Hydrodynamic boundary conditions at the surface of an ablating material

Abstract

The boundary conditions for a vapor at the surface of an ablating or vaporizing material are obtained. The vapor pressure, temperature, and mass flow rate are obtained when the initial state of the solid or liquid material and power absorbed at the phase transition layer are specified. These boundary conditions are derived from the hydrodynamic jump conditions and one equation from the thermodynamics of irreversible processes for a single component system. The results show that, for small mass flow rates, the vapor temperature rise is linearly proportional to the mass flow rate and the pressure drop varies as the square of the mass flow rate. These dependencies are the reversal of Vulliet’s results. Two application examples are considered: the ablation of iron, and the ablation of condensed hydrogen. It is shown that these boundary conditions for the ablation of condensed hydrogen are useful in studies of the refueling of present-day tokamak plasmas by injection of hydrogen pellets.