SPECIAL FEATURES OF DRYOUT DEVELOPMENT IN PIPES WITH POROUS COATINGS

Results are given of experimental investigation of dryout under condit ions of upward disperse-annular vapor-water flow in pipes with a porou s coating. The range of parameters is defined in which the presence of porous coatings leads to a ''delay'' in the dryout development and pr ovides a possibility of crisis-free operation of vapor-generating chan nels up to values of vapor quality close to unity. Changes are discuss ed in the mechanisms of moisture exchange between the flow core and th e wall liquid film, which are due to the presence of porous coatings. Of these changes, the main part is played by the variation of the rang e of droplet sizes in the flow, the presence of an appreciable fractio n of ''slip-through'' droplets, the expansion of the region of effect of bubble entrainment of moisture up to boundary values of vapor quali ty, capillary effects in the body of coatings, and intensification of repeated wetting in the dryout region.