Theoretical study on deposition of flexible and stiff fibrous aerosol particles on a cylindrical collector

Abstract

The aim of this paper is to analyze theoretically the deposition of fibrous aerosol particles from a gas stream on the cylindrical collectors in fibrous filters. Two limiting (from the point of view of mechanics) cases of a perfectly flexible and of a completely stiff elongated particle are discussed. The governing equations for these models are given. The results of numerical simulations are presented and the influence of the following parameters on the deposition efficieny is discussed: for a flexible particle its size and aspect ratio (slenderness), the gas velocity and the fiber initial orientation, and for the case of a rigid body the particle slenderness and the electric charge on it. For stiff elongated particles the electrostatic effects were taken into account. The observation was made that the fibrous particles tend to follow fluid streamlines, which is achieved by the shape deformation for the flexible fibers, or by rotation for the rigid fibers. The results of computations for the elongated particles were compared with data for spherical particles of same volume. It has been calculated that in the absence of electrostatic interactions the lowest deposition efficiencies are reached by flexible fibers, significantly higher efficiencies correspond to the spherical particles and usually even higher efficiencies are reached by the stiff fibers. It was also shown that the concept of equivalent aerodynamic diameter for fibrous particles is unimportant and invalid. Behavior of the fibrous particles is still not very well understood and, because of the known influence of such aerosols on human health, further studies are necessary.