Influence of Impaction Plate Diameter and Particle Density on the Collection Efficiency of Round-Nozzle Inertial Impactors

Abstract

This study has investigated the influence of impaction plate diameter ( Dc ) and particle density on the particle collection efficiency of single round-nozzle inertial impactors numerically assuming incompressible flow. The study shows that computed St 50 values range from 0.473 to 0.485, which are nearly independent of W/Dc ( W is the nozzle diameter) for the nozzle Reynolds number, Re > 1500, and when W/Dc < 0.32. St 50 values agree quite well with the theoretical values of Rader and Marple (1985), 0.49, and Marple and Liu (1974), 0.477. For a smaller impactor plate diameter such that W/D c > 0.32, St 50 will increase slightly. It increases from 0.483 to 0.507 (Re = 3000) or from 0.479 to 0.495 (Re = 1500) when W/Dc is increased from 0.32 to 0.48. When the nozzle Reynolds number is smaller than 1500, the influence of W/Dc on St 50 is found to be much more pronounced. The effect of particle density on the collection efficiency has also been investigated. When particle gravity is included, the results show that St 50 is not affected by particle density ranging from 0.5 to 10 g/cm 3 , although the particle collection efficiency increases slightly with increasing particle density at high ends of the collection efficiency curves at high nozzle Reynolds number due to an ultra-Stokesian effect. The particle interception effect does not affect the collection efficiency curves at high Reynolds numbers at all, and the effect is negligibly small at low Reynolds numbers.