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# How to calculate air quantity entering container

## How to calculate air quantity entering container

(OP)
Hello,

I have to design sealed container with pressure relief valve in order to maintain same pressure inside the container and the environment. The pressure relief valve works both ways.
The question is how to calculate the air entering in the container when it is exposed to environment with great pressure than inside the container?
I need that air quantity in order to know how much moisture absorbing material i need to put inside the container in order to maintain humidity less than 20%.

Thank you

### RE: How to calculate air quantity entering container

Just make sure the air supplied has less than 20% humidity. Cool the air supply with refrigerated dryer or desiccant dehumidifier.

### RE: How to calculate air quantity entering container

sealed container with pressure relief valve --> so then it's not really sealed, is it?

air entering in the container when it is exposed to environment with great pressure than inside the container --> since you have a pressure relief valve that works both ways (aka 'a hole') how does this condition ever exist?

### RE: How to calculate air quantity entering container

But, is it a hole or a leak? We used to have a system that leaked, and it turns out that other things potentially conspire to make leak behavior non-symmetrical. The box would get heated by the sun during and air would go out; when the sun went down, the box sucked air back in, but it came with condensation, which stayed liquid. The next cycle, the moisture would evaporate, but only a small fraction went out. Over the course of several weeks, we got to the point of having standing water in the system all day.

As for volume, can't you use the Ideal Gas Law as a starting point?

TTFN (ta ta for now)
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### RE: How to calculate air quantity entering container

A leak is different to a pressure relief. A leak flows at any value of DP - a relief valve only flows when DP exceeds the set value.

Why not attach a desiccator and a vented surge tank to the relief valve? (The surge tank will conserve dry air vented from your vessel during discharge events).

je suis charlie

### RE: How to calculate air quantity entering container

"maintain same pressure inside the container and the environment" = differential pressure is zero. So why bother with a valve when a hole will do.

Anyway, thinking further, if you are willing to accept the assumption that real air is close enough to an ideal gas than PV=nRT. Solve for n at the interior pressures of interest and go from there.

### RE: How to calculate air quantity entering container

The only way the OP makes sense is that the "relief valve" is actually a breather vent. The process of air going in and out of the vent is called breathing. Breather vents that contain desiccant are commercially available. A "surge tank" will not help. It would have to breathe as well, unless it could expand and contract freely, which is an option. The amount that your tank breathes depends on the magnitude and frequency of temperature and pressure changes, the tank's air volume, and fluid level changes. This is not something that is calculated. Use a vent desiccator and change it out when the desiccant changes color.
http://www.drytechinc.com/tank-vent-dryers.html

### RE: How to calculate air quantity entering container

"maintain same pressure inside the container and the environment" = differential pressure is zero. So why bother with a valve when a hole will do.

The only way the OP makes sense is that the "relief valve" is actually a breather vent.

Perhaps the OP meant to say "maintain similar pressure inside the container and the environment"? The purpose of a relief valve is then to reduce venting events.

A vented surge tank would increase the life of the desiccant, especially if the surge tank "vent" was a long tube to reduce mixing.

je suis charlie

### RE: How to calculate air quantity entering container

(P1V1)/T1 = (P2V2)/T2

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