Advanced freeze valves for energy production and conversion systems using molten salts

Mateusz Pater

Research output: Book/ReportPh.D. thesis

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Abstract

Molten salts are being increasingly considered for use in energy production and conversion systems, as well as in energy storage systems. Nuclear reactors and concentrated solar power plants have been utilizing or intending to utilize molten nitrites, fluorides, and chlorides. This industrial PhD project adds on to the research on these salts with a focus on a new alternative, molten sodium hydroxide.

A nitrite-based solar salt and sodium hydroxide are investigated in two different thermal convection loops equipped with freeze valves. The molten salt loops have been designed, assembled, and operated by the author to provide data for thermal hydraulics studies, analyses of melting and freezing, and corrosion measurements. The freeze valves, including a novel C-shaped design, are tested as integral safety components of the loops to inform the design of future facilities and ensure smooth operation of the loop experiments. Computational fluid dynamics models are created to validate the temperature data collected during the experiments of salt natural circulation and salt phase change. A numerical benchmark is created to compare capabilities of different codes to model salt phase change. Additionally, density and viscosity of molten sodium hydroxide are measured at very high temperatures to increase the understanding of the salt’s behavior and aid modelling thereof.

Candidates for industrial development of mechanical and freeze valves for use in molten salt systems are compared. Past and ongoing research on freeze valves and molten salt loops is summarized, and a dedicated design approach is suggested. The holistic view at the molten salts allows for understanding of the complexity of the molten salt based systems, and for making correct decisions with respect to the design of such systems, taking into account thermal hydraulics, material compatibility issues, and the influence of corrosion products.
Original languageEnglish
Place of PublicationKgs. Lyngby
PublisherTechnical University of Denmark
Number of pages302
Publication statusPublished - 2023

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