Verification of radiation heat transfer analysis in KSTAR PFC and vacuum vessel during baking

Highlights: • Thermal network is used to analyze heat transfer from PFC to VV. • Three heat transfer rate equations are derived based on the thermal network. • The equations is verified using Experimental data and design documents. • Most of the heat lost in tokamak is transferred to experimental room air. • The heat loss to the air is 101 kW of the total heat loss of 154 kW in tokamak. - Abstract: KSTAR PFC (Plasma Facing Component) and VV (Vacuum Vessel) were not arrived at the target temperatures in bake-out phase, which are 300 °C and 110 °C, respectively. The purpose of this study is to find out the reason why they have not been reached the target temperature. A thermal network analysis is used to investigate the radiation heat transfer from PFC to VV, and the thermal network is drawn up based on the actual KSTAR tokamak. The analysis model consists of three equations, and is solved using the EES (Engineering Equation Solver). The heat transfer rates obtained with the analysis model is verified using the experimental data at the KSTAR bake-out phase. The analyzed radiation heat transfer rates from PFC to VV agree quite well with those of experiment throughout the bake-out phase. Heat loss from PFC to experimental room air via flange of VV is also calculated and compared, which is found be the main reason of temperature gap between the target temperature and actually attained temperature of KSTAR PFC.