Turbulent heat mixing of a heavy liquid metal flow within the MEGAPIE window geometry: The heated jet experiments

The use of heavy liquid metals (HLM) serving both as coolant and as spallation source facilitates simple beam window geometries. An adequate cooling of the beam window requires a conditioning of the flow. Within the MEGAPIE window this is realized in a cylindrically shaped geometry, in which the main flow is guided in an annular gap downwards and then u-turned close to a hemispherical shell into a riser tube. In order to avoid stagnating fluid domains leading to unacceptably high window temperatures a jet flow is injected in direction of the lower shell. In this study the turbulent mixing of hot jet into a cold main flow is investigated both experimentally and numerically for the MEGAPIE geometry on a 1:1 scale. The experiments have been conducted in the Karlsruhe Lead Laboratory (KALLA). In parallel a numerical simulation has been performed. Close to the technically most interesting positions in the lower shell, a reasonably good agreement between numerical and experimental data has been found. Here, a sufficient description of the turbulent heat transfer in a lead–bismuth flow was obtained. However, as the flow proceeds downstream not only qualitative but quantitative differences appear, which have to be analyzed in more detail in the future.