RH CGS-240 - Page 8

Theory of operation
CGS-240 Manual 6/15/2021
Page 8 of 148
The enhancement factor, for an air and water-vapor mixture, is determined at a given temperature and pressure
from the formula












−+






−= 11expƒ
e
P
P
e

(4)
with
i
i
i
Ta

=
=
3
0

(5)
and








=

=
i
i
i
Tb
3
0
exp 
(6)
where P is the total pressure in the same units as e
T is temperature in Kelvin
and a
i
, b
i
depend on temperature range and are given as
for water:
223.15 K to 273.15 K (–50 °C to 0 °C) 273.15 K to 373.15 K (0 °C to 100 °C)
a
0
= –5.5898101·10
–2
a
0
= –1.6302041·10
–1
a
1
= 6.7140389·10
–4
a
1
= 1.8071570·10
–3
a
2
= –2.7492721·10
–6
a
2
= –6.7703064·10
–6
a
3
= 3.8268958·10
–9
a
3
= 8.5813609·10
–9
b
0
= –8.1985393·10
1
b
0
= –5.9890467·10
1
b
1
= 5.8230823·10
–1
b
1
= 3.4378043·10
–1
b
2
= –1.6340527·10
–3
b
2
= –7.7326396·10
–4
b
3
= 1.6725084·10
–6
b
3
= 6.3405286·10
–7
for ice:
173.15 to 223.15 K (–100 °C to –50 °C) 223.15 to 273.15 K (–50 °C to 0°C)
a
0
= –7.4712663·10
–2
a
0
= –7.1044201·10
–2
a
1
= 9.5972907·10
–4
a
1
= 8.6786223·10
–4