Thermal-fluid modeling of single- and two-phase flows in the W7-X high heat flux divertor scraper element

The Wendelstein 7-X (W7-X) stellarator experiment is scheduled to begin operation in 2015 with steady-state operation planned for 2019. During the steady-state operation, certain simulated plasma scenarios have been shown to produce heat fluxes that surpass the technological limits on the edges of the divertor target elements. To reduce the heat load on the target elements, the addition of a “scraper element” (SE) in ten divertor locations is under investigation. Two aspects of thermal-fluid modeling for the W7-X SE components are analyzed in this paper using the ANSYS CFX 15.0 software: (1) sensitivity to turbulence models in single-phase and (2) two-phase modeling with the standard k-epsilon model. The results from the single-phase survey of seven turbulence models reveal a significant sensitivity to the selected model in the thermal-hydraulic analysis. Two-phase modeling is completed with the k-epsilon turbulence model, but no vapor generation is recorded. A significant temperature gradient between the liquid-solid interface indicates the need for a turbulence model that can achieve higher mesh resolution in the near-wall region.