Tesla's Ambient Heat Engine revisted

Discussion on Stirling or "hot air" engines (all types)
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Tom Booth
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Re: Tesla's Ambient Heat Engine revisted

Post by Tom Booth »

Stroller wrote: Sat May 04, 2024 2:07 pm If only I could afford the shipping I'd take your junk off your hands for you.

12kW of solar energy costs no more than time and effort, plus some space blankets and ingenuity,

Over at my petite ruine in France I have many 20' lengths of 2" bamboo to lash up a parabolic framework with. And an acre of land to site it on. I have 5 cubic metres of rainwater stored onsite for cooling.
The culmination of about 250 million dollars in R&D prototyping etc. your going to need more than shipping. Anyway it's not for sale.

The linear generator and flexure bearings are probably worth salvaging.

Still completely impractical IMO, but who knows. I might change my mind when and if I ever get it running. Doubt it though.
Tom Booth
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Re: Tesla's Ambient Heat Engine revisted

Post by Tom Booth »

Stroller wrote: Sat May 04, 2024 12:36 pm
Tom Booth wrote: Sat May 04, 2024 9:24 am
150° temperature difference between boiling water on the hot side and 60° ambient air on the other seems sufficient to see some heat flow across a 3/4 inch displacer chamber, unless something were holding it back or taking the heat away or both.
In the video you linked, you'd placed a scalpel scalloped piece of insulation foam in the bottom of the displacer cylinder. That'll hold back the heat nicely then. What little does get through is sufficient to keep the engine ticking over.
I suppose you didn't watch the other video of the engine running?

The "scalloped piece of insulation foam in the bottom of the displacer cylinder" is known as a (drumroll) displacer. Usually anyway. A new design but still a displacer. Still goes up and down pushing air down against the hot plate. And yes designed with the intention that: "What little [heat] does get through is sufficient to keep the engine ticking over."

Which is the whole idea, and all that is needed to run the engine, proving flooding the engine with four or five times more excess "waste heat" is hardly necessary, and just that. A waste. Not a "Law of the universe".

If the engine did additional work, the gas would get colder and be able to take in more heat faster to compensate for the work load.

No need to throw 80 or 90% of your heat down the drain any more than you need to flood your car engine until gasoline is coming out the tailpipe.
Stroller
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Re: Tesla's Ambient Heat Engine revisted

Post by Stroller »

I at least skimmed through all the videos you linked. They are interesting. I missed that the scalloped foam piece rose and fell (how far?) and thought the air was being moved by the spiral cut white material "thermal valve"attached to the displacer rod.

What was the start and end time, the initial water temperature and final water temperature?
From those you can calculate the rate of energy passing through the engine. This has to be the starting point for a worthwhile discussion.

I don't think the majority of the elevated temperature of the power piston and cylinder is due to friction. If it was, the engine would have stopped. I think it's due to them being made of materials which pass heat more readily than the acrylic plastic and aerogel.

Apart from your IR thermometer and thermocouples to measure temperatures, how have you gone about measuring the work done? In one of your previous videos you showed some fairy lights being lit up briefly, but you had to supplement the energy from a tea-light candle with a gas blowtorch to achieve that.

It seems to me that this is the most difficult measurement to make, because the energy going into keeping the flywheel spinning by overcoming any friction in the system is so small that any measuring apparatus will slow and stop it. But without proper measurement, the main thrust of your contention about extracted work cooling the upper part of the engine is moot.
Stroller
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Re: Tesla's Ambient Heat Engine revisted

Post by Stroller »

Tom Booth wrote: Sat May 04, 2024 2:54 pm
Stroller wrote: Sat May 04, 2024 2:07 pm If only I could afford the shipping I'd take your "junk" off your hands for you.

12kW of solar energy costs no more than time and effort, plus some space blankets and ingenuity,

Over at my petite ruine in France I have many 20' lengths of 2" bamboo to lash up a parabolic framework with. And an acre of land to site it on. I have 5 cubic metres of rainwater stored onsite for cooling.
The culmination of about 250 million dollars in R&D prototyping etc. your going to need more than shipping. Anyway it's not for sale.

The linear generator and flexure bearings are probably worth salvaging.

Still completely impractical IMO, but who knows. I might change my mind when and if I ever get it running. Doubt it though.
Do not vandalise this magnificently engineered piece of Stirling engine history!
matt brown
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Re: Tesla's Ambient Heat Engine revisted

Post by matt brown »

Stroller wrote: Sat May 04, 2024 11:04 pm
It seems to me that this is the most difficult measurement to make, because the energy going into keeping the flywheel spinning by overcoming any friction in the system is so small that any measuring apparatus will slow and stop it. But without proper measurement, the main thrust of your contention about extracted work cooling the upper part of the engine is moot.
Hey Stroller, there was a thread here last year on a massive LTD type engine by Koichi Hirata. Have you seen the thread ?

http://www.stirlingengineforum.com/view ... 933#p18933

http://www.stirlingengineforum.com/view ... 7253#p7253
Stroller
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Re: Tesla's Ambient Heat Engine revisted

Post by Stroller »

Thanks Matt. There's some data there we can calculate with. I've summarised it in this image.

Info from here: http://www.bekkoame.ne.jp/~khirata/acad ... index.html

Unfortunately, they don't tell us which of the three configurable stroke lengths the power piston had been set at for the test.

Image

Supplied heat is 0.33litres/sec of 128C Ethylene Glycol dropping to 118C
Calc 1 will be to compute the number of Joules transferred to the engine per second.
Specific heat capacity of Ethylene Glycol in liquid form at 25C is 149.5 J/(mol·K)

Peak output power is around 145W at ~100rpm at the shaft = 145J/sec.
Last edited by Stroller on Sun May 05, 2024 1:51 am, edited 1 time in total.
matt brown
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Re: Tesla's Ambient Heat Engine revisted

Post by matt brown »

One of the forum members posted a few translations of Koichi's research. Scroll down part way in this page to get to his LTD monster.

http://www.stirlingengineforum.com/viewtopic.php?t=5520

I keep a copy of the screenshot in the following post where the dimensions are shocking (note DP vs PP details).

http://www.stirlingengineforum.com/view ... 002#p19002

BTW original project focused on 100W from 100C differential (which req'd minor mod)
Stroller
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Re: Tesla's Ambient Heat Engine revisted

Post by Stroller »

Molar mass of Ethylene Glycol is 62.068 g/mol
Specific gravity is 1.13
in 0.33litres there will be 376.66/62.068 = 6.068 mol
Specific heat capacity of Ethylene Glycol in liquid form at 125C is 149.5 J/(mol·K)
149.5 * 6.068 mol * 10K temperature drop = 9072J

Is this right or have I fouled up?
9072 Watts in to get 145 Watts shaft power out seems very poor.

Surely they'd have been better off slapping electric underfloor heating elements all over the base of the displacer cylinder than running heated Ethylene glycol round a small area of the sidewalls?
Stroller
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Re: Tesla's Ambient Heat Engine revisted

Post by Stroller »

matt brown wrote: Sun May 05, 2024 1:50 am BTW original project focused on 100W from 100C differential (which req'd minor mod)
Maybe they were looking at the viability of generation from the waste heat of watercooled ICE engines. Hence the antifreeze at 130C. I guess it doesn't matter so much how small the output is if the input energy is 'free' (or otherwise wasted).
VincentG
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Re: Tesla's Ambient Heat Engine revisted

Post by VincentG »

Tom, in the name of science I spray painted half of a Pyrex bowl flat black and tested with the thermal gun at room temperature and after hot water exposure.

There was no discernable difference except for a small variation where the paint transitioned to clear glass.

I also tested a piece of black plastic and stainless steel side by side at room temperature.

No difference.

I have previously seen large differences between surfaces but thinking back that was at much higher temperatures in automotive applications.

Maybe at lower temperatures there's much less variation.

Still, I think these tiny engines have too much thermal transfer through the body compared to the miniscule amount of gas inside to make any concrete conclusions.

Once the volume of gas can transfer more energy than the body of the engine itself, then IMO, conclusions can be drawn.
VincentG
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Re: Tesla's Ambient Heat Engine revisted

Post by VincentG »

Is this right or have I fouled up?
9072 Watts in to get 145 Watts shaft power out seems very poor.

Surely they'd have been better off slapping electric underfloor heating elements all over the base of the displacer cylinder than running heated Ethylene glycol round a small area of the sidewalls?
Agreed 100% the heat exchangers were the major flaw in that design.

Note how hot water outlet temperature continues to fall at the max rpm, while power drops to nothing. The energy is moving through the gas but the machine is not effective at harvesting it.
Tom Booth
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Re: Tesla's Ambient Heat Engine revisted

Post by Tom Booth »

VincentG wrote: Sun May 05, 2024 8:07 am Tom, in the name of science I spray painted half of a Pyrex bowl flat black and tested with the thermal gun at room temperature and after hot water exposure.

There was no discernable difference except for a small variation where the paint transitioned to clear glass.

I also tested a piece of black plastic and stainless steel side by side at room temperature.

No difference.

I have previously seen large differences between surfaces but thinking back that was at much higher temperatures in automotive applications.

Maybe at lower temperatures there's much less variation.

Still, I think these tiny engines have too much thermal transfer through the body compared to the miniscule amount of gas inside to make any concrete conclusions.

Once the volume of gas can transfer more energy than the body of the engine itself, then IMO, conclusions can be drawn.
Don't know what your suggesting or trying to say exactly.

My thermal gun/camera thing, as I said, uses colors as an indicator of RELATIVE temperature.

Hotter<white,red,,green,blue,black>Colder

Actual temperature readings are digital.

Spot temperature, Highest, Lowest are all displayed digitally simultaneously.

The display color. contrast is adjustable. If a temperature difference of say 0.1°C is not showing up you can increase the contrast until it does. You might call that the "sensitivity".

So if your target has only a few degrees ∆T and the temperature difference color display is not showing up on the screen you can very easily increase the contrast/sensitivity by just clicking on up and down arrow buttons on the handle until it does.

Can't draw "any" conclusions? from temperature readings?

Are you loony? A temperature reading is a temperature reading. Easy peasy. It isn't rocket science.

One has to wonder why some forum members here pile mounds of horse shit on top of quite clear and obvious temperature readings and simple irrefutable video recorded experimental findings.
VincentG
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Re: Tesla's Ambient Heat Engine revisted

Post by VincentG »

No the point I was making is that the claims of inaccuracies due to the different emissivity of various materials is perhaps negligible. (I and others have made these claims.)


I'm just suggesting that these models are just too small to sway anyone's belief.
Tom Booth
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Re: Tesla's Ambient Heat Engine revisted

Post by Tom Booth »

Stroller wrote: Sat May 04, 2024 11:04 pm ...

I don't think the majority of the elevated temperature of the power piston and cylinder is due to friction. If it was, the engine would have stopped. I think it's due to them being made of materials which pass heat more readily than the acrylic plastic and aerogel.

...
Compress_20240504_125427_7507.jpg
Compress_20240504_125427_7507.jpg (22.73 KiB) Viewed 2589 times

Your observation skills and reasoning abilities are obviously skewed by your mountains of preconceptions and prejudices.

The engine cold side pictured in the above image and in the video is not insulated with anything. The entire engine top, cold ambient side is metal and fully exposed to the ambient air.

The heat being generated by work/friction at the power piston is clear and obvious.

Also clear and obvious is the adjacent metal temperature has not risen above the surrounding ambient. It is reading 1° colder!

This is after three hours running on boiling hot water.

That entire engine top has an aluminum cylinder fused together with the aluminum top plate. A stock engine. The power cylinder and cold plate are stock, as they came in the kit, unmodified, not insulated, no acrylic, no aerogel.

Only the sides are insulated. The above image is a clip/screenshot from this video:

https://youtu.be/P11q-BAhvqk
VincentG
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Re: Tesla's Ambient Heat Engine revisted

Post by VincentG »

Hey Tom have all your below ambient results been with an acrylic hot plate? I just realized that and it explains why my engine with metal plate always heat soaks the cold plate.

I know the metal hot plate is way overkill for these small ltd engines and have been meaning to test a plastic hot end.
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