High Resolution Study of Micrometer Particle Detachment on Different Surfaces

In an effort to identify particle initial motion prior liftoff interactions of micrometer glass beads (10-100m) on glass, ceramic, and hardwood substrates were investigated experimentally. Particles were deposited on the lower surface of a 10cm(2) wind tunnel by gravitational settling. Air flows were imposed from an open entrance at average velocities up to 16m/s. Individual particle trajectories obtained by high-speed imaging reveal three different types of motion: rolling/bouncing (saltation caused by the movement of hard particles over an uneven surface in a turbulent flow of air), immediate liftoff (particles completely leave the surface with no or minimal initial rolling/bouncing) and complex motion (particles travel with rolling/bouncing motion on the surface for a certain distance before final liftoff). Surface roughness significantly affects the particle initial motion prior to liftoff. The majority of particle trajectories from the glass substrate were parallel to the surface with complex motion. Hardwood substrates took the longest time for initial particle movement (t >1s) causing a more rapid liftoff. The ceramic substrate showed the most rolling/bouncing motion, for 80% of the particles. The detachment percentage initially follows an exponentially increasing trend for a period of approximate to 1s, followed by a plateau phase for a period of 5s. Changing the velocity, substrate, and particle size significantly affects particle detachment. Incorporating the different types of particle motion prior to liftoff into detachment mode models, and understanding how their relative contributions change with different particle and substrate materials, can potentially yield improved predictive capabilities. Copyright 2013 American Association for Aerosol Research