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MR> BTW, one very interesting thing about viscosity is that,
MR> with increasing temperature, viscosity decreases in
MR> liquids, but increases in gases.  All the more reason
MR> to fill slowly.

MR> -Mike Rodriguez
MR> <mikey@ma*.co*>

This may help explain why the "hot" mixes are slow to mix while a
"thirty-something" mixes instantaneously. Provided we go oxygen first
there'll be a lot of air cascading into the system starting at a relatively
low pressure. Conversely, if stratification comes into play at high
pressures that means trickling in air on top of a "sluggish gel" of
oxygen. If this is true, trimix would be a problem too, provided the
helium went in last. That would leave a lighter gas on top of denser
one and there would be little turbulence due to the lower output from the
gas booster. In practice it's helium and oxygen first, blowing
cascades of air on top of it (or rather, into it!).

It makes sense that while stratification does not occur at medium
pressures it will present problems at high pressures (viscosity) and
low flow rates, both of which occur at the end of a fill.

In any event this goes beyond theorizing since I experience this all the
time -- bottom gas mixes instantaneously while "hot" deco mixes need
to lie down for a while or go for quick spin on the floor. Otherwise they
invariably give a low reading, indicating that the last gas administered (air)
stays up in the dome of the cylinder, resting on a sea of dense
oxygen.


Best regards,
 Hans                            mailto:proverud@on*.no*


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