Ventilation of enclosed porous media by the application of periodic pressure variations

Periodic pressure oscillations applied to the opening of closed containers packed with small beads or granular material result in an enhanced washout of undesired gases from those containers. The amplitude of oscillation pressures need not be higher than a small fraction of an atmosphere and the oscillation frequency is just below the auditory range. The time constant of the washout is reduced by two to three orders of magnitude compared to the passive equilibration by diffusion alone. The mechanism is based on gas dispersion within the gaseous phase of the containers and on gas compressibility. It may be used to remove an undesired gas out of a closed container or space filled with granular material such as solid fuel. It is also useful in the purging of porous material such as active coal.