I'm not a tech diver, so I have the following question about statements related to compressibility of He and related "fudge factors" which are carried in the Oxy Hacker, Vol III:
On page 43, there is the following: >>>If a trimix is prepared by adding O2 to an empty tank, then He, and topping up with air based on ideal gas calculations, one can expect the final mix to contain approximately 10% more oxygen than the intended........<<<
>>>The almost universally accepted way of doing so in the techdiving community is to add the O2 first, and simply put in 10% less than the ideal gas calculations call for. Since the compressibility of He in the 2000-3000 psi range is about 10%, this pretty well does the trick.<<<
However, on page 46, worksheet #2, the caculation uses a compressibility fudge factor of POSITIVE 10%; in other words, the gas mixer is supposed to use a fudge factor which ADDS 10% MORE O2 than calculated.
Help me understand this. TIA
On page 43, there is the following: >>>If a trimix is prepared by adding O2 to an empty tank, then He, and topping up with air based on ideal gas calculations, one can expect the final mix to contain approximately 10% more oxygen than the intended........<<<
>>>The almost universally accepted way of doing so in the techdiving community is to add the O2 first, and simply put in 10% less than the ideal gas calculations call for. Since the compressibility of He in the 2000-3000 psi range is about 10%, this pretty well does the trick.<<<
However, on page 46, worksheet #2, the caculation uses a compressibility fudge factor of POSITIVE 10%; in other words, the gas mixer is supposed to use a fudge factor which ADDS 10% MORE O2 than calculated.
Help me understand this. TIA
