Untersuchungen zum Partikelabscheideverhalten submikroner Partikel in Faserfiltern im elektrischen Feld
The filtration efficiency of fibrous filters shows in the submicron particle regime a bold reduction. The reason for this behavior is the transition from interceptional to diffusional particle capture. Particle size dependent filtration mechanisms cause a minimum in filtration efficiency at particle sizes about 0,2 micrometer. Previous investigations have shown that a reduction of particle penetration, i. e. enhancement of filtration efficiency due to variation of the filterstructure (diameter of fibres, packing density, depth of filterlayer) results in a higher resistance to flow and causes a higher pressure drop. Another way to improve filtration efficiency without changing the filter structure is the use of additional electric particle capture mechanisms. The main advantage is the higher filtration efficiency without increasing the pressure drop. Today electric particle capture mechanisms are mainly applied in electret filters, which consist of electric inhomogeneous charged fibres. However, the fibres of electret filters loose their charge with time and particle loading. The electric field inside the filter layer will be neutralized so that filtration efficiency decreases. To avoid this disadvantage a new type of filter can be used, in which dielectric fibres become polarized by an external electric field. This field maintains an inhomogeneous electric field inside the filter layer. Aim of this thesis is the development of a new filter, which will be optimized for filtration efficiency without increased pressure drop in conjunction with external electric fields. The new filter will be produced with alternating thin translucent conducting layers and filterlayers of dielectric fibres. In that way it will be possible to obtain strong electric fields at low applied voltages inside the filter layers. The applied voltage should be in the range of 220V. The flow direction is perpendicular to the layers and parallel to the direction of the electric field.