CFD Annular Flow Modelling Based on a Three-Field Approach

Abstract: This master thesis aim to model the annular flow that occurs in the final section between the fuel rods inside Boiling Water Reactors, by approximating the geometry to a cylindrical pipe. Simulations were performed in the software ANSYS Fluent, as a step in the development of replacing the 1D correlations currently used in the nuclear industry with CFD models in 3D. An Eulerian-Lagrangian approach was used for the three fields of steam, liquid film and liquid droplets in the model. Entrainment was modeled based on 1D correlations from Okawa [7] and deposition with the built in Discrete Phase Model in ANSYS Fluent. The work focused on making the process less time consuming, and increasing accuracy of the model by comparing the results with empirical data based on experimental values. A transverse velocity was applied on the droplets at the point of entrainment with better correlating results with the Okawa model.