Forced convection heat transfer analyzes of self-heating pebble bed nuclear reactor experiments with openfoam code

The Very High-Temperature Reactor (VHTR), which is one of the new generation nuclear reactors, can be in a packed bed arrangement depending on the type of fuel elements. The fuel of this type of reactor is spheres of the same size and are placed in the reactor core in no particular order. The reactor can transfer heat with the coolant passing through the pores between these spheres. The phenomenon of removing the heat produced in the core is an important safety issue of nuclear reactors. For this reason, reactor heat transfer parameters should be investigated in detail, experimentally, and numerically. In the literature, various mechanisms have been set up or simulations have been made for packed bed systems and the properties of the heat transfer data have been compared. Theoretical models and quasi-experimental formulas have been developed to predict these heat transfer phenomena. To investigate these effects and to determine their accuracy, data to characterize the packed bed structure are needed. Therefore, the focus of this study is to compare the forced convection simulations of thermal flow modeling pebble bed nuclear reactor systems with experimental data with OpenFOAM, an open-source code currently used in the field of fluid mechanics. Within the scope of this thesis, in experimental and numerical (simulation) studies carried out as a TÜBİTAK - NRF (South Korea) Bilateral Cooperation Project, sphere diameters of d=0.004 m, d=0.010 m and H/d (5.10 and 20) ratios; heat transfer calculations with forced convection were performed for temperature, velocity, turbulent kinetic energy distributions, and Nusselt numbers. The results were compared with the results of experimental forced convection by South Korea.