I have a cylinder whose liquid volume is 9.2 litres. It is to be filled with pure Nitrogen at a pressure of 150 bar.
What will be the volume of the Nitrogen gas filled in Cu.feet and Cu. metres?
What will be the weight of the filled gas?

The volume of the cylinder is the space inside of it. If you fill it with liquid, that volume is 9.2 litres. What do you think the volume in litres will be if it's filled with gas? Does it get bigger? Smaller? Once you have the volume in litres, you can convert to cubic metres, thanks to the miracle of the Systeme Internationale (aka metric system). Then, you'll also have to find some crazy conversion factor to get cubic feet. Yuck. Google is your friend.

As for the weight of the gas, you're probably going to have to use the ideal gas law to find out how many molecules of nitrogen you have, then use your periodic table to figure out how much mass you have. Remember that molecular nitrogen is not the same as atomic nitrogen! When you have mass in grams, you can convert to weight (force) in Newtons, using acceleration due to gravity.

This whole thing sounds like a horrible practice in unit conversion to me. Pressure in bars, volume in litres, then volume in cubic feet, then weight (not mass! Very different values!)

Good luck!

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Originally Posted by dmatos

The volume of the cylinder is the space inside of it. If you fill it with liquid, that volume is 9.2 litres. What do you think the volume in litres will be if it's filled with gas? Does it get bigger? Smaller? Once you have the volume in litres, you can convert to cubic metres, thanks to the miracle of the Systeme Internationale (aka metric system). Then, you'll also have to find some crazy conversion factor to get cubic feet. Yuck. Google is your friend.

As for the weight of the gas, you're probably going to have to use the ideal gas law to find out how many molecules of nitrogen you have, then use your periodic table to figure out how much mass you have. Remember that molecular nitrogen is not the same as atomic nitrogen! When you have mass in grams, you can convert to weight (force) in Newtons, using acceleration due to gravity.

This whole thing sounds like a horrible practice in unit conversion to me. Pressure in bars, volume in litres, then volume in cubic feet, then weight (not mass! very different values!)

Good luck!

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Thanks dmatos. The answer is theoretical which most of us know.
Can someone help to seriously solve the problem?

Volume of Gas in Cylinder
To find the volume of gas available from a compressed gas cylinder, we apply the Ideal Gas Law (PV = nRT). In a high-pressure cylinder, the volume will be affected by the content's compressibility factor Z (PV = ZnRT). For example, an AL cylinder of pure helium may contain 134 cu. ft. of gas while the same cylinder of pure air may contain 144 cu. ft. under the same conditions. For these practical calculations, however, we assume ideal gas behavior for simplicity.

The Ideal Gas Law PV = nRT

Where:
P is pressure
V is volume
n is the number of moles
R is the gas constant
T is the absolute temperature

When the temperature is kept constant, we can derive the equation:

P (1) x V (1) = P (2) x V (2)

Where:
P (1) is the pressure of the compressed gas in the cylinder (psi)
V (1) is the internal volume of the cylinder, often referred to as water volume (liter)*
P (2) is the atmospheric pressure (1 atm - 14.7 psi)
V (2) is the volume of gas at pressure P (2) (liter).

For example, an AL sized cylinder is filled with nitrogen at 2000 psi. What is the gas volume of nitrogen from the cylinder?
P (1) is 2000 psi
V (1) is the internal volume of AL cylinder 29.5 liter*
P (2) is 14.7 psi
V (2) is the unknown volume of gas

Solving the equation above for V (2) gives:

V (2) = [p (1) x V (1)]/P (2) = (2000 psi x 29.5 liters)/14.7 psi = 4013 liters (approximately 140 cu. ft.)

It would be better to keep all your units either imperial or metric i.e. change psi to bar. However, in your equation, you're dividing psi by psi to get a unitless ratio so it may not matter, just not good practice.
Regards.