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VincentG wrote: ↑Sun May 05, 2024 11:04 am 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.

Short answer is no.

Long answer:

Most of my experiments involved trying to "BLOCK" the heat with insulation so I couldn't see or get any actual readings from the top.

Logically the top of the engine can't really go below ambient when in direct contact with the ambient air. The very slight cooling would be nullified by the ambient heat.

I built this engine with a similar regenerator on the side walls.

The original intent of the insulation with the lid (in the following video) was to put a little container of ice inside the compartment and let ambient heat come up through the bottom to run the engine, so I kept the metal bottom plate for ambient heat input.

This worked great. The engine ran very well at a pretty high RPM. (With just ice in the little compartment under insulation) and I went to show this to my wife all excited, and suddenly the engine just jammed and wouldn't move. It seemed as though the piston had frozen in the cylinder. Literally.

I can't confirm that. A minute after the engine stopped the piston came free again. By the time I got the tape off and opened the compartment the ice had already started melting.

Later I ran this experiment with the same engine but just heated "normally" with a cup of hot water. (Following video)

The cup by the way is a double wall vacuum insulated cup. The idea of using that was just to retain the heat of the hot water as long as possible and so that most of the heat would go up through the engine.

There is some temperature difference between areas on the table in "shade" from the overhead lamp.

Anyway, it can be seen that the heat from the hot water radiates through the walls of the vacuum insulated cup immediately.

The top of the engine, however, does not go above the general ambient. It is in the "shade" under the insulation and the temperature goes up immediately when the insulation is removed letting light in from the overhead lamp, as well as ambient heat.

Maybe not "below ambient" exactly, but I thought it rather remarkable that more heat went through the sides of the double wall vacuum cup much faster than it went up through the engine/regenerator.

This was several years ago, before I had a thermal image gun or thermocouples.

I'm not sure I've seen ANY verifiable "below ambient" of any real significance, just the lower end of ambient.

My main "claim" is that these "near ambient" readings are contrary to the results predicted by the Carnot Limit, which should be showing much more "waste heat" coming through the engine.

Clearly the engine is doing enough "work" to generate heat from friction at the power piston to be detectable by instruments. Yet the "waste heat" that should be, according the the Carnot limit, several times GREATER cannot be detected at all.

The cold side of the engine is no hotter than ambient, and almost looks slightly colder, but it certainly isn't higher. Not receiving ANY "waste heat", which I think indicates extremely high, near 100% efficiency.


https://youtu.be/P11q-BAhvqk

Sorry, that was the wrong video, still in my clipboard from the last post. Not sure why it wasn't updated. Anyway, this is the video of the engine with the "compartment" intended for running it on ice.

https://youtu.be/cR31i09PnNQ

I had been running the engine with ice previously. So perhaps there was residual "cold" in the regenerator, but the engine had been sitting idle on the table for some time, I'm pretty sure long enough that that wasn't much of a factor.

Anyway, for that reason I would not use this video as "proof" of anything.

The other more recent videos were run without any ice anywhere near the engine. It ran on hot water for literally hours, with the same results.

I thought maybe there was heat getting held back by the regenerator and going out the sides, which is why I had insulation on the sides.

As can be seen in this video, when I pull down the insulation, the sides around the regenerator do get quite hot.

https://youtu.be/NtrYSpYD43w

The actual "sink" or cold side does not go above ambient, except at the power piston.

In that engine the entire top, including the power cylinder are the same material (aluminum) so emissivity or other material differences should not be a significant factor. No aerogel. No acrylic. Just all aluminium.

I thought by extending the throw, increasing the potential for expansion cooling, the "self-cooling" might be sufficient to overcome having the cold plate being inadvertently heated from direct contact with the ambient air so that a slight "refrigeration" effect might be apparent.

Something else to keep in mind.

The infrared cannot see THROUGH the acrylic top. What it sees is only the temperature of the outer surface.

I need to get some thermocouples inside the interior of the displacer chamber.

Unfortunately most of my thermocouples are toast from trying to get readings from inside the microwave kiln. I need to get some replacements.

BTW, I just sent for two of these:
If there really is no heat getting through, putting two of these together, cold bottom plates adjoined. They should, in effect, refrigerate each other, helping keep each other's cold sides cold.

Since they would be sandwiched together, there would be virtually no outside contact with the surrounding "hot" ambient air to worry about. Just the outer edges of the plates would contact ambient.

All the heat from friction would be transfered to the remote/elevated power pistons and flywheel bearings.

These are rather small "heat of your hand" LTD engines, only about 3" across the displacer chamber. But require only a 5°C ∆T

A major outlay. Rather expensive little buggers, but hopefully worth it.

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.

Did you try measuring the temperature of boiling water ? When I was taste testing various coffee at home during covid, I was shocked to find out how bogus my IR gun readings were...

VincentG wrote: ↑Sun May 05, 2024 8:07 am 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.

Bingo, you nailed it again.

Yes, I actually measured my aluminum plate, painted black over boiling water and saw 250 degrees f. They are good for comparison but definitely dont seem accurate in all circumstances.

matt brown wrote: ↑Sun May 05, 2024 3:46 pm

VincentG wrote: ↑Sun May 05, 2024 8:07 am ...
Once the volume of gas can transfer more energy than the body of the engine itself, then IMO, conclusions can be drawn.

Bingo, you nailed it again.

What does the transfer rate through the engine body or working fluid have to do with the accuracy of IR camera readings? Or anyone's ability to draw conclusions from observations?

Sounds like maybe your IR camera needs calibrating.

Oh boy, your baseless dismissal with no logical foundation sure "nailed it".

Metal conducts heat better than air. Guess we all just have to throw up our hands and call it a day.

Maybe some day when air conducts heat better than metal we might be able to draw some conclusion about something but until then we can just stick with Carnot.

I keep thinking that acrylic is transparent to infrared, so what is the camera reading that has that temperature?

Also when there is a wall, the temperature difference between the inside and outside is an indicator of how much heat is being ejected. A function of delta T and R value.

I also think that an LTD Stirling of the diminutive size here isn't ejecting much energy, because it can't.

Air inside heating "up" the cold plate, air outside cooling it off, equal equal, what would the outside temperature be? I would think that half way through the wall the wall temperature would be halfway between the two.

Of course, again, acrylic is transparent, so what surface is it reading?

Move an acrylic piece between camera lens and a known temperature and see if it can detect boiling and freezing?

Anyway looks like these engines have no problem running on ice.
https://youtu.be/ZP2Rxvm5bxc

Should the ice melt faster under just one engine?

Or will it melt faster sandwiched between two engines.

Carnot would predict, I think, that because between two engines heat is flowing through to the ice in twice the quantity it should melt twice as fast. Right?

Or, because 2 engines are converting 2x more heat to work, it should take 2x longer to melt.

Anyone care to guess?

The engines will probably take about a month to get here so no rush in submitting a response.

Fool wrote: ↑Sun May 05, 2024 7:14 pm
Air inside heating "up" the cold plate, air outside cooling it off, equal equal, what would the outside temperature be? I would think that half way through the wall the wall temperature would be halfway between the two.

...

The problem with your theory here is heat does not transfer between "equal" temperatures.

The inner surface of "the wall" needs to be cooler than the working fluid and the outer surface needs to be hotter than the outside ambient.

That you have three distinct layers of temperature "equal equal" on the outer surfaces and half way in between in the center is delusional nonsense. Pure impossible fantasy.

Were talking about a thin plate, maybe 1 or 2 mm thick.

Seeing so much irrational, illogical reaching for some convenient way to dismiss simple, clear and obvious experimental evidence is rather astonishing.

Tom Booth wrote: ↑Sun May 05, 2024 7:23 pm
Should the ice melt faster under just one engine?

Or will it melt faster sandwiched between two engines.

Anyone care to guess?

Hmmm, how about 2 identical setups (on ice) with one engine running while other engine is not. I tried to find your recent graphic with 2 engines to review, but couldn't.

matt brown wrote: ↑Sun May 05, 2024 9:42 pm

Tom Booth wrote: ↑Sun May 05, 2024 7:23 pm
Should the ice melt faster under just one engine?

Or will it melt faster sandwiched between two engines.

Anyone care to guess?

Hmmm, how about 2 identical setups (on ice) with one engine running while other engine is not.

Already did that years ago. Many times.

I tried to find your recent graphic with 2 engines to review, but couldn't.

Not that recent I don't think. Or maybe I'm thinking of something else.

The two engines sandwiched together was suggested by someone on the physics forum a long time ago. Maybe you mean something else?

This maybe:

Anyway, wouldn't hurt to do it again.

Yeah, that's the graphic. Maybe I saw a forum link to it somewhere recently. Anyway, what was the story behind the graphic? (I notice tesla-test capture)

edit: in graphic, is one engine running while other is not?

matt brown wrote: ↑Sun May 05, 2024 10:37 pm Yeah, that's the graphic. Maybe I saw a forum link to it somewhere recently. Anyway, what was the story behind the graphic? (I notice tesla-test capture)

edit: in graphic, is one engine running while other is not?

Are you kidding me?

Are you the same "Matt Brown" who's been in here discussing this for two years already?

Shift change at the internet forum oil shill duty station recently?

Multiple personality disorder?

Long term/short term memory loss?

I don't have the time to read everything here and elsewhere. I'm still a working stiff and my day job has been brutal the past year (company move).

So, where did you post this here?

matt brown wrote: ↑Sun May 05, 2024 11:53 pm I don't have the time to read everything here and elsewhere. I'm still a working stiff and my day job has been brutal the past year (company move).

So, where did you post this here?

Well, here:

viewtopic.php?p=12838#p12838

And also way way back in 2012 at the very start of that same thread when I first suggested the experiment:

The image may not show up, depending on your browser though, as it is hosted off site, but it can still be viewed by "view image" if necessary

viewtopic.php?p=12838#p12838

There is also the whole science forum debacle where I got banned for posting the results of that experiment:

https://www.physicsforums.com/threads/s ... ne.991714/

You've been in here badgering me about this topic for two years already. Now you suggest doing an experiment we've been arguing about all this time, like you just thought of it?

Very strange.