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LTD Stirling engine with vertical shaft - perhaps

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kwackers:
The problem with giving the displacer thermal mass is the time it'll take to heat/cool. Unless it's a very slow engine the displacer will simply take on an average value of temperature and hardly change.
Quite likely giving the displacer a thermal lag will make the engine run worse, since it'll take heat from the warm air cooling it and giving it back to the cool air warming it which would basically try to keep the air temp in the displacer chamber constant, I think in essence you want as little thermal mass in the displacer chamber as possible (except for the hot and cold plates which ideally would never change temperature...)

Better would be to increase the surface area of the hot/cold surfaces to faster raise/lower the air temperature - but then you need to increase the rate you can move heat to/from them otherwise you very quickly end up with an engine who's temperature difference drops too low to work.

picclock:
Hi Kwackers

The displacer is still very much an insulater - its just that the foil either side of it will decrease the thermal impedance to the gas. One side of the displacer would be cold and the other hot.

Before I make the ones for my kids I will make an experimental one to check it out and sort out the bugs. Using the bellcrank idea it should be easy to balance any displacer weight difference.

I was thinking of making a zoetrope (?) to go round on the top with perhaps pictures of a cat chasing a mouse or something similar.

Best Regards

picclock



 

John Hill:
I think a porous displacer of the right material would work as an economiser taking heat from the hot air as it is heading to the cold end and adding heat to the cold air on its way to the hot end.

cidrontmg:

--- Quote from: John Hill on November 29, 2010, 05:50:57 PM ---I think a porous displacer of the right material would work as an economiser taking heat from the hot air as it is heading to the cold end and adding heat to the cold air on its way to the hot end.

--- End quote ---

Indeed. That was actually R.Stirling´s first patent, an economizer, for glass and other furnaces, and for the hot air engine. The economizer is also known as regenerator, and it is usual in "serious" alpha and beta Stirlings, which aim for good fuel efficiency and high power output. In a gamma type Stirling, it´s not common practice, but could be achieved with suitable (porous) displacer piston material. The piston would be at some temperature between the cold and hot side, and act alternately as a pre-cooler or pre-heater for the passing air. But in a "toy" engine, I think it is not worthwhile to worry about economy. Just make sure there´s no unnecessary friction anywhere, and heat it with a bigger flame if it doesn´t want to run... And in an LTD Stirling, a smaller power piston, and a bigger displacer (swept volume)...
 :wave:

John Hill:
Cidrontmg,  indeed, somewhere I read that in fact technically speaking it is not a 'Stirling' engine unless it has an economiser.

The point about this for the gamma engines is that the displacer could be made from a bunch of tightly compressed metal wool or somesuch. You could jam the wool inside a thin walled metal tube to make the displacer, for example.

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