The TRUTH? η = 1 – (Qc / Qh) = 1 – (Tc / Th)

[Tom Booth]

Common sense would seem to dictate that if a heat engine is running there is at least heat>0 going in and work(mechanical motion or a running engine)>0

On the other hand, heat is a form of light is it not? Or at a minimum can take the form of infrared light, and light has some unfathomable properties and behaviors



https://youtu.be/b9O6iCM4vCg?si=lLqQZJtP0Dl3ftBn


At least when nobody's looking.

[Tom Booth]

The theory or claim I keep hearing and reading is that it is not a thermodynamic process where heat cannot be transformed into work 100% but a CYCLICAL process.

It IS possible to transform all the heat into work during expansion but heat has to be rejected during compression. Is this correct, or does everyone agree with this?

[matt brown]

The theory or claim I keep hearing and reading is that it is not a thermodynamic process where heat cannot be transformed into work 100% but a CYCLICAL process.

Basically correct. However, using your 300-400k thermal cycle example, 300k ambient air has 3/4 the internal energy U of 400k engine air, so it's kinda a tug-of-war between Uhigh and Ulow, engine vs ambient. Both are usually manipulated via PVT values which obscure U, but U is lurking, and the heavy hitter behind Carnot Theorem (not girlie T).

It IS possible to transform all the heat into work during expansion but heat has to be rejected during compression. Is this correct, or does everyone agree with this?

Yes on expansion part, no on compression part. Common "isothermal" cycles like Stirling and Ericsson reject heat to sink during compression vs common "adiabatic" cycles like Otto and Brayton reject heat to sink prior compression, not during compression.

[Fool]

Visible light enters a solar cell and energy leaves a solar cell as electricity and as infrared light. The efficiency is going to be less than 38%, early ones were only 5% , or less. I don't know what the market solar cells are rated at, probably higher than they typically can demonstrate. I would be happy with 20%, which is very good for a heat engine.

A swing or pendulum would appear on a PV diagram as a cycle with zero internal area. That would be similar to adiabatic bounce. Pushing a swing would give it a tiny little blip of micro energy somewhere near the center. Not an effective power producer.

An pneumatic or hydraulic cylinder must be pressured in each direction, unless an outside force is used to recompress it. The outside force robs energy from the expansion. A heat engine requires heat addition for expansion, and heat removal for compression.

Matt, you forgot to mention that both the Otto and Brayton Cycles are significantly less efficient than the Stirling and Carnot Cycles. It would also help to mention that iit s from lack of heat of compression rejection. And they both are large quantities of heat rejectors, venting it out the exhaust.

Isotherms are the key to maximum efficiency. Allegedly proven mathematically. According to ivo Kolin. They must occured during both the expansion and compression stroke.

The second law of thermodynamics only applies to full cycles. Single strokes can be more efficient or less, often way less. Especially for the compression stroke.

[Fool]

Matt, almost forgot. Thanks for the he complement on doing the numbers the hard way. It's the only way I can drive the implications into my brain. I appreciate the numbers you've provided here. I don't fully appreciate their implications. The worst part, LOL, is that I understand most of them. Probably a sign of my upbringing. I saw those ratios in that thread, thumbs up. I've wanted to post a chart of Delta T"s corresponding to Delta P's for ideal gasses. It, I think, would add perspective on how difficult it is for a LTD Stirling Engine to even run. Your baby's breath point is spot on.

Early this millennium, LOL, I thought it would be fun to break Senft"s LTD 30 year record, so was brainstorming a bunch of ways to do that. All of them revolved around pressurization to maximize the pressure increase.

I didn't really come here to contemplate numbers and theories. What intrigued me was the experiments and creative inspirations Tom has put forth. I just seem to be bogged down in defending 200 years of intertied solid engineering which appears simple to me, however a bit too much for many.

Tom's attempt to create a foam carbon displacer from a slice of bread wrapped in aluminum foil, is a good example. Both inspiring and, when he tried eating it, quite entertaining. I keep wondering if wrapping it in a lot more aluminum foil could produce a carbon, aluminum foam composite that would be tougher and stronger. The aluminum may oxidize becoming very heat resistant. Think about an aluminum oxide carbon foam composite? Years ago I heard of an aluminum terracotta composite that allegedly was stronger and tougher, but haven't seen it since.

[Tom Booth]

....

The second law of thermodynamics only applies to full cycles. Single strokes can be more efficient or less, often way less. Especially for the compression stroke.
...

Well, "can be more efficient" is good enough I think.

What the "Carnot Limit" claims is a hard limit imposed by physical law limiting exactly how much heat can be converted to work.

The "Second Law" is much more liberal in its interpretation than the Carnot formula (as it is being applied).allows.

Anyway, if, lets say 30% of the heat supplied by you is converted to work output during expansion and the "Carnot Limit" is 20% how do you make up, or put back the 10% difference? Never mind if the conversion on expansion is 100%

If you have already "used up" more than allowed in the first operation, even if only 1% more than a typical 20% limit where do you get this 1% to put back in order to "reject" the necessary 80% to come in under the "Carnot limit"

What if you convert 50% of the heat on expansion and the Carnot limit is 20% you have a difference of 30% to make up. etc. etc

[Fool]

What if you convert 100% of the heat on expansion, and the theoretical Carnot limit is 20%?

Would you have 80% to "make up"?

I don't know what are saying? If you manage to get an engine to convert 100% of the input heat into work energy during the expansion, do not confuse this with attempted supplied heat, it has to actually enter the engine, the return stroke will require %80 of that work to reject 80% of the input heat. Back work against the gas pressure in the engine and expulsion of the heat of compression.

Any deviation of this will produce worse efficiency. You won't make up any difference. You will lose it. In other words, if back work is greater than forward work, the engine will stall. If it converts 30% you will get way less.

[Fool]

Take my example 300 K, 400 K, 25% cycle. It takes 75 Joules of back work. If less than 75% or 75 J are converted to work on the forward stroke, the engine will stall and the efficiency will go to zero. If 69% are produced on the forward stroke, it will run with a 1% efficiency.

[Tom Booth]

What if you convert 100% of the heat on expansion, and the theoretical Carnot limit is 20%?

Would you have 80% to "make up"?

I don't know what are saying? If you manage to get an engine to convert 100% of the input heat into work energy during the expansion, do not confuse this with attempted supplied heat, it has to actually enter the engine, the return stroke will require %80 of that work to reject 80% of the input heat. Back work against the gas pressure in the engine and expulsion of the heat of compression.

Any deviation of this will produce worse efficiency. You won't make up any difference. You will lose it. In other words, if back work is greater than forward work, the engine will stall. If it converts 30% you will get way less.

Your analysis is illogical.

The more heat converted to work on expansion, the LESS heat remaining in the working fluid to necessitate "back work" to compress the gas, which would only be hot and expanded due to supplied heat (heat supplied to and entering the working fluid) that had NOT been converted to work.

What distinction you are trying to make between "input heat" and "attempted supply heat" I don't know.

A Joule is a joule.

We could have a heating element inside the engine so virtually no heat is lost or does not "actually enter" the engine. In such a case the "LAW' would still apply, would it not?

[Tom Booth]

What if you convert 100% of the heat on expansion, and the theoretical Carnot limit is 20%?

Would you have 80% to "make up"?

I don't know what are saying? If you manage to get an engine to convert 100% of the input heat into work energy during the expansion, do not confuse this with attempted supplied heat, it has to actually enter the engine, the return stroke will require %80 of that work to reject 80% of the input heat. Back work against the gas pressure in the engine and expulsion of the heat of compression.

Any deviation of this will produce worse efficiency. You won't make up any difference. You will lose it. In other words, if back work is greater than forward work, the engine will stall. If it converts 30% you will get way less.

You are saying, (in the highlighted sentence above), that 80% of the heat that has been converted to work is required to compress the gas to expell the same 80% of the heat.

Not only is that illogical, it would be a violation of conservation of energy because the same energy doing the compression is the same heat (thermal energy) being expelled.

Or the 80% energy stored in the atmospheric "buffer" outside the engine compressing the working fluid on the return stroke is the same energy being expelled from the working fluid from inside the engine.

Only someone thoroughly indoctrinated into thermodynamic "science" is capable of holding such contradictory ideas as if they make perfect sense.

[matt brown]

Thanks for the he complement on doing the numbers the hard way. It's the only way I can drive the implications into my brain. I appreciate the numbers you've provided here. I don't fully appreciate their implications.

I tend to use 'the numbers' for a specific answer, but I'm more interested in concepts. Thermo is loaded with ratios, so I play with values to expose obscure relationships. A good example is that pt 2-4 isobar thing where any such PV should have Tr = Vr.

bogus PV.png (40.47 KiB) Viewed 2322 times

Once those 2 pts are an isobar, if Tr = Vr fails, then it's bogus. I don't recall where I got this, but if PV is this bad, the paper is probably worse.

Meanwhile, some PV are just careless

Green cycle PV.png (11.68 KiB) Viewed 2322 times

Again, "the isobar" with well proportioned plot. The problem here is whether or not Tr = Vr when V scale is so abstract. It turns out V scale is correct and maybe just a lame editorial thing. BTW this is from a student paper on Stirling cycle mod that is half-baked while pushing the limits. In another 10 yrs, this guy might realize that he was onto something and only needed a different mech than common SE.

I've wanted to post a chart of Delta T"s corresponding to Delta P's for ideal gasses.

Do you mean adiabatic PVT index ?

It, I think, would add perspective on how difficult it is for a LTD Stirling Engine to even run. Your baby's breath point is spot on.

Yup, "air" is whimpy, but this is what makes it a challenge...

[matt brown]

Or the 80% energy stored in the atmospheric "buffer" outside the engine compressing the working fluid on the return stroke is the same energy being expelled from the working fluid from inside the engine.

Correct via energy vs "heat" buzz.

[Tom Booth]

Or the 80% energy stored in the atmospheric "buffer" outside the engine compressing the working fluid on the return stroke is the same energy being expelled from the working fluid from inside the engine.

Correct via energy vs "heat" buzz.

Maybe you could expand on that little blurb or "buzz",

Are you agreeing that this is illogical as well as impossible or by "correct" you think it's just fine and dandy?

If you ask me, it takes the post hoc, ergo propter hoc fallacy to a whole new level. This goes beyond simply a false assignment of causality but the effect has become its own cause. The energy doing the compressing is also the energy compressed as well as the energy being "rejected" back into itself.

Complete and utter nonsensical bullocks.

[Tom Booth]

What if you convert 100% of the heat on expansion, and the theoretical Carnot limit is 20%?

Would you have 80% to "make up"?

I don't know what are saying? If you manage to get an engine to convert 100% of the input heat into work energy during the expansion, do not confuse this with attempted supplied heat, it has to actually enter the engine, the return stroke will require %80 of that work to reject 80% of the input heat. Back work against the gas pressure in the engine and expulsion of the heat of compression.

Any deviation of this will produce worse efficiency. You won't make up any difference. You will lose it. In other words, if back work is greater than forward work, the engine will stall. If it converts 30% you will get way less.

This is an interesting question I've asked before many times on various science and physics forums. What does "rejection" actually refer to?

"Attempted supplied heat" that never entered the working fluid of the engine?

If that were the case the whole Carnot Limit "Law" would be rendered meaningless, as literally any quantity of heat could be "attempted supplied heat".

But IMO, however you slice it the Carnot Limit formula makes no sense.

Take a P-19 Ultra LTD. It can operate on 0.5°C temperature difference.

According to the "Carnot Limit" with a cold side of 299.5°C and a hot side of 300°C the engine could have no more than 0.08724% efficiency.

As generally interpreted, this would mean that of every 100 joules supplied to the engine over the course of some time interval, 99.91276 joules would be "rejected".

That is, of every 100 joules "supplied" (actually entering the working fluid) more than 99.9% of this supplied heat goes into the working fluid and is then subsequently "rejected" by means of compression of the working fluid so that the "heat of compression" is transfered out of the working fluid to the cold side "sink".

But, supposedly, we could have nearly 100% efficiency (conversion of heat into work) during the expansion phase of the cycle during the time while heat is entering into the working fluid.

Let's pretend that all that energy is stored in the flywheel.

The piston reverses direction and the stored energy in the flywheel compresses the working fluid.

How does this cause the "supplied heat" supposedly still present in the working fluid to be "rejected" if that thermal energy has already been transformed (stored as kinetic energy in the motion of the flywheel)?

You have 99.9% of the energy having been "stored" as kinetic energy in the flywheel now working to compress the same 99.9% of the "supplied" energy, supposedly somehow still residing in the working fluid awaiting removal.

[Fool]

You keep thinking that anytime energy is put into an engine you get to keep it. The energy you are putting in is to return the engine to zero. When you get done putting the work in the cycle will be back at the starting point. In other words, Qcz.

Work goes into the gas compressing it. It would get hotter above Tc and Qcz unless that heat of compression is let back out. This works out as 100% tit for tat, work in heat out, and is 25% lower than the forward stroke because it is 25% lower in temperature. It is the way isothermal processes work.

Not only is that illogical, it would be a violation of conservation of energy because the same energy doing the compression is the same heat (thermal energy) being expelled.

Yes, conservation of energy, and zero change in internal energy for a complete cycle, science upheld. Work in equals heat out for isothermal compression. Internal energy back to Qcz, the starting point. If the expansion stroke isn't isothermal, more heat will need to be rejected.

What distinction you are trying to make between "input heat" and "attempted supply heat" I don't know.

A Joule is a joule.

Your temperature reading experiment where you used an 85 W steamer, supplied 85 W to an engine that cannot absorb any more than gan 0.005 Watts. The amount supplied is mot the amount entering the engine. Even if the heater is in the engine, heat will be escaping from the hot end directly to the atmosphere. So not all the supplied heat will turn into work and DQc, some will be rejected directly out of the hot plate.

Infrared heat goes through a acrilic wall like it's not even there, and many other materials.

And a Joule is not a Joule. I thought by now you'd understand why a Joule of heat is not as useful as a Joule of, Work, or Electricity. Some, up to all, of the Joule of heat must stay as heat, when any attempt to convert it to work is performed and the Joule of heat, or what's not converted exists at a lower temperature than before the conversion. In other words, after conversion, some of the Joule, is work, the rest energy is colder. If it isn't colder, by heating up a Tc plate very slightly, the back work will be equal to the front work, adiabatic bounce, zero work to output, ideally. In reality, much worse.

A pendulum swing has equal front work and back work, hence, zero work output. Trying to get work from a pendulum stops it quickly. Just raise the weight on a clock to test this. Very little work to run a clock. Very small mgh, mass, to drop a short distance to keep it running. Yet the pendulum stopps quickly without it. Very little energy stored in the pendulum.

The more heat converted to work on expansion, the LESS heat remaining in the working fluid to necessitate "back work" to compress the gas, which would only be hot and expanded due to supplied heat (heat supplied to and entering the working fluid) that had NOT been converted to work.

Heat doesn't remain in the working fluid. What you are talking is internal energy. Internal energy remains constant during a isothermal expansion. And zero total change for a complete cycle.

Or the 80% energy stored in the atmospheric "buffer" outside the engine compressing the working fluid on the return stroke is the same energy being expelled from the working fluid from inside the engine.

Please leave 'buffer' and atmospheric pressure out of this discussion. I've already explained why outside effects completely cancel in the energy analysis of a complete cycle.

Tom, I maybe wrong about how you think in regard to the following, but please hear me out. I think you are battling the following beliefs :

1: 200 years of thermodynamics and engine building are somehow wrong.

2: 2000 year old mathematics, such as Calculus and graphs, are wrong.

3: Current science classroom education is wrong.

4: Your experiment can't possibly be wrong or even misunderstood.

5: You want to have greater efficiency, maybe even over unity, so everyone scoffing at such is wrong.

6: Being hands on educated is more important than classroom learning, and that no one with a classroom degree, not the easiest thing to get, has any hands on experience.

I will try to explain, in hopes that it starts people thinking.

1: A scientific theory is only as good as it is useful. If another comes along that is more useful, the previous will be scrapped. Science is mathematics. If the new theory doesn't have new better math, the old theory will continue. Case in point, relativity theory is more accurate than Newtonian theory, but Newtonian theory is still used where it is easier. Relativity theory is only used where the errors in Newtonian theory are too great.

2: The Egyptians used that mathematics to build the pyramids. Mathematical rigor has continued to confirm what we calculate and discover even today. Again, if something comes along that is more useful, it will be scrapped. Until then it is all we have. IMHO, if you can't beat it use it Schmitt Theory is a useful starting place for Stirling Engines.

3: Of course current education has errors and in it. They teach that in school. Tell you to watch out for it. Provide mental tools to look for it. Those tools are also useful to identify and expose charlatans.

4: This one is hard for anyone to swallow. The first rule of science is, beware of the fact that you will fool yourself more often than anyone else. I've caught myself by changing my mind set from how come I'm right, to why is this wrong. If it stands up to both, then quietly ask someone more educated/experienced than yourself. Spend a lot of time thinking about their input. If they disagree, it's probably you. If many many disagree, it is you, or your explanation. Try to understand them, you asked them for help.

5: Trying to prove you can do over unity before you can do over unity is self contradictory. No one will want to help prove something that appears unprovable. If continuing in this request, expect lots of resistance.

6: I have a classical BSME degree, but I've been repairing lawnmowers since I was 11 and cars since I was 13. All my own, and friends, mostly for free. My current mower is a John Deere F1145 diesel, plus 5 other riders that are running. Plus at least 5 that I haven't run lately and I'm suppose to be working on, and an uncountable number of smaller and walk behinds. More than a dozen vehicles. Army 6x6 Duce and a half. Excavator, backhoe Caterpillar bull dozer, Timber Jack skidder, saws, sawmill, pond system Chum Salmon incubators, ... Short list... Shall I continue? Fun!

I pretty much takes one to know one and I'm probably a fool for even trying to knock a fool straight, but I'm here as a friend. You ask to know. All I've done is display what I know. If you have better math modeling please present it. If not. Please stop the following :

Complete and utter nonsensical bullocks.

I'd really rather use math logic and experimentation. You seem to agree.