# Gas pressure differentials and permeability

In summary: The pressure in both compartments would remain stable indefinitely?No, there would be a loss of pressure over time as the gas diffuses from one compartment to the other.
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.

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.

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?

sophiecentaur
mjc123 said:
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?

Last edited:
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.)

mjc123 said:
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 -

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.

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?

## What is gas pressure differential?

Gas pressure differential refers to the difference in pressure between two points in a gas system. It is typically measured in units of pressure per unit length, such as pounds per square inch per foot.

## How does gas pressure differential affect permeability?

Gas pressure differential plays a critical role in determining the permeability of a material. When there is a large pressure differential, gas molecules are forced through the material more quickly, resulting in a higher permeability. On the other hand, a smaller pressure differential will result in a lower permeability.

## What factors influence gas pressure differential?

The gas pressure differential is influenced by a variety of factors, including the type of gas, the temperature, the pressure, and the properties of the material through which the gas is flowing. Additionally, the length and diameter of the material also play a role in determining the pressure differential.

## What is the relationship between gas pressure differential and gas flow rate?

There is a direct relationship between gas pressure differential and gas flow rate. As the pressure differential increases, the gas flow rate also increases. This is because the higher pressure differential forces more gas molecules through the material, resulting in a higher flow rate.

## How can gas pressure differentials and permeability be measured?

Gas pressure differentials and permeability can be measured using various methods, such as pressure gauges, flow meters, and permeability tests. These tests involve creating controlled pressure differentials and measuring the resulting flow rates to determine the permeability of a material.

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