Boiling in porous media: experimental analysis of the stability of the front between the liquid and the two-phase zone

We are interested in the problem of boiling in a porous column made up of glass beads saturated with water. The temperature of the plate at the bottom of the column is fixed at a value higher than the boiling point of water. The temperature at the top of the column is imposed at a value allowing a liquid zone to be present (by re-condensation), whereas the pressure is kept at the atmospheric value. We report In this paper different: tests for which we have modified the size of the beads in order to obtain stable and unstable situations. In the last case, instabilities appear in the form of periodic oscillations of the temperature field and are accompanied by outlet then inlet of water through the permeable upper surface ('Geyser effect'). After having mentioned the 1D treatment of stable situations, we examine unstable ones for which the convection in the liquid zone plays a disturbing effect. A simplified linear stability analysis taking into account the increase of effective conductivity of the liquid zone with free convection is carried out with a view to obtaining a new stability criterion. (C) Elsevier, Paris.