Volumetric Ratio Calculation
Volumetric Ratio Calculation
(OP)
Hi,
I'm trying to determine the proper equation required to calculate volumetric ratios between compressed, liquified gases and the same gas at atmospheric pressure. For example, let's assume that I have 10cc of liquified CO2 in a pressure vessel at room temperature ( Vapor pressure = 849 psig @ R.T.) and I release it to the atmosphere (also at room temperature). What volume of gas would I have at atmospheric pressure? Any assistance with the proper equation would be greatly appreciated.
Thanks
I'm trying to determine the proper equation required to calculate volumetric ratios between compressed, liquified gases and the same gas at atmospheric pressure. For example, let's assume that I have 10cc of liquified CO2 in a pressure vessel at room temperature ( Vapor pressure = 849 psig @ R.T.) and I release it to the atmosphere (also at room temperature). What volume of gas would I have at atmospheric pressure? Any assistance with the proper equation would be greatly appreciated.
Thanks





RE: Volumetric Ratio Calculation
"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek
RE: Volumetric Ratio Calculation
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
RE: Volumetric Ratio Calculation
CO2 Liquid Density @ 20degC: .77g/cc
CO2 Molecular Weight: 44.01g/mol
Assume 1cc compressed liquid volume to keep things simple
Mass=DV=(.77g/cc)(1cc)=.77g
n=Mass/Molecular Weight=(.77g/44.01g/mol)=.0175mol
V=nRT/P=(.0175mol)(82.057cm^3atm/Kmol)(293.15K)/1atm=420.9cm^3
Does this look correct? The reason I ask is that its approximately half of what is listed on AirLiquide's website HERE so I'm trying to figure out why there's a discrepancy.
RE: Volumetric Ratio Calculation
CO2 Liquid Density @ 20degC: .77g/cc
Assume 1cc compressed liquid volume to keep things simple
Mass=DV=(.77g/cc)(1cc)=.77g
Gas Density @ 1atm, 20degC: .0018394g/cc
V=M/D=.77g/.0018394g/cc=418.6cc (basically the same as above).
So I'm assuming the data on Air Liquide's website is incorrect or could I be failing to account for something?
RE: Volumetric Ratio Calculation
RefProp says that at 20C and 1 bara the fluid is superheated and the density is 1.8152 kg/m^3. Dividing mass by density gives me 429 cm^3. I think you gave Air Liquide an incorrect parameter.
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
RE: Volumetric Ratio Calculation
I have done this type of calculation many times in the past and, like David, always resorted to simple, direct available thermo data. Please refer to the attached Excel Workbook for the explanation and calculation of the coresponding gas volume to 10 cm3 of liquid CO2.
I also have found various mistakes in the AirLiquide compressed gases website some years back, so I wouldn't be surprised if their algorithm for detrmining the gas/liquid ratio was inaccurate.
The main point I would draw attention to in this thread is that the liquid CO2 - as defined by McCawley (the OP)- is definitely in the saturated state. This is the normal way you would find liquid CO2 if it is pure. And the OP has stated that it is CO2, so we must assume that it has pure properties. The OP has failed to state this fact, as well as identifying his atmospheric pressure and so-called "room" temperature. But note that since the liquid CO2 has to be saturated at the stated vapor pressure, this then identifies what the OP's "room" temperature is: 21.6 oC.
The calculation is simple; what is harder is understanding the phase equilibria taking place when one has a pure, liquefied gas. There is no supercooling.