設計並校正一氣膠流量16.7 LPM之單極微粒充電器

Abstract

In this study, a unipolar particle charger with operation flow rate of 16.7 L/min was designed and tested. The charger has a cylindrical casing with inner diameter of 38 mm in which a platinum wire of 6 mm in length and 100 μm in diameter is used as the discharge electrode. To test its performance, both the charging efficiencies of the present charger and that of the electrical low pressure impactor (ELPI+TM, Dekati Aerosol Instrument) were calibrated experimentally. For the experiment, monodisperse DOS (Dp=10-900 nm) and oleic acid particles (Dp=1.7-4.7 μm) were used, and the charging voltages of the present charger and the ELPI were adjusted from +2.6-3.8 and +3.6-4.0 kV, respectively. Results show that when the charging voltage adjusted by +3.6 kV, the present charger will yield the highest charging efficiency (Pn, P: particle penetration through the charger; n: average number of charges per particles) of 2.22 to 521 for Dp from 56 nm to 4.7 μm, which is similar to that of the ELPI (Pn=1.97-566 for Dp=56 nm to 4.7 μm). However, for the smaller particles with size range from 10 to 56 nm, the Pn of the present charger (0.1-2.22) is significant higher than that of the ELPI (4.2  10-4-1.97) by 93 to 11 %, respectively. This is mainly due to the material difference in the foundation of the discharge electrode, in which the copper covered with Teflon is used for the present charger while stainless steel is used for the ELPI. For the latter, an additional electric field between the discharge electrode and the foundation will be created during the charging process, which may lead to a higher particle electrostatic loss in the charger especially for the particles with diameter smaller than 56 nm.