Thermal diffusivity measurement on Molten Salts using LFA 1000
The measurement of the temperature conductivity of the molten salt FLiNaK was conducted in a helium atmosphere from 773 K to 973 K using a Linseis LFA1000 system.
A specially designed crucible was inserted into a sample robot capable of accommodating up to three samples simultaneously. Prior to the actual test, the sample was preheated several times slightly above the melting temperature to allow degassing of the material and avoid bubbles in the salt melt.
The thermal conductivity of the molten salt can be calculated with the aid of the thermal diffusivity measured by the LFA and the data on specific heat capacity and density using the following relationship:
λ: Thermal conductivity, α: Thermal diffusivity, ρ: Density, cp: Specific heat capacity, T: Temperature
The results for thermal diffusivity and thermal conductivity are depicted in the following graph. Both properties exhibit a fairly linear increase in values with temperature.
In summary, the thermal conductivity of FLiNaK molten salt was determined to be 0.652-0.927 W/m∙K with an uncertainty of +/- 0.023 W/m∙K in the temperature range of 773 K to 973 K . This demonstrates good agreement with previously published values.
In conclusion, the Laser Flash technique, combined with the specially designed crucible and the combined model by Dusza, proves to be a reliable method for determining the thermal diffusivity of molten salts at high temperatures.*
*See X.-H. An et al. (2015): thermal conductivity of high temperature fluoride molten salt determined by laser flash technique, in: International Journal of Heat and Mass Transfer, pp. 872 – 877.