Abstract
The potential of a flat surface to act as a source of air-borne particles was investigated by exposing deposited particles of known size to measured air flow in a low speed wind tunnel. An hypothesis for the mechanisms involved in particle re-entrainment was proposed and verified. The two-part mechanism includes: (a) initiation of particle movement when shear stresses on the particles exceed friction forces acting on the particles and (b) movement of particles downstream from the point of initiation caused by momentum transferred from initially moving particles. The hypothesis was verified by comparison of prediction equations and experimental results. The experimental results were obtained by measurement of the distance downstream from the leading edge of the surface at which re-entrainment began. This distance was found to be a function of free-stream air velocity, turbulence of the free-stream and particle size. The results confirm that flat surfaces of sufficient size can be sources of air-borne particles even when air velocities are magnitudes normally existing in enclosed spaces.
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