Abstract

The evaporation of polyatomic liquids into near-vacuum conditions is investigated by using the Enskog–Vlasov model. Molecules are approximated as classical rigid rotators, and the collisional energy exchanges between the translational and rotational degrees of freedom are dealt with by the Borgnakke–Larsen method. The distribution function of evaporated molecules and the evaporation coefficient are evaluated in a wide range of liquid bulk temperatures and inelastic collision fractions. It is found that the translational velocity distribution function is well approximated by a drifted bi-Maxwellian, while the rotational energy follows the Boltzmann distribution at a temperature that varies between the separation and the parallel temperatures as the inelastic collision fraction increases. The evaporation coefficient based on the separation temperature turns out to be independent of the inelastic collision fraction and only mildly dependent on the liquid bulk temperature.