Stirling engine and cooler?

[Tom Booth]

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Even if you could eliminate all "excess heat", depending on the definition, the heat of adiabatic compression would still occur when the cycle reverses. That heat would need to go somewhere? It is only the heat of compression that I'm talking about. If it stays in the working fluid, you will get adiabatic compression, and the Stirling engine will produce Zero net power.

The reason IC engines can live with adiabatic compression is that the heat added isn't constrained by a maximum hot exchanger temperature.

...

There is no mechanism by means of which the internal temperature of the gas in a Stirling engine is "constrained" by the hot heat exchanger temperature or source input temperature (hot reservoir). Infact the previous chart shows just that.

Temperature_vs_angle(1).jpg (11.36 KiB) Viewed 1939 times

That curved line is the internal temperature of the engine going above the input (hot reservoir) temperature during the compression stroke.

The "heat of compression" is simply added to the "normal" input heat from the heat source giving the engine that much more power - a contribution of atmospheric pressure.

Both (the heat from both sources) are then converted to work during the subsequent expansion.

Your idea, or insistance that the compression work done by the atmosphere is somehow a bad thing, somehow "negative" is a bit perplexing, but nevertheless wrong.

After the expansion and cooling, the piston motion stops and reverses as atmospheric pressure accelerates the piston for the compression stroke, the piston, in a Thermal Lag type engine, then drives the gas, compresses it, really SLAMMING it, directly BACK INTO the hot end, back to the heat source, much like a fire piston or a diesel engine.

That is not draining power resulting in "zero work". It is concentrating the heat for an explosive rebound and power drive, for the power stroke work output.

That is easy to see in the thermal Lag, a bit more difficult in other more complex engines, but there also, a similar process of heat concentration takes place. (compression stroke) followed by expansion.

[Tom Booth]

A heat engine has to take in heat. Your assumption that that "excess heat" must somehow end up going through the engine to the sink is where our interpretations diverge.

I have never had that assumption. Nor have I written that anywhere. Your implications, of Caloric flow theory, died over 100 years ago. Serious scientists no longer use that, if they know what they're saying.

My mistake I guess.

I thought you rather consistently stated that the - Carnot limit holds -. or words to that effect. Have you not?

The "Carnot limit" is what dictates that for the Stirling engines under discussion here, (LTD's running on hot water and the like) 80% or more of the heat supplied to the engine MUST flow through, be "rejected to" the sink.

Now you are starting to talk about heat of compression being all that is "rejected". ?

It is only the heat of compression that I'm talking about. If it stays in the working fluid, you will get adiabatic compression, and the Stirling engine will produce Zero net power.

How would it not "stay in the working fluid"? By being rejected to the sink, as per the Carnot efficiency limit? I don't know what else it might be you are saying here.

"Heat of compression" has nothing to do with the heat supplied by the "hot reservoir" or the Carnot Limit.

Feel free to explain this or elaborate on what you mean then, that "the Carnot limit holds".

Or to add a direct quote or two:

The delta heat is subjected to the Carnot efficiency rule. If you build or find an engine that brakes that law, please put it forth for testing.

That is what we have. Carnot and the Kinetic Theory are correct. They have been found to be reliable, repetitively.

It seemed to me that you were in support of "the Carnot efficiency rule". You called me a pseudoscientist for disputing it, as I recall, though your more caustic comments have apparently been deleted by the admin.

shedding of heat continues until the momentum is exhausted. Hence what Carnot observed and calculated in all heat cycle experiments of his day. Since then it has been reaffirmed

etc. etc.

Please clarify your position, I guess I got it wrong

When I wrote: "But when, for instance, I'm told that 80% or more of the heat used to run a heat engine not only should, but absolutely must, under any and all circumstances, pass through the engine as "waste heat" to the sink, and I see by direct experiment that a simple model Stirling engine appears to conduct ZERO heat to the "sink", under certain circumstances, by actual measurement, I don't just dismiss the cumulative evidence of dozens of objective experiments off hand on the basis that someone thinks the second law says that is "impossible".

You replied:

That is a claim which violates the laws of thermodynamics. Specifically "conduct ZERO heat to the "sink",".

Do you only object to "zero" heat going to the sink, or anything less than the "Carnot limit", or what exactly?

[Nobody]

Carnot's heat rejection is the heat of compression. And the same as the negative work needed to do so.

[Tom Booth]

Carnot's heat rejection is the heat of compression. And the same as the negative work needed to do so.

That's a common conjecture, too often put forward as fact by various online explanations of "how a Stirling engine works" etc. If you find that explaination satisfying and complete, good for you

From my observations, I say it's wrong.

Compression takes place on the return stroke and as can be easily observed and demonstrated, this return/compression stroke takes place despite the complete absence of any flywheel. The return/compression stroke must therefore be by outside atmospheric pressure, which indicates a lower internal pressure during compression, which low internal pressure could not be possible except as a result of a drop in internal temperature below ambient.

The piston is drawn back by cooling and contraction. A consequence of the conversion of heat to work. The working gas is cold and contracting during the "compression" phase. The "work" or heat of compression by atmospheric pressure is therefore easily absorbed by the working fluid.

Heat "flows" from a hotter region to a colder region does it not? Heat cannot be "rejected" from a colder region to a hotter region.

So, how do we have "heat rejection" from the internal colder gas out to the warmer ambient?

The theory or statement: "Carnot's heat rejection is the heat of compression. And the same as the negative work needed to do so" must therefore be rejected by simple logic and common sense. It does not hold true under observation and rational, logical analysis.

[Nobody]

Breaking the Carnot limit, making a more efficient engine, even by a little bit, may sound like a worthy endeavor, and if you succeed it would be, but, IMHO, it would be far more valuable to try to learn more engineering principals and mathematics, found to be reliable for the 100 plus years, and apply them, creatively, to making known engines more efficient, powerful, cheaper, and safer. Enthusiasm for building things should be encouraged. That is why I came here. Us learning what mistakes others, and ourselves, have made, helps prevent them from being made again. Another way to say, pointing out a more productive direction.

It is obvious from our discussion here you don't want that. Sorry, but it would help you.

[Tom Booth]

Breaking the Carnot limit, making a more efficient engine, even by a little bit, may sound like a worthy endeavor, and if you succeed it would be, but, IMHO, it would be far more valuable to try to learn more engineering principals and mathematics, found to be reliable for the 100 plus years, and apply them,...

"Breaking the Carnot limit" is not my goal. Simply making observations to see how these engines operate and making improvements is.

Hystronics regarding my experiments and "the Carnot limit" originate elsewhere.

The "Carnot limit" appears to be "an article of faith" with some, indoctrinated in thermodynamics. That is none of my concern, however, when I am attacked, insulated and ridiculed as a "pseudoscientist", banned from Science and Physics forums, etc.for simply posting video of my various experiments, I'm forced to defend myself and try to insert some logic and reason, and point out where this "Carnot efficiency" doctrine appears to contradict observations anyone can make, and experimental results, anyone with access to a $30 model Stirling engine can verify for themselves.

...creatively, to making known engines more efficient, powerful, cheaper, and safer. Enthusiasm for building things should be encouraged. That is why I came here. Us learning what mistakes others, and ourselves, have made, helps prevent them from being made again. Another way to say, pointing out a more productive direction.

It is obvious from our discussion here you don't want that. Sorry, but it would help you.

You're "help" so far, has been to insult me and make disparaging comments regarding my character and my motives, along with repeatedly calling for a cesation of inquiry and offhand dismissal of experimental results.

Your statements here: "IMHO, it would be far more valuable to try to learn more engineering principals and mathematics" etc. imply that I am ignorant of Stirling engines and the various principles involved, should ignore my own observations and yield to your higher, more sophisticated opinionations. While we all have more to learn, I am not ignorant. I've studied and investigated these matters thouroughly and in some cases discarded outmoded theories, the supposed "Carnot limit" as commonly interpreted and applied, being one. I don't think I need to apologize for that, or be strong armed into some kind of retraction, or backtrack.

If you wish to debate "Carnot efficiency" I would suggest, again, start another thread on the subject. This thread is for investigating examples of the Stirling engine "self cooling" effect, and/or ability to function as a heat engine and cooler simultaneously.

It is the function of a Stirling engine to convert heat into work. Such a process of heat conversion IS itself a cooling/refrigeration process.

You have made your opinions and concerns known, that this line of inquiry is going in the wrong direction or is a waste of time, but I will continue my research, wherever it may lead, with honesty and integrity. I am not going to tip toe around or try to avoid this alleged "Carnot limit", which, as far as I can see is a complete fiction that should be entirely disregarded.

Any further attempts on your part to derail this, or other topics of mine into debate and argument about the "Carnot limit" will be immediately reported to the forum owner/moderator as off-topic.

Please, if you wish to expound upon or debate the merits of the Carnot limit, the principles and mathematics involved, I'm sure you are free to do so on another thread and that could provide some insights and prove to be a valuable resource for other forum visitors and members.

[Nobody]

It is the function of a Stirling engine to convert heat into work. Such a process of heat conversion IS itself a cooling/refrigeration process.

No. A cooler is a machine that takes heat from a cold space making it colder. Unless it is 100% efficient, it will put out heat to a warmer place.

An engine takes in heat from a hot place making it colder. Unless it is 100% efficient, it will put heat out to a cooler place.

For a reversible mechanism it must be reversed. It can't do both at the same time. < This was answered long ago in this thread.

The warmer place and the cooler place can be the same place.

The rest of your last comment is full of contradiction. You are trying not to break the Carnot limit, but you are trying to throw it out? Good luck with both of those. It is your contradictions that we strive to point out.

I don't think you are being attacked. It may feel that way. I think people are kindly trying to point out your errors in logic and understanding. You seem to recoil by denial and attacking back. If this is just your style, I can accept that. I tried reflecting it, but you seem to hunker down and ignore any point I'm making even more so, all while making even more errors. Too many to the point of being difficult as to know where to start. Don't assume your experiments are showing anything, nor that others are less informed than you.

Read the book Evolution of the Heat Engine by Ivo Kolin. It will delight you.

[Administrator]

Mr "Nobody", please read your PM's
Administrator

[dlaliberte]

After reading a large number of these discussions, which I find fascinating on many levels, I suggest it would be fantastic if we could get objective measurements of temperature and pressure in the various chambers and surfaces of different models in various operating conditions. Creative alternative designs and speculative observations are also essential ingredients in a productive investigation, so I would not discourage any of that. Attempts to understand what is going on based on new or old theories are also essential. But I would like to see some resolution of the many uncertainties so we can move forward rather than spinning our wheels, which we can only do by finding sufficient evidence that we can all agree on.

[Tom Booth]

After reading a large number of these discussions, which I find fascinating on many levels, I suggest it would be fantastic if we could get objective measurements of temperature and pressure in the various chambers and surfaces of different models in various operating conditions. Creative alternative designs and speculative observations are also essential ingredients in a productive investigation, so I would not discourage any of that. Attempts to understand what is going on based on new or old theories are also essential. But I would like to see some resolution of the many uncertainties so we can move forward rather than spinning our wheels, which we can only do by finding sufficient evidence that we can all agree on.

Easier said than done, given the limited response time of available instrumentation.

[Tom Booth]

There are some few "real time" PV readings taken of very slow running LTD Stirling engines, which has mostly already been covered earlier in the discussion.

https://youtu.be/ck8thAoi_rA

The results IMO are quite interesting.

Most notably, I think, if 0 pressure on the graph can be assumed to represent baseline atmospheric pressure, the pressure of the working gas begins to drop about 1/3 of the way through the power/expansion stroke of the piston, and then, after falling sharply, to a pressure below atmosphere at BDC continues to drop through about 1/3 of the compression stroke and remains below atmospheric pressure almost all the way to TDC when there is a rather sudden sharp increase.

Though no actual temperature readings are given for the working fluid, probably due to the response time problem, as well as the poor conductivity of the gasious medium, I think some idea of temperature can be inferred from the pressure. That is, a drop in pressure would have been preceded by a corresponding drop in temperature.

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[Tom Booth]

The above pv diagram IMO, suggests the internal temperature dipping below atmospheric. Though only the pressure and volume are shown.

I'm not entirely sure what to make of the following graph:

Resize_20221108_123553_3142.jpg (239.35 KiB) Viewed 1423 times

This purports to be readings from a "real" Stirling engine "heat exchanger". The nature of the heat exchanger is not clear, a regenerator or the hot and cold plates or cylinders. But the mention of "adiabatic" - "compression and expansion" resulting in gas temperature deviations "above and below" the "solid portions" of the heat exchanger, this appears to indicate real temperature readings showing that the working gas does indeed pass through an adiabatic expansion phase that produces a cooling effect.

Due to the apparent fact that even "ultra fast" thermal couples are subject to considerable lag or delay in response, I would tend to think that if anything, the adiabatic cooling (and heating) could be greater than what could actually be measured.

I'd be particularly interested in the temperature of the working gas in a thermoacoustic engine. That could, however, present even more problems. Theoretically, there being some "pressure wave" with hot and cold "nodes" that in some mysterious way phase shift or some such thing from hot to cold and back.

[Tom Booth]

My own theory regarding how a Stirling engine might act simultaneously as engine and "refrigerator" is based on the flowing facts:

A Stirling engine and a Stirling Cryocooler ARE the SAME machine, rotating in the same direction. A Stirling Cryocooler is NOT a Stirling engine driven in reverse direction.

In other words, when a Stirling engine is just sitting there being heated, it does nothing much except perhaps equalize pressure by pushing the piston out a bit. When someone attempts to get it started by turning it over by hand, at that point it is being DRIVEN in the manner of a Stirling Cryocooler. Every time the engine is cranked over by hand, but fails to start, there is a heat pump effect, if only very slight. Keep cranking it over by hand, however, and eventually it will start.

But which way is the heat being pumped?

It is generally assumed, I think, that when acting as a cooler or heat pump a Stirling engine takes heat from the normally heated end, and transfers that heat through to the normally cold end. This however is apparently not actually the case. At least not always.

https://youtu.be/2CnNOY1OVhc

So it appears, in the case of the engine in the above video, at least, the driven engine refrigerates what would normally be the "sink", making the cold end colder and heats up the end that would normally be heated, making it hotter.

So, turning the engine over by hand would then have a heat pump effect making the cold side COLDER, increasing the temperature difference rather than reducing it, by pulling heat from the hot side and depositing it at the cold "sink" end.

This seems to entirely contradict long standing opinion regarding how these engines are assumed to operate.

It seems rather a shame that just a few amateur experimenters with virtually no resources are even aware of this sort of thing or have made these kind of observations, which are otherwise completely ignored or overlooked, or actually vehemently denied as impossible, due to the fact that it seems to contradict "well established science".

From this, and the previous charts and graphs, I would assume that with an actual load (work output) the cooling or heat pump effect (cooling in particular) would probably be even more pronounced.

[dlaliberte]

Thanks for these replies. I'll have to study more, but, by the way, I tend to agree with you that there are significant unexpected phenomena going on, especially regarding the temperature of the cold "sink" end. Unexpected, relative to "normal" science that is.

Getting even a moving average temperature measurement of the cold side, and the ambient air in the volume of space around the cold side should be easy enough, and that measurement, combined with similar measurements on the hot side, and the amount of work being done e.g. to generate electric power, should answer the question of how much heat is flowing where. I don't think I have seen that anywhere yet.

[dlaliberte]

Regarding the ultra fast thermocouple and the lag in response,l time, if the amount of lag can be determined then it can be factored out to synchronize with actual time.

I wonder if there is some material that could be used merely as a fast response radiator, to not measure temperature directly but respond in a way that can be picked up remotely, such as converting heat to light. Then we could calibrate the response to calculate the temperature.