Molecular Kinetic Approach to the Modeling of Condensation

The rapid gas dynamic expansion in a free jet is used as a tool to investigate the creation of the condensed phase out of the gas phase by nucleation and cluster growth. Starting from experimental results that yield information about the existence of clusters and the heat transferred to the gas phase, the modeling of a gas-cluster system is presented using a molecular kinetic approach which considers the mass and energy transfer between gas and clusters in the free-molecular flow regime. Some numerical results are presented which show fair agreement with the experimental results. However, it is stressed that considerably more detailed information, which could possibly obtained now from numerical experiments, is needed to be able to further refine models for the fluxes at phase interfaces, especially for small systems.