Investigation on Thermal Hydraulics Characteristics of a Thermosiphon for Efficient Decay Heat Removal

A thermosiphon can be used as a passive safety component, which can be used for the removal of decay heat from the nuclear reactor core. By investigating the characteristics of the fluid flows in a thermosiphon, the heat transfer characteristics of a thermosiphon for decay heat removal can be analyzed. The focus of this study is to simulate and analyze the heat transfer and fluid flow characteristics in terms of an onsite power failure and normal shut-down for maintenance. In this study, a comparison of heat transfer has been shown between an open loop and a closed loop thermosiphon, and a comparison of fluid flow characteristics is determined. The finite element method has been used to conduct the study within 300-400K temperature. Reynolds Number and Nusselt Number are the main dimensionless number to study. High Reynolds and Nusselt numbers have been found in the closed-loop thermosiphon than in the open loop, indicating more efficient heat transfer along closed-loop thermosiphons. The Navier-Stokes equation and the continuity equation, the basis of Computational Fluid Dynamics (CFD), have been used as the principle governing equations to conduct the study. ANSYS has been used to experience numerical investigation. At the beginning of this study, the models of open-loop and closed-loop thermosiphons were created. Proper meshing, boundary condition and initial condition were applied to the model for CFD simulation to get the desired results. The results of the simulation were compared with an experimental result for validation. The study's key findings are that the Reynolds number and Nusselt number of the closed-loop thermosiphon are higher than the open-loop thermosiphon. Thus, faster heat removal of the decay heat from the reactor core can be achieved through the closed-loop thermosiphon.