Effects of Surface Coating on Nucleate Boiling Heat Transfer From a Downward Facing Surface

As part of a joint U.S.-Korean International Nuclear Engineering Research Initiative investigating methods to enhance external reactor vessel cooling (ERVC) under severe accident conditions, it was proposed that surface coating be used to facilitate the process of downward-facing boiling. Toward this end, metallic micro-porous layer coatings were selected and different compositions of the coating material were evaluated to obtain a mixture with desirable qualities. Durability and adhesion tests were also done to study the performance of each of the resulting coatings. Quenching of the candidate coatings were then conducted under downward facing boiling conditions using hemispherical test vessels to obtain the local boiling curves. Compared to the case of plain vessel surface under identical experimental conditions, considerable enhancement was observed in nucleate boiling heat transfer and the critical heat flux (CHF) for the case with surface coatings. Optical and SEM (Scanning Electron Microscope) photos showed that the candidate coating possessed the desired porous microstructure with interconnecting channels and pores, leading to appreciable increases in the boiling heat transfer and the local CHF limits.