Formation of condensation aerosols at high vapor supersaturation

Abstract

A method is suggested for calculating the formation of condensation aerosols at high supersaturations. The method is applicable to the processes in which the nucleation time is no more than two orders of magnitude higher than the mean time interval within which a critical cluster collides with a vapor molecule. The concentrations of subcritical molecular clusters at any moment of time are assumed to be equal to the equilibrium concentrations for the existing temperature and vapor concentration. The equilibrium concentrations are expressed in terms of the partition functions of the clusters with allowance made only for pairwise interaction between the nearest neighbors. The calculation scheme also takes account of the coagulation of growing supercritical clusters. The scheme is used for step-by-step calculation of condensation in a free turbulent jet. The results are compared with the surface area measurements of the powders obtained by precipitation of the aerosol formed by condensation of silver vapor contained in a hot argon stream issuing into cold air. At the silver vapor concentrations at the nozzle outlet equal to 5 × 10 14 − 5 × 10 16 molecules/cm 3 the experimental values obtained are 47-11 m 2/gm; calculated values are 174 − 31.5 m 2/gm. The particle size in aerosols formed under such conditions is determined by the coalescence and sintering of particles in the process of coagulation. The experimental dependence of the surface area F of the powders upon the vapor concentration c is well approximated by the relation F ∼ c ∼- 1 3 .