Tesla's Ambient Heat Engine revisted

[Tom Booth]

The condenser is the ambient temperature heat rejection exchanger. Yes it is isothermal. It gets hotter than ambient so heat will come out. A delta T is needed for heat transfer.

If it were quasi static it would be more efficient. It isn't, so it can, and does, have a higher wattage. It cools faster at the expense of a little efficiency.

Emphasis above to identify statements that contradict the following (emphasis added):

The Vuilleumier cycle requires hot and ambient to run the machine. It requires a insolated space to cool. As you point out, three temperatures. And the heat absorbed from that cold space is rejected to ambient. It won't work trying to cool the ambient temperature and reject to the hot space. It needs all three.

A motor driven refrigerator absorbs heat from an insulated cold space, and rejects it to ambient. It doesn't have a "hot space" just the two temperatures.

Thanks for corroborating that with your last post. It obeys Carnot Theory, not yours. Yours fails to describe the reason for three temperatures. Show us a PV diagram for your Theory. Please.

"Yours fails to describe the reason for three temperatures."

No it doesn't.

You've included the "hot" temperature and why it is necessary in your updated statement, proving your own previous statement to be in error.

[VincentG]

There is a much simpler reason for three temperatures.

We exist in the third temperature. If there was hot and cold on tap, we would have no need for heat pumps and much less need for electricity in the first place.

[Tom Booth]

The condenser is the ambient temperature heat rejection exchanger. Yes it is isothermal. It gets hotter than ambient so heat will come out. A delta T is needed for heat transfer.

If it were quasi static it would be more efficient. It isn't, so it can, and does, have a higher wattage. It cools faster at the expense of a little efficiency.

Just for laughs,

How does a gas under pressure, increasing in temperature have a "higher wattage"?

The bolded text is also self contradictory:

"Yes it is isothermal. It gets hotter than ambient so heat will come out. A delta T is needed for heat transfer".

Isothermal means there is no temperature change throughout the process. The gas inside must remain in thermal equilibrium with the outside ambient for the process to be isothermal.

"Quasistatic" is inherent or implied by "Isothermal" by definition. It is an idealization to simplify mathematical computations, not a "real" process.

An actual REAL refrigerator has a working fluid that is compressed to make it hot because, as you stated correctly,; "It gets hotter than ambient so heat will come out. A delta T is needed for heat transfer."

In that case it is not ACTUALLY isothermal is it?

In fact, there is really no such thing as "isothermal" in the real world, that transfers heat without a temperature difference, even if given "forever".

Unfortunately thermodynamics itself is replete with such impossible self-contradictory concepts.

[Tom Booth]

Sorry, this is incorrect:

In fact, there is really no such thing as "isothermal" in the real world, that transfers heat without a temperature difference, even if given "forever".

Boiling water and similar phase change processes can be ACTUALLY isothermal.

Both the temperature of the boiling water and the temperature of the water vapor are 100°C

Heat is supplied continually to boil the water without a change in the temperature of the water.

The term is applicable to steam engines.

It makes no sense when you try to apply it to a Stirling engine where there is no phase change and no latent heat.

A refrigerator also has some near isothermal processes associated with the changing phase of the refrigerant, but "heat rejection" to ambient by hot compressed refrigerant is not one of them.

[Fool]

https://en.m.wikipedia.org/wiki/Heat_pu ... tion_cycle

RefrigerationTS.png (12.66 KiB) Viewed 2110 times

Apparently the condenser has both changing temperature space and an isothermal space. The isothermal area of the condenser is where the condenser "condenses". I wonder how much heat is transfered by the gas only space, verses, how much is transferred by the condensation space? Possibly one is very small compared to the other.

An isothermal transfer of heat is in cooperation with an expansion or compression. The heat flow must be in balance with adiabatic temperature change for the temperature to remain constant. That is the point I was trying to make in the isothermal thread.

The heat flow rate is determined by the temperature difference. The adiabatic temperature change rate is determined by the volume change rate. If the same Temperature stays the same.

Quisi static: Static means stationary. Quisi means close to, kinda, sorta. The engineering idea is that a quasi static process is happening so slowly that the dynamic properties, mv, f=Ma can be ignored as they are negligible, not to be misspelled negotiable. LOL

In thermodynamics, quasi static isothermal heat transfer is a model that is changing so slowly that the process stays the temperature of a source or sink for the entire compression or expansion. In a real engine, there will be both a temperature difference and a change. Hopefully a small amount. But one is caused by the process being faster than heat can transfer. It balances somewhat because as the heat lags behind the speed, the temperature difference increases, speeding up the heat transfer. Thus there can still be an isothermal temperature, but with a greater temperature difference. The gas will stay the same temperature for the entire expansion, but be significantly lower than the hot plate.

That is why refrigerator coils get warm. A compromise between efficiency and speed, and power to size ratio.

[MikeB]

For heat to be removed from the cold end, by the working fluid, it must have an _average_ temperature throughout the cycle, that is below that of the cold end.
It's easy to postulate that the working fluid temp might drop below that temp briefly, but I'm really struggling to see how it could be below Tc on average while the engine still runs.

Why "on average"?

What is the temperature of the working fluid in a conventional household refrigeration system "on average"?

Tom,
What I meant was that we only get energy/temperature transfer from hot to cold, don't we?
Now, we all know that the temperature of the working fluid will vary during the cycle.
And that the rate of transfer depends on the temp difference?

So if we assume for a moment that the cold end had a temp of 200k and the working fluid varies evenly between 210k and 190k we would expect that the heat transfer from fluid to sink would exactly balance the transfer from sink to fluid, wouldn't we? This is what I mean by "on average".

And to finish the point, your suggestion seems to be that in your engine, the working fluid drops at its coldest to below zero C (Sorry to mix units.)
If we stick a finger in the air, and suggest that it drops to minus 10C, then I don't see how we could get net transfer of heat into the fluid unless the max temp of the working fluid never exceeds 9.9C

A household fridge is a totally different beast.

[Fool]

MikeB, you are correct.

[Tom Booth]

For heat to be removed from the cold end, by the working fluid, it must have an _average_ temperature throughout the cycle, that is below that of the cold end.
It's easy to postulate that the working fluid temp might drop below that temp briefly, but I'm really struggling to see how it could be below Tc on average while the engine still runs.

Why "on average"?

What is the temperature of the working fluid in a conventional household refrigeration system "on average"?

Tom,
What I meant was that we only get energy/temperature transfer from hot to cold, don't we?
Now, we all know that the temperature of the working fluid will vary during the cycle.
And that the rate of transfer depends on the temp difference?

So if we assume for a moment that the cold end had a temp of 200k and the working fluid varies evenly between 210k and 190k we would expect that the heat transfer from fluid to sink would exactly balance the transfer from sink to fluid, wouldn't we? This is what I mean by "on average".

And to finish the point, your suggestion seems to be that in your engine, the working fluid drops at its coldest to below zero C (Sorry to mix units.)
If we stick a finger in the air, and suggest that it drops to minus 10C, then I don't see how we could get net transfer of heat into the fluid unless the max temp of the working fluid never exceeds 9.9C

A household fridge is a totally different beast.

Finger in the air?

Sounds like incoherent gibberish to me, who knows what you're trying to to say

[Tom Booth]

MikeB, you are correct.

Likely you are both wrong, if anyone knew what either of you are talking about.

[Tom Booth]

For heat to be removed from the cold end, by the working fluid, it must have an _average_ temperature throughout the cycle, that is below that of the cold end.
It's easy to postulate that the working fluid temp might drop below that temp briefly, but I'm really struggling to see how it could be below Tc on average while the engine still runs.

Why "on average"?

What is the temperature of the working fluid in a conventional household refrigeration system "on average"?

Tom,
What I meant was that we only get energy/temperature transfer from hot to cold, don't we?
Now, we all know that the temperature of the working fluid will vary during the cycle.
And that the rate of transfer depends on the temp difference?

So if we assume for a moment that the cold end had a temp of 200k and the working fluid varies evenly between 210k and 190k we would expect that the heat transfer from fluid to sink would exactly balance the transfer from sink to fluid, wouldn't we? This is what I mean by "on average".

And to finish the point, your suggestion seems to be that in your engine, the working fluid drops at its coldest to below zero C (Sorry to mix units.)
If we stick a finger in the air, and suggest that it drops to minus 10C, then I don't see how we could get net transfer of heat into the fluid unless the max temp of the working fluid never exceeds 9.9C

A household fridge is a totally different beast.

As far as I can figure, your confusion stems from having no idea what your talking about.

In a refrigerator the working fluid is first compressed and made hot so it can "reject" heat, then expanded and made cold so it can take in heat. The hot and cold sections are separated by the expansion valve and the compressor.

In a Stirling engine, generally, the heated/compressed and cooled/expanded working fluid is shifted between hot and cold areas by the displacer.

There is no "average" anything at any time anywhere.

It's called engineering.

[Fool]

LOL, great entertainment.

[MikeB]

Tom,
IIRC you were the first to mention fridge's. We seem to be in agreement that they have little relevance to this discussion.

Average <anything> is ALWAYS a thing, and while it may not be entirely easy to predict, the average temperature of the working fluid of a hot-air engine is definitely a thing: the engine can only work if there is a cycle of pressure changes within. Since pressure and temperature are directly linked we can be sure that the temperature of the working fluid varies roughly in sync, does it not?

[Tom Booth]

Tom,
IIRC you were the first to mention fridge's. We seem to be in agreement that they have little relevance to this discussion.

What?

I have no idea how you arrived at that conclusion.

Refrigeration systems generally are HIGHLY relevant. For one thing Stirling engines ARE a kind of refrigeration system. Expansion cooling is a common element, so is compression, so is conversion of heat into work in some systems, specifically air-cycle and Claude air liquefaction type systems using expansion engines, turbo-expanders and so forth.

Average <anything> is ALWAYS a thing,

You are implying that because temperature "average" is neutral, hot and cold or high and low pressure at different times has no effect, which is ridiculous.

... and while it may not be entirely easy to predict, the average temperature of the working fluid of a hot-air engine is definitely a thing: the engine can only work if there is a cycle of pressure changes within. Since pressure and temperature are directly linked we can be sure that the temperature of the working fluid varies roughly in sync, does it not?

No real idea what your trying to say there, so I cannot commit to agreeing or disagreeing.

All I know, if I burn my hand on a hot stove then put ice on it, it may be soothing, but just because the "average" temperature cancels out does not mean the burn never happened or the heat never produced any effect.

[Tom Booth]

at least I tried to.... you can't measure what isn't there.

Of course fool and company just say I'm not getting an increase in temperature because my little toy Stirling engines use such an infinitesimal amount of heat and are so so inefficient and produce such little power the heat leaving the engine is not enough to be measurable.

I agree with you that heat-energy entering the hot side and being converted to kinetic-energy in the form of flywheel acceleration and electricity generation etc will mean a lower temperature on the cold side than you'd get if you simply powered a displacer from a different energy source external to the system.

And it is difficult to measure such small systems. I'll have a go at building some sensors into my much larger LTD stirling and bring some data to the discussion.

That will be fantastic. I hope you do.

In the mean time you might be interested in this experiment.

The engine has an acrylic dome-like engine body except for the metal bottom. Acrylic, of course has a very low heat conductivity. I've covered this engine with a silica aerogel blanket, and put the whole thing inside a glass cylinder to cut down on drafts.

It is being heated by a steam generator, which boils a small amount of water continuously. The steam is contained and directed up to the bottom of the engine by a section of automotive radiator tubing.

The upper outside of the tubing reached the temperature of about 180°F

I assume inside it must have been hotter.

I was expecting, at the end of the video, to find that the metal bottom of the engine would be nearer to 200°F, but instead it was only about 120°F

There was a bit of fumbling around with the camera, but I remember being shocked by the relatively cool temperature of the bottom of the engine.

What seems most remarkable however, is the top of the engine, above the aerogel blanket barely went up above ambient in temperature.

IMO an approximate 50° ∆T between the hot steam inside the tube near the bottom of the engine. The tube itself being about 180° on the OUTSIDE and the bottom of the engine indicates the engine was taking in heat at a rather fast rate so that the bottom of the engine remained relatively cool.

Using "fools" method for equating 1 degree with 1 Joule, it might be supposed the engine was absorbing 50 joules to bring the 180° down to 120° at the bottom heat intake.

On top the ∆T between the engine and ambient reached maybe 3°

I let the engine run in this way for about 3 hours in another experiment and the engine maintained this low upper side temperature.

So, it looks like maybe 3 joules out the top for every 50 joules going in the bottom. Some of the heat reaching the top might very well have been due to heat conducted around the engine by the glass, or generated by friction at the power cylinder.

Conservative estimates IMO. But I'd be more than happy to get additional data from another researcher.

You seem to be at least open to the idea that heat can be converted.

https://youtu.be/l2XcnN6QdfA

[Tom Booth]

Maybe you might also be interested in this experiment.

A different model but this engine also has acrylic sides and top for retaining heat, or put another way, to eliminate the cold "sink".

In addition to the low heat conductive acrylic, I also put additional Styrofoam insulation on the inside.

There isn't a whole lot of room on the interior, so maybe only 1/4 or 1/3 the normal volume of working fluid. Not sure exactly.

https://youtu.be/Aci_RjTli_o?si=IFRfJwKUBNLgx3sU

If your interested in how the interior insulation was constructed and put together, this next video also gives an idea of the small amount of space remaining inside with the added insulation.

These videos are really about testing out a new "heat valve" design, as opposed to a conventional "displacer", but the thermodynamics aspect is interesting as well.

https://youtu.be/IedJtatFubg?si=4KRcqjWZ1iKS2HCU

Not sure what more could be done to demonstrate that these engines will still run without a "cold side" or "sink'.