EFFECT OF SUBCOOLING ON POOL BOILING HEAT TRANSFER IN WATER USING SINTERED COPPER MICROPOROUS COATING
Effect of subcooling on pool boiling heat transfer was experimentally studied using copper microporous coating in gassy subcooled water of 10 K, 20 K, and 30 K at one atmospheric pressure by comparing to subcooled plain copper surface data. The microporous coating, High-temperature Thermally-Conductive Microporous coating (HTCMC), was made by sintering copper powder of an average particle size of 67 μm onto a 1 cm × 1 cm plain copper surface with the coating thickness of ~300 μm. This thickness showed significant enhancement for both critical heat flux (CHF) and nucleate boiling heat transfer coefficients compared to those of a plain copper surface at saturation. Experimental results showed that nucleate boiling heat transfer of HTCMC and plain copper surface maintained about the same wall superheat values for different subcooling levels respectively. On the other hand, the CHF increased linearly with the degree of subcooling for both HTCMC and the plain copper surface due to the required additional heating for the bulk liquid to reach saturation and the reduced departing bubble size in subcooled water. The increase in the CHF for every degree of subcooling was ~60 kW/m2 from saturation for both HTCMC and plain surface resulting in a difference of CHF between HTCMC and plain copper surface maintained at ~1,000 kW/m2 throughout the tested subcooling levels.