charles law question

[11x]

well i got a few dives in now and i am the kind of person that dosent want to know that something works but i want to know why or how it works. i have been reading some theorys and laws of gasses and i came up with a question maby someone here can help me with. charles law states that a gas that is heated expands and builds about 5psi per degree of tempature and that is why when a scuba tank gets cooled (like taking it down below a 50deg thermocline) that the pressure drops because the cooling gasses condense. well my question is this. has anyone ever tried to heat a tank at depth? or even insulate the tank to keep the tempature swing to a minimum? i think a person could possiably aleviate some of the problems we face with breathing compresed air at depth.

 

[Bubbletrubble]

charles law states that a gas that is heated expands and builds about 5psi per degree of tempature and that is why when a scuba tank gets cooled (like taking it down below a 50deg thermocline) that the pressure drops because the cooling gasses condense. well my question is this. has anyone ever tried to heat a tank at depth? or even insulate the tank to keep the tempature swing to a minimum? i think a person could possiably aleviate some of the problems we face with breathing compresed air at depth.

I think of Charles's Law as a specific case of the Ideal Gas Law, in which "p" (pressure) and "n" (moles of gas) are held constant.

What specific "problems" are you attempting to solve?

Practically speaking, how much of a psi swing do you expect to encounter due to a hot tank cooling down in the water? Think about how this might affect gas management, in particular turn pressure and reserve gas.

 

[jhelmuth]

well i got a few dives in now and i am the kind of person that dosent want to know that something works but i want to know why or how it works. i have been reading some theorys and laws of gasses and i came up with a question maby someone here can help me with. charles law states that a gas that is heated expands and builds about 5psi per degree of tempature and that is why when a scuba tank gets cooled (like taking it down below a 50deg thermocline) that the pressure drops because the cooling gasses condense. well my question is this. has anyone ever tried to heat a tank at depth? or even insulate the tank to keep the tempature swing to a minimum? i think a person could possiably aleviate some of the problems we face with breathing compresed air at depth.

Well.... indirectly that was what kinda what Charles said...

But more importantly - why would anyone want to bother with heating a cylinder? You would just reduce the number of molecules of gas by doing so (as you still have to work at rated pressure). What problem do we face with breathing air (a gas) at depth that you belive heating it would solve?


BTW... you 5psi / degree is NOT absolute. Read more on real gas laws and how temperature and pressure affect a gas variably with changes in either or both attributes.

 

[11x]

first of all i want to make shure it is clear that i am trying to learn here not prove anyone wrong.this is the stuff i am wanting to hear from people who know alot more than me. thanks for you input. i was thinking that if a person had a tank at 80 deg with 3000 psi than you plan your dive acordingly and then you take that tank to 40 deg water well instantly you have (5psi per deg for example only) you instantly have 200 less psi correct or not? 200 more psi would give me some more bottom time. plus if you compound the fact at a given depth the gas compresses and your static lung volume takes more gass from your cylinder with each breath. if warmed the tank would you be offsetting some of the gass compression in your cylinder giving you more bottem time. i was also wondering about the fact of lets say your static lung volume was .25 cf wich equales 100 molocules ( i know way off but easy for math) than you are breathing roughly 80 moc. of nitrogen and 20 of o2 at the surface with each breth. well at 5 ata your lung volume does not change and you are now breathing 400 moc. of nitrogen and 100 moc of o2 for the same .25 cf per breath . i think is why the deeper you go the more nitrogen a person loads for a given time. if you could keep that gas from becoming less dense by some means of stabalisation ie. heat than would this give you more bottom time or less nitrogen loading for the same time without heat? maby i am wrong but i dont think a persons body requires more air at a given depth than it soes at the surface.

 

[jhelmuth]

first of all i want to make shure it is clear that i am trying to learn here not prove anyone wrong.this is the stuff i am wanting to hear from people who know alot more than me. thanks for you input. i was thinking that if a person had a tank at 80 deg with 3000 psi than you plan your dive acordingly and then you take that tank to 40 deg water well instantly you have (5psi per deg for example only) you instantly have 200 less psi correct or not? 200 more psi would give me some more bottom time. plus if you compound the fact at a given depth the gas compresses and your static lung volume takes more gass from your cylinder with each breath. if warmed the tank would you be offsetting some of the gass compression in your cylinder giving you more bottem time. i was also wondering about the fact of lets say your static lung volume was .25 cf wich equales 100 molocules ( i know way off but easy for math) than you are breathing roughly 80 moc. of nitrogen and 20 of o2 at the surface with each breth. well at 5 ata your lung volume does not change and you are now breathing 400 moc. of nitrogen and 100 moc of o2 for the same .25 cf per breath . i think is why the deeper you go the more nitrogen a person loads for a given time. if you could keep that gas from becoming less dense by some means of stabalisation ie. heat than would this give you more bottom time or less nitrogen loading for the same time without heat? maby i am wrong but i dont think a persons body requires more air at a given depth than it soes at the surface.

Just as a way to help...


Q: What happens to a gas when you breathe it in (relative to temperature)?


Go back to your instructor and ask him/her why they did not emphasize how on/off gassing is not relative to the volume of gas you breathe - but is strictly a function of the pressure over time and your individual body mechanics at the tissue level on gas absorbtion and release. (shame on them!)


All the best!

Jim

 

[11x]

i guess i rember that dissucion. just sitting here brainstorming i guess that sliped my mind alittle . but i still think if you breathed less in that there would be less to absorb. to some extent

 

[Bubbletrubble]

Typical tidal volume in humans ranges from 390 mL (female) to 500 mL (male). Please feel free to convert from metric to imperial units.

Assuming that tidal volume does not change based on depth, then, yes, you're correct that more molecules of gas will leave your tank for a given breath at greater ambient pressure (greater depth).

Please re-read the section of your OW manual that discusses what factors influence nitrogen loading in divers. You are confusing heating up gas molecules with a change in the partial pressure of the gas. There's a big difference between the two -- one is temperature-dependent, whereas the other is pressure-dependent.

Perhaps this example will clarify things for you: Take a person sitting on a couch at 1 atm and ask him to double his tidal volume. This increases the number of nitrogen molecules in his lungs for a given breath by a factor of 2. What will happen to his nitrogen loading at 1 atm? Will it increase, decrease, or remain unchanged (relative to maintaining his normal tidal volume)?

If you are curious about decompression theory, you may want to read "Deco for Divers" by Mark Powell.

 

[fisheater]

Here's the short answer.

By increasing the pressure in the tank by increasing the temperature, you're NOT increasing the amount of gas, just the pressure. Thus, you're NOT giving yourself more air to breath.

You'd get the same senseless result from simply compressing your tank to increase pressure.

 

[captndale]

Gas absorption is not dependent on the volume of gas you breathe, only on the partial pressure.

Also: The temperature of the gas in your lungs is not the temperature of the gas in the tank.

 

[NJScubaSteve]

i guess i rember that dissucion. just sitting here brainstorming i guess that sliped my mind alittle . but i still think if you breathed less in that there would be less to absorb. to some extent

As others have pointed out this is not an issue of volume. Look at the tables you use for dive planning. There are 2 parameters you input, depth and time. Tank size/pressure is not a factor when considering gas loading.

It's the pressure you are breathing that is relevant, not tank pressure. The pressure you are breathing is dependent on your depth. A diver will have the same nitrogen loading for a given dive whether they use a high pressure tank at 3442 psi or a low pressure tank at 2400 psi. Why? Because in both cases the diver is breathing gas at the same pressure. That is what your expensive regulators are doing for you.

As for getting extra bottom time, for a new diver learning to relax will be the biggest thing. Later on if you want to extend your diving take additional training and you will learn how to do it safely.