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On the theory that a lot of heat input is needed but not a lot of heat rejection, I've come up with a new kind of heat input device.

I'd call it an accordion type "displacer" or perhaps "regenerator" but it is not really either. It doesn't displace air and does not really function as a regenerator. It's function is strictly heat input and increasing heat exchanger surface area without introducing "dead air space".

I had a similar idea ages ago, but back then there would have been a complementary cold side "accordion" for heat removal. That could be tried, but I no longer believe heat removal is necessary or desirable. The goal at any rate is complete heat CONVERSION, so that heat REMOVAL is unnecessary.

Anyway, this is the idea reduced to a sketch which should be pretty self explanatory.


The thickness of the "spot welds" is greatly exaggerated so as to make them clearly visible in the sketch. Ideally however, the thin metal plate surfaces should be in close contact when not expanded for maximum surface to surface heat exchange..

I forgot to add it to the drawing, but probably there should also be a top plate made of some non heat conducting or insulating material to isolate the "accordion" when heat input is not needed.

This heat input device should probably also be controlled or lifted by means of a scotch yoke type mechanism with dwell, as illustrated in this video:.

https://youtu.be/3SCbTB50csM?si=uQ750DUszVZj3jnH

Two reasons for the scotch yoke with dwell, or some similar mechanism.

The dwell would be desirable for allowing the stack of plates to remain in close contact for a period of time long enough to actually take in heat.

Secondly, the heat input should be multiplied 10 times or more over a conventional "hot plate" heat exchanger. The scotch yoke would allow the heat input phase to be sufficiently brief at TDC

The plates should, of course be thin and flexible so they can be easily expanded without resistance and probably perforated to facilitate rapid and relatively unrestricted air flow through the stack.

Likely timing of the "lift" of this heat input device should be a quick rise and fall which should commence perhaps 20° BTDC and be completed (the accordion back down or closed) at or soon after TDC.

This timing would be similar to the ignition timing in an internal combustion engine, providing a more concentrated and "explosive" heat input than the conventional Stirling engine with sinusoidal displacer.

Possibly graphite sheets might have better heat transfer and conductivity than metal, be more flexible and withstand higher temperatures: maybe not. (Can take 3000° in inert gas).

Maybe used between metal sheets?

https://youtu.be/ZAEhyY1_czM?si=CKRzBUgQF2IK07nv

https://youtu.be/f_TIXwAoSiw?si=yYa5J2S2n8aAvuM3

It appears I briefly floated this idea several years ago, the later part of this post after considerable rambling on some other topic:

viewtopic.php?f=1&t=2668#p12874

I posted a couple alternative potential accordion styles or types there:

These paper seed starting trays, for example. Something similar could be constructed out of foil disks:


https://youtu.be/Lvaw3H7yoGQ?si=kJuty2WyYyfO3Z1X


Or these honeycomb type decorations


https://youtu.be/G-hUYBgvBSA?si=j9epm-llxiV33-zr


Something more like a stack of spiral planar springs might work also.

Seems this would be pretty effective Tom. But my thoughts and prayers go out to the guy tasked with making one. Big industry could definitely make it happen but might be tough in the garage.

VincentG wrote: ↑Tue Sep 12, 2023 8:03 pm Seems this would be pretty effective Tom. But my thoughts and prayers go out to the guy tasked with making one. Big industry could definitely make it happen but might be tough in the garage.

Don't know why.

I just made this Origami slinky thing in a few minutes out of a strip of aluminum foil


https://youtu.be/G_kgUccXs_w?si=vPd3rdQTWDcmU8qF


Using this method, then trimmed off the corners


https://youtu.be/tuwZDmV4QjM?si=SUlA-sfvGXnhFsCA


There is a cylindrical origami pattern that looks interesting and potentially easy to make.

https://youtube.com/shorts/JpAeP18mCq8? ... R5bbIobJyM

https://youtu.be/ar7dMtsA-dY?si=MP4dlLxAbY1NWMf7

Something like this for an "accordion" style displacer would probably be much easier and possibly even more effective:


It could be made out of something as simple as some coffee can lids, for a small LTD type engine.

The spacing between the plates could be kept to a very close tolerance, like 0.7 mm (probably want a little less air flow restriction than a Tesla turbine 0.5 mm)

The plates could be easily stacked, more added or removed, the spacing adjusted etc. just by bending over the tabs.

Theoretically, just one additional plate could quadrouple the effective heat input/surface area.

VincentG, maybe incorporate your spring for the dwell in the upper plate as you posted earlier:

viewtopic.php?f=1&t=5516

And some perforations to reduce air resistance.

There should be some advantage in having seperated rigid plates held together loosely with tabs rather than needing flexible plates that are either bent from a single sheet or welded.

The seperated plates would not need to flex or bend so probably less losses.

The flat rigid plate idea seems much more practical. They should pick up heat well when they flatten out on each other. I may borrow this idea in the future if that's ok Tom.

I've recently discovered that graphene sheets are readily available at a reasonable cost. They would work exceptionally well for this, with a thermal conductivity orders of magnitude above even copper.

One thing that looks like a possible draw ack with graphene, depending on the application, the heat tolerance in an oxygen environment seems rather limited.

With tabs, there could be recesses that would still allow the plates to make full contact.

Again, depending on the application, the idea of multiple plates with "dwell" would be, less need for very rapid, near instantaneous heat exchange.

I'm also not sure about the heat retention properties.

Stainless Steel for example, makes a good regenerator material because it has a balance of heat retention and heat dissipation and is actually a rather poor conductor.

In other words, graphene might actually be too good of a conductor, drawing heat instantaneously through towards the cold side and releasing it in a way that might be difficult to control, or insulate.

Even my little model engines often get red hot just from a propane torch, and I'm also leaning towards hydrogen fuel, which burns even hotter which kind of rules our graphene as it would degrade at such high temperatures, except maybe in an inert gas environment.

It's getting a little too far outside my DIY, homestead energy comfort zone.

Also, if I post a thought on the forum, it's intended for sharing. I'm more than thrilled when anyone picks up and goes with something. Unfortunately that usually doesn't happen for ten years or more.

Anyway, I'm in no way saying graphene is "bad" or possibly not the way to go. In many ways it seems ideal, and may very well be. But for some applications, something else might work better.

It takes direct testing/experimenting to be sure.

I like the idea of something like a stack of tungsten plates glowing red hot, so I was disappointed to read that graphene could only withstand moderately high temperatures.

At least I can get a tin can lid red hot without worrying and it doesn't cost anything.

Also, though graphene conducts heat faster than copper heat radiates at the speed of light.

I was not aware of those drawbacks of graphene. But lately I'm stuck in the lower Tmax range of under 300 degrees Fahrenheit where it would still work well. Should be easy enough to work up a quick prototype of this style plate stack with either material.

Since it is oxygen that limits the temperature, maybe if the graphene were coated with something to keep the air from contacting it directly. Could it be electroplated?

If oxygen can't get to it it could take extremely high temperatures.

I've found a few articles that seem to suggest electroplating graphene with a metal could be done though, for different reasons.

One here for example using copper:

https://pubs.aip.org/aip/apl/article-ab ... ted-copper

Something very similar to Stirling Works spiral displacer innovation could be a good solution for what I was attempting to accomplish here.

Not exactly an accordion, but a simple means of accomplishing the objective of regulating the heat input effectively.


https://youtu.be/knhXOnILotk?si=Q9GjTwI71T-MfGdm


I would, of course, though, only use something like this on the hot, heat input side.

Stirling engines have no mass flow. The only thing they take in is ENERGY which is CONVERTED so there is really nothing to "exhaust". No need to throw away or "exhaust" energy.

Such a spiral displacer could be easily created by 3D printing, or simply cutting a spiral in a cardboard (or other suitable material) disk with a razor blade.

Similar to your displacer innovation as well VincentG, though the spiral encompasses the entire displacer rather than just the central region and serves a different purpose, or is intended to solve a different problem.

My application is yet again a further departure and modification.

Some ideas for the spiral displacer.

A large dome-like piston similar to the Sun Pulse:

https://youtu.be/v_e0981CLDI?si=exre6GD3QDKaMSc0

But with a spiral, magnetic displacer.

Crank:


Or "free piston"


When the displacer lifts and the air heats and expands it passes through impacting the piston across the entire surface:


To give the illustration a bit more meat, what I had in mind with this drawing is basically a small BETA type LTD, but instead of the potentially difficult to engineer displacer connecting rod passing through the power piston with the inherent seal issues and what not, the displacer is actuated magnetically.

The potential for minimal dead air space and relatively high compression ratio is similar to that of a Beta without the complicated linkage.

Maybe the entire engine could double as linear generator? (Note electric coils on the sides of the last drawing and embedded magnets)

For the piston, I had in mind that dense blue styrofoam board.

I've been really eyeing the Sunpulse lately as the best basic layout for a large engine. It would lend itself well to Tom's idea of no cold side. I do like the spiral displacer layout but I see it as a materials problem again, trying to keep the top side of the displacer cool enough to not hinder the return stroke. Making it thicker by adding insulation on top seems appropriate.