The separating effect at the fibre within the filter is different from the separating efficiency of a fibre regarded in isolation. Fibres in a deep bed always have a higher separating efficiency than a single fibre. The filtering efficiency inside the deep bed is a function of the filter porosity, i.e. the packing coefficient. The mean flow velocity is higher and changes in the speed distribution occur around individual fibres due to the influence of neighbouring fibres. The relative position of individual fibres in relation to each other within the bed are random. Flow of the gas through this bed of fibres causes a permanent diversion of the gas current. The continuous friction of the fluid at the boundary layer of this fibre surface builds up an electrostatic charge on the fibre surface. Smallest particles up to 0.01 mm can be caught due to the electrostatic effect.
