  Molten salts are a leading candidate for high-temperature heat transfer
fluids (HTFs) for thermal energy storage and conversion systems in concentrated
solar power (CSP) and nuclear energy power plants. The ability to probe molten
salt thermal transport properties in both stationary and flowing status is
important for the evaluation of their heat transfer performance under realistic
operational conditions, including the temperature range and potential
degradation due to corrosion and contamination. However, accurate thermal
transport properties are usually challenging to obtain even for stagnant molten
salts due to different sources of errors from convection, radiation, and
corrosion, let alone flowing ones. To the best of authors' knowledge, there is
no available in-situ technique for measuring flowing molten salt thermal
conductivity. Here, we report the first in-situ flowing molten salt thermal
conductivity measurement using modulated photothermal radiometry (MPR). We
could successfully perform the first in-situ thermal conductivity measurement
of flowing molten $NaCl-KCl-MgCl_2$ in the typical operating temperature (520
and 580 $^oC$) with flow velocities ranging from around 0.3 to 1.0 $m$$s^-1$.
The relative change of the molten salt thermal conductivity was measured.
Gnielinski's correlation was also used to estimate the heat transfer
coefficient h of the flowing $NaCl-KCl-MgCl_2$ in the given experimental
condition. The work showed the potential of the MPR technique serving as an
in-situ diagnostics tool to evaluate the heat transfer performance of flowing
molten salts and other high-temperature HTFs.
