Lee-Kesler method
The Lee-Kesler method - named after Byung Ik Lee and Michael G. Kesler - allows the saturation vapor pressure P s at the temperature T for any substance by means of the critical pressure P c , the critical temperature T c and the acentric factor ω to estimate the substance according to the following equation:
With
(reduced vapor pressure) and (reduced temperature)
In the case of polar substances and low pressures, the error can be up to 10%, in general the calculated pressure is too low. At pressures above 1 bar, i.e. above the boiling point, the error is less than 2%.
Sample calculation
For benzene results with
- T c = 562.12K
- P c = 4898 kPa
- T b = 353.15K
- ω = 0.2120
following calculation for T = T b :
- T r = 353.15 / 562.12 = 0.628247
- f (0) = −3.167428
- f (1) = −3.429560
- P r * = exp (f (0) + ω f (1) ) = 0.020354
- P s = P r * P c = 99.69 kPa
Correct would be P = 101.325 kPa, the normal pressure. The deviation is thus −1.63 kPa or −1.61%.
It must be ensured that T and T c as well as P and P c are each used in the same units; but which unit it is is irrelevant due to the use of the reduced quantities T r and P r . A limitation of this statement is that an absolute temperature unit must be used, e.g. Kelvin and Rankine , but not degrees Fahrenheit , degrees Celsius or degrees Réaumur .
See also
literature
- ↑ Lee BI, Kesler MG, “A Generalized Thermodynamic Correlation Based on Three-Parameter Corresponding States”, AIChE J., 21 (3), 510-527, 1975.
- ^ Reid RC, Prausnitz JM, Poling BE, " The Properties of Gases & Liquids ", 4th edition, McGraw-Hill, 1988
- ^ A b Brunner E., Thies MC, Schneider GM, J.Supercrit.Fluids, 39 (2), 160-173, 2006
- ↑ Silva LMC, Mattedi S., Gonzalez-Olmos R., Iglesias M., J. Chem. Thermodyn., 38 (12), 1725-1736, 2006
- ↑ Dortmund database