When a fine material is loaded into a bunker, air can become trapped between the particles and is gradually expelled as the material consolidates. Two effects need to be considered when analysing the deaeration process; the changing density of the gas as the pressure falls and the changing voidage of the material as it consolidates.
If only the first factor is important and the voidage of the material in the bunker uniform, the theoretical analysis of the deaeration process is straightforward. For modest initial pressures, the pressure at the base of the hopper decays with a half-life of about 0.3H2E/k pa, where k is the Darcy's Law constant, H the height of the fill, E the void fraction and pa is atmospheric pressure.
When consolidation is important, the calculations are very much more difficult due to the changing height of the top surface. A detailed numerical analysis has been performed and the predicted values of the half-life of the deaeration process are presented graphically for a number of cases.
A detailed description of the theoretical analysis and of the computer program is included for the benefit of those wishing to extend the work,