Abstract
We investigated critical heat flux phenomena in metallic and porous structures characterised by low thermal conductivity. These structures are used to cool various thermal power plant equipment; their operation involves both gravity and capillary forces. The paper describes the failure mechanism in metallic steam generator surfaces and poorly thermally conductive low-porosity coatings made of natural mineral media (such as granite). We determined how heat flows depend on their duration and penetration depth of thermal disturbance. Tubular porous systems are less bulky and feature high intensity, higher thermal conductivity and reliability. We show that for granite coatings the maximum thickness of the particles detached due to compression forces is (0.25...0.3)·10--2 m. The compression curve sections that govern detachment of particles larger than 0.3·10--2 m are shadowed by the melt curve for high heat flows and short exposure times and by the tension curve in the case of low heat flows and short periods of time. The investigation should help us to design porous coatings usable in cooling systems.