LTD model "Stirling" uses Lenoir Cycle

[Tom Booth]

By "negative pressure" I mean below the atmospheric pressure we all walk around in. What, in practical terms, would be considered a partial vacuum, where atmospheric pressure would exert a force to push a piston inward.

Normal atmospheric pressure is something like 100000 Pascals, right?


I would guess 0 zero on that scale represents the equivalent of normal atmospheric pressure, but who knows?

Yes 0 on that scale represents normal atmospheric pressure, what ever that was at the moment.
...

Atmospheric pressure is 1, you can not go below 0 (negative) only a fraction of 1. Even when combining all available energy in the world no chance of going below 0.
...
Below atmosphere is not negative, it is lower (less) pressure.

Sure, though, on the scale you provided, below atmosphere (zero 0) is indicated in negative values.

If atmosphere is taken as zero, which you agree (bolded above), that is the scale used on the PV diagram you provided, then below atmosphere is less than zero, or a negative value.

In the same way -10°F is "ten BELOW zero" though not literally below ABSOLUTE ZERO.

Resize_20220312_050818_8747.jpg (90.61 KiB) Viewed 7403 times

Atmospheric pressure is 1, you can not go below 0 (negative) only a fraction of 1.

Yes you can go below zero (1 atmosphere) if using a scale where 1 atmosphere is set at zero, as in the PV diagram you provided, quite obviously.

Yes 0 on that scale represents normal atmospheric pressure, what ever that was at the moment.
Atmospheric pressure various with location and weather changes so mean sea-level pressure of 101325 Pa at 15°C (59°F) is used as base.

Atmospheric pressure is 1, you can not go below 0 (negative) only a fraction of 1

Given that a Stirling engine, on this planet, situated within earth atmosphere, unless pressurized, starts out at atmospheric pressure, using atmospheric pressure as the baseline makes sense.

Below atmosphere then is commonly referred to as a "vacuum"; i.e. less than atmospheric pressure.

Since you readily admit: "Yes 0 on that scale represents normal atmospheric pressure", I'm at a loss to understand what point you are trying to make, or why it seems like an issue.

If the pressure on one side of the piston is higher at atmospheric pressure, and pressure on the other side of the piston is lower, below atmosphere, the piston will move in the direction of lower pressure, if you want to call the lower pressure "fractional", fine, but the PV diagram you provided shows this "fractional" pressure as negative, below zero, values.

[Tom Booth]

99% of Stirling engines have no active cooling, without it, it is impossible to go below atmospheric pressure. There simple is nothing there to do so.

Yes, there is.

Heat is added to the engine. This expands the working fluid/gas/air and pushes the piston out.

If simply left to cool back down to it's original temperature, atmospheric pressure will push the piston back to where it started.

That is, of course, assuming there are no air leaks.

So, upon cooling back down, the internal pressure drops below atmospheric pressure.

Why you say this is "impossible", I have no idea.

Such passive cooling, however, is generally a rather slow process, so the bulk of the actual cooling is due to the conversion of heat into work, which is a direct instantaneous transfer of kinetic energy. The effect, however is the same. The working fluid cools due to loosing energy and the pressure drops back down, below atmosphere, until the piston returns to re-equalize the pressure, as it was before heat was added.

[Nobody]

Look up the definitions of:
Absolute Pressure
Gauge Pressure
Differential Pressure

Hint: Gauge Pressure is a special type of Differential Pressure.

PV=nRT

P1V1/T1 = P2V2/T2

Expansion only happens when the volume gets larger. Heating doesn't always produce expansion. Only when there is a volume change.

Any container with a moving wall will be extracting work from an expansion, regardless of the end motion of the wall, ( Slowed by a brake or just by MV of the piston, doesn't matter.) Slowing the wall with a brake will not pull more work from the gas, it will just leave less MV in the piston. Same amount of work, different energy-form out.

So you can't get more cooling by putting on a brake. Cooling will be the same, dictated by PV=nRT.

Compression/contraction only happens when there is a volume change. Compressing a gas causes it to heat because kinetic energy is being added to it. I.e., the molecules are being sped up by bouncing off an advancing piston wall. Contraction doesn't happen just from cooling, there must be a volume change.

[Nobody]

The more adiabatic expansion (with conversion of heat into work) results in internal cooling and pressure drop, below atmosphere/buffer, the more efficient the engine.

Proof of concept Engines needed, with outside reviews.

[airpower]

By "negative pressure" I mean below the atmospheric pressure we all walk around in. What, in practical terms, would be considered a partial vacuum, where atmospheric pressure would exert a force to push a piston inward.

Normal atmospheric pressure is something like 100000 Pascals, right?


I would guess 0 zero on that scale represents the equivalent of normal atmospheric pressure, but who knows?

Yes 0 on that scale represents normal atmospheric pressure, what ever that was at the moment.
...

Atmospheric pressure is 1, you can not go below 0 (negative) only a fraction of 1. Even when combining all available energy in the world no chance of going below 0.
...
Below atmosphere is not negative, it is lower (less) pressure.

Sure, though, on the scale you provided, below atmosphere (zero 0) is indicated in negative values.

If atmosphere is taken as zero, which you agree (bolded above), that is the scale used on the PV diagram you provided, then below atmosphere is less than zero, or a negative value.

In the same way -10°F is "ten BELOW zero" though not literally below ABSOLUTE ZERO.


Resize_20220312_050818_8747.jpg

Atmospheric pressure is 1, you can not go below 0 (negative) only a fraction of 1.

Yes you can go below zero (1 atmosphere) if using a scale where 1 atmosphere is set at zero, as in the PV diagram you provided, quite obviously.

Yes 0 on that scale represents normal atmospheric pressure, what ever that was at the moment.
Atmospheric pressure various with location and weather changes so mean sea-level pressure of 101325 Pa at 15°C (59°F) is used as base.

Atmospheric pressure is 1, you can not go below 0 (negative) only a fraction of 1

Given that a Stirling engine, on this planet, situated within earth atmosphere, unless pressurized, starts out at atmospheric pressure, using atmospheric pressure as the baseline makes sense.

Below atmosphere then is commonly referred to as a "vacuum"; i.e. less than atmospheric pressure.

Since you readily admit: "Yes 0 on that scale represents normal atmospheric pressure", I'm at a loss to understand what point you are trying to make, or why it seems like an issue.

If the pressure on one side of the piston is higher at atmospheric pressure, and pressure on the other side of the piston is lower, below atmosphere, the piston will move in the direction of lower pressure, if you want to call the lower pressure "fractional", fine, but the PV diagram you provided shows this "fractional" pressure as negative, below zero, values.

Only because they plotted a wrong graph does not mean to follow the footsteps. It is still not a negative pressure. It is 850 Pa below atm, ask around if 100475 is a negative number.
There is no such thing as negative pressure, doubling down on wrong speak does not make it right.
At an altitude of 20 000 meter pressure is 5474 Pa, what 71589 Pa can do we have seen. 384 403 000 meter is it to the moon.

When you walk around in negative pressure, don't forget the special pressure protection suit.
https://upload.wikimedia.org/wikipedia/ ... g_pose.jpg

[Tom Booth]

It is not particularly "wrong speak" if everybody agrees on the terminology and what it means.

I'm not "doubling down".

I've stated several times I agree, it is technically inaccurate, perhaps, but that is entirely irrelevant.

You are using this to claim it is impossible for the pressure in a Stirling engine to go "below atmosphere" going as far as to say: "atmosphere is ~ 850 Pa below"

How does that make sense?

It seems you don't know what you're talking about, can't read a PV diagram properly, can't tell a PV diagram of a "real" Stirling engine from a simulation, or a heat pump etc. but are trying to instruct everybody else in how a Stirling engine functions, or what it can or can't do.

[airpower]

Flywheel will take a standard passive cooled Stirling engine below atm.
If cooling fins can get temp below environment then give me the link for the cooling fins freezer i buy a buch of them.

Another serious case of negative pressure.
https://twitter.com/i/status/1502421292888301573

[matt brown]

Here's a more visual example...consider a large 'flame licker' style vacuum engine where its crankcase is enclosed in a 'high pressure' reservoir. Once you grasp the PVT values for any such bugger, you'll see how limited isobaric compression schemes are. Yes, it might work on paper, but anything larger than a small model would likely fail due to various scalar issues.

[Tom Booth]

I disagree. On my solar engine, which has a diaphragm power piston, when the displacer moves the air to the cold side you can see a strong negative pressure pulling the diaphragm in. If I stop it with my hand I can feel the negative pressure for a few seconds till the vacuum equalizes.
The engine seems to have equal pressure and vacuum on corresponding power strokes.
Nothing scientific, just my observations.

Making observations is science.

[Tom Booth]

The more adiabatic expansion (with conversion of heat into work) results in internal cooling and pressure drop, below atmosphere/buffer, the more efficient the engine.

Proof of concept Engines needed, with outside reviews.

Try any "off-the-shelf" model Stirling engine.

Now, let's see a "proof of concept" Carnot engine. LOL

For two centuries, nothing.

Double standards among these Carnot limit advocates.

[Tom Booth]

Try an overlay.

What does that tell you?

More work, steeper/faster/deeper temperature drop.

The colder the engine gets each cycle, the more heat it can take in each cycle.

Resize_20220313_060536_6821.jpg (113.93 KiB) Viewed 7333 times

[matt brown]

The more adiabatic expansion (with conversion of heat into work) results in internal cooling and pressure drop, below atmosphere/buffer, the more efficient the engine.

Tom - that was what Watt achieved with his condenser, but this was only due to meager back work of boiler feed pump. You are transfixed on work 'process' while dismissing cycle issues. I like PV plots, since they're hard to cheat, but they NEVER show heat input, so they can be misleading. An xlnt example is where heat req'd between 2 different internal energy states is NOT path independent, but path dependent. IOW, consider 2 isotherms (think 300k and 600k) where - by accepted definition - each isotherm has constant internal energy. The heat energy req'd to get from 300k to 600k IS NOT FIXED, but depends on "how you get there" (is path dependent). The 2 most common examples are "heat capacity at constant volume" (aka Cv) vs "heat capacity at constant pressure" (aka Cp). So, a good PV will reveal PVT values, but the heat and/or work per process will normally require calculations (sometimes one can gather heat, work, eff from PVT ratios).

I posted the heat triangle and it's Stirling Cycle extension to expose (quantify) regen heat vs simply hashing it around as an unknown quantity (Stirling sucker bait). Once you get a grip on process heats per my Stirling Cycle regen nickel tour, consider similar Ericsson Cycle where...same heat input, same work output, would require larger engine by temperature ratio AND larger regen by Cp/Cv. So, Ericsson vs Stirling with same 300k-600k cycle, both have same relative inputs & outputs, but the Ericsson engine will be 2x the size (due to thermal ratio of 2) with a much larger regenerator due to greater regen heat (Cp>Cv) which will vary by monatomic or diatomic gas. The only advantage the Ericsson gains over Stirling (in this example) is that the Ericsson has a much lower peak pressure.

Now, let's see a "proof of concept" Carnot engine. LOL

For two centuries, nothing.

Double standards among these Carnot limit advocates.

OK, the pig/s in your driveway !!! Besides cycle concept, Carnot also nailed the adiabatic compression process, but it would be another 50 yrs until Otto stumbled across it. Bottom line: scheming ways to minimize heat input process (the secret sauce) exceed scheming ways to maximize work output process.

[airpower]

[Tom Booth]

....You are transfixed on work 'process' while dismissing cycle issues.

Work, (that is, the conversion of heat to work) is a major cycle issue. THE major, primary cycle issue which historically has been almost entirely overlooked and ignored because of a completely erroneous basic understanding, or rather, lack of understanding or complete misunderstanding of how heat engines actually operate.

If the input heat is not converted to work, then it can only build up. Then yes, a "sink" is needed to get rid of the "excess".

I think it is more productive to focus on how to efficiently convert more heat into work rather than how to build bigger and better heat sinks for all the "waste heat" which has been the conventional approach, because everybody has been indoctrinated into believing the so-called Carnot efficiency Theorem, taking it as a veritable "LAW".

Now, let's see a "proof of concept" Carnot engine. LOL

For two centuries, nothing.

Double standards among these Carnot limit advocates.

OK, the pig/s in your driveway !!! Besides cycle concept, Carnot also nailed the adiabatic compression process,...

How so?

Carnot's main focus was on isothermal compression, which he conceived as "transporting" Caloric through the engine to the "cold reservoir". A completely fictitious idea, bordering on delusion. A kind of mental psychosis that still, unfortunately, infects people's thinking regarding heat engine efficiency, or just basic operation.

You think Carnot "nailed it" LOL

I believe Carnot's ridiculous declarations need to be completely eradicated. The sooner the better, for the future benefit this could bring to all of mankind.

The so-called "Carnot Limit" has had a stranglehold on people's thinking about heat engines long enough.

[Tom Booth]

According to Carnot, the most efficient heat engine possible is one that transports ALL of the "caloric" to the "cold reservoir" without converting any heat whatsoever to work output.