High-speed particle beam generation: Simple focusing mechanisms

Ramakrishna V. Mallina, Anthony S. Wexler, Murray V. Johnston

Research output: Contribution to journalArticle

27 Scopus citations

Abstract

Modern chemical characterization instruments employ an aerosol inlet that transmits atmospheric aerosols to the low pressure source region of a time-of-flight mass spectrometer, where particles are ablated and ionized using high energy irradiation. The ions when analyzed in the mass spectrometer yield information about the elemental composition of airborne aerosols. Often, the rate at which particles are analyzed is limited by the transmission rate of the inlet used. Depending on their size, particles are lost during sampling usually due to inertial effects or diffusion. Often simple capillaries and conical nozzles are used as primary focusing elements in the formation of high-speed particle beams. Due to the basic nature of the focusing mechanism, such elements transmit particles efficiently over a narrow size range. This size range strongly depends on the nozzle geometry and operating conditions. In this work, numerical techniques are used to (a) simulate fluid and particle transport in axi-symmetric nozzles, (b) help understand and identify the mechanisms by which particle beams are formed in capillaries and conical nozzles, and (c) illustrate the contrasting nature of the beams thus formed. Particle focusing is also simulated in some typical inlets to validate the predictions and illustrate the merits and drawbacks of each design.

Original languageEnglish (US)
Pages (from-to)719-738
Number of pages20
JournalJournal of Aerosol Science
Volume30
Issue number6
DOIs
StatePublished - Jul 1999
Externally publishedYes

ASJC Scopus subject areas

  • Atmospheric Science
  • Environmental Science(all)

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