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Partic. vol. 37 pp. 81-90 (April 2018)
doi: 10.1016/j.partic.2017.07.008

Enhancement of filtration efficiency by electrical charges on nebulized particles

Hui Chena, Zhenyi Zhanga, Zhenzhong Zhanga,b,*, Feng Jianga, Ruiming Dua

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zhangzz@mail.tsinghua.edu.cn

Highlights

    • Charge state of particles generated by nebulization was studied. • NaCl aerosol was overall positively charged with a mixture of neutral and charged particles. • Diethylhexyl sebacate aerosol was found to be electrically neutral. • Charges on nebulized NaCl aerosol enhanced the filtration efficiency of HEPA filters.

Abstract

There have been few investigations of effects of electrical charge, carried by lab-generated particles, on filtration efficiency testing. Here, we measured the elementary charge on particles and the fraction of particles carrying that charge with a combined electrometer, differential mobility analyzer, and scanning mobility particle sizer. A typical solid NaCl aerosol and liquid diethylhexyl sebacate (DEHS) aerosol were generated with Collison and Laskin nebulizers, respectively. Our experimental results showed that NaCl aerosols carried more charge after aerosol generation. The average net elementary charge per particle was approximately 0.07. The NaCl aerosol was overall positively charged but contained a mixture of neutral and charged particles. Individual particles could carry at most four elementary charges. According to constant theorem, we speculated that original NaCl aerosol contained 17% neutral, 45% positive-, and 38% negative-charged particles in the diameter range from 30 to 300 nm. A Kr-85 neutralizer was used to decrease the charge on the NaCl particles. Our results indicated that the DEHS aerosol was electrically neutral. The effects of electric charge on particle collection by electret and electroneutral high efficiency particulate air (HEPA) filters were analyzed. Theoretical calculations suggested that charges on original NaCl aerosol particles enhanced the filtration efficiency of HEPA filters.

Graphical abstract

Keywords

Nebulization; Artificial aerosol; Electrical charges; Charge distribution; Electret HEPA filter; Penetration