Full-range drift-flux correlation for upward co-current boiling two-phase flows in vertical rod bundles

Rod bundles are commonly found in power plants. Examples of such structures are found in heat exchangers, steam generators, and nuclear fuel assemblies, and geometries of these structures affect fluid flows. Accurately predicting the void fraction is crucial for understanding the flow and heat transfer characteristics of two-phase flows in rod bundles. The drift-flux model is widely used for various purposes, such as predicting void fractions and formulating interfacial drag force based on operating parameters. The drift-flux model requires constitutive equations for the distribution parameter and drift velocity (hereafter, drift-flux correlation). Most existing drift-flux correlations for two-phase flows in vertical rod bundles are flow-regime-dependent, which limits their practical applicability. This study focused on the development of a full-range drift-flux correlation for upward co-current boiling two-phase flows in vertical rod bundles, applicable to the entire range of void fractions from 0 to 1. This study first evaluated the performance of existing full-range drift-flux correlations, including the Chexal-Lellouche, Choi, and Bhagwat-Ghajar correlations. Then, a new full-range drift-flux correlation for upward co-current boiling two-phase flows in vertical rod bundles was developed with less empiricism. The developed full-range correlation was validated using 276 data points collected from five data sources, covering pressures from 0.25 to 12 MPa. The developed full-range drift-flux correlation demonstrated superior predictive performance to that of the existing correlations. The prediction bias of the developed drift-flux correlation was negligible, with a mean relative error of 2.49 % and a mean absolute relative deviation of 12.1 %. © 2025 Elsevier Ltd