A composite heat transfer correlation for saturated flow boiling in small channels

Recent reviews of flow boiling heat transfer in small tubes and channels have highlighted the need for predictive correlations that are applicable over a wide range of parameters and across different studies. A composite correlation is developed in the present work which includes nucleate boiling and convective heat transfer terms while accounting for the effect of bubble confinement in small channels. The correlation is developed from a database of 3899 data points from 14 studies in the literature covering 12 different wetting and non-wetting fluids, hydraulic diameters ranging from 0.16 to 2.92 mm, and confinement numbers from 0.3 to 4.0. The mass fluxes included in the database range from 20 to 3000 kg m−2 s−1, the heat fluxes from 0.4 to 115 W cm−2, the vapor qualities from 0 to 1, and the saturation temperatures from −194 to 97 °C. While some of the data sets show opposing trends with respect to some parameters, a mean absolute error of less than 30% is achieved with the proposed correlation.