Towards Optimization of Swirl-Generators for Nuclear Fusion Application

The present trends in development of plasma-facing components (PFCs) fusion power plants are towards higher heat removal capability and lower structural material activation. The critical heat flux is an important criterion in the design of these types of components. Since the burnout condition (i.e., the hot spot expansion) limits the power and operation, the effective management would be advantageous. Several researches have been undertaken in an effort to show that critical heat flux can be increased by enhancement techniques such as hypervaportron, porous coating, screw tubes and swirl tape configuration. Considerations of data base availability for prototypical conditions, lifetime, and compatibility with the preferred monoblock type of option led to the swirl tape being selected as reference configuration for the high heat flux regions of the divertor in ITER. However, recently, the excessive pumping penalty of swirl tape has replaced the configuration to screw tube. Even though the screw tube for initially suggested Cu-alloy as an effective cooling material showed the enough CHF margin, the large amount of neutron load required selection or development of better structural material with much lower thermal conductivity conflicting with higher thermal dissipation of hot spot condition. Even though the lowered CHF margin is not issue of ITER operation, it limits the development of fusion power plants. Therefore, the present work is interested in optimization of the enhancement techniques such as swirl tube with twisted tape and screw tube more effectively and a possibility for compound enhancement concepts of a combination of two or tree existing means or new means. The latter, for example, means the combination of screw tube and swirl tape. The heat transfer enhancement achieved by means of twisted-tape inserts is generally accompanied by an increase in pressure drop. The pressure drop increase causes not only higher pumping power, but it can also alter the heat transfer or CHF values, Thus, in order to optimize the design of a thermal device, both thermal and hydraulic performance must be carefully considered and balanced. This work ultimately aims to optimize the design through comparisons of the overall heat/flow performance (HFP) for heat transfer enhancement means such as swirl tube with twisted tape, screw tube and rifled tube based on CFX simulation work for single phase convection flow. As a preliminary work, this paper shows the results of tubes with twisted-tape inserts