Experimental and numerical investigations of heat transfer in the first wall of Helium-Cooled-Pebble-Bed Test Blanket Module—Part 2: Presentation of results

This paper is the continuation of the first report on investigations of heat transfer in the first wall of Helium-Cooled-Pebble-Bed Test Blanket Module for ITER submitted to this Journal (see Ilić et al. [1]). The investigations have been performed experimentally by manufacturing and testing of a mock-up and numerically through the development of corresponding 3D CFD models. The experimental tests have been conducted for HCPB TBM relevant conditions – the test channel made of Eurofer steel, helium coolant at pressure of 8 MPa and inlet temperature of 300 °C and heat flux of 270 kW/m2 at the channel side representing plasma facing side of the first wall. In total six measuring series have been performed in which surface roughness, helium inlet temperature and heater power have been considered as parameters. For each measuring series corresponding 3D CFD computational scenarios have been conducted. By use of experimental data for Eurofer temperature it was possible to verify 3D CFD models. On the other side, 1D CFD approaches failed in comparison with experimental data. Further, a critical analysis of the use of microscopic surface roughness as a method for heat transfer improvement in the first wall has been presented. Finally, based on a detailed analysis of experimental and 3D CFD data obtained in the framework of these activities the main directions for an improvement of cooling channels in the first wall could be proposed.