The Physics of Water Transfer in Stone - Environmental Geomechanics - page 259

Figure 9.9. Schematic of a device for measuring
permeability with nitrogen [DES 95]

9.3.2. Different expressions of the liquid water flux

Instead of flow in cubic meters per second, Q , liquid water transfers inside
porous materials are usually quantified in terms of mass fluxes, J l . Liquid water
flow is expressed in

-2 −
s

1

[kg.m . ] . The correspondence between these two variables

is then given by:

ρ

l

J = Q [9.20]

l

s

and Darcy's law can be re-written:

k

J = ρ ∇ P [9.21]

l l c

η

or:

J = ρ K ∇ h

[9.22]

l l l

if the suction head h is taken as the state variable, thus introducing the liquid
hydraulic conductivity K l [m.s -1 ].