Mathematical model of unsteady flow in a natural circulation helium loop

Abstract

This article presents a one-dimensional transient mathematical model of a helium thermosyphon, which was validated experimentally and shows agreement with measurement. The novelty stems mainly from its complexity, ability to cover real-world scenarios and a large variety of (not only) large-scale thermosyphon devices. The model uses scenario-driven boundary conditions that replicate the operation of the physical model, including the accumulation of heat energy in the solid parts of the heat exchangers and changes in mass of the flowing medium. The model is implemented using both the Eulerian fixed control volume approach and the Lagrangian particle moving approach, along with the pressure correction algorithm, which is innovative too. This paper contains a comprehensive description of the model algorithm, testing of numerical properties, such as sensibility to time step value and grid density; and the heat accumulation effect. The optimal model settings are presented. In addition, a comparison with experimental data is provided. The best agreement between model and measurement was obtained for pressure values (97% of data samples were below 5% of relative error), followed by temperature values (71% of data samples were below 5% of relative error). The model and measurement exhibited the poorest agreement in velocity values, with only 33% of data samples falling below the 5% relative error threshold.