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Tom Booth

Heat engine experiments and 2nd law of thermodynamics.

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explain why your ice melts, if no heat is flowing

The experiment in question is an engine running on boiling hot water, not ice, in an ambient environment at 85F.

Let's not confuse things beyond what is necessary and treat one example at a time.

 
Quote

 

But, heat cannot be "rejected" at a temperature equivalent to the sink.

Why?

 

how can it? Heat flows from hot to cold.

In a Stirling engine the working gas is sealed in the engine. Heat cannot just be exhausted as in an internal combustion engine. If the temperatures are equal there is no heat flow from hot to cold as there is no hot or cold.

Heat engine efficiency is a mathematical calculation based on the formula Th - Tc / Th.

at the temperatures in this experiment, that works out to 18.9%

That maximum efficiency represents the point where heat is converted into work, bringing the temperature down to Tc.

Tc is the temperature of the sink.

It can't just be asserted that an 18.9% efficient engine is 100% efficient.

heat flow cannot continue where the "heat rejection temperature" is equivalent to the sink.

It is two different heat scales being conflated.

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6 hours ago, Tom Booth said:

Not really.

The formula for heat engine efficiency is: Th - Tc / Th.

Where did you get this formula and do you understand its proper use?

I agree with your calculation that with a hot plate at 672o R and the cold plate at 545o R the maximum efficiency is just under 20%.

But the definition of efficiency is the same for all machines and systems


[math]efficiency = \frac{{output}}{{input}}[/math]


To get a % the fraction is multiplied by 100.

 

In the case of a Stirling engine this fraction becomes


[math]\frac{{workoutput}}{{inputheat}}[/math]

 

Now how are you accounting for the work?

You have a diaphragm type engine, which expands and contracts the volume of the working fluid as it changes temperature.

The bulk of this work is done against atmouspheric pressure against the diaphragm, leaving very little to turn the crank.

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2 hours ago, Tom Booth said:

The experiment in question is an engine running on boiling hot water, not ice, in an ambient environment at 85F.

That’s weird. I could have sworn you mentioned ice a dozen or so times, and linked to a bunch of videos that mentioned it.

 

2 hours ago, Tom Booth said:

Let's not confuse things beyond what is necessary and treat one example at a time.

That would be helpful, but the ship had sailed, so to speak.

 

2 hours ago, Tom Booth said:
 

how can it? Heat flows from hot to cold.

In a Stirling engine the working gas is sealed in the engine. Heat cannot just be exhausted as in an internal combustion engine. If the temperatures are equal there is no heat flow from hot to cold as there is no hot or cold.

But there is hot and cold. The one side in contact with water that was brought to boil. The other side is at ambient. You even calculated the efficiency using the temperatures. The temperature gradient means there is heat transfer across the engine.

As you said, let’s focus on this example. 

 

2 hours ago, Tom Booth said:

Heat engine efficiency is a mathematical calculation based on the formula Th - Tc / Th.

at the temperatures in this experiment, that works out to 18.9%

That maximum efficiency represents the point where heat is converted into work, bringing the temperature down to Tc.

Tc is the temperature of the sink.

It can't just be asserted that an 18.9% efficient engine is 100% efficient.

Nobody is asserting this.

2 hours ago, Tom Booth said:

heat flow cannot continue where the "heat rejection temperature" is equivalent to the sink.

It is two different heat scales being conflated.

You own mental model is flawed. Heat isn’t a substance; it doesn’t have a temperature.

When the gas strikes the “cold” plate, it transfers energy to it. That’s the heat transfer taking place at Tc. The plate at ambient temperature seems to remain there because the reservoir is large. In reality the reservoir temperature would be increasing, but this is infinitesimal.Over a long time, with a finite reservoir, the temperature will increase (and Th will decrease) but this is generally ignored in a simple analysis

This system is ~20% efficient because ~80% of the energy goes into heating the cold plate and the reservoir it’s coupled to. The rest goes into doing work.

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Posted (edited)
Quote

Now how are you accounting for the work?

You have a diaphragm type engine, which expands and contracts the volume of the working fluid as it changes temperature.

The bulk of this work is done against atmouspheric pressure against the diaphragm, leaving very little to turn the crank.

I've highlighted some statements here that are incorrect, or perhaps are using inapplicable terminology, that at any rate doesn't reflect the actual structure or operation of these engines.

First of all, there is no diaphragm.

I'm not sure what you assume to be, or are referring to as a "diaphragm". 

It is a piston engine.

The large disk is not a diaphragm or piston but a "displacer".

The displacer does not do any work "against atmospheric pressure", if by chance, by "diaphragm" you are actually referring to the displacer, which does not itself do any actual or appreciable work whatsoever. 

The engine does no work to expand and contract the volume of the working fluid.

Heat itself, the heat applied to the engine effects expansion of the air trapped inside the engine. Heat expands the gas, or causes the gas to expand. The expansion of the gas drives out the piston which by means of a connecting rod, turns the crank.

The "WORK", is performed by the expanding gas which is expanding due to the application of heat. "Working fluid", I believe, refers to the fact that the heated and expanding gas is what is "working" doing the work of driving the piston which in turn drives the entire machine along with any load.

All of the work performed is performed by the expansion of the gas, or by atmospheric pressure after the gas spends it's heat energy and becomes cold.

The displacer does virtually no work, rather it simply controls the intake of heat to the engine by periodically uncovering the hot plate heat exchanger.

What moves the displacers position is again, the heat, expanding the gas and driving the piston which turns the crankshaft which controls the positioning of the displacer which brings the air or "working fluid" into periodic contact with the hot plate.

There is no diaphragm.

The Carnot heat engine efficiency formula does not take into account "work".

Carnot had no concept of heat being converted into work. Nevertheless, the formula is still used and treated as accurate. (Just for the record, that does not reflect my own personal opinion).

My personal opinion is that Carnot had no actual familiarity with how engines actually work. His Carnot engine, which is supposed to be "the most efficient heat engine possible", is an intellectual abstraction with no real world functionality, It is not "efficient". It's effective work capacity is zero. It requires outside assistance just to be moved from one reservoir to another and back, and outside assistance to apply weights and such, I have difficulty imagining how or why anyone ever took it seriously, never mind considering it "the most efficient engine possible". It's efficiency for converting heat into work is, taking a look at it myself, as an engine mechanic, exactly zero. It's completely non-functioning!

The "science" of thermodynamics today, resembles a hodge podge of obsoleted nonsense.

Hardly anyone alive today has any real practical knowledge of the actual inner workings and functionality of Stirling heat engines, and those who think they know are mostly wrong.

Edited by Tom Booth
Typo

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You can ask questions about thermodynamics, or you can explain some idea you have about the subject.

But you can’t do both.

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46 minutes ago, swansont said:

That’s weird. I could have sworn you mentioned ice a dozen or so times, and linked to a bunch of videos that mentioned it.

That is true, I apologize for any confusion, there were several different experiments, but a few posts back I suggested we focus on just my first experiment, where I ran the engine on hot water, then covered the sink or cold heat exchanger in an effort to block the "rejection" of heat to the sink.

That post where I suggested focusing on that one experiment to begin with is linked above.

2 minutes ago, swansont said:

You can ask questions about thermodynamics, or you can explain some idea you have about the subject.

But you can’t do both.

My purpose is to report on the results of some experiments. I don't have questions about thermodynamics, though I welcome any suggestions regarding how the experiments might be improved.

I have ideas about how Stirling heat engines work, from my personal experience in building them and doing independent research, which may be right or wrong, but which seems contrary to accepted theory.

I predicted ten years ago that covering the cold plate of the engine would make the engine run better and improve efficiency which everyone I knew on the Stirling engine forum thought was preposterous.

I wrote: "If more heat is extracted as work than what actually reaches the heat sink, then theoretically, insulating the cold end of the displacer chamber against the external ambient temperatures would improve engine efficiency."

A few days ago I received my model Stirling engine in the mail and finally got around to running the actual experiment.

The results were as predicted, which actually surprised me greatly.

Generally, a theory that accurately predicts experimental results carries some weight in science, usually.

But I'm not insisting my theory is correct. There may be other explanations, but my main intention is to simply put the results of the experiments out there and get some feedback.

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26 minutes ago, Tom Booth said:

I've highlighted some statements here that are incorrect, or perhaps are using inapplicable terminology, that at any rate doesn't reflect the actual structure or operation of these engines.

First of all, there is no diaphragm.

I'm not sure what you assume to be, or are referring to as a "diaphragm". 

It is a piston engine.

The large disk is not a diaphragm or piston but a "displacer".

The displacer does not do any work "against atmospheric pressure", if by chance, by "diaphragm" you are actually referring to the displacer, which does not itself do any actual or appreciable work whatsoever. 

The engine does no work to expand and contract the volume of the working fluid.

This is exactly why I asked for a proper description of your machine.

In the absence of one I chose perhaps the wrong type, but I was nearly right.

I hope you understand that there are diaphragm type Stirling engines ?

The difference between a displacer (not a very good engineering term) and a diaphragm is that the diaphragm seals the working fluid, and you did say there was such a seal.
Further the displacer is a rigid plate which creates the expansion space by bodily movement, whereas the diaphragm creates the expansion space by deflection.
Either way work must be done against the atmouspheric pressure.
And either way each drives the crank via what I would call a push rod.

38 minutes ago, Tom Booth said:

Heat itself, the heat applied to the engine effects expansion of the air trapped inside the engine. Heat expands the gas, or causes the gas to expand. The expansion of the gas drives out the piston which by means of a connecting rod, turns the crank.

 

So if you change diaphragm to displacer, this is exactly what I said.

 

51 minutes ago, Tom Booth said:

The engine does no work to expand and contract the volume of the working fluid.

So what do you think does the isothermal expansion work shown in the Stirling cycle diagram ?

stirling1.jpg.afd54bd0001670c465e9df63381db0f7.jpg

 

The isothermal work is given by the formula


[math]w =  - q = nRT\ln \left( {\frac{{{V_2}}}{{{V_1}}}} \right) = nRT\ln \left( {\frac{{{P_1}}}{{{P_2}}}} \right)[/math]


You did not offer a derivation of your efficiency formula I asked for, but you may like to know that the work formula I just quoted is used to derive it.

 

58 minutes ago, Tom Booth said:

The Carnot heat engine efficiency formula does not take into account "work".

Carnot had no concept of heat being converted into work. Nevertheless, the formula is still used and treated as accurate. (Just for the record, that does not reflect my own personal opinion).

My personal opinion is that Carnot had no actual familiarity with how engines actually work. His Carnot engine, which is supposed to be "the most efficient heat engine possible", is an intellectual abstraction with no real world functionality, It is not "efficient". It's effective work capacity is zero. It requires outside assistance just to be moved from one reservoir to another and back, and outside assistance to apply weights and such, I have difficulty imagining how or why anyone ever took it seriously, never mind considering it "the most efficient engine possible". It's efficiency for converting heat into work is, taking a look at it myself, as an engine mechanic, exactly zero. It's completely non-functioning!

The "science" of thermodynamics today, resembles a hodge podge of obsoleted nonsense.

Hardly anyone alive today has any real practical knowledge of the actual inner workings and functionality of Stirling heat engines, and those who think they know are mostly wrong.

 

With an attitude like that I am not suprised with your lack of headway interesting others in your topic.

I recommend the following reading

Quote

Sadi Carnot 1824

Refelxions sur la Puissance motrice du Feu.

 

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1 hour ago, swansont said:

 

This system is ~20% efficient because ~80% of the energy goes into heating the cold plate and the reservoir it’s coupled to. The rest goes into doing work.

That would be the conventional viewpoint.

My hands on experience indicates otherwise.

With the engine running on scalding hot water poured into a vacuum flask to prevent incidental heat loss, the cold plate remained cold.

Then blocking the cold plate so heat could not escape to the reservoir, the plate, apparently became colder, though other possible explanations have been offered.

As I said, I need to aquire some temperature probes to get an objective measure as I may simply be seeing what I want to see.

If I fail to respond to any additional comments, I'm not ignoring them. This thread is moving too fast for me to keep up with and I need a break. I am very busy working on the house, pouring a new concrete foundation between posts.

I will have to catch up here when that project is completed.

I also have additional modifications to make and more engines to build and supplies to pick up, like the probes.

Without proper "control" engines and such, and basic measuring equipment, discussing the "results" of experiments is inconclusive at best.

I apologize for the interlude but I will be back.

Many thanks to everyone for all the input, and feel free to carry on the conversation in my temporary absence. I'll catch up when I'm not so overloaded by other responsibilities.

 

 

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Posted (edited)

In relocating the thread, an edit to the previous post was lost apparently.

I had added:

Quote

This system is ~20% efficient because ~80% of the energy goes into heating the cold plate and the reservoir it’s coupled to. The rest goes into doing work.

The 20% represents the potential drop in temperature for a "perfect engine" with no friction or other losses, in which case the working fluid heated to 212F can at the absolute maximum be brought down to the ambient temperature of 85F, not by rejecting heat to the sink, but by conversion of that heat to work.

Below that point and heat would have to flow from the sink back into the engine.

The remaining 80% represents the remaining heat, which if it could be utilized by the engine to produce work would bring the temperature of the working fluid down the rest of the way to absolute zero.

My contention is, at or below the point  of equalization, which in this case is 85F, no "heating the cold plate and the reservoir it's coupled to" is actually possible as this would require heat to flow across an equilibrium and simultaneously reduce the temperature of the engine to zero Kelvin, all in an instant.

If that were to happen the engine would implode becoming a Bose-Einstein condensate or some such thing.

Edited by Tom Booth

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Posted (edited)
4 hours ago, studiot said:

This is exactly why I asked for a proper description of your machine.

In the absence of one I chose perhaps the wrong type, but I was nearly right.

I hope you understand that there are diaphragm type Stirling engines ?

The difference between a displacer (not a very good engineering term) and a diaphragm is that the diaphragm seals the working fluid, and you did say there was such a seal.
Further the displacer is a rigid plate which creates the expansion space by bodily movement, whereas the diaphragm creates the expansion space by deflection.
Either way work must be done against the atmouspheric pressure.
And either way each drives the crank via what I would call a push rod.

 

So if you change diaphragm to displacer, this is exactly what I said.

 

So what do you think does the isothermal expansion work shown in the Stirling cycle diagram ?

stirling1.jpg.afd54bd0001670c465e9df63381db0f7.jpg

 

The isothermal work is given by the formula


w=q=nRTln(V2V1)=nRTln(P1P2)


You did not offer a derivation of your efficiency formula I asked for, but you may like to know that the work formula I just quoted is used to derive it.

 

 

With an attitude like that I am not suprised with your lack of headway interesting others in your topic.

I recommend the following reading

 

I'm finding it a nearly hopeless task to try to sort out what your thinking may be in regard to how a Stirling engine operates. I don't mean that to be insulting or anything.

It took me literally years of dedicated study and research to arrive at an understanding of how these engines work. It is not intuitive, yet, it really is not complicated, it just doesn't make sense, in some ways.

For example, a Stirling engine actually, it could be said; "destroys heat".

Heat goes into the engine and goes out of existence. It no longer exists in the form of energy we recognize as sensible heat.

In that sense a Stirling engine is a cryo-cooler. In converting heat into work the engine creates an absence of heat, which we sense as "cold".

Heat being conducted, we understand, convection, radiation, are understandable intuitively. Heat simply disappearing and leaving cold is not a phenomenon we are familiar with in life.

Heat converted into Work is no longer heat but cold, the absence of heat.

So efforts to trace the heat as it passes through the engine are liable to result in confusion.

Quote

 

displacer is a rigid plate which creates the expansion space by bodily movement, whereas the diaphragm creates the expansion space by deflection.

Either way work must be done against the atmouspheric pressure.
And either way each drives the crank via what I would call a push rod.

 

I don't know what you mean exactly by "expansion space". I have no idea what you mean by "the diaphragm creates the expansion space by deflection."

As far as this statement: "Either way work must be done against the atmouspheric pressure.
And either way each drives the crank via what I would call a push rod." It is entirely wrong.

The displacer does not drive the crank.

The displacer is not a power piston or diaphragm.

I did not intend this thread to be a course on how a Stirling engine works, I assume if people are interested they would research the subject. But I'll try to clarify things if I can.

But it seems you are thinking of a power piston or diaphragm that drives a crankshaft. The function of a displacer is not to drive the crankshaft. It does not drive the crankshaft. It does not do work against atmospheric pressure.

Basically the displacer is a kind of valve that allows heat into the engine in metered bursts. Heat enters the engine through the hot plate or hot heat exchanger, but not while the displacer is blocking the heat from entering.

The displacer is, rather than a valve, it is more like an umbrella used for shade, to block the heat of the sun.

When the displacer moves out of the way temporarily, some radiant heat is allowed into the engine, expanding the gas to do work.

When the gas has used up it's energy performing work, the displacer moves out of the way again, allowing in another burst of heat for another cycle. In that sense the displacer serves the same function as the spark plugs which ignites that fuel mixture in an internal combustion engine to deliver heat.

Edited by Tom Booth
Typo

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Posted (edited)
On 7/31/2020 at 1:37 AM, Markus Hanke said:

No, the second law follows directly from fundamental considerations of statistical mechanics and some basic maths, and as such is not in contention. It also follows more or less directly from Z2 symmetry and unitarity, so it is fundamentally motivated by manifest symmetry considerations. Essentially, in a world where unitarity holds for quantum systems (as is evidently the case in our universe) you can't not have the second law of thermodynamics, if that makes sense.

I am not sure what the point of all this really is, since the setup you have there is not an isolated system in the thermodynamics sense - so what does it have to do with the second law at all? Note also that the second law is a global statistical statement, and as such it does not contradict temporary (even long-lasting) local decreases in entropy. 

What exactly are you attempting to show here?

I think in general what I'm examining or testing is the nature of heat, and how it really interacts with a heat engine, or how it is utilized by a heat engine.

Popular ideas or statements regarding how these engines work and what their potential may be does not square well with my own experience.

For example, above, the statement:

" This system is ~20% efficient because ~80% of the energy goes into heating the cold plate and the reservoir it’s coupled to. "

(Not to pick on Swansont or anyone in particular)

Generally this 80% pass through of heat into the sink is not what happens.

Here is a link to another experiment conducted by someone else years ago using a thermal imaging camera.

As can be seen in this thermal image of a running Stirling engine on a hot cup of water compared with a non operational  dummy engine.

In the same environment the real heat engine is clearly maintaining a cold temperature. The heat is not passing through to the top plate.

In my own experiments I found the same situation. The bottom plate above boiling hot water was too hot to touch. I'm sure hot enough to raise a blister. At the same time the top plate remained cool to the touch.

This does not seem to support the common assumption that the majority of heat passes right through the engine.

In my experience virtually no heat makes it through these engines to the sink. Also, nearly all the incidental and parasitic heat loses are preventable to a great degree with proper insulation.

The implications are far reaching, IMO.

 

stirling2 (1)_crop_46_resize_24.jpg

Source: https://concord.org/blog/an-infrared-investigation-on-a-stirling-engine/

 

Edited by Tom Booth
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2 hours ago, Tom Booth said:

This does not seem to support the common assumption that the majority of heat passes right through the engine.

I’m not an expert on the engineering applications of thermodynamics, so others here are more qualified to address this. I’m more of a theory guy - so in what way do you think this is related to the second law? I don’t see a direct connection, and most certainly not anything that would put the law into question.

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4 hours ago, Tom Booth said:

 

Here is a link to another experiment conducted by someone else years ago using a thermal imaging camera.

As can be seen in this thermal image of a running Stirling engine on a hot cup of water compared with a non operational  dummy engine.

In the same environment the real heat engine is clearly maintaining a cold temperature. The heat is not passing through to the top plate.

How does the image “show” this? A thermal imaging camera captures thermal radiation, which indicates temperature, not heat.

Do you understand what a reservoir is in thermodynamics? This picture is perfectly in accord with the cold plate operating at Tc, exactly as the theory states.

 

Quote

In my own experiments I found the same situation. The bottom plate above boiling hot water was too hot to touch. I'm sure hot enough to raise a blister. At the same time the top plate remained cool to the touch.

IOW, the thing supposed to be at Th is at Th, and the thing supposed to be at Tc is at Tc.

Hardly an indictment of the theory.

Quote

This does not seem to support the common assumption that the majority of heat passes right through the engine.

It does not support your misunderstanding of thermodynamics.

Heat is not a substance. It does not have a temperature. Whatever you think heat is, it is not what thermodynamics defines as heat. And that stands in the way of any fruitful discussion.

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

This does not seem to support the common assumption that the majority of heat passes right through the engine.

Heat never passes through a heat engine.
That is a popular metaphor only.
There is another popular metaphor of the bank account,
but this is also flawed

Amounts of heat enter and leave any system by various routes.

But within the system the heat becomes something else (internal energy), so it is not the same heat leaving as entering.

This is where it differs from the bank account analogy.
In the bank account different dollars enter and leave but this is of no account (pun intended) since they are still dollars within the bank and all dollars are equivalent.

5 hours ago, Tom Booth said:

I don't know what you mean exactly by "expansion space". I have no idea what you mean by "the diaphragm creates the expansion space by deflection."

As far as this statement: "Either way work must be done against the atmouspheric pressure.
And either way each drives the crank via what I would call a push rod." It is entirely wrong.

The displacer does not drive the crank.

The displacer is not a power piston or diaphragm.

I did not intend this thread to be a course on how a Stirling engine works, I assume if people are interested they would research the subject. But I'll try to clarify things if I can.

Sigh

Then the appropriate response would be to ask, would it not ?

I don't know how to converse with someone who seems to believe that things can expand without work being done, within our atmousphere.

I find Wikipedia articles normally a bit over the top to recommend but in this case they seem to have it right.

Quote

Stirling engine - Wikipedia

 
 
A Stirling engine is a heat engine that is operated by a cyclic compression and expansion of air or other gas (the working fluid) at different temperatures, ...

 

Edited by studiot

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6 minutes ago, studiot said:

Heat never passes through a heat engine.
That is a popular metaphor only.

Put another way, the diagrams with Q’s and W are schematics, not maps. They show a concept, not a physical path.

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Posted (edited)
6 hours ago, Markus Hanke said:

I’m not an expert on the engineering applications of thermodynamics, so others here are more qualified to address this. I’m more of a theory guy - so in what way do you think this is related to the second law? I don’t see a direct connection, and most certainly not anything that would put the law into question.

Years ago I designed a heat engine. As a lifelong engine mechanic and repair person I thought it was a great design.

I was told it would not work because it violated the second law.

Now I'm doing experiments with model heat engines. I posted results on another forum. The discussion was locked and I was banned, because the moderators determined it was "a perpetual motion machine of the second kind" and that it violated the second law. (Or would if it was real).

How does it violate the second law? is actually MY question!

I'm not saying it does, that is what OTHER PEOPLE have been throwing in my face for the past 25 years.

If there is no such violation that's wonderful news to me!

Edited by Tom Booth

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BTW, I do have a question.

My original engine design works similar to and/or incorporates heat pump/refrigeration.

In thermodynamics, is a vapor compression system, (refrigerators, heat pumps, freezers etc ) considered an "open system" or a "closed system", so does the second law apply or not?

The "working fluid" is contained in a closed loop, but part of the "system" is the heat exchangers and the air being blown through them.

Some say the second law applies to everything because the whole universe is a closed system, so... How exactly do we determine if a system is open or closed so we know if the second law is supposed to apply or not.

It all seems vaguely philosophical to me with no clear cut answer.

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Posted (edited)
On 7/31/2020 at 9:39 AM, Tom Booth said:

Specifically, this second law, in its early formulations seems very slippery, and I don't have a clear picture as to, does it apply to this "open system" or not.

Now that I have some finances available, I've just gone and purchased six model engines to run some common sense tests and experiments to see if, in principle, my engine design is impossible or not.

The first order of business, I thought, should be to settle this Caloric theory that a heat engine works by heat flowing through it from a hot reservoir THROUGH to a cold reservoir.

Blocking the path or outlet from the engine is, according to Carnot's theory equivalent to stopping up the outlet of a fluid turbine. Without an outlet for the heat, according to Carnot, the engine should quit.

In my experiment however, insulating the path or outlet of the model Stirling engine had the opposite result. The engine, rather than overheating and stopping or something, ran measurably faster and longer.

I would suggest that the silicon inside of the tube is just acting like an oscillating diaphragm which is just increasing the intensity of the changes in volume of the air.  It would be like taking a slinky and putting it on a vibrator, but then it creates bigger waves at the other end from the smaller waves being added together.  Then having a better seal would increase performance.  It would make the diaphragm react better to the changes in density created from the heat traveling to the other colder side of the tube which has the piston.  The heat may just be traveling to the other chamber in steps or burst to make the silicon resonate.  You may try using different materials there and see how that affects the performance.

If I was you, the next step I would take would be attaching an AC unit to the Stirling engine in an up scaled model to improve performance.  You could have the hot side chamber have the compressed freon, and you could try to seal the piston chamber with cold freon.  If that was too difficult, you could simply have the cold air of the AC to blow on the piston to make it run as long as it has power to start out with.  Basically, it should at least just have a radiator to functionally drive something.   

If I am correct, it may not matter which side is hot or cold.  It may be better to have the piston be the hot side.  It would have friction which would naturally cause heat to make it more energy saving and efficient.  That could make a big difference when trying to scale it up to actually run something which needs a piston driven motor.   

On second thought, it may not actually be a good idea to have heat driven pistons, because it would cause the engine to overheat to where it could have mechanical failures.  That is the reason why combustible engines use a radiator to begin with.

Edited by Conjurer

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Great ideas! I'll get to work on that right away! :huh: LOL

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Posted (edited)
11 hours ago, studiot said:

I don't know how to converse with someone who seems to believe that things can expand without work being done, within our atmousphere.

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

The displacer is not any kind of power piston.

Imagine an empty soup can. Completely sealed, containing a gas. Inside the can is another smaller loose fitting soup can.

If you tip the can on one end, gravity will cause the inside can to fall to the bottom so the air in the can will be DISPLACED to the top.

Tip the can around the other way, again the can inside falls and DISPLACES the air back to the opposite end.

Now heat one end of the can.

Do the same flip flop and the inside can, or "displacer", still DISPLACES the air in the can but now, when the air is displaced to the hot side the air gets hot and the pressure in the can increases.

Tip the can the other way and the air is displaced to the cold side, cools down and the pressure in the can drops.

Hopefully, it can be seen that the small can inside is not performing any appreciable work to turn a crankshaft or to work against the pressure of the outside atmosphere.

It is just a means of periodically delivering heat to the inside of the can to heat the air and create pressure. It does this by moving away from the heated end of the can, displacing the air to the hot end, or put another way, simply uncovering the hot heat exchanger.

Often, in a Stirling engine the displacer is not attached to the crank at all. It may be moved back and forth by other means, such as a magnet., Or in some cases by actually tilting the engine.

Here the displacer is some marbles in a test tube. They full back and forth by gravity, have no connection to any crank and do not work against atmospheric pressure. They just displace air to the heated side of the engine periodically.

 

 

Edited by Tom Booth

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

BTW, I do have a question.

My original engine design works similar to and/or incorporates heat pump/refrigeration.

In thermodynamics, is a vapor compression system, (refrigerators, heat pumps, freezers etc ) considered an "open system" or a "closed system", so does the second law apply or not?

The "working fluid" is contained in a closed loop, but part of the "system" is the heat exchangers and the air being blown through them.

Some say the second law applies to everything because the whole universe is a closed system, so... How exactly do we determine if a system is open or closed so we know if the second law is supposed to apply or not.

It all seems vaguely philosophical to me with no clear cut answer.

 

Questions are fine.

In both Fluid Mechanics and Thermodynamics systems are sometimes analysed by (theoretically) replacing some part of or all the system with an equivalent one which is easier to work with.

This can be true of refrigeration cycles and compressors, turbines and jet engines.

This is a practical engineer's approach.

To help with this and some other questions you haven't yet asked here is a link to  an excellent engineering glossary of Thermodynamics

https://www.engineersedge.com/thermodynamics.htm

 

Look particularly at "Air standard assumptions" and "Air standard cycle"

 

Edited by studiot

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4 hours ago, Tom Booth said:

In thermodynamics, is a vapor compression system, (refrigerators, heat pumps, freezers etc ) considered an "open system" or a "closed system", so does the second law apply or not?

The second law always applies.  Refrigeration cycles are open systems, in that the heat of condensation of the refrigerant is transferred to the ambient air.  IOW the entropy of the universe increases from a refrigeration cycle. 

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11 minutes ago, Tom Booth said:

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

It’s not a vacuum, right? So work is being done against atmospheric pressure, i.e. there is a pressure on the plunger. There is a difference between expansion in those two conditions

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2 minutes ago, swansont said:

It’s not a vacuum, right? So work is being done against atmospheric pressure, i.e. there is a pressure on the plunger. There is a difference between expansion in those two conditions

What?

I have no idea what you're driving at.

What plunger? What "two conditions?"

What does a vacuum have to do with anything?

How is work being done against outside atmospheric pressure by those marbles rolling back and forth.

Yes their rolling away from the heat source causes the displacement of the air which results in increased pressure in the test tube, but the pressure has no effect on the marbles, they are isolated from the atmosphere. 

The DISPLACER has ample clearance around it and air moves freely around it, it does not form any seal or work against any pressure.

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10 minutes ago, Tom Booth said:

What?

I have no idea what you're driving at.

That’s obvious.

Quote

What plunger? What "two conditions?"

Vacuum and atmosphere

Quote

What does a vacuum have to do with anything?

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

Quote

How is work being done against outside atmospheric pressure by those marbles rolling back and forth.

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

Quote

Yes their rolling away from the heat source causes the displacement of the air which results in increased pressure in the test tube, but the pressure has no effect on the marbles, they are isolated from the atmosphere. 

But you keep saying work is not being done against atmosphere, and that’s not right. (You said “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. 

 

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