Nikola Tesla Vs. The Second Law Of Thermodynamics

[TomBooth]

Yes, you’re right. The max theoretical Carnot efficiency is 20% and that is the 72,500 joules of heat energy released by one cup of water falling in T from 373 K to 300 K. What I am saying is that all of that energy cannot be converted to useful work to run the engine. There must be some heat lost from the cylinder when the gas expands. For no particular reason, I stayed with 20 % system thermal efficiency, which is rather low, and I should have explained what I was doing.

 

However, even if I were to go with a thermal efficiency, of the overall system, being half of the theoretical limit, then 50 % of the 6.7 Watts of continuous power is converted to mechanical work and the other 50 % is dissipated as waste heat.  (Actually, everything eventually winds up as heat, including the mechanical energy, as energy is conserved). Now, instead of 5 W being dissipated by the heat sink, there is only a 3.5 W dissipation.

I don't think there is anything wrong with sticking with 20%. That is what we have been working with. That is the theoretical "Carnot efficiency" of my model engines when running on hot water (approximately), and I don't have a problem with the fact that there are loses, so that all of the 20% of the theoretically "available heat" cannot be utilized, because of friction, conduction of heat through the engine body, etc.

 

What I have an issue with, that I think needs ironing out, if possible, is the seemingly universal assumption that the remaining 80% of "heat" that cannot be used passes through to the "sink".

 

That 80% represents a whopping big amount of heat that would dwarf loses due to friction and such to the realm of virtual insignificance.

 

In a Stirling engine there is no steam or air/fuel mixture actually carrying latent heat. Heat only enters the engine when there is an imbalance above equalibrium, and leaves the same way, when there is a temperature difference.

 

I think that this is an entirely different dynamic from a Steam engine or gasoline engine, where a physical fuel passes through the engine. Only energy enters a Stirling engine. Energy above the ambient, so IMO, the 80% below ambient is irrelevant and can be, or should be ignored.

 

So, with that, the 20% is really 100% of the heat flowing into the engine. (For a Stirling engine).

 

So, yes, some of that 100% of heat entering the engine due to heat spontaneously flowing from hot to cold will be lost to friction, etc.

[TomBooth]

I thought the epoxy piston seemed a little too loose in the cylinder, I also wanted to check the actual diameter of the original piston, so picked up some calipers, which I've needed, and will come in handy anyway.

 

The epoxy piston is about 5 thousandths of an inch too small. I did lap it in with some fine grinding compound, but I didn't think that much. Apparently, over time, as it dried, the epoxy shrunk. I'm guessing. It was a really snug fit to begin with, but it had only dried overnight.

[TomBooth]

OK, thanks for clarifying.

 

Carnot efficiency is just the best theoretical efficiency:

 

[math]Efficiency\quad =\quad 1\quad -\quad \frac { { T }_{ C } }{ { T }_{ H } } \quad x\quad 100 %[/math]%

 

In your example Tcold is 300K and Thot is 373K so the efficiency is 19.6 %

 

But, I don’t consider that to be a hard limit. I consider the limit to be at Tcold = 0K

 

At that point the efficiency is hard-limited to 100 % as it should be in any sane system.

 

In your example, there is still a lot of heat energy at the ambient (cold) T of 300 K. The trick would be to devise some way of collecting that energy without the need to input any additional heat energy beyond the 373 K already being used.

 

I don’t know if it is possible, but I would argue that it is not necessarily impossible. There may be some way to bootstrap the engine so that the Tcold dips below ambient, even if only intermittently,...

Congratulations if you do not consider Carnot efficiency a hard limit. I don't think I do either, but it is supposed to be the second law of thermodynamics. Or one of the legitimate ways of expressing it.

 

As appears in the link posted earlier by Dubbelosix:

 

"The second law of thermodynamics has a third form:

 

"A Carnot engine operating between two given temperatures has the greatest possible efficiency of any heat engine operating between these two temperatures."

 

So, according to that, assuming my Stirling engine is in the category of a heat engine 19.6 % is a hard limit, according to the second law of thermodynamics.

 

Tesla said poppycock!

[TomBooth]

Whatever the cause. Hawking evaporation is a theory of how a heat engine in nature gives up its thermal abilities to the environment. Believe me when I say, it's not entirely hypothetical since we have observed analogue radiation from analogue black holes.

You are talking about such things as this, presumably?: "Hawking radiation, stimulated by quantum vacuum fluctuations, emanating from an analogue black hole in an atomic Bose-Einstein condensate is reported (references)" source: https://www.sciencedirect.com/science/article/pii/S2405844019361572

 

I was joking about Bose-Einstein condensates in connection with heat engines and Carnot efficiency, about 7 years ago:

 

https://www.physicsforums.com/threads/assumed-violation-of-physics-heat-vs-work.667129/post-4247322

 

My threads were locked, and I was banned from that forum. For what? questioning the veracity of "Carnot efficiency"?

Edited August 25, 2020 by TomBooth

[TomBooth]

"Believe me when I say, it's not entirely hypothetical since we have observed analogue radiation from analogue black holes."

 

Who is "we" anyway? Just curious.

[TomBooth]

Something else Tesla mentioned in his 1900 article, that he viewed as a potential contradiction of the second law of thermodynamics, as then stated by Carnot and others as applied to heat engines:

 

"I came to the conclusion that it was possible to construct a machine which would do the same.

 

"As the first step toward this realization I conceived the following mechanism. Imagine a thermopile consisting of a number of bars of metal extending from the earth to the outer space beyond the atmosphere. The heat from below, conducted upward along these metal bars, would cool the earth or the sea or the air, according to the location of the lower parts of the bars, and the result, as is well known, would be an electric current circulating in these bars. The two terminals of the thermopile could now be joined through

an electric motor, and, theoretically, this motor would run on and on, until the media below would be cooled down to the temperature of the outer space. This would be an inanimate engine which, to all evidence, would be cooling a portion of the medium below the temperature of the surrounding, and operating by the heat abstracted."

 

As fantastic as a thermopile to outer space may seem, or how impractical, we are talking about possibility, not practicality.

 

Tesla saw that the cold of outer space is actually a potential heat sink and that the enormous heat contained in the atmosphere, heated by the sun, could, in theory be tapped into.

 

All that is needed to run a heat engine is a temperature difference.

 

So to get "free energy" from the heat in the air, all we need is a way to tap the cold of outer space, and who says that can't be done?

 

It seems primitive people have been taping into the cold of outer space to make ice for, I suppose, thousands of years, by radiative cooling. Why couldn't the temperature differential between ambient heat and radiative cooling be used to run a heat engine?

 

https://youtu.be/7a5NyUITbyk

[Dubbelosix]

Well, a Casimir battery has been theoretically speculated upon. It could tap into vacuum energy.