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Hi!
App. year ago there were discussion about this
effect on local Slovenian list www.norik-sub.si
and peoples from Faculty of Mechanical engineering
and Physics explained basics of this benefit.
Facts:
1) The higher percentage of He in mixture decrease
it thermal capacity.
a) The needed thermal flux from outside water
to inside of second stage is lower and temperature
drop is smaller - less danger of freezing
b) The 40% of buddy lost energy is because of
breathing (cooling and vapouring). In the case of
He rich mixture the this quantity is lower.
2) The He is the only element in nature which has
inverse (not the triple point) thermodynamic
temperature much lower than typical living
temperature so in the process of expansion of He
the final temperature is higher than if you
calculate as ideal adiabatic expansion. The simple
way: Joule-Thompson effect.
Conclusion:
We recommend usage of He in cold diving because it
helps diver in conservation of thermal energy and
little help in process of expansion. The humidity
in compression mixture stays as one of the most
danger subject in freezing of second stages. So
please check humidity absorber filter in your
compressor.
Once again: He is friendly gas.
Have you a nice day.
Viktor Sajn
--
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