> I'm not sure that this would be trivial; remember the navy units had/have 
> metal scrubbers so that temp is significant due to poor insulation of the 
> absorbent material.  Second, I grant you that you dive in warm water and 
> the greatest flucation I've seen over on Ohau is 78 on the surface to 75 
> at depth or so.  Here, in S. Cal. on a recent dive to 220fsw next to the 
> Redondo trench (on the wreck of the Sacramento, an old side wheel 
> steamer) we went from 66 at the surface to 49 at depth. Not only a larger 
> change in overall temp, but colder temps period.  That alone could 
> explain the Navy's reccomdendations etc.

I know the temps have a big effect, but we were talking depth, not temp. 
Sure, it's colder at depth, but I am certain the USN was smart enough to
independently test for temp & depth as separate variables.  The reason
alluded to of why depth does have an indirect affect on temp is that at
depth, gas is denser, so has more total heat capacity for a given volume,
so is more efficient and bringing the temp of the absorbent down.  That
means, even if the water temp at depth is identical to that in shallow
water, if the water temp is lower than the absorbent temp, then the gas
passing over the absorbent will take heat away much more efficiently in
deep water than in shallow water (more mass).  Of course, if you switch
from nitrox to heliox during the descent, then the mass of the loop gas
suddenly goes down.  Sure, heliox conducts heat faster, but if you assume
both nitrox & heliox approach thermal equilibrium during its pass through
the canister, then the nitrox will (in most cases) be taking the heat away
more efficiently than the heliox, even if the nitrox is used much
shallower. 

Aloha,
Rich

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