Gettiing to 32%

[mala]

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.

1. yes sorry..typo.
2.the pressure is transferred immediately throughout the tank but the temperature is not.
conduction through gas is a time dependant thing.
3. I agree .the gas density of all 3 elements is irrelevant although if you want to be pedantic they do all exhibit different thermal capacities.
4/5the gas at the bottom of the tank will be the gas that is heaviest.as you have pointed out the atomic weight is very similar so therefore the gas at the bottom must be the gas that is the coolest.
the gas in the tank will be at one pressure and temp half way during filling.at the end of filling the gas pressure and temp will be higher.ergo the later gas is at a higher temp to the earlier gas.

the gas enters the tank because it has a higher pressure than the gas already in the tank.it enters at the valve.at the valve therefore the temp must be higher than at the base of the cylinder.

6.yes

if the 02 readings didn't change over time after blending then we wouldn't be having this debate.

they do change-so its obvious that there is some unconformity in the tank.

its one of 3 things
1 pressure
2 composition
3 temp.

the pressure and composition do not change over time.

so what does that leave.?

 

[RJP]

1. yes sorry..typo.
2.the pressure is transferred immediately throughout the tank but the temperature is not.
conduction through gas is a time dependant thing.
3. I agree .the gas density of all 3 elements is irrelevant although if you want to be pedantic they do all exhibit different thermal capacities.
4/5the gas at the bottom of the tank will be the gas that is heaviest.as you have pointed out the atomic weight is very similar so therefore the gas at the bottom must be the gas that is the coolest.
the gas in the tank will be at one pressure and temp half way during filling.at the end of filling the gas pressure and temp will be higher.ergo the later gas is at a higher temp to the earlier gas.

the gas enters the tank because it has a higher pressure than the gas already in the tank.it enters at the valve.at the valve therefore the temp must be higher than at the base of the cylinder.

6.yes

if the 02 readings didn't change over time after blending then we wouldn't be having this debate.

they do change-so its obvious that there is some unconformity in the tank.

its one of 3 things
1 pressure
2 composition
3 temp.

the pressure and composition do not change over time.

so what does that leave.?

The temperature change of the gas in the tank is via the change in pressure - which increases the kinetic energy of the gas, as the molecules collide with each other more frequently - not due to transfer of heat via conduction between the gas coming in and the gas already in the tank.

If you had a rigid cylinder, with a plunger at one end, containing 1l of gas and pressed the cylinder to compress that gas to 0.5l... the temperature would rise.

Since the change in pressure is the same for all the gas in the cylinder the change in temperature is the same for all the gas in the cylinder.

Either was, the change in temperature (and therefore pressure) of the gas in the cylinder cannot explain a change in the reading over time, since the neither temperature nor pressure does anything to alter the ratio of N2 to O2 in the tank - the absolute number of molecules of each doesn't change.

The only thing that could cause the readings to change is the existence of some sort of diffusion gradient that needs time to reach equilibrium - but temperature/pressure wouldn't impact this.

Also, keep in mind that temperature in gas law equations is in kelvin, so we're really talking very small differences in temperature. For instance, going from 25C(77F) to 30C(86F) is actually 300 kelvin to 303 kelvin - only a 1% change in absolute temperature from a gas law standpoint.

 

[mala]

The temperature change of the gas in the tank is via the change in pressure - which increases the kinetic energy of the gas, as the molecules collide with each other more frequently - not due to transfer of heat via conduction between the gas coming in and the gas already in the tank.

If you had a rigid cylinder, with a plunger at one end, containing 1l of gas and pressed the cylinder to compress that gas to 0.5l... the temperature would rise.

Since the change in pressure is the same for all the gas in the cylinder the change in temperature is the same for all the gas in the cylinder.

ok.
im frustrated because of my poor explanation of basic physics.

how about this.

there are 2 tanks -one is being filled the other has been filled.
the one being filled is hotter.

the mix in the filled tank is constant.

the mix in the hot tank does not become constant until it has cooled.

therefore it is the temperature change in the tank that has caused the pp02 to change as everything else has remained the same.

if this were not the case then why would rolling the contents make a difference?

 

[ianr33]

therefore it is the temperature change in the tank that has caused the pp02 to change as everything else has remained the same.

ppO2 in an aluminum 80 full of air is around 45 atm. Or are you talking about % O2? (it's not the same thing)

I do agree that heating a tank will increase the ppO2 though !

 

[RJP]

ok.
im frustrated because of my poor explanation of basic physics.

how about this.

there are 2 tanks -one is being filled the other has been filled.
the one being filled is hotter.

the mix in the filled tank is constant.

the mix in the hot tank does not become constant until it has cooled.

therefore it is the temperature change in the tank that has caused the pp02 to change as everything else has remained the same.

if this were not the case then why would rolling the contents make a difference?

The mix in both tanks is constant - once the valve is closed no more molecules of either N2 or O2 enter the tank. Given that truth, it would seem to be a pure diffusion issue, from a physics standpoint. Accordingly the temperature difference between the two tanks in your example is immaterial. It's the difference in "time since filling" that would explain the difference in analysis.

If you think about it, if you could control for all other variables, gas in a hot tank should diffuse faster than a cold tank - since the molecules in it are moving faster.

 

[mala]

The mix in both tanks is constant - once the valve is closed no more molecules of either N2 or O2 enter the tank. Given that truth, it would seem to be a pure diffusion issue, from a physics standpoint. Accordingly the temperature difference between the two tanks in your example is immaterial. It's the difference in "time since filling" that would explain the difference in analysis.

If you think about it, if you could control for all other variables, gas in a hot tank should diffuse faster than a cold tank - since the molecules in it are moving faster.

yes.
the hot tank has faster molecules because of the heat.
the heat comes from the gas entering the tank.
it enters at the top.
the top is hotter.
the gas at the top is moving faster and therefore is different from the gas at the bottom.(its only a small%).
Until the heat has equalised throughout the tank then the pp02 will read low.

or

its magic

or

you can tell me why a reading from a new mix partial pressure tank reads low.?

 

[RJP]

I do agree that heating a tank will increase the ppO2 though !

:d

And the ppN2 as well.

The real question is whether the ppO2 of the cold 02 at the bottom of the tank is equal to the ppO2 of the warmer O2 at the top of the tank?

 

[mala]

ppO2 in an aluminum 80 full of air is around 45 atm. Or are you talking about % O2? (it's not the same thing)

I do agree that heating a tank will increase the ppO2 though !

its late.
% is fine.

---------- Post added December 1st, 2013 at 01:12 AM ----------

ok its been fun.

the 02 in a hot tank of nitrox may be wrong.
the 02 in a cool tank is right.


the only difference is time and temperature.

so either time effects the mix or temp does.

ought to have a poll.

 

[RJP]

yes.
the hot tank has faster molecules because of the heat.
the heat comes from the gas entering the tank.
it enters at the top.
the top is hotter.
the gas at the top is moving faster and therefore is different from the gas at the bottom.(its only a small%).

You keep missing the point about where the heat comes from.

The heat does not "come from the gas entering the tank" (ie - the heat does not "travel into the tank with the gas entering the tank") nor does that heat exist "at the the top of the tank, even though that is where the new gas enters the tank.

The change in heat in the tank comes from the increase in pressure in the tank. That increase in pressure occurs uniformly throughout the tank. Therefore the change in temperature of the gas in the tank occurs uniformly throughout the tank. This would be different if we were talking about a tank being heated by sitting in the sun or over an open flame, where gas nearest the source of the heat would warm faster than gas on the other side of the tank.

If your theory were correct, the gas at the top of the tank should actually be COOLER, since it's pressure has DROPPED from the fill whip (otherwise it wouldn't have moved from the fill whip into the tank.)

I'm still not sure about the precise reason why the tank reads differently - though suspect it's a pure diffusion gradient - but gas laws would suggest that it's can't be existence of a temperature/pressure gradient within the tank itself.

 

[mala]

You keep missing the point about where the heat comes from.

The heat does not "come from the gas entering the tank" (ie - the heat does not "travel into the tank with the gas entering the tank") nor does that heat exist "at the the top of the tank, even though that is where the new gas enters the tank.

The change in heat in the tank comes from the increase in pressure in the tank. That increase in pressure occurs uniformly throughout the tank. Therefore the change in temperature of the gas in the tank occurs uniformly throughout the tank. This would be different if we were talking about a tank being heated by sitting in the sun or over an open flame, where gas nearest the source of the heat would warm faster than gas on the other side of the tank.

If your theory were correct, the gas at the top of the tank should actually be COOLER, since it's pressure has DROPPED from the fill whip (otherwise it wouldn't have moved from the fill whip into the tank.)

I'm still not sure about the precise reason why the tank reads differently - though suspect it's a pure diffusion gradient - but gas laws would suggest that it's can't be existence of a temperature/pressure gradient within the tank itself.

i understand where you are coming from.

the pressure is the same
the temp is the same
the mix is the same.

but the mix isn't the same until a period of time/cooling has occurred.

in post 2 i said it was a theory.
just kick it around and see what happens.