Flow boiling heat transfer in minichannels at high saturation temperatures: Part II - Assessment of predictive methods and impact of flow regimes

In order to evaluate the reliability of the current flow boiling heat transfer prediction methods for conditions of high saturation temperatures, this paper focuses on the comparison between experimental results (presented in the first part of this two-part article) and results predicted with the commonly used correlations or models from the literature. The dataset was obtained with R-245fa as working fluid in a 3.00 mm inner diameter stainless steel tube. It is characterized by a saturation temperature ranging from 60 °C to 120 °C. The database is composed of 5964 data points covering four flow patterns: (i) intermittent flow, (ii) annular flow, (iii) dryout flow, and (iv) mist flow regimes. An extensive literature review was performed to select the flow boiling heat transfer prediction methods that were classified according to their theoretical background. Finally, thirty flow boiling prediction methods were assessed against our database. The results are presented graphically but also statistically. The effect of the saturation temperature and the kind of flow pattern on the ability of the methods to predict the flow boiling heat transfer coefficient were investigated. At 60 °C, most of the prediction methods produce homogeneous results and are able to predict with accuracy the flow boiling heat transfer coefficient. On the contrary at 120 °C, the existing methods fail to predict the heat transfer coefficient with accuracy. The only methods able to capture the experimental trends are those developed from carbon dioxide data with or without other fluids.