Abstract

Molten salts form an ideal heat transfer fluid for advanced energy generation systems, including molten salt reactors (MSR). Accurate characterization of molten salt thermal conductivity is needed to confidently predict transient thermal behavior and optimize salt properties. Measurements are hindered by salts' challenging material properties, which---in the case of the needle probe device---induced unaccounted physical changes that limited its accuracy and repeatability. Sparse thermal conductivity data in general is exacerbated by a limited fundamental understanding of molecular energy transfer in liquids. This work extends the experimental capacity for compositional studies using the needle probe and proposes a theoretical model for predicting molten salt thermal conductivity as a function of composition and temperature. A calibration approach using gaseous argon as a reference fluid was developed to characterize the needle probe device. The resulting calibrated needle probe enabled accurate profiling of compositional variation in a case study of solar salts (NaNO3-KNO3) with varied concentrations of SiO2 nanoparticles. Measurements of the solar salts yielded theoretically consistent negative dependencies, with measurement uncertainty within 12.7%. The compositional study provided the resolution necessary to discern the influence of nanoparticle-mediated structural effects on thermal conductivity enhancement. An extensive review of theories of thermal conductivity compared to the existing measurement data indicated the need to directly link molten salt structure to the mean free path. A structural coherence model was introduced to estimate the average propagation distance of energy carriers, informed by the partial pair distribution function (PDF). Model predictions were compared to a range of unary and higher-order mixtures, including actinides, exhibiting a mean average error of 15.6% across all salts. For the first time, predicted deviations were within experimental uncertainty for both actinide and non-actinide salts. The results of this work extend experimental and theoretical approaches to the comprehensive characterization of molten salt thermal conductivity, with broader implications for understanding fundamental liquid-phase energy transport.

Degree

College and Department

Ira A. Fulton College of Engineering; Mechanical Engineering

Rights

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