Compressibility of Nitrogen Gas and Liquid Water

[tb012]

I need to pressurize a volume of 4823 cubic inches to 9500 psi using a set volume of water and nitrogen gas on top. What I don't understand is how to relate the compressibility of the gas to the volume of water and nitrogen needed. The temperature will be around 80 degrees F. I need to develop a relationship to determine the volume of Nitrogen needed, using the compressibility of Nitrogen, pressure of the chamber, and the water volume. Is that enough known information to develop the equation?

 

[georgeverghese]

Compressibility factor z is roughly 1.61 for N2 at this high pressure from T-S diagram of N2 in Perry Chapter 3
Find n

n=P.V/z.R.T

n= kgmoles of N2 gas
V= actual volume of gas space in m3
P=pressure = 656e2 kpa abs
R=8.314kJ/kgmole/degK
T= 300degK

Actual mass of N2 required, kg = n x 28
Standard volume of N2 required, Sm3 = n x 23.645

Henry's Law solubility of N2 in water is most likely small and is ignored here.

 

[georgeverghese]

Accounting for N2 solubility in water at 655 barg, Google tells me H = 6e-5 / MPa, where solubility of N2, the Henry's Law constant, is expressed as mole fraction of N2 / kgmole of water. Simplifying, this works out to 6.2kg of N2 dissolved / m3 of water. Add the corresponding mass dissolved in your volume of water to the mass of N2 in the gas space. Note : Standard volume for gas in Sm3 references 1atm, 15.6degC

 

[pierreick]

George,
My calculation using PR EOS is 1.42 for Z at 26.66C and 656 bars Abs.
Pierre