Investigations of the effect of electrode gap on the performance of a corona charger having separated corona and charging zones

• An efficient and a versatile indirect unipolar corona charger was developed.
• Many of the features can be modified for a better control of the charging process.
• Varying the electrode gap distance results in an efficient way to regulate the Nit-product.
• A broad range of charging efficiencies is obtained, with decreasing losses.
• Charging levels can be adjusted to be similar to bipolar chargers.

An efficient and a versatile unipolar corona charger was developed. It has indirect charging characteristics, with corona and charging regions separated. Ions were generated by a needle electrode and then driven to the charging region by a sheath flow in order to reduce the electrostatic loss of nanoparticles. The distance of the electrode to the walls can be adjusted by a micrometer, modifying the onset voltage and Nit-productNit-product, and therefore the intrinsic and extrinsic charging efficiencies and loss of charged particles. Experimental results indicate that the generated ion current is practically the same independent of the variation in the applied voltage or corona current, but varying the electrode gap distance seems to be a much more efficient way to regulate the Nit-productNit-product. The charging efficiency can vary from high values, comparable to the higher efficiency chargers presented in the literature, to lower levels such as reached with bipolar chargers.