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 V.V. Konovalov, T.P. Lyubimova ⇑ Institute of Continuous Media Mechanics, The Ural Branch of RAS, Perm 614013, Russia article info Article history: Received 25 July 2017 Received in revised form 27 September 2017 Accepted 28 September 2017 Keywords: Rayleigh–Taylor instability Phase transition Thermal inhomogeneity convective and radiative heat transfer 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 bal- anced 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 mod- ified model allows to avoid the underestimation of the critical value of the heat flux in the subcooled liq- uid, 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. Ó 2017 Elsevier Ltd. All rights reserved. 1. Introduction There are two main boiling regimes–nucleate boiling and film boiling (see, for example, [1]). The film boiling regime differs from the nucleate boiling regime in that the surface of a heater, immersed to a liquid, is covered by a rather stable vapor film. Heat insulating properties of such film essentially decreases the rate of heat transfer to the liquid, which can cause an unacceptable rise of the heater temperature. Under normal conditions, a transition from the nucleate boiling to the film boiling regime (the first boiling crisis) and backward transition (the second boiling crisis) occur in a critical manner at certain values of the heat flux. The peculiarity of these transitions is that the heat flux of the first boiling crisis is considerably higher than that of the second boiling crisis. The hydrodynamic theory of boiling crises (see, for example, [2]) associates these phenomena with the two base types of instability encountered in multi- phase systems. The first one is the Kelvin–Helmholtz instability for the first boiling crisis, which arises at the liquid–vapor interface of the vapor jets penetrating the bulk of the liquid. Breaking of these jets requires a critical rate of vapor efflux. The second one is the Ray- leigh–Taylor instability (see, for example, [3]) for the second boil- ing crisis, which is initiated under the action of gravity force at the surface of the vapor film due to a difference between the liquid and vapor densities. This leads to a continuous detachment of vapor bubbles from the film, in which the loss of vapor is compensated by its generation. It is assumed that, via the wavelength of the most rapidly growing disturbances, the Rayleigh–Taylor instability specifies the size of the vapor bubbles separated from the film and the diameter of the vapor jets. The modulation of the gravity field, caused by vertical vibra- tions of the horizontal surface of the heater, is able to damp the Rayleigh–Taylor instability. Such modulation can also lead to the excitation of parametric instability at the liquid–vapor interface. In general, these effects of gravity modulation allow to control the second boiling crisis, increasing or decreasing the associated critical heat flux [4]. Under microgravity conditions, the film boiling regime occurs at significantly lower values of the heat flux in the system than under terrestrial gravity conditions [5,6]. This is due to the fact that buoy- ancy is the main mechanism that detaches the generated vapor bubbles from the surface of the heater and removes them away. https://doi.org/10.1016/j.ijheatmasstransfer.2017.09.120 0017-9310/Ó 2017 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: lubimova@psu.ru (T.P. Lyubimova). International Journal of Heat and Mass Transfer 117 (2018) 107–118 Contents lists available at ScienceDirect International Journal of Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ijhmt