Effects of Surface Coating on the Critical Heat Flux for Pool Boiling from a Downward Facing Surface

Abstract

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 enhance the critical heat flux (CHF) for downward facing boiling. Toward this end, metallic microporous coatings were selected, and different compositions of the coating material were evaluated, in order 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 was then conducted under downward facing boiling conditions, using hemispherical test vessels to obtain the local boiling curves. Compared to a plain vessel surface under identical experimental conditions, considerable enhancement was observed in the critical heat flux for vessels 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 local CHF limits.