Depostition of submicron aerosol particles in turbulent and transitional flow



Brownian and turbulent diffusive deposition of submicron aerosol particles from pipe flow is studied experimentally and theoretically. A theoretical model for evaluating the turbulent diffusive deposition is presented in which a turbulent flow in a circular pipe is numerically calculated based on the k-ϵ turbulent flow model and deposition velocities are derived by solving the convection-diffusion equation. Deposition velocities of monodisperse aerosol particles, 0.01–0.04 μm in diameter, are obtained experimentally by measuring the decrease in the particle number concentration of an aerosol at two cross-sections of a circular test pipe through which the aerosol is flowing. The deposition velocities obtained when Re is larger than about 3,000 agree well with those predicted by the present analysis which are proportional to the 0.92nd power of Reynolds number and the 0.33rd power of Schmidt number. The particle deposition rates are measured when 1, 000 ≲ Re ≲ 2,000 suggest a transitional state for particle deposition which cannot be explained by the present analysis nor by the laminar pipe flow deposition theory.