STABILITY OF BOILING IN POROUS-MEDIA

The onset of two-dimensional roll convection in the presence of boiling is studied for a fluid-saturated horizontal porous layer. The layer is heated from below and cooled from above. The rest-state phase structure consists of a liquid region overlying a two-phase region. The two important parameters in the problem are the Rayleigh number in the liquid region (Ra) and the dimensionless heat flux at the bottom boundary (Qb). Both liquid-dominated and vapor-dominated two-phase regions are investigated. For liquid-dominated systems, the convective instability is driven mainly by bouyancy in the region, while for vapor-dominated systems the instability is driven by the gravitational instability of the overlying layers. For liquid-dominated systems, a stability diagram in Ra-Qb parameter space is used to interpret prior laboratory experiments. © 1990.