On 17/12/2014 23:24, Dave Liquorice wrote:
Need a couple of chunky peltier coolers, one around 120 W another
above 60 W. Recommended are 12709 and 12710, plenty of suppliers on
Amazon/eBay but they all seem to be Far East based.

CPC etc have such devices but at £15 to £20 each, where as the Far
Eastern ones are less than a fiver delivered. Can anyone recommend
(or not) a Far Eastern supplier?

The lad wants to build a cloud chamber as a Christmas present for
himself. Old ATX PSU for the peltiers, hefty CPU heatsink, sealable
clear bowl, sponge soaked in isopropanol and Americium-241 from old
smoke detector as a source. Peltiers are a bit more convenient than
dry ice, though might not work quite as well.

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. I
used methylated spirits in mine way back. You need really good black
velvet and a powerful compact light source.

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

I have long suspected although never actually tried it that you can
almost get to cloud chamber conditions in the gap above a cup of freshly
made coffee in a cold room.

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

http://www.amazon.co.uk/Scientific-A...ur+scien tist

Book out of print CD version also available but no idea what it is like.
(BEWARE that US edition includes some vivisection experiments that have
been illegal in the UK for several decades)

I have a friend who built half the atom smasher - the Van de Graph.

--
Regards,
Martin Brown