Evaporation and condensation flows of a vapor-gas mixture from or onto the condensed phase with an internal structure

Transient motions of a vapor-gas mixture due to the evaporation and condensation processes from or onto the plane condensed phase with a temperature field as its internal structure have been studied numerically based on the Boltzmann equation of BGK type for a binary gas mixture. The condition of the continuity of the energy flow across the interface surface has to be imposed in addition to the conditions at the surface of the condensed phase without the internal structure because the temperature of the surface in this case becomes an unknown parameter to be determined as part of the solution. The transient flow fields of the mixture occur owing to the phase change processes caused by the continuous change in temperature of the surface of the condensed phase. The effects of the internal structure of the condensed phase coupled with the presence of a noncondensable gas, which is small in amount here, on the transition process of the transient flow fields and, hence, the formation and the propagation of the shock waves and the contact regions may clearly be recognized. Some of the features of the present flows are that 1) the maxima of the mass and energy flows may exist at a certain value of the latent heat parameter, the phenomenon of which may be ascribed to the coupling effects of the latent heat parameter and the existence of the internal structure of the condensed phase; 2) the negative mass flow appears in a short period of time during the transitional state of the flow fields when the latent heat parameter is extremely small. However, it disappears soon as time goes on. These two phenomena, which are affected here by the presence of a noncondensable gas, are also found in a pure-vapor case.