From: "Chuck Guzis" <cclist at
sydex.com>
On 9 Jun 2007 at 21:43, jd wrote:
> Helium is a very good thermal conductor but I
would suspect that
it is used
because it is cleaner and dryer than air and
nitrogen and truly inert
and won't
chemically react with the medium. The helium was
likely under pressure
to reduce
the chance of air getting in. Since it can leak
out much faster than
nitrogen
and air, thanks to the physics of helium, the
seals and sealing surfaces
must be
in excellent condition. But no matter how good
the seal, helium still
leaks out
so it needs to be replenished from time to time.
So why wasn't another noble gas used, such as argon? I don't doubt
that helium might have been used, but I don't understand why.
Hi Chuck
The only two things I can think of where mentioned by others. One
was thermal conductivity and the other was friction. Helium has almost
zero friction.
Still, the stuff leaks out of things so fast. Even solid surfaces.
I find it funny that it is cheaper than argon. There is a lot of
argon but I'd guess the extraction from natural gas, where it
is undesired for burning, makes helium cheaper than argon that has to
be intentionally removed from air. Two percent of air is argon
as I recall.
Dwight
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