Development of an OpenFOAM non-equilibrium condensation model for flow loss and performance prediction in steam transonic flows

Efficient prediction of wet steam behavior is essential for optimization of high-speed nozzles, supersonic separators and steam turbines, where non-equilibrium condensation (NEC) induce entropy generation, performance loss, and component erosion. This study develops a modular OpenFOAM-based solver incorporating IAPWS-IF97 thermophysical properties to simulate both equilibrium and non-equilibrium condensation with flexible nucleation and droplet growth models. Five condensation models-non-condensation, equilibrium, Wilson line, monodisperse, and moment method-are systematically evaluated using the Moses–Stein nozzle as a benchmark, with experimental validation and mesh independence verification. To ensure consistent assessment, five classical droplet growth laws (Hertz-Knudsen, Gyarmathy, Fuchs-Sutugin, Young, and Blend) are examined, and the Gyarmathy model is selected for unified non-equilibrium analysis. Results show that equilibrium and Wilson line models underpredict entropy generation and flow losses, while non-equilibrium models capture delayed nucleation, finite droplet growth, and condensation-induced pressure recovery. Among them, the moment-based model provides the most realistic prediction of pressure evolution, entropy rise, and nozzle efficiency, which are crucial for loss evaluation and turbine design. A temperature-dependent analysis further reveals that higher inlet superheat delays nucleation and modifies the balance among potential, kinetic, and entropy losses, leading to a monotonic increase in overall thermal efficiency. Analysis of inertial and thermal relaxation times demonstrates asynchronous droplet responses to momentum and heat transfer, elucidating the microscopic origins of irreversible losses. The established solver offers a validated and extensible framework for studying NEC phenomena and guiding the design and optimization of wet steam energy systems.