Thermal properties of helium

[wedivebc]

I have heard it claimed many times that breathing helium makes you feel colder. This is false in my observation which seems to me if you don't put it in your drysuit you should actually lose less heat with helium, but I'm not a chemist and don't know how to prove that theory.
Anyone have any real data to support or refute my theory?

 

[LiteHedded]

if it's a poor insulator on your skin why would it be better in your lungs?

I dont have the data you're looking for. might be on rubicon though

 

[LiteHedded]

derp.

 

[Slamfire]

Because of helium's relatively low molar (atomic) mass, its thermal conductivity is greater than any other gas except hydrogen.

Air has a thermal conductivity of 0.024 W/(mK)
He has a thermal conductivity of 0.142 W/(mK)

Just as a reference 1 W/(mK) = 0.5779 Btu/(ft hr ^oF)

 

[wedivebc]

if it's a poor insulator on your skin why would it be better in your lungs?

I dont have the data you're looking for. might be on rubicon though

Because when you breath any gas it gets heated to body temperature in your lungs. If the gas has a lower heat capacity then it should take less heat to raise it to that temperature.

 

[LiteHedded]

Because when you breath any gas it gets heated to body temperature in your lungs. If the gas has a lower heat capacity then it should take less heat to raise it to that temperature.

so that heat is transferring to the gas quicker...and being exhaled

 

[wedivebc]

so that heat is transferring to the gas quicker...and being exhaled

No, for every given lungful of gas a certain amount of heat is lost from the body. If the volume of gas is the same and if the temperature of gas is the same (remember gas in your lungs is raised to body temp) then the amount of heat required to raise a given helium mixture to body temp should be less than that with a N2/O2 mix.
I am also not convinced that the temperature of a helium mix is lower when leaving the regulator because of thermal expansion so I am assuming the beginning gas temperature is approximately the same for both mixes.

 

[Doppler]

Dave: You dive a bloody rebreather! What the heck do you know about getting cold and heating up lungfuls of air. You only have to heat up a little dribble of diluent at the start of the dive and that's it... away to the races... skittles and beer, feet up, telly on, box of chocolates close at hand.



:mooner:


DUCKS: then runs away.

 

[wedivebc]

Dave: You dive a bloody rebreather! What the heck do you know about getting cold and heating up lungfuls of air. You only have to heat up a little dribble of diluent at the start of the dive and that's it... away to the races... skittles and beer, feet up, telly on, box of chocolates close at hand.



:mooner:


DUCKS: then runs away.

Actually I am putting together a powerpoint for an upcoming (OC) trimix class and reading from a certain training manual saw a passage that suggested breathing helium made you colder. I tried to wiki the information but I realized there is a lot I don't know about chemistry

 

[lobstah]

I believe there no theory to prove here, just simple calculations based on well known parameters

He has higher conductivity than air:
Thermal Conductivity of some common Materials

He has also higher heat capacity than air:
Gases - Specific Heat Capacities and Individual Gas Constants

When breathing both get heated up to same temperature, so we can completely ignore conductivity.

Lots of scuba math below.

one cuft of air weights 0.0807lbs
one cuft of He weights 0.011lbs

one human breath is roughly 1/6th of cuft

Amount of energy required to heat up ~1 lbs of He by 1 degree Kelvin is 2500 Joules. 1 Joule is expending energy of 1 Watt per second.

We are heating up from say 32F to 90F which is 36 K. So total energy to heat up 1lb of He from freezing point to human body temperature is 36 * 2500.

1 lb at normobaric is roughly 90 cuft.
90 cuft is roughly 540 breaths

so to heat up one breath we need 36 * 2500 / 540 Watts total. = 166W.

same calculations for air render = 172 Watts (it has lower heat capacity but each breath weights more)

One breath lasts 15 seconds? 10 seconds? I have seen various estimates of how much radiation human body expels in a second and the lowest I come across was 50W. So not only difference is small, but also it seems that we radiate way more than needed anyways.