The effect of natural convection in a liquid layer and the thermal inhomogeneity of vapor on the stability of a vapor film on a flat horizontal heater

Abstract

The linear stability of a vapor film, formed on the surface of a flat horizontal heater in a subcooled film boiling regime under conditions of terrestrial gravity, is studied. The study is aimed to estimate the role of natural convection in a liquid cooled from above, which is influenced by an additional flow caused by the redistribution of matter in the phases, in the process of stabilization of a stationary base state with a balanced heat flux at the interface between the two media. A modification of the conventionally used model of convective heat transfer (Newton–Rikhman’s law) is proposed. The calibration of the presented model, which is characterized by a dependence of the local coefficient of convective heat transfer on the rate of phase transition, is carried out on the basis of the experimental data available in the literature. The modified model allows to avoid the underestimation of the critical value of the heat flux in the subcooled liquid, at which a complete suppression of the Rayleigh–Taylor instability by a phase transition is achieved. In addition, it is demonstrated that the inhomogeneity of thermophysical properties of vapor and heat transfer by radiation at the boundaries of the vapor layer exert, respectively, stabilizing and destabilizing effects under the condition of a significant overheating of the heater surface.