Free-Surface Liquid Lithium Flow Modeling and Stability Analysis for Fusion Applications
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ORIGINAL RESEARCH
Free-Surface Liquid Lithium Flow Modeling and Stability Analysis for Fusion Applications Andrei Khodak1
•
Fan Yang2 • Howard A. Stone2
Accepted: 20 September 2020 Ó This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply 2020
Abstract Liquid metal plasma facing components are considered an attractive design choice for fusion devices including pilot plants. Virtual prototyping of such devices includes modeling of free-surface flow of the electrically conductive liquid, which requires computational fluid dynamics (CFD) and magnetohydrodynamics (MHD) simulations. Numerical tools capable of simulating flows and heat transfer in the free-surface MHD flow were developed at PPPL based on the customized ANSYS CFX. MHD is introduced using a magnetic vector potential approach. Free-surface flow capabilities are available in the code and were tested. Special stabilization procedures were derived and applied to improve convergence of the momentum equations with the source terms due to the Lorentz force and surface tension. Important characteristics of the fusionrelevant liquid metal flow is free surface smoothness and stability. Heat flux from the plasma impacts the liquid surface at a very acute angle, so any change of the free surface from axisymmetry can dramatically increase the local heat flux density and thus create excessive evaporation of liquid lithium into the plasma, which is detrimental to operations. Stability analysis of the liquid metal film flow was performed to determine applicable flow regimes. Thin film flow along horizontal wall is considered. Effects of gravity, magnetic field, and surface tension are included in the analysis. Keywords Liquid lithium CFD MHD Stability analysis
Introduction In present paper, a stagnant liquid lithium layer is placed on the wall above the plasma as shown in Fig. 1. This represents the upper divertor region of the fusion device. In such a concept, the liquid lithium layer is subject to the Rayleigh–Taylor instability due to gravity, and also magneto-hydrodynamics (MHD) effects due to magnetic field. Stability analysis of this situation based on a thin film approach was presented in [1]. Lithium has an acceptable liquid state temperature range, excellent retention properties for hydrogen deuterium and tritium, and a low Z value, making it the primary choice for the majority of liquid metal plasma facing & Andrei Khodak [email protected] 1
Princeton Plasma Physics Laboratory, Princeton, NJ 08543, USA
2
Department of Mechanical and Aerospace Engineering, Princeton, NJ 08544, USA
components (PFC) concepts. Although current analysis is limited to the isothermal case, temperature-dependent properties of liquid lithium [2] are used in the models, with the ranges presented in Table 1.
Governing Equations Continuity, momentum and energy equations are solved simultaneously for the plasma–quid metal system: ~ oqV ~ qV ~p þ r ~ ðsÞ þ ~ ~ ~V
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