Enhancement of the collection efficiency of fibrous filtration in the region of maximum penetration

The various topics investigated in the course of the preparation of this thesis can by unified under the common theme of fibrous fIltration enhancement from both experimental and theoretical perspectives. Fibrous filtration is by far the most common method of gas pUrification in use today and further improvements will require a better understanding of the various mechanisms contributing to the collection of particles. The lack of agreement between experimental results and the latest theoretical models found in the literature which have been put forward to predict fIlter efficiency led to the development of a complex computer simulation of a fIltration process. The model simultaneously accounts for particle collection in the inertial impaction, interception and Brownian diffusion regimes and also recognizes that real fIlters do not consist of a simple array of fibres, but are a complex mixture of fibres positioned randomly in space. Test fIlters carefully manufactured from well characterized glass fibre components were used to challenge monosize sodium chloride aerosols. Since most of the filtration parameters are known, our model was used and directly compared with the leading theoretical models and our experimental results. The enhancement of fibrous filters by gradual clogging was investigated. The filtration characteristics; pressure drop and upstream & downstream concentrations were monitored as loading progressed. A discussion of the changes in the quality factor which was found to be dependent upon aerosol size is given. The fractal dimension of the particle deposits on individual fibres was measured and found to be dependent on the fIltration dynamics present. The fundamental forces of electrostatic filtration (Coulomb, image and polarization forces) were clearly demonstrated in a system of test aerosols and fibrous fIlters which were identical except for the amount of charges the particles and fibres contained. The size ranges in which these forces are effective were accurately measured.