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I've been fascinated with liquid piston Stirling engines. They have perfect, nearly frictionless power piston seals, seem to be able to operate with very little heat input.

But the problem is, how exactly might someone get actual power out of the liquid piston?

Well, here are a couple of videos that have me groping towards some kind of solution, though I'm not entirely sure what exactly yet.

Possibly something to experiment with anyway.


https://youtu.be/tQ_KVvaErcQ


Not sure what exactly is going on in the next video, or if it is actually real but, putting 2 & 2 together, combined with the first video, there are various elements of some kind of idea.


https://youtu.be/LawWNFsbLy0

It appears that by stroking the magnet on the ferrofluid, the result is supposed to be a liquid magnet, or at least some kind of magnetically charged ferrofluid.

That is the part I'm skeptical about. Can ferrofluid be permanently magnetized?

If so, then just float some on a liquid piston and make it pass through a coil surrounding the power cylinder and you could get alternating current. Add a bridge rectifier for DC if necessary for whatever the end use might be.

I guess I actually had some such idea prior to searching youtube for videos in an effort to asses the feasibility of some such thing.

Maybe just put a neodymium magnet on a cork. I'm pretty sure at least that would work, but an actual magnetic ferrofluid liquid piston would likely be more efficient, in theory, maybe, sort of, I think, possibly.

It would be more cool than a magnetic boey bobbing around. Such a cork would likely cause friction, get jammed in the tube, and it could not have as close contact with the coil.

But if the coil could actually just be submerged in the fluid as it rises and falls, that might be something.

Because, in the presence of an actual magnet, the ferrofluid becomes, itself, magnetized, and to a degree, kind of "solid"

Possibly a neodymium magnet coated with ferrofluid could be itself used as a liquid piston, or floated on, or contained within a liquid piston, if it becomes buoyant.

Note for example how the strongly magnetized ferrofluid causes a coin to become buoyant when dropped onto it.

And note too, for example the ferrofluid coated magnet floating above the superconductor. The superconductor is not necessary, but a ferrofluid coated magnet could make a piston having a perfect, nearly frictionless seal.


https://youtu.be/aQPh6paW_js


Amazing frictionlessness demonstrated:


https://youtu.be/bkRxYf9oETo

Well, I guess it works, the ferrofluid coated magnetic piston.

This video is 13 years old:


https://youtu.be/21WzdjqAG0s


But, a perfect, frictionless seal is one thing.

Let's wrap some could around that to make a linear generator ?

Could this be better than flexure bearings ?

So, here is a concept, that might be doable:


The ferrofluid, being an oil suspension, should float on water, which, maybe, would allow the ferrofluid coated magnet to "float" as well.

The coil could be submerged between the magnet and the cylinder wall.

The weird repellent properties of the magnetized ferrofluid would, theoretically, keep the magnetic piston centered within the coil.

I show a single turn coil for clarity of illustration, but certainly a coil with multiple turns would work better, I guess, but more clearance between the magnet and cylinder wall would be necessary, the larger the coil.

I can't imagine any more efficient generator than to have a liquid magnet actually flowing through a coil.

In theory anyway

But, apparently ferrofluid does not float in water (?)

I guess the iron component increases the density, or, not all ferrofluid is in an oil suspension (?)

Not sure:

https://youtu.be/gVMtyThvPAo


At any rate, I can't find any examples of ferrofluid floating in water, with or without a magnet, so..

Maybe the ferrofluid coated magnet driven by the fluidyne Stirling engine could just, so to speak, sink to the bottom of the loop or tube. Or some other arangement.

Maybe just such a piston in a more conventional free piston or thermal lag, or ordinary Ringbom would work just as well, without the need for any water to float the piston on. It would still have the advantages of the fluidyne, liquid piston component, but more consolidated

One good thing, discussed in one of the previous videos as a problem is, once the ferrofluid is coating the magnet, it is just about impossible to get off, but in this application, it needs to stay on and not drip of run or vibrate or float off, so that is a good thing.

It might be worth experimenting with this inexpensive DIY ferrofluid. (Or ferro-paste ).

Try different oils and surfactants to produce something that with the right consistency that floats on water.


https://youtu.be/CWH9C__jn2w

For high temperature engines, flammability could be an issue.


https://youtu.be/Fw-PemqRN3A

Maybe not so much if submerged in water.

Just got this ferrofluid kit in the mailbox yesterday:
Not sure when I'll get around to experimenting with it, but it will be on hand at least, anyway.

I'm not sure if this will work for what I had in mind, but might be worth a try anyway.

Several sites recommend reducing the ferrofluid by heating it at 100°C until it thickens, then suspend it in salt water, mostly to help prevent it from sticking to, and staining the glass. Other treatments, like treating the glass bottle with Rain-X etc.

But what I'm interested is how to make it float, which is something others want to prevent, so, do the opposite?

https://www.google.com/amp/s/www.instru ... _page=true


Making the water extra dense with dissolved salt should help, but instead of reducing the ferrofluid, maybe thin it with a little more of some light weight hydrocarbon ?

Or maybe heat it to drive off the kerosene and then substitute some lighter weight oil of one sort of another.

This all may be futile if the magnet itself is too heavy I suppose.

Anyway, it seems there is at least the possibility of unadulterated ferrofluid floating in salt water.

I had considered that a ferrofluid piston in a Stirling engine could get messy. Maybe the ferrofluid would splash out of the cylinder, of blow out from pressure, when the engine got going, but apparently not.

I found this old video from 13 years ago. It looks like the engine is running pretty good and not making a big mess spraying ferrofluid everywhere.

https://youtu.be/3Uh0pBJ5QW0

According to this paper, a ferrofluid seal can work up to 1.6 MPa, which is over 200 psi. That's quite a lot of pressure, though this is a little bit of a different application.

https://www.sciencedirect.com/science/a ... 4709002143

This is a similar concept:

https://youtu.be/dmvlI7lsv80

It isn't really clear in the video what's going on, but from the comments:

The apparatus is suspended or resting on a cushion of ferrofluid which is held in place by magnets, making a near frictionless thrust bearing of sorts.

In other words the whole thing is held up by ferrofluid coated magnets attached to the bottom of the shaft.

So, the rotating ferrofluid coated magnets act as both frictionless bearing support AND generator.

This is a rotary generator and I'm working on a linear generator but the principle is pretty much the same.

Though, the ferrofluid coated piston would serve three purposes. Frictionless seal, power piston and generator all in one.

I was thinking, an advantage of this might be that the cylinder, probably need not be a material that can withstand a lot of heat from friction, as there really would be no heat generated from friction.

In other words, the power cylinder could just be some PVC pipe

This could allow the construction of a very inexpensive and easy to put together Stirling engine/generator.