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Tom Booth

Heat engine experiments and 2nd law of thermodynamics.

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Is this the type of engine you are referring to  ?

 

American Stirling Company

Displacer Type Stirling Engine

Displacer Type Stirling Engine Animation

Gas expands when heated, and contracts when cooled. Stirling engines move the gas from the hot side of the engine, where it expands, to the cold side, where it contracts.

DISPLACER PISTON

When there is a temperature difference between upper displacer space and
lower displacer space, the engine pressure is changed by the movement of
the displacer. The pressure increases when the displacer is located in the
upper part of the cylinder (and most of the air is on the hot lower side).
The pressure decreases when the displacer is moved to the lower part of
the cylinder. The displacer only moves the air back and forth from the hot
side to the cold side. It does not operate the crankshaft and the engine.
In other words, the connecting rod to the displacer could be a string in
this engine and it would still work.

POWER PISTON

When the engine pressure reaches its maximum because of the motion of the
displacer, a power piston is pushed by the expanding gas adding energy to
the crankshaft. The power piston should ideally be 90 degrees out of phase
with the displacer piston. The displacer type Stirling engine is operated
by the power of the power piston.

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7 minutes ago, swansont said:

That’s obvious.

Vacuum and atmosphere

You claim work is not being done against atmosphere. it’s the only other option.

That’s not what I said, or what’s going on.

But you keep saying work is not being done against atmosphere, and that’s not right. (“I was just trying to clarify that "work" is not done to expand the gas”) 

The fact that you are focused on the marbles suggests you aren’t getting what other people are talking about. 

 

You aren't or haven't been following the conversation.

Much earlier Studiot said the displacer: "drives the crank via what I would call a push rod".

I'm just trying to clarify the function of the displacer. It does not drive the crankshaft, it is in no way in direct contact with atmosphere.

I'm not trying to say no work is being done by the piston, I'm trying to clarify the function of a displacer. The marbles are the displacer! You are the one who is not focused on what the topic of the conversation is and not getting what is being talked about.

Nobody says no part of a Stirling engine does work against the atmosphere.

9 minutes ago, studiot said:

Is this the type of engine you are referring to  ?

 

American Stirling Company

Displacer Type Stirling Engine

Displacer Type Stirling Engine Animation

Gas expands when heated, and contracts when cooled. Stirling engines move the gas from the hot side of the engine, where it expands, to the cold side, where it contracts.

DISPLACER PISTON

When there is a temperature difference between upper displacer space and
lower displacer space, the engine pressure is changed by the movement of
the displacer. The pressure increases when the displacer is located in the
upper part of the cylinder (and most of the air is on the hot lower side).
The pressure decreases when the displacer is moved to the lower part of
the cylinder. The displacer only moves the air back and forth from the hot
side to the cold side. It does not operate the crankshaft and the engine.
In other words, the connecting rod to the displacer could be a string in
this engine and it would still work.

POWER PISTON

When the engine pressure reaches its maximum because of the motion of the
displacer, a power piston is pushed by the expanding gas adding energy to
the crankshaft. The power piston should ideally be 90 degrees out of phase
with the displacer piston. The displacer type Stirling engine is operated
by the power of the power piston.

Exactly, thank you.

"The displacer only moves the air back and forth from the hot
side to the cold side. It does not operate the crankshaft and the engine.
In other words, the connecting rod to the displacer could be a string in
this engine and it would still work."

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15 minutes ago, Tom Booth said:

You aren't or haven't been following the conversation.

I was previously admonished and directed to focus on one example, so much like the second law, I can’t win.

 

Did you, or did you not say “I was just trying to clarify that "work" is not done to expand the gas”?

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14 minutes ago, Tom Booth said:

Exactly, thank you.

So can we all analyse the system in my picture in relation to the laws of Thermodynamics ?

Like other members I have already said that this machine in in perfect accord with these laws, including the second law.

We have also asked why you think the second law is appropriate, when this is really a First Law matter.

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Posted (edited)
1 hour ago, swansont said:

I was previously admonished and directed to focus on one example, so much like the second law, I can’t win.

 

Did you, or did you not say “I was just trying to clarify that "work" is not done to expand the gas”?

We can discuss whatever you like, but let's just try to be clear what is being discussed. I'm talking about an engine running on hot water, and you interject, so why does the ice melt.

It's like I'm talking about a submarine and someone asks about the airplane wings I mentioned in another conversation two days ago. One thing has nothing to do with the other.

Quote

Did you, or did you not say “I was just trying to clarify that "work" is not done to expand the gas”?

I may have said something like that, or possibly those words exactly, but that is out of context.

It is true though that no mechanical element, not the displacer, not the piston, is doing work to expand the gas.

HEAT expands the gas and the GAS does work as it expands. So that is probably a perfectly valid statement in context, as Studiot was talking about the piston and displacer at the time if I'm not mistaken.

Would it be a valid statement to say that the heat does work? I don't think so, but it might be a way of looking at it.

Edit: as a matter of fact, this was my statement:

Quote

I was just trying to clarify that "work" is not done to expand the gas, or to work against atmospheric pressure BY THE DISPLACER

You left off the bolded and underlined part I had emphasised. Why?

Edited by Tom Booth
Clarification

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16 minutes ago, Tom Booth said:

We can discuss whatever you like, but let's just try to be clear what is being discussed. I'm talking about an engine running on hot water, and you interject, so why does the ice melt.

You’ve posted lots of stuff. Everyone else is responding to it. If you wanted to focus on one example, we could have done that. But you’re the one who has presented multiple examples.

 

Quote

It's like I'm talking about a submarine and someone asks about the airplane wings I mentioned in another conversation two days ago. One thing has nothing to do with the other.

That’s what new threads are for. To keep things separate. And also why mods admonish responders for thread hijacking. But that all goes out the window when the thread starter keeps bringing up more examples.

And it’s not fair to people who might not have visited in a day or two to try and tell them they can’t participate because you posted something a couple of days ago. One thread = one conversation

Quote

I may have said something like that, or possibly those words exactly, but that is out of context.

I copy-pasted, so there is no doubt you said it.

Quote

It is true though that no mechanical element, not the displacer, not the piston, is doing work to expand the gas.

HEAT expands the gas and the GAS does work as it expands. So that is probably a perfectly valid statement in context, as Studiot was talking about the piston and displacer at the time if I'm not mistaken.

Would it be a valid statement to say that the heat does work? I don't think so, but it might be a way of looking at it.

A common theme here has been people explaining that heat is converted to mechanical work. (but not all of it can be converted)

 

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Posted (edited)
7 minutes ago, swansont said:

You’ve posted lots of stuff. Everyone else is responding to it. If you wanted to focus on one example, we could have done that. But you’re the one who has presented multiple examples.

 

That’s what new threads are for. To keep things separate. And also why mods admonish responders for thread hijacking. But that all goes out the window when the thread starter keeps bringing up more examples.

 

I copy-pasted, so there is no doubt you said it.

A common theme here has been people explaining that heat is converted to mechanical work. (but not all of it can be converted)

 

In case you missed my edit above:

Here it is again:

Edit: as a matter of fact, this was my statement:

  Quote

I was just trying to clarify that "work" is not done to expand the gas, or to work against atmospheric pressure BY THE DISPLACER

You left off the bolded and underlined part I had emphasised. Why?

You copy pasted completely out of context.

Edited by Tom Booth
Emphasis added to Swansont's quote "I copy pasted...

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Just now, Tom Booth said:

In case you missed my edit above:

Here it is again:

Edit: as a matter of fact, this was my statement:

  Quote

I was just trying to clarify that "work" is not done to expand the gas, or to work against atmospheric pressure BY THE DISPLACER

You left off the bolded and underlined part I had emphasised. Why?

I was focusing on the part of the statement about work and gas expansion.

You do understand the function of the word “or”, right?

 

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You can be deliberately obtuse and try to drag this out but my sentence is perfectly clear. I was referring to THE DISPLACER!!!

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A closer look at the displacer. As can be seen, just a thin, lightweight, loose fitting disk of styrofoam.

 

 

 

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11 hours ago, Tom Booth said:

You can be deliberately obtuse and try to drag this out but my sentence is perfectly clear. I was referring to THE DISPLACER!!!

Then you should have not constructed such a poor sentence. I can’t read your mind, and given the glaring misconceptions you have demonstrated, there was no way to know that you didn’t mean what you said. If it was a mistake, own it, rather than blaming others for it.

 

Quote

A closer look at the displacer. As can be seen, just a thin, lightweight, loose fitting disk of styrofoam.

Your point? (nobody can read your mind. It’s not just me)

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Posted (edited)

In talking about Stirling engines there are some technical terms that can't be avoided. "Displacer" is one. It is, as far as I know, unique to Stirling heat engines.

I've explained the function of the displacer in as many ways as possible and from as many different angles as possible. Displacement is not a common word, but the dictionary definition for displacement describes what the displacer does in a Stirling engine.

It makes no difference what I say or how I say it, if you don't know the technical terminology and what it means in the context of Stirling engines, it will have no meaning 

There is nothing wrong with my sentence structure.

18 hours ago, studiot said:

So can we all analyse the system in my picture in relation to the laws of Thermodynamics ?

Like other members I have already said that this machine in in perfect accord with these laws, including the second law.

We have also asked why you think the second law is appropriate, when this is really a First Law matter.

Sorry, I think your post slipped in and I did not see it until now. Sounds great.

 

17 hours ago, swansont said:

 

And it’s not fair to people who might not have visited in a day or two to try and tell them they can’t participate because you posted something a couple of days ago. One thread = one conversation

And it IS fair to drop in on the middle of a conversation you haven't been following and start criticising because you don't know what's being discussed?

It helps to go back and read and find out what you may have missed. Discussions progress. Usually.

The topic is "Heat engine experiments and 2nd law of thermodynamics."

Notice the plural in "experiments"? The "s" at the end of the word means more than one.

Edited by Tom Booth

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Posted (edited)
19 hours ago, studiot said:

 

19 hours ago, studiot said:

So can we all analyse the system in my picture in relation to the laws of Thermodynamics ?

Like other members I have already said that this machine in in perfect accord with these laws, including the second law.

We have also asked why you think the second law is appropriate, when this is really a First Law matter.

The picture/animation originated here:

http://www.bekkoame.ne.jp/~khirata/english/anime_c.htm

There is a ton of information on that site, as well as the American Stirling Engine site.

Originally I had wanted to, and intended to order engines from the ASE company, but their website was inaccessible at the time.

The animation is overly simplistic and does not really begin to delve into the thermodynamics of the engine.

For example, the illustration shows water cooling of the top plate, which is common. But imagine that instead of cooling the top plate with water, it were insulated, as in my experiment, which would, presumably, retain most of the heat from the burners.

Without the active cooling, one might expect the engine to overheat and quit working. But in my experiment, that is not what happened.

Insulating the top, instead of cooling it, did not cause the engine to quit. Instead it ran measurably better. Something else was keeping the top plate cold. Something not shown or discussed on that page.

Edited by Tom Booth

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Posted (edited)
1 hour ago, Tom Booth said:

Sorry, I think your post slipped in and I did not see it until now. Sounds great.

Thank you for the very useful animations I fully understand this machine now so progress can be made.  +1

(I had to go look on a modern computer to view them, mine is Windows XP)

 

I also see what you mean about a 'displacer', not a bad term although I would have chosen mixer or stirrer as that is what it does.

To summarise;

1) The unit comprises an air chamber with a small offset piston, (small being the volume displaced as the piston moved is small compared to the total volume of the chamber)
2) If one end of the unit is heated ( or cooled) relative to ambient the heat flowing into the air in the chamber results in an increase (reducion) in pressure, which displaces the piston a small amount.
3) The piston drives an output shaft with a flywheel, via a conventional conrod and some gearing.
4) The output shaft drives a liftrod and crank which lifts and lowers the displacer within the chamber.
5) The mixed or stirred air away from the heat or cold source experiences a pressure reduction (increase), maintaining the cycle.
 

 

Edited by studiot

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In regard to these experiments, this article is also significant:

https://www.stirlingengine.com/#5

The section on Stirling cryo-coolers. There is also additional information on Stirling coolers in the FAQ on this website.

 

What is important to understand, I think, is that a Stirling cryo-cooler is not a Stirling heat engine "running backwards".

As a cooler, the engine runs in the same direction as for power output. It functions in almost exactly the same way, mechanically, as a cooler as it does as an engine.

A Stirling engine is really a refrigeration device that works by converting heat into work to effect cooling. Running the engine with a motor, the same way, in the same direction, simply amplifies the cooling effect, so that the engine can produce much colder temperatures, all the way down to the cryogenic range.

The effect in a small toy engine is so minute, though, it requires very careful insulating to produce any measurable effect.

 

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I've decided to see what happens if the aluminum cold plate, which might sink a lot of heat even insulated, is replaced with plexiglass, which is over 1000 X less heat conducting.

 

 

 

IMG_20200803_164342250_crop_96_resize_85.jpg

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Posted (edited)
14 hours ago, Tom Booth said:

A closer look at the displacer. As can be seen, just a thin, lightweight, loose fitting disk of styrofoam.

I watched the movie clip where the engine is removed from the insulation. I notice that it looks like the whole engine is insulated, not only the cold plate but also the hot side of the engine.

4 hours ago, Tom Booth said:

Insulating the top, instead of cooling it, did not cause the engine to quit. Instead it ran measurably better. Something else was keeping the top plate cold. Something not shown or discussed on that page.

Is there any chance that the observed effect is caused by the insulation on the hot side? I mean if the insulation makes the cold side lets say 5 degrees warmer for a while but the hot side 10 degrees warmer that means the temperature difference is increased. What effect would that have? 

 

Edited by Ghideon
grammar

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Posted (edited)
1 hour ago, Ghideon said:

I watched the movie clip where the engine is removed from the insulation. I notice that it looks like the whole engine is insulated, not only the cold plate but also the hot side of the engine.

Is there any chance that the observed effect is caused by the insulation on the hot side? I mean if the insulation makes the cold side lets say 5 degrees warmer for a while but the hot side 10 degrees warmer that means the temperature difference is increased. What effect would that have? 

 

Good point.

The hot bottom plate was insulated everywhere except between that and the Dewar flask mouth, so indeed that certainly cut down on heat loses from the hot plate, which would have made it hotter.

However, thinking about it, the bottom periphery had been insulated the whole time as well s the whole Dewar and all.

The increase in RPM took place after the cold plate was covered.

The sides of the engine are mostly a short section of plexiglass tubing, so is not very conductive, but the air spaces between the nylon bolts could transfer heat between the plates by convection. So that was insulated.

Also, I had run the engine with the same setup, insulation everywhere, except on top. If I'm not mistaken, it ran faster and longer only after the top was insulated, everything else being the same, but I was not being as careful as I should have been, and times of day, ambient temperature, and probably other variables were not well controlled.

That is why I ordered so many kits, to run engines side by side at the same time, but I only have one built so far.

What I do know for sure is after I covered the sink, the RPM increased, which was what my theory told me might happen but was the opposite of what everyone else thought would happen.

Really if the engine did not continue running and instead speeded up as it did, I would have discarded the whole theory and nobody would be seeing this.

Edited by Tom Booth

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Posted (edited)
42 minutes ago, Tom Booth said:

Also, I had run the engine with the same setup, insulation everywhere, except on top. If I'm not mistaken, it ran faster and longer only after the top was insulated, everything else being the same, but I was not being as careful as I should have been, and times of day, ambient temperature, and probably other variables were not well controlled.

You should be able to measure the temperatures of the hot and cold plates with and without insulation.

That would be useful information, as well as the speed and timing of the running ( since you now have an idea of the timings, there is no need to babysit it like your earlier experiments)

Also please let us deal with the simple machine first, before moving on to the more complicated one you have mentioned.

Edited by studiot

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Posted (edited)
12 minutes ago, studiot said:

You should be able to measure the temperatures of the hot and cold plates with and without insulation.

That would be useful information, as well as the speed and timing of the running ( since you now have an idea of the timings, there is no need to babysit it like your earlier experiments)

Also please let us deal with the simple machine first, before moving on to the more complicated one you have mentioned.

Yes, I do plan on getting some sort of temperature probes. I don't know of anywhere locally that would carry that sort of thing. Anyone have any recommendations? Something thin preferably, that maybe could be taped to the hot & cold plates.

The first engine is still intact, except for having stripped off the insulation for that video.

I'm building another engine.

This time my plan is to add Regenerator matrix. I'm not sure what you mean by, let us deal with the simple machine first.

My time for working on this stuff is very limited, so when I have time, I'm not just going to twiddle my thumbs.

 

Edited by Tom Booth

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Posted (edited)

I've been looking for some kind of "authoritative" confirmation of my statement, that a Stirling cryo-cooler is THE SAME as a Stirling engine running in The SAME direction as a Stirling engine, as very often, there is quite a bit of misinformation on the internet that a Stirling cooler runs in the opposite direction from a Stirling engine.

There is, at least, this old video:

This does not seem to be a very well documented point of fact. "The machine running in the same forward direction in both cases".

Edited by Tom Booth
Added quote from video

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7 hours ago, Tom Booth said:

I've been looking for some kind of "authoritative" confirmation of my statement, that a Stirling cryo-cooler is THE SAME as a Stirling engine running in The SAME direction as a Stirling engine, as very often, there is quite a bit of misinformation on the internet that a Stirling cooler runs in the opposite direction from a Stirling engine.

If it runs in the same direction, how does it cool?

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9 hours ago, Tom Booth said:

I've been looking for some kind of "authoritative" confirmation of my statement, that a Stirling cryo-cooler is THE SAME as a Stirling engine running in The SAME direction as a Stirling engine, as very often, there is quite a bit of misinformation on the internet that a Stirling cooler runs in the opposite direction from a Stirling engine.

There is, at least, this old video:

This does not seem to be a very well documented point of fact. "The machine running in the same forward direction in both cases".

!

Moderator Note

Please stop using videos as support for your ideas. The membership is not required to watch them, and you're basing too much of this discussion on their content. Please adhere to the rules you agreed to when you joined.

 

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Posted (edited)

.

Quote

Moderator Note

Please stop using videos as support for your ideas. The membership is not required to watch them, and you're basing too much of this discussion on their content. Please adhere to the rules you agreed to when you joined

How does that post violate any rule? The video is highly relevant to the discussion, the relevant points are written out and quoted in the text of my post. The relevant content is at the very beginning of the video, nobody is required to watch the entire video, or any of it for that matter to participate in the discussion, the video and the point being made are certainly open to discussion, it is the point of the discussion. It is not MY video, is not in my YouTube lineup at all, so it's not to boost my YouTube ranking which is not even monetized  I've read the rules pertaining to videos and have complied in every possible way  Videos as supporting material are useful and add to the discussion. This used to be, years ago, quite a friendly forum, but if simple links and videos are so intolerable here now, it has become less useful IMO. What rule specifically does my previous post violate? None that I'm aware of.

 

5 hours ago, swansont said:

If it runs in the same direction, how does it cool?

The same way it normally does. 1. By converting heat into work. Heat converted to work is heat that is absent, otherwise known as cold. 2. Momentum in the piston is utilized for expansion. When a gas is mechanically expanded it cools. The engine is doing the same thing, the same processes are taking place, but by eliminating the heat input and driving the engine mechanically, everything takes place at a "lower octave" so to speak. The same cycle at a lower temperature. In reality, a Stirling engine, as part of its normal functioning, is a kind of refrigeration machine.

Edited by Tom Booth

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16 minutes ago, Tom Booth said:

.The same way it normally does. 1. By converting heat into work. Heat converted to work is heat that is absent, otherwise known as cold.

Heat converted to work to drive a piston is not how a refrigeration cycle works

 

16 minutes ago, Tom Booth said:

2. Momentum in the piston is utilized for expansion. When a gas is mechanically expanded it cools. The engine is doing the same thing, the same processes are taking place, but by eliminating the heat input and driving the engine mechanically, everything takes place at a "lower octave" so to speak. The same cycle at a lower temperature. In reality, a Stirling engine, as part of its normal functioning, is a kind of refrigeration machine.

"Driving the engine mechanically" is not a conversion of heat into work.

Hot things cooling off/cool things warming up requires no engine; it happens spontaneously. A refrigerator takes the cold bit and makes it colder. This requires and engine, as it will not happen spontaneously.

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