Flow-regime based non-equilibrium heat-transfer model of in-tube flow condensation of binary zeotropic mixtures

Accurate prediction of condensation heat transfer in binary zeotropic mixtures remains a central challenge for designing next-generation heat exchangers employing low-global-warming-potential refrigerants. While recent non-equilibrium models have improved understanding of interfacial resistance and concentration gradient effects, most formulations remain limited to annular flow, despite the prevalence of diverse flow regimes under practical operating conditions. In this work, a non-equilibrium framework is developed to explicitly incorporate multiple flow regimes by integrating two established flow pattern maps: the mechanistic El Hajal–Thome–Cavallini model and the empirical Shah correlation map. The framework couples regime identification with regime-dependent condensate-side heat transfer correlations, accounting for both convective and film condensation contributions. Validation against a comprehensive database of 2046 experimental points covering 27 binary mixtures demonstrates model robustness across stratified, stratified-wavy, intermittent, annular, and mist flows. Results show that the predicted flow regime can differ significantly between the two maps; yet, both yield similar predictive accuracy exceeding 90% within ±30% error bounds, confirming the consistency and flexibility of the approach. Benchmarking against a generalized non-equilibrium model further highlights the superior capability of the present framework to capture axial and radial concentration gradients, leading to enhanced prediction fidelity across flow regimes. This extension establishes a versatile and reliable tool for the design and optimization of condensers operating with modern zeotropic refrigerants, leading to a more accurate prediction of heat transfer area, thermal performance, and overall system efficiency, thus more accurate condenser sizing and systems operation with low-GWP refrigerants.