Applications of an adaptive multigrid FEM-code to thermal problems in HDR-experiments

The purpose of the present contribution is to demonstrate the efficiency and reliability of an adaptive multigrid FEM-code by applying it to the HDR-TEMR experiments. The injection of cold water results in a stratification of cold water at the bottom of the horizontal pipe and of hot water above. In several test cases, the thermal separation zone was smaller than 50 creating a step-like temperature change at the circumference. In such cases, numerical simulations should use a nodalisation which resolves thin layers and, thus, should have a finer grid were gradients are steep. Such a task can be performed by hand - which is time consuming - or by a sufficiently sophisticated preprocessor. Nowadays a new generation of computer codes is available which automatically refine the grid and adapt it to the specific problem. Such as mesh refinement process starts with a relatively coarse grid which usually needs very few man power time for construction and implementation. In this contribution, we shall present a finite-element-program of this type and corresponding numerical results for a specific TEMR experiment. (orig./GL)