Re: Helium(?) gap test.

To: tesla-at-pupman-dot-com
Subject: Re: Helium(?) gap test.
From: Jim Lux <James.P.Lux-at-jpl.nasa.gov> (by way of Terry Fritz <terryf-at-verinet-dot-com>)
Date: Tue, 08 Sep 1998 19:46:01 -0600
Approved: terryf-at-verinet-dot-com

Tesla List wrote:
> 
> Original Poster: Terry Fritz <terryf-at-verinet-dot-com>
> 
> Hi All,
>         I repeated my spark gap voltage test with helium from a balloon
filling
> kit sold at the party store today.  As Bill mentioned a few days ago, this
> stuff is NOT pure helium.  It will allow contact burning.  I don't know
> what the other gasses are but they do cause gap damage.  This gas also has
> very different properties from the argon.  Instead of having a clean arc at
> the gaps, it tends to have more of a plasma glow.  The losses are very
> high.  Helium has a very high heat capacity that may account for the loss.

Actually, the heat capacity of helium is about 5 times that of air (5200
J/kgK vs 1000 J/kg K), but its density is 1/7.25, so the capacity of a
given volume is about 70%. Argon's heat capacity, by the way, is 520
J/kg K (roughly 1/10 that of helium), but its density is 10 times that
of He, so, oddly enough, its heat capacity on a per unit volume basis is
also 70% of air. Monoatomic vs diatomic gases...

You may be thinking of the problems with deep saturation divers
breathing heliox and being cold all the time because of the properties
of helium.  They are working at a pressure of some 30 atmospheres, so
the thermal capacity of the gas they are immersed in is some 27 (!)
times that of air at STP. Any sort of movement of the fluid at all, and
you'll get cold. Compare water with a capacity of 4200 J/kg K and a
conductivity of .55 W/m K (air is .024 W/m K).

Jim

<<<< Thanks for the info...  This can get really confusing! - Terry >>>>