microwave induction stirling

[fullofhotair]

This was theropods idea. I just started a new thread, since it was infringing on vamoose's thread. A microwave is focused internally on the bottom of the displacer/ regenerator. The cylinder is made of an RF transparent material like silcon nitride ceramic. When the displacer reaches the bottom of the cylinder a focused burst of microwave is released from the outside the cylinder onto the bottom of the displacer. The bottom of the displacer is metallic and causes induction heating . No heat is lost from the hot side.

This is my contribution. The displacer/ regenerator is made up of heat conducting metallic disks. The disks are closely stack on an axil like a lazy suzan. Each disk has a magnet embedded in its edge. There are magnets embedded in the wall of the cylinder. As the displacer moves by a series of magnets, individual disks are moved to line up matching holes or moved to close alignment. These holes control convection heating and cooling of the regenerator/ displacer.

[Ian S C]

You could have problems with heat on the magnets, with heat magnets loose their magnetisim.
Alnico 540*C
Ferrite 300*C
Sm Co 140*C (rare earth magnets).
Mild steel 770*C becomes non magnetic
Also the effect of vibration causes a drop in magnetisim. Ian S C

[fullofhotair]

Ian SC,
The cold end on a stirling engine stays relatively cool. Do you know what the gradient is toward the hot end? By this I mean is the center of the cylinder exactly 1/2 the difference of the hot end and cold end.? If you can figure where the temp. is to high for the magnets ,you can have the magnets do most of their work above that threshold. It looks like staying below say 350c for alnico would be workable. I just realized you would probably have to have an internal heat sink at the hot end to retain heat through the cycle, since the microwave is just firing at the bottom of each cycle.

[Ian S C]

I think the best place for the magnets would be on the power piston, rather than the displacer, or if it must be on the displacer side, have it on the rod, and outside the cylinder, on a free piston motor a magnetic spring on the displacer might be used this way. Ian S C

[Bumpkin]

Fullofhotair, other than as a novelty, I only see electric heated Stirlings as another way to waste high quality energy that's best used elsewhere. But it's interesting. You mentioned in another post the possibility of neon as a working gas for Stirlings. Not that it was what you meant, but I immediately envisioned a see-through neon Stirling, lit up (and thus heated) electrically with proper timing. It might be fun to watch. But on further thought, since you could time the heating externally I wonder if it would need to be a Stirling at all? You'd lose the regenerator, but you could simplify the concept by making it more like a thermal lag engine. Just rambling… Bumpkin

[fullofhotair]

Bumpkin,
That did paint a pretty picture. A neon flashing heat engine.

[fullofhotair]

Bumpkin,
Electrical heat might be expensive for most application but there are circumstances where an open flame would impractical. You have toxic exhaust to deal with . They use electric chain saws for underwater work. You don't need an extra air line or oxygen tank. I don't know about in general but in the kitchen ,the microwave is cheaper than an electrical element.

[Ian S C]

Bumpkin, The microwave oven is still using some where about a 1000W when it's cooking, an electric stove might be 2000W, the MW is more efficient---------BUT? I think that prolonged use would probably melt any material, metal or ceramic that any of us could find, and work with, unless there is a way of reducing the Wattage of the Magnetron, if it could be reduced to 100W or 200W for a start, and if need be turned up a bit to the required out put (or down). Ian S C

[Bumpkin]

Fullofhotair, by mentioning novelty I meant to be positive. Fun and science are often more important than efficiency and I was only saying that's one direction electrically timed and heated engines could take. It was just a random thought; my own interest is still wood-fired power.

Ian, I think maybe you misjudged my involvement in the thread, or equally likely I might just be too dense to connect with what you're saying. No worries though.

Bumpkin

[Ian S C]

Fullofhotair, I wonder if rather than Micro wave energy, one might be better thinking of induction heating, as in induction cook tops in the kitchen. With Micro waves you could spend more than the engine is worth designing the wave guides, I learned a little about these from my dad who was, during WW2, a radar tech with the RNZAF, and served in Britain. Ian S C

[fullofhotair]

Ian SC,
I've had those ranges before. I always thought it was just like any other electric stove but with a disk of pyrex glass on top of the element. Is there something unique to those stoves ?

theropod,
No , I realized it was just a flicker on your part ! I was just trying to gin up discussion on anything Stirling engine related.

[Ian S C]

No the induction stove top does not in its self heat up, but the metal pot does, its the high frequency current, must go and read up a bit on it, I know what I mean, its just explaining it that I'm a bit out of my depth. Its an electro magnetic process, at a frequency of about 24M hz. It was first invented in 1909, so its been around a year or so, although it wasn't until the 1970s when suitable semiconductors became available that they became practical. Ian S C

[fullofhotair]

Sorry,
I meant Bumpkin I realized that you weren't that involved in the idea !

Ian SC,
I get the jest of how it works now. Heck ya , Ian ! That is definitely the way to go. It is more efficient than a regular element. It loose only a small amount of heat to the non metallic cylinder and most of the heat is captured inside the cylinder by something ferro magnetic. And you don't have to shield it like you would a microwave.

[Irene Tulloch]

The core to working of a microwave oven is a “Magnetron” that generates waves of electromagnetic energy. This electromagnetic energy, when it reaches water molecules, charges them, thus in turn heats them. On the contrary when it reaches a metallic surface, the metallic surface reflects them.