playing with stirling engine

Today I replaced the closely wound copper (?) wire regenerator in my
Ross type stirling engine with a much looser one (lower fill factor, more
area) made of knitted stainless wire (actually one of those kettle
lime-scale traps). With the inner sleeve and regenerator fitted into
the hot cap I performed a flow test (alright, I blew down it!) which
showed that the looser mesh did indeed give significantly
lower resistance to air flow.
Once started and thoroughly warmed through (this takes some time, I
think due to the substantial lump of iron on the top end of the inner
sleeve) the engine ran up to a higher speed than before, no doubt due
to lower pumping losses, it did not however feel significantly more
After a good long run I took the hot end apart and was rewarded with
a nice range of oxide colours on the regenerator mesh indicating the
temperature gradient through the engine. If I could remember the
colour/temperature relationship from school metalwork (and wasn't
colour blind) I might even be able to estimate the temperatures
Next material I have to hand is pan scourer made of coiled up
stainless strip.
Photo of regenerator and sleeve after run at :-
formatting link

(last pic in 'all hot air' album)
Nick H.
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Nick H
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Thanks for that Martin. As I said, my colour vision is not all that it might be, but Helen reckons that the full range of tempering colours are there with blue (300 C) just about half way up the matrix. Given that the hot cap is probably at about 6-700 C and the cooling water at 60-70 C, then that would make sense.
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Nick H
Oxide colours vary with temperature AND time, which is why eye-ball hardening and tempering is an art.
It also mean you can't really infer you engine temperatures.
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"bugbear" wrote :-
Oh well another theory bites the dust!
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Nick H

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