Thermophoretic and evaporational losses of ultrafine particles in heated flow

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Abstract
The transport, wall deposition and evaporation of nanometer‐sized aerosol particles are studied using a nonisothermal laminar flow in a pipe. The test aerosol particles, monodisperse Ag and NaCl particles of 7–40 nm dia., are introduced into a vertical circular pipe with wall temperature distribution in the axial direction. The measured particle loss during transport through the pipe increased with the wall temperature difference. The enhancement of particle loss due to diffusive and thermophoretic deposition is examined by the gas flow, temperature, and particle concentration distribution equations. Predicted particle losses agreed with the experimental results when the local variation of gas properties, particle Brownian diffusion, and thermophoretic migration are considered. Sudden increases in the particle loss due to particle evaporation were also observed at very high temperatures (about 700°C for Ag particles and 400°C for NaCl particles). The measured reductions of particle diameter due to evaporation showed good agreement with calculation based on aerosol evaporation theory for free‐molecule regime.