On Thu, 18 Dec 2014 09:12:04 +0000, Martin Brown wrote:

Chances are you are only going to use it a few times so I'd suggest
buying in a block of dry cold after you have built the contraption.

This is probably true but *IF* it works it should just work provided
there is enough propanol in the chamber. It could be left running...

You need really good black velvet and a powerful compact light source.

The blacking I've yet to really consider, depends on what chamber we
can get. Powerful light sources are easy these days with 5 W LED
tourches...

It is actually quite hard to maintain large temperature differences on
Peltiers and you will probably need the hot side heat sink fan cooled
with forced air ventilation (or possibly even water cooled).

Air cooled, f'ing great CPU cooler, 120 mm fan, supposed to be able
to handle 180 W. Heat pipes transfer the heat from the CPU contact
area into the heatsink fins. Hum, they'll actually be upside down, so
might no work as well as they might. ie the condensed heatpipe
"stuff" won't be running back to the hot bit, hum....

you will end up with the cold side -80C below the hot side which will
end up about 50C or maybe even warmer.

We shall see... Needs to get down to around -25 C, so provided the
heat sink doesn't get much above 40 C it should work.

The old design in Scientific American by C. L. Stong is pretty robust
and relatively easy to get working. Beware of frostbite!

Is that based on dry ice? I sort of looked at using dry ice but the
places I could find only wanted to sell rather large quantities, 10
kg or more.

--
Cheers
Dave.