Performance of Electrically Augmented Fibrous Filters, Measured with Monodisperse Aerosols

A study of the performance of filters in an external electric field has been carried out in controlled conditions using monodisperse aerosols with a charge distribution close to a Boltzmann. The effects of electric field strength, particle diameter, fiber diameter, and filtration velocity have been measured. The results are in basic agreement with existing theory for the capture of particles by polarization forces and indicate that this process is dominant, although other filtration processes are also significant, particularly when the electric field is low. Reasonable correlation between single fiber efficiency and the dimensionless parameter for capture by polarization forces is observed. The agreement is improved by the inclusion of the hydrodynamic factor into the calculation, but this does not remove all discrepancy. If filters are exposed to an electric field for a protracted period, a small persistent residual polarization of the fibers is observed. Loading the filter with aerosol in the laboratory has little effect on its performance, though eventually the aerosol captured in the vicinity of the live electrode causes shorting out.