Mean field kinetic theory description of evaporation of a fluid into vacuum

The evaporation of a liquid slab into vacuum is studied by numerical solutions of the Enskog– Vlasov equation for a fluid of spherical molecules interacting by Sutherland potential. The equation provides a simplified description of the microscopic behavior of the fluid but it has the capability of handling both the liquid and vapor phase, thus eliminating the necessity of postulating ad hoc models for boundary conditions at the vapor-liquid interface. This work focuses on obtaining the structure of the vapor-liquid interface in nonequilibrium conditions as well as the distribution function of evaporating molecules. The results show that the molecules crossing a properly defined vapor-liquid boundary have an almost Maxwellian distribution function and that the vapor phase is reasonably well described by the Boltzmann equation with diffusive boundary condition.