Abstract
For the generation of the quasi-monodispersed standard (calibration) aerosols, the electrical separation of particles from the aerosol with wide size spectrum can be used in quite a wide particle diameter range, from some nanometers up to approximately 10 micrometers. A solution to the problem of multiple elementary charges on the particles, degrading the quality of the separated aerosol in the range of large particles, was proposed in a separate paper. In this paper, a unique very long DMA for the separation of such large particles is described, together with a technology for its manufacturing. Effects of some possible non-ideal properties of the DMA, arising from the manufacturing techniques used, are investigated both theoretically and experimentally; no significant distortions of the DMA transfer function were found. A new method for the experimental determination of the transfer function of the DMA, using Microsphere Size Standards (highly monodisperse polystyrene aerosols) is described. It was confirmed, that electric wind can be a distortion factor of the DMA transfer function and the continuous tracking of it, when separating standard aerosols, is necessary. Effect of gravity on the DMA transfer function is also discussed.
Highlights
For the experimental calibration of the aerosol spectrometers, the quasimonodisperse standard aerosols can be generated by various methods, among which the electrical separation of particles from the polydisperse aerosol is one of the most popular ones
For the generation of the quasi-monodispersed standard aerosols, the electrical separation of particles from the aerosol with wide size spectrum can be used in quite a wide particle diameter range, from some nanometers up to approximately 10 micrometers
The settling velocity of 10 μm particles is vg § 3 mm/s; to avoid too long measurement cycle times when scanning over the particle size spectrum of the separable aerosol, the mean linear speed v of the air flow between the DMA electrodes should be substantially higher than vg, v 5vg is chosen
Summary
For the experimental calibration of the aerosol spectrometers, the quasimonodisperse standard aerosols (calibration aerosols) can be generated by various methods, among which the electrical separation of particles from the polydisperse aerosol (separable aerosol) is one of the most popular ones. Particles in some narrow mobility interval move to the output slit in the inner electrode and are sucked out together with the thin layer of the sheath air near the inner electrode (flow rate ĭ3), forming the calibration aerosol.
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