PERFORMANCE OF A UNIPOLAR SQUARE-WAVE DIFFUSION CHARGER WITH VARIABLENT-PRODUCT

A recently developed unipolar diffusion charger is described in detail and is investigated. A square wave voltage across the charging zone g uarantees minimized electrostatic particle losses. Subsequently, ultra fine particles can be efficiently charged employing high ion concentra tions. An analytical description of the spatial distribution of ions i n the charging zone illustrates the strong influence of the space char ge field in the charging zone. The distribution of the charging parame ter nt (product of the spatial ion concentration and the residence tim e of particles in the charging region) is shown. This calculated charg ing parameter is described by an averaged single ntBAR. An increasing discrepancy between the experimental and theoretical charging efficien cy size relation is observed by varying the voltage operation paramete r in the charging area. The experimental efficiency size relation is f itted to theory, leading to an effective charging parameter nt(ef). An extrinsic charging efficiency E(ex), which accounts for particle loss es, is defined. E(ex) is shown to exhibit a maximum with respect to nt (ef). The maximum E(ex) is high in comparison with conventional charge r designs, especially for particles in the ultrafine size range.