Glass-fibre filters with bimodal fibre size distributions

Fibrous filters, produced from binary mixtures of glass fibres of two diame ters and a range of proportions, have been tested with submicrometre-sized monodisperse aerosols. The results have been interpreted with the help of p ressure drop calculations based on a variational Stokes flow model. The the ory predicts that the pressure drop across a mixed-fibre filter is similar to that of a single component filter with the same packing fraction, compos ed of fibres with the surface area mean diameter of the mixture, and the ex perimental results verify the calculation. The filtration efficiency is not treated by rigorous theory, but power law fits show capture by interceptio n to have a stronger dependence on fibre size than capture by diffusional d eposition, though both relationships are weaker than theory predicts. This aspect of behaviour, along with the position and shape of the maximum penet ration peak, also shows reasonable agreement with theory for a uniform filt er composed of fibres with the surface area mean diameter of the mixture. C rown Copyright (C) 2001 Published by Elsevier Science B.V. All rights reser ved.