Environmental Engineering Reference
In-Depth Information
c
: salt concentration (mole.m
-3
);
R
: ideal gas constant (8.3143 J.mole
-1
.°K
-1
); and
T
: temperature (°K).
The sum of all these potentials gives the total hydraulic head
H
:
ψ
+
ψ
c
g
H
[
m
]
=
=
h
+
z
[9.11]
ρ
g
l
Externally imposed potentials can also be applied in drying experiments by
reverse osmosis, for example.
9.2.3.
Capillary condensation
9.2.3.1.
Kelvin's law
Kelvin's law expresses the equilibrium of pore liquid water with its vapor in a
porous medium. It is obtained by writing the equality between matric and vapor
potentials [CAM 98, DAI 96]. With the previous notations, it gives:
RT
h
=
ln
φ
[9.12]
gM
where:
M
: water molar mass (≈0.018 kg.mole
-1
);
φ: air relative humidity (RH/100).
9.2.3.2
. Conditions for condensing water inside a porous medium
Combining Laplace's law [9.7], capillary suction
h
definition [9.8] and Kelvin's
law [9.12], we get:
2
σ
cos
α
1
r
=
−
[9.13]
ρ
RT
ln
φ
l
which has the inverse form:
2
σ
cos
α
−
ρ
RTr
φ
=
e
[9.14]
l
