Thermal-fluidic characteristics of a high temperature heater in an experimental helium loop for VHTR simulations

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A medium-scale helium loop for simulating a VHTR (Very High Temperature Reactor) is now under construction in KAERI (Korea Atomic Energy Research Institute). Two electric heaters of the test helium loop heat the helium fluid up to 950°C at a pressure of 1–9MPa. To optimize the design specifications of the experimental helium loop, conjugate heat transfer in the high-temperature helium heater was analyzed using CFD (Computational Fluid Dynamics) simulations. The main factors tested in this CFD analysis were the effects of turbulence, radiation, gravity, and geometrical configuration of the heater. From the analysis results, the optimum design configuration was selected confirming that the thermal characteristics of the heater meet the design requirements well. In this study, the interrelated effects of buoyancy forces and radiation heat transfer on the geometrical configuration were closely investigated. It was concluded that the buoyancy effects on the helium flows of the heater would be suppressed by the radiation heat transfer inside the heating channel. Various emissivity values of the reflector materials were also tested. Gravity had greater effect on the temperature distribution for a lower emissivity, but the maximum temperature variations due to the emissivity changes from 0.1 to 0.9 were limited to within a few tens of degrees. Finally, more detailed analyses on the HTH (high temperature heater) of the medium scale helium loop including the spacers were performed, and it was confirmed that the thermal-fluidic characteristics of the HTH satisfied the design requirements.