Thermal–hydraulic assessment of cooling air inlet configurations in the ITER upper port 18 Interspace Support Structure

This study presents a thermal–hydraulic optimization of the ITER upper port 18 interspace support structure (ISS) cooling system based on three-dimensional (3D) conjugate heat transfer analysis. It represents the first systematic 3D computational fluid dynamics investigation of cooling-air inlet configurations using full conjugate heat transfer. The effects of cooling-air inlet configurations on the thermal–hydraulic performance were evaluated. Eight inlet arrangements were examined by varying the inlet location (lower versus upper faces), effective inlet area, and associated flow distribution, while maintaining a total airflow rate of 3,500 m 3 /h. The simulations resolved the full interspace geometry, including steel structures, heavy concrete shielding, insulation, and complex piping, using a steady Reynolds-averaged Navier–Stokes approach with the k – ω shear-stress transport turbulence model. Upper face inlets provide significantly better cooling of the ISS main frame than lower face inlets by directly accessing the hottest components. Increasing the total inlet area with multi-inlet layouts reduced the pressure drop and yielded more uniform enthalpy distributions. The corresponding heat-to-power ratio also indicated an improved thermal effectiveness per unit fan power. Flow-field analysis demonstrated that large, slow recirculation cells were correlated with elevated structural temperatures, whereas more homogeneous vortex patterns promoted uniform heat removal. Among these configurations, balanced upper multi-inlet designs with flow splitting between the two upper faces offered the best compromise between structural temperature control, outlet temperature, and hydraulic efficiency, providing design guidance for the UP18 interspace cooling system.