Evolution of the efficiency and pressure drop of a filter media with loading

A model for calculating the filtration efficiency and the pressure drop of a fiber filter media in dynamic regime was used and modified to take accoun t of both the fiber and the particle size distributions. Measurements mere carried out on two medias employed in industry and two loading aerosols to test the possibilities offered by the model to predict the evolution of bot h the efficiency and pressure drop characteristics. The results show that t he model satisfactorily reflects the variations in efficiency and pressure drop of a media with respect to the loading if its structure is homogeneous and if the deposit of particles takes place within the thickness of the fi ltering layer. On the other hand, the divergence between the model and prac tical experience becomes significant as soon as surface filtration regime o ccurs or when the media has a heterogeneous structure. A test rig was devel oped to determine the filtering characteristics, such as fractional efficie ncy and pressure drop in relation to the degree of loading, from aerosols o f various particle sizes. This study has highlighted the necessity of takin g into account the influence of loading in the methods for testing filters, especially those used in the industry, and demonstrates that the particle size of the test aerosol is a very sensitive parameter.