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Numerical Simulation of Annular Flow Boiling in a Vertical Pipe Using Two-Fluid Model

The goal of this paper is to develop a numerical model for computation of annular flow boiling in a vertical pipe under 70 bar pressure and 10 K inlet subcooling. The model is based on two-fluid formulation in conjunction with an extended formulation of Rensselaer Polytechnic Institute model for boiling flows. Here, the successful modeling of the annular flow boiling is achieved by use of closure correlations for interfacial transfer proposed by [1]. This refers to constitutive relations for vapor-bubble diameter and interfacial lift force, both being computed as flow regime dependent. A uniform wall heat flux is applied at the pipe wall, while the inlet mass fluxes were varied. The model validation is done by comparison of vapor volume fraction at specific points near the pipe outlet with the data extracted from measurements conducted by [2]. The obtained results agree well with the experimental data, thus indicating the reliability of the developed model in computation of such multiphase flow phenomena.

Annular flow boiling, Two-fluid model, CFD

[1] S.-J. Yoon, G. Agostinelli, E. Baglietto. Assessment of multiphase CFD with zero closure model for boiling water reactor fuel assemblies, in: 17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH 17), Xi'an, China, 2017. [2] C. Adamsson. Measurements of Film Flow Rate in Heated Tubes with Various Axial Power Distributions. PhD Thesis, KTH Sweden, 2006.