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Title:Natural convection of molten salt in laterally heated and top cooled vertical cylinders
Author(s):Khattak, Divyansh
Advisor(s):Brooks, Caleb S.; Vanka, Surya P.
Department / Program:Mechanical Sci & Engineering
Discipline:Mechanical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Natural circulation
spectral element method
lateral heating
Abstract:Molten salt reactors offer a promising reactor technology with higher efficiency, lower pumping power and increased power density. Due to the lower operating pressures, high heat capacities, and the ability to transfer heat through natural circulation, they are especially suitable for passive safety. Unlike the common reactor designs with fuel in the form of solid pellets, molten salt reactors use a liquid fuel form where the fissile materials are dissolved in the molten salt. Natural circulation characteristics within the molten salt FLiNaK (Prandtl number = 16) in a vertical three-dimensional cylindrical geometry are numerically studied. The cylinder is laterally heated with an isothermal cooling at the top and an insulated bottom. The effect of the Rayleigh number is investigated for different aspect ratios (0.5, 1.0, 1.5, 2.0) for a total of nine cases. The spectral element method with high polynomial resolution is used to perform the simulations, using the open-source code Nek5000. The different flow patterns and temperature distributions observed for the nine cases are documented. Validation of the results obtained is done by performing a grid-independent study to ensure all the length scales have been captured appropriately. Spatial variation of azimuthally-averaged Nusselt number is presented across height for the steady state cases. Results show a departure from axisymmetry for higher aspect ratios in the steady cases. For the cases where the flow becomes unsteady, the nature of the flow is characterized by using Fast Fourier Transform on the time evolution of axial velocity. Temporal variation of the average Nusselt number of the configuration is also presented for the unsteady cases.
Issue Date:2020-09-18
Rights Information:Copyright 2020 Divyansh Khattak
Date Available in IDEALS:2021-03-05
Date Deposited:2020-12

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