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Brad is correct. There are two types of specific heat, constant volume (Cv) and constant pressure(Cp). I think the one we are concerned with in dry suits or your lungs is the constant pressure, since the volume of the dry suit (or lung) is not fixed. In your tank, it would be a different story, since the volume is fixed and the pressure is slowly varying, but who cares how chilly your tank is? There is not much difference the magnitude of Cv and Cp. Argon Cp=1.14 kJ/(kg*C) Helium Cp=22.8 kJ/(kg*C) Nitrogen Cp=2.06 kJ/(kg*C) As you can see, the Helium Cp differs by a bunch. Roughly speaking, at the same mass (kg) and initial temp (C), Helium would carry away 22 times the energy (aka heat) (kJ) as Argon. The Nitrogen is included as a reference, since that's about what air would be... To do Brad's second reccomendation (amount of body eat "lost" when filling with Air vs. Argon), we would have to use the first law of thermodynamics, but that is another bullet in another foot. Chris Brown Suffolk, Virginia --- Brad Beskin <bradb@ex*.ne*> wrote: > Helium is lighter (less dense)than air, and > therefore it conducts heat much more quickly. This > is the reason you do not inflate your drysuit with > backgas. Use an independent inflation system with > argon or air (argon is very dense and therfore > insulates well). > > To answer your physics question: > c = the specific heat of a gas (the amount of heat > necessary to change 1 kg of the substance 1 degree > celcius) > This would be helpful (in that shoot yourself in the > foot kind of way) to calculate the joules of body > heat you're gonna lose if you fill your drysuit with > He instead of Ar or Air. > -CB > From: moorea(uol) > To: techdiver@aquanaut.com > Sent: Tuesday, February 20, 2001 8:05 AM > Subject: Helium thermal properties > > > Hello all ! > I�ve been diving since 86, and nowadays i made my > own mixes, but now, i decided to go certified. > My instructor, talking about thermal loss in a > trimix class, explain me that the heat exchange is a > direct relationship with gas density. > I�ve read and learn in the past (including in > phisics class at regular school) that heat exchange > depends of thermal conductivity of the media (Q = > mc delta t) where "c" is the thermal conductivity. > Can you help me with that ? > Am i right ? > > thanks > > Marcelo Moorea > __________________________________________________ Do You Yahoo!? Yahoo! Auctions - Buy the things you want at great prices! http://auctions.yahoo.com/ -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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