Inertial impaction of aerosol particles on single and multiple spherical targets

Inertial deposition of aerosol droplets (diameter: 1–14 μm) on steel spheres (diameter: 3–9 mm) was investigated. Air velocity was varied between 7 and 28 m/s (corresponding sphere Reynolds numbers: 1400–17000). The impaction on single spheres as well as that on linear arrays of eight spheres was measured. Theoretical results, based on potential flow investigations were verified by single sphere experiments. Of special interest was the range of lower Stokes numbers, where the theoretically predicted limit of deposition cannot be verified. The experiments on sphere arrays were for the first time performed in the low Stokes number range. Deposition on the leading sphere, relative to that on the shielded spheres, exhibits a maximum in the high Stokes number range, but this changes drastically in the low Stokes number range. Here, maximum deposition can be found on the shielded spheres while the leading sphere shows a markedly lower deposition.