Tesla's Ambient Heat Engine revisted

[matt brown]

Tom - probably best to start a new thread with 2024 in title. The thread drift in this forum makes finding previous comments a challenge.

BTW my original intent on this thread was that Tesla's cold hole appears valid on paper, but achieving such has an obscure issue where the Carnot 'tax' is double his normal tax. However, this downside is offset by the upside of free ambient energy.

[matt brown]

Over the years, I've often heard of Tesla's ambient heat engine (cold hole) and blown it off as just another one of his wacky schemes (he had many). However, a recent post made me reconsider the possibility.

Which post, Matt?

Vincent - I just saw this, I borrowed your planet Bob analogy somewhat...

http://www.stirlingengineforum.com/view ... 279#p22279

[matt brown]

The average bulk temperature is what the engine reacts to. Any pressure sensors will react similarly to the engine, so it is a fair representation to use for analysis. The sensor will react as fast or faster than the engine.

The theoretical pressure change due to volumetric change in an unheated engine turned over by hand is easy to calculate and plot. That could then be used to calibrate a pressure sensor set into the engine. Then if pressure is sampled at a high rate in the running engine with heat applied, the volumetric change due to mechanical compression could be subtracted from the data obtained. We could then derive the difference between Th and Tc from the max and min pressures obtained.

I've been looking for an affordable datalogging pressure sensor online - no luck yet... Any suggestions or links?

Stroller, check out this recent post of mine on another thread

http://www.stirlingengineforum.com/view ... 072#p22072

You don't need any fancy test gear to chase down LTD since the ambient compression process tells us everything we need to know. In post above, I use typical Tr=temperature ratio and Vr=volume ratio, and when pts 2 and 4 are an ambient isobar then Tr=Vr. However, when Tr>Vr or Tr<Vr then pts 2 and 4 are not an isobar. This proves the Tr=Vr relationship for ambient compression process, but this is an ideal relationship where out-of-phase dynamics will alter values, somewhat (not much at meager LTD values). The point here is that common LTD is a vacuum engine, just different from common flame eater.

It all boils down to understanding the difference between vacuum schemes vs atmos schemes vs compression schemes. Modern thermodynamics didn't exist until after Otto got lucky with 'his' compression cycle. Prior the Otto cycle, any compression process was considered major Wneg taxing meager Wpos. The Otto cycle proved that compression could easily increase output, but the headbanger at the time was that it also could increase efficiency, and this took a long time to sort out...

[Tom Booth]

...
BTW my original intent on this thread was that Tesla's cold hole appears valid on paper.

I've got a few problems with it.

Tesla wrote:

the virtue of the principle I have discovered resides wholly in the conversion of the energy on the downward flow."...

In other words. His thinking was still rooted in caloric theory. That heat "flows down" the temperature scale with some gravitational-like force or power like a river and the energy of this "flow" can be easily harvest.

A heat engine simply does not work that way. It isn't a "water wheel" kind of device, it's more like an oscillator.

There is no heat flowing down into the "cold hole". A heat engine, (or Stirling engine anyway, don't know about all types of heat engines) cycle starts at the BOTTOM of the "cold hole" not the top.

The real deep down core of his argument, or idea though, that heat is energy that can be converted seems valid, but there is no "downward flow". Not with any independent driving force behind it anyway.

Expansion is the driving force and that is a bottom up operation that starts with cold.

Really, it's not entirely one or the other. More like a seesaw. In some cases a Stirling is literally a seesaw:

https://youtu.be/VffvNIo-QP4

But I'm talking in principle. It oscillates between higher outside vs inside pressure continually, an oscillation rather than a directional flow.

I'm not certain this is fatal to his core insight that heat is energy that can be converted so that the imbalance that set the engine in motion is not destroyed by "filling up the cold hole" with "waste heat".

A bottom up addition of heat however is a somewhat different engineering problem than a "downward flow" type intercept.

but achieving such has an obscure issue where the Carnot 'tax' is double his normal tax. However, this downside is offset by the upside of free ambient energy.

I don't believe in any "Carnot Tax", which I think is also based on the fallacious Caloric theory, so 2 X 0 = 0.

I'll bite though, against my better judgement. What is this "obscure issue"?

[Tom Booth]

...The Otto cycle proved that compression could easily increase output, but the headbanger at the time was that it also could increase efficiency, and this took a long time to sort out...

So what's the answer? How was it sorted out? How does compression increase efficiency?

The best explanation I've heard so far is that by compressing the gas into a very small volume, and only then adding heat, the resulting expansion becomes that much more explosive.

I think there is a little more to it than that.

I think by concentrating the expansive force into one brief moment primarily right at TDC the later part of the expansion and energy extraction is mostly, for lack of a better term, adiabatic. By that I mean less heat and more "work" crosses the system boundary. So your work output has the side benefit of "free" cooling. A useful reduction in the internal energy of the working fluid that makes subsequent compression much easier.

[MikeB]

Atmospheric pressure across the entire globe varies very little from 14.7 psi

Good point. However that is exactly why we have wind - air mass "moving itself" in order to equalise _pressure_ differences caused (largely/entirely?) by temperature differences.

Which rather brings me back to the initial question - how fast does temperature and pressure equalise within the vastly smaller, largely confined spaces of a hot-air engine?
Where the earth is concerned, the distances involved means that the speed of sound is very pertinent, however on a global scale the atmosphere is entirely uncontained by pipes and displacers and regenerators, and yet predicting air movement is still a massively complex problem.

[Tom Booth]

Atmospheric pressure across the entire globe varies very little from 14.7 psi

Good point. However that is exactly why we have wind - air mass "moving itself" in order to equalise _pressure_ differences caused (largely/entirely?) by temperature differences.

Which rather brings me back to the initial question - how fast does temperature and pressure equalise within the vastly smaller, largely confined spaces of a hot-air engine?
Where the earth is concerned, the distances involved means that the speed of sound is very pertinent, however on a global scale the atmosphere is entirely uncontained by pipes and displacers and regenerators, and yet predicting air movement is still a massively complex problem.

I think the difference in temperature in a Stirling engine is largely time dependent. (What part of the cycle).

Heat is introduced. Temperature increases near TDC.

Gas expands, energy is transfered to the piston, work is done. Gas temperature drops around BDC.

Heat is added, increasing temperature. Work is taken out, decreasing temperature

At different TIMES. Different periods in the cycle.

Just as an illustration, how much "mixing" is there between the warm air at midday and cool air at midnight?

There is a time separation rather than a separation by physical barrier.

At the TIME when the gas is compressed and heated the displacer shifts the location of the gas. At the TIME when the gas is expanded and cold, the displacer again shifts the location.

[Tom Booth]

Wow, I just checked. It looks like the two Kontax engines will be delivered today!

[MikeB]

I think the difference in temperature in a Stirling engine is largely time dependent. (What part of the cycle).

I'm quite happy to accept that that is true, but only if someone can point me at some science that says how fast temperature equalises / quantifies a temperature gradient in the working fluid.

It seems perfectly reasonable to model the fluid in one of our engines as having a nice steady temp gradient between the two ends, just like with a solid material, yet it also seems perfectly reasonable to assume that temperature and pressure equalise themselves at the speed of sound - and we all seem pretty content to assume that pressure does this, even if temp doesn't.

But those are completely contradictory theories/models.

[Tom Booth]

Not sure what your saying, but my point was basically that the gas is compressed making it hotter. Expanded making it colder.

Work is taken out making it colder, work put in making it hotter.

Even without a displacer, these events take place at different times changing the state of the working fluid over time. It is impossible to "equalize" the temperature of the expanded cold gas with the compressed hot gas. It is the same gas either expanded or compressed, heated or cooled at different times.

[Tom Booth]

Just arrived:

Crop_20240513_144629_9282.jpg (71.16 KiB) Viewed 2697 times

[Tom Booth]

As far as I can tell, this video appears to be legitimate.

https://youtu.be/g5uFyf9_1GM

At least the simple refrigeration system appears to be constructed using conventional refrigeration system principles.

The question is, could the cold produced be used to operate a Stirling engine on the surrounding ambient heat and could that engine produce enough output to run the small 12 volt pump/compressor and fan.

The setup shown is not ideal. For example, the fan under the cold evaporator tubing is really counter productive, like opening your ice box, and putting a fan inside with the door open and circulating hot ambient air. Not sure why he would do that other than the visual effect of rapid frost formation. The cold coil/tubing should really be inside an insulated box.

(Well, he's using it as an "air conditioner". A different application. So it makes sense. However, the other fan is blowing heat, so actually useless)

If, as I've been asserting, a Stirling engine consumes or "destroys" the heat entering into it, little heat would get to the little freezer box. A Stirling engine running a small 12 volt generator could store excess energy in a battery to run the little refrigerator when necessary. Theoretically, that might not have to be very often since the engine is operating not from the ice so not "using up" the cold, but from the limitless supply of surrounding ambient heat, "destroying" or using up the heat, in actuality helping maintain the cold, preventing heat from getting to it by converting the heat into work.

Another point to keep in mind. The "freezer" is also generating heat at the other coil, which, while being used to cool the engine, this heat need not go to waste but could give the Stirling engine an extra boost of additional above ambient heat while operating the little freezer.

[Tom Booth]

The power supply to run that little freezer was allegedly, just 2A

Compress_20240514_164949_9056.jpg (16.15 KiB) Viewed 2677 times

24 watts for an alleged nearly instant -30°C in open air.

I guess I'm probably wrong, but that doesn't seem like that high of a bar for a small Stirling engine.

4 watts from this setup:

https://youtu.be/s2I9OoZs4Wc

But let's say the cooler only needs to run one or two minutes every 10 minutes.

Probably more efficient if it could run the compressor pump directly rather than generate and store electricity to run a motor to run a compressor.

[Tom Booth]

-32°C with a 9 volt battery?

https://youtu.be/26uq_qHKRjU

I think I'd have to see it to believe it.

The guy does seem to understand air conditioning systems though.

[Fool]

Nothing I've seen is more obviously faked than those garbage cooler unit videos. Nice try. There are scads of them too. The amazing thing is how many people those fraudulent videos seem to fool. Take a look at how uneven the coils develop frost and location of first frost. How little an amount "refrigerant" butane is used. How they expect us to believe it stays in there with such loose connections. Read the comments. The only thing worse is the number of "views". Perhaps one day people will get tired of seeing the same crap over and over by the same sinister people.

Watch the end of the following video, especially the last 5%. LOL

https://m.youtube.com/watch?v=Jb_bD4xTnwk