A Generalized Non-Equilibrium Film Theory Heat Transfer Model for Annular Flow Condensation of Binary Zeotropic Mixtures

Zeotropic mixtures are widely used alternatives to pure fluids due to their favorable thermodynamic properties, environmental benefits, and regulatory compliance. However, their complex condensation behavior driven by concentration gradients and mass transfer resistance presents challenges for accurate heat transfer characterization. To address this, we developed a heat transfer model for annular flow condensation of binary zeotropic mixtures in horizontal tubes, based on non-equilibrium film theory. The model accounts for axial and radial concentration gradients in the vapor phase and uses iterative corrections for interface temperature and heat flux across the vapor phase, mixture, and condensate layer. The model’s performance was validated against an extensive experimental database of 14 binary mixtures from 8 sources, with 92% of predictions falling within ± 30% of experimental data. By evaluating eight annular flow correlations for the condensate side, the model demonstrated adaptability across diverse conditions and provides recommendations for selecting specific correlations for particular binary pairs to enhance accuracy. Additionally, it tracks evolving composition gradients and temperature profiles, offering valuable thermal insights. This versatile model is a critical tool for optimizing condensation heat transfer in zeotropic mixtures, supporting the efficient design and operation of advanced heat transfer systems.