Evaporation/condensation boundary conditions for the regularized 13 moment equations

The regularized 13 moment equations (R13) are a macroscopic model for the description of rarefied gas flows in the transition regime. The equations have been shown to give meaningful results for Knudsen numbers up to about 0.5. Here, their range of applicability is extended by boundary conditions for evaporating and condensing interfaces, derived from the microscopic interface conditions of kinetic theory. Simple 1-D problems are used to test the R13 equations with evaporation and condensation.