Design ideas for displacer cylinder

[rustybarrel]

Hi
I am thinking of brazing an aluminium heat sink from PC to the end of displacer cylinder for improved heat transfer. The question nagging me most is which way to put the heat sink? Should I put it with its fins facing outside so it can gather more heat. Or should i put it with fins facing inside to transfer more heat to air inside. The later option will increase the dead volume of the engine. Have anyone of you tried this before? What was your experience. Or you can comment on the feasibility of this idea.
Thanks
Rustybarrel

[Ian S C]

How are you going to braze the aluminium? A bit pointless really if your motor is a high temp one, the temperature at the hot end will melt the aluminium. A similar arraingment has been done with internal stainless steel fins, see Andy Ross's book "Making Stirling Engines" (free down load, about 68 pages). Ian S C

[AlacratStore]

I noticed that stroke length is not be so really large, won't this mean that the engine is slow and it won't reach as higher pressure inside the engine?The length of the displacer is important- it should take up about two thirds of the space inside the cylinder.

[Ian S C]

Rustybarrel, The size and shape of the displacer depends on which temperature range you intend to design the motor for. The traditional engine is the high temperature motor, 600*C+, with these ones the displacer space has a volume of 1.5 to the space for the power piston of 1, ie a ratio of 1.5 : 1. The displacer should be three times the length of its diameter, the actual stroke will depend on what you choose for a power stroke, short stroke, high revs, low torque, long stroke, lower revs, higher torque. Say we'v got a BETA motor, its concentric, dameters the same, power piston 1/2", displacer stroke 3/4".
An LTD, low temperature motor is completely different(its just the same), the one I have here has a 6" diameter displacer, about 1/2" thick, and a stroke of 1/2", the power piston is 1" diameter, with a 1/2" stroke.
With a GAMMA motor, by using a smaller diameter for the power piston, Than the displacer cylinder, you can get the 1.5 : 1 ratio required for the high temp motor.
For an intermediate temperature, in say a Tin Can motor, the ratio can be increased to 2:1 or greater, its a case of experimenting, best to look at the TinCan motors on the net.
These are not my figures, but the ones that Robert Stirling (and others) used.
On a low temp motor, a heat sink could be attached to the out side, I would bolt/rivit it on with electronic heat sink compound between it and the bottom plate. You could do the same for the cold side. Ian S C