1979 Volume 5 Issue 6 Pages 630-636
To obtain a more simplified method for analyzing the internal dehydration mechanism of granular beds in the gravitational field, the conventional equation for flow in capillaries is empirically modified in view of the existence of flow of a filmwise liquid. In the new equation, the effects on deliquoring rates due to movement of a filmwise liquid are represented in the term of change in the so-called equivalent drainage height hc in behalf of Nenniger-Storrow's film drainage concept. A simple equation for predicting the average saturation Sav vs. the time θ is derived. A mathematical method for calculation of the moisture distribution in beds at a given time is also presented, by visualizing the beds as an assemblage of capillary tubes of various radii determined from the final equilibrium moisture distribution in accord with the conventional method, and also in consideration of capillary flow accompanied by a filmwise flow in each tube. It is shown that the time changes in average moisture content and moisture distribution can be easily calculated.
Experimental data for gravitational drainage of packed beds of glass beads, calcium carbonate particles and Soma standard sand compare very favourably with calculations under the conditions where the ratio of final drain height to bed height (hc·∞/H) ranges from 0.32 to 0.72.
