Fwd: Re: [PATCH] Fix up SAC calculations for ATM/bar confusion

[Jukka]

On 25.02.2013 22:45, Chris Lewis wrote:
>
> The reality is that the temperature in the cylinder is a mystery to 
> us. Sure we can assume local ambient temperature at the start of the 
> dive (assuming no solar heating effects) but then what is the 
> temperature of the gas in the cylinder during the dive.
> We would have to account for both cooling due to immersion of the 
> cylinder in water and adiabatic effects of dropping pressure inside 
> the cylinder.
>

The temperature problem is actually not directly connected to 
compressibility. Temperature causes the same error also in lower 
pressures and in ALL air volume calculations. Yet nobody suggests we 
should ditch all gas volume calculations because we cannot know the real 
gas tempartures.

> All seems more hassle than its worth. I would suggest some simple 
> correction factor over a certain pressure.
>

Today it's well enough. But I've been torturing my spreadsheet to 
calculate "real" air volumes based on Van der Waals and any 
oxygen-nitrogen-helium-mix and any (constant) gas tempareture. The math 
is terrible and it'll take a few days (=nights).

Jukka