Enhanced saturation and subcooled boiling of FC-72 dielectric liquid

Experiments are conducted which investigated enhancements in nucleate boiling of FC-72 dielectric liquid on porous graphite and compared results with those on a smooth copper surface of the same dimensions (10 × 10 mm). Also investigated is surface temperature excursion at boiling incipience and the obtained values of CHF are compared with those of other investigators on copper, silicon, and micro-finned silicon surfaces and micro-porous coatings. Results showed no temperature excursion at boiling incipience on porous graphite but as much as 14.0 K in saturation and 9.0-13.3 K in subcooled boiling on copper. The nucleate boiling heat transfer coefficients on porous graphite are significantly higher than on copper and the values of CHF (27.3, 39.6, 49.0, and 57.1 W/cm2 in saturation and at ΔTsub = 10, 20, and 30 K, respectively) are 63-94% higher than on copper (16.9, 21.9, 26.9, and 29.5 W/cm2, respectively). The surface superheats at CHF on porous graphite (11.0 K in saturation and 17.2-19.5 K in subcooled boiling) are lower than on copper (21.3 K and 22.9-24.9 K, respectively). The nucleate boiling heat transfer coefficient increase with subcooling and CHF increased linearly with ΔTsub. The subcooling coefficient of CHF on porous graphite (0.041) is slightly smaller than those on micro-porous coatings (0.044 and 0.049) but much higher than those on micro-finned silicon surfaces (0.022, 0.036), and on Cu, Si, and enhanced SiO2 (0.018) surfaces.