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Jsuw@ao*.co* wrote: > 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 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 loose 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 -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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