In-situ Thermophysical Measurement of Flowing Molten Chloride Salt Using Modulated Photothermal Radiometry

TL;DR

This paper introduces the first in-situ method using modulated photothermal radiometry to measure the thermal conductivity of flowing molten salts at high temperatures, enabling better evaluation of heat transfer performance in energy systems.

Contribution

The study presents a novel in-situ measurement technique for flowing molten salt thermal conductivity, overcoming previous limitations and providing real-time diagnostics under operational conditions.

Findings

Successfully measured thermal conductivity of flowing molten salt at 520-580°C.

Demonstrated the technique's ability to monitor changes in thermal conductivity with flow conditions.

Estimated heat transfer coefficient using Gnielinski's correlation.

Abstract

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.