On Draining of Water by Capillary Flow

Abstract

In order to study the draining of water from a vessel by means of capillary rise, experiments were carried out by using two kinds of capillary bundles. One was a packed column of glass beads or silica sands. The other was a bundle of cotton fibers (sterilized gauze) having no column wall.
It was obtained experimentally that the rate of draining Q by capillary flow was given as follows:
(1) In a packed column with a glass wall, Q can be calculated by Kozeny-Carman's Eq. (2) in H_X<h_d.
(2) In a bundle of gauze without a column wall, Q is proportional to the head difference Δ_h and inversely proportional to L', which is the length of a bundle exposed to the air. This is because the draining through the bundle depends on the water surface.
(3) In both cases, Q decreases with increasing the height of capillaries H_X except the lower H_X, due to the decrease of water saturation in the bundles by capillary rise.
As a result, it is suggested that it is possible to drain a supernatant liquid during settling in a sedimentation tank by means of capillary flow in the bundle without a column wall.