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At 12:34 PM 3/16/00 -0800, Steve Hogan wrote: Andreas Hagberg wrote: > > 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 I believe this is the most simple approach to understanding heat capacity: We breathe gas by volumes, not kilos or pounds. Since a a lungful of helium based gas is much lighter you can't compare a kilo of helium with a kilo of nitrogen / oxygen. If you compare the weight of a given _volume_ of helium with the same volume of nitrogen you'll find that the corresponding volume of helium has the lower heat capacity. By the same token, when you fill your tanks to capacity they'll be heavier when filled with air than with trimix / heliox. You'd fill a volume of gas rather than a weight of gas. If, on the other hand, you went to your dive store and bought 5 kilos of heliox you'd need much bigger tanks to hold this volume than for holding 5 kilos of air -- about 6 times bigger, depending on oxygen percentage. The total heat capacity of all this heliox would be slightly above that of 5 kilos of air but your minute volume respiratory heat loss would be less since it would take you 6 times longer to breathe it all. regards, Hans -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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