something.

There should be a forum badge we can pass around Tom.

[Fool]

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The JT effect requires thermodynamic friction, called 'throttling'. The friction is in the form of: an orifice: capillary tube: semi poris material: ETC... Yes it is mechanical thermodynamic friction. No it is not kinematic friction.

I don't see how pointing out classical theory is picking on anyone but intentional liars.

I don't have a problem with you all chasing rainbows. Just have a problem when you are making the claim that there is a pot of gold at the end, yet you haven't found it, and want someone else to prove you all wrong.

I know that rainbows seen from an airplane are a complete circle with the shadow of the airplane in the middle. Quite dramatic. Since that means that all rainbows are complete circles, there is no end. The Earth's shadow blocks half of it. At the very best, no end, no pot of gold. There never was a pot in the first place.

A proof of this is simple enough to produce with a garden hose set for mist fan spray. Spray it away from you opposite the sun. Move it around until you get the effect. Full sunshine. Full circle.

Definition. Friction Drag, also known as Skin Friction Drag, is drag caused by the friction of a fluid against the surface of an object that is moving through it

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[Tom Booth]

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The JT effect requires thermodynamic friction, called 'throttling'. The friction is in the form of: an orifice: capillary tube: semi poris material: ETC... Yes it is mechanical thermodynamic friction. No it is not kinematic friction.

I don't see how pointing out classical theory is picking on anyone but intentional liars.

I don't have a problem with you all chasing rainbows. Just have a problem when you are making the claim that there is a pot of gold at the end, yet you haven't found it, and want someone else to prove you all wrong.

I know that rainbows seen from an airplane are a complete circle with the shadow of the airplane in the middle. Quite dramatic. Since that means that all rainbows are complete circles, there is no end. The Earth's shadow blocks half of it. At the very best, no end, no pot of gold. There never was a pot in the first place.

A proof of this is simple enough to produce with a garden hose set for mist fan spray. Spray it away from you opposite the sun. Move it around until you get the effect. Full sunshine. Full circle.

Definition. Friction Drag, also known as Skin Friction Drag, is drag caused by the friction of a fluid against the surface of an object that is moving through it

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You're the one chasing rainbows "fool".

Other knowledgeable AI bots appear to disagree with your friction theory.

Resize_20241006_123915_5709.jpg (285.86 KiB) Viewed 974 times

While certainly some negligible or incidental friction occurs between some gas molecules and the orifice, and/or between the gas molecules themselves, such incidental friction does not cause the JT effect and any influence from friction is beside the point, in addition to the Joule Thomson effect not a cause of Joule Thomson.

If you think friction has a big influence or some causative role in JT, please explain the inversion temperature in terms of friction.

Why does friction cause cooling when a gas expands below the inversion temperature but the same gas heats up when expanding above the inversion temperature?

If friction were the cause, why the inconsistency?

Basically "fool" you don't know what your talking about. Just spewing lies and misinformation as usual.

If anyone here is an "intentional liar" it's you.

[Fool]

I didn't say it was caused by friction. I said friction is necessary. It is the sudden expansion after the friction that allows the molecules to interact. Not intermolecular friction. Skin friction.

[Fool]

Basically "fool" you don't know what your talking about. Just spewing lies and misinformation as usual.

If anyone here is an "intentional liar" it's you.

This is what we tell little school children is unacceptable behavior.

Furthermore, you constantly misread, misinterpret my postings. Slow down and read them more carefully. Read what you look up more carefully too. I was talking about throttling, your reference is talking about throttling. Gee I guess I do know what I'm taking about, you just don't know what you are reading about. Please grow up. Your errors aren't as bad as your abrasiveness. Of course that is completely unacceptable.

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