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The following I pasted from rec.scuba some time ago.Hth. Matthias From: Ed Newberg G_Edward_Newberg@cc*.or*.lm*.co* Subject: Re: Argon gas for dry suit inflation Organization: Lockheed Martin -- Information Systems Center > > > > > > Argon gas molecules are more dense than air there fore it is a better > > > insulator. > > > > Based on this logic, I suppose water, being even more dense, > > is an even better insulator. Therefore we need no thermal > > protection at all. Of course, it also follows that my vaccuum > > bottle can't possibly keep my coffee hot. > > Sigh. > > Yes, argon has lower thermal conductivity. No, it's not because > > "it's more dense." > > Sigh. > > Ed > > Hey Ed, why don't you fill us in on why it works, instead of just being > an asshole. Sorry. I was hoping a chemist would jump in and clarify, but I'll do my best. Thermal conductivity is directly proportional to the specific heat of the gas molecule and inversely proportional to the cross sectional area and the square root of the molecular mass. Because of the square root, density is less of an effect than the specific heat. Specific heat is greater in more complex molecules than in simpler ones (if anyone cares to elaborate, be my guest), and the simplest gasses are monatomic. That is, gases in which the molecule is a single atom, such as helium, argon, krypton, xenon, and radon. Air is mostly nitrogen (N2) and oxygen (O2), which are diatomic (2 atoms per molecule). Diatomic gases have about 70% greater specific heat than monatomic gases. What this leads to is that the best gas for insulation is one which has a low specific heat and a large molecule; that is , we want the biggest molecule we can get in a monatomic gas. Rule out He (too small), radon (radioactive), xenon (too expensive), and krypton (also too expensive), and we are left with argon. Argon has about 46% lower thermal conductivity than air. Hope this helps. Ed -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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