Evaporation from or condensation onto a sphere: Numerical analysis of the Boltzmann equation for hard-sphere molecules

A steady weak evaporation from or condensation onto a spherical condensed phase in its vapor gas is investigated, mainly numerically, on the basis of the Boltzmann equation for hard-sphere molecules. The numerical method is the combination of the hybrid-difference-scheme method, which can describe the discontinuity of the velocity distribution function in the gas, and the numerical kernel method [1]. The velocity distribution function, macroscopic variables (pressure, temperature, flow velocity, heat flow), as well as mass and heat fluxes from the sphere into the gas, are obtained for the whole range of the Knudsen number. In addition, the solution of the heat transfer problem of a nonvolatile sphere in a rarefied gas is obtained as a special case of the present problem. The problem is also discussed from the standpoint of nonequilibrium thermodynamics.