Stirlingengineforum.com

The way I look at it. If the cold side is 62°F and the power piston is 75°F from heat from friction, after three hours, since the two are in direct contact 62°F is likely the average temperature between the the power piston and the working fluid.

Logically some heat from friction would be leaving the power piston and heating up the top plate.

Room temperature is closer to 65°F

To me that suggests the working fluid, when it expands and is mostly on the top side is likely much colder. Maybe 55°F ? as the top plate is also in constant contact with ambient near 55° the pp climbing to 75° and the top plate is at lest intermittently subject to heat of compression. Not to forget the boiling water it's been sitting over for three hours. Something has to be keeping it so cool it stays at ambient if not below while surrounded by all that heat.

Anyway the Stirling engine sandwich experiment should shed some light on what's going on.

I got an email from Kontax that they sent out the order, but it will take about three weeks to get here.

VincentG wrote: ↑Wed May 08, 2024 3:36 pm

Not sure how you figure "hot" gas is expanding into the power piston.

The cold gas, for the most part, is heated and expanded below the displacer as the displacer raises up and drives cold air down to be heated.

Aside from that, we can generally say the gas does not actually heat up that much, it expands as it takes in energy.

Expanding gas also tends to cool down as it expands.

At any rate, the hot gas rising up from the bottom, if we assume it does, would have to pass through the upper cold side of the displacer chamber warming the cold plate before it reached the power cylinder.

How do you figure the hot air can skip past the upper cold zone and stuff itself up into the power cylinder without first, or also transferring heat to the upper cold plate it would have to get past first?

I don't literally mean "hot". The "hot" gas is trying to expand into the piston but is cooled by the displacer and cold side and cylinder, etc. In a standard engine it's probably warm gas by the time it gets there.

It's not like these little engines have valves and camshafts to isolate distinct events.

It's just one wishy-washy sequence in essentially an open chamber. The gas is free to move around. Even with the displacer fully raised, convection causes the cold gas to sink and be replaced by hot gas, which in turn is cooled, and again sinks.

It's the same thing that causes a free piston to move proportionally to the displacer position.

Astonishing.

You do know, I mean you are familiar with these LTD engines.

Also I've extended the throw, so not only is the power piston driving all the air out of the cylinder into the displacer chamber a few times per second, the piston itself is dropping down into the chamber a bit also.

Then the displacer moves up and down mixing the air I would think rather thoroughly.

This is not a stagnant environment inside the engine.

Anyway, with the two engines together, one will likely be upside down. We can check if the cylinders get hot or warmer, in the upper engine, from hot air rising or cold from cold air falling in the upside down engine.

I still think the most likely and obvious explanation why the power cylinder is hot is FRICTION. In fact, it's a dry lube, fairly rough aluminium cylinder. There is undoubtedly friction. Seems obvious, common sense. In all engines the pistons going up and down in their cylinders experience friction which generates heat.

Fool wrote: ↑Wed May 08, 2024 9:40 am Your power piston cylinder appears at a higher temperature than the top of the cold plate. I can only guess why from the information recorded. Work is certainly a factor to consider. What it read before running wasn't given to me.

I would expect the top of the cold plate to not be changing temperature after three hours of running, unless recently disturbed. There may or may not be a temperature change in the top of the cold plate in the first few minutes after introducing hot water and starting it running.

The purpose of the cold plate is to have a temperature identical to ambient. Heat coming out should make it slightly higher. I don't have an answer as to why it appears not to be higher. I can only guess. You have eliminated some of my guesses already. So I'm running low on guesses.

If you have a valid experiment, and have found something unusual, you are in the 1800's wooden ship scurvy alleged cure from oranges stage. Yohan ate oranges on the last trip and was the only one that didn't get scurvy. Tom is the only person that has run a Stirling Engine with the cold side insulated, and he claims it runs faster and colder. Now we need to correlate it with numbers predicting it. I have no idea how to do that, except starting with an indicator diagram.

If I come up with a workable prediction, not likely, I will share it with you. We would probably earn a Nobel. Unless we find some other reason for it and disprove it. Then we'll just get a bunch of I told you so's. I guess I'm in the trying to disprove phase, "falsifiability". I need to retest it myself, not likely either, I still haven't built the engine I want to build from 20+ years of research, study, and pondering. Maybe this summer or fall.

I found it interesting when you peeled down the insulation and pointed at the side. Unfortunately you waved it around too much, but briefly I thought I saw hot on one side of the displacer and cold on the other, going up and down. The "chain regenerator" blocked the view too. Stable readings from that vantage point, maybe in slow or stop motion, would be fun to look at.

This post seems to have appeared out of nowhere. Apparently edited 10 minutes after something else? Was posted?

Anyway:

Your power piston cylinder appears at a higher temperature than the top of the cold plate. I can only guess why from the information recorded. Work is certainly a factor to consider. What it read before running wasn't given to me.

Logically, I would think the engine was room temperature, don't you think?

My phone has limited memory for recording videos. Five or six minutes maybe, if I delete all the old videos. I can't record a 3 hour video. If the experiment runs longer than a few minutes I pause the recording and only start it up to show pertinent details. Sorry, I don't have a movie studio.

The purpose of the cold plate is to have a temperature identical to ambient

Heat does not transfer between temperatures that are "identical". Sorry.

I found it interesting when you peeled down the insulation and pointed at the side. Unfortunately you waved it around too much, but briefly I thought I saw hot on one side of the displacer and cold on the other, going up and down. The "chain regenerator" blocked the view too. Stable readings from that vantage point, maybe in slow or stop motion, would be fun to look at.

The IR camera is really two cameras. One black and white to show the physical objects and the IR heat signatures of the actual IR camera are superimposed over the b/w image.

Unfortunately the two camera lenses, of necessity are separated by a short distance and the two images don't line up perfectly, depending on the angle the camera is held. So it's hard to know exactly where the line between hot and cold was exactly.

At any rate, the IR camera can not "see" through the acrylic sidewall at all, so the readings are the outside surface not the displacer, which as you pointed out, cannot be seen at all behind the regenerator.

Tom Booth wrote: ↑Wed May 08, 2024 7:34 pm Not to forget the boiling water it's been sitting over for three hours.

Did you measure the temperature of that three hour old "boiling" water?

Stroller wrote: ↑Wed May 08, 2024 11:38 pm

Tom Booth wrote: ↑Wed May 08, 2024 7:34 pm Not to forget the boiling water it's been sitting over for three hours.

Did you measure the temperature of that three hour old "boiling" water?

The water was poured into a dewar double wall vacuum insulated flask, which by previous tests, filled with boiling water could keep a Stirling engine running at least three hours.

As I said in the video, the water was freshened/replaced with a fresh supply of boiling water every 20 minutes.

As can also be seen in the video the water was "freshened" again at the start of the video, the water being replaced was still steaming hot.

And yes, as can also be seen in the videos I did check the temperature from time to time.

But of course, you're prone to pass judgement, criticise and comment on videos of experiments you haven't bothered to watch but supposedly "skimmed through".

viewtopic.php?p=22459#p22459

Video showing how the regenerator was made from an acrylic canister, just a little smaller than the engines acrylic displacer cylinder leaving a space between the two that was filled with the metal lamp pull chain.

https://youtu.be/t_0mYKcy9nE

The other two videos were simply, or originally mostly just testing the effectiveness of the regenerator.

Something else to consider: as effective as that regenerator appears to have been, there does not appear to be all that much of a temperature gradient.

Probably making the displacer chamber deeper with a thicker displacer so more layers of pull chain could be fitted in would have given better thermal separation between the hot and cold sides.

There should really be about 20 layers, which research has found to be ideal, or most effective.

viewtopic.php?p=18525#p18525

How to build an effective regenerator:


viewtopic.php?p=16599#p16599

https://www.researchgate.net/publicatio ... ass_ratios

Tom Booth wrote: ↑Thu May 09, 2024 1:19 am as can also be seen in the videos I did check the temperature from time to time.
But of course, you're prone to pass judgement, criticise and comment on videos of experiments you haven't bothered to watch but supposedly "skimmed through".

I'm not passing judgement, and my criticisms are only made to try to get you to provide the data I don't have enough spare time to garner from watching all the way through all the videos I'd like to.

I'd like to help you get to the bottom of the question about the power piston being ~6.5K warmer than the top plate, and that's why I'm asking about the temperature of the water at that time. If those top plate and PP temperatures, and that differential persist for the 20 minutes between 'refreshes' of the water, give or take, then that's telling us something about the throughput rate of the baseplate and engine.

If it is friction that causes the higher T of the pp, then a simple way to test for this would be to stop the engine, and see what rate the T differential diminishes at as the PP starts to equilibriate with the power cylinder wall, and by conduction, the rest of the top plate.

If it's mainly due to the different emissivity of the PP material from the emissivity of the power cylinder wall and top plate, then you'd expect the T differential to persist more.

Stroller wrote: ↑Thu May 09, 2024 2:17 am

Tom Booth wrote: ↑Thu May 09, 2024 1:19 am as can also be seen in the videos I did check the temperature from time to time.
But of course, you're prone to pass judgement, criticise and comment on videos of experiments you haven't bothered to watch but supposedly "skimmed through".

I'm not passing judgement, and my criticisms are only made to try to get you to provide the data I don't have enough spare time to garner from watching all the way through all the videos I'd like to.
...

Sorry, but I took the time to make and post the video. As well as all the expense of buying engines and testing equipment, etc.

I don't have much time or patience for people who waste MY time answering stupid questions over and over ABOUT a video they didn't bother to watch.

And bull shit, you are and have been "passing judgement" and plenty of it. Who are you trying to kid?

How about do your own experiments and stop wasting my time with your idiotic insinuations.

The phrasing of your question:

Did you measure the temperature of that three hour old "boiling" water?

Along with all your other accusations and put downs is quite obviously tongue in cheek to put it mildly.

Kindly take your friend "fool" and get lost.

OK, no problem. I'll leave you with a last attempt to be helpful.
If your power piston is graphite, just be aware that it has an emissivity around 4x that of aluminium. That means it radiates energy much more effectively than the top plate. That will cause it to have a higher temperature, given proximity to the same environment.
That's why survival blankets are aluminized. They reflect radiant energy back rather than absorb and tre-radiate it. But aluminium transmits conducted heat well, which is why it's the material of choice for water cooling blocks.
Cheers, and good luck with your endeavours.

VincentG wrote: ↑Wed May 08, 2024 3:36 pm It's just one wishy-washy sequence in essentially an open chamber. The gas is free to move around. Even with the displacer fully raised, convection causes the cold gas to sink and be replaced by hot gas, which in turn is cooled, and again sinks.

I know I mentioned the speed of sound before, but as I understand it, so long as that doesn't come into play, we can assume that the pressure within the working fluid of an engine is equal _everywhere_ at all times, to within a negligible fraction of a percent.

If that is truly the case, then the gas laws imply that the temperature of the fluid must also be equal, everywhere.
This is another case where it helps to think of energy flow into the engine, rather than heat.

MikeB wrote: ↑Thu May 09, 2024 3:59 am we can assume that the pressure within the working fluid of an engine is equal _everywhere_ at all times, to within a negligible fraction of a percent.

I was wondering if, in the case of LTD engines, which have wide displacers, whether the situation might be complicated by the velocity of the working fluid towards the centre of hot plate as the displacer starts being lifted from its lowest position. Might that velocity, plus the heating/expansion of the air, cause a briefly raised pressure which helps accelerate the displacer upwards before the power piston expansion stroke gets fully underway?

If that is truly the case, then the gas laws imply that the temperature of the fluid must also be equal, everywhere.
This is another case where it helps to think of energy flow into the engine, rather than heat.

Glad when you chime in Mike B. I think this ties in nicely with your thoughts on "average temperature". The position of the displacer affects the average air temp, and therefore the average pressure.

But if we were to analyze a snapshot in time, I don't believe the gas is really the same temperature above and below the displacer.

Stroller wrote: ↑Thu May 09, 2024 3:44 am OK, no problem. I'll leave you with a last attempt to be helpful.
If your power piston is graphite, just be aware that it has an emissivity around 4x that of aluminium. That means it radiates energy much more effectively than the top plate. That will cause it to have a higher temperature, given proximity to the same environment.

So what? The power cylinder was also aluminium just like the top plate, as I've already said.

That's why survival blankets are aluminized. They reflect radiant energy back rather than absorb and tre-radiate it. But aluminium transmits conducted heat well, which is why it's the material of choice for water cooling blocks.
Cheers, and good luck with your endeavours.

"I'll leave you with a last attempt to be helpful"


"Helpful" .my ass.

Your attempting to dismiss obvious clear unequivocal evidence/data simply because it does not validate your own predetermined, fixed, died-in-the-wool opinions.

I've been using the IR image camera for years now and have seen the same FRICTION heat signatures on Stirling engines around the connecting rod joints, flywheel bearings, bushings, anywhere there are moving parts in contact with each other.

But who would have ever thought such a thing had any significance or would become an issue, be doubted or need explaining? It's completely ridiculous and a waste of time debating a non-issue at such agonizing ridiculous lengths.

Hell, everybody in the world who has ever rubbed their own two hands together on a cold day to keep warm knows friction causes heat

Wonder of wonders. Now we have FRICTION DENIERS.

Somehow, because it is an engine and supposedly subject to the "Carnot Limit", the laws of physics, including mechanical parts rubbing together create heat from friction no longer apply. The laws of the universe bend the knee to the supreme "LAW" of the "Carnot Limit" that can never be broken under any circumstances.

What lunacy.

You guys are so desperate to uphold your antiquated, obsolete, pre-scientific world view your beside yourselves.

You or anyone can see the same kind of hot spot heat signature around any power piston, gear, axle, or bearing, be it graphite, aluminum, acrylic, glass, epoxy, cast iron, you name it. Anywhere there is friction, heat is generated.

"That means...."

Followed by a river of nonsensical rationalizations desperately trying to uphold a completely nonsensical, obsolete, antiquated world view.

A new class of skepticism. Friction denial. Of course, the "perfect" Carnot engine had no friction, transfered heat freely without a temperature difference, ran on "pebbles" that had to be moved by hand to add and remove weight from the piston. Took infinity to complete each revolution, was powered by the "FALL" of your thermometer reading, spawned 101 versions of "the second law of thermodynamics" many of which make no sense, are in conflict with themselves, each other, or known science and observable facts.

There seems to be no end to the depth of irrationality and contradiction and sheer willful blindness.

Anyway, I'd like to move on from this non-issue. Moving parts create heat from friction. Period. It is a known fact, actual established science. The Carnot Limit was never scientifically established. Complete nonsense.

MikeB wrote: ↑Thu May 09, 2024 3:59 am

VincentG wrote: ↑Wed May 08, 2024 3:36 pm It's just one wishy-washy sequence in essentially an open chamber. The gas is free to move around. Even with the displacer fully raised, convection causes the cold gas to sink and be replaced by hot gas, which in turn is cooled, and again sinks.

I know I mentioned the speed of sound before, but as I understand it, so long as that doesn't come into play, we can assume that the pressure within the working fluid of an engine is equal _everywhere_ at all times, to within a negligible fraction of a percent.

If that is truly the case, then the gas laws imply that the temperature of the fluid must also be equal, everywhere.
This is another case where it helps to think of energy flow into the engine, rather than heat.

the temperature of the fluid must also be equal, everywhere.

This is not actually true. Temperature and pressure are linked but not identical.

If it is cold below the displacer or on one side of a regenerator and hot on the other, an increase or decrease in pressure does change the temperature equally throughout the working fluid. That does not mean that the temperatures become literally equal.

Say the temperatures are 300° on the cold side and 600° on the hot side.

An increase in pressure may elevate the temperatures to 320° and 620° respectively. The temperatures do not suddenly become equivalent.

Same with a drop in pressure.

300°/600° may become 280°/580° or something like that.

Equivalent pressure does not mean equivalent temperature.

Tom Booth wrote:Kindly take your friend "fool" and get lost.

Tom, please don't despair. Stroller appears to be a kind and knowledgeable experienced person whom I don't know or collaborate with. I'm sure that we could have a great time talking shop. I'm having fun talking shop with you. You may think I'm talking ludicrously, but I've noticed that every once in a while you see some hope in me. A point, a ponder, something valid.

Stroller, VincentG, Matt Brown, Alphfax, MikeB, I like all of you and hope you continue here. Please, Illegitimi non carborundum. And Please continue tying.

My gotos are integral calculus, thermodynamics, heat transfer, kinematics, PV and TS plots. It is very frustrating to have a battle of wits with people who are defenseless. When doing so they tend to use slippery slope and other logical fallacies with ad homonyms followed their own cognitive dissonance. Once dissonance sets in nothing penetrates.

Tom, it all boils down to the fact that expanding internal gas outputs energy. Compressing gas absorbs energy. Both for the entire stroke.

The system, engine, will put out energy during expansion and or absorb it depending on which way the pressure difference is compared with the motion. Higher pressure inside during expansion, energy output. Lower pressure inside during expansion, energy is absorbed, instructor pulling on the piston, energy in.

The Carnot limit is based on W=Qh-Qc. One value can be equated from the other two. In other words, two need to be determined to calculate the third. Measure two not one. Temperature isn't in that equation. Additionally n=W/Qh=1-Qc/Qh. To calculate n, to compare with Carnot, two values are needed there too.

Work is the easiest to measure. All that is needed is RPM and torque. RPM is easy, torque requires a spring, arm, pivot, and, brake or propeller. And a way of calibrating it. Alternately a generator and voltamp meter could suffice.

Tom Booth wrote:Sorry, but I took the time to make and post the video. As well as all the expense of buying engines and testing equipment, etc.

As I've said before, it very hard to do good science. It takes a lot of time money and patience. And all you get for it is people trying to tear it apart. Welcome to the club, and thank you very much for the efforts. They are much appreciated.

MikeB, pressure being the same doesn't equate to temperature being the same. The equation PV=NRT can't use the assumption that M is constant for the entire volume. The variation will be density. Hotter areas will have lower densities.

That is why computer simulations, finite element analysis, of Stirling Engines is so difficult. That and not enough computing power. If the engine is diced up into small volumes mass flow must be modeled, then volume changes during the mass flow. It's worse if dicing it up by small chunks of mass. Volume changes from mass flow, and locations become chaotic. It gets really dicey (pun noted), as the chunks are made smaller they expand in numbers by distance to the third power. Yikes.

You are probably thinking that a bulk pressure can be equated to a bulk, or average, temperature. I think that is appropriate for PV diagram modeling. Good one.