Heat engine experiments and 2nd law of thermodynamics.

[Tom Booth]

This is a continuation of another thread (kind of):

https://www.scienceforums.net/topic/46143-stirling-turbine/?tab=comments#comment-1148735

but it is also something of a fresh start. So, I'm here starting a new thread 

To get right into it, I purchased several identical Stirling engines from https://www.stirlinghobbyshop.com/ that is not a promotion, just a fact.

What I liked about these were they came in kit form, so I could do various modifications.

The first modification was simply to cut down on heat loss by replacing the steel bolts that came with the engine with nylon bolts, and also to add insulation where necessary, and to use a vacuum insulated flask, basically to minimize all heat transfers as much as possible, other than heat transfer through the working fluid (air) inside the engine.

This was the first test, which I had been thinking about for years. I first mentioned the idea on the Stirling Engine forum back in the year 2010:

https://stirlingengineforum.com/viewtopic.php?f=1&t=478

I wrote (edited for length)

Quote

Stirling Engine Thermodynamics

I've been reading quite a bit about thermodynamics lately. Especially in regard to the fact that when a gas is "made to do work" it looses heat...

Now, formerly I had been under the impression that a Stirling engine functions by means of a temperature differential... the air travels back and forth from one end of the chamber to the other and picks up or looses heat in that way...

But I'm becoming aware that there is also apparently something a little more subtle going on, that is, when the air in the chamber heats up and expands and then does work against the piston - the heat does not only travel to the "heat sink" at the cold end of the chamber but some of the heat is actually converted into work. In other words, what cools the hot expanding air back down is not so much, or not only coming into contact with the cold end of the chamber but heat is also lost on account of the gas being made to do work against the piston.

What I'm wondering is just how much heat is actually being absorbed in this way i.e converted into work as opposed to the heat being absorbed by the heat sink (the cold end of the chamber at ambient temperature).

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.

Nobody agreed with this.

Everyone tried to educate me about how a Stirling engine works. The sink is colder than the engine. Heat flows from the engine to the sink.

Nobody seemed interested in running such an experiment.

Now, my observation of Stirling engines over the years, mostly on YouTube, seemed to show that at least some Stirling engines converted ALL the heat, not transferring any to the sink.

This was mainly due to seeing an engine which someone discovered could run quite well without a flywheel.

There are several other examples that can be found.

My reasoning was that the engine was moving too fast to "sink heat" by conduction so as to cause the piston to return "on its own" without the stored momentum in a flywheel to push it back down the cylinder. 

It seemed to me that if ALL the heat added in one cycle were not used up (converted to work) then the piston would not be able to return against the remaining hot expanding gas, without help from the flywheel.

My reading of old thermodynamics books and books on liquifying gases and such also had me convinced that when a gas expands and does work in a cylinder driving a piston, very cold temperatures can result, potentially, much colder than ambient.

So the first thing I did when I got one of my kits together was to run this experiment:

The engine is running on scalding hot water from the tea kettle, but without the steel bolts to conduct heat, the top of the engine felt- room temperature.

The heat could be going either way.

I really had expected, probably everybody was right and insulating the sink would quickly bring the engine to a stop.

But it did not stop.

After it recovered from the insulation rubbing on the flywheel, it actually ran, by my friends stopwatch, about 18 RPM faster, and it also ran in this condition, with the sink insulated, about an hour longer than it ran previously without the insulation.

Certainly I could not be the only one in the past century to notice these things, or do some such experiment, right?

So I did more experiments with the engine using ice.

It took 33 hours before the engine stopped running as the ice had all melted.

Repeating the experiment with an identical vacuum flask full of a solid cylinder of ice, but not starting the engine; this time the engine quit running and the ice had all melted five hours sooner.

Apparently, the engine running, actively converting the incoming ambient heat to "work" meant less heat reached the ice, so the ice took five hours longer to melt, and the engine continued running for those additional five hours. In fact I got so tired of the engine not stopping I added a piece of aluminum on top from an old appliance electric outlet box to draw down more heat.

Now both of these outcomes were predicted based on basic thermodynamics principles, but the moderators on the other forum said such a result would be "perpetual motion" and "a violation of the second law of thermodynamics", locked the thread and banned me from the forum for "invoking perpetual motion".

I tried to point out that these were stock model Stirling engines and that I was not advocating perpetual motion,  l just ran the experiments because, as far as I could find, no one else ever did before.

And obviously these TOY engines were not anywhere near 100% efficient and in all cases did stop running eventually, but

I was banned anyway.

 

 

More detailed descriptions are uploaded to a YouTube playlist:

That basic theory I'm developing to explain these results is that the Carnot mathematical limit for a heat engine efficiency, between the two reservoirs, is based on the fact that if the engine were to produce cold lower in temperature than the sink, heat flows back into the engine from the sink which directly limits how cold the engine can get and therefore it's maximum theoretical efficiency.

But in reality, the engine can expand the gas to the point where it may be colder than the "sink", in which case, insulating the sink, thereby blocking backward heat infiltration into the engine can allow it to run better, faster, longer.

The engine will still use up the heat, and the temperatures will equalize and the engine will stop running, at least in the case of added heat.

With cold applied, below ambient, the heat comes from the atmosphere, heated by the sun, which heat may take a little longer to exhaust. But no insulation is perfect, so the ice still melts.

Could the second law of thermodynamics be a result of not making complete observations by neglecting to conducting such simple experiments?

I haven't come to any hard conclusions at this point. I have many additional modifications to make and many more experiments to run, but the results are such that at this point I would already like some comments and feedback.

Please!

 

[Markus Hanke]

29 minutes ago, Tom Booth said:

Could the second law of thermodynamics be a result of not making complete observations by neglecting to conducting such simple experiments?

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 \(Z_2\) 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?

[studiot]

6 hours ago, Tom Booth said:

This is a continuation of another thread (kind of):

https://www.scienceforums.net/topic/46143-stirling-turbine/?tab=comments#comment-1148735

but it is also something of a fresh start. So, I'm here starting a new thread 

Thank you for your presentation.
I note the previous thread referred to was 2010.

So +1 for your dedication to the subject.

I would like to offer some words of encouragement, but also echo Markus' comment.

 

5 hours ago, Markus Hanke said:

What exactly are you attempting to show here?

I have called your OP a presentation since I too am not sure what you want to discuss.

 

Having said that I can't see any connection or need for one to Statistical Mechanics.
Stirling Engines belong firmly in the realm of classical thermomechanics IMHO.

 

Theoretically Stirling cycles offer advantages over internal combustion engine cycles in that they form a good meaty area block on indicator diagrams (PV or TS)  as opposed to the very thin shapes of say Otto and Diesel cycles. This area, of course, corresponds directly to available work and indirectly to efficiency.

Practically they suffer from the fact that simple analyses do not take the variation of specific heat with temperature into account or the conductivity of the working fluid.
This makes them less attractive that at first (theoretical) sight.

 

Now for some encouragement.

History has shown many gifted practical people who may have been amateurs or professionals who introduced dramatic engineering developments.
Examples include,

The violin makers of old.
The hovercraft (I see the rescue hovercraft was out again on the Severn Mudflats pulling someone out of the quicksand) was invented in a garage using a domestic vacuum cleaner.
Last year another mechanical genius invented a super enhancement to refrigerated lorries for save energy.
Harrison was a carpenter and thus considered beneath scientific contempt!

So press on with your experiments, but please do clarify the point of this thread.

 

 

[Tom Booth]

To offer some context: growing up in the country there was always machinery breaking down which was very expensive to get repaired all the time, so in 10th grade (high school) my dad suggested I enroll in a vocational course for engine repair.

There was some basic theory, but mostly we just tore down and rebuilt engines all day.

After graduation I opened a repair shop out of my parents garage, then spent most of my life working in engine repair shops

Fast forward to about 20 years ago, I was asked to help with designing a solar Stirling engine for a semi retired government contractor.

I worked hard on this because it seemed like a big opportunity at the time, and I came up with what I thought was a great design that exceeded specifications.

He ran it past some associates in, I think, the Dept. of Energy and their verdict was that it was impossible because it violated the second law of thermodynamics.

So, instead of a plane ticket to California and a lucrative job, I was left with a rejected plan for a Stirling type heat engine.

So, not knowing the reason why my design was supposed to be "impossible" and in violation of some law of physics I never heard of I casually began doing research on the subject in my spare time as a kind of hobby.

Carnot's theorem was, as far as I know, the earliest formulation of the second law:

https://en.m.wikipedia.org/wiki/Carnot's_theorem_(thermodynamics)

Derived from the Caloric Theory of heat:

https://en.m.wikipedia.org/wiki/Caloric_theory

After that we have Clausius, Lord Kelvin (William Thompson) etc.

This Second law (specifically as it is supposed to apply to heat engines) has gone through so many iterations I am not really able to pin down exactly what it is supposed to be saying.

But, the long and short of it is that my engine design was a fusion of a Stirling engine and an air cycle heat pump.

It did not use solar directly, but rather drew in atmospheric air to run through a compression/expansion refrigeration cycle which would produce the temperature difference to power the Stirling engine.

As a combined machine, it had few moving parts and several shared functions.

The thing that seems to have gotten under someone's craw was that it ran on "one reservoir", or a single heat source. Solar heated warm air, directly from the atmosphere.

Such a thing has been declared "impossible" at various times in various ways, all such statements having been wrapped up together as valid statements of the second law.

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.

Edited July 31, 2020 by Tom Booth
Typos

[studiot]

54 minutes ago, Tom Booth said:

To offer some context: growing up in the country there was always machinery breaking down which was very expensive to get repaired all the time, so in 10th grade (high school) my dad suggested I enroll in a vocational course for engine repair.

There was some basic theory, but mostly we just tore down and rebuilt engines all day.

After graduation I opened a repair shop out of my parents garage, then spent most of my life working in engine repair shops

Fast forward to about 20 years ago, I was asked to help with designing a solar Stirling engine for a semi retired government contractor.

I worked hard on this because it seemed like a big opportunity at the time, and I came up with what I thought was a great design that exceeded specifications.

He ran it past some associates in, I think, the Dept. of Energy and their verdict was that it was impossible because it violated the second law of thermodynamics.

So, instead of a plane ticket to California and a lucrative job, I was left with a rejected plan for a Stirling type heat engine.

So, not knowing the reason why my design was supposed to be "impossible" and in violation of some law of physics I never heard of I casually began doing research on the subject in my spare time as a kind of hobby.

Carnot's theorem was, as far as I know, the earliest formulation of the second law:

https://en.m.wikipedia.org/wiki/Carnot's_theorem_(thermodynamics)

Derived from the Caloric Theory of heat:

https://en.m.wikipedia.org/wiki/Caloric_theory

After that we have Clausius, Lord Kelvin (William Thompson) etc.

This Second law (specifically as it is supposed to apply to heat engines) has gone through so many iterations I am not really able to pin down exactly what it is supposed to be saying.

But, the long and short of it is that my engine design was a fusion of a Stirling engine and an air cycle heat pump.

It did not use solar directly, but rather drew in atmospheric air to run through a compression/expansion refrigeration cycle which would produce the temperature difference to power the Stirling engine.

As a combined machine, it had few moving parts and several shared functions.

The thing that seems to have gotten under someone's craw was that it ran on "one reservoir", or a single heat source. Solar heated warm air, directly from the atmosphere.

Such a thing has been declared "impossible" at various times in various ways, all such statements having been wrapped up together as valid statements of the second law.

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.

Thank you for the response.

That is an interesting story.

However this is a discussion site not a story site so it does not clarify what you want to get out of the discussion within ScienceForums rules.

May I suggest you use it to seek help formalising your practical work?

I do not believe that your actual machine contravenes the Second Law, or that it has only one heat reservoir, which would be a problem if it did.

Formal Thermodynamics can be quite tricky, so if inappropriate statements are inadvertantly made in a formal submission, they will be struck out by recipients and may be used to disbar the submission itself as may have happened in your case.

 

The ball is in your court.

 

[Tom Booth]

At this point, the focus of the discussion is, though the caloric theory is recognized as obsolete, there is a persistent remnant stated in a somewhat vague way in courses on thermodynamics that some heat must always be rejected to the sink in a heat engine.

My insulation is not perfect, so indeed, it is within the realm of possibility that "some" heat is still getting through, but if the functionality of a heat engine depends in any way on such "flowing through" of heat, then insulating the sink is roughly equivalent to stuffing a potato in the tailpipe of a car. Or shutting off the outlet in the water turbine of Niagra falls.

The. Expected result SHOULD BE, if flow through of heat is a functional necessity of the engine; a slowing down or stopping of the engine should be observed.

We are not talking about MY engine at this point, the focus is just a stock model "off the shelf" Stirling engine readily available from several internet markets.

We are talking about expected results of an experiment.

How can it be explained that blocking the path of heat flow to the sink to any degree results in higher RPM and a longer run on a finite heat source? In this case a vacuum flask containing hot water.

My story is just some background. The topic is the experiment. The results suggest there may be something wrong with the general "flow through" theory of heat engine operation.

If not, why not?

It seems a peculiar result, does it not?

My supposition is that since a Stirling engine's efficiency increases with increased temperature differential, blocking the so-called "sink" in some way increases the temperature difference.

My tentative explanation is that contrary to popular opinion, a Stirling heat engine does not actually always reject heat to the sink, but rather, under some circumstances; infiltration of heat into the engine (in reverse) through the sink reduces the temperature difference that the engine itself is maintaining by converting incoming heat from the source into "work", including momentum and then using that momentum for cooling by expansion, which brings the cold side temperature down below ambient. So an engine with an insulated cold side runs better by blocking reverse heat flow.

For now the focus is on this experiment:

 

Heat is delivered into the engine through the bottom.

I then insulated the sides and replaced the bolts in an effort to minimize loses, so the heat can only escape the Dewar by passing into the engine and up and presumably out through the top, That way most of the heat must pass into or through the "working fluid".

 

Now insulating the top, should block the flow of heat, causing a slow down, logically, shouldn't it?

But it doesn't.

Instead, my friend and I using a stop watch and counting the revolutions, fount that the engine ran at an RPM of +18 with the top insulated. The RPM increased by 18 revolutions per minute.

 

[studiot]

2 hours ago, Tom Booth said:

The results suggest there may be something wrong with the general "flow through" theory of heat engine operation.

If not, why not?

It seems a peculiar result, does it not?

I have already said that I doubt there is anything wrong with conventional theory.

You have a modified Stirling Engine but although you are flooding this thread with material no pertinent details are provided.

I have no idea of your arrangment so can't comment except to suggest you stop slagging off existing theory, especially when your statements suggest you do not really understand Thermodynamics.

A simple block diagram like any of these (pretty colours are not needed) showing the Thermodynamic essentials is all that is necesary.

We could then work through the correct analysis in the light of your results.

https://www.google.co.uk/search?q=how+do+model+stirling+engines+work&tbm=isch&source=iu&ictx=1&fir=gbKxL9_-JzzJXM%2CQYli5R_LoI-dKM%2C_&vet=1&usg=AI4_-kT6y-LofehZ6GMnPjFmkzxEowig5w&sa=X&ved=2ahUKEwiY38L7m_jqAhXZiVwKHTWTDX0Q_h0wAHoECAUQBA&biw=1366&bih=646

 

This would then give you something to present that others would listen to.

Please note that every single one of these device has a cold reservoir and a hot reservoir, although they take different physical forms.

 

2 hours ago, Tom Booth said:

At this point, the focus of the discussion is, though the caloric theory is recognized as obsolete, there is a persistent remnant stated in a somewhat vague way in courses on thermodynamics that some heat must always be rejected to the sink in a heat engine.

Do you wish to discuss this claim which does not correspond to my studies of Thermodynamics to find out what they are (or should be) actually saying. It is all about cycles.

You can perform this miracle of not rejecting the heat by continually throwing away the working fluid, rather than completing the cycle and returning it to its original state, thus conserving it reasy for the next cycle. The penalty for that is you require a continuous supply of new working fluid. An extravagance any worthwhile engineer would not wish to expend.

[Tom Booth]

 

Quote

no pertinent details are provided.

I have no idea of your arrangment

I provided video ("worth a thousand words").

The engine is an unmodified (model  JAJ 838 KIT) ordered here: https://www.stirlinghobbyshop.com/english/stirling-engine-solar-ltd-low-temperature-stirling-engine-ltd-stirling/ltd-stirling-engine-ja-828/#cc-m-product-9759217783

stock engine, except for replacing the steel bolts with nylon bolts to minimize parasitic heat loss. A comon practice with Stirling engine model builders.

Hot water from the teapot about 212F presumably. It had just boiled 

The ambient room temperature was approximately 85F.

Insulation consisted of Corning fiberglass, styrofoam packing the engine was shipped with, and on top, 1/4 inch foil face styrofoam "house wrap".

Before placing the 1/4 inch foil faced styrofoam over the "sink" the RPM of the engine was a steady 162 RPM.

Immediately after completely securing the top disk of styrofoam, the RPM climbed to 180 RPM and remained there for several hours.

This is a very simple and straightforward experiment. I'm at a loss to imagine what more I could add that isn't already completely transparent.

This is one typical course in thermodynamics:

These engines are virtually hermetically sealed. The "working fluid" itself is entirely retained in the engine not thrown away or continually replaced in any way.

Part Ii

 

 

I cannot agree with this presentation because, if the engine were to convert enough heat into work to simply reduce the temperature 1 degree below ambient, heat would begin flowing backward. Heat always flows from hot to cold.

In a room at 85 degrees F, that would mean the engine would only need to bring the temperature down from 212 F to 84 F by means of conversion to work, for the heat to begin reversing direction. (Not as presented, down to an impossible 0Kelvin or absolute zero where mater as we know it ceases to exist.)

Edited July 31, 2020 by Tom Booth
Spelling typo

[Endy0816]

Does it stop once the heat source reaches the cooler ambient temperature?

 

Somewhat separate, but is there any chance your vacuum flask has developed micro cracks?

[Tom Booth]

 

Quote

Does it stop once the heat source reaches the cooler ambient temperature?

Of course.

 

Quote

Somewhat separate, but is there any chance your vacuum flask has developed micro cracks?

Possibly.

[studiot]

From your link

Quote

 

The stirling engine runs on ice and hot water. It show the conversation of heat or cold into mechanical movement. The engine typically runs at rpm 100+.

 

The top and bottom plates are aluminium. 

 

If a source of neat is placed under the engine, the rotation will be counter clockwise. On the other hand, is a cold source is placed under the engine, the the rotation will be clockwise.

 

The driving energy could be a cup of hot water/ coffee or a block of ice. The only stipulation is that the difference temperature is great enough to overcome by friction generated by the motion of moving parts.  The greater change of temperature ,the more the engine will react to the change in pressure inside the engine. 

 

 Place this Low Temperature Stirling Engine on a cup of hot water / hot coffee  & it may needs some time to start. The time is depends on the heat source given & is generally within 30 seconds to 2 minutes...

 

The engine won't start by itself, but given a little push in the proper direction (strong enough to coast the parts over for several cycles), the engine will take off and continue running on its own.

 

In what way do you think this engine has only one reservoir  ?

The makers are very clear that there are two reservoirs.

11 hours ago, Tom Booth said:

These engines are virtually hermetically sealed. The "working fluid" itself is entirely retained in the engine not thrown away or continually replaced in any way.

Yes and the makers are very clear that this engine works in cycles.

12 hours ago, studiot said:

It is all about cycles.

 

Tom, I have read what you wrote and at least some of what you linked to off site (requiring this is in theory against the rules here).  I do you the courtesy of not disputing how you arranged your practical setup, which you have gone overboard in describing.
You know what you did, I don't.
Your mechanical skills are probably far in excess of mine.
So if I wanted to make or modify or repair something mechanical you are the sort of chap I would go to.

So please return that courtesy by reading what I have to say about theoretical Thermodynamics, rather than spending time and effort posting poorly digested material on theoretical Thermodynamics.
I would agree that those diagrams are poorly conceived and imply lots that is not happening, even though they quote the correct end formula for certain situations.
I do like the fact that they do not try to use differential notation for the heat and work as that can be confusing, since they are never differential quantities.

 

So let is forget that presentation, if you don't like it, and I don't like it.

11 hours ago, Tom Booth said:

I cannot agree with this presentation because, if the engine were to convert enough heat into work to simply reduce the temperature 1 degree below ambient, heat would begin flowing backward. Heat always flows from hot to cold.

In a room at 85 degrees F, that would mean the engine would only need to bring the temperature down from 212 F to 84 F by means of conversion to work, for the heat to begin reversing direction. (Not as presented, down to an impossible 0Kelvin or absolute zero where mater as we know it ceases to exist.)

 

Instead look at the manufacturers instructions.
See how much information they have packed into a few short lines.

Can you not provide a similar summary of what you did ?

Then we can start analysing that using proper theoretical Thermodynamics.

[Tom Booth]

Quote

In what way do you think this engine has only one reservoir  ?

I don't. The moderator that banned me from the other forum made that assertion.

The experiment was intended to determine what would happen if the path to the cold "reservoir" were blocked by insulation.

Internally the engine still maintains a temperature difference.

However, I really need to repeat the experiment with some temperature probes to determine objectively what is actually going on.

My supposition is that, observing an increase in RPM with the cold sink shielded, the likely explanation is that, internally, the cold side of the engine became incrementally cooler as a consequence of protecting the engine from backward heat flow from the sink.

 

Quote

this engine works in cycles.

That is a given. I don't believe I ever suggested otherwise.

 

30 minutes ago, studiot said:

Tom, I have read what you wrote and at least some of what you linked to off site (requiring this is in theory against the rules here)

How is this against the rules? The material I've linked to is relevant and open to discussion. It is not spam or advertising. Not off topic.

Quote

So please return that courtesy by reading what I have to say about theoretical Thermodynamics

I've read everything you've posted or linked to. Was there something specific you wanted me to respond to?

Quote

So let is forget that presentation, if you don't like it, and I don't like it.

That presentation is just an example.

The assertion made that a heat engine can only avoid dumping unused heat to the sink by converting ALL the energy that exists, down to absolute zero is a universally repeated dictum in modern thermodynamics, and the Crux of the issue the experiment was intended to address.

The statement made in that video is presented as an absolute, unquestionable truth or law of nature, and typical of any and all such presentations I've ever seen, and I've read and seen a lot.

But how can that be true when quite obviously, not only would heat flow to the sink stop, when the cold heat exchanger equalized with the ambient, heat would flow into the engine from ambient as soon as the engine got any colder. The flow to the sink would stop when the cold side reached ambient (85F or approximately 302 Kelvin) not absolute zero 

Quote

Instead look at the manufacturers instructions.
See how much information they have packed into a few short lines.

Can you not provide a similar summary of what you did ?

Then we can start analysing that using proper theoretical Thermodynamics

I have provided absolutely every detail, as you have already said, to the point of going "overboard in describing".

I simply took a Stirling engine and blocked heat flow to the sink with insulation, to determine if such heat flow is really necessary.

If heat were a fluid, insulating the sink should slow or stop the engine cold. Instead the engine began running faster.

If heat is kinetic energy, then such "fluid flow" to the sink should be no more necessary than a baseball hit with a bat requires a "cold sink" to "flow" to the bleachers.

Kinetic energy, generally, does not flow from high to low or hot to cold like a fluid, it propagates through collisions.

A Stirling engine operates by marshaling the kinetic energy of billions of energetic air or gas molecules to collide with a piston.

The collisions reduce the kinetic energy of the gas, transferring that energy to the piston.

A gas molecule with a lot of energy is "hot".

A gas molecule with little energy after a collision, having transfered the energy to a piston is "cold".

A Stirling heat engine converts heat into work, by providing a moveable piston for the hot gasses to collide with. Something to transfer their kinetic energy to.

Carnot's concept of the caloric seems to be pure mythology. Why any "fluid flow" through a heat engine as some kind of absolutely unavoidable necessity is still adhered to in any branch of modern science is beyond me.

This simple experiment appears to demonstrate that this "flow" of "fluid" through a heat engine is a fallacy.

 

[Strange]

34 minutes ago, Tom Booth said:

How is this against the rules? The material I've linked to is relevant and open to discussion. It is not spam or advertising. Not off topic.

!

Moderator Note

Rule 2.7: you need to make your argument here, not require people to follow links, watch videos or read documents to know what you are saying

 

37 minutes ago, Tom Booth said:

Carnot's concept of the caloric seems to be pure mythology.

!

Moderator Note

"The caloric theory is an obsolete scientific theory" https://en.wikipedia.org/wiki/Caloric_theory

It is also against the rules to use logical or rhetorical fallacies (in this case, a straw man argument).

 

[Bufofrog]

56 minutes ago, Tom Booth said:

If heat were a fluid, insulating the sink should slow or stop the engine cold. Instead the engine began running faster.

I don't think anyone who is educated thinks heat is a fluid.

56 minutes ago, Tom Booth said:

If heat is kinetic energy, then such "fluid flow" to the sink should be no more necessary than a baseball hit with a bat requires a "cold sink" to "flow" to the bleachers.

I don't think anyone who is educated thinks heat is kinetic energy.

Temperature is the average translational kinetic energy of the atoms in a material.  When a material with a lower temperature (lower translational KE) is in contact with higher temperature material, the high KE atoms will transfer some their energy to the lower KE atoms.  The transfer of this energy is called heat.  The KE of the atoms is called temperature.  The hot material will continue to transfer it's translational kinetic energy to the cooler material until the 2 bodies are the same temperature (the same translational KE energy level).  The exchange of translational kinetic energy between the 2 bodies is often referred to as heat flow, but of course there is no actual flow of any material, just a transfer of energy.

Edited August 1, 2020 by Bufofrog

[swansont]

18 hours ago, Tom Booth said:

At this point, the focus of the discussion is, though the caloric theory is recognized as obsolete, there is a persistent remnant stated in a somewhat vague way in courses on thermodynamics that some heat must always be rejected to the sink in a heat engine.

It’s the second law of thermodynamics dynamics; no conversion of het to work will be 100% efficient. Not really vague, and not  dependent on caloric theory

Quote

My insulation is not perfect, so indeed, it is within the realm of possibility that "some" heat is still getting through, but if the functionality of a heat engine depends in any way on such "flowing through" of heat, then insulating the sink is roughly equivalent to stuffing a potato in the tailpipe of a car. Or shutting off the outlet in the water turbine of Niagra falls.

Of course heat is getting through. Insulation reduces heat flow, it does’t stop it.

Quote

 

How can it be explained that blocking the path of heat flow to the sink to any degree results in higher RPM and a longer run on a finite heat source? In this case a vacuum flask containing hot water.

When you reduce losses, more of the energy is available to do work. When you reduce heat flow, it takes longer to deplete the energy.

Also, you need to recognize that increasing RPM is not a continuous increase in energy loss. Once the system has sped up, its rotational energy is constant. 

 

Quote

 

If heat were a fluid, insulating the sink should slow or stop the engine cold. Instead the engine began running faster.

If heat is kinetic energy, then such "fluid flow" to the sink should be no more necessary than a baseball hit with a bat requires a "cold sink" to "flow" to the bleachers.

 

Heat is energy transfer owing to a temperature difference

[Tom Booth]

1 hour ago, swansont said:

It’s the second law of thermodynamics dynamics; no conversion of het to work will be 100% efficient. Not really vague, and not  dependent on caloric theory.

Let's look at this statement: "no conversion of heat to work will be 100% efficient." 

What does that actually mean in real terms?

Can we agree that if the temperature of a heat engine is equal to the temperature of the surroundings, no heat will "flow" into the engine?

Also, if the temperature of the heat engine is the same as the surrounding ambient temperature, then no heat will "flow" out of the engine?

[studiot]

3 hours ago, Tom Booth said:

Quote

In what way do you think this engine has only one reservoir  ?

I don't. The moderator that banned me from the other forum made that assertion.

The experiment was intended to determine what would happen if the path to the cold "reservoir" were blocked by insulation.

Internally the engine still maintains a temperature difference.

However, I really need to repeat the experiment with some temperature probes to determine objectively what is actually going on.

My supposition is that, observing an increase in RPM with the cold sink shielded, the likely explanation is that, internally, the cold side of the engine became incrementally cooler as a consequence of protecting the engine from backward heat flow from the sink.

Oh good. I must have misunderstood that. Sorry about the other forum they are rather snooty there.

Thank you for the extra information we are getting somewhere.

39 minutes ago, Tom Booth said:

Let's look at this statement: "no conversion of heat to work will be 100% efficient." 

What does that actually mean in real terms?

Can we agree that if the temperature of a heat engine is equal to the temperature of the surroundings, no heat will "flow" into the engine?

Also, if the temperature of the heat engine is the same as the surrounding ambient temperature, then no heat will "flow" out of the engine?

You talk about heat flowing. That's OK but only part of the story.

This is a spontaneous process ie can (note I did not day will) occur of its own accord.

Heat may also be transferred or transported, as in a heat pump.

Swansont has provided some very concise basic statements that need careful thought to understand fully.

But again I say let's get the details of the machine clear then move on to the theoretical analysis.

I think you will need to understand the First Law a little better, before moving on to the Second.

And we will do that in due course.

[Tom Booth]

2 hours ago, Bufofrog said:

The exchange of translational kinetic energy between the 2 bodies is often referred to as heat flow, but of course there is no actual flow of any material, just a transfer of energy.

Recognizing this, I have put the word flow in air quotes.

Thank you Bufofrog for that clarification.

So can we all agree that "flow" is a figurative expression, that in this context refers to energy transfer?

[swansont]

1 hour ago, Tom Booth said:

Let's look at this statement: "no conversion of heat to work will be 100% efficient." 

What does that actually mean in real terms?

It means that heat will be rejected. Qin > W

 

Quote

Can we agree that if the temperature of a heat engine is equal to the temperature of the surroundings, no heat will "flow" into the engine?

Also, if the temperature of the heat engine is the same as the surrounding ambient temperature, then no heat will "flow" out of the engine?

Sure. But I don’t see how this applies to your discussion thus far. You have a reservoir at a higher temperature than ambient.

It’s also clear that you haven’t studied physics in any depth; your use of non-SI units and misuse of terminology. You can’t expect understand what’s going on without a better grasp of the basics. studiot has started to explain this; you should take them up on the offer.

3 hours ago, Bufofrog said:

Temperature is the average translational kinetic energy of the atoms in a material.  When a material with a lower temperature (lower translational KE) is in contact with higher temperature material, the high KE atoms will transfer some their energy to the lower KE atoms.  The transfer of this energy is called heat.  The KE of the atoms is called temperature.  The hot material will continue to transfer it's translational kinetic energy to the cooler material until the 2 bodies are the same temperature (the same translational KE energy level).  The exchange of translational kinetic energy between the 2 bodies is often referred to as heat flow, but of course there is no actual flow of any material, just a transfer of energy.

To clarify, this translational KE is of the individual atoms, not of the sample as a whole, what is being described is conduction, which is not the only heat transfer process (there is also convection and radiation)

[Tom Booth]

2 minutes ago, swansont said:

It means that heat will be rejected. Qin > W

Not really.

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

On a scale that begins at absolute zero.

So if a heat engine reduces the temperature of the heat from T-hot down to T-cold that is simply the percentage of cooling produced on the absolute temperature scale, or how far the engine has cooled the "working fluid" on the way down to absolute zero.

It simply states that at best, the engine cannot reduce the temperature any lower than Tc.

It derived from Carnot who conceived the "flow of caloric" as including all that caloric down to the absolute zero temperature.

The "rejected" heat is the un-utilized percentage of caloric below Tc down to absolute zero, which Carnot conceived as also flowing through the engine.

That is the actual original basis of this engine efficiency formula.

That is, of course, my understanding after some rather extensive reading and research on the subject.

 

So this "maximum efficiency" represents a potential for heat reduction or energy conversion which (theoretically), bottoms out at Tc.

[Endy0816]

3 minutes ago, Tom Booth said:

Not really.

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

On a scale that begins at absolute zero.

So if a heat engine reduces the temperature of the heat from T-hot down to T-cold that is simply the percentage of cooling produced on the absolute temperature scale, or how far the engine has cooled the "working fluid" on the way down to absolute zero.

It simply states that at best, the engine cannot reduce the temperature any lower than Tc.

It derived from Carnot who conceived the "flow of caloric" as including all that caloric down to the absolute zero temperature.

The "rejected" heat is the un-utilized percentage of caloric below Tc down to absolute zero, which Carnot conceived as also flowing through the engine.

That is the actual original basis of this engine efficiency formula.

That is, of course, my understanding after some rather extensive reading and research on the subject.

 

You'll always have some losses though.  You mentioned swapping out the bolts to reduce parasitic losses for instance.

Note the idealized nature of the Carnot equation. Any real engine will have all kinds of issues reducing theoretical efficiency.

[Tom Booth]

3 minutes ago, Endy0816 said:

You'll always have some losses though.  You mentioned swapping out the bolts to reduce parasitic losses for instance.

Note the idealized nature of the Carnot equation. Any real engine will have all kinds of issues reducing theoretical efficiency.

My point is that for an engine to be 100% Carnot efficiency it would have to cool the working fluid down to an impossible 0 K not Tc.

[swansont]

On 8/1/2020 at 10:25 AM, Tom Booth said:

Not really.

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

Work is not in your equation, so “not really” isn’t something you show here. And since W = Qin -Qout, my statement is correct.

 

Quote

On a scale that begins at absolute zero.

So if a heat engine reduces the temperature of the heat from T-hot down to T-cold that is simply the percentage of cooling produced on the absolute temperature scale, or how far the engine has cooled the "working fluid" on the way down to absolute zero.

It simply states that at best, the engine cannot reduce the temperature any lower than Tc.

It’s not like this is an independent step. The rejected heat is into a reservoir at Tc. So it’s true the temperature won’t go lower, since you can’t have spontaneous heat flow from cold to hot.

 

Quote

It derived from Carnot who conceived the "flow of caloric" as including all that caloric down to the absolute zero temperature.

The "rejected" heat is the un-utilized percentage of caloric below Tc down to absolute zero, which Carnot conceived as also flowing through the engine.

But caloric theory is wrong, so understanding thermodynamics this way will lead to problems.

 

On 8/1/2020 at 10:40 AM, Tom Booth said:

My point is that for an engine to be 100% Carnot efficiency it would have to cool the working fluid down to an impossible 0 K not Tc.

Which means it must reject heat. 

[Tom Booth]

Let's try this.

In my experiment using boiling water (212F) at ambient temperature (85F), "maximum efficiency" can be calculated to be 18.9% if the engine "rejects heat" at a temperature of 85F.

That is, it would have to extract enough work to bring the input temperature of 212F down to 85F output temperature.

But, heat cannot be "rejected" at a temperature equivalent to the sink. Setting that fact aside for the moment we have the fact that my engine only needs to have a Carnot efficiency of 18.9% (not 100%) to no longer have a condition where heat is being "rejected".

At 18.9% efficiency heat is no longer being rejected. Temperatures are equivalent, so no "flow" can result.

An efficiency of a mere 19% would have heat flowing backward from the ambient sink back into the engine.

Therefore, to say the engine must reject heat because no engine is 100% efficient is apples to oranges.

It is not necessary to have 100% efficiency on an absolute scale, or bring the temperature down to absolute zero, rejection to the sink ceases at any efficiency >= 18.9%

[swansont]

 

Quote

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

Why?

Quote

Setting that fact aside for the moment we have the fact that my engine only needs to have a Carnot efficiency of 18.9% (not 100%) to no longer have a condition where heat is being "rejected".

No...

If no heat were rejected, your efficiency would be 100%

Quote

At 18.9% efficiency heat is no longer being rejected. Temperatures are equivalent, so no "flow" can result.

You need to explain why you think this is so. IOW, explain why your ice melts, if no heat is flowing

 

Quote

An efficiency of a mere 19% would have heat flowing backward from the ambient sink back into the engine.

Therefore, to say the engine must reject heat because no engine is 100% efficient is apples to oranges.

It is not necessary to have 100% efficiency on an absolute scale, or bring the temperature down to absolute zero, rejection to the sink ceases at any efficiency >= 18.9%

Again, you need to explain why you think this is so

Actual thermodynamics doesn’t work this way.