Size Shifts in Measurements of Droplets with the Aerodynamic Particle Sizer and the Aerosizer

Details

• Personal Author:
  Baron, Paul A. ; Bennett JS ; Deye GJ ; Jones EN ; Martinez AB
• Description:
  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. [Description provided by NIOSH]
• Subjects:
  Aerosols Occupational Health Particulate Matter Safety
• Keywords:
  Aerosol-dispensers Aerosol-generators Aerosol-particles Mathematical-models Models Particle-aerodynamics
• ISSN:
  0278-6826
• Document Type:
  Text
• Genre:
  Journal Article
• Place as Subject:
  Ohio ; OSHA Region 5
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Division:
  DART - Division of Applied Research and Technology
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  201-209
• Volume:
  42
• Issue:
  3
• NIOSHTIC Number:
  nn:20033555
• Citation:
  Aerosol Sci Technol 2008 Mar; 42(3):201-209
• Contact Point Address:
  Paul Baron, NIOSH, R3, 4676 Columbia Parkway, Cincinnati, OH 45226, USA
• Email:
  pbaron@cdc.gov
• Federal Fiscal Year:
  2008
• NORA Priority Area:
  Work Environment and Workforce: Emerging Technologies ; Manufacturing
• Peer Reviewed:
  True
• Source Full Name:
  Aerosol Science and Technology
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:a2e2f4d9666efc62e805c670d63200f49724e5c91328daf2da502c9637cbd8b0fdab719844ffaf06c9e6f1203afd66583f615cc88e64b5418a7aa543c48c3b17
• Download URL:
  https://stacks.cdc.gov/view/cdc/189089/cdc_189089_DS1.pdf
• File Type:
  [PDF - 422.25 KB ]