Comparison of different CFD approaches for the simulation of developing free surface two-phase flow in straight and bent pipes

Two-phase flows in feed pipes of thermal separation columns have complex flow patterns and are difficult to predict during sizing and design for geometries with non-straight pipes. Numerical simulation codes have only been validated for very few pipe geometries. This work benchmarks the state-of-the-art Volume-of-Fluid model (VoF) and the Algebraic Interfacial Area Density model (AIAD) for the simulation of two-phase flows with the Eulerian/Eulerian CFD approach for straight pipes and horizontal bends as well as for different pipe diameters and flow rates. Both models are compared and shortcomings of the predicted velocity fields from AIAD in the vicinity of horizontal bends are highlighted. While phase dynamics, e.g., for wavy or disperse flows, are not well reproduced by either model, the phase distribution patterns in straight tubes and bends agree reasonably well with experimental data. Regardless of the geometry, better void fraction prediction is obtained for higher flow velocities and the larger pipe diameter. From the numerical results, recommendations for the selection of feed inlet devices are derived.

Comparison of different CFD approaches for the simulation of developing free surface two-phase flow in straight and bent pipes