[AR] Re: scuba or astronaut gas temperature question
- From: Timothy J Massey <tmassey@xxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Fri, 21 Aug 2015 10:21:57 -0400
Timothy J Massey <tmassey@xxxxxxxxxxx> wrote on 08/21/2015 10:09:20 AM:
Very much so. As scuba divers, we are swimming in liquid water but
can easily freeze up a regulator when we are in water that is near
freezing because of gas expansion.
A little more detail: that can happen both on the first stage (the reg on
the tank: 200 bar to 10 bar above ambient), or even on the second stage
(10 bar above ambient to ambient). The larger pressure drop (and
therefore larger cooling) on the first stage is offset by the fact that
it's usually solid metal and sitting in (theoretically) warmer liquid
water (and hopefully designed for cold-water diving, if that's what you're
doing). The second stage is usually plastic, so it doesn't get as much
heat from the water to offset the cooling, and the valve is not near the
actual water, so even the much smaller pressure drop will freeze up a
second stage.
You can have a freeze up in water below 40F or so (especially with
poorly-designed regulators used improperly), though the only time I've had
them is usually when the water is close to freezing: 34-36F (in
freshwater: ice diving in a lake or at depth in the Great Lakes).
There is an entire protocol behind diving in icy conditions to avoid this
problem.
Tim Massey
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