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LTD Stirling engine with vertical shaft - perhaps

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picclock:
Hi

I decided to make a vertical shaft coffee cup stirlings for my kids for next christmas (I like to plan in advance  :lol:).

This would involve the conventional displacer but with the power piston at right angles to it. The displacer would be driven by a bellcrank from the vertical shaft, and its weight could be counterbalanced by extending the bellcrank and weighting it.

It then occurred to me that if the top arm of the bellcrank to crankshaft joint were made to have a lot of play this would result in the displacer staying in the hot or colder position for longer intervals, increasing the power of the machine.  The displacer piston would stay in position over the slop period because the air pressure encourages it to do so.

Any thoughts on this concept and its snags ?

picclock

picclock:
As a further thought, has anyone tried sticking aluminium foil to either side of the displacer piston ?

This should increase the speed of heating and cooling of the gas by near doubling the surface contact area. The foil would be reheated/cooled as it comes close to or in contact with the hot or cold plates. Possibly foil from a pie case or similar would be about the correct thickness (and a good excuse to eat pies to find the correct tray :clap:)

As a further bounus could probably be made to look cool  ::)

picclock

Bogstandard:
Picclock,

I don't think the reflectiveness or heat absortion of the displacer piston comes into the operation, it is there just to separate the hot and cold areas.

But I have painted some of my displacers with water colour acrylic paints without adding much to the overall weight. The usual red/white/blue combination.



Bogs

picclock:
bogs, your engineering parts always look so good - a sort of in built bling - I'm definitely envious :bugeye:.

The rational behind the foil idea is that it will increase the energy available to the engine by near doubling the heating/cooling energy available to the gas. As the current design goes when the displacer is at the bottom - hot end- it prevents the heat from warming the gas, but does little else.  By adding the sheet of foil at the bottom of the displacer, it will become warmed by convection/radiation , possibly conduction if it touches.  When the stroke of the displacer is at the top - cold end- and the gas flows over it, far more energy will be available to heat the gas.

The same is true of foil on the the cold end of the displacer, basically more efficient cooling.

One reason for posting this before proving it, is that if I am correct, a lot of almost running heat engines could be made to work with just the addition of some pie dish foil on either side of the displacer.

I think the end result will be a faster more powerful engine, or an engine which will run from lower temperature differentials.

It will also cool the coffee more quickly  :(. 

picclock

BillTodd:

--- Quote ---I don't think the reflectiveness or heat absortion of the displacer piston comes into the operation, it is there just to separate the hot and cold areas.
--- End quote ---

Interesting, the books on Stirling engine design I read as a lad, usually suggested using a porous or perforated displacer, the idea being that the heat would be transferred to and from the displacer as it did its job. Yet, most of the model designs I see now have a light weight thermally neutral displacer. :scratch:

Bill

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