Condensation rate of light vapour molecules in the transition regime

In order to overcome uncertainties of semi-empirical models based on the flux matching theory and to resolve discrepancies between more accurate interpolation formulas, obtained from various solutions of the Boltzmann equation, a new approach, similar to that recently proposed by the authors to consideration of the heavy vapour molecules condensation, is applied to light vapours. In this limit the transport of light vapour molecules to the central particle can be strictly considered as specific random walks, characterized by the exponential distribution of the elementary displacement distances for each walker migrating with a fixed speed and changing direction randomly, whereas the condensation rate is related to the mean volume swept per unit time by the migrating effective particle of radius equal to the radius of the central particle. Results of numerical calculations of the condensation rate at different values of the Knudsen number are approximated by the interpolation expression with a relatively high accuracy in comparison with the traditional expressions.