#50
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there are a lot of replies here, but none of them are really answer the question Greg asked...
replies like the one that says that a gas under pressure, or is being pressurised has less space between molecules. hence more collisions / Friction between them causes heat, Sounds good and are quite close to being correct.
However the question was referring to a "Scuba Tank" which would include the Gas passing through a "restriction, Orifice, Valve"
so the effect you are all referring to is "Joule-Thomson effect"
http://en.wikipedia.org/wiki/Joule%E2%80%93Thomson_effect
http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Joule%E...3Thomson_effect.html
It explains the phenomenon of the heating of a gas during compression, as well as the Cooling effect of a gas when it is expanding after passing through an Orifice.
Its one of my favourite questions for Divemaster students, to ask them if they can find the answer to why even the High pressure hose heats up when a regulator is pressurised, the same as a Tank when it’s filled etc.
By the way, putting a scuba tank in a water tank when they are being filled is not good for the tank at all, and since the water is not moving cools the tank very little, while it does cause a temperature difference within the tank itself.
I have also heard that it is done fore safety, in case of an explosion it would channel the explosion if the tank were to burst.
First off what the water would do is cause a difference in temperature in the tank wall when it’s being filled.
This can actually cause some of the moisture that is left in the compressed air to come out of the vapour state and condense on the cooler part of the tank wall, this results in mosture in a liquid state in droplet form.
These would roll down to the bottom of the tank, and in the High partial pressures of O2 within the tank easily cause corrosion / Pitting at the bottom of the tank (this is one of the things you have to inspect and measure when doing your Tank VIP’s, the amount and depth of pitting in the bottom of the tank)
secondly, According to the State of Florida fire department, a tank that was filled to approximately 2/3’s full exploded when it was being checked for pressure (not being filled)
the Tank was in a Water bath when it exploded however there was significant structural damage to the building.
The concrete pad the water bucket was on was about 3 feet lower than the rest of the floor, there were "Walls" missing, luckily the young fellow (Chris) that was working with the tank only lost part of his hand, (2 finger and the Thumb) as well as other blast related injuries (I don’t remember what all happened to him without looking the indecent up) but I do remember that they said it was enough energy released to lift one of their articulating fire engines up in the air about 20 meters in the air.
I spent a long time working with explosives myself, and you can take my word for it, if you were to put a charge in a large Bucket of water and set it off, if you were close enough to it, you would be dead, maybe a little Damp, but dead all the same.
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