Performance study of a DC-corona-based particle charger for charge conditioning

A new DC-corona-based charge conditioner for particles was developed for the processes in which electrical charges on particles are critical to successful operations. The prototype conditioner consists of an outer metal case and a corona discharge tube module capped with a metal screen at one end. A pointed tungsten needle was used in the tube module to produce ions via corona discharge. Ions produced in the tube module were driven into particle charging zone via the voltage difference between the module and conditioner cases. The particle charging zone of the conditioner was designed for quick particle exit once the particles are electrically charged, thus reducing the loss of charged particles. Two unique design features were included in the prototype conditioner, i.e., the implementation of parallel directions of electrical and aerosol flow fields, and variable control of ion concentration in the charging zone. Through the experimental evaluation, we found that the conditioner achieved its highest extrinsic charging efficiency, equivalent or higher than those of existed DC-corona-based particle chargers, when operated at the condition of a 3 lpm (liters per minute) aerosol flow rate, a 2 μA corona current and a 600 V ion-driving voltage. A tandem-DMA technique was utilized to characterize extrinsic charge distributions of particles with various sizes. Last, the birth-and-death charging model with the Fuchs limiting sphere theory for calculating the ion–particle combination coefficient was applied to obtain the charging ion concentration under the various operations of the prototype.

Research highlights► A new DC-corona-based charge conditioner for particles was developed for the processes in which electrical charges on particles are critical to successful operations. ► Two unique design features were included in the prototype charge conditioner, i.e., the implementation of nearly parallel directions of electrical and aerosol flow fields, and variable control of ion concentration in the charging zone via the ion-driving voltage. ► The conditioner design further enables the operation of charge conditioner with either positive or negative ions, offering the great flexibility in controlling the charges on particles. ► For particles in the nanometer size range the prototype achieves the charging efficiency at the same level as those of existed unipolar chargers. ► For large particles the prototype minimizes the overcharging issue by reducing the ion concentration in the charging zone.