-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Wednesday, 2017-11-22 at 04:12 +0100, David Haller wrote:
Hello,
On Tue, 21 Nov 2017, Carlos E. R. wrote:
They do need some drought, to fly. With no friction (vacuum) the heads would crash.
Question is: how much? :)
Maybe the word "friction" is not appropriate. Friction, aerodynamics, viscosity, whatever :-) Apparently it is enough whatever with helium, or it would not work - the plater linear speed must be high.
The implication is the hydrogen (weight 2) would be even better, but I suspect the fact that helium is a noble gas has something to do with it.
It burns. It burns very well, even explode in the right mixture. I know that from personal experience :-)
And it is more difficult to contain for 5 years.
As I said, Helium is a metal which is probably why, what heat is generated, helium conducts it away much better.
Maybe. I know nothing about why different gases may conduct heat differently, even if they do.
After some Wikipediing:
https://en.wikipedia.org/wiki/Covalent_radius https://en.wikipedia.org/wiki/Van_der_Waals_radius https://en.wikipedia.org/wiki/Molar_volume https://en.wikipedia.org/wiki/Thermal_conductivity
cov.r VdW r Molar volume Density Th.cond pm pm 10^~6 m3/mol kg*m^~3 W/(m*K) H: 31±5 120 11,42(solid) 0,0899 0.1805 He: 28 140 21,00(solid) 0,1785 0.1513 N: 71 155 13,54(solid) 1,250 0.02583
Curious. Nitrogen has a very low thermal conductivity. Both He and H have it higher. The molar volume was the same for all gases, wasn't it? I don't remember.
From the He-"uses" section: "Helium is used for many purposes that require some of its unique properties, such as its low boiling point, low density, low solubility, high thermal conductivity, or inertness."
Couldn't find stuff on molecular H_2. I'd guess a H_2 molecule is larger. Hm. If I read that right, a H_2 molecule has a radius of twice the covalent radius of H, i.e. ~62, i.e. it is larger than that single He atom flying about. And He is just about always single. And H just about never and is "corrosive", cue your good ole NiMH accumulators. And N can get very nasty if not in a pair as N_2[1] and N is about 6 times less thermally conductive as He. He though is AFAIK as inert as it gets.
I forgot that Hidrogen is normally a molecule of two.
-dnh
[1] http://blogs.sciencemag.org/pipeline/archives/2013/01/09/things_i_wont_work_... "The compound exploded in solution, it exploded on any attempts to touch or move the solid, and (most interestingly) it exploded when they were trying to get an infrared spectrum of it." I suppose you could say "if as much as a gnat farts ... in the next room ..."
Nitrogen is used here to fill car tyres by some people (I don't know percent). It is more inert that plain air, although I have my doubts it makes a measurable difference on tyres. I replaced mine yesterday: I made 91000 Km with them (filled with plain air). The mechanic told me the average is 45000. I don't think they would last longer for me if filled with nitrogen. - -- Cheers, Carlos E. R. (from openSUSE 42.2 x86_64 "Malachite" at Telcontar) -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iEYEARECAAYFAloVdCYACgkQtTMYHG2NR9UqEQCdH3MMOEEjSNyRwcSXoewoDx1W h5oAmwe9HyGYnbkm2/Jo71vhIPKdBVRX =jaMO -----END PGP SIGNATURE-----