LTD model "Stirling" uses Lenoir Cycle

[Nobody]

The question I keep thinking is: How much temperature change is expected when, heat in, and, work out, are less than 1/100 Watt? Or 1/1000 Watt. As these engines tend to process?

[matt brown]

@Nobody

Exactly what I've always wondered. I can kinda grasp 5-10F dT, but where would anymore heat go ??? There's simply no dV to do diddley squat when these buggers are so small.

[Nobody]

Exactly. If it is only heating up the cold plate by .01 F per hour it may take lots of hours before it raises a half a degree F let alone where it really becomes measurable. 5F to 10F would be measurable but even then it would leave many scientists skeptical.

Think about if it only heats it by .001 F/hr or .0001F/hr? These are very small engines with thick plate heat exchangers. Lots of thermal lag, little thermal pressure. They are LTD Stirling Engines.

[matt brown]

Which begs the question: how do LTD 'run' at all ??? Assuming piston speed equals cycle speed, how does any micro dT get enough heat in fast enough for the piston speeds we see ? Maybe their small size provides some scalar advantage ('cheating') like gaming boundary layer or something.

[Nobody]

I think the piston speeds and cycle rates we see are because the heat moves through the heat exchangers at a rate that allows the inside to remain at a fairly constant temperature. Thus the air inside picks up more heat when running slowly, and less when running faster. It doesn't pick up enough to stay isothermal, but enough to run. The displacer motion seems to combine with heating and piston motion to distort the plot. It's getting heating from the displacer during volume change. Or the instrumentation lags the actual pressure changes.

That is apparent from the PV diagram of the runing engine where it is loaded and unloaded. As it speeds up, the cycle shrinks inwardly away from any isotherm that it was following when going slower. It then follows that new shrunken curve iso-something.

It never even gets close to an adiabatic line. It appears to heat less than isothermal and way less than adiabatic.

We tend to call that polytropic?

[Tom Booth]

Exactly. If it is only heating up the cold plate by .01 F per hour it may take lots of hours before it raises a half a degree F let alone where it really becomes measurable. 5F to 10F would be measurable but even then it would leave many scientists skeptical.

Think about if it only heats it by .001 F/hr or .0001F/hr? These are very small engines with thick plate heat exchangers. Lots of thermal lag, little thermal pressure. They are LTD Stirling Engines.

You guys are talking utter nonsense. One one thousandth or one ten thousandth of one degree per hour?

"Thick plate heat exchanger" ?

You can't explain the absence of "waste heat" leaving the sink by imagining that virtually zero heat is entering the engine.

Even "heat of hand" is likely a 20° temperature difference, depending on the ambient temperature. But taking a typical "room temperature" of say 68°F body temperature of 98°F.

So one ten thousandth of a degree per hour heat input to run a Stirling engine is just ridiculous nonsense.

I asked simply, show me some record of any actual experimental verification, or any empirical evidence whatsoever that validates or ever in the history of the world, actually demonstrated the accuracy and validity of the Carnot efficiency equation

That request should not be so difficult to fulfill if the equation had any real validity. All either of you have shown are theoretical "idealizations" based on NOTHING but speculation.

Just a simple LTD running on hot water is taking in plenty of measurable/observable heat

Thermal imaging shows plenty of heat at the hot plate and the interior of an LTD running on a cup of hot water, but the top plate (sink) remains relatively cold

Resize_20220316_115713_3079.jpg (100.5 KiB) Viewed 5998 times

https://concord.org/blog/an-infrared-in ... reloaded=1

That is actual concrete experimental evidence that "Carnot efficiency" is wrong.

Show me some actual counter evidence.

Where is all the heat that "Carnot efficiency" predicts is supposed to be there at the top cold plate.

Compare that with the "dummy" engine.

[matt brown]

I asked simply, show me some record of any actual experimental verification, or any empirical evidence whatsoever that validates or ever in the history of the world, actually demonstrated the accuracy and validity of the Carnot efficiency equation

That request should not be so difficult to fulfill if the equation had any real validity. All either of you have shown are theoretical "idealizations" based on NOTHING but speculation.

Tom - all the Carnot buzz (and a lot of thermo) is derived from PV=nRT which is the basis of the kinetic theory. A bunch of guys spent a lot of time arriving at this famous equation and no one has disproved it. It goes back to Herapath and Waterson where PV/T was a well 'observed' constant.

Thermal pic shows bottom plate hot with top plate nearly ambient. So what ?..it's the heat RATE in and out of gas that matters, not temperature of each plate, tho there must be some dT. It appears top plate is insulated from main unit.

Are you suggesting that a thermal scan like this is telling us that any/all heat going into gas is transformed into work since the 'cold' plate remains ambient, whereby Qout=0 ???

[Nobody]

I don't know what good it will do to explain this, because it is like carefully describing to you what happens to volume/surface area ratio when scale sizes are changed. You only seem to see in that photo and other data what you want to see, blatantly ignoring points that clearly show the contrary.

I see a top plate that appears 3 to 10 degrees hotter than ambient. That means it is emitting heat to the surroundings. If that is more than 5 times the power you are getting out of the engine you have failed to prove Carnot wrong. Even if it is only 1 or 1/2 degree hotter, difficult to measure or observe.

It appears you are getting zero power out. All generated power is used up by the machine just by its running. (I.e., converted to heat. Windage. Friction. Etc... The power cylinder appears hotter than the cold thick top flat plate heat exchanger.)
Zero power out with a tiny heat out, for 0% efficiency, doesn't even come close to Carnot's limit, let alone breaking it. Please stop this sidetrack until you've learned more engineering and science.

Read the book Evolution of the Heat Engine, by Ivo Kolin. It is filled with the data you ask for. Look up advertised efficiencies for any engine. Quit ignoring the data and comments you don't like. We are all here to help and learn.


Read that book, or at least skim it and study it. Please.

[Tom Booth]

I asked simply, show me some record of any actual experimental verification, or any empirical evidence whatsoever that validates or ever in the history of the world, actually demonstrated the accuracy and validity of the Carnot efficiency equation

That request should not be so difficult to fulfill if the equation had any real validity. All either of you have shown are theoretical "idealizations" based on NOTHING but speculation.

Tom - all the Carnot buzz (and a lot of thermo) is derived from PV=nRT which is the basis of the kinetic theory. A bunch of guys spent a lot of time arriving at this famous equation and no one has disproved it. It goes back to Herapath and Waterson where PV/T was a well 'observed' constant.

Thermal pic shows bottom plate hot with top plate nearly ambient. So what ?..it's the heat RATE in and out of gas that matters, not temperature of each plate, tho there must be some dT. It appears top plate is insulated from main unit.

Are you suggesting that a thermal scan like this is telling us that any/all heat going into gas is transformed into work since the 'cold' plate remains ambient, whereby Qout=0 ???

Simply put, in the process of researching the question; how does a Stirling engine actually work, from an engineering point of view, that is, as a life long engine mechanic/repair man, I wanted to build and use one, I came across a number of conflicting points of view, theories, explainations, and alleged "Laws".

Historically, as far as I could tell, some of these conflicts, or differences of opinion had never been fully resolved, including the actual nature of "heat" itself.

High on the list of conflicting theories is the "Carnot efficiency equation" which carries with it a number of basic assumptions

In the case of the thermal image in question above, 80% (or more) of the heat entering the engine through the bottom plate should be (according to E=1-Qh/Qc) passing through to the top plate each cycle. A mere 20% (or less) being converted to work.

Taking this image, along with several experiments, temperature readings (that show no rise in temperature at the point of "heat rejection" at the "sink"), running engines on ice, (that re-freezes rather than melting), engine performance improving when heat flow out of the engine is blocked, etc.

All taken together, the indication is that the Carnot efficiency equation, or how it is being interpreted, is invalid.

Further, there is no historical empirical support for it. PV=nRT is not E=1-Qh/Qc

Neither of those equations directly address the conversation of heat into work.

There is, as far as I can find, no scientific basis for assuming that the ratio between the high and low temperatures has anything to do with engine efficiency, or how effective the engine is at converting the available heat into work.

Carnot himself, it appears, rejected this formula, though this was unknown until many years later when his personal journals were published.

I've already pointed out, it is accepted that 100% conversion of heat into work is possible, linearly.

That is, in expansion work, to drive a piston out 100% conversion of heat into work is possible.

The issue is supposed to be associated with completing the cycle. Supposedly the piston has to be pushed back to its starting position and this takes work and supposedly to get the gas to contract after expanding heat has to be removed.

These assumptions also appear to be inaccurate in actual practice.

All in all, the idea that efficiency (% utilization of available heat) is strictly limited by the ∆T ratio appears to have no factual basis. Observably, experimentally, measurably, it doesn't hold up.

To assert something is true on the basis that "it has never been proven wrong" is not science. That would be called faith.

E=1-Qh/Qc (or how it is being interpreted) is more a kind of religious conviction than a well established scientific fact.

The temperature difference is just the temperature difference. It has not been proven to be a limiting factor on the utilization of the available heat.

[Tom Booth]

Are you suggesting that a thermal scan like this is telling us that any/all heat going into gas is transformed into work since the 'cold' plate remains ambient, whereby Qout=0 ???

To address your specific question, you accurately state: "It appears top plate is insulated from main unit".

And yet, we know that in a running engine, the displacer is forcibly agitating the air, pushing it down against the hot plate, then up into the cold plate.

Logically, air being agitated between a hot and a cold plate should show more heat transfer than passive convection. The air is being mechanically circulated between the two plates. Is that really "insulation"?

So why does it appear that the "top plate is insulated from main unit"?

We also know, because the engine is running, heat is entering into the gas and causing it to expand and drive the piston, otherwise the engine would not be operating.

So logically, given these facts, there should, according to E=1-Qh/Qc be much more heat leaving the top of the engine than is being utilized to drive the piston.

Yes, heat is being prevented from passing through the engine IN SOME WAY, obviously. It LOOKS LIKE, the top plate is in some way insulated from the heat, but logically that is not the case.

The truth is that the heat entering into the gas is being converted to mechanical motion before it has a chance to reach the top plate

[Nobody]

And the "Mechanical Motion" is being converted completely into heat (Friction, Windage), and dissipated into the air around the device. Net energy out, zero. Net efficiency, zero.

Proving, nothing.

Please read Ivo Kolin.

[Tom Booth]

And the "Mechanical Motion" is being converted completely into heat (Friction, Windage), and dissipated into the air around the device. Net energy out, zero. Net efficiency, zero.

Proving, nothing.

Please read Ivo Kolin.

That is just silly IMO.

If the energy is first converted into mechanical motion then it is already converted. Normal friction can be minimized. With modern methods, magnetic/air bearings, high tolerance frictionless piston/cylinders etc friction can be virtually eliminated.

Anyway normal friction loses are well understood and controllable, and have nothing to do with the theoretical and completely arbitrary "Carnot limit", which is a "best case" limitation. That is, it does not include normal friction loses, as I'm sure you must be well aware.

The Carnot limit applies BEFORE any additional friction loses. So your argument is apples to oranges, really.

[Nobody]

It is not silly to read an educational book. Please read the book, "Evolution Of The Heat Engine, by Ivo Kolin).

Failing to do so will only mean that you are choosing to be ignorant.

[matt brown]

Anyone who sits outside long enough will "observe" that the sun appears to go around the earth, but (nearly) everyone knows that the earth goes around the sun. Hmmm, why do so many guys believe the latter, when so few can prove this (and the proof ain't rocket science).

[Tom Booth]

It is not silly to read an educational book. Please read the book, "Evolution Of The Heat Engine, by Ivo Kolin).

Failing to do so will only mean that you are choosing to be ignorant.

Obviously I was not talking about the book. I've been a big fan of Ivo Kolin for many years.

If there is something I one of his writings that supports your opinion, why don't you just reference it?