Hybrid model of thin film boiling: Insights into the unique behavior and ultrahigh heat flux

Abstract Ultrahigh heat flux of over 1 kW/cm2 can be achieved by a new thin film boiling regime, of which the variation of boiling curve is considerably different from that of pool boiling. However, there is a lack of quantitative analysis for the distinctive thin film boiling. In this work, comprehensive comparison was made between the well-studied pool boiling and the newly-achieved thin film boiling. The boiling curve of thin film boiling was divided into three segments and mathematical models were set up for each segment in a way that correlations for pool boiling were adopted and modified according to the similarity and difference between pool boiling and thin film boiling, respectively. It was found that the modeling results agreed very well with the experimental results, indicating that the hybrid model revealed the underlying mechanism for the unique behavior and ultrahigh heat flux of the thin film boiling. In brief, the higher heat transfer coefficient or larger slope of the boiling curve was related to the special water supply mode of thin film boiling, in which the water flowed vertically through the heat surface and consequently enhanced heat transfer by promoting the spread of superheated layer and the bubbles on the heating surface. As for the ultrahigh heat flux and the unique negative slope of the boiling curve, it was attributed to the very thin yet continuously decreased thickness of the liquid layer, which was another essential feature of the thin film boiling. The hybrid model in this work can provide both quantitative insight for fundamental understanding and future guidance for practical application of thin film boiling.