Capture and rebound of dust in granular bed gas filters

Experimental data for the efficiency of filtration of gases by fixed beds of granular solids are used to evaluate the reliability of the ‘cell’ and ‘constricted tube’ models for gas flow and aerosol transport. The dominant capture mechanisms are Brownian diffusion and inertial deposition. For Brownian diffusion, both models give sensible estimates for capture efficiency, but this process is shown to be insensitive to the model assumptions. Inertial deposition provides a much more sensitive test, and it is shown that neither model gives satisfactory predictions for the efficiency of inertial capture. Whether a dust particle adheres or rebounds on contacting a filter granule depends on the relative importance of kinetic and adhesion energies. An approach is proposed which enables the theoretical analyses to be applied to predict the limits of adhesion.