Deposition of aerosol particles in a straight tube with an abrupt obstruction

Abstract

Deposition of aerosol particles in a straight tube with an abrupt local obstruction was determined experimentally in model tubes with tube Re ranged between 140 and 2800. Various types of obstruction whose hydraulic throat diameters ranged between 0.22 and 0.25 cm were created locally in the middle of smooth 0.5 cm i.d. glass tubes. Aerosol deposition occurred mostly behind the obstruction within a distance equalling 10 tube diameters. The deposition in this segment was increased rapidly with increasing flow rate and reached up to more than 100 times greater for particles of 3.1 γm diameter than in the unobstructed tube. The deposition increased with increasing particle size and was well correlated with pressure drop across the obstruction regardless of the types of obstruction. Stokes number ( Stk) represented the deposition only for a specific type of obstruction. Despite the difference in flow structure, the deposition behind the obstruction was well correlated with deposition parameters used for fully developed turbulent pipe flow, dimensionless deposition velocity and relaxation time and agreed closely with turbulent deposition in a rough pipe.