Particle deposition after crossing a sudden expansion

Abstract

Monodispersed aerosols of 5 and 10 μm diameter DOP droplets tagged with sodium fluorescein were deposited on tube walls and the annular disc at the exit plane of expansion sections with ratios D 2/ D 1 = 1.5,1.8,2.25,3.0, and 4.5 ( D 2 = 5.72 cm). Aerosol stream flowrates varied from 6.4 to 21.3 m s −1 (7.29 × 10 3 < Re < 5.10 × 10 4 based on D 1). Tape segments attached to the wall and disc were removed after each test, washed and analysed fluorometrically to determine deposition rates and patterns, both radially and axially. Little differences in deposition were found between disc and tube walls or at various distances along the tube wall up to five diameters from the expansion. Sherwood numbers for deposition correlated well with the group Re p −0.66Stk eff −1 Velocity profiles were measured both radially and axially up to five diameters ( D 2) downstream from the expansion, and turbulent flow properties (Peclet numbers) were compared with published data. Eddy diffusivities for particle concentration and momentum were correlated with the effective Stokes number.