Deposition of aerosol particles in fibrous filters

The collection efficiency of glass fiber pads was investigated with a super cooled liquid aerosol. A filter‐velocity range of 0.02 to 20 ft./sec. was covered with filter pads having a bulk density ranging from 1 to 10 lb./cu. ft. and a fiber diameter ranging from 1 to 30 μ. For the aerosol employed the results showed a minimum collection efficiency at a velocity of 2 to 5 ft./sec., dependent on fiber size. At the lower velocities, where diffusion is controlling, collection efficiency increased with decreased velocity; at higher velocities, where inertia is controlling, efficiency increased with increased velocity. For purposes of generalization the data were correlated in terms of dimensionless parameters which allow for the combined effects of flow‐line interception, inertial interception, and diffusinal deposition. Evaluation of the data in terms of existing theories of deposition indicated nominal agreement with the theory of Langmuir, as modified by Natanson, for diffusional deposition. For inertial deposition the measured collection efficiencies were considerably lower than would be predicted from the theoretical values reported by Langmuir and Blodgett for potential flow around the fibers, presumably because of the viscous‐flow (low Reynolds number) conditions that prevailed in this study.