# Compressed nitrogen v flow rate question

1. Feb 8, 2015

### yoyo28

Currently i have a system using bulk argon and i am changing to nitrogen. To trial this i am going to use cylinders
of OFN(oxygen free nitrogen). how do i caculate how many cylinders i need based on a flow rate of 16 liters/min.

Thanks

2. Feb 8, 2015

3. Feb 9, 2015

### yoyo28

Its a 44-w (9.78 Cubic Mtrs) @200bar going into a machine that consumes 16 liters of gas per minute. how many of these cylinders would i need and how do you calculate usage?

Thanks

4. Feb 9, 2015

### Bystander

You know how fast you're using it.
You know how much is in a cylinder.
You can calculate how long a cylinder will last at that rate. Decide how long you'll run on nitrogen and calculate the number of cylinders you need.

5. Feb 10, 2015

### yoyo28

Does it matter what pressure the cylinder is at(200bar) v machine (6bar).

6. Feb 10, 2015

### Bystander

The way I read the link for the "44-W," the 9.78 is the content of the cylinder at STP. Now you've given me a lower service pressure of 6 bar (gauge or absolute?) which changes things. For your purposes the cylinder will be empty at 6 bar, gauge will be different from absolute. Any other details to add before we start a rough calculation?

7. Feb 10, 2015

### yoyo28

this is gauge pressure. what formula are you using?

8. Feb 10, 2015

### Bystander

For seven atm., the ideal gas equation of state should be good enough. 9.78 over 7 is 1.4 m3 for your use, - 44 liter left in the cylinder when "empty" is 1.35, over 16 liter/min is an hour and 20 minutes per bottle. You'll want to check with the vendor about the 9.78 m3, but that looks about right.

9. Feb 10, 2015

### yoyo28

Thanks, would this be the same calculation for other gas(argon). ie machine with flowrate of 0.5l(argon/nitrogen) per minute. So 1.35/0.5 = 2700 min.
why are you deviding by 7?

10. Feb 10, 2015

### Bystander

You're running at an absolute pressure of seven atmospheres.