Wall Deposition of Ultrafine Aerosol Particles by Thermophoresis in Nonisothermal Laminar Pipe Flow of Different Carrier Gas

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Abstract
Deposition of ultrafine aerosol particles by Brownian diffusion and thermophoresis in a nonisothermal laminar pipe flow is investigated theoretically and experimentally. The deposition rates of Ag and TiO2 particles of 8–30 nm in diameter suspended either in N2, Ar or He gas are measured using a circular pipe with a nonuniform wall temperature distribution. The numerical calculation results considering the gas flow, temperature and particle distributions in the pipe show good agreement with the measured values. The particle deposition is enhanced with the increase of the wall temperature variation, but does not depend on the particle material. The difference in the deposition rates among the carrier gases is mostly attributable to the values of the Brownian diffusion coefficient. The enhancement of deposition by thermophoresis is of a similar magnitude among the carrier gases, which is explained in terms of the temperature distribution of the gases in the pipe.