Universal approach to predicting saturated flow boiling heat transfer in mini/micro-channels – Part II. Two-phase heat transfer coefficient

This second part of a two-part study examines the prediction of saturated flow boiling heat transfer in mini/micro-channels. The first part culminated in a technique for determining the dryout incipience quality corresponding to substantial deterioration in the heat transfer coefficient. In this part, a consolidated database for flow boiling in mini/micro-channels is amassed from 31 sources, of which 10,805 data points are designated as pre-dryout. The pre-dryout database consists of 18 working fluids, hydraulic diameters of 0.19–6.5 mm, mass velocities of 19–1608 kg/m2 s, liquid-only Reynolds numbers of 57–49,820, qualities of 0–1, and reduced pressures of 0.005–0.69. The pre-dryout database is used to evaluate prior correlations that have been recommended for both macro-channels and mini/micro-channels. A few of these correlations are shown to provide fair overall performance, but their accuracy is compromised against specific portions of the database, especially high pressures and very small diameters. A new generalized correlation is constructed by superpositioning the contributions of nucleate boiling and convective boiling. This correlation is shown to provide very good predictions against the entire pre-dryout database, evidenced by an overall MAE of 20.3%, with 79.9% and 95.5% of the data falling within ±30% and ±50% error bands, respectively. Evenly good predictions are achieved for all working fluids and all ranges of the database parameters.