Coagulation rate of highly dispersed aerosols

The coagulation rate of uncharged NaCl aerosols with mean particle radii of 25 and 45 A. was measured by means of a flow method: the aerosol was passed through a pipe and the ratio of particle concentrations at the inlet and the outlet of the pipe was measured nephelometrically after “developing” the particles by condensing DBP vapor on them. Corrections for particle losses due to diffusion to the walls of the pipe were estimated in separate experiments with diluted aerosols. The absolute value of the particle concentration was determined by ultramicroscopic counting of developed aerosols. The average residence time of the aerosols in the pipe, i.e., the coagulation time, was measured by means of a coarse oil mist. Experimental values 13.4 × 10⁻¹⁰ and 15.0 × 10⁻¹⁰ cm.³/sec. were obtained for the coagulation constant of the aerosols with r = 25 and 45 A., respectively. The values calculated by means of the formula for the number of collisions between gas molecules, taking into account the molecular attraction forces between the particles, are 10.5 × 10⁻¹⁰ and 14.1 × 10⁻¹⁰ cm.³/sec., respectively.