RH CGS-240 - Page 7

Theory of operation
CGS-240 Manual 6/15/2021
Page 7 of 148
where e is the saturation vapor pressure (in Pascals) over liquid water in the pure phase
T is the temperature in Kelvin
and g
0
= –2.8365744·10
3
g
1
= –6.028076559·10
3
g
2
= 1.954263612·10
1
g
3
= –2.737830188·10
-2
g
4
= 1.6261698·10
–5
g
5
= 7.0229056·10
–10
g
6
= –1.8680009·10
–13
g
7
= 2.7150305
2.3.2 SATURATION VAPOR PRESSURE OVER ICE
Saturation vapor pressure over ice at a given ITS-90 temperature in the range –100 °C to 0.01 °C is defined by the
formula








+=
−
=

TkTke
i
i
i
lnexp
5
1
4
0
(2)
where e is the saturation vapor pressure (in Pascals) over ice in the pure phase
T is the temperature in Kelvin
and k
0
= –5.8666426·10
3
k
1
= 2.232870244·10
1
k
2
= 1.39387003·10
–2
k
3
= –3.4262402·10
–5
k
4
= 2.7040955·10
–8
k
5
= 6.7063522·10
–1
2.3.3 ENHANCEMENT FACTOR
The “effective” saturation vapor pressure over water or ice in the presence of other gases differs from the ideal
saturation vapor pressures given in Equations 1 and 2. The effective saturation vapor pressure is related to the
ideal by
é = e·ƒ (3)
where é is the “effective” saturation vapor pressure
e is the ideal saturation vapor pressure (as given in Equation 1 or 2)
and ƒ is the enhancement factor