Gas pressure differentials and permeability

[adam walker]

We are trying to design a new product which uses gas pressures
in various ways. We are a little foxed about partial pressures:

Imagine a small cylinder; 6in long + 1in in diameter.
The cylinder is made from steel.
The cylinder is divided into two equal compartments – A and B.
Each compartment holds pressurized gas at 80psi
In compartment A. the gas is air
In compartment B. the gas is Nitrogen
The wall that divides the cylinder is made from rubber.
The rubber is gas permeable.

Oxygen has a higher partial pressure than Nitrogen.
Oxygen is 21% of the gas in compartment A.

QUESTION:

Would that cause a change in the gas balance between the compartments over time?
For example: Would there be a transfer of gas from A to B?

Thanks Very Much.

 

[sophiecentaur]

Would that cause a change in the gas balance between the compartments over time?

Isn't this just a diffusion question? Oxygen molecules would eventually spread out so that their concentration is the same on both sides. Likewise for Nitrogen.

 

[mjc123]

We are a little foxed about partial pressures:

It looks like it. Why do you say that oxygen has a higher partial pressure than nitrogen?

 

[adam walker]

It looks like it. Why do you say that oxygen has a higher partial pressure than nitrogen?

Thanks for comment.
I think I have phrased this all badly.
The core issue is that oxygen diffuses through a material more easily than nitrogen.

So my confusion relates to the degree to which the nitrogen on one side and the air on the other side would mix or exchange when the starting pressure on both sides is equal. And the rate at which that would happen.
e.g. one side is 21% oxygen 79% nitrogen; the other is 100% nitrogen;
does that mean that over time an exchange will occur until each side is 89.5% nitrogen and 10.5% oxygen?
While the 80psi pressure remains the same on both sides?

 

[mjc123]

Eventually, yes, that is what will happen. In the short term, the pressure will be higher in B as oxygen diffuses from A to B faster than nitrogen diffuses from B to A, but eventually the system will equilibrate. (Coming back to partial pressures, diffusion of a gas will occur until the partial pressure of the gas is the same on both sides, but this process will be faster for oxygen than nitrogen.)

 

[adam walker]

Eventually, yes, that is what will happen. In the short term, the pressure will be higher in B as oxygen diffuses from A to B faster than nitrogen diffuses from B to A, but eventually the system will equilibrate. (Coming back to partial pressures, diffusion of a gas will occur until the partial pressure of the gas is the same on both sides, but this process will be faster for oxygen than nitrogen.)

Thanks for your opinion I find it most valuable.
What we are designing does not need nitrogen – we only considered it because we thought it might extend the period before there was any loss of pressure;

So -

As a follow up:
Assuming an air tight cylinder with two compartments
Assuming both compartments have an equal pressure of 80psi
And BOTH contain air (no nitrogen)
And the wall between them is permeable
On the basis of what you have said thus far:
Is it the case that the pressure in both compartments would remain stable indefinitely?
Or is there something else that would alter that?
(again assuming there was no leakage from the cylinder)

Many Thanks.

 

[mjc123]

And BOTH contain air (no nitrogen)

Air is 79% nitrogen, so they must. You mean no pure nitrogen, as distinct from air?
If both compartments have the same pressure and same composition, why should anything change?