Evaluation of bubbler sensors for In Situ measurement of density, liquid depth, and surface tension in molten salts

• Single- and triple-bubblers measure density, surface tension, and liquid depth. • Bubbler systems accuracy is comparable to the Archimedes method for measuring density. • Bubbler systems allow property tracking under transient thermal conditions. • Bubblers prove to be ideal for low-intervention monitoring in harsh environments. • Various NaCl-MgCl 2 compositions were analyzed for temperature-dependent density. Molten salts are employed as heat-transfer fluids in energy systems, including concentrated solar power, thermal-energy storage, and molten salt reactors. Accurate characterization of the thermophysical properties of these materials is crucial to model and operate these systems. In situ measurement of these properties is particularly important when the composition of molten materials changes due to thermal decomposition, corrosion, radiation exposure (radiolysis and fission), or during nuclear-waste treatment processes such as pyroprocessing. This study evaluates the accuracy and reliability of single- and triple-bubbler sensors for simultaneously measuring density, surface tension, and liquid depth. The density of molten sodium chloride-magnesium chloride (NaCl-MgCl 2 ) was characterized using these techniques and was compared with density measurements by the Archimedes method. Our findings indicate that single- and triple-bubbler techniques provide density measurements of comparable accuracy to the Archimedes method, with the added benefits of simultaneously measuring surface tension and liquid depth, allowing easy implementation and automation for in situ measurements during operations in energy systems. Additionally, single- and triple-bubblers enable property tracking under transient thermal conditions, allowing measurements as temperature varies. These results suggest that single- and triple-bubbler methods are suitable for application in harsh environments requiring low-intervention monitoring.