設計並校正一氣膠流量16.7 LPM之單極微粒充電器

Abstract

本研究設計一氣膠流量為16.7 L/min之單極微粒充電器，本充電器由進、出口管(內徑38 mm)及充電座組成，充電座上裝有一長度為6 mm、外徑為100 μm的鉑(Platinum, Pt)線作為放電電極。為了解本充電器之充電效率，本研究以實驗校正本充電器之及商業化儀器ELPI+(Electrical Low Pressure Impactor, ELPI+TM, Dekati Aerosol Instrument)。本研究以癸二酸二辛酯(Dioctyl Sebacate, DOS)(Dp=10-900 nm)及油酸(Oleic Acid, OA)( Dp=1.7-4.689 μm)單徑微粒，校正兩充電器之充電效率。實驗校正時，本充電器之充電電壓範圍介於+2.6-3.8 kV，而ELPI+之充電電壓介於+3.6-4.0 kV。 實驗結果顯示，當充電電壓為+3.6 kV時，本充電器有最佳之充電效率Pn (微粒對充電器之穿透率P、微粒平均帶電量n)。粒徑56 nm-4.689 μm之充電效率為2.22-521，而ELPI+充電器為1.97-566，兩充電器沒有太大的差異。然而本充電器對粒徑10-56 nm之充電效率Pn為0.1-2.22，明顯高於ELPI+的4.210-4-1.97，本充電器之充電效率明顯優於ELPI+，差異達到93-11 %。探討兩充電器之內部結構，本充電器之充電座內部為銅棒，外殼則以鐵氟龍絕緣，而ELPI+充電座整體皆為接地的不鏽鋼。這會導致ELPI+在充電過程中，額外的電場在電極線與充電座間形成，使得微粒受到靜電損失影響，尤其是小於56 nm之微粒較劇。

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.