Liquid Transport in Porous Media
When a dry porous medium, such as a brick or a wick, is brought into contact with a liquid, it will start absorbing the liquid at a rate which decreases over time. For a bar of material with cross-sectional area A that is wetted on one end, the cumulative volume V of absorbed liquid after a time t is
where S is the sorptivity of the medium, with dimensions m/s1/2 or mm/min1/2. The quantity
is called the cumulative liquid intake, with the dimension of length. The wetted length of the bar, that is the distance between the wetted end of the bar and the so-called wet front, is dependent on the fraction f of the volume occupied by liquid. This number f is the porosity of the medium; the wetted length is then
Some authors use the quantity S/f as the sorptivity. The above description is for the case where gravity and evaporation do not play a role.
Sorptivity is a relevant property of building materials, because it affects the amount of rising dampness. Some values for the sorptivity of building materials are in the table below.
| Material | Sorptivity (mm min-1/2) |
Source |
|---|---|---|
| Aerated concrete | 0.54 | |
| Gypsum plaster | 3.50 | |
| Clay brick | 1.16 |
Read more about this topic: Capillary Action
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