Simplified Model Predicting Contact-Line-Length Density at Critical Heat Flux Based on Direct Observation of Boiling Structure

Great efforts have been made to attain a good understanding of boiling heat transfer, but we have a poor understanding for the boiling structures in high heat-flux boiling. For example, there are still opposing opinions for the mechanism of the critical heat flux in saturated boiling and there are no rigorous models for that in subcooled boiling. In the present paper, the nucleation site density (NSD) was measured using high-speed video pictures and an image processing technique. The video pictures were taken from below the boiling surface made of single crystal sapphire with a total reflection technique. Based on the experimental results of NSD, a simplified model predicting the contact-line-length density (CLLD) at CHF is proposed.