Effect of surface treatment by thermal spray coating on boiling heat transfer performance.

This study deals with a boiling heat transfer enhancement by a thermal spray coating. The coating was fabricated by vacuum plasma spraying using fine copper particle. The boiling heat transfer performance in a narrow channel was experimentally examined. The effects of the flow condition, the heating condition, and the channel inclined angle, on the heat transfer coefficient and the critical heat flux were considered. The experiments were conducted for saturated flow boiling of HCFC-123 and subcooled flow boiling of FC-72. The experimental results show that the coating could improve the boiling heat transfer coefficient. There was a little effect of the channel height on the boiling heat transfer for each surface. The effect of the channel inclined angle was observed only for the coating in the low quality and the low mass flux condition. The horizontal flow with the top heating produced the highest heat transfer coefficient for the coating. There is no marked effect of the channel inclined angle in the high quality and the high mass flux region. For the subcooled flow boiling, the critical heat flux, CHF, increased about 20% by the coating in the condition with large subcooling degree of 40 K. The reason might be that vapour bubbles over the coating were immediately condensed due to the smaller diameter.