Stirlingengineforum.com

On the other hand, maybe having "nowhere to go" isn't so much of a dilemma.

Basically you've got something like a pulse jet engine with air amplification that unfortunately dead ends at a reciprocating piston.

Maybe just get rid of the piston.

Something like this:

Might have to open up the other end

While browsing around looking for info on pulse jets and stuff, I came across this.

Not particularly relevant I guess but pretty crazy.

https://youtu.be/H26f8uGP20Y?si=zOgqiYNotRryN76K

Is there such a thing as an EXTERNAL combustion Pulse Jet ?

One thing though, the illustrations in the above videos about the venturi effect are not entirely accurate.

Once the stream goes through the narrow passage and reaches high velocity it does not just drop back down to low velocity the moment that it exits the other end, the high velocity jet stays "laminar".

Of course, this likely depends on the nozzle dimensions and profile.

Here is a more realistic look at what happens:

https://youtu.be/mQ50xamE-O8?si=pBc8GFOWsI0325lo


This topic has also come up before in connection with scaling up a lamina flow engine.

That was years ago. I had posted this illustration of what would likely be seen if the air in the power cylinder could be made visible during the power/expansion stroke.


https://www.stirlingengineforum.com/vie ... 105#p12927

Now, I've seen various conflicting or alternative theories as to why this narrow orifice is there in the first place, it's function or purpose and the question; is it actually necessary or helpful?

It seems to be absent in the "thermal lag" patent.

The "thermal lag" theory I think is that it introduces a delay or "lag" in the thermal heat transfer in some way that has never been clear to me.

I look at it as a means of "organizing" the gas molecules into a laser-like high velocity HIGH KINETIC ENERGY stream for maximizing impact on the piston.

It effectively CONVERTS disorganized heat and pressure into highly organized kinetic energy.

Therefore, it produces "Negative Entropy".

Sure, we know, supposedly:

Negative entropy means a decrease in entropy when a system moves from a more disordered state to an ordered state. This is not possible spontaneously

https://psiberg.com/negative-entropy/

Entropy:

Just another crap theory to strangle creativity and innovation IMO, but if someone want's to actually believe in entropy, I might ask, what is "spontaneous" about a highly precision engineered heat engine?

"Negative Entropy" is not impossible it just requires energy, but supposedly when entropy decreases, as it appears to do through air flow through a narrow orifice in a heat engine, entropy must increase somewhere else in the universe.

Sigh,...

How do you suppose this kind of nonsense manages to proliferate through the centuries?

Suppose you have wind blowing through a gorge between two mountains? Is that "spontaneous"?

There is so much pure philosophical nonsense and mumbo jumbo surrounding the whole "second law" business, there really is no making any sense of it all. Best to just ignore it IMO.

If sending the air through an orifice works to increase engine power, well, let's use it. Entropy be damned, there's no such thing as far as I'm concerned. No such force or "Law" of entropy in the universe.

The Second Law of Thermodynamics states that the entropy of a closed system will never decrease

OK so is a thermoacoustic engine a "closed system"?

A closed system is a natural physical system that does not allow transfer of matter in or out of the system, although – in the contexts of physics, chemistry, engineering, etc. – the transfer of energy (e.g. as work or heat) is allowed.

https://en.m.wikipedia.org/wiki/Closed_system

Well... looks like, according to that definition, a thermoacoustic engine IS a ""closed system".

There is no transfer of matter, just transfers of heat and/or work, but it does say:

"A closed system is a natural physical system...."

Is a Stirling heat engine "natural"?

Is an engineer "natural"?

Is the venturi effect "natural"?

Are the products of human intelligence "natural"?

All this Entropy crap just boils down to philosophy. It has about as much scientific and/or engineering values as...

Well, I can't really come up with a good analogy that is not potentially offensive to someone.

Let's just say, it has no scientific or engineering value whatsoever.

'You should call it entropy,... no one knows what entropy really is, so in a debate you will always have the advantage.” - Von Neumann

The basic idea is to put some holes behind the back "wall" of the "plug" where I've written "low pressure" in the above illustration. Theoretically this should entrain more air during expansion of the gas through the orifice making the jet, and therefore the power stroke more forceful.

This is rather astonishing:


I did a search with the words: [ pulse jet air entrainment. ] in the search box and up popped this NASA research paper from 1978.


The above image is from that paper, and basically identical to the idea I had in mind for boosting the power in a laminar flow engine, which I'm now theorizing operates on a principle very similar to a pulse jet.

https://ntrs.nasa.gov/api/citations/198 ... 001885.pdf

Actually, the nozzle design I have in mind is a little bit different but conceptually at least it's very much in the same ballpark.

While watching this video just now

https://youtu.be/jAJld70e6XU?si=YrjMnC8QAtItMDLa

My thoughts wandered as the video continued playing, the link to the video was one I had posted on the linear alternator thread here:

viewtopic.php?f=1&t=1585&p=18015#p18020

Thinking about wind, as the TNT guy was talking a lot on all the various kinds of wind generators don't ask me why exactly, I don't know, but the image of the waves on a flag in the wind appeared in my mind and I started thinking about possible ways to harness such wind/wave energy:

After a search, this video shows a good wave formation of a flag in the wind, watch especially the lower left hand quadrant.

https://youtu.be/M3GzOEHIEMg?si=K1AyQGCP9o5J1vQp

In my "waking dream" though I saw the wave formation from a different angle as if I were standing behind the flag and watching the waves traveling away from me, and I was imagining how the air was pushing these waves from side to side, or really simultaneously on both sides.

Then suddenly the image of the flag waving was replaced by the drawing I made recently of a possible duel vane rotary Stirling engine:


Not exactly a NEW idea but this one seems to keep recurring.

Imagine taking a flag waving in the wind, bending it around into a disk so the front edge attaches to the back and the waves continue round and round this disk, the "flag" stripes oriented. So they form wavy circles kind of like the groves in an old warped vinyl record album.

Now that spawned another idea.

Would such a "warped record album" work as a kind of disk design for a Tesla turbine-like "bladeless turbine"(?

Instead of the sliding vanes that would have all manner of friction and wear/seal issues, "vanes" in the form of ocean waves or fabric flag waves on a disk would have some "natural" aerodynamic advantage.

I've seen videos where thin blades of a Tesla turbine becomes warped into such a 'warped record" shape. Why?

The same wave shape emerges with any thin high speed rotating disk actually. Not sure if there is an actual connection.

If a wave vane rotor actually worked it would have a great advantage as the wave-shaped vanes would be formed in the disk itself, no sliding, no friction other than the hub bearing which could be air or magnetic.

Why does wind driving a flag, water or sand form into a wave shape?

Might be worth experimenting with.

I wonder.

If you think about it. With wind blowing against the windward side of a wave. The wind, or lack of wind on the back or leeward side would tend to produce a vacuum.

If a Tesla turbine rotates due to boundary layer viscus drag on the surface of a flat plate, what happens when that "drag" is assisted by vacuum all along the plate surface, in effect, producing "lift" like an airplane wing, but repeating around the entire disk or disks and on both sides of the disk or disks?

Dunno if it relates and I can’t remember if it was this forum or somewhere else, but there was a conversation sometime back about how the roughness of shark-skin actually made it slicker. Yeah I know, hydrodynamics vs aerodynamics, but it might be relevant.

Bumpkin

I believe the warped disc is forming because of turbulence. Even a disc is never completely flat, and when you drive it to high speeds every minor change in flatness gets affected by the airstream.

Vanes are actually a low friction solution already. They're usually made from graphite, which is self lubricating. But you're talking about sealing air with air (or a vacuum)? That's another holy grail in itself.

Bumpkin wrote: ↑Sat Dec 16, 2023 6:23 pm Dunno if it relates and I can’t remember if it was this forum or somewhere else, but there was a conversation sometime back about how the roughness of shark-skin actually made it slicker. Yeah I know, hydrodynamics vs aerodynamics, but it might be relevant.

Bumpkin

It's certainly relevant.

The theory there however is that the wave shape reduces "drag".

It would be interesting to experiment.

I can see reasons for either possibility. Or it could be both, depending on the wave profile and spacing.

Drag is strongest near to the surface within the boundary layer. A Tesla valve type "wave" or shark skin-like profile might reduce drag, while a low profile wing-like wave might create "lift".

A Tesla valve reduces drag, or is supposed to (in one direction only) but the walls of the valve are spaced relatively far apart, but the closely spaced plates in a Tesla turbine increases drag by forcing the air to travel within the boundary layers near the surface.

I think it may be drag when the wind blows on the surface of water when relatively smooth that starts wave formation, then as the wave forms and begins to move along with the wind, drag is greatly reduced.

Anyway an idea or theory is mostly empty speculation until tested and demonstrated.

My idea here is that a low profile wave on a disk, probably with a relatively long slope on the "windward" side to produce drag and a pretty abrupt, but still smooth, wing like down slope on the leeward side might produce a combination of both drag and lift, but I've got a vivid imagination sometimes, in both a good and a bad way I guess.

To create drag the "waves" would need to be closely spaced on the windward side, and for lift (or vacuum) the space would diverge, but not so much as to cause turbulence.

Jack wrote: ↑Sat Dec 16, 2023 8:30 pm I believe the warped disc is forming because of turbulence.

I always assumed it was torsional forces from the high speed rotation, but who knows?

.... But you're talking about sealing air with air (or a vacuum)? That's another holy grail in itself.

Well, sealing air, sort of, with drag at the boundary layer, like in a Tesla turbine, but giving it some extra "lift" with an airplane wing disk surface profile.

Like a Tesla turbine but with wing-like waves on the inner surfaces of the turbine disks.

I can imagine the fluid dynamics in my imagination but don't know if the air would actually cooperate or behave the way that I imagine it might.

It would be kind of like airplane wings with no underside as under the wing is another wing with a mirror profile.

So the '"lift" on the "wing" instead of lifting a plane off the ground would drive the rotor forward.

Or water waves driven by the wind, but no water, because under the wave on top is another wave on bottom. Like the waves of a flag in the wind are on both sides of the flag. Like two ocean surfaces without an ocean.

Or a relatively thin ocean in the form of a solid disk.

Maybe I need to draw a picture.

While we wait for that drawing. I'll write down some of my theoretical findings. haha

I can't find a more efficient way in my imagination to build a Stirling engine than the vane model. Not only is it ideal because the work is done in the actual direction it is needed, but also because of the flexibility it brings. We can basically decide the volume evolution completely.
Mechanically it combines a few things so moving parts are down to an absolute minimum, reducing friction and inertia.

The other thing I can't really find an answer to is the difference between heat transfer between air and a metal or between air and air.
To limit heat losses, reusing hot air/fluid in stead of trying to transfer it to metal and later picking it up again.

Jack wrote: ↑Sat Dec 16, 2023 11:29 pm ...
To limit heat losses, reusing hot air/fluid in stead of trying to transfer it to metal and later picking it up again.

Are you referring to the regenerator here?

IMO, if a regenerator provides any benefit, there is something strange going on. If It "stores" excess heat that can be used later.

Let's say, for example it's raining. Rain represents the heat inflow at say 1 gallon per minute. There is a water powered turbine that is limited to .75 gallons per minute.

We could add a temporary storage for the excess that holds maybe 2 gallons.

To me, logically, there is already an excess of .25 gallons per minute which is unusable. Accumulating it does not, or logically should not increase the rate of consumption so in a few minutes your "storage" will be overflowing. The heat will still be wasted and your rate of utilization has still not increased.

But, if the regenerator does something "weird" and unexpected to actually increase the power conversion rate then maybe... I don't see that as entirely out of the question. Experimentally, some people report seeing a performance boost using a regenerator (including myself). But I haven't figured out a logical "scientific" reason why that should be true.

I do have an idea that just occured to me this moment.

If the regenerator somehow DOES increase the rate of utilization by increasing the "pressure"..

In the rain analogy for example.

If you have a rain spout feeding water to a turbine in excess of what the turbine can handle and the excess water just spills out on the ground, what can you do?

An overflow tank just overflows as well.

But what if the overflow is sufficiently high above the turbine and the storage volume sufficiently large that the volume of accumulated water in the storage tank increases the pressure at the lower turbine inlet, causing the turbine to run faster, increasing the rate of utilization?

If a regenerator is a heat accumulator that in some way causes more heat to be utilized per cycle, then maybe it is of some benefit. For that, though, I would have to assume the accumulation of heat somehow increases the heat input temperature, which would be the analog of "pressure".

OK, well I have a theory already that could account for that possibility, if the engine is acting as a heat pump.

There is evidence that at times compression by the power piston DOES elevate the working fluid temperature above the heat source temperature.

So, if what the regenerator is accumulating is actually this hotter higher grade heat from the "heat of compression" perhaps it is doing more than just acting as an overflow for storing excess low grade heat but is actually sustaining a higher heat input temperature and actually increasing the effective temperature differential therefore increasing the rate of heat utilization rather than just being a useless overflow for excess low grade heat.

I don't really see how regenerators in the general sense do anything else than basically change the timing of heating and cooling. So the most work would be done at a different crank angle.

For my idea I'm trying to store some heat in the fluid so I can use it to extend the heating cycle. Haven't fully figured it out yet though.