Thermal convection and boiling in a porous medium

Experimental observations of boiling in a water-saturated porous medium are reported. The porous medium is contained in a vertical circular cylinder of diameter D and height H which is heated from below and cooled from above. Single-cell thermal convection occurs prior to the onset of boiling. With the onset of boiling, an isothermal two-phase zone forms above the bottom in regions of ascending convection. The size of the two-phase zone increases with increasing heat flux. At high heat fluxes the cellular convertion flow disappears; a horizontal water layer is then observed to overlie a two-phase layer. A vertical countercurrent flow of liquid and vapor dominates heat transfer in the two-phase layer. In the layered state, an oscillatory boiling mode can develop which is attributed to the periodic formation of a vapor layer at the heating surface.