Stirlingengineforum.com

I don't really comprehend how some people do not see how an equal amount of heat going in, and also being removed to the "sink" along with additional energy production (power out to the load), is not a violation of the conservation of energy.
your mistake is to think that the two amounts of heat are the same, energy conservation says that the difference is precisely the mechanical work produced.
Maxwell questioned the second law, Carnot's idea, in a very clever way with his Maxwell demon paradox. You can study it if you want, it's difficult stuff, only resolved by Leo Szilard in the 20's.
Not useful to make engines to work, better stick to conventional thermodynamics, Carnot's work, which is well proven and working wonderfully.
To replicate the PV diagram would be a useful exercise for you, it would help you learn what works.

omblauman wrote: ↑Tue May 04, 2021 2:31 pm ...
your mistake is to think that the two amounts of heat are the same,..."

Not my mistake, I said "some people" referring to some who believe that ALL the heat MUST pass through. (That includes Carnot himself, originally)

"better stick to conventional thermodynamics, Carnot's work, which is well proven and working wonderfully."

Nothing personal, but, you must be joking, right? According to Carnot: 'The production of motive power is then due... not to an actual consumption of caloric, but to its transportation from a warm body to a cold body'.

His analogy given is precisely that of water over a waterfall: "The motive power of a waterfall depends on its height and on the quantity of the liquid; the motive power of heat depends also on the quantity of caloric used, and on what may be termed, on what in fact we will call, the height of its fall, that is to say, the difference of temperature of the bodies between which the exchange of caloric is made. In the waterfall the motive power is exactly proportional to the difference of level between the higher and lower reservoirs."

IMO, complete nonsense through and through. Carnot's so-called "perfect" heat engine is a function-less joke from the point of view of an actual engineer or mechanic, requiring outside intervention to do anything whatsoever. I don't know how in the world any sensible person ever swallowed his nonsense.

Here is, in Carnot's own words, his description of his engine:
Aside from the fact his engine runs, or fails to run, rather, on the fictional "caloric", a non existent, magical material substance, Carnot states, among other illogical nonsensicalities:

"(3) The body A is removed, and the air is then no longer in contact with any body capable of furnishing it with caloric. The piston meanwhile continues to move, and passes from the position ef to the position gh. The air is rarefied without receiving caloric, and its temperature falls. Let us imagine that it falls thus till it becomes equal to that of the body B at this instant the piston stops, remaining at the position gh."

Let us imagine! and we must indeed imagine. Why should the piston suddenly stop whenever the temperature of the gas reaches this arbitrary temperature of "body B" to which at the time it is making no connection whatsoever?

No logical reason for this magic is given.

What if "body B" happens to be some arbitrary temperature that is much colder?

Somehow Carnot's magic engine will know about this change and the piston will continue until the temperature of the gas cools further to match whatever temperature will happen to be supplied in the future.

He goes on: "(4) The air is placed in contact with the body B; it is compressed by the return of the piston as it is moved from the position gh to the position cd. This air remains, however, at a constant temperature because of its contact with the body B, to which it yields its caloric. "

He has already stated that the gas and "body B" have reached the same exact temperature in step #3.

We all know heat flows from hot to cold, so why should this "caloric" flow from the air into "body B" when they are both, as stated "equal" in temperature?

For two hundreds years this clearly impossible engine has been held up as the ideal to be striven for and people wonder why little progress has been made in the development of heat engines.

"better stick to conventional thermodynamics, Carnot's work, which is well proven and working wonderfully."
I wasn't referring to any of Carnot's actual words, everybody knows not to interpret caloric as heat, but to what today is meant by Carnot theory as for ex in https://en.wikipedia.org/wiki/Carnot%27 ... %20details.
When one says
"better stick to conventional thermodynamics, Carnot's work, which is well proven and working wonderfully."
one means that the second principle, which Carnot formulated correctly even with the wrong picture of a gas in mind, works well regardless of how one pictures the actual microscopic underlying "reality". Thermodynamics is an axiomatic theory which was formulated on the basis of experience well in advance of statistical mechanics, or even kinetic theory for gases, it doesn't correspond to any specific physical system and has a much wider applicability than to thermal engines.

The whole design of a Stirling engine is based on Carnot's old fallacy that heat is a fluid.
So forget about Carnot's actual words but consider modern thermodynamics ,"Carnot theory", which is as right as a theory can be, proven by centuries of experimentation.
If you are curious to understand why thermodynamics is right, and when it's applicable, as it certainly is in the Stirling engine case, you need to dig into the studies of its foundations and you will learn that the problem isn't that heat is not a fluid but that heat is particle motion which is not knowable. Or equivalently not worth knowing of, too expensive to learn all which is needed to get its energy out. It's obviously not a question of energy conservation, the first principle is saved, it's a matter of "cost of information".
As you already know there is no in principle difference between the "ordered" kinetic energy of your car molecules moving on the road and their "random" kinetic energy, their heat. Except that, as with regenerative braking, you can recover all of your car motion energy, as it would have been at infinite temperature, but you can recover only that amount of random motion of the molecules your car is made of that Carnot says you can recover. If you find a lower temperature reservoir to attach to, that is. If there isn't any lower temperature reservoir than you can't recover any of that thermal energy, which is why we can't extract energy for the water of the seas.
As said earlier I can't think of a better description of this stuff than in the developments of the Maxwell demon paradox as for example in H.Leff, A.Rex, Maxwell's Demon 2 Entropy, Classical and Quantum Information, but it's not quick learning. I would be happy to find out that there is a youtube video on this subject. Thinking about it we could make one ourselves exploiting our new LTD experiment.

For starters, an "axiomatic theory" is a contradiction in terms. Theories are always open to question.

"Thermodynamics is an axiomatic theory which was formulated on the basis of experience."

Carnot, confessedly, in his magnum opus, had little if any direct practical experience with steam engines, or engines of any kind for that matter. His ponderous assertions hang in the air; chimera, without foundation.

Like the material used for a heat engine has no bearing, only the "fall" or temperature difference.

You think the microscopic details about particle behavior are unimportant, "not worth knowing"?

I think it perfectly possible and legitimate to create a "heat engine" entirely powered by the crystalization of ice.

Ice as it freezes and expands exerts a force of some 100,000 pounds per square inch. Crystalizing ice could power a piston, six inches in diameter, to lift a weight of some two million pounds or so. Attached to some ratchet or other and cycling through freezing and thawing this could be a "heat engine" (or "thermal engine", perhaps, being less prejudicial).

To say that all that matters is temperature difference and the material substance used is of no consequence flies in the face of any actual observable. Can it be said that a Stirling engine runs no differently on air than it does on helium?

I observe a huge difference.

https://youtu.be/uysxKgr8Qjk

To say nothing of compressed helium. None of this matters, only the "height of the fall"?

What height are we falling from when ice freezes and exerts it's force of expansion?

https://youtu.be/erlZb8QiPkg

W = Qh - Qc

How does that thermodynamic equation work out for the "ice bomb"?

"If there isn't any lower temperature reservoir than you can't recover any of that thermal energy, which is why we can't extract energy" (from) "the water of the seas."

Again, nothing personal, but this sort or assertion just stifles thought and bars investigation, research and experimentation, (and potential funding for R&D etc.) and has done so when it comes to the question of heat engines, for the past 200 years. Why waste time on something "everybody knows" is impossible? So nobody bothers or dares. What a shame.

IMO Tesla was 10,000 times more of a practical genius who's work produced real world results, but his work on heat engines is still mostly ignored. He said a "lower reservoir" was not a requirement. I think his statements on the subject, at least, deserve some thoughtful consideration, rather than a blanket dismissal, with an appeal to the authority of the great and infallible Sadi Carnot.

The only way the Second law of thermodynamics has held true is by studiously avoiding making any observations that contradict it.

Which is the policy of many a science forum where I've attempted to post my experimental observations over the years. Here for example:

But PF (Physics Forum) does not discuss perpetual motion machines even for the purpose of debunking them, so either way, unfortunately this thread will need to be closed.

Source https://www.physicsforums.com/threads/s ... ine.991714

If an observation contradicts the holy and sacred second law, the evidence is ignored. If it can't be entirely ignored, it's sanctioned (in the sense of banning, such an ambiguous term).

I said nothing about, nor did I advocate "perpetual motion" there BTW. Just presented the curious results of an informal experiment, using an off-the-shelf, model Stirling engine.

Since when is a Stirling engine a "perpetual motion machine"?

When it appears to run on boiling water without access to a "sink" I guess.

Or when it runs on ice, but causes the ice to melt more slowly rather than faster (from the waste heat Qc) being rapidly delivered to the "sink" by the engine, as might be expected.

Or

As said earlier I can't think of a better description of this stuff than in the developments of the Maxwell demon paradox as for example in H.Leff, A.Rex, Maxwell's Demon 2 Entropy, Classical and Quantum Information, but it's not quick learning. I would be happy to find out that there is a youtube video on this subject. Thinking about it we could make one ourselves exploiting our new LTD experiment

Thanks for the reference. I may send for the book, or maybe download the PDF sometime. I'm always interested in that kind of stuff, but I'm trying to finish up the book on Vuilleumier and already have several books on Arduino on the way.

While on the subject of Maxwell's demon and the 2nd law, have you ever read Tesla's article on the subject?

Or I should say, his article that touches on the subject. Tesla became, as he states, "intensely interested" in Carnot and Thompson's scientific pronouncements about the impossibility of a perpetual or "self-acting" heat engine.

When I'm not here, I'm often on some science forum or other debating the subject. If not actually down in my workshop trying to build the damn thing myself.

Tesla's "Self Acting Engine" that is.

You can find my plans and diagrams all over the internet.

I stumbled across one iteration that I posted a long time ago on the crowdfunding site: https://experiment.com and forgot about.
It boggles my mind when educated people on the various science forums assert the absolute impossibility of a "self acting" heat engine when a toy heat engine that can run "with only ONE reservoir" has sold, no doubt, by the millions, at least since I was a little boy.

My family had one on our fireplace mantle when I was almost too small to remember, but I used to climb up on a chair and keep the glass filled with water for I don't remember how many days, or weeks, or months.
Ok, so it requires occasional maintenance involving the addition of a little cooling water, what engine doesn't? That could easily be automated, as it is for millions of toilet tanks and livestock watering troughs. Hasn't anyone ever heard about float valves?

I don't think that utilizing evaporative cooling negates the fact that the toy is operating within a single heat reservoir, considering the fact that the same heat at the same temperature in the same room is driving evaporative cooling as well as the toy itself. Which is keeping itself cool under its own power by dipping it's beak and swaying back and forth, which speeds up evaporation.

There are other, much more effective methods of refrigeration. Why nobody has ever attempted to use the same principle to scale up something bigger and more practical, with some actual power output is beyond me, but infact. It has been done.

For a while there was something of a media craze in the papers over Charles Tripler's liquid air generator that he humbly claimed, he found, could produce ten gallons of liquid air, then he could turn around and use three gallons that he just produced to run the machine to produce ten more gallons.

The liquid air boiled at room temperature powering a steam engine that compressed the air, which compressed air he cooled down with water supplied from a nearby stream.

Up until he was slandered and derided and accused of fraud in the press and the scientific journals, he was shipping his liquid air all over the continent in wooden barrels to anyone that wanted it.

Nobody understood how it worked. Not even Tripler.

It basically worked on the same principle as the toy bird: water cooling, not much different than the Lind process.

Cooling compressed air makes the compression much easier. Especially given a steady flow of cold water already refrigerated by nature.

Cold water and atmospheric heat are two resources for which there is really no lack on this planet.

I think Tesla was too ambitious though, attempting to extract heat down to cryogenic temperatures. The toy bird, I think, clearly demonstrates that to be unnecessary. It runs quite steadily at room temperature, but Tesla was trying to power the world. That would require more cooling power than provided by the water evaporating off the head of a toy bird covered with a square inch or so of slightly damp felt.

Anyway, Tesla says his workshop was destroyed by fire. He never returned to it to try and complete the project.

Everybody thinks Tesla's big "free energy" machine was some gigantic tower throwing lightning bolts. Really, it was a humble heat engine.