Abstract
Particle trajectories and collision efficiencies have been computed for unequally-sized fine particles settling in air, taking into account their hydrodynamic interaction and interparticle attraction. In the continuum, the resistance force of one particle moving towards another increases as the separation distance between particles decreases and becomes infinite just before touching. However, the resistance force of a fine particle diameter of which is less than several dozen microns does not increase infinitely in air because the air between two colliding particles the Knudsen number of which is more than 10-3 behaves like a discontinuum. Thus, a fine particle in air would collide with another particle more easily. In this study, experimental data on the resistance force of a particle in the discontinuum was applied to the resistance coefficient of particles in air. The calculated results indicate that the calculated collision efficiency of a fine particles in air is 1.5-8 times larger than that based upon the continuum theory.
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