Development and application of computational fluid dynamics approaches within the European project THINS for the simulation of next generation nuclear power systems

Experimental Validation of ANSYS CFX for Transient Flows With Heat Transfer in a Tubular Heat Exchanger

Within the European SESAME project, extensive experimental work was performed and complemented by the development, application, and validation activities of thermal-hydraulic simulation tools for different scales. The TALL-3D experimental facility, operated by KTH Royal Institute of Technology in Stockholm, is designed for thermal-hydraulic experiments with lead-bismuth eutectic (LBE) coolant at natural and forced circulation conditions. The heat generated in the primary TALL-3D circuit is transferred via a double-tube counter-flow heat exchanger (HX) to the secondary side, which is cooled by glycerol oil. Validation calculations with the coupled simulation code ATHLET-ANSYS CFX within the European THINS project showed that one of the major challenges for this one-dimensional–three-dimensional (1D–3D) simulation of the experimental facility lies in the calculation of the HX with ATHLET. This is due to the fact that glycerol oil properties are not yet available for ATHLET. In order to better understand the flow and heat transfer phenomena inside the HX, 3D stand-alone calculations with ANSYS CFX were carried out for the SESAME experiment TG03.S301.03. The data generated in this experimental run is challenging for validation of computational fluid dynamics (CFD) codes, because the test combines heat transfer between buoyancy-driven LBE flow in the primary circuit and a turbulent oil flow in the secondary TALL-3D side. Moreover, the validation gets even more difficult for the CFD approach due to the fact that both coolants are nonunity Prandtl fluids, and this requires a careful modeling of the turbulent heat flux. In this paper, the TALL-3D HX behavior during test TG03.S301.03 is analyzed, and the results of the ANSYS CFX calculations are compared with measurements.

Research Challenges of Heat Transfer to Supercritical Fluids

Supercritical fluids (SCFs) become more and more important in various engineering applications. In nuclear power systems, SCFs are considered as coolant of the reactor core such as the supercritical water-cooled reactor (SCWR), superconducting magnets and blankets in the fusion reactors, or as fluid in the energy conversion systems of the next generation nuclear reactors. Accurate determination of heat transfer and the temperature of the structural material (e.g., fuel rod cladding) is of crucial importance for the system design. Thus, extensive studies on heat transfer to SCFs have been carried out in the past five decades and are still ongoing worldwide. However, no breakthrough is recognized or expected in the near future. In this paper, the status, main challenges, and future R&D needs are briefly reviewed. Three aspects are taken into consideration, i.e., experimental studies, numerical analysis, and model development for the prediction of heat transfer coefficient (HTC). Several key challenges and also the important subjects of the future R&D needs are identified. They are (a) data base for turbulence quantities, (b) multisolution of wall temperature, (c) extensive Reynolds-averaged Navier–Stokes (ERANS) method, and (d) new prediction method for HTC.