Improvement of the Nanoparticle Charging Efficiency of a Single-Wire Corona Unipolar Charger by Using Radial Sheath Airflow: Numerical Study

Abstract

A single-wire corona unipolar charger with radial sheath air was proposed to enhance the nanoparticle charging efficiency. The charger consists of an insulated Teflon tube (inner diameter = 6.35mm) with a 6mm-long grounded porous metal tube placed at its center from which radial sheath air is introduced, and a discharge gold wire of 50m in the outer diameter and 6mm in the effective length. The performance of the charger was evaluated and optimized numerically. The effect of the position of the sheath air opening on reducing charged particle loss was found to be important and two designs were studied. In design 1, both ends of the 6mm wide sheath air opening are aligned with the ends of the 6mm-long discharge wire, while in design 2 the sheath air opening is shifted 2mm toward the left of the leading edge of the wire. At the same operating condition, design 2 was found to have less electrostatic loss than design 1 because of its smaller deposition region for charged particles. Compared to two unipolar chargers with the highest extrinsic charging efficiency for particles smaller than 10nm in diameter, design 2 operated at the applied voltage of +3.5kV, aerosol flow rate of 0.5 L/min, and sheath airflow rate of 0.7 L/min has a comparable extrinsic charging efficiency of 17.2%-70.5% based on particle number for particles ranging from 2.5 to 10nm in diameter. Copyright 2013 American Association for Aerosol Research