Capillary rise is one of the most complicated transport phenomena in porous media. So far there has been no theory which can claim to describe it adequately. As for fine powders, adequate experimental data in cases of imbibition do not even exist.
Both measuring and evaluation methods have, therefore, been developed by which the most essential parameters can be obtained. Tests on fine powders show that the capillary rise is decisively influenced by dynamic effects. Static capillary pressure-so far regarded as the driving force-can only be decisive at very low transport velocities. The penetration rate of liquid into fine powders is characterised by a dynamic capillary pressure, at least in the initial stages of high velocities.
The newly developed theory was tested with fine powders of different substances.
The results confirmed the original assumptions. Whether, or to which extent, this theory can also be applied to fibrous materials, remains to be seen from tests still
to be carried out.