Mechanism of Particle Impaction and Filtration by the Dry Porous Metal Substrates of an Inertial Impactor

This study has investigated numerically the particle collection efficiency curves of inertial impactors with a dry porous metal substrate covering a wide range of particle diameters. The results show that the penetrating air causes higher inertial force for particles near the surface of the dry porous metal substrate than that of the flat plate, which increases the collection efficiency due to inertial impaction mechanisms. The calculated collection efficiency curve will be sharper than that assuming 100% filtration efficiency (ideal filtration) and there is a minimum value of <2% at $\sqrt {\bf St}$ = 0.05 ∼ 0.07 (corresponding to d_p = 0.1 ∼ 0.5 m) for different Re and K. The collection efficiency increases to 15% for the ultrafine particles with a diameter of 0.01 m when Re = 3,000 and K = 568,000 cm⁻². When $\sqrt {\bf St}$ → 0, the collection efficiency will approach the curve considering ideal filtration due to diffusion mechanisms.