Stirlingengineforum.com

We have been working on the house at home, and I ended up at Lowes to get some Rockwool insulation for under the floor we've been repairing, but while at the store, as I sometimes do, I browsed around for potential Stirling engine supplies.

When I lifted up a sheet of this particular foam board, the way it kind of easily floated above the stack of other foam boards reminded me of how the displacer behaved in the little magnetic Stirling engine.


https://youtu.be/_YVtWf6Knh4?si=mdwI49tYa224MLZ6


In the Stirling, the displacer was lifted by the magnet, then kind of floated off to the side, back and forth, changing direction each time, kind of partly floating on a cushion of warm air the whole time.

The foam board in the store, when lifted, did something similar. It seemed air trapped under the board traveled down the length of the board, so just lifting the edge a little caused the air that got trapped to travel like a wave under the board lifting the whole thing.

The board was not that light that the whole thing could easily be lifted with a pinky finger, it seemed to depend on the dimpled surface of this particular type of foam board, because when I tried it with other types, some of which were even lighter, it did not work. The smooth surface of the other types caused too much. "suction" when trying to lift the board. The surfaces were too smooth.

Anyway, I went out to the truck and got my phone to shoot some video, to show what I mean.

Now I think I'm going to try building a huge LTD that takes advantage of this effect.

I may not get to it right away, but I figured I may as well get some of this foam board to have on hand when I do.

I think that this effect is likely amplified in a Stirling engine, due to the fact that when the displacer is lifted slightly, the air that moves under it is heated and expands, so the expanding hot air does some of the lifting.

In the store, on a flat surface, or rather, the somewhat textured surface of the other foam board, the board seemed light as a feather and I could basically lift the whole thing with my pinky finger fairly easily. I just lifted one edge and the air did the rest.

Out in the truck, without the layer of trapped air under it, the foam board seemed much heavier. It did not have that nice trapped cushion of air to float on.

I was thinking of maybe having the displacer lifted from the edge instead of in the middle. Instead of lifting the entire weight of the displacer the "wave" of hot air do the work.

Instead of lifting the entire weight of the displacer

I never really understood the focus on the weight or mass of the displacer, piston, or other moving parts. What am I missing? I get friction being an issue of course, but the mass of the moving components should be nulled out by the counterbalance (often built into the flywheel, but could be elsewhere.) In other words, the flywheel, at rest, should not be feeling the downward pull of the displacer no matter what it weighs, since there's a counterbalance that offsets that weight.

So why the focus on the mass of the displacer? Properly counterbalanced it should not consume any more energy to move it, be it 1g or 1kg, and if anything, the extra mass should contribute to a smoother running engine. It would take larger linkages however.

skyofcolorado wrote: ↑Mon Feb 05, 2024 1:09 pm ...
So why the focus on the mass of the displacer? Properly counterbalanced it should not consume any more energy to move it, be it 1g or 1kg, ...

Inertia? In most cases, in a reciprocating engine. The moving parts, like the piston and displacer are initially at rest, then have to move to a different position and stop, reverse direction, get moving again back, etc. constantly accelerating then stopping. Accelerating again and stopping, reversing direction. The work needed to keep doing that, all that speeding up, slowing down and stopping, changing direction etc. comes from the engine. Newton's first law of motion. Not weight so much as inertia.

To put it in perspective, if it was your job to lift and lower a large six foot diameter ball up and down or roll it back and forth from one place to another and back again just to displace the air, which would you prefer to move back and forth or up and down about 10 times a second. A hollow 6 foot diameter ball made of styrofoam or a 6 foot diameter ball made of solid Stainless Steel. You have to get this thing moving, get it rolling as fast as possible and then bring it to a stop.

Both the Stainless Steel and the Styrofoam shell will do the job of displacing the air, one just as well as the other, but which requires more work to keep moving back and forth?

Now I guess, technically, you could engineer a counterbalanced flywheel to lift the Stainless Steel ball up and down and that could lift the SS ball just as easily, once it got going. Supply it with frictionless air bearings. So, yeah, you aren't wrong.

In this case I'm just interested in the air cushioning phenomenon, and, well, using styrofoam is cheaper and easier, in the short run, at the moment.

I was thinking, maybe a big flat panel solar engine similar to this:


https://youtu.be/8QE-CmKxz40?si=Z50JTfCes9iZ8xfB


The problem though is how to get the sun to shine underneath so the displacer can "float" on a cushion of warm air.

Maybe the foam board could be suspended from springs or rubber bands? Reflect the sunlight underneath with mirrors or aluminized Mylar (space blanket) or something. Or just stick with geothermal or heat from a compost?

I know!

Use a trough parabolic reflector and circulate solar heated fluid, water, or in winter, antifreeze or whatever, under the big box with the floppy sheet of styrofoam.

On top it could have a water reservoir for evaporative cooling. Or, maybe even better, a solar water distiller. Produce both power as well as clean, pure distilled water.

Maybe it could run at night by sky cooling the top.

https://www.fieldstudyoftheworld.com/pe ... ce-desert/