Tank chilling

[ajtoady]

I hope I'm in the right spot for this. I am a cold water diver. Ice, drysuit and anytime I can.(St. Lawrence River in back yard) Does anybody know how long it takes a tank of air to reach the ambient water temp if for example: Tank temp 55* F Water temp 34* F . Tank is a HP 117 Steel and is currently full at 3442 psi. I am in the habit of keeping all my gear warm in my shop at about 55-60* F thru the winter and was curious if a warm tank does in fact help towards the end or say 45 minutes into the dive. I do in fact realize yes it is a benefit, but for how long? Thanks in advance to any physics majors out there!!!

 

[fisheater]

Do you mean that you believe a warm tank will have more air?

If so, lose that thought. The air the tank has is the air that the tank has. The pressure of that air will change with temperature, but the amount of air won't. (Save for what you use for breathing and buoyancy control.)


Sent from my iPhone using Tapatalk

 

[ajtoady]

Sorry, should have clarified. Relating to free flows due to icing.:shocked2:

 

[sambolino44]

I doubt your tank would retain any heat after ten minutes, probably less. I highly doubt the temperature of the tank at the start of the dive would affect the likelihood of free-flow after 45 minutes. But I don't have any hard evidence to back this up, just my guess from experience.

 

[AfterDark]

Keep the reg dry and don't breath the reg until underwater. That's the only way I know of to prevent icing. It goes aginst my grain to do it, but after hundreds of dives during New England winters including ice diving with the same 40 year old Scubapro MK5 piston reg, it seems to work. Never has that reg iced up on me. My tanks are in my cellar 50'sF at best, when I go diving my tank(s) are on the cold ground and in the cold air. By dive time the temp of the air in the tank is probably close to the water temp. I doubt if it makes any difference.

 

[spectrum]

When a tank is filled by all but the most ideal means it probably warms by 20-30 PSI. It can take 40 hours for that mass of gas to equilibration to ambient (70F) for a legitimate pressure check. A drop of 200-300 PSI is possible, especially on a HP fill. That cooling process can take 4 hours. Air being the insulator that it is relies on convection and minor conduction to re;ease it's heat energy.

However, to use the OP's numbers a cylinder that has equilibrated in a 50 degree storage/transport situation will see a nearly instant pressure drop of what can seem like 200-300 PSI when getting into 30 something degree water. Water will of course cool strip heat from the cylinder walls 25 times faster than air so that plays a big part in the disconnect. All that being said the 20 temperature difference is probably very short lived once in the water. Also the air flow of drawing from the tank promotes further circulation and heat exchange.

Adiabatic cooling that takes place as air expands in the regulator process probably plays a more significant roll than surrounding temperature. To be more specific, the load on the regulator can be the promoter of failure. Goosing the drysuit and BC valves while huffing and puffing can put the 1sts stage at risk and severely chilled LP air can result in downstream problems in delivery valves.

I'll opine that a starting difference of 20F is of little significance.

Pete

 

[spectrum]

Way to late to edit but in the prior post the sentence: It can take 40 hours for that mass of gas to equilibration to ambient (70F) for a legitimate pressure check.

Was mean to be:
It can take 4 hours for that mass of gas to equilibration to ambient (70F) for a legitimate pressure check.

 

[ed.hamilton1]

When diving on an aluminium tank I have found that usually within the first five minutes the tank will have reached the ambient water temperature judging by the cylinder pressure and although steel transfers and conducts heat slower I would imagine the difference in tank wall thickness would make this negligible. As a general rule of thumb cylinder pressure will change 0.6 bar for every 1 degree Celsius or 5psi for each degree Fahrenheit.

 

[spectrum]

You will see a big hit as you start your dive from water cooling which is 25X that of still air and initial use. Also since you are drawing from the cylinder there will be turbulence in that mass of air defeating some of it's self insulating properties. Elevated usge as you start the dive and expansion cooling all combine for a sudden initial drop.