<p>Fundamental metrics of primary interest in thermal-hydraulic predictions include pressure drop and heat transfer. Historically, experiments focused on flow through standard geometries (e.g., pipes) have enabled 1-D and 0-D systems level codes to capture these metrics. Such codes have been used to design and license most reactors currently in operation. For advanced reactors employing molten salt, there is a need to further validate existing models and conduct additional investigations in non-standard flow topologies. For both of these needs, the turbulence model applied can greatly affect the thermal hydraulic metrics of highest importance. The purpose of this work is to perform an assessment of low fidelity turbulence modeling in molten salt flows. We consider different Reynolds averaged Navier Stokes (RANS) models for FLiNaK flow in a circular pipe and quantify the effect of changing models on thermal-hydraulic properties. Commercially available Computational Fluid Dynamics (CFD) code Star CCM+ is adopted to run forced convection simulations. Five different turbulence models were studied, namely Realizable k-ɛ, k-ω Standard Wilcox, k-ω SST, Spalart-Allmaras, and the V2F model. For each model, five different Reynolds numbers ranging from 14,800 to 30,000 were investigated. Nusselt number trends of the five models showed a good agreement with Sieder-Tate and Dittus-Boelter correlations in the fully developed region where all simulation data was within 10% of those correlations. The maximum spread between all five models in that same region was 12.8%. However, that difference was almost double for the entry region (spread of 22%). Since “fully developed” conditions are not realistic expectations for real flow in an actual reactor, and defining the turbulent entry length is still controversial topic, this research suggests further studies to be conducted for reactor specific flow geometries. This will help establish a more trusted framework upon which molten salt thermal-hydraulic predictions can be based</p>

Turbulence Modeling for Developing and Fully Developed Molten-Salt (Flinak) Flow in a Circular Pipe

Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE28/volume/85246

2021 28th International Conference on Nuclear Engineering (ICONE28)

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