Wagner equation
The Wagner equation describes the relationship of the saturation vapor pressure P with the temperature T . It is a purely empirical equation.
the equation
In the original publication the following equation is defined:
with , the reduced pressure and , the reduced temperature, and .
Ambrose changed the exponents as follows:
and used this form in the Ambrose-Walton method , a correspondence principle method for estimating the saturation vapor pressure.
The parameters n 1 , n 2 , n 3 and n 4 are substance-specific and are adapted to experimental saturation vapor pressures. The Wagner equation is able to describe the entire saturation vapor pressure curve from the triple point to the critical point with high accuracy.
Example parameters
The parameters apply to the 2.5 / 5 variant:
n 1 | n 2 | n 3 | n 4 | P c / kPa | T c / K | |
---|---|---|---|---|---|---|
water | −7.18274 | −0.00412 | 0.00825 | −4.46463 | 22048 | 647.3 |
Ethanol | −9.28741 | 3.15687 | −7.72514 | 6.07037 | 6383 | 516.2 |
benzene | −6.84783 | 1.01932 | −1.02347 | −5.1528 | 4894 | 562.1 |
acetone | −7.66267 | 1.95961 | −2.54259 | −2.23283 | 4701 | 508.1 |
Further examples:
n 1 | n 2 | n 3 | n 4 | P c / bar | T c / K | |
---|---|---|---|---|---|---|
water | −7.8687 | 1.9014 | −2.3004 | −2.0845 | 220.64 | 647.096 |
ammonia | −7.4648 | 2.1046 | −2.6357 | −0.9621 | 113.5 | 405.5 |
2,2-dimethylpropane | −6.9511 | 1.5422 | −1.7735 | −3.3642 | 31.99 | 433.8 |
literature
- ^ Wagner W., "New vapor pressure measurements for argon and nitrogen and an new method for establishing rational vapor pressure equations.", Cryogenics, 13 (8), 470-482, 1973
- ↑ Ambrose D., "The correlation and estimation of vapor pressures", J. Chem. Thermodyn., 18, p45-51, 1986
- ↑ Dortmund database