SPECIFIC VOLUME
SPECIFIC VOLUME
(OP)
I need to calculate the specific volume of nitrogen (in m3 / kg) of Nitrogen at different conditions of Pressure and temperature ( eg 424.7 kPa and 183 K). Thermodynamics is not my strongest area, but I have tried to calculate values as follows:
Using gas law, From V = n R T /P :
n = amount of substance of gas.
If amount = 1kg, then n = number of moles in 1kg of nitrogen . Molecular weight of N2 = 28.0134 g/MOL, therefore in 1g, n = 1000/28.0134 = 35.69720205 moles
R = gas constant. = 8.314472m3 Pa K-1MOL-1
T = 183.7074046 K
P = 424710 Pa
Now, v = 35.69720205 x 8.314472 x 183.7074046 / 424710 = 0.128381672 m3/kg
However, I am not sure if this is correct ( for example, should I be using a value of R which is specific to Nitrogen ? )
Any guidance much appreciated.
Using gas law, From V = n R T /P :
n = amount of substance of gas.
If amount = 1kg, then n = number of moles in 1kg of nitrogen . Molecular weight of N2 = 28.0134 g/MOL, therefore in 1g, n = 1000/28.0134 = 35.69720205 moles
R = gas constant. = 8.314472m3 Pa K-1MOL-1
T = 183.7074046 K
P = 424710 Pa
Now, v = 35.69720205 x 8.314472 x 183.7074046 / 424710 = 0.128381672 m3/kg
However, I am not sure if this is correct ( for example, should I be using a value of R which is specific to Nitrogen ? )
Any guidance much appreciated.





RE: SPECIFIC VOLUME
http://en.wikipedia.org/wiki/Ideal_gas_law
Regards,
SNORGY.
RE: SPECIFIC VOLUME
Regards
RE: SPECIFIC VOLUME
γ = R(air) * T /(SG*P)
With R(air) in units of m^3*Pa / (K * gm) [or kg]
David
RE: SPECIFIC VOLUME
Z (ratio between real and ideal Gas)
"R = gas constant" for any gas!
RE: SPECIFIC VOLUME
Even with the exclamation point, "R" is just the 18th letter of the alphabet. R(universal) or R(bar) is a symbol used in some contexts for the universal gas constant that applies to any gas, like you seem to be trying to say. There is also a gas-specific version which is the universal gas constant divided by the molecular weight of a gas that is pretty useful for a lot of real-world calculations.
Also, I can't see any reference to compressibility in anyone's posts above. What exactly are you talking about?
David
RE: SPECIFIC VOLUME
Isn't it better to use the data from
RE: SPECIFIC VOLUME
David
RE: SPECIFIC VOLUME
In any event, at T = 183 K and P = 427 kPa, I suspect Z is almost equal to 1.0?
Regards,
SNORGY.
RE: SPECIFIC VOLUME
http://www
RE: SPECIFIC VOLUME
David
RE: SPECIFIC VOLUME
RE: SPECIFIC VOLUME
For nitrogen the critical temperature is 126.2K so you are still above this, but getting close. You can expect a 1 or 2% deviation for Z. By contrast, hydrogen has a critical temperature of 33.2K and at 183K you could take Z=1 with confidence (at the low pressure you are working at). Carbon dioxide with a critical temperature of 304.2K would have a significant deviation of Z from 1 at your temperature.
As a free alternative to the excellent software recommended by zdas04 you could download the Uconeer units conversion program from my web site - see signature below. (Disclaimer - I am the author of Uconeer.) Uconeer has a function to convert gas flows from mass basis to volume basis and obviously you need the gas density to be able to do this. The software estimates the density using the Peng Robinson EOS and reports the density and compressibility.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: SPECIFIC VOLUME
PV = (m/M)RT (m/M = n)
Maybe this is what mikebb was getting at for the element specific equation?
Mike McCann
MMC Engineering
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