Vapor Film on a Flat, Hot, Vertical Surface

The article presents a study of film boiling in a vapor-liquid system in a rectangular pool with an open top surface and with one of its vertical walls heated to a temperature above the liquid boiling point. The specific features of this process are that vapor constantly flows into the environment and that the vapor-film thickness consists of a stationary part and waves that propagate over the liquid-vapor interface. A special, nonviscous vortex flow regime is studied in a stationary analysis. The solutions of continuum equations are drawn up with the multiscale asymptotic expansions method, and the shape of the phase boundary separating the adjacent to the hot vertical wall vapor from cold liquid is found. The heat-transfer characteristics can be calculated with the obtained solution. The stability of the obtained stationary configuration of vapor and liquid and of the phase boundary separating them is studied. It is shown that the waves propagating along the boundary differ from the known gravity waves in isothermal liquid medium. As in the case of film boiling on a horizontal surface, these surface waves are generated in a non-isothermal medium due to the change of heat flux caused by warping and displacement of the liquid-vapor interface, and they are also connected with the dependence of the saturation pressure on temperature. Like the well-known Gibbs-Thomson effect, deformation of the liquid-vapor interface entails a change in the boiling temperature and, accordingly, the saturation pressure. The study identifies three classes of medium flows over a vertical surface (a liquid layer, a generating condensate layer, and a vapor film) that share a common feature: the presence of a wave interface between two media.