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Measuring and Predicting the Thermal Conductivity of Molten Salts for Nuclear Energy Applications

Gallagher, Ryan C.
http://orcid.org/0000-0002-5372-6644
http://rave.ohiolink.edu/etdc/view?acc_num=osu1669594076226674

Abstract Details

2022, Doctor of Philosophy, Ohio State University, Nuclear Engineering.
Molten salts have favorable properties for advanced energy systems, including thermal energy storage, molten salt nuclear reactors, concentrating solar power systems, and fusion reactors. However, uncertainties and knowledge gaps exist in many molten salts' chemistry, thermophysical properties, and thermodynamics. The thermal conductivity of molten salt is relatively lacking in experimental data and features high uncertainties and discrepancies in the existing experimental data. The limited knowledge of molten salt thermal conductivity inhibits the development of new technologies that can utilize molten salt. Thus, there is a need for improved understanding and standardized experiment techniques to provide the property data critical for these applications. To address this need, a steady state variable gap thermal conductivity measurement system was designed, fabricated, and tested on high-temperature helium and nitrate salt. The tests showed reasonable agreement with the standards but showed increasing error with increasing temperature. The design was considered suitable for further development and testing, but additional modifications to limit the effects of heat losses through the structure were required. A modified system was used to measure eutectic LiF-NaF-KF molten salt. This salt mixture has discrepancies between existing data sets and shows a positive trend of thermal conductivity with temperature, which disagrees with current theoretical predictions and the behavior seen in many other salt mixtures. The experimental results were compared to a kinetic theory-based (Gheribi) thermal conductivity model and molecular dynamics predictions to validate the models. The experimental data were found to agree with the models, showing a negative dependence of thermal conductivity with temperature for the first-time using experiments leading to further investigation of the Gheribi model in the subsequent studies. The Gheribi model assumes that density, which strongly influences the temperature dependence of thermal conductivity, can be estimated by the molar fraction weighted sum of the unary component densities. To verify this assumption for LiF-NaF-KF, the density was measured experimentally with the displacement method and predicted semi-empirically using the Redlich-Kister expansion method. The model was compared to the experimental data showing agreement with the magnitude of density and the thermal expansion. Further, the parameters of the semi-empirical model proved that the density of the LiF-NaF-KF system can be predicted reasonably well with the assumption of ideal mixing. Lastly, predictions from kinetic theory models were compared to empirical data for other mixtures to provide further validation of their predictive capability. The systems considered in this section included LiF-NaF-KF, KCl-MgCl2, NaCl-KCl-MgCl2, NaF-KF-MgF2, and LiCl-KCl molten salts. The model’s predictions showed agreement with the experimental data, further proving the capability of these models. Finally, the models were used to predict the thermal conductivity of several molten salt mixtures containing RbX (X = Cl- or F-), which have not been investigated computationally or experimentally.
Lei Cao (Advisor)
Vaibhav Sinha (Committee Member)
Tunc Aldemir (Committee Member)
Lei Cao (Committee Chair)
Nuclear Engineering
molten salt; thermal conductivity; variable gap; thermal analysis; density; experiments

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Citations

  • Gallagher, R. C. (2022). Measuring and Predicting the Thermal Conductivity of Molten Salts for Nuclear Energy Applications [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1669594076226674

    APA Style (7th edition)

  • Gallagher, Ryan. Measuring and Predicting the Thermal Conductivity of Molten Salts for Nuclear Energy Applications. 2022. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1669594076226674.

    MLA Style (8th edition)

  • Gallagher, Ryan. "Measuring and Predicting the Thermal Conductivity of Molten Salts for Nuclear Energy Applications." Doctoral dissertation, Ohio State University, 2022. http://rave.ohiolink.edu/etdc/view?acc_num=osu1669594076226674

    Chicago Manual of Style (17th edition)

osu1669594076226674
443
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This open access ETD is published by The Ohio State University and OhioLINK.