Cox equation

The Cox equation , named after Edwin R. Cox , describes the temperature dependence of the saturation vapor pressure .

the equation

${\displaystyle \ln P=\ln P_{\mathrm {B} }+\left(1-{\frac {T_{\mathrm {B} }}{T}}\right)e^{A+B{\frac {T}{T_{\mathrm {B} }}}+C\left({\frac {T}{T_{\mathrm {B} }}}\right)^{2}}}$

With

• ${\displaystyle P_{\mathrm {B} }}$: Atmospheric pressure (101.325 kPa, 760 mmHg, 1 atm etc.)
• ${\displaystyle T_{\mathrm {B} }}$: Normal boiling point in Kelvin
• ${\displaystyle T}$: Temperature in Kelvin
• ${\displaystyle P}$: Saturation vapor pressure (unit like ) ${\displaystyle P_{\mathrm {B} }}$
• ${\displaystyle A}$, , : Adjustable parameters ${\displaystyle B}$ ${\displaystyle C}$

Example parameters

The parameters apply to the pressure in kPa .

	A.	B.	C.	T B [K]
water	2.84752	−0.373817	0.115553	373.15
Ethanol	2.88861	−0.337726	0.080293	351.45
benzene	2.75247	−0.548608	0.183931	353.24
acetone	2.82386	−0.616847	0.216375	329.25

literature

1. ^ Cox ER, "Pressure-temperature chart for hydrocarbon vapors", Ind.Eng.Chem. Ind.Ed., 15 (6), 592-593, 1923
2. ↑ Dortmund database