The Right Theory of the Real Stirling Engine.

[Bumpkin]

Sadi, could you clarify your definition of the Stirling Cycle? I consider it to be represented by a closed-loop regenerating heat engine. Numerous sources credit Robert Stirling with that development. (I like the book "Air Engines" by Theodor Finkelstein and Allan Organ.) You're probably already familiar with that book, but for the record, it covers a lot of the discussion points you listed.

I would add my two cents to your point of finding a "useful use." There are some fringe applications like submarine and spacecraft, but I like to keep my feet on the ground. Photovoltaics have developed far past the practicality of concentrated solar engines, and it's very unlikely that even a perfectly optimized Stirling could supplant internal combustion, so I don't see much point in wasting a solar budget or processed fuels on high-temperature Stirlings. My own interest is in mid-temperature engines for low-tech biomass-fueled cogeneration in single-home use. Inconsistent fuel and inconsistent people and the realities of a clean burning stove are some considerations. It's a small niche, but an engine made in that interest might also be useful for waste heat recovery.

Bumpkin

[Bumpkin]

Sadi, could you clarify your definition of the Stirling Cycle?

Bumpkin

[Tom Booth]

I don't know about the Stirling cycle. To me a heat engine is a heat engine. I'm certainly not a Stirling engine purist. Whatever works, works. Personally, I think the "pure" Stirling cycle engine has been surpassed, probably for decades, with "free piston" engines

I'm not at all sure what type of heat engine this one is, but I'm anxious to find out. It sounds like something out of the Indy 500!

I'd say; very impressive for a "tin can" size engine, but really, impressive for any heat engine.

https://youtu.be/r9lYsW0Df08

[Tom Booth]

Carnot wrote: "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"

Carnot took no account of heat being converted into work In that regard the entire theoretical basis for his so-called "engine" was erroneous A Carnot engine which transfers all of its heat to the sink as Carnot originally imagined would have ZERO efficiency and ZERO work output.

A Carnot engine could not meet your criteria of lifting even an empty bottle of beer.

A Stirling engine lacks efficiency to the extent it is modeled after Carnot's concept of a machine that efficiently transports heat from a hot body to a cold body only incidentally performing some work as a side effect, in the same way that water turns a mill wheel, and all that matters is the "height of the fall" or the temperature difference.

To hold up the Carnot engine as an ideal to be striven for is so nonsensical I'm not going to waste any more of my time debating the issue.

You might as well say that an airplane can fly around the world, not by burning fuel but by transporting it. All you need to do is fill the tank in one location and empty it out after arriving at the destination, and the further you fly, the more efficient the engine.

No Carnot engine exists not because it is so great, but because it is nonsense.

[Tom Booth]

Your animation: https://austav.eu/camstirling.gif

Is interesting.

I'm not sure it would work, but I'm not sure it wouldn't.

I can't say with certainty what parts you reference in your post are what, like, the three metal plate regenerator. I'm not sure where that is supposed to be.

Are the half round bumps heating and cooling channels?

Some sort of annotation with named or numbered parts with an explanation of the function of each could help, similar to a patent drawing.

I also don't see how it meets your criteria for: "3. STE must at least perform cold-hot heat regeneration at "constant volume",

It appears to function the same as a typical Alpha-type Stirling, though making it double acting may be an innovation, I don't see how it is different otherwise.

It might be easier to achieve the kind of movement you are looking for, if the two pistons were to run on separate grooves having two different cam configurations. It would give you more freedom to play around with anyway.

[Tom Booth]

"The movement of the cold and hot piston along the same curve ensures hot-cold regeneration at a constant volume (when the cold piston goes down the hot piston goes up at the same speed "

I wouldn't think that two systems with changing but opposite volume would qualify as "constant volume" just because they are joined.

I did not forget that there is water falling over the water mill wheel.

That is why this cycle serves as a reference for comparing thermodynamic cycles according to thermodynamic efficiency.

Carnot "efficiency" is nothing more or less than a mathematical obfuscation of the temperature difference. As such it has nothing to do with practical efficiency.

[Tom Booth]

Correctly, your statement should read: "all that matters is energy flow (fluid flow) between two heights or two temperatures".

Just to be clear; my intent in that statement is to point out what is wrong with "Carnot efficiency", heat is not water. Heat is not a fluid. Heat is a form of energy. The purpose of a heat engine is to convert heat to mechanical electrical or some other form of energy NOT to have a "fluid" flow between two heights or two temperatures.

You can believe whatever you want, but I think that the idea that heat is supposed to flow to the sink and that is what powers the engine is putting effort in the wrong direction.

"A Stirling engine lacks efficiency to the extent it is modeled after Carnot's concept of a machine that efficiently transports heat from a hot body to a cold body only incidentally performing some work as a side effect, in the same way that water turns a mill wheel, and all that matters is the "height of the fall" or the temperature difference." << that is Carnot's concept of a heat engine which I believe is wrong. The temperature difference is far from the only thing that influences efficiency. It does not influence efficiency at all.

Carnot was only measuring available energy.

Compare that with photovoltaics. The amount of sunshine available at a certain latitude is not a measure of solar cell efficiency. Similarly, the temperature difference only tells how much energy is available, not how efficiently it is utilized.

[Tom Booth]

Dear Tom,
Have you perhaps seen or used water without "heat"? Have you perhaps seen or used "heat" outside of fluid or any material? I hope you didn't! Heat is simply the kinetic energy of the molecules of a fluid, ie, materials !!! The water turbine converts the kinetic energy of water into useful work! Heat engine converts the kinetic energy of fluid molecules into useful work! The principle is the same! The fluid and its energy must flow between two different heights or two different temperatures!

I think that such an idea is fundamentally inaccurate.

Hot air does not need to flow through a person to warm a person.

A moving billiard ball can convey energy to another, regardless if the other ball is also moving or not, relative to the other.

Air does not flow through a Stirling engine carrying heat with it as it passes through in the same way water flows through a turbine.

Energy is not matter. Not a substance.

[tibsim]

Carnot doesn't know what efficiency machine we is going to build, he just says at most how efficient it can be maximum if it works at all!
Stirling machines sometimes achieve efficiencies of up to 40% in practice. The best models sometimes 1% because they work with atmospheric pressure air.