Volume of gas in vessel 1

[cougarfan]

I am stumped or forgot to to do a calculation - if I have a 1000 gallon under zero pressure ( atmosheric) - I have about 133 cf of air ( 7.5 gallons per CF).. but if I pressurze that vessel with air, then I will have more air in the vessel but I forgot how to figure that volume out.....
please help me out....

 

[PUMPDESIGNER]

I believe you stated the last part of your problem incorrectly. Volume inside the tank cannot change.
Do you agree?
Look up and operate Boyles law to calculate anything like you are requesting.

PUMPDESIGNER

 

[Cockroach]

Yeah, buddy probably means mass. If so, the calculation is straight forward, basic chemistry actually:

P = rho x R x T given rho=density, R=gas coefficent, T=temp
R = 29.2 Nm/NK, (gas constant)
T = C + 273.14, (temperature C, Celsius to Kelvin, K)

given pressure P in pascals or N/m^2, compute density, pho. Noting that density is mass over volume, it is trivial to get mass since you know volume, 1000 gal.

m = rho x V

Putting it all together, m = PV/RT.

As all as you now need is the final air pressure at the required temperature and you can solve the equation.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[Assumptions]

Back to basics. Unfortunately we do forget things as we age but fortunately we happen to remember that it is out there somewhere. And if we don't use it it requires a back to basics search.

PV = Z NRT

PV = (m/MW) ZRT

m = PV(MW)/(ZRT)

P : ABSOLUTE PRESSURE
V : VOLUME
MW : MOLECULAR WEIGHT
Z : COMPRESSABILITY ( COOK FACTOR FOR DEVIATION FROM IDEAL GAS)
R : GAS CONSTANT TO BE COMPATABILE WITH UNITS USED
T : ABSOLUTE TEMPERATURE

Calculate "m" at first pressure, may be P=14.696 PSIA if one is at sea level.

Then calculate "m" at your new pressure. (Z may be different at this condition)

Voila now one has the origional mass and the mass at the new conditions.

Hope this twigs some electrons.

Good calculations.

 

[zdas04]

In Oil & Gas we do this all the time to convert from actual cubic feet (ACF) to standard cubic feet (SCF). The ideal gas law works here (i.e., {PV)/(nRT) = constant) so with a bit of manipulation and adding a non-ideal gas compressibility factor, you get:

V(f) = V(i)*[(P(f)*T(i)*Z(i)]/(P(i)*T(f)*Z(f)]

Use your atmospheric pressure, ambient temp, and un-pressurized volume for the initial values and your elevated pressure and temp for the final values (all must be in absolute terms).

This is one of those really nice cases where the theoretical values are damn close to the actual values.

David