To understand T-s diagrams and J-T expansion is another task to study. I have
been browsing for the subject but as yet found no T-s graphs including decent
explanations. Those practical diagrams were not part of our thermodynamics
courses which were mainly about laws and cycles.
There was that large helium tank (used for gas chromatography) standing outside
the lab. Outside near the cold exhaust tube on it were indeed large chunks of
(water) ice de-sublimated on it from the environment air.
Related: throwing chunks of solid carbon dioxide in water makes it bubble with
sublimated cold CO2 vapor. But why does that gas produce a *lingering* fog on
rock&roll stages?
jd
From: arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx] On
Behalf Of Timothy J Massey
Sent: vrijdag 21 augustus 2015 22:15
To: arocket@xxxxxxxxxxxxx
Subject: [AR] Re: scuba or astronaut gas temperature question
The water that freezes is, I'm sure, not from the air in the tank. You are
right: that is very, very dry air. It's the water in the natural outdoor air
that is cooled by a super cool jet of recently and quite quickly freed scuba
air.
This isn't speculation: I've seen it and done.
Maybe snow is overstating it: it's not exactly large snowflakes. But there is
definitely condensation coming out of the air in a visible white cloud.
Timothy J. Massey
Sent from my iPad
On Aug 21, 2015, at 1:08 PM, (Redacted sender "JMKrell@xxxxxxx" for DMARC)
<dmarc-noreply@xxxxxxxxxxxxx> wrote:
John,
The compressed air temperature drop will be approx 30 C from 200 to 1 bar.
Reference T-s diagrams for N2. The largest T drop occurs at the first stage of
the regulator, 200 to 10 bar. In water >10 C the 10 bar air is reheated to near
water temperature. Diving in water at temperatures <5 C does present a
regulator freeze issue. Special regulators and procedures are required.
Dumping a full dive tank will not produce snow in the summer. Done that. SCUBA
air dew point of -53 C (<24 PPM H2O).
Krell
In a message dated 8/21/2015 7:05:51 A.M. Pacific Daylight Time,
johndom@xxxxxxxxx writes:
Is there an expansion due air (gas) temperature drop, say from a 200 bar
cylinder to a diver’s mouthpiece after the pressure regulator? Like a JP
expansion effect? Of course with scuba diving, the regulated pressure is depth
dependent, but still. Any values in °C?
jd