Abstract
Some fundamental problems, arising in the filtration of gases by fixed beds of granular collector, are reviewed. Capture of gas-borne particles by the collector normally occurs mainly by the processes of Brownian diffusion, inertial impaction and electrophoretic migration. Diffusional and electrophoretic capture are controlled by processes occurring close to the surface of the collector, and theoretical models are reasonably successful in predicting capture rates. Theoretical estimates for inertial impaction are much less reliable, and reasons for this are discussed. Retention of a particle by the collector is governed by a balance between particle kinetic energy and adhesion energy; trajectory calculations can be used to estimate conditions under which a captured particle is retained by the collector.