Particle capture by interception and its relevance to nuclear reactor containment sprays

Abstract

A falling drop may capture aerosol particles by one of a number of mechanisms, depending largely on the particle size. Submicrometre particles, which are the hardest to capture, tend to follow the streamlines of the suspending fluid and collide with the drop only by virtue of their finite radii. Many earlier calculations of the capture efficiency by this mechanism have neglected the boundary layer around the drop: it is shown that this can lead to significant error. A new interception formula is derived, taking the boundary layer into account, in which the efficiency depends on the Reynolds number of the drop as well as the ratio of the particle and drop radii. This formula is compared with an empirical formula derived experimentally by other workers, and both are applied to the removal of airborne particles by a nuclear reactor containment spray.