A numerical investigation of the steady evaporation of a polyatomic gas

The evaporation and condensation of a polyatomic vapor in contact with its condensed phase has received much less attention than the monatomic case. In this paper we investigate the structure of the Knudsen layer formed in the steady evaporation of a vapor whose molecules behave as rigid rotators. The vapor motion is obtained by the numerical solution of the Boltzmann equation by the Direct Simulation Monte Carlo (DSMC) method. The obtained results are also compared with the solutions of a simplified kinetic BGK-like model equation. It is shown that density and temperature drops across the Knudsen layer are reasonably well reproduced by approximate methods proposed in the literature.