Cold air due to pressure of tanks

[Thalassamania]

The hose does have some heat sink value, the metal fittings even more. A feature of some cold water regulators is the absence of hose protectors on the second stage connections (Sherwood Oasis vs. Blizzard as an example) allows greater conduction to the water which can be relatively warm.

Think for a moment, have you ever seen, underwater, ice from on the IP hose or any of it's fittings? Where have you seen ice form? The drop from 3000 to IP is huge, the drop from IP to ambient is only about 130 PSI. Where does the cooling occur?

Cold air that has been subjected to severe adiabatic cooling (as in a free flow) while in cold water can result in a seizure of the glottis, the precise term I forget. It addition to gear malfunctions it can be a threat to the body.

Pete

I have never heard of this occurring. That does not mean that it is impossible, just that I've not heard of it. Do you have any references or links to folks writing about this?

 

[spectrum]

Think for a moment, have you ever seen, underwater, ice from on the IP hose or any of it's fittings? Where have you seen ice form? The drop from 3000 to IP is huge, the drop from IP to ambient is only about 130 PSI. Where does the cooling occur?
I have never heard of this occurring. That does not mean that it is impossible, just that I've not heard of it. Do you have any references or links to folks writing about this?

I was addressing the question in post #8 pertaining to the LP side of the system. A cold water second stage certainly has measures intended to prevent frosting and the ribbed exposed fitting is one of them. The hose isn't much of a conductor but it has some albeit minor effect. I realize the first stage has it's own challenges and control measures.

With regard to the effect on breathing the term cited is respiratory shock and the reference is attached.
View attachment Respiratory Shock.pdf

Pete

 

[GrimSleeper]

I am doing a college engineering project which involves diving equiptment.I have found that when the air in a high pressure tank is released it is extremely cold. I understand the priniciples of why this happens but I was wondering if someone can tell me how diving equiptment gets over this problem?One would assume the air is at first too cold to breath so there must be a way that it absorbs heat?Your help is greatly appreciatedHugh (Ireland)

Am I missing the point here? I don't think the question is about regulators freezing, IP hoses being heat sinks or anything else. I think the OP is saying, essentially, that he has observed - as we all probably have - that when you crank the valve open on a high-pressure gas tank, adiabatic cooling means that the air coming out is cold. Scuba equipment gets past this by the simple fact that the regulator attached to the HP gas cylinder prevents that sudden fast drop in pressure. Yes, the reg will, in the instant that you open the tank valve, be exposed to cold air that has suddenly reduced in pressure. But the reg will also warm up because it is being rapidly pressurized. And the reg is a tiny volume, so the pressure drop in the supply tank is minimal. After that, the pressure in the supply tank reduces slowly as the gas is breathed, so adiabatic cooling is not an issue. As Thal said earlier, PV=nRT and once there is a regulator attached to a tank the changes in P and V (and therefore T) are, well, regulated, so there are no major thermal effects.

Of course, that all goes out of the window once you have a free-flowing reg in cold water, which brings us neatly back to where the thread seemed to be going...

 

[Agility]

only a relatively small volume of air is released from the tank at every breath (under normal breathing conditions).
The diving equipment is surrounded by water which warms the metal first stage in which the expansion takes place.
Many second stages are made of metal or have metal heat sinks to further warm the breathing gas.
Nevertehless some medical conditions as cold induced asthma are (relative) contraindications to diving.

 

[spectrum]

only a relatively small volume of air is released from the tank at every breath (under normal breathing conditions).
The diving equipment is surrounded by water which warms the metal first stage in which the expansion takes place.
Many second stages are made of metal or have metal heat sinks to further warm the breathing gas.
Nevertehless some medical conditions as cold induced asthma are (relative) contraindications to diving.

The possible case of respiratory shock I witnessed involved a freeflow during an ice dive.

Pete

 

[bwbake]

I agree with the response that grimsleeper posted. I work for a control valve company and that basically describes what we have to take into consideration for our valves and regulators as we are taking rather large pressure drops through the valve and icing or freezing can start to cause problems in the valves. The big consideration is how large of a pressure drop is being taken and is that drop being dropped from say 3000 pounds to atmosphere in that very short period of time. Outside environmental issues can also start to factor in, as many were eluding to as in a free flow condition in cold water. I would suggest that for some of your research, look at some of the pressure drop properties that control valve manufatures use in there valve calculations and designs. Like I said it's the same issue that we deal with on a daily basis.

 

[MichiganScott]

You got some pretty good answers, but I'd suggest if you're doing a project on diving equipment, you actually dive. If you're not certified, you could find an LDS who offers a "discovery" scuba. See if you like it- You Will, and then get certified.

 

[DivemasterDennis]

The only cold air I have breathed from a scuba unit has been breathing from a free flow regulator as an exercise in training. That air is, however, very cold. I second the motion that the researcher experience air temperature from a regulator in his mouth, as well as a thermometer.
DivemasterDennis