The drop in pressure takes heat away thus cooling. Its normal If the air is dry in the tank it should have no effect internally and it will just condense water on the outside and perhaps make ice.
how long to keep air ?
- Thread starter Corlett
- Start date
Please register or login
Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.
Benefits of registering include
- Ability to post and comment on topics and discussions.
- A Free photo gallery to share your dive photos with the world.
- You can make this box go away
About 4.5 billion years, give or take.
N
N
Heat is actually movement (see: kinetic gas model/theory).. Temperature is just a measure of average speed of particles/atoms/molecules (flying around/vibrating). If you touch something hot, it will shake you skin to pieces and you'll get burnt. It may be a small invisible movement but fast and powerfull as you can feel.
Pressure tells what force these particles exert per square feet or so. It is natural that temperature measurement and pressure measurement are related.
It has been found out that pressure times temperature (in Kelvin scale) is a constant in some circumstances. If pressure drops then so does temp, and if one goes up so does the other.
When you empty a cylinder, the pressure drops, and so does the gas temperature. The cold gas cools the cylinder (or: cylinder heats the gas; they will reach equal temp sooner or later). The cylinder cools the air nearby and then water condenses. The valve gets wet and finally ice may form.
If you let the gas out very slowly then cooling is slow and the surrounding room temperature may well keep the cylinder warm/less cold. Less or no ice is formed then, but a lot of time passes.
Pressure tells what force these particles exert per square feet or so. It is natural that temperature measurement and pressure measurement are related.
It has been found out that pressure times temperature (in Kelvin scale) is a constant in some circumstances. If pressure drops then so does temp, and if one goes up so does the other.
When you empty a cylinder, the pressure drops, and so does the gas temperature. The cold gas cools the cylinder (or: cylinder heats the gas; they will reach equal temp sooner or later). The cylinder cools the air nearby and then water condenses. The valve gets wet and finally ice may form.
If you let the gas out very slowly then cooling is slow and the surrounding room temperature may well keep the cylinder warm/less cold. Less or no ice is formed then, but a lot of time passes.
Re: why tanks get cold when gas is released...
Nerd Alert!!
This thread is a few months old, but I just stumbled across it. The previous explanations are all fine, and cover all you need to know regarding air and nitrox cylinders, but I can't resist adding this little "fun fact" about gases.
Different gases are affected by expansion to different degrees - the operative parameter is the Joule-Thompson (J-T) coefficient. The J-T coeffs for most gases (including nitrogen and oxygen) are positive, which means they cool when expanding. But a few gases have negative J-T coeffs, most notably hydrogen and helium. When expanding through a constriction (i.e. valve) these gases get warmer! For most of us this totally goes against "common sense" (or at least common experience), but it was taught (and explained) in a thermodynamics class I took a few decades ago.
Divers and shops don't normally work with hydrogen (H2), but there is a common warning / lore in my lab at work: H2 escaping from a pin-hole leak in a HP hose or fitting can get sufficiently HOT to auto-ignite, which qualifies as a VBT (Very Bad Thing.) I have never seen this in action, but I keep the fact filed away along with "never grease the threads on the O2 cylinder used for glass blowing."
Helium, of course, is nonflammable, so while leaks can be really expensive, they don't cause fires.
Happily providing more than you ever wanted to know about the reversible adiabatic expansion of non-ideal gases,
-Don
Nerd Alert!!
This thread is a few months old, but I just stumbled across it. The previous explanations are all fine, and cover all you need to know regarding air and nitrox cylinders, but I can't resist adding this little "fun fact" about gases.
Different gases are affected by expansion to different degrees - the operative parameter is the Joule-Thompson (J-T) coefficient. The J-T coeffs for most gases (including nitrogen and oxygen) are positive, which means they cool when expanding. But a few gases have negative J-T coeffs, most notably hydrogen and helium. When expanding through a constriction (i.e. valve) these gases get warmer! For most of us this totally goes against "common sense" (or at least common experience), but it was taught (and explained) in a thermodynamics class I took a few decades ago.
Divers and shops don't normally work with hydrogen (H2), but there is a common warning / lore in my lab at work: H2 escaping from a pin-hole leak in a HP hose or fitting can get sufficiently HOT to auto-ignite, which qualifies as a VBT (Very Bad Thing.) I have never seen this in action, but I keep the fact filed away along with "never grease the threads on the O2 cylinder used for glass blowing."
Helium, of course, is nonflammable, so while leaks can be really expensive, they don't cause fires.
Happily providing more than you ever wanted to know about the reversible adiabatic expansion of non-ideal gases,
-Don
Similar threads
