Question

How is the compression factor calculated? Show the derivation of the feasible equations for determining the compression factor that can be used.

Answer 1

Compressibility factor, usually defined as Z = pV/RT, is unity for an ideal gas.

In most engineering work, the compressibility factor is used as a correction factor to ideal behavior. Thus, v_real = Z is used to calculate the actual volume, vreal, as the product of the compressibility factor and the ideal gas volume, all at the same pressure and temperature. Z is most commonly found from a generalized compressibility factor chart as a function of the reduced pressure, p_r = p/p_c, and the reduced temperature, T_τ = $\frac{T}{T_c}$ where p_c and T_r are the reduced variables and the subscript 'c' refers to the critical point.