Gettiing to 32%

[RJP]

temperature equalization is not possible?

drysuits work because air does not conduct heat easily. diver warm-water cold.


next time you get a fill put your hand on the tank.
top hot
bottom not so hot
gas in top hot
gas at bottom not so hot.

work it out.

Please don't confuse "the tank" with "the gas inside the tank." The tank is warmed or cooled via conduction based on the temperature of the gas inside it. I assure you, that if you could put two pressure gauges inside the tank - one at the top and one at the bottom - you would see that the pressure at the top of the tank is always the same as the pressure at the bottom of the tank. Accordingly, the temperature of the gas in the top of the tank must be the same as the temperature at the bottom of the tank. (Again, unless you were so ehow able to rig up a system that blended compressed air with liquid O2.

And please dont don't bring dry suits - or potato pancakes, for that matter - into the conversation as neither have anything to do with the pressure/temperature relationship of gases in a rigid container. Drysuit insulate by preventing conduction of heat, not via any gas pressure/temperature dynamics. You have to "think inside the tank" on this one.

The fact of the matter is that the relationship between a gasses temperature and pressure is direct and absolute, and the relationship/equation does not include a variable for time.

All that said, let's go back to your theory that adding 02 to an empty tank actually cools the tank... via expansion. Keep in mind that the tank can never be "empty" because at 0psi it actually has 1atm of some gas in it. Accordingly, any 02 added to the tank increases the pressure of the gas in the tank (because it is being compressed, rather than expanding) and therefore raises the temperature of the gas in the tank. (Take an "empty" tank to your LDS ask them to hook it up to the fill station and begin filling it. Put your hand on it. Does it get warmer or colder? Note - doesn't matter if 02 or air, gasses behave the same.)

 

[mala]

Please don't confuse "the tank" with "the gas in the tank." The tank is warmed or cooled via conduction based on the temperature of the gas inside it. I assure you, that if you could put two pressure gauges inside the tank - one at the top and on at the bottom - you would see that the pressure at the top of the tank is always the same as the pressure at the bottom of the tank. Accordingly, the temperature of the gas in the top of the tank must be the same as the temperature at the bottom of the tank. (Again, unless you were so ehow able to rig up a system that blended compressed air with liquid O2.

And please dont don't bring dry suits - or potato pancakes, for that matter - into the conversation as neither have anything to do with the pressure/temperature relationship of gases in a rigid container. Drysuit insulate by preventing conduction of heat, not via any gas pressure/temperature dynamics. You have to "think inside the tank" on this one.

The fact of the matter is that the relationship between a gasses temperature and pressure is direct and absolute, and the relationship/equation does not include a variable for time.

All that said, let's go back to your theory that adding 02 to an empty tank actually cools the tank... via expansion. Keep in mind that the tank can never be "empty" because at 0psi it actually has 1atm of some gas in it. Accordingly, any 02 added to the tank increases the pressure of the gas in the tank and therefore raises the temperature of the gas in the tank. (Take an "empty" tank to your LDS ask them to hook it up to the fill station and begin filling it. Put your hand on it. Does it get warmer or colder? Note - doesn't matter if 02 or air, gasses behave the same.)

pressure isn't temperature.

yes the pressure of the tank is equal at the top to the bottom.
immediately after filling the top is hotter than the bottom
the gas is hotter in the tank at the top than at the bottom.
the atoms at the top are more active and take up more space than the atoms at the bottom.
if fact the only thing that is constant in the tank is the pressure.

when you compress something it heat up.
the opposite for expansion.
a 100bar j of 02 will expand its gas into a 1 bar tank that is empty.
so to start with the expanding 02 will cool a tank until the pressure has equalized.

the devil is in the detail as my astrophysics lecturer used to say.

there is a law called the combined gas law.
its not really a law-its a guidline that only works sometimes at standard temps and pressures.

 

[dumpsterDiver]

Please don't confuse "the tank" with "the gas in the tank." The tank is warmed or cooled via conduction based on the temperature of the gas inside it. I assure you, that if you could put two pressure gauges inside the tank - one at the top and on at the bottom - you would see that the pressure at the top of the tank is always the same as the pressure at the bottom of the tank. Accordingly, the temperature of the gas in the top of the tank must be the same as the temperature at the bottom of the tank. (Again, unless you were so ehow able to rig up a system that blended compressed air with liquid O2.

And please dont don't bring dry suits - or potato pancakes, for that matter - into the conversation as neither have anything to do with the pressure/temperature relationship of gases in a rigid container. Drysuit insulate by preventing conduction of heat, not via any gas pressure/temperature dynamics. You have to "think inside the tank" on this one.

The fact of the matter is that the relationship between a gasses temperature and pressure is direct and absolute, and the relationship/equation does not include a variable for time.

All that said, let's go back to your theory that adding 02 to an empty tank actually cools the tank... via expansion. Keep in mind that the tank can never be "empty" because at 0psi it actually has 1atm of some gas in it. Accordingly, any 02 added to the tank increases the pressure of the gas in the tank (because it is being compressed, rather than expanding) and therefore raises the temperature of the gas in the tank. (Take an "empty" tank to your LDS ask them to hook it up to the fill station and begin filling it. Put your hand on it. Does it get warmer or colder? Note - doesn't matter if 02 or air, gasses behave the same.)

Wow you are so wrong...

 

[RJP]

when you compress something it heat up.
the opposite for expansion.
a 100bar j of 02 will expand its gas into a 1 bar tank that is empty.
so to start with the expanding 02 will cool a tank until the pressure has equalized.

Think only about the tank being filled and the gas inside that tank - the gas inside that tank is NOT expanding as that tank is filled. It is being compressed. If this was not the case, you couldn't get the gas into the tank. (Nor would a gauge attached to that tank show the psi increasing from zero to whatever.)

As as to needing the tank to equalize in order for the temperature to begin to increase, are you suggesting that a tank hooked up to a 4000psi bank will not warm if is filled to 1,500psi --- because the two tanks have not equalized? If this were the case, scuba cylinders would never get warm.

Either way, we've gone far enough afield on this thread. The op should buy an analyzer.

 

[mala]

Think only about the tank being filled and the gas inside that tank - the gas inside that tank is NOT expanding. It is being compressed.

yes it is

12l of air at 1 bar is being compressed by 12 l of gas that was at 100 bar and is now at 1.01bar.

at the end of the day after 30 mins it really doesn't matter.

but the reason for the fudge factor has always interested me.

 

[RJP]

yes it is

As long as the tank size remains constant, the gas inside that tank cannot expand as more gas is added. It's just not possible. In fact, in a closed system of rigid containers, there is no expansion anywhere merely flow of gas along a pressure gradient. The concentration of molecules changes (more molecules in the same volume tank, as pressure increases) but that's not the same as expansion. Two 12l tanks connected to each other can never contain more than 24l of gas at any given pressure*. Different than if a 12l tank was connected to a 500l flexible balloon. Gas released into such a balloon would expand, since the container is not rigid the can, and does, expand.

*they could contain LESS than 24l if one of the tanks were vacuumed to remove all gas. Gas released into a vacuumed tank WOULD expand until the pressure in the tank reached 0psi - because the system would effectively go from being a 12l system to being a 24l system. From the point that the second tank increases above 0psi, the gas in that tank would stop expanding and start being compressed.

(This topic has been beaten to death in the aforementioned thread...)

 

[mala]

ok I find this interesting.

right or wrong there must be a reason why a nitrox mix done using the partial pressure method gives an inconsistent result initially but after a period of time settles down to the calculated mix based on the volume method.

1. high pressure 02 is added to a low or empty tank.
the 02 must expand from its high pressure into the lower pressure vessel unless the mix is very high 02.(that's deco mix or higher)
temp change would be nil or low

2. high pressure air is then added to top the tank to working pressure.

as air flows only from high pressure to low we can assume that the air entering the tank must be of a higher pressure on the feed pipe than that in the tank.
lets say this takes 10 mins.
at all time during this 10 mins the air is always of a higher temp(pressure) than the air in the tank.

as this higher temp air enters the top of the tank it is extremely unlikely(impossible)that it will pass on its higher energy to all the contents of the tank immediately and that the colder(relatively denser gas) at the bottom will be last to mix.

so when you test the gas immidiatly after mixing the hot air is at the top and the cold 02 is at the bottom.

roll it around and it all changes like magic.

please if you can find a better explanation let me know.

 

[NAM001]

I find that when PP blending that you have to let the tank cool before toppiing off with air. The faster the o2 fill the worse it gets. If they are putting 450 of 02 in a tank with a relativly fast fill. the 450 will drop to 400 or so. and that creates lass than 32 nitrox. i did this with a tank of 40% and filled 780 o2 or better to get the cooled 720 or so needed for the 40% mix. I have never seen a mix difference from time of mixing to use time more than a couple of tenths. its all in how you do it. as far as rolling tanks, it makes no sence to me... You are shooting a spray of air in an o2 environment and thinking it wont stir the existing gas in the tank. I will normally do the o2 the night before topping off with air.

 

[RJP]

as air flows only from low pressure to high we can assume...

as this higher temp air enters the top of the tank it is extremely unlikely(impossible)that it will pass on its higher energy to all the contents of the tank immediately and that the colder(relatively denser gas) at the bottom will be last to mix.

please if you can find a better explanation let me know.

Forgetting the whole "does EANx analyze properly immediately" thing, you've got the basic laws of physics all messed up in your attempt to figure out why that may or may not happen.

1.) Gas flows from high pressure to low, not the other way around.

2.) The pressure from gas entering the tank does transfer energy to all gas molecules in the tank immediately and uniformly

3.) The density of 02 (Atomic weight 15.9) and N2 (Atomic weight 14) is for all practical purposes the same.

4.) The gas already in the tank is not "at the bottom" of the tank; it fills the entire volume of the tank.

5.) The gas already in the tank is not "more dense because it's colder" because - in a non-liquid state, and at a normal ambient temperature - at all points in time during the fill process the temperature of all gasses in the filling tank (and therefore the pressure/density) all the gas in tank is uniform. (Pressure/density, and temperature are not "the same thing" but they do vary uniformly.)

6.) The gas in the tank being filled is actually LESS dense (few molecules per volume) by definition, than the density of the gas coming from the compressor or fill bank, becuase it must be at a lower pressure in order for pressure gradient to exist and therefore the tank "receiving" gas during the filling process. The density (pressure) of the gas increases during this process.

 

[billt4sf]

I consider that my question was answered back by BoulderJohn in post #15. And it also helped me to read a nearby thread.

Maybe Santa Claus will bring me an analyzer for Christmas.

But Hey! Feel free to keep discussing as long as you wish. Personally, I'm going diving.

- Bill