Why a temperature differential?

[Fool]

Why a temperature differential? And how to get and maintain it.

According to alleged experiments, a LTD Stirling will run with "insulation" covering the cold side. My contention is that somehow heat is still being removed from the gas on the cold side through a unidentified process, mostly from lack of good laboratory practices. To investigate this certain questions come to mind.

1: If no heat is getting out, how does the cold side stay cold?

2: Heat should at least move from the hot side to the cold side through other means, such as infrared radiation. Since the claim is 'that is not happening', what is stopping that heat transfer, or what is removing that energy transfer?

3: The engines won't run until a forced temperature difference is instigated. Why can't they produce their own just by manually spinning?

4: Why do they need that difference? Cooling?

5: If no heat is being released to the cold side, couldn't one at room temperature be insulated, gotten running by heating the hot side to 150°F? Then put into a 150°F oven and expect the cold side not to heat up? Wouldn't it run forever self cooling the cold side?

1: Somehow the cold side is being cooled by the cold room. How, will eventually turn out to be obvious. Maybe just slow conduction of very little engine power through the insulation, with a very small temperature gradient.

2: I think it is being both cooled and it is warming. It is just less and slower than detectible with the laboratory techniques being used.

3: Because engines require active cooling to remove heat flowing to the cold side. They need energy removed from the gas to return to the beginning of the cycle. They pump energy to the cold side not the other way, as proven by spinning an engine with a motor.

4: They need that difference for cooling of the gas as part of the return to the beginning of the cycle processes. Without cooling all forward work would be needed for the return stroke.

5: Attempting that experiment will add valuable data to this discussion. It will work the same as trying to get an engine to run on one temperature such as atmospheric. There will be no free lunch by expending energy/work to build a "cold hole". It won't work because heat needs to be shed to a colder environment, not pumped to a hotter one.

Perhaps there is mathematical reasoning disproving 200 years of mathematical reasoning proving it. I'm standing by, relaxing in comfortable furniture when possible and continuing to get what I need done, done, by being busy.

[Jack]

I've been following all the other discussions with shallow attention.

You mention here that the piston needs the fluid to be cooled in order to return. Why would that need to be rejected to the cold side?
Maybe it's my inexperience with these engines, but I could imagine a situation where the piston, on the power stroke, goes a little further than needed using momentum or flywheel power, so it rarifies the fluid and cools it down.
Maybe in a perfectly timed and tuned engine that wouldn't even be necessary as the work already takes out that heat.

What am I missing here?

[Tom Booth]

Why a temperature differential? And how to get and maintain it.

According to alleged experiments, a LTD Stirling will run with "insulation" covering the cold side. ...

Are you referring to these "alleged" experiments?

https://m.youtube.com/playlist?list=PLp ... Q9pQZzY7Eu

Therein lies the problem in discussing this subject with you. My investigation into this matter began with an experiment attempting to demonstrate the necessity for removing heat. I happened to record that experiment, included in the playlist above.

You apparently don't even believe any experiments took place. I don't blame you for being skeptical, but that is where you should start if you are really interested in answering any of your questions. Do your own experiments so you can figure out what I did wrong or at least demonstrate the phenomenon.Then presumably you can rule out hidden magnets or batteries or wind up springs inside your engine.

No point in discussing experiments that you think may have never taken place or were conducted under some false pretense of trickery.

Otherwise the conversation just degrades into name calling. Tom Booth is uneducated, a poor experimenter, doesn't know enough math, doesn't show respect for venerable past scientists, is dishonest or fooling himself etc. etc.

I'm standing by, relaxing in comfortable furniture

If. You want answers you could start by getting up off your "comfortable furniture" and do an experiment yourself. Then we can talk about that instead of my "alleged" experiments.

[VincentG]

but I could imagine a situation where the piston, on the power stroke, goes a little further than needed using momentum or flywheel power, so it rarifies the fluid and cools it down.
Maybe in a perfectly timed and tuned engine that wouldn't even be necessary as the work already takes out that heat.

This could likely be demonstrated by a piston based vacuum pump. If all you do is rarify the fluid(pull a vacuum), with no compression stroke to pump the heat away, there is no net temperature reduction.

[Tom Booth]

This question came up in 2010. The prediction was insulating the cold side would cause the engine to overheat and stall:

viewtopic.php?p=1228#p1228

My experiments are an attempt to demonstrate that. So why doesn't it work?

[Fool]

Jack,

Expanding further reduces the temperature but requires work input to do so, colloquially called "sucking a vacuum". Unfortunately when the return stroke returns to the original expanded bottom volume from the extra large volume, the temperature comes back. It's colloquially called "heat" of compression. You do get the work back during this part of the compression stroke, so you end up zero zero, nothing gained, nothing lost except friction, for the effort. It is technically internal energy that is changing, not heat, no heat transfer.

The extra expansion idea you speak of has been known for around 200 years. It is the Carnot engine principle. He also theorized heat addition during expansion and heat removal during compression to maximize work output and minimize heat in. He also mentioned quasi static processes, and isothermal processes. This all led up to the abandonment of Caloric Theory along with the second law of thermodynamics, and Entropy. The first and second law, along with the Carnot theorem and Entropy all conspire to refute Caloric Theory.

Since then it's been verified mathematically using ideal gas law and other means. I posted several proofs in the "Truth" thread.

After expansion to the point inside and outside pressure is equal, maximum work output, the temperature of the gas is higher than Tc. That residual energy can be dumped, bad idea.

It can be expanded further to Tc, then the "heat" of compression can be rejected isothermally to Tc, Carnot Engine style.

Or it can be stored in a regenerator bringing the temperature down to Tc for again the isothermal compression at Tc, then put back in raising the Temperature to Th for the isothermal expansion, in the Stirling Engine style.

Using a crankshaft gives a compromise on the ideal theory.

Thanks for asking.

[VincentG]

A good read explaining the efficiency formula with a very different approach.

https://books.google.com.au/books?id=ci ... es&f=false

[Jack]

Jack,

Expanding further reduces the temperature but requires work input to do so, colloquially called "sucking a vacuum". Unfortunately when the return stroke returns to the original expanded bottom volume from the extra large volume, the temperature comes back. It's colloquially called "heat" of compression. You do get the work back during this part of the compression stroke, so you end up zero zero, nothing gained, nothing lost except friction, for the effort. It is technically internal energy that is changing, not heat, no heat transfer.

The extra expansion idea you speak of has been known for around 200 years. It is the Carnot engine principle. He also theorized heat addition during expansion and heat removal during compression to maximize work output and minimize heat in. He also mentioned quasi static processes, and isothermal processes. This all led up to the abandonment of Caloric Theory along with the second law of thermodynamics, and Entropy. The first and second law, along with the Carnot theorem and Entropy all conspire to refute Caloric Theory.

Since then it's been verified mathematically using ideal gas law and other means. I posted several proofs in the "Truth" thread.

After expansion to the point inside and outside pressure is equal, maximum work output, the temperature of the gas is higher than Tc. That residual energy can be dumped, bad idea.

It can be expanded further to Tc, then the "heat" of compression can be rejected isothermally to Tc, Carnot Engine style.

Or it can be stored in a regenerator bringing the temperature down to Tc for again the isothermal compression at Tc, then put back in raising the Temperature to Th for the isothermal expansion, in the Stirling Engine style.

Using a crankshaft gives a compromise on the ideal theory.

Thanks for asking.

Can't it be so that with that extra expansion you give the residual heat in the fluid a way out as work? In that way the expansion is still helped by any residual heat in the fluid and the way back would bring back less heat of compression because you don't actually have to push it back that hard.

When you keep in mind that the lower the delta is the longer it takes for the temp to equalize. This extra expansion forces out heat that usually goes wasted.
Yes it needs work to do it, but I'm talking about an ideal engine with this tuned to a minimum.
I do think that's a way to get all the heat to turn into work. In stead of rejecting it. I don't know how efficient or useful that can be, but that's what testing is for.
Admittedly, this would be very difficult to isolate and tune.

[Jack]

Let's say I have an engine at rest with the power piston at BDC. I add, random number, 50 degrees of heat to the fluid. Of this it uses 40 degrees to push the piston up. The remaining 10 aren't strong enough to overcome friction by itself, but if I use the momentum or stored energy in the flywheel I push the piston a little further so it takes out the additional 10 degrees as well. Ideally of course.
Then my fluid would be back to starting point and the piston would want to go back to BDC by itself.

So I'm basically putting in a little work to create a condition where all the heat is used.

Am I still missing something here?

[Tom Booth]

but I could imagine a situation where the piston, on the power stroke, goes a little further than needed using momentum or flywheel power, so it rarifies the fluid and cools it down.
Maybe in a perfectly timed and tuned engine that wouldn't even be necessary as the work already takes out that heat.

This could likely be demonstrated by a piston based vacuum pump. If all you do is rarify the fluid(pull a vacuum), with no compression stroke to pump the heat away, there is no net temperature reduction.

You seem to be making assumptions, drawing a conclusion about the outcome of an experiment that you haven't actually performed. Have you?

"This could likely be demonstrated..." doesn't sound like it. So mere assumptions and speculations there, which is the whole problem with the Carnot Limit theory, IMO. Assuming there is some empirical basis for it when there actually isn't.

[matt brown]

Am I still missing something here?

Yep, you're missing the most basic issue where heat equals work (ie Q=W) regardless of direction. This basic thermo tenant is what Tom struggles with where Qin=Wout and...Win=Qout. Just as the "heat of expansion" = work out, the returning piston will require work in = the "heat of compression". An ideal Stirling cycle supplies source in at a Thigh DURING expansion and sink out at Tlow DURING compression (2 distinct temperatures) where work out from expansion exceeds work in from compression proportional to the temperature differential measured via the absolute scale (deg K). Another way to view this is simply that the MEP (mean effective pressure) during expansion must exceed the MEP during compression, regardless whether the compression force comes from a flywheel or ambient pressure (aka, there's no free lunch).

An ideal Stirling cycle supplies both Thigh and Tlow isothermally (constant temperature) and whining that there's no such thing as an isothermal process is lame, since an Otto type cycle with 2 adiabatic processes will follow a similar sequence.

[VincentG]

You seem to be making assumptions, drawing a conclusion about the outcome of an experiment that you haven't actually performed. Have you?

"This could likely be demonstrated..." doesn't sound like it. So mere assumptions and speculations there, which is the whole problem with the Carnot Limit theory, IMO. Assuming there is some empirical basis for it when there actually isn't.

Tom are you claiming that you can convert mechanical work directly to temperature reduction without pumping the heat away?

[Tom Booth]

You seem to be making assumptions, drawing a conclusion about the outcome of an experiment that you haven't actually performed. Have you?

"This could likely be demonstrated..." doesn't sound like it. So mere assumptions and speculations there, which is the whole problem with the Carnot Limit theory, IMO. Assuming there is some empirical basis for it when there actually isn't.

Tom are you claiming that you can convert mechanical work directly to temperature reduction without pumping the heat away?

I'm not claiming anything. Just pointing out that you seem to be making assumptions about the outcome of an experiment without actually doing the experiment, or even having made any clear proposal.

Part of what Jack said was: "...that wouldn't even be necessary as the work already takes out that heat."

Some potential slight additional cooling is a moot point.

However this guy seems to suggest, and explain why, there is cooling from "pulling a vacuum" alone due to the gas "hitting a moving target". during expansion alone, no "pumping the heat away" with compression.

https://youtu.be/PMKPZuCj9a0

Seems like standard accepted physics.

If true, such cooling would be in addition to the internal energy of the gas simply being "spread out" more.

IMO such additional cooling might help accelerate the piston toward TDC during the compression stroke, where that extra velocity would be transformed back into heat at TDC for the following power stroke.

"Aligning the heat vectors" as it were.

The higher the piston velocity at the 90° advance point during compression the stronger the oscillation.

[Jack]

Another way to view this is simply that the MEP (mean effective pressure) during expansion must exceed the MEP during compression, regardless whether the compression force comes from a flywheel or ambient pressure (aka, there's no free lunch).

I get that you're quite knowledgeable and I really have to focus to turn these terms into the layman terms in my head. But what you're saying here is in line with what I mean. Or at least it doesn't contradict it in my understanding.

[Tom Booth]

Let's say I have an engine at rest with the power piston at BDC. I add, random number, 50 degrees of heat to the fluid. Of this it uses 40 degrees to push the piston up. The remaining 10 aren't strong enough to overcome friction by itself, but if I use the momentum or stored energy in the flywheel I push the piston a little further so it takes out the additional 10 degrees as well. Ideally of course.
Then my fluid would be back to starting point and the piston would want to go back to BDC by itself.

So I'm basically putting in a little work to create a condition where all the heat is used.

Am I still missing something here?

Personally, I don't think you are missing anything. You seem to be the only one seeing what others have been missing.

"Then my fluid would be back to starting point and the piston would want to go back to BDC by itself. "

I've been saying the same thing in a little bit different way.

It's recognized, even by Matt, that using up all the heat is possible during the expansion. 100% efficiency in a single stroke.

I don't know why it isn't completely obvious to all that this would result in the working fluid "back to starting point and the piston would want to go back to BDC by itself."

Though I think you mean TDC.

Just to confirm Matt's previous position:

Compress_20240624_015513_3022.jpg (15.9 KiB) Viewed 2753 times

Further he recognizes there is a pressure drop:

Compress_20240624_015512_2972.jpg (38.84 KiB) Viewed 2753 times

So with all the heat gone and the working fluid at low pressure, why wouldn't the piston want to return "by itself".?

But no need to rely on Matt's great authority or any authority or theory or opinions, it's quite easily demonstrated experimentally.

Just look at it. The piston always returns, makes a complete oscillation in both directions. The engine runs. No need for any speculation.

Experimental results outweigh all the theories, "ideal cycles", mathematical calculations, PV diagrams, speculations, opinions, charts, graphs, etc etc

All the blowhards don't dare try doing any actual experiment because they already know they will only get the same results I've gotten proving their own theories and opinions wrong.