Heat Engines (Stirling & Nitinol)

[Tom Booth]

Hi Tom welcome to the forum and thanks for sharing all your amazing research it is definitely welcomed here!! Life is not a closed book but an infinitely open one of possibilities. I am very interesed in nitinol engines and want to experiment with this too at some point.

Again, my pleasure.

It is a refreshing change from my experiences "out there" on the science and physics forums where I often get dog piled by people insisting my idea, or even the clear results of an experimental demonstration are "impossible".

I had another idea just this morning.

There is relatively "new" research into solid state heat pumps using Nitinol. Generally labeled with the unfortunate term "elastocaloric" refrigeration, or heating and cooling.

A property of Nitinol is that it heats up when put under stress, by bending or stretching. Correspondingly it cools down when allowed to return to its original shape. What is used in this case is Nitinol with a higher nickel content or "super elastic" Nitinol (as opposed to "shape memory" Nitinol used for heat engines)

Nitinol heat pumps with a COP greater than most vapor compression type heat pumps (COP of 7) have already been developed.

What I had in mind is a "regenerative" Nitinol heat pump.

Super-elastic Nitinol is basically a kind of spring metal. Bend it and it springs back. What is unusual about Nitinol is that it also changes phase so when stretched or bent it releases quite a lot of heat as it changes phase,  and when allowed to spring back it absorbs heat.

But, it "wants" to spring back. 

In other words, like winding a clock, the energy you put into winding up the spring is returned as mechanical force when the spring unwinds.

So... Imagine you wind up a spring that gives off heat as it is wound up, but then produces refrigeration as it unwinds, but also producing mechanical force equal to the force used to wind it up as it absorbs heat.

This would be similar to regenerative breaking. Stopping your car by having the momentum wind up a big spring, then use the energy stored in the spring to get the car back up to speed.

So, for a regenerative Nitinol heat pump I came up with this basic design:

   

Sorry for the rather poor quality of the sketch. I haven't had my morning coffee yet.

Basically though, the Nitinol springs are at the end of rocker arms, that are like seesaws, pivoting in the center.

The arms slide up and down ramps on a circular band or runway.

So, hopefully, as can be seen in the drawing, as the seesaw is rotated the force required to stretch the springs as the seesaw-like bars go up the ramp on one side is balanced by the force of the springs contracting on the other side 

So basically this device would require almost no external power input, other than to overcome friction.

Of course the bars could be on rollers or other means can be used to reduce friction.

I'll include a few links for some additional info:

https://techxplore.com/news/2022-06-air-...nable.html

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9671324/



There are dozens more articles/pdf's and research papers. Most of which I haven't read myself yet.

As far as I am aware, this "regenerative" Nitinol heat pump concept is an original idea. The part about using a seesaw type rocker arm at least.

---

Also, I've only drawn a single "seesaw". The sketch is just to illustrate the basic concept of the "regenerative" "seesaw" like mechanism. In reality, there would, of course, be many more, arranged more or less like spokes on a wheel.

[Tom Booth]

The above posted video, I just noticed, has a somewhat similar cam/ramp arrangement, but only one sided. 

   

The arrangement is different, but if I'm not mistaken, should still have a "regenerative" effect as the Nitinol springs contract and theoretically at least, assist in the rotation by pulling the rider down the slope of the cam.

Now I'm not sure if seeing that video before helped to seed the idea I thought was entirely original.

Anyway, in this video, the advantages and disadvantages (mostly disadvantages) of a nitinol heat pump are covered briefly, dismissing a Nitinol heat pump as an option due to the difficulty in bending a Nitinol bar.

Not a valid argument for dismissing the concept as unworkable

First of all, more than likely very thin flexible Nitinol wire or springs would be used, not thick bars, which would be pretty useless for heat exchange, and he does not mention at all the potential for regenerative recovery as I go into here:



https://youtu.be/e8fDMKr77bA

[Tom Booth]

Seeing how a Nitinol wire or spring will leap out of a hot fluid with such apparent explosive force; example:



I woke up this morning with another Nitinol heat engine concept that I think should work.

I've only had opportunity to fool around with Nitinol for a few weeks now, but from what I've seen, doing a few experiments, it exhibits the same heat into work conversion cooling effect as an expanding gas in an expansion engine.

That is, when it does work, in the process of changing shape it cools down.

This leads to some surprising consequences.

Normally, if a metal is heated it will take a long time to cool down again. The same goes for a gas really.

But, if you heat a gas briefly, causing the gas to expand, then as it expands, if it is made to do work, but the heat is removed, it will cool back down instantly and contract again. (or be more easily compressible for those who don't believe gas molecules have mutual attractive force i.e. kinetic theory of gases).

I get some arguments from the "ideal gas law" and whatever crowd that such a thing is not actually possible, whatever.

Regardless, I see the same thing with Nitinol. If you heat it up, it will generally stay hot for a long time like any metal would, but if it does some "work" after or while heat is added, like leaping out of hot water, it will cool back down instantly.

Take a soft Nitinol wire and heat it and it will stiffen and be very difficult to bend until if eventually cools off again, but crumple it up and heat it suddenly in such a way that it has to do some "work" as it expands and it will become cold and flexible again instantly.

Heat (motion on a microscopic scale) converted into work (motion on a macroscopic level)

As heat is used to perform work to create a motion in an object the heat, in essence "disappears" or is converted. The result is instantaneous cooling.

OK, enough for theory, but I've done the experiment in the above video, tossing Nitinol wire into hot water and having it leap out because it straightens out and becomes rigid. Well, in doing work, it cools right back down again.

In order for the Nitinol to cool back down again instantly and be ready to repeat the process, the heat conversion into work needs to be total, or at least very close to 100% otherwise the Nitinol spring would expand and stay expanded and it would not be possible to immediately compress it once again. So, if my "theory" about heat being converted to work and "disappearing" instantaneously is not correct, this engine would not work, as it depends on that principle. 

Basically, for this engine to operate continuously it would have to violate the second law of thermodynamics as well as exceed Carnot efficiency.

Not a problem.

(Or, worst case scenario,  the engine would require a very long cycling time to allow time for the heated Nitinol to cool back down between dunks in hot water).

   


So, I'll call that Nitinol engine #2.

Now really, that drawing should have had at least two more cylinders to be balanced, or instead of cylinders: Nitinol pogo sticks, as really, the "cylinders" need not be sealed or tight fitting. A few guide rods should do.

The reddish fluid in the bottom could be anything. Hot water, hot oil, jello, whatever.

The Nitinol spring is compressed down into the hot liquid and naturally wants to leap out or straighten itself.

From what I've seen this can be as sudden, powerful and explosive as the ignition of a fuel in the cylinder of a gasoline engine. (See above video)

Eventually I intend to get around to building some proof of concept or prototype engines. 

When and if that happens I'll be starting new threads for each build in my workbench area.

The way this forum is arranged and organized is really tops, and much appreciated. Thank you!

[Jack]

If I understand the concept right, notinol is replacing the fluid? I mean the gas or air in a heat engine.

Does the energy it takes to fabricate notinol come into account somewhere?
Since the fluid is now a wear and tear item with limited amounts of cycles.
So the fabrication of nitinol is basically a way of saving energy. Or did I smoke a little much tonight?

[Tom Booth]

...
Since the fluid is now a wear and tear item with limited amounts of cycles....

Reportedly Nitinol "doesn't wear out". 

As a phase changing material, a combination of just two elements, that would be kind of like wearing out H2O by putting it through too many freeze/thaw cycles.



Watch at about 3:00 to 3:50 the more times it cycles the better it works. "It just keeps getting better and better". Also at 8:15~ "gets stronger with repetition".

[Tom Booth]

Another possibility for super strong but relatively inexpensive DIY Nitinol under consideration is to weave inexpensive Nitinol wire into bands or ribbons.

This seems to be a simple weave for making macrame wrist bands, belts and so forth that can incorporate virtually any number of individual strands to any with desired and without sharp bends or knots.



Of course, a high temperature (flexible at room temperature) Nitinol would be required (readily available at a modest price)  and would need to be "set" with heat treatment after weaving.

[Tom Booth]

Before making any attempt at making Nitinol cable or woven straps, I figured I'd try getting the hang of it using ordinary string.

Any kind of plastic lid with the middle cut out and some slits in the sides seems to work just fine, or even just cardboard.

Anyway, I think I've pretty much got the hang of it.

   

   

[Tom Booth]

Nitinol wire is pretty readily available with shape transition temperatures set between 80°C down to 0°C in 20° increments.

That is, 80, 60, 40, 20, 0 and I think below, but not useful for what I have in mind, probably, though, using a brine solution or some other type of antifreeze going lower could be useful.

Anyway, in theory at least, a Nitinol engine would take heat out of a fluid, such as water, that could be circulating down a trough of some sort.

So, let's say the water starts out 90°C goes through the engine with 80°C Nitinol, and is cooled to 70°C that 70°C fluid could then continue through another engine using 60°C Nitinol cooling the fluid to 50°C, pass that to an engine with 40°C Nitinol...

The engines could be coupled together on the same shaft to basically comprise "cylinders" of a single multi-stage engine.

Not so different from a multi-stage geothermal heat pump type power plant using different working fluids to extract as much energy as possible from a relatively low grade heat source .

How far could the cooling in such a cascading system be taken? At 0°C the fluid would be below ambient in many locations in summer time at least. Then the fluid could be reheated with ambient heat. The engine itself, however, would likely have to be contained within a refrigerated environment.

As the fluid piped to the engine is cooled by the engine in the process of energy extraction, it may be that little energy would be required in order to maintain such a refrigerated space

This could possibly be another way of implementing Tesla's "Self-Acting" ambient heat engine.

My impression, however, watching various videos of Nitinol engines in operation being driven by a hot water bath is that the water is cooled imperceptibly, if at all, but I don't really know.

Theoretically, the energy to run the engine comes from the hot water, so the water must cool down as the engine extracts energy.

Would the water cool down enough, about 20°C to make a second stage practically possible?

Of course Nitinol can be custom manufactured to work at virtually any temperature within the range of possible temperatures, but custom made Nitinol can be much much more expensive than the standard types available.

[Tom Booth]

Four years ago, I ran this experiment:

https://youtu.be/DmkVR7hF14Y



The ice cube took 4 hours and 17 minutes to melt while the engine was running.

Repeating the experiment with the engine not running at all, the ice melted in just under 4 hours.

This experiment was repeated several times and the ice always lasted longer when the engine was running.

Fairly recently I bought a couple new engines as kits. I have one assembled but still have the other one to put together yet. But just out of curiosity, last night I decided to run a similar experiment, but this time without insulation. I really don't have time to run more 5 hour long experiments.

I was just curious to see how quickly the ice would melt without insulation.

I used, instead of just one ice cube, a whole hand full of ice, about five or six ice cubes.

https://youtu.be/YXiCGg2YwuM



Mostly I just wanted to get a general idea of how long this new series of experiments would take if I didn't insulate the ice.

I was rather surprised at how quickly all the ice melted without the insulation.

Breaking that down,

With insulation 1 ice cube melted in 4 hours and 17 minutes.

Without insulation 5 or so ice cubes melted in 45 minutes.

So 45/5 = 9 minutes for 1 ice cube to melt, with no insulation.

60x4+17 = 257 minutes

That's 28.5x longer per ice cube insulated vs not. (9 goes into 257 28.5 times)

Not particularly meaningful as the engines were not identical. The ice came out of a different refrigerator than I had four years ago so conditions were not exactly the same

But, I just did not really expect to see that big of a difference.

Anyway, as soon as I get the other engine put together, I'll be running additional experiments to again test to see if the ice takes longer to melt when the engine is running. Without insulation in the way, it will be easier to keep track of what's going on.

Overall, this indicates to me that there is very little heat passing down through the engine into the ice and that most of the heat that is causing the ice to melt rapidly is coming from the surrounding ambient air, not through the engine.

Not much heat is going through the engine because the engine is converting the heat it takes in to mechanical motion, as a result, most of the heat going into the engine does not reach the ice.

That's the theory anyway, and the result predicted by Tesla.

This was not an actual experiment, but using just 1 ice cube without insulation, the experiments should take no more than 10 minutes or so (rather than nearly 5 hours).

[Tom Booth]

This evening, while just fooling around with my newest Stirling engine I bought for experimenting with, mainly because with the design of this engine, all the heat generated from friction is up on top, I noticed again an unusual phenomenon that I don't think is explainable by conventional heat engine theory.

Running the engine on ice, the engine gets adhered, stuck to, or seemingly gets  frozen onto the bottom of the engine.

https://youtu.be/GbKdxY_jb8k



Something similar happened a long time ago with another engine, but that time the ice was much better insulated and kept re-freezing (apparently anyway) over and over. I'd break the engine loose from the ice and a few minutes later it would be "stuck" fast again and would be difficult to pry loose.

https://youtu.be/2b2dIR8Eql8



This time to show that the ice is not merely adhearing due to being wet on a smooth surface, I try to show how hard the ice is stuck, apparently frozen fast to the engine, by turning the engine sideways. The ice does not simply slide off. It had to be forcibly broken loose by rapping it against the bowl.

Another observation is that the ice at no time adhered to the glass bowl. The ice could be stirred around freely in the bowl and was starting to melt even before I put the engine on top and started it running.

I've also seen the same thing, or what appears to be the ice re-freezing to the bottom of a Stirling engine: on other videos:

https://youtu.be/L6Jmdve1JK8

When the guy picks up the engine the big ice cube doesn't fall off.

Most people will say that a Stirling engine running on ice in this way operates by the heat flowing down through the engine from the relatively hot ambient air to the ice, but Tesla did not agree.

Tesla wrote in the year 1900 that heat is energy and only goes into the engine  where the heat, once inside is converted to other forms of energy, so "heat" does not pass through.

What Tesla wrote on the subject contradicted what Kelvin and others were saying at the time, and what is still generally believed today.

My experiments with Stirling engines however, appear to demonstrate that the various "fathers of thermodynamics" were wrong and Tesla was correct.

If heat was being transfered from the 72°F  ambient air, through the engine into the ice, I would not expect the ice to stay frozen to the bottom of the engine for so long or even re-freeze. If it were true that the heat is going right through the engine to the cold side, logically,  the ice, in contact with the engine would begin melting immediately.

This, and numerous other experiments seem to demonstrate that Tesla was correct all along and it is the modern teachings of thermodynamics that has it wrong.