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[Thermo] Derivation of compressibility factor vs reduced pressure

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May4-10, 10:55 PM
P: 2
1. The problem statement, all variables and given/known data
derivation of compressibility factor vs. reduced pressure
I am supposed to derive the graph by solving equations

2. Relevant equations
Van der Waals equation of state
compressibility factor, Z = (Pv)/(RT)
reduced pressure = P/critical pressure
Z = f(Tr, Pr)

3. The attempt at a solution
I sat for 12 hours attempting to find a solution but just spent time trying to understand what I was doing instead.
Is there a way to get the graph mathematically without using any values for critical pressure or temperature?

Thank you!
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution
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May5-10, 03:35 PM
P: 374
Compressibility charts are derived from experimental data from 10 gases such as propane, Nitrogen, Carbon Dioxide etc. Select a gas you have properties for such as propane. Tc propane is 370 K. Pc propane is 42.7 bar. Assume a constant temperature of let's say 555 K to generate the Tr=1.5 line. Vary pressure from 42.7 to 300 bars (Pr 1 to 6). Use propane tables to find v (specific volume) solve for Z. Plot Tr(Z,Pr)
May6-10, 06:42 PM
P: 2
After solving the Van der Waals equation for the compressibility factor and
deriving the critical temperature, pressure, and volume

knowing that a horizontal inflection point occurs on the isotherm at critical point

am I supposed to solve PV3-(Pb+RT)V2+aV-ab=0
for the cubic root?

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