We study an instability of thin liquid-vapor layers bounded by rigid parallelwalls from both below and above. In this system, the interfacial instability isinduced by lateral vapor pressure fluctuation, which is in turn attributed tothe effect of phase change: evaporation occurs at a hotter portion of theinterface and condensation at a colder one. The high vapor pressure pushes theinterface downward and the low one pulls it upward. A set of equationsdescribing the temporal evolution of the interface of the liquid-vapor layersis derived. This model neglects the effect of mass loss or gain at theinterface and guarantees the mass conservation of the liquid layer. The resultof linear stability analysis of the model shows that the presence of thepressure dependence of the local saturation temperature mitigates the growth oflong-wave disturbances. The thinner vapor layer enhances the vapor pressureeffect. We find the stability criterion, which suggests that only slighttemperature gradients are sufficient to overcome the gravitational effect for awater/vapor system. The same holds for the Rayleigh-Taylor unstable case, witha possibility that the vapor pressure effect may be weakened if theaccommodation coefficient is below a certain critical value.
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