Compressibility chart

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[edit] Compressibility chart

A Compressibility chart is used to find Z, the Compressibility factor used to alter the ideal gas equation :

Z=\frac{P \tilde{V}}{R T}

rearranged:

P = {RT\over{\tilde{V}}}

For ideal gas behaviour, Z = 1. Ideal gas behaviour occurs when

  • PR \ll 1
  • TR > 2 (except when PR \gg 1)

Where PR and TR is the reduced pressure and temperature respectively, and Pcr and Tcr is the critical pressure and temperature of the fluid in question then:

P_R = {P \over {P_{cr}}} , T_R = {T \over {T_{cr}}}

The greatest deviation from ideal gas behaviour occurs in the vicinity of the critical point, where Z can be as low as 0.2.

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