Displacer designs

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secretan15
Posts: 2
Joined: Fri Nov 10, 2006 11:02 am
First Name: Frank
Last Name: Secretan

Displacer designs

Post by secretan15 »

I have a displacer design for a Stirling engine which differs from a conventional Stirling
engine displacer. I call it an "H" displacer. This displacer has an "H" cross section when
sliced open.
This displacer has no enclosed volume. It is a thin wall cylinder open at each end with a
thin wall disc welded in the center at right angles to the cylinder's axis. The "H" displacer
is designed to run up and down in a heat exchanger cylinder and regenerator just as is
done with a conventional displacer.The difference ,however, is that the two open ends of
the "H" displacer are partially occupied by an extension of the heater and cooler thus
increasing the surface area of the heater and cooler significantly. As the displacer moves
up and down, it displaces gas from one end ( hot ) to the other end ( cold ) . The gas is
forced to flow along the inner wall of the "H" displacer (along extensions of the heater and
cooler) as well as along the outer wall of the "H" displacer (along the heater and cooler)
thus resulting in a large increase of surface area to heat and cool the gas.
You will note, if you draw a sketch of this configuration, that the gas gets heated or
cooled as it gets displaced through the heater or cooler but winds up in the identical
volume within the engine at the end of each heating or cooling stroke.
Are there any oversights in this idea? Has anyone designed one of these?
I hope to get a drawing of this configuration soon so that the design can be more easily
visualized.
Frank Secretan
stan.hornbaker
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Response to Displacer designs

Post by stan.hornbaker »

This new displacer is an interesting development. A drawing or illustration of the parts would assist both in visualizing the arrangement but also to evaluate its performance. I will be looking forward to the drawing.
stevesat
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Joined: Sun Nov 26, 2006 12:30 am
First Name: Steve
Last Name: Graehl

Response to Displacer designs

Post by stevesat »

How funny, I have in front of me the same concept. I think I know exactly what you have in mind (No, I'm sure I'm not the only one or the first one to think of it) I was thinking of it as two opened cans connected at their bottoms, the each hot and cold side would have a bump inside allowing more surface area. The displace could then "cover" each side on it's perspective cycle. I have not built anything with a "normal" displacer yet and I think anything that could increase inside surface area would be a positive thing as long as there isn't "dead" air right?
secretan15
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Joined: Fri Nov 10, 2006 11:02 am
First Name: Frank
Last Name: Secretan

Response to Displacer designs

Post by secretan15 »

Hi Steve. You certainly understand what I have suggested. It seems that the biggest problem
with the "H" displacer is the excessive dead volume that it introduces. The gains by adding
more serface area to heat and cool the gas might be offset by the increase of dead volume
( eg. un-swept volume ). I plan to design two engines , one with the "H" displacer and one
with a conventional displacer. This will take me considerable time, and meanwhilr I will
continue to think of novel ways of increasing the surface area without introducing too much
dead volume. Incidentally, the "H" displacer has the nice feature of having no internal volume
so it gets easier to design an engine that operates at high pressure without collapsing the
displacer.
rtopf
Posts: 21
Joined: Fri Jun 28, 2002 6:49 am
First Name: Richard
Last Name: Topf

Response to Displacer designs

Post by rtopf »

Hi,

This is not a totally new idea. John Ericsson's had a design with a "U" shaped displacer. The firebox was actually on the inside of the "U".
Several hot cap extension designs have popped up since 1856.

This is also similar to the "Transferator" designs that use a "U" shaped displacer with the outside heated and the inside cooled.

The "H" shape is interesting, however. I suppose you would need a good insulator for the center disk.

Rick
iron_goober
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Response to Displacer designs

Post by iron_goober »

If anyone has read Jim Senft's book "The Ringbom Engine" I believe he mentions this design in one of the chapters.(it may be in another one of his books though.

If you want to take a look at a really neat displacer idea, that I think is really interesting and have devised a similar idea, but with a few small improvements(I think) based off of it, Check out this link

There are a few other engines on this page that are worth taking a look at as well.
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