Stirlingengineforum.com

Your beliefs provide zero scientific relevance. Frame 5 contains an error. It is impossible to extract positive work while attempting to suck a vacuum.

Try it with a hand powered vacuum pump. See if it will pump itself. That is what a piston in a cylinder is, a pump.

Nobody wrote: ↑Fri Nov 26, 2021 11:20 pm Your beliefs provide zero scientific relevance. Frame 5 contains an error. It is impossible to extract positive work while attempting to suck a vacuum.

Try it with a hand powered vacuum pump. See if it will pump itself. That is what a piston in a cylinder is, a pump.

As anyone can see, at the begining of this thread, when I introduced that diagram here:

viewtopic.php?f=1&t=2695#p16163

I clearly stated:

I created this diagram of the Stirling engine cycle - reinterpreted somewhat, according to my theories and observations regarding how a Stirling engine ACTUALLY operates.

Or, rather, how I've personally decided that I think it operates.

The momentum of the flywheel and crank, and/or the piston itself are what "pull a vacuum" and as explained in the video about expansion cooling:


https://youtu.be/PMKPZuCj9a0


The gas molecules, "hitting a moving target" do continue to transfer kinetic energy to the piston which results in cooling of the gas as it looses energy. This contributes to the "work" of driving the piston. As long as the piston is moving and the gas is expanding, work is being done by the gas to drive, or assist in driving out the piston, along with whatever contribution from stored energy or momentum in the flywheel.

If the internal gas pressure was not involved in helping drive the piston, "pulling a vacuum" would be much more difficult. There is not a total vacuum.

The work needed to "pull a vacuum" comes from that stored in the piston mv^2. If you extract energy from the piston, the expansion will be less, shorter. The compression stroke will be shorter. If you attempt to get more expansion, there will be less mv^2 to harvest for power out.

I.e., your 5 frame is in error because you won't be able to do both.

Getting work out (Adding load) will slow the piston.
Pulling a vacuum will slow the piston.

On the return stroke
Getting work out (Adding load) will slow the piston.
Pushing compression will slow the piston.

I'm not even sure that you will be able to pull enough vacuum to get any cooling while completely unloaded. This is the error.

Nobody wrote: ↑Sun Nov 28, 2021 1:23 am
I'm not even sure that you will be able to pull enough vacuum to get any cooling while completely unloaded. This is the error.

First of all:


Perhaps the orange text is not easy for some to see, but as I've said before, any running engine is doing some work, friction, air resistance, vibration, noise. Further, the diagram reads in frame #5 "Shaft work to load" with an arrow pointing out in line with the crank, there is a flywheel.

So to say frame five is in error because the engine is "completely unloaded", doesn't appear to have any basis in fact.

If you extract energy from the piston, the expansion will be less

The piston is an insert mass. Though in theory, if the piston has weight, or if there is a flywheel, some energy from the momentum may help to "pull a vacuum", but that isn't essential, and not what the diagram is intended to illustrate.

Heat enters the engine, passing into the gas, accelerating the gas molecules. The expanding gas is the only significant working fluid doing work to drive the piston, and by extension any attached load. The piston is not expanding to do work. Any "work" it might contribute to the process originated with the expanding gas that set it in motion.

You are also failing to understand that the expansion is adiabatic, not isothermal. Isothermal expansion is a fictional attribute of the imaginary Carnot engine requiring infinite time to carry out an "ideal" process that does not exist in a real engine in the real world.

You also have again, in spite of your revision, excluded or sidestepped inclusion of any actual factoring in the conversion of heat into work. "Work" is; first; the mechanical motion of the engine. If the engine moves at all there is already conversion of heat into work. The expanding and contracting gas is already "loaded" doing thermodynamic "work" to make the piston move and the engine itself operate.

Further, you neglect to consider not just the heat energy added to the gas, but the potential energy due to compression on the one hand and expansive cooling ADIABTICALLY on the other.

Adiabatic expansion and cooling, that is, rapid expansion without heat input, (because the engine is running fast and there is not enough time for heat transfer into the gas) forces the gas to draw on its own internal energy.

The more the gas is compressed, the more it will draw on internal energy while expanding (rather than external heat input from the environment).

In practice, the gas has much more internal energy than the heat supplied to it. The gas is capable of expansion to the point where it looses so much energy and gets so cold it changes state and condenses into a liquid.

Any incremental cooling of the engines cold heat exchanger by such adiabatic cooling of the "sink" or cold plate, increases the potential for the engine to do more work, that is, it increases the temperature differential.

The effects you mention, -. "... If you extract energy from the piston, the expansion will be less, shorter. The compression stroke will be shorter. If you attempt to get more expansion, there will be less mv^2 to harvest for power out." ..."Getting work out (Adding load) will slow the piston. ...Pulling a vacuum will slow the piston....
Getting work out (Adding load) will slow the piston.
Pushing compression will slow the piston."


It should be considered too that needlessly dumping heat to a "sink", just to cool the engines cold side rob's the engine of it's ultimate energy source and... Slows the piston.

Cooling the sink by internal adiabatic cooling has several not so obvious potential advantages.

External cooling can only be carried out to whatever "cold reservoir" might be available, or the cold needs to be supplied by ice or refrigeration.

Adiabatic cooling is not so limited. The cooling can, in theory, continue down to cryogenic temperatures without external energy input that needs to be supplied.

The greater the temperature swing, the more energy can be supplied to the engine by atmospheric pressure on the return compression stroke.

The diagram is to help illustrate a theory.

The theory itself may be "wrong", but if the diagram were in some way "corrected" to conform to some other "right" idea, it would not serve the purpose for which it was intended, which is, to help to convey a new theory, or perhaps a not so new theory. Rather an alternative theory, that can actually be traced back more than 100 years, including the entire history of refrigeration, gas liquefaction processes, in particular "air cycle" refrigeration and the Claude cycle engine.

It can also be seen in Tesla's article:

This apparatus, by continually transforming heat into mechanical work, tended to become colder and
colder,... This seemed to be contrary to the statements of Carnot and Lord Kelvin before referred to, but I concluded from the theory of the process that such a result could be attained. This conclusion I reached, I think, in the latter part of 1883, when I was in Paris

Of course, Tesla may have been wrong, however his heat engine theories, to my knowledge, have never been tested experimentally. So far, IMO, my various experiments with modern model LTD and other model Stirling engines have failed in proving the theory (outlined in Tesla's article and my own diagrammatic interpretation) conclusively wrong.

Cryogenic air-cycle refrigeration and Claude process liquefaction involve compressing a gas to a high pressure and then releasing it to power an engine.

Obviously a model Stirling does not achieve such a high compression ratio but the principle of operation, the engine cycle of a Stirling engine is identical to a cryogenic expansion engine.

Actually, a Stirling engine, as a mechanical apparatus, IS also a potential cryogenic refrigerator or air liquefier, without modification. As discussed on another thread here, even a very crude "tin can" Stirling engine when driven, can also exhibit a below ambient cooling effect.

The diagram may be "wrong" in your opinion, but it serves it's intended purpose.

Giving a Stirling engine a slight nudge, because of the construction, starts an oscillation that increases and grows stronger and more forceful over time. It appears that the engine is gradually increasing its own internal temperature differential. That increase is limited by the external environment, primarily because if the engine "self cools" below the temperature of the ambient sink heat from the ambient environment will immediately neutralize it. It hits a wall.

But, it appears that simply isolating the cold side of the engine, (that is a standard unmodified Stirling engine) with insulation, allows the engine to cool itself below ambient.

There are, I believe, a number of optimizations that could increase this effect.

Show an actual indicator diagram that supports your fifth frame. All your descriptions have no support.

Nobody wrote: ↑Tue Nov 30, 2021 4:41 am Show an actual indicator diagram that supports your fifth frame. All your descriptions have no support.

Do your own experiments, come up with your own interpretations, draw your own diagram, write up a paper, start your own thread or whatever, but please stop following me around, spamming my and others threads with your so-called "help".

I don't have the instrumentation to hook up to my model engines to generate any such diagrams. As I've said before, and will say again for the last time, that diagram represents my own theory, based on my own observations, presented as something to consider, nothing more.

My descriptions have the support of my own research, tests, observations, experiments, deductions and logical conclusions, along with considerable supporting documentation.

You are free to disagree. Conduct your own research and test your own theories, but please, whatever you do, do it someplace else.

My discussion here is based on 200 years of indicator diagrams, engine design, scientific study, challenged by the smartest minds in the world,. running engines, theories that produced those engines, and countless hours of college instruction and questioning. You seem to defend yours by reiterating your errors. Your orange work out words on, your diagram 5, are the error as show on any indicator diagram of any working engine.

Even the Phillip's video you posted clearly describes that work must be put in to get cooling. It is obvious when all scientific information is used.

Theories aren't scientific without working examples. Without an indicator diagram from a working engine/cooler your theory can be considered unreliable.

With 200 years of indicator diagrams showing the error in your theory, we can safely say it is wrong. That is what we have. Carnot and the Kinetic Theory are correct. They have been found to be reliable, repetitively. Yours has never been found to be reliable, except by you.

Nobody wrote: ↑Fri Dec 03, 2021 4:18 am My discussion here is based on 200 years of indicator diagrams, engine design, scientific study, challenged by the smartest minds in the world,. running engines, theories that produced those engines, and countless hours of college instruction and questioning. You seem to defend yours by reiterating your errors. Your orange work out words on, your diagram 5, are the error as show on any indicator diagram of any working engine.

Even the Phillip's video you posted clearly describes that work must be put in to get cooling. It is obvious when all scientific information is used.

Theories aren't scientific without working examples. Without an indicator diagram from a working engine/cooler your theory can be considered unreliable.

With 200 years of indicator diagrams showing the error in your theory, we can safely say it is wrong. That is what we have. Carnot and the Kinetic Theory are correct. They have been found to be reliable, repetitively. Yours has never been found to be reliable, except by you.

I don't have any issue with kinetic theory.

If you think "shaft work out" during the power stroke of an engine is an "error", what else can I say?

work must be put in to get cooling

Clearly that is not true for, say, an absorption refrigerator that runs on heat from a gas flame, not mechanical "work" input, or a Vuilleumier heat pump.

As the heated gas expands and drives the piston out it is doing work. Energy is transfered to the load. The result is, the gas, loosing energy cools. There is not anything controversial about that. It is a well known effect used in air cycle refrigeration and liquefaction of gasses.

A bit of additional cooling may result from mechanical expansion due to the momentum of the piston/crankshaft/flywheel, if present, all taking place during the power stroke.

Here is a reference:

https://chemistry-desk.blogspot.com/201 ... s.html?m=1

...when a gas expands adiabatically against a piston in an engine, it does some external work, hence its internal energy falls and consequently the temperature of the gas falls

It could not be any clearer.

Here is an additional reference to air cycle refrigeration:

https://grimsby.ac.uk/documents/frperc/ ... search.pdf

When the pressure and temperature, during the power stroke, drops below the ambient pressure and temperature, as depicted in your drawing 5, the power stroke ceases putting out power, and either stops, or requires work input to the expanding gas, or more correctly, work into the ambient pressure.

The pressure will be greater on the outside. Inside less work than outside. Net work negative.

Nobody wrote: ↑Fri Dec 03, 2021 10:30 pm When the pressure and temperature, during the power stroke, drops below the ambient pressure and temperature, as depicted in your drawing 5, the power stroke ceases putting out power, and either stops, or requires work input to the expanding gas, or more correctly, work into the ambient pressure.

The pressure will be greater on the outside. Inside less work than outside. Net work negative.

That's your opinion, that is all. As explained quite clearly and graphically already by me, as well as in this video:

https://youtu.be/PMKPZuCj9a0

Even while the instructor is putting physical work into expanding the gas, (or as you point out, doing work against the external atmospheric pressure) the internal gas molecules are striking a "moving target" and so continue to loose energy and cool. Infact, that is the only demonstrated process in the video, "pulling a vacuum" the same as might occur in an engine due to inertia of the piston after being set in motion by the expanding gas. Even the gas itself, on both sides of the piston, carries some inertia.

There is only one source of energy, ultimately, HEAT. The heat expands the gas. The expanding gas drives the piston. There is no outside "work input", only heat input and work output.

Even if the momentum of the piston is construed to contribute some "work input" from stored momentum, that stored energy in the piston/flywheel originated with the expansion of the gas, expanding and doing work at the expense of it's internal energy, cooling down in the process.

If the piston, once set in motion by the expanding gas, then, in turn, due to momentum/stored energy, further expands and cools the gas, that in no way contradicts my diagram.

If, as you claim, there are 200 years of indicator diagrams to contradict this, go ahead and present one as evidence, and explain how the measurements disproves my theory. My theory is at least in part, based on such PV diagrams of actual measurements of actual Stirling engines. However, Stirling engines existed in relative obscurity, mostly ignored for the past 200 years, so in actuality, I don't think there are all that many, but if you can present something, go ahead and do so, otherwise your assertion is just empty talk. There is no reason for me to reinvent the wheel, I've never noticed any contradiction between my theory or diagram and such indicator diagrams.

The volume expands, the pressure drops, the gas cools. That is what my diagram shows. That is what the actual measurements show. As far as that part of the cycle is concerned, #5 in my diagram, it is even consistent with the corresponding portion of the Carnot Cycle, adiabatic expansion.

The only difference being that Carnot imagined that the piston would somehow miraculously stop and change direction the moment the internal gas temperature reached the temperature of the sink. Logically, IMO, there is no reason to make such a supposition. I think there is abundant evidence to suggest that the cooling could proceed beyond that, to the point where the gas cools to a temperature slightly below that of the sink. Possibly more than just "slightly".

With 200 years worth of indicator diagrams at your disposal, what reason do you have to demand another from me? Just present some actual evidence, if you have any.

Even the diagram you did present already clearly shows the internal gas temperature dipping below the temperature of the sink.

Shows an engine operating inside isotherms.

The chart out of your Senft book showed it even better. Maybe you could supply it again here.

Here it is,

The full chart:
Yes. For the cold heat exchanger space. Summed up for the entire engine, the overall average temperature stays between the isotherms. The little bit in the heat exchanger has less influence on the work performed during expansion.

When the temperature is being kept low by an isotherm, it will dip below, but overall it will transfer more heat out. Because the compression is hotter for longer.

Look at the hot side for the same period. Now visualize the main body of fluid, which during expansion, starts out 400 degrees hotter than the cold side. In a displacer engine, the cold plate would be covered, insulated, during that expansion stroke. In an Alpha, most of the fluid would be in the hot cylinder.

Idealizations, theoretical PV diagrams, are just that. Imaginary, made up, not actual measurements. "Indicator diagram" is mostly a term used to refer to actual engine measurements, which I assumed is what you were talking about.

Those are more realistic theoretical Stirling PV graphs, not actual measurements.

More heat in than out is a given.

A heat engine has to take in heat. Your assumption that that "excess heat" must somehow end up going through the engine to the sink is where our interpretations diverge.

Heat is not a conserved quantity. Heat is only a FORM of energy.

Heat goes in as "sensible heat", but is converted to mechanical "work".

That the chart shows MORE heat going in on the hot side than goes out on the cold side is to be expected.

Here is what I would call an ACTUAL example of a REAL "indicator diagram" being generated:

https://youtu.be/dvomod6SsA0

Notice how, with a uniform thermal heat "reservoir", the source of heat, is not changed, but the diagram changes, with a load (break on the flywheel) and without a load.

A heat engine has to take in heat. Your assumption that that "excess heat" must somehow end up going through the engine to the sink is where our interpretations diverge.

I have never had that assumption. Nor have I written that anywhere. Your implications, of Caloric flow theory, died over 100 years ago. Serious scientists no longer use that, if they know what they're saying.

Even if you could eliminate all "excess heat", depending on the definition, the heat of adiabatic compression would still occur when the cycle reverses. That heat would need to go somewhere? It is only the heat of compression that I'm talking about. If it stays in the working fluid, you will get adiabatic compression, and the Stirling engine will produce Zero net power.

The reason IC engines can live with adiabatic compression is that the heat added isn't constrained by a maximum hot exchanger temperature. It's maximum can even go higher yet, if the ambient goes higher. There is no upper limit, except detonation, then it becomes a diesel ICE cycle.

Heat, per se, doesn't exist. Heat is kinetic energy, but that doesn't tell us what it "is". < A bit of Feynman there.

We calculate kinetic energy from measurable properties. Mass and Velocity.

KE = 1/2 M V^2

Heat is said to enter an engine by, something with higher kinetic energy, bumping into, a lower kinetic energy state engine. It's not that you don't know that. It just sounds better, IMHO, than, "A heat engine has to take in heat."

Thanks for the video. I noticed that, when the engine ran faster, the working fluid temperature pulled away from the isotherms. That is the point I've been trying to show. (It will not heat the hot plate, or cool the cold plate. Not even close.) It also seems to be pulling away from any adiabatic processes. I.e. it becomes more isothermal, less adiabatic, and further away from the hot and cold plates. Logical if you think about it.

You started this thread with several questions, the following being, IMHO, the most relevant:

So I would like to ask, from anyone who has experience with this, is this video accurate when it states that a Stirling engine AND cooler both turn in the same direction?

The answer is yes yes. A Stirling Engine powered in the same rotational direction by a motor, will cool the hot side, (should the heat be stopped). The cold side will receive heat, and more than is coming out of the hot side.

It will not cool the cold side unless the direction, that shaft power is entered, is reversed.