CFD analysis of actively cooled divertor target element for stellarator W7-X

The study focuses on the CFD analysis of a possible prototype of water-cooled divertor element for the experimental stellarator-type fusion machine Wendelstein W7-X. The coupled solid-fluid analysis was performed on the selected type of divertor target element. The singlefluid modelling approach was used to explore the effect of the cooling water on the local wall temperature distribution in the cooling channel. Comparison of the wall temperature profile with the local coolant saturation temperature at critical location is presented to detect local superheating regions that may lead to the evolution of boiling flow. The effect of two different heat flux profiles, material of the tiles (tungsten or tungsten heavy alloy) and the effect of the twisted tape was investigated. Maximum temperatures of target materials were compared. The results also included analysis of cooling channel parameters (e.g. superheating, water temperature distribution, pressure drop) and temperature distribution in the cooling channel wall. It is interesting to note that the maximum velocity region is not necessarily located just below the heated wall, but rather near the bottom of the pipe in the colder flow region. The single-fluid results show the necessity to perform realistic simulations in the two-phase flow regime.