# Pressure drop / dissolved oxygen

• I
Hello Everyone,

I've been trying to find an answer to this but am not getting anywhere. Any help would be greatly appreciated!

I need to be able to calculate (or more likely estimate) the pressure drop I can expect when putting water under pressure if I know there is air in the system.

For example if I have a plumbing system that I pressurize to 100 PSI then removed the pressure source. I know how much water is in the system and can estimate how much air is trapped in sections where I can not purge it. I know the pressure will drop as air is dissolved into the water but at what PSI will it reach equilibrium and no longer dissolve air into the water?

Can anyone help point me in the right direction?

## Answers and Replies

Chestermiller
Mentor
Google Henry’s law.

Thank you. Henry's law looks like what I need, but I cannot for the life of me figure out how to use it to calculate the pressure drop I will have. Sorry to be so needy but any help would really be appreciated

How about this? I've been able to calculate the difference in concentration of air in the solution after applying the 100 PSI to it using Henry's law. Now if I know the previous and current concentration and the volume of water and air I must be able to use some formula for the pressure. Am I on the right track here?

Chestermiller
Mentor
How about this? I've been able to calculate the difference in concentration of air in the solution after applying the 100 PSI to it using Henry's law. Now if I know the previous and current concentration and the volume of water and air I must be able to use some formula for the pressure. Am I on the right track here?
Why don't you specify a problem, and I'll work an example for you? Specify the total amount of water and the total amount of air, and the pressure you want to consider.