Lee–Kesler method


The Lee–Kesler method
allows the estimation of the saturated vapor pressure at a given temperature for all components for which the critical pressure Pc, the critical temperature Tc, and the acentric factor ω are known.

Equations

with
and .

Typical errors

The prediction error can be up to 10% for polar components and small pressures and the calculated pressure is typically too low. For pressures above 1 bar, that means, above the normal boiling point, the typical errors are below 2%.

Example calculation

For benzene with
the following calculation for T=Tb results:
The correct result would be P = 101.325 kPa, the normal pressure. The deviation is -1.63 kPa or -1.61 %.
It is important to use the same absolute units for T and Tc as well as for P and Pc. The unit system used is irrelevant because of the usage of the reduced values Tr and Pr.