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

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 withTc = 562.12 KPc = 4898 kPaTb = 353.15 Kω = 0.2120
the following calculation for T = Tb results:Tr = 353.15 / 562.12 = 0.628247f = −3.167428f = −3.429560Pr = exp + ω ''f = 0.020354P'' = Pr · Pc = 99.69 kPa
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.