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Equation of state for non-ideal gases

  • The P-V-T relationship for real gas needs modification of ideal gas laws.
     1) Compressibility factor
       The compressibility factor Z is a correction term to the ideal gas laws.
     PV=ZRT, z : compressibility factor
  - Z can be estimated using the concept of “corresponding states”.
    It states that gases behave similarly with respect to non-ideality;
    that is, they have the same Z value when they are in corresponding
    states relative to their respective critical pressure and critical
    temperature.

   - Thus, Z can be determined by knowing reduced pressure P, and
    reduced temperature T.

   - The Z values are tabulated (graphed) as a function of P, T, thus Z
    depends on P, T.

                

     where P, and T are the actual pressure and temperature and Pc
     and Tc are the critical values.

 2) Van der Waals (vdw) equation of state
From ideal gas law, corrections in
① Volume
    Real gas has finite volume (ideal gas = volume-less)
    → subtract the gas volume from the total volume.

② Another consideration
    Particles are interacting each other. This correction should be     considered in the pressure term.

              +   =

     Interaction correction     Volume correction

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This article is from the free online course:

Thermodynamics in Energy Engineering

Hanyang University