Thermal conductivity of high temperature fluoride molten salt determined by laser flash technique

The thermal conductivity of high temperature liquid fluoride salt was measured by laser flash technique for the first time. A graphite crucible was specially designed to exclude the dissolved gas and avoid overflowing of molten salt, meanwhile, a special treat process was used for preparing homogeneous sample. The combined model is feasible for data analysis. The reliability of laser flash method involving crucible structure, sample preparation and data analysis is verified by distilled water and pure KNO3 molten salt. Further, the thermal diffusivity of 46.5 mol%LiF-11.5 mol%NaF-42 mol%KF (FLiNaK) molten salt is determined to be 1.64 × 10−3-2.48 × 10−3 cm2/s at the temperature range of 773-973 K with the blanket atmosphere of helium. Based on specific heat capacity determined by differential scanning calorimetry (DSC) as a constant of 1.88 ± 0.08 J/g K and density measured by our group, the thermal conductivity of FLiNaK molten salt is calculated to be 0.652-0.927 W/m K with the uncertainty of ±0.023 W/m K in the temperature range of 773-973 K.