Stirling Engine Thermodynamics

[Tom Booth]

This shod help demonstrate the 2nd Law of thermodynamics.

Here is a snippet from a website on the subject:

Resize_20230219_153936_6038.jpg (161 KiB) Viewed 3965 times

https://www.ux1.eiu.edu/~cfadd/1360/22H ... gines.html

The problem with verifying this theory or LAW, however, experimentally has been, among other things, how to accurately determine the heat transfer into the "cold reservoir" through the heat engine and how to distinguish that heat from any potential heat entering the "cold reservoir" via the surrounding ambient environment.

Mere insulation does not seem to be adequate, as test after test has demonstrated that with the engine insulated from the "cold reservoir" the engine still runs. (Sometimes better than without the insulation).

The conclusion of the best minds within the various online science forums has been that the insulation acts as a conductor, transferring heat through to the cold even better than air, regardless, and/or, the model engines admit such an infinitesimal amount of heat to begin with, it's arrival at the sink is virtually undetectable anyhow.

So, this methodology was suggested as, it seems now, as a means of demonstrating the second law conclusively by actual experiment.

Resize_20230219_155814_4888.jpg (226.07 KiB) Viewed 3965 times

In this way, there is, virtually, no "cold reservoir" for the heat to spirit away into other than the cold side of another heat engine.

This arrangement also greatly limits infiltration of environmental heat into the "sink" through any avenue other than through the engines.

[Tom Booth]

Generally these efforts have met with considerable hostility on the science forums; for example:

...you are not going to overturn 150 years of engineering experience and thermodynamic theory with some badly done Mickey Mouse experiments in your garage.

Source: https://www.scienceforums.net/topic/128 ... nt=1229667

In that thread, I suggest that in my observations, a Stirling engine appears to function in a way that is reminiscent of "Maxwell's Demon" or, like a heat pump, even during it's ordinary mode of operation as a heat engine, always working in such a way as to keep the heat to one side, actually using atmospheric pressure on the return compression stroke to drive the heat back to the heat source, magnifying the heat by combining the heat input with the additional heat of compression.

https://www.scienceforums.net/topic/128 ... /#comments

[matt brown]

RE: "It is impossible to construct a CYCLIC heat engine that produces NO OTHER EFFECT than the absorption of heat from a reservoir and the PERFORMANCE of an equal amount of work".

What a lame academic load of crap !!! where the grammar is meant to be all inclusive and sound authoritative. At first glance, this statement seems to circumvent stuff like thermo couples and focus on conventional heat engines, but still a bogus statement:

(1) non-compression cycles like Cayley and whimpy compression cycles like Ericsson caloric basically consume heat and produce no work
(2) common compression cycles will adhere to Carnot

OK, so the world runs on #2 and 'goofballs' study #1, and both would fit this lame academic statement. However, there's other 'known' cycles that exceed Carnot, and some effectively with 100% ideal thermal efficiency. Granted, not common cycles, but nothing NASA either. These all have 'clever' use of regen, reservoir/s, or phase change, etc.

The reason most guys are clueless is not due to Big Oil or communist conspiracy, but due to cost & complexity (it's hard to beat a Briggs & Stratton until there's no fuel available).

[Tom Booth]

When I first made this video, the thermal camera was for me, a new toy, and I really paid no attention to the spot temperature reading in the upper left corner.

Now, though, after re-watching the video several times, and paying particular attention to these spot readings I notice something quite remarkable, IMO.

Here is a spot reading of the Aerogel blanket, directly above the top plate of the engine near the start of the experiment:

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This is the LOWEST reading I could clearly make out on the top of the Aerogel: 86° F

This was higher than the room temperature and may have been partially due to heat from my hand when holding down the blanket to prevent it from rubbing on the flywheel.

But sitting directly over boiling water for 2+ hours, I would have though the temperature would have gone up.

However, after two hours, except at the power piston/cylinder where there is some friction, the readings when pointing at the Aerogel blanket directly above the engine were actually lower than at the start of the experiment:

Resize_20230219_204105_5559.jpg (73 KiB) Viewed 3941 times

Resize_20230219_204106_6197.jpg (72.88 KiB) Viewed 3941 times

I'm not "cherry picking" here much, I don't think. A lot of the footage is unclear and not focused on the spot reading in the upper left corner.

After two hours mostly covered by the glass globe and the additional insulation keeping our drafts, set on top of a steam generator the entire time, shouldn't the temperature have gone up rather than down?

I guess we can conclude that the cheap infrared camera from Harbor Freight is a bit wonky and not reliable, OK, so more, better experiments need to be conducted using better equipment by more qualified researchers before jumping to conclusions. However, I seem to be the only one with any interest in carrying out any such experiments.

The general attitude (on the science forums) seems to be, thet my "claimed" results can be dismissed out of hand as contrary to established science, and are therefore not worth investigating.

https://youtu.be/WveuREfKwVg

[Tom Booth]

RE: "It is impossible to construct a CYCLIC heat engine that produces NO OTHER EFFECT than the absorption of heat from a reservoir and the PERFORMANCE of an equal amount of work".

What a lame academic load of crap !!! where the grammar is meant to be all inclusive and sound authoritative. At first glance, this statement seems to circumvent stuff like thermo couples and focus on conventional heat engines, but still a bogus statement:

(1) non-compression cycles like Cayley and whimpy compression cycles like Ericsson caloric basically consume heat and produce no work
(2) common compression cycles will adhere to Carnot

OK, so the world runs on #2 and 'goofballs' study #1, and both would fit this lame academic statement. However, there's other 'known' cycles that exceed Carnot, and some effectively with 100% ideal thermal efficiency. Granted, not common cycles, but nothing NASA either. These all have 'clever' use of regen, reservoir/s, or phase change, etc.

The reason most guys are clueless is not due to Big Oil or communist conspiracy, but due to cost & complexity (it's hard to beat a Briggs & Stratton until there's no fuel available).

I'm a little lost regarding the two bolded (by me) lines above. Is #1 and #2 representative parts of what you consider "bogus statement" or your opinions or counter arguments.

In particular: "common compression cycles will adhere to Carnot".

Is that your own matter of fact statement or something you consider "bogus".

Anyway, my main issue with "carnot efficiency" generally is that it was advanced as a "LAW" out of Natural Philosophy, precursor of modern physics. The so-called "Carnot efficiency formula" (or LIMIT) was not arrived at or determined or ever verified experimentally and seems to be nothing more than the calculation of the temperature difference on the absolute scale.As such, it is simply descriptive of environmental conditions outside of the engine. It really says nothing about any real quantities of heat available to, or entering or leaving any engine in actual Joules or BTU's

Furthermore, the results of actual experiment does not appear to correspond with the predictions of the formula in regard to the amount of "waste heat" to be expected at the sink, or cold waste heat "rejection" side of the engine.

In the case of the above experiment, the waste heat "rejected" out the top of the engine should be at least about 80% of whatever heat is entering through the bottom.

If that were true, how is it possible for there to be any drop in temperature after 2 hours of continuous operation?

Because of this, I am told, repeatedly over the years that it is not worth bothering with trying to improve on any Stirling engine because of this "Carnot Limit", as it is hopeless. A waste of time. It is a "Law of the Universe" that cannot ever be broken.

[Tom Booth]

However, there's other 'known' cycles that exceed Carnot

It's a bit puzzling to me how that might be determined.

The "Carnot limit" is an equation based on the temperatures of a hot and a cold "reservoir" in the environment outside of, apart from the engine itself and is therefore inalterable by any conceivable modification or alteration of the engine.

Unless, I suppose, the engine is capable of altering the temperature of it's environment. That is, by in some way acting as a heat pump.

Theoretically, if heat is a form of energy a "cold" source is only less hot, or less energetic than a hot source.

Obviously a heat pump can extract energy from a relatively "cold" heat source.

The arguments against a heat engine operating a heat(fuel) pump for its energy supply seem logically flawed to me.

I'll draw an energy flow chart to illustrate what I mean.

[Tom Booth]

This chart for exame:

Resize_20230220_120505_5357.jpg (51.15 KiB) Viewed 3927 times

From this post:

https://physics.stackexchange.com/quest ... -heat-pump

Seems logically incorrect to me.

In such a situation, the heat pump would not be taking heat from the cold "reservoir" and "lifting" that heat, it would only be moving heat within the hot reservoir, from the surrounding environment to the engine (within the upper 300K reservoir).

If the heat engine is actually, or nearly 100% thermally efficient the heat engine would not be dumping any "waste heat" to the "cold reservoir" either, it would be converting that heat to some other form of "work" output, only a fraction of which would be needed to operate the "fuel pump".

In other words, these illustrations commonly used to debunk the heat engine/heat pump idea are not consistent with the actual proposed circumstance.

[matt brown]

Anyway, my main issue with "carnot efficiency" generally is that it was advanced as a "LAW" out of Natural Philosophy, precursor of modern physics. The so-called "Carnot efficiency formula" (or LIMIT) was not arrived at or determined or ever verified experimentally and seems to be nothing more than the calculation of the temperature difference on the absolute scale.As such, it is simply descriptive of environmental conditions outside of the engine. It really says nothing about any real quantities of heat available to, or entering or leaving any engine in actual Joules or BTU's

This is quite true, and it reminds me of one of my favorite quotes: "I never let my schoolin' interfere with my education." (Mark Twain) I'm going to respond in bits (vs inline) so that I don't get timed out. I was over on that physics forum on the weekend and couldn't believe what a bunch of pedantic blowhards those guys are...like a bunch of academics fighting for Dept. Head.

My point 1 & 2 that you bolded would adhere to that lame academic statement, but point 2 is for common compression cycles only. I get what they mean, but the statement is bogus since they consider it all inclusive for all heat engines. Again, I agree with the statement for points 1 & 2, but not ALL heat engines.

[matt brown]

In particular: "common compression cycles will adhere to Carnot".

Is that your own matter of fact statement or something you consider "bogus".

Yep, "common" compression cycles will always adhere to Carnot, but this is mere coincidence, and not a cosmic connection or whatever. Note that 'common' compression cycles are ALL 4 process cycles with 'opposed' compression & expansion AND 'opposed' heating & cooling (and some have '2' heating & cooling processes due to regen).

Carnot is hard to beat, and even most 'irregular' cycles like Atkinson & Lenoir will adhere. Many have suggested that Stirling & Ericsson were trying to beat Carnot (prior Carnot) via regen, and there's a lot of merit to this speculation. The thing to remember is that Carnot barely survived thanks to a few guys like Rankine & Joule, until Otto and his compression cycle 'accident' made many reconsider 'hot air engines'.

[matt brown]

However, there's other 'known' cycles that exceed Carnot

It's a bit puzzling to me how that might be determined.

The short answer: decades and graph paper, no computer req'd.

Some guys experiment with existing models and some guys machine their own designs. I opted for a deep dive into basic thermo and studied integrating processes into numerous cycles before scheming engines that often mime ICE thinking (pistons, cylinders, cranks, etc) before ECE 'optimization'. My favorite HAE is the Rider (the 'Alpha' version).

[Tom Booth]

Yesterday, and all last night I was experimenting with my new inverted engine in preparation for joining it with a second engine with the cold sides together.

That idea was one good thing to come out of those discussions IMO. My wife is always asking me "why do you bother?" Well, I think skepticism is not necessarily a bad thing. It keeps me sharp and on my toes, there might always be something I'm missing. I don't mind being proven wrong, heck I welcome it! Please prove me wrong. It would save me a lot of time and effort, as well as a lot of money I can scarcely afford to be wasting, as little as it's worth these days.

Anyway, yesterday and last night I'm testing all kinds of regenerator material in my new stationary LTD regenerator. Also making various modifications as far as the throw and timing of the engine.

By coincidence, I have a small box full of lamp pull chains I picked up from a yard sale, with a bunch of other tools and shop materials,; nuts, bolts, screws, hinges, springs etc.

The pull chains slipped just perfectly down into the regenerator space and I got the engine running pretty well. I won't go through all the hours and hours I spent previous to that trying layers of different combinations of material. I did not try ordinary steel wool, just because I didn't have any on hand and the hardware store was closed (after midnight).

After the engine had been running steadily for 2 hours I made this video of the results using the pull chain regenerator:

https://youtu.be/NtrYSpYD43w

It seemed that the top of the engine remained cool, about the same as room temperature, though the regenerator itself on the sides of the engine got quite warm.

After uploading and rewatching that video a few times, I noticed something peculiar. The infrared thermal camera has two little square boxes that track around following the hottest and coldest spots on the viewing screen. Red for hot and green for cold.

I don't pay attention to such details while trying to just shoot a video, fumbling around with camera and phone just trying to get things in focus and avoid glare and trying not to drop anything. But on rewatching the video, I noticed that the green square spent quite a lot of time tracking the top of the engine as the coldest point, even when panning around at other objects in the table, taking readings.

The temperature in the upper left corner of the infrared viewing screen is the spot temperature. (At the cross hairs in the center of the viewing screen)

After noticing this green square apparently tracking the engine, I thought, possibly the metal of the top of the engine had a different "emissivity", so that it only looked cold to the camera.

To test that hypothesis, I put several other metal objects in the vicinity of the engine. The green dot continued tracking the engine.

As the engine continued running, after another hour passed, (now the engine had been running for three hours), I made an additional video before going to bed. By that time the sun was rising.

I especially tried to show how the tracking followed the engine and went as far as to offer my own explanation of what was going on.

https://youtu.be/P11q-BAhvqk

[Tom Booth]

In particular: "common compression cycles will adhere to Carnot".

Is that your own matter of fact statement or something you consider "bogus".

Yep, "common" compression cycles will always adhere to Carnot, but this is mere coincidence, and not a cosmic connection or whatever. ...

I guess that's where we differ.

I see no evidence anything, any engine adheres to Carnot.

Should we write another exception for Stirling engines, like was done for heat pumps. Just redefine "efficiency" while clinging to an outmoded theory that should have been discarded long ago?

IMO, the "Carnot limit" is pure crap through and through. Altogether, pure nonsense that doesn't apply to anything.

If that results in also discarding the second law, "entropy", the big bang and the ultimate heat death of the universe, and anything else emanating from it, so much the better.

[Tom Booth]

I just started this thread on the Science forum about a month ago:

https://www.scienceforums.net/topic/128 ... /#comments

"Is Carnot Efficiency Valid"

It quickly became one of the most active threads on the forum. Now up to 9000 views, even though moved to the "pseudoscience" section and locked.

Anyway, one of the first posts there stated: (emphasis added)

...If you are trying to insulate the cold end, the presumption must be that its temperature is not the ambient temperature of the room but significantly higher. If the insulation is perfect, then what will happen is that the waste heat rejected by the engine will progressively raise its temperature, eventually reaching that of the input temperature. As this takes place, the engine will run progressively slower and eventually stop.

What is for sure is that for the cold end heat exchanger to reject heat into the room, its temperature must be quite a lot higher than the ambient temperature. Recall Newton's law of cooling, according to which the rate of heat transfer is proportional to the temperature difference. So, no temperature difference, no heat transfer.

https://www.scienceforums.net/topic/128 ... nt=1227274

I responded:

... I'll run the experiment again with temperature probes"

That will though, of course, take some time.

The infrared thermometer, I had thought would be adequate as it provides spot,as well as maximum and minimum readings, but unfortunately, as I only discovered in the course of the experiment, cannot penetrate either the pyrex? Coleman lantern glass or the acrylic.

I don't think there is a need for anyone to take an adversarial stance. The suggestion is a good one. As I said, I'll repeat the experiment using temperature probes ASAP. That is not likely to be today or tomorrow. Maybe within a week.

I was pretty overwhelmed trying to field responses and answer questions, as well as being very busy at home, but within about two weeks:

...Thread closed due to insufficient support...

What?

What do you call a dozen videos showing zero temperature difference between the cold side of the engine and ambient. But if I post a video that's some kind of major crime to be banned for as well. Trying to simply present evidence and the discussion is closed for "soapboxing", so if you don't then it's closed for "insufficient support".

Anyway, the general scientific consensus is, of course, as stated above:

What is for sure is that for the cold end heat exchanger to reject heat into the room, its temperature must be quite a lot higher than the ambient temperature. Recall Newton's law of cooling, according to which the rate of heat transfer is proportional to the temperature difference. So, no temperature difference, no heat transfer.

But this experiment, and half a dozen others, in one way or another, show clearly IMO, that the cold end heat exchanger is NOT "quite a lot higher than the ambient temperature" far from it.

If there is no temperature difference, and therefore no heat rejection, then I think it can be concluded that there is something very close to 100% efficiency.

But the Carnot limit for this engine, calculated on the basis of the temperature difference, using the Carnot efficiency formula is at best, about 20%

So where is the 80% heat "rejection" at the cold end heat exchanger?

I think these experiments show clearly that there is a huge, monumental discrepancy between the so-called "Carnot efficiency limit" and reality.

[VincentG]

Tom, I am very much looking forward to testing the LTD coffee cup engine I have just ordered.

The LTD, specifically, must by nature be the most efficient stirling engine we have access to if it can run on such low differentials. The name is sort of misleading as I think it should be called something like "High Efficiency Gama".....or whatever floats your boat.

At these very low temperatures I hope to find they are MUCH more efficient than your science friends would like to accept. Though I think efficiency will drop dramatically with temperature increases unless the size of the machine scales up accordingly or much more efficient heat sinks are used.

[Tom Booth]

Tom, I am very much looking forward to testing the LTD coffee cup engine I have just ordered.

The LTD, specifically, must by nature be the most efficient stirling engine we have access to if it can run on such low differentials. The name is sort of misleading as I think it should be called something like "High Efficiency Gama".....or whatever floats your boat.

At these very low temperatures I hope to find they are MUCH more efficient than your science friends would like to accept. Though I think efficiency will drop dramatically with temperature increases unless the size of the machine scales up accordingly or much more efficient heat sinks are used.

I haven't noticed much if any difference with high temperature Stirling engines either. Blasting an engine like this for example with a propane torch, the cold side will stay cold for a very long time. Eventually some heat will conduct over but that is a controllable loss, by using less heat conductive materials.

https://youtu.be/R_QB5amihko


I have some plans for making little engines like these out of non-heat conducting ceramic, and doing away with the cooling fins altogether.

The reason I think it matters is I'm trying to design engines to build and use myself and/or possibly sell and it makes a huge difference in how the engine should be designed. For example, is a tremendous amount of water cooling necessary to carry away all the excess "waste heat"? Or is perhaps water cooling actually detrimental, robbing the engine of it's "fuel". Should materials be used to retain heat or dissipate heat rapidly?

If the conventional wisdom is wrong, then maybe the conventional wisdom is doing more damage than good, in terms of designing a really useful, practical engine. Throwing away heat, where logically, it should be retained and converted to power output, just because 200 years ago some guy imagined a heat engine was something like a water wheel.

Do we really need "much more efficient heat sinks"???

In my opinion, that's completely backwards, but that has been the rule of thumb for centuries. But if heat is a form of energy/fuel then what we really need to do is just the opposite. Instead of a big heat sink to get rid of heat we need to use insulating material to retain as much heat as possible rather than deliberately throwing it away.

The mind set that heat in a heat engine is a bad thing and the "waste heat" needs to be gotten rid of as quickly and efficiently as possible is so solidly and deeply engrained it seems nearly impossible to counter, regardless of a mountain of evidence.