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> > > The density of air is ca. 7.5x that of He. > Thus 1 kg of He will contain more 'moles' of He. > > The issue here is what is to B compared. Since it > is > the gas being breathed, it is best to compare the > amount of heat it takes to 'warm up' a volume of > breath, say 1000 ml. Since the specific heat of He > is > < spec heat of air, it will take < energy to > condition > same volume of He. > Safe bubbles > Esat Atikkan > > > > --- Steve Hogan <Steve.Hogan@tr*.co*> wrote: > > > > > > -----Original Message----- > > From: Andreas Hagberg > > [mailto:andha513@st*.li*.se*] > > Sent: Thursday, March 16, 2000 8:13 AM > > To: Steve Hogan > > Cc: techdiver@aquanaut.com > > Subject: Re: Helium > > > > > > > Helium is a small molecule. It does not take > much > > energy to heat an amount of it (relatively > speaking > > to lets say air). > > > > > > err... So you're saying that it takes LESS energy > > to heat Helium than air?? > > Well, not according to a nationally used > collection > > of tables and formulas in Sweden. > > The specific heat-capacity of air is 1 > > kiloJoule/kg*K. (Which means that is takes one > > kiloJoule to heat 1 kilo of gas 1 degree (Kelvin)) > > And the specific heat-capacity of Helium is 5.1 > > kJ/kgK. Which in the same way as above means that > it > > takes 5.1 kiloJoule to heat 1 kilo of Helium 1 > > degree. > > > > Since when is 5 kiloJoules LESS than 1 kJ??? > > > > This seems all pretty simple to me, but I might > have > > misunderstood the whole thing. If so, please > > correct me. > > /Andreas > > > > > > Andreas, > > > > Look at it like this. While it does take more > energy > > to heat a sample of helium vs a sample of > > air, what happens in the lungs is different. When > > the heating is happening, the body is loosing > > energy heating the HE, but the HE is transferring > > the energy back to the body (due to its high > > thermal conductivity). The overall effect (the > > important one) is less energy is required by the > > body > > due to the combination of the two properties. > > > > Does that make sense to you? > > I should have done a more complete answer (like HE > > as a molecule, that is what I get > > for not proof-reading) > > > > I was digging through the archives so you could > have > > the math behind it. > > > > Helium also has a higher heat capacity than > > nitrogen. > > Thats right (He: cP = 5.23 kJ/kg*K vs N2: cP = > 1,038 > > kJ/kg*K), > > but thats only half of the story. You have to take > > the mass of the > > employed gases into the calculation, too. > > Lets first look at the breathing cycle: > > * Inhale breathing mix at ambient > > temperature/pressure > > * Hydrate and warm up the gas > > * Exhale breating mix with 100% relative > humidity > > and body temperature > > The body loses its heat by breathing off the warm > > gas (ie. convection). > > The energy which is expended can be calulated > with: > > Q = cP * m * delta T > > Q: Energy [kJ] > > cP: heat capacity [kJ/kg*K] > > m: mass [kg] > > delta T: temperature difference [K] > > The temperature difference delta T is the > difference > > between body > > temperature > > and the ambient pressure, both do not change while > > breating another mix. > > The mass of a gas is dependent on the number of > > molecules and their > > specific > > weight. The number of molecules in a fixed gas > > volume (loung) is only > > dependent > > on the temperature, therefore if the temperature > is > > constant the number > > of > > molecules is constant, too. The specific weight is > > proportional to the > > relative > > molecular weight Mr (Mr_He = 4, Mr_N2 = 28). > > Now you can see that Q ~ cP * Mr. > > What does this mean? > > You lose less energy when you breath high helium > > mixes!!! > > > A diver will feel > > > colder breathing heliox than when breathing > mixes > > containing at least some > > > nitrogen. > > Right, but that has to do with the heat transfer > > characteristics of > > helium. > > Helium transfers heat much more rapidly than > > nitrogen. This is also the > > reason > > why you dont want helium as dry suit inflation > gas. > > Regards > > Frank Riffel > > > > Regards > > > > Steve > > > > > > > > -- > > Send mail for the `techdiver' mailing list to > > `techdiver@aquanaut.com'. > > Send subscribe/unsubscribe requests to > > `techdiver-request@aquanaut.com'. > > > > __________________________________________________ > Do You Yahoo!? > Talk to your friends online with Yahoo! Messenger. > http://im.yahoo.com > -- > Send mail for the `techdiver' mailing list to > `techdiver@aquanaut.com'. > Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. __________________________________________________ Do You Yahoo!? Talk to your friends online with Yahoo! Messenger. http://im.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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