Kinetics of diffusion-limited nucleation in a diffusion cloud chamber

Abstract

Abstracts of the 5th International Aerosol Conference 1998 supersaturation, the gas temperature and, that is quite new, the carrier gas pressure. It is shown that the usual conditions of experiments in diffusion cloud chambers where the concentration of the vapor is small, meet the requirements of the model validity that means this model can be adopted to explain a mechanism of the carrier gas pressure in- fluence on the nucleation kinetics (Itkin, 1998) o b served in experiments (Bertelsmann et al., 1996). In particular, as follows from our analysis instead of a usual supersaturation S all expressions of the theory contain a product SO where 0 o( l/P0 and depends upon the cross-section of the carrier gas and condensing molecules. The main conclusion which can be made based on the above results is that at certain values of the temperature and, that is more important, pressure of a carrier gas a special regime of nucleation may establish. As follows from the presented analysis this case is realized at high pressures of the carrier gas, a large effective diameter (or cross-section) of the condensing molecules, comparatively low temperatures. We call this regime “diffusion- limited nucleation”, but such processes are well known and even rather wide occur in chemical kinetics (Frank-Kamenetskii, 1947). H owever, for nucleation this effect here is considered for the first time. From the results obtained it follows that in addition at the diffusion-limited nucleation the quasisteady concentrations of clusters as well as the rate of the evolution of the monomer’s mass fraction crl become no longer be a function of two parameters -