Hm. Chein et Da. Lundgren, A VIRTUAL IMPACTOR WITH CLEAN-AIR CORE FOR THE GENERATION OF AEROSOLSWITH NARROW SIZE DISTRIBUTIONS, Aerosol science and technology, 18(4), 1993, pp. 376-388
An improved virtual impactor with interchangeable nozzles was designed
and fabricated. One impactor nozzle, of 1.98-mm diameter, was calibra
ted with monodisperse polystyrene latex spheres. The results show that
the separation efficiency of this impactor can be predicted on a semi
empirical basis. With a clean air core in the center of an aerosol flo
w, this impactor has a better separation characteristic than the conve
ntional virtual impactor. Aerosols with narrow size distributions were
obtained by passing Arizona road dust particles through this impactor
. The mass median diameter (MMD) of these aerosols varies from 10.0 to
3.3 mum with the geometric standard deviation (GSD) ranging from 1.16
to 1.48. The mass concentrations (M(a)) of these aerosols ranges over
several orders of magnitude from 0.03 to 13 mg/m3. Aerosols with the
MMD values ranging from 2.0 to 0.98 mum were obtained with this virtua
l impactor followed by a real impactor. The GSD values of these aeroso
ls vary from 1.44 to 1.28 and the M(a) range from 0.07 to 3.57 mg/m3.
The effects of varying total flow rate (Q(t)), clean air flow ratio (q
), and minor flow ratio (r) were investigated. As Q(t) decreases, the
MMD becomes larger and the GSD is decreased. With increasing q, the di
stribution curve becomes narrower and the M(a) decreases. In addition,
the fine particle contamination increases as r increases.