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Size shifts in measurements of droplets with the aerodynamic particle sizer and the aerosizer.

Authors
Baron-P; Deye-GJ; Martinez-AB; Jones-EN; Bennett-JS
Source
Aerosol Sci Tech 2008 Mar; 42(3):201-209
NIOSHTIC No.
20033555
Abstract
Observations of the size of liquid droplets using the Aerodynamic Particle Sizer (APS) and the Aerosizer indicated that the measured size was significantly different from the aerodynamic diameter as calculated by measuring droplet settling velocity. The size shifts appeared to be caused by droplet distortion in the detector flow field for the Aerosizer. However, for the APS, droplet sizing was further affected by droplet impaction on the upstream side of the focusing nozzle. It is suggested that liquid accumulated in and constricted the nozzle, resulting in a particle velocity increase at the sensor. The size shift can occur with the deposition of <0.5 microL liquid onto the nozzle; the size shift can occur in 1-10 minutes even at concentrations of 1000 particles/L; and the size shift can disappear after cessation of liquid aerosol sampling. CFD calculations provided information about the amount of velocity increase at the APS sensor for a selected constriction. Both solid and liquid particles are affected by the nozzle constriction, which produces approximately the same percentage size shift throughout the measurement range. The size shifts (delta) were related to droplet aerodynamic diameter (microm), viscosity (Pa-s), and surface tension (N/m) by the following empirical equation: delta=-a diameter(b)/(surface tension(c) X viscosity(e)). The value of b was arbitrarily set to two. The values for a, c, and e for the APS (including both droplet distortion and nozzle constriction) and for the Aerosizer were determined by a regression analysis of the available data.
Keywords
Mathematical-models; Models; Particle-aerodynamics; Aerosols; Aerosol-particles; Aerosol-dispensers; Aerosol-generators
Contact
Paul Baron, NIOSH, R3, 4676 Columbia Parkway, Cincinnati, OH 45226, USA
CODEN
ASTYDQ
Publication Date
20080301
Document Type
Journal Article
Email Address
pbaron@cdc.gov
Fiscal Year
2008
NTIS Accession No.
NTIS Price
Issue of Publication
3
ISSN
0278-6826
NIOSH Division
DART
Priority Area
Work Environment and Workforce: Emerging Technologies; Manufacturing
Source Name
Aerosol Science and Technology
State
OH
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