Brownian coagulation of aerosols in the transition regime

Abstract

Earlier experimental studies of Brownian coagulation of aerosols have been extended into the transition regime, i.e. Knudsen number values 0.8-1.6. This was done by working with the same range of particle size as earlier, but at a reduced pressure. A number of modffications were made in the experimental technique, including the use of diethylhexylsebacate instead of dibutylphthalate in order to avoid the possibility of loss to the walls by evaporation. The rate of coagulation at Kn = 0.2 agreed closely with that predicted, using Smoluchowski's coagulation constant for the continuum regime as modified by the Cunningham correction. The rate at higher Knudsen numbers (Kn = 0.8-1.6) was somewhat lower (about 20%) than that predicted by Fuchs' formula for interpolation between the continuum and free molecule regimes.