Stirlingengineforum.com

According to numerous sources:

Thermodynamic Process:

In a thermodynamic process complete conversion of heat to work is possible. Consider a reversible isothermal expansion or compression process of an Ideal Gas. For an Ideal gas Internal Energy is a function of temperature alone, hence if Q=∆u+w, then ∆u (change of internal energy is zero), hence, Q=w.

So from TDC, adding x number of Joules expanded to BDC 100% of the heat CAN be converted to work, so that Q=w (ignoring negligable friction which can be reduced to near zero).

So the issue involves the return stroke only.

In my observations and experiments it appears that

1. The expansion stroke does work against atmospheric pressure (or buffer pressure) We can, perhaps call this "negative work" but actual conversion of heat into mechanical motion nonetheless.

2. After reaching BDC and having used up 100% of the supplied heat the piston is now in a new position. The "internal energy" of the gas, however, has already returned to the condition it was in originally at TDC before heat was added. What does that tell us mathematically according to the ideal gas law? If the gas expanded from V1 to V2 but everything else is the same, ALL the heat added having been converted to work, then the working fluid must cool down and the pressure must drop. The pressure WAS equal to the atmospheric pressure, but now it is below atmospheric pressure. It is at the exact same state at which it began, so...

3. Atmospheric pressure MUST drive the piston back to TDC. This is inevitable

The"negative work" to drive the piston out against atmosphere is equivalent to loading a spring. The energy is returned from the spring Atmospheric pressure is the "spring".

Maybe this "negative work" is not particularly "useful" but the "heat" that was supplied has been effectively converted 100% into mechanical motion and the cycle has completed returning to the state at which it began.

There is no "pressure" preventing "compression" because according to PV=nRT the volume of the working fluid should be what it was at the start. But because the piston is in a new position at BDC there is a "vacuum". The energy required to effect the return of the piston is again, negligible.

Now this is a rather odd phenomenon. But it is utilized in air cycle refrigeration and many industrial processes involving the liquefaction of gases.

How can a gas expand "isothermally" without a change in temperature but also no change in internal energy, by virtue of the fact that there was no change in temperature?

Because: "For an Ideal gas Internal Energy is a function of temperature alone".

But if the piston moved and the temperature is the same and the internal energy is the same, the pressure must drop?

But pressure is what drove the piston out in the first place, right?

So now what?

Maybe there is some quantization going on. Perhaps expansion must take place as a result of electrons jumping orbital paths. When a certain threshold is exceeded there is a sudden large expansion pressure. Then once expansion exceeds a certain limit the electron orbits fall back towards the nucleolus all at once and there is a sudden large reduction in pressure.

At any rate, when compressed gasses are expanded in an engine in a gas liquefaction plant the expanded gas suddenly condenses into a liquid.

Very strange.

But, watching videos and reading I come across the same statement, this happens because "For an Ideal gas Internal Energy is a function of temperature alone".

A gas can apparently be heated under pressure in such a way that when finally allowed to expand it can be TRICKED into expanding beyond some limit that causes it to suddenly cool and condense into a liquid.

But that is extreme. In our little Stirling engines there is just cooling and a sudden drop in pressure that results in the piston stopping its outward motion and suddenly reversing direction back towards TDC, the gas doesn't quite loose enough energy to condense into a liquid, but the principle is the same.

Tom Booth wrote: ↑Tue Apr 02, 2024 11:07 am According to numerous sources:

Thermodynamic Process:

In a thermodynamic process complete conversion of heat to work is possible. Consider a reversible isothermal expansion or compression process of an Ideal Gas. For an Ideal gas Internal Energy is a function of temperature alone, hence if Q=∆u+w, then ∆u (change of internal energy is zero), hence, Q=w.

So from TDC, adding x number of Joules expanded to BDC 100% of the heat CAN be converted to work, so that Q=w (ignoring negligable friction which can be reduced to near zero).

So the issue involves the return stroke only.

In my observations and experiments it appears that

1. The expansion stroke does work against atmospheric pressure (or buffer pressure) We can, perhaps call this "negative work" but actual conversion of heat into mechanical motion nonetheless.

2. After reaching BDC and having used up 100% of the supplied heat the piston is now in a new position. The "internal energy" of the gas, however, has already returned to the condition it was in originally at TDC before heat was added. What does that tell us mathematically according to the ideal gas law? If the gas expanded from V1 to V2 but everything else is the same, ALL the heat added having been converted to work, then the working fluid must cool down and the pressure must drop. The pressure WAS equal to the atmospheric pressure, but now it is below atmospheric pressure. It is at the exact same state at which it began, so...

3. Atmospheric pressure MUST drive the piston back to TDC. This is inevitable

The"negative work" to drive the piston out against atmosphere is equivalent to loading a spring. The energy is returned from the spring Atmospheric pressure is the "spring".

Maybe this "negative work" is not particularly "useful" but the "heat" that was supplied has been effectively converted 100% into mechanical motion and the cycle has completed returning to the state at which it began.

And Tom has just proven what he's been missing for years...


Kudos Tom, it's not that 100% of heat input is not converted to work, it's that 100% of heat input is not converted to net work (aka shaft output). Despite Q=W, Wnet=Wpos-Wneg, whereby n=(Wpos-Wnet)/Wpos

This is why I favor W proof for Carnot vs T proof, but this is far from all inclusive (just an isothermal proof).

Next, consider LTD 'compression'...when m is constant (think charge pressure constant) then Wnet is constant BUT the buffer pressure will determine where the Wpos occurs.

As I've said before, Senft did thermo a disservice with LTD. Sure, they got guys into ECE, but these buggers have warped reality beyond common gamma issues. Thermo requires years of careful study, not jerk knee responses to illusions...

Tom Booth wrote: ↑Tue Apr 02, 2024 1:22 pm
How can a gas expand "isothermally" without a change in temperature but also no change in internal energy, by virtue of the fact that there was [and] no change in temperature?

Highlighted part makes your statement sound like a consequence vs removing this part makes your statement sound like a coincidence.

Tom Booth wrote: ↑Tue Apr 02, 2024 1:22 pm Because: "For an Ideal gas Internal Energy is a function of temperature alone".

But if the piston moved and the temperature is the same and the internal energy is the same, the pressure must drop?

But pressure is what drove the piston out in the first place, right?

So now what?

The takeaway here is that "PV" work is pressure dependent, not temperature dependent. Temperature only enters the grand scheme on the basis of energy balance, and why the kinetic theory is the basis of thermodynamics.

Not entirely sure what all you're driving at there Matt.

My basic point is that heat added does not pass THROUGH the engine, through the working fluid, across the the "sink".

It is converted 100% into work. A portion of that work output may be "stored" as potential energy to help nudge the piston back to TDC. But storing some potential energy in the "buffer" is similar to lifting a weight and then letting it go. The return to the 'ground state" is inevitable and the stored potential energy does not convert back into heat until the object lifted hits the ground.

In a Stirling engine that sequence of events just returns any heat stored as potential energy back to where it came from for the start of a new cycle at TDC.

I can agree, I think, that this may reduce net work output, but that is not the point.

The point is, the "heat" has not resulted in any net rise in temperature at the cold side. The heat did not pass through the engine it is ALL converted to work. Some of the work is converted to potential energy. The potential energy ends up being used to return heat back over to the hot side of the engine.

This is not just theory. I have a dozen or so videos of recorded experiments that prove it.

Who cares about this "work neg" "work pos"? It's all WORK. and no longer "heat".

Some work is stored as potential energy to be used later to help return the piston, but no "heat" is transported through to the "cold reservoir".

Why is that significant? If we are only concerned with efficiency in terms of "useful" work output and "work neg" is not "useful".

Well, it serves a purpose. It returns the piston to TDC to start another cycle and generates some heat that can be incorporated or "recycled" to initiate expansion at the start of another cycle.

Sure the net "useful" work output is reduced, some heat is used to "pump" heat back, but the interpretation of "Carnot efficiency" is that heat must be rejected to the "cold reservoir" passing through the engine.

So, if heat DOESN'T pass through, then running a Stirling engine on ICE does not result in ambient heat passing through the engine to melt the ice.

Experimentally, I've confirmed this.

If some ice is kept insulated, it will stay frozen longer when used to operate a Stirling engine.

Rather than the engine passing heat through to the "sink" the engine prevents heat from passing through. The engine holds the heat back and converts it to mechanical work output.

https://youtu.be/lFhUkzHRbWo?si=xR_qZ9Y-pwihQXyJ

In that experiment, the cup of ice lasted 5 hours longer with the engine running vs. not running.

Who cares about Net efficiency when the heat source is the ambient heat in the environment?

What matters is how much heat passes through to the ice. If the heat is ALL converted to work, positive OR negative, it is still being converted rather than passing through.

No insulation is perfect, but it appears Tesla was right and some energy could be derived from ambient heat.

Theoretically with perfect insulation the engine running on ice could run indefinitely, busily converting the heat in the ambient air to work and the ice would never melt.

That last comment really seems like a promotion of perpetual motion. And at that, the engine would produce zero work output. You have yet to demonstrate any work output, not even half the power supplied. Do not confuse power supplied with power actually entering the engine.

Tom Booth wrote:A proof in experimental science is an experimental result that validates the hypothesis.

https://en.m.wikipedia.org/wiki/Scienti ... 0community.

Wikipedia wrote:While the phrase "scientific proof" is often used in the popular media,[22] many scientists and philosophers have argued that there is really no such thing as infallible proof. For example, Karl Popper once wrote that "In the empirical sciences, which alone can furnish us with information about the world we live in, proofs do not occur, if we mean by 'proof' an argument which establishes once and for ever the truth of a theory."[23][24] Albert Einstein said:

The scientific theorist is not to be envied. For Nature, or more precisely experiment, is an inexorable and not very friendly judge of his work. It never says "Yes" to a theory. In the most favorable cases it says "Maybe", and in the great majority of cases simply "No". If an experiment agrees with a theory it means for the latter "Maybe", and if it does not agree it means "No". Probably every theory will someday experience its "No"—most theories, soon after conception.[25]

However, in contrast to the ideal of infallible proof, in practice theories may be said to be proved according to some standard of proof used in a given inquiry.[26][27] In this limited sense, proof is the high degree of acceptance of a theory following a process of inquiry and critical evaluation according to the standards of a scientific community.[26][27]

I would say there is no such thing as "no" . Contradiction intended. There is such a thing as probably not, which appears stronger than maybe not.

There is no high degree of acceptance of your experiments, nor your theories. What you have so far is interesting anecdotal evidence, that you are hoping to get people to look at. Leaving your work for others to say, maybe not.

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

It's a very meticulous process to do good science. It's very easy to confuse data taking with good science. Case in point: Cold fusion, Pons and Fleischmann. They took lots of data with a thermometer poorly enough to get erroneous conclusions. Conclusion: Thermometer used wrong, as it was for professor Waxman and his time machine. Probably wrong.

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

Wikipedia wrote:Criticism of cold fusion claims generally take one of two forms: either pointing out the theoretical implausibility that fusion reactions have occurred in electrolysis setups or criticizing the excess heat measurements as being spurious, erroneous, or due to poor methodology or controls.

Cold fusion appears to go against some current theories. Both maybe wrong.

You are battling both. If you go against current theory/mathematics, and practice, you'd better have stellar methods. I and others, have tried to suggest improvements to your practices, the reasons you are using, for not accepting those suggestions are, disarming your maybe wrong maybe right statements. You are going against current theory. No matter how much you think it's ludicrous, it is the currently backed up maybe right theory.

Tom Booth wrote:2. After reaching BDC and having used up 100% of the supplied heat the piston is now in a new position. The "internal energy" of the gas, however, has already returned to the condition it was in originally at TDC before heat was added.

The volume is larger and compressing it to V1 will cause the temperature to increase back up to Th and require Pin to equal Pout in doing so, unless of course DQc is rejected. In other words, the gas will get hotter during compression.



Let us look at a heat pump:

Total work input 25 Joules. Tc=300, Th=400. Qcz=MCbTc.

A: Starting at the same point as above engine Tc=T1, P1, V1, internal energy is Qcz, Tc is the cold plate. Powered expansion, Work input from electric motor, or such. The volume increases to V4, Pressure P4 is lower than P1/atmospheric. T4 would be much lower than T1 but isn't because of heat conduction. This allows DQc to be picked up keeping the temperature close to Tc, in an ideal case it would stay at Tc.* The internal gas does positive work but it is way less than the work input from the atmosphere. So requires electrical input, or such.

B: Heat is added to bring the Temperature of the gas to Th. Two ways to do this are, adding work energy Carnot compression, and, regenerator/displacer Stirling. T3=Th, P3, V3.

C: Compression stroke from V3 to V1. The gas is in conduction with the hot plate. T2 stays close to Th and T3, ideally they are the same. Compressing the gas allows DQh to be rejected by work input to the hot plate.* The atmosphere does positive work but is much smaller than the negative work the gas does. This requires work input from an electrical motor, or such.

D: Heat is removed to return to the starting point T1, V1, P1. Two ways to do this are:

1: Work output Carnot from expansion. This is where the Carnot work added is cancelled.

2: Heat is stored in the regenerator/displacer, Stirling.

Using the Carnot Theorem to calculate the maximum amount of heat transfered for temperatures of 300 K and 400 K, gives:

25 J work in, 75 J picked up from the cold plate, 100 J deposited into the hot plate. This is a COP of 4 Or 400%. Ideally.

* Real pumps will be worse, because the gas needs to be much colder than Tc to pick up heat, and much hotter than Th to deposit heat.

Blah blah blah, more side stepping, avoidance, changing the topic and ad hominem.

I asked for ANY experimental evidence of any kind whatsoever in support of the "Carnot Limit". Your still coming up dry and hastily changing the topic. Heat pumps are not the subject of this thread. The Carnot limit equation as applied to Stirling engines and it's questionable validity is.

The Carnot limit is not based on "stellar methods" of experimental procedure or even "anecdotal" evidence. How about ANY evidence at all?

It's based on guesswork Heat as a fluid falls down like a waterfall. A complete fallacy.

Anyway, Mr "fool", I could really care less about your opinions regarding scientific standards. This is basically a hobby. I do experiments for my own self edification to my own satisfaction out of curiosity and personal ambition to build engines. I need to know how they work. Not trying to prove anything to you or anyone else. Just sharing results of my research as objectively as possible, mostly through video to remove my personal bias as much as possible. You or anyone are free to form your own opinions.

In general though, I agree about the high bar of scientific evidence but you apparently have a double standard. The. Carnot Limit was never subject to modern scientific standards that you are demanding from my hobby. Yet I've at least done some actual experiments

In support of the "Carnot Limit" you've got nothing. It gets a pass. It's so old it's just grandfathered in with nothing to back it up at all.

Tom Booth wrote:This is basically a hobby. I do experiments for my own self edification to my own satisfaction out of curiosity and personal ambition to build engines.

I guess that is fare enough. Although I'd have to say, if experiments are done without serious scientific methods, there is very likely nothing learned, or worse, fraudulence.

Lots of scientists use the 200+ years of thermodynamics to create very impressive engines. That is stellar enough data for support of those theories. Including Carnot.

Stirling engines and Stirling heat pumps are the exact same device. As proven by many, including Phillips. The Carnot Theorem applies to both. Why wouldn't it, they are the exact same machine.

Here's one of your references:

https://galileo.phys.virginia.edu/class ... Engine.htm

How remarkable, it says:

Efficiency = TH−TC/TH.


This was an amazing result, because it was exactly correct, despite being based on a complete misunderstanding of the nature of heat!

Amazing indeed!

However nothing to back up the assertion ".. it was exactly correct" is offered, experimentally, historically or otherwise and unfortunately it appears you can do no better.

When you actually adhered to some sound mathematics you managed to prove my point.


As far as heat pumps, most in use these days are phase change vapor compression cycle units. If you want to elaborate on Stirling cycle beat pumps have at it.

Fool wrote: ↑Wed Apr 03, 2024 1:25 pm ...
Lots of scientists use the 200+ years of thermodynamics to create very impressive engines. That is stellar enough data for support of those theories. Including Carnot.
...

Still nothing but your own conjecture and opinion based squarely on nothing at all.

Maybe you could at least point out which if any of your recently revised mathematical "proofs" have been finalized or have you given up on that exercise?

Fool wrote: ↑Wed Apr 03, 2024 7:28 am That last comment really seems like a promotion of perpetual motion.
...

Well, aside from the fact that hydrogen atoms have been in motion, oscillating, or whatever atoms do, since the big bang, it looks like the entire universe is in perpetual motion. I don't personally have any prejudice against the idea, or the possibility in general.

But I don't consider intelligent utilization of an available source of energy as "perpetual motion". The energy in the air molecules in the atmosphere, the ambient heat, was put there by the sun, it's just indirect solar energy or fuel, the same as firewood or oil or coal, but less messy.

Tom Booth wrote: ↑Wed Apr 03, 2024 1:40 am
Theoretically with perfect insulation the engine running on ice could run indefinitely, busily converting the heat in the ambient air to work and the ice would never melt.

Yikes, is this what you're thinking:


an "ideal" alpha where pts 2 = 4 = 1 bar_Thigh = ambient_thermal ratio = volume ratio:

and Tlow (cold hole) that would make Tesla shiver...

R14 maybe? (Liquid at 145K)