Insulating the "sink", again.

[Tom Booth]

Since my previous experiment involving insulating the cold plate appeared to INCREASE the engines RPM slightly,

https://youtu.be/fFByKkGr5bE


I decided to repeat the experiment with my new LTD Stirling with the Regenerator, and using even more thicker insulation.

Also, due to a comment on one of the science forums, I did not insulate the bottom hot plate, as someone thought this might have increased the heat input which could possibly account for the results. This made some sense, though the bottom plate had been insulated from the start. The speed increase did not occur until the top plate was insulated. Regardless, to help rule that out, the bottom plate was left uninsulated.

https://youtu.be/zEqg1TgLqXI

Again the RPM increased. This time by quite a bit from 270 RPM without insulation to 295 RPM with insulation.

Insulation on the cold plate seems to make these engines run better, almost like putting an ice cube on top.

This engine is running again, on exactly 1 cup of boiled water. Same as before, without insulation.

Yesterday the thread was locked on another Science forum where I tried posting these experimental results. I've been a member of that forum for ten years.

https://www.scienceforums.net/forum/8-c ... l-physics/

They never objected to me talking about and theorizing about these ideas, when they could just dismiss it by throwing equations and formulas at me, but now they object to me posting videos of actual experiments?

[Tom Booth]

To possibly reduce heat flow across the cold side of the engine a bit more, I'm trying to make an epoxy piston, which apparently is about 150 times LESS heat conducting than graphite.

I haven't had any experience with this before, so any guidance how to make it work is welcome, or suggestions for some better non-heat conducting piston material

IMG_20200816_115527872_crop_42_resize_66.jpg (35.63 KiB) Viewed 11321 times

[Tom Booth]

This is kind of weird, I guess:

https://youtu.be/2b2dIR8Eql8

The engine keeps refreezing the ice???

Anyway, I swapped the epoxy piston in place of the graphite. Graphite has a conductivity of 168 ( W/(m K) whatever exactly that means ).

Epoxy, by comparison, has a conductivity of 0.35 that is 480 times LESS heat conducting than graphite.

The piston is really small, but it is the main focus of activity, as far as where the engine actually converts heat into mechanical motion or "work".

I've left the engine to run on ice, for five or ten minutes, then checked and it had refrozen what had started out as partly melted ice. I checked every five or ten minuets and each time the bottom of the engine had become frozen to the ice again. I say the ice started out "partly melted" because I ran the engine on hot water first, and it was still very warm when I put it on the ice and melted the surface of the ice.

This does not seem to be due to suction from being wet, or adhesion or some such "suction cup" type thing. The engine was really frozen solid onto the ice.

I first noticed this years ago in someone else's YouTube video, but I could never be sure, but it looked to me like this guys engine became frozen to the block of ice when he went to pick up the engine:

https://youtu.be/L6Jmdve1JK8

Notice how in the beginning the engine keeps sliding around on the wet ice. He keeps having to reposition the engine that is sliding around. The same thing with my engine, at first it was sliding around on the wet ice that was beginning to melt.

For now, I'm just going to attribute it to my cup of ice having been kept in the freezer for more than a week. It just got really really cold, and also because the ice is in a vacuum insulated cup. But has anyone ever seen ice refreeze by itself after it has already started to melt? I haven't.

It was 69 degrees Fahrenheit outside, but we had been using the oven in the kitchen so it was likely much warmer in the room.

I've left the engine to run overnight to see what happens. I wouldn't be too surprised if the ice still melts, even if the engine is somehow causing it to freeze, just because the insulation is probably letting heat through. I would be extremely surprised if the ice has not started to melt by tomorrow morning.

I'm still rather surprised that the engine became refrozen to the ice so many times, over and over. I had ice cream for desert after dinner and it was not that hard. The freezer does not seem unusually cold or anything. Also I've run these engines on ice several time before and this did not happen, or if it did, I didn't notice it.

But the piston is conducting nearly 500 times less heat than previously, so who knows. The epoxy piston might have something to do with it.

[Tom Booth]

According to the engineering toolbox:

https://www.engineeringtoolbox.com/ther ... d_429.html

Air has less thermal conductivity than pretty much anything. So, would that account for the engine apparently running faster/cooler, with styrofoam and/or fiberglass helping conduct heat away from the engine?

If that were the case, it doesn't say much for the insulation in the walls of my house.

Yet, air is listed as less heat conductive than either type of insulation.

About the only thing that insulates better than nothing (air) would be silica Aerogel, or a vacuum.

If that is actually the case, it kind of nullifies the experiment, if insulation actually increases heat conductivity.

[Tom Booth]

I think, (short of figuring out some means of creating a vacuum without any means of containment) I am going to stick by the results of my experiment, i.e. an LTD Stirling runs better/faster with the so-called "sink" or "cold source" insulated so virtually no heat escapes. (less anyway)

Because, though styrofoam is very very slightly more conductive than air:

Air: 0.026

Styrofoam: 0.033

Air above the engine is free to circulate, carrying away heat by not only conduction (direct contact) but also by convection (air circulation).

This is surely why it pays to insulate ones walls, and attic, because the insulation traps air preventing heat loss by convection.

It seems inconceivable and contrary to logic IMO to conclude that an LTD engine losses heat through the top of the engine much faster, (causing it to run much faster), when the top is entirely covered with styrofoam insulation.

I could be wrong, I suppose, but all I do know is that in my experiments the engine, siting on top of a cup of near boiling water, ran demonstrably and measurably faster with the pathway to the "sink" blocked by insulation.

When running on ice, the observation that partially melted ice re-freezes rather than melting faster, also seems to lend additional weight to the theory that a Stirling engine does not send heat to the sink at all, but may actually cool the so-called sink to the extent possible.

It should be noted that unrestricted (free to circulate) ambient air represents a virtually infinite reservoir of heat that is virtually impossible to cool measurably.

Correcting for a possible flaw in the experiment, someone suggested heat was mostly still escaping from the piston cylinder where a hole was cut out of the insulation allowing air to circulate in that critical area.

So I carefully insulated the piston cylinder as well.

https://youtu.be/Iq6snxiXbGg

The results were the same as before. With the sink insulated (so heat could not "flow through"), the engine ran considerably faster than without the insulation.

[Nobody]

I'm thinking of an experiment:
Insulate the top plate. Put the LTD Stirling Engine on the frozen cup of water. Get it running, as you have done previously. Once running well, and the top side sealed with insulation, put the whole thing in the freezer. Insulation, ice, engine, and all.

If the insulation is working, the Stirling should stay running forever, according to your earlier test.

If the insulation is conducting heat, the Stirling may run for a short period however then soon stop, as classical thermodynamics predicts.

[Tom Booth]

I'm thinking of an experiment:
Insulate the top plate. Put the LTD Stirling Engine on the frozen cup of water. Get it running, as you have done previously. Once running well, and the top side sealed with insulation, put the whole thing in the freezer. Insulation, ice, engine, and all.

If the insulation is working, the Stirling should stay running forever, according to your earlier test.

If the insulation is conducting heat, the Stirling may run for a short period however then soon stop, as classical thermodynamics predicts.

Some small amount of ambient heat could be stored in the insulation, but would soon be used up and converted to "work" and finally dissipated into the ice box due to friction and air resistance.

I'm not sure why "the Stirling should stay running forever", even with perfect insulation.

I think you may be confusing experiments running on ice, like this:

https://youtu.be/dQVRVL1OUBg

Where the top plate is (mostly) left exposed to ambient heat. There is a cup of ice buried inside the insulation in a thermos under the engine. The engine ran 33 hours with this set up.

Towards the end, after about 30 hours, I even added an old aluminum electrical box to try to draw down more heat.

This is that same experiment at 32 hours. The ice had still not melted completely and the engine kept running for another hour after shooting this video. Note the aluminum tower.

https://youtu.be/lFhUkzHRbWo

In the other experiments, running on cups of hot water, the top of the engine was insulated.

https://youtu.be/fFByKkGr5bE


Take note of the condensation on the bottom of the engine from the steam or water vapor from the hot water)

https://youtu.be/Iq6snxiXbGg

Now, I take responsibility as the source of any confusion, because while running the engine "on ice" I did place the insulation loosely on top also, for a while, just to see what would happen.

https://youtu.be/s4MzYMen2Ow

The engine continued running a surprisingly long time in this condition, but did, very gradually slow down and almost came to a complete stop, but before it did I removed the top piece of insulation to let more heat back in.

I did the same thing with the "control" just for consistency for the same amount of time. (about an hour):

https://youtu.be/3-DPAIlzDVc

I don't think the engine would run "forever" on any finite heat source, and the bit of heat stored in a few ounces of insulation is certainly not inexhaustible.

Now, running on a thoroughly insulated cup of ice, powered by ambient heat. The heat of the atmosphere, if it can be kept circulating around the top of the engine, is virtually inexhaustible, as long as the sun continues to warm the atmosphere each day.

One problem with my experiment with the engine running on ice was that there was very little air circulation and the exposed top of the engine was somewhat below the insulation. Next time, if I ran the experiment again, I would put some kind of fins, like fan blades on the flywheel to increase the circulation of the ambient air.

As it was, it was evident due to the appearance of condensation under the flywheel, that even the flat flywheel alone DID cause some circulation of air:

This video was taken 12 hours into the experiment running on ice:

https://youtu.be/-7zntz8kwIk


Again, condensation on the HOT (now ambient) side.

Note that the condensation is only appearing in a line underneath and parallel with the flywheel, presumably because that is where the rotation of the flywheel is pulling down some warm ambient air. It seems the engine may have been in part, running on the heat of condensation, similar to the steam condensing when running on hot water. As water vapor contacted the cold engine it releases heat, cools and condenses.

I may try your experiment idea anyway, just out of curiosity. If the engine continued running more than a minute or two in the freezer, I'd be very surprised, but who knows right? Nothing can be learned from NOT doing an experiment.

[Tom Booth]

The behavior of the magnetic Stirling engine with the acrylic body and top with the top "sink" side insulated with a silicon Aerogel blanket.

The Aerogel blanket is taped down to the top and on the sides to hold it in place and prevent the insulation from rubbing on the flywheel.

The first time I ran this magnetic engine this way the sides were covered with insulation also, so I couldn't film what was going on inside.

Later I ran the engine with the side insulation off, and noticed the behavior of the displacer was unusual. The engine running somewhat faster than it normally does, the displacer barely had time for the magnet to lift it off the bottom. That was with the engine running on continuous steam heat over actively boiling water.

This time however, I just used a cup of water heated up in the microwave.

I was a bit surprised to see nearly the same results. I had thought the effect was due to the VERY hot continuously boiling water, but apparently it was due more to just the insulation.

Generally any LTD engine I've tried this with (Insulating the "sink" or cold side) runs noticeably better, at a higher RPM with the cold side insulated.

https://youtu.be/i9nz0vt7eQA

By combining the slow motion function on my camera with the slow motion setting on the video editing app, I was able to get some extra slow, slow motion clips and put them together:

https://youtu.be/F8P_g8Vwoz0

[Tom Booth]

There was something I meant to film but forgot.

When a load is applied, like holding a sponge against the flywheel, the engine will then slow down and the displacer will have more time to be attracted to the magnet and so it will rise up higher and higher until it hits the ceiling, but by that time the engine is going so slow it's rather difficult to maintain the load on the engine without stopping it all together.

In general though, the engine will run at a slower speed and the displacer will rise up higher hitting the ceiling and making more noise when operating "normally" without insulation.

I couldn't say for sure, but I can't really say that the engine going slower and the displacer rising up higher let's in enough more heat to compensate for the load when it is applied, or the additional work involved in raising the displacer up further. I suspected that SHOULD be the case. The higher the displacer rises, the more heat introduced, more power...

The engine can also only go so slow before the magnetic piston and displacer actually get stuck together and the engine stops.

I get the impression that the displacer being pulled up higher by the magnet doesn't really introduce more heat in the process but just gives the engine more work to do lifting the displacer, but hard to tell really, just pressing a sponge against the flywheel by hand.

[Tom Booth]

There has been a repeated and ongoing debate on these pages for and against the virtues or lack thereof of ADIABATIC expansion.

I've been, more or less the sole advocate of the idea that work performed by the engine during adiabatic expansion results in the very rapid cooling that allows the piston to instantly return to Top Dead Center performing the compression stroke and completing the cycle of operation, rather than depending upon the inherently slow process of heat "rejection" by conduction.

To be fair, others have frome time to time chimed in or tentatively expressed the same or similar idea.

I was Just reviewing Carnot's and others writings for a post to be made on another thread, and happened across a remarkable passage written by the editor of the second edition. R. H. Thurston relevant to this subject.

The entire essay titled "THE WORK OF SADI CARNOT" is astonishing and well worth a thorough reading as it addresses directly many of the questions and debates that are continuing today on this forum. Unfortunately, or perhaps fortunately, long passages of quotations from Carnot himself are preserved in the original French and left untranslated, which makes reading difficult for me, but with the ease with which text can be translated today, it removes al possibility of coloration or bias on the part of the translator giving a more direct window into the thoughts and ideas of the original author, untarnished.


Referring of course to Carnot:

In the enunciation of the essential principles of
efficiency of the heat·engine, we find the proofs of
this same wonderful prescience. He asserts that,
for best effect: "(1) The temperature of the
working fluid must be raised to the highest degree
possible, in order to secure a commensurate range
of temperature; (2) The cooling must be carried
to the lowest point on the scale that may be found
practicable; (3) The passage of the fluid from the
upper to the lower limit of temperature must be
produced by expansion;" i.e., "it is necessary
that the cooling of the gas shall occur sponta·
neously by its rarefaction;" which is simply his
method of stating the now universally understood
principle that, for highest efficiency, the expansion
must be adiabatic, from a maximum to a mini-
mum temperature. He goes on to explain these
principles, and then says that the advantage of
high-pressure engines lies "

(passage from Carnot in French which unfortunately Google translate cannot decipher from the PDF)

" This principle, as a practical system of
operation, had already, as he tells us, been enunci-
ated by M. Clement, and had been practised, as
we well know, since the days of its originator,
Watt; but Carnot saw clearly the thermodynamic
principle which underlies it, and as clearly states
it, for the first time.

I don't expect the debate regarding adiabatic vs. isothermal to end there, but it is interesting to discover this apparent support for my "non sense" theories from unexpected quarters. Watts, Carnot, Clement and in fact the principle is stated to be back then in 1897 (the date of publication) to reiterate, a "now universally understood principle that, for highest efficiency, the expansion must be adiabatic, from a maximum to a minimum temperature"

I feel I could go around and post this on half a dozen other threads where this topic has come up, but I'll leave it there. I decided on this thread mostly because it is not just theoretical but there is the more recent experimental confirmations as well.

[Tom Booth]

I've been attempting to generate a translation by copying the passage in French into Google translate from various sources. I've managed to get some better results, though far from perfect, I think the sense of it comes through:

The French copy pasted in English characters from a PDF so not entirely accurate.

"essentiellement dans la
faculte de rendre utile vne plus grande chute de ca-
loriqne."

Googles "translation"

mainly in the
ability to make a greater drop in revenue useful
loriqne.

In context then, he is saying essentially that the virtue of high compression is that it facilitates greater adiabatic expansion with a subsequent "greater drop" in temperature.

This is, of course, another point that I have been trying to drive home here. High compression with rapid adiabatic expansion. Regardless of opinions and theories, that is what has been found to work in practice from Watts onward.

[Tom Booth]

I should have removed the hyphen:

the advantage of high-pressure engines lies ...

"mainly in the ability to make a greater drop in calories useful."

This is, of course, a fundamental principle in refrigeration and cryogenics and low temperature science for the purpose of liquefaction of gases. High compression followed by adiabatic expansion through an expansion engine or turbine, with work output. For the greatest possible conversion of heat into work.

Carnot did not actually discover the principle, it was already the practice since Watt invented the steam engine. Carnot just tried to explain the practice based on the Caloric theory of heat.

The physical fact that this works in practice is the bedrock. Caloric theory is obsolete. We need something better than the waterfall analogy, as it leads to errors and irreconcilable contradictions.

[Tom Booth]

As far as #2:

(2) The cooling must be carried
to the lowest point on the scale that may be found
practicable;

Personally, I think this is, well, maybe not exactly a mistake. What does "practicable" mean?

Also, the subject matter for the most part is the steam engine, so in all likelihood I think nobody in those days contemplated going below the freezing point for water.

But after repeated experiments and careful observation, I have an alternative theory to the primitive concept of heat "falling down" like water at a waterfall. Heat does not automatically travel in a straight line from a hot object to a cold in the same way that water falls straight down. Heat disperses outward in all directions.

We know however that heat only flows in any direction when there is a difference in temperature. Essentially that is the very definition of heat. A transfer of energy due to a difference in temperature.

As a reciprocating engine needs to transform or "use up" thermal energy leaving the working fluid in the cylinder in a low energy or "cold" state, what might be the best way to preserve the cold that results after an energy transformation from "heat" into "work" output?

Well, logically, by thermal matching. If the cold end or side of the heat engine, or the unheated side grows cold due to the conversion of heat into work, and that cold allows the rapid return to TDC then, if the engine is efficient enough to use a bit more heat than that being supplied, then it would need to be cooled below the temperature of the ambient surroundings.

This cold however is not a "sink" to take away excess heat. It is not to receive a "flow" of heat traveling through and exiting the engine, rather, the additional cold provides an equivalence.

That is, as the engine utilizes more and more heat it may begin to function as a refrigerator cooling the working fluid to a temperature below the ambient surroundings.

To preserve the efficiency, heating of the working fluid by those same ambient surroundings needs to be prevented. This can be accomplished by surrounding the cold side of the engine with an environment at a temperature equivalent to the temperature that the engine is able to reach by means of compression and expansion, and as we know from the field of cryogenics and gas liquefaction methodologies utilizing expansion engines, that can be pretty darn cold. Well below ambient

However this is not a result of the application of cold. That is, the engine does not automatically become more efficient the more it is externally cooled. This is a fallacy.

The engine must be engineered for such efficiency. Then it can take advantage of the.additional cold (thermal matching) provided. Where the temperatures are the same, there can be no "flow" of heat in either direction, into or out of the engine.

So, cooling the engine works due to this thermal matching or thermal equivalence, and can do no more good than what the engine could, in theory, do on its own, for example, by, instead of supplying cold for thermal matching, some "perfect" insulation were used.

Experimentally this has been shown to actually work, if the engine is sufficiently efficient to begin with. Insulating the cold side of the engine can increase power and increase RPM and torque as-if additional cold were supplied.

Now, that is not to suggest that an inherently inefficient engine, made out of copper for example, will not heat up the supplied cooling water. In such a case however the water heats up due to conduction through the engine body not through the working fluid.

[Fool]

Heat disperses outward in all directions.

Yes. I've been wanting to discuss that point for quite some time now.

Heat and gas flow are very closely related. Gas flows outward from higher pressure to lower pressure. Heat flows outward from higher temperature to lower temperature. They both are often called dispersion. Even if the pressure is the same all around a gas volume the gas will flow outward in all directions mixing with the like pressure. And the like pressure will flow inward mixing too.

Heat will flow outward even if surrounded by hotter, it is just that the heat flowing inward is greater. That gives the illusion, the observation that heat only flows from hot to cold. Maybe?

It takes thermal energy to have a high temperature. Called "internal energy". If there is a high enough energy level at a low enough pressure, all the contained mass is turned into a gas. Gas produces pressure. Without heat being put into a mass there would be zero pressure. There would only be zero gas, hence zero pressure, at zero Kelvin. Vapour pressure is never zero above zero Kelvin. Tiny, miniscule, and perhaps negligible, but a positive pressure.

I type too much. Going to sleep now, Zzzzzzzz.

[Tom Booth]

Heat disperses outward in all directions.

Yes. I've been wanting to discuss that point for quite some time now.

Heat and gas flow are very closely related. Gas flows outward from higher pressure to lower pressure. Heat flows outward from higher temperature to lower temperature. They both are often called dispersion. Even if the pressure is the same all around a gas volume the gas will flow outward in all directions mixing with the like pressure. And the like pressure will flow inward mixing too.

Heat will flow outward even if surrounded by hotter, it is just that the heat flowing inward is greater. That gives the illusion, the observation that heat only flows from hot to cold. Maybe?

It takes thermal energy to have a high temperature. Called "internal energy". If there is a high enough energy level at a low enough pressure, all the contained mass is turned into a gas. Gas produces pressure. Without heat being put into a mass there would be zero pressure. There would only be zero gas, hence zero pressure, at zero Kelvin. Vapour pressure is never zero above zero Kelvin. Tiny, miniscule, and perhaps negligible, but a positive pressure.

I type too much. Going to sleep now, Zzzzzzzz.

On an absolute scale, sure.

Most temperature scales have some zero point above the absolute zero of the Kelvin scale. Likewise with pressure.

What matters, I think in this general context is balance of energy. It is generally recognized that if the ∆T = 0 then there is no "flow" of heat between objects of two different temperatures, as both objects are the same temperature. Likewise in a 1 earth atmosphere environment, a pressure of 1 atm inside a container results in zero pressure differential. Nobody is saying there is not still pressure (1 atm).

If the air is sucked out of a container with a vacuum pump then the energy level inside the container, the "pressure" is below the 1 atm "baseline" or zero mark on most pressure gauges. This is quite often refered to as a "vacuum" or "negative pressure". though obviously relative and obviously, on an absolute scale, not negative but positive.

Conversion between different scales can lead to all sorts of misunderstandings and errors to be sure, but I think most people understand all this.