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:

${\displaystyle \ln P_{r}^{*}=f^{(0)}+\omega \cdot f^{(1)}}$

${\displaystyle f^{(0)}=5{,}92714-{\frac {6{,}09648}{T_{r}}}-1{,}28862\cdot \ln T_{r}+0{,}169347\cdot T_{r}^{6}}$

${\displaystyle f^{(1)}=15{,}2518-{\frac {15{,}6875}{T_{r}}}-13{,}4721\cdot \ln T_{r}+0{,}43577\cdot T_{r}^{6}}$

With

${\displaystyle P_{r}^{*}={\frac {P_{s}}{P_{c}}}}$(reduced vapor pressure) and (reduced temperature) ${\displaystyle T_{r}={\frac {T}{T_{c}}}}$

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

• Ambrose-Walton method

literature

1. ↑ Lee BI, Kesler MG, “A Generalized Thermodynamic Correlation Based on Three-Parameter Corresponding States”, AIChE J., 21 (3), 510-527, 1975.
2. ^ Reid RC, Prausnitz JM, Poling BE, " The Properties of Gases & Liquids ", 4th edition, McGraw-Hill, 1988
3. ^ ^{A b} Brunner E., Thies MC, Schneider GM, J.Supercrit.Fluids, 39 (2), 160-173, 2006
4. ↑ Silva LMC, Mattedi S., Gonzalez-Olmos R., Iglesias M., J. Chem. Thermodyn., 38 (12), 1725-1736, 2006
5. ↑ Dortmund database