UCLA

In liquid metal (LM) blankets of a fusion power reactor, the fluid flow is under the influenceof strong electromagnetic forces resulting from applied plasma-confining magnetic field. The two major concerns of the blanket design are: (1) the compatibility issues between structural materials and high-temperature flowing LM and, (2) high 3D Magnetohydrodynamic (MHD) pressure drop that arises from the interaction between the magnetic field and induced electric currents. To help address these issues, three topics are investigated numerically using the COMSOL Multiphysics software. The first topic is a characterization of a LM (PbLi) flow in the thermal convection loop (TCL), which is used in the experimental corrosion studies. Two modeling tools, a thermohydraulics code and a computational model in COMSOL Multiphysics, have been developed, tested and then applied to the analysis of fluid flow and heat transfer in a TCL. Such a device has recently been used to experimentally evaluate corrosion compatibility of APMT (Fe–21Cr–5Al–3Mo) steel with high-temperature molten eutectic lead-lithium (PbLi) alloy at Oak Ridge National Lab, TN, USA. The 1D thermohydraulics code allows for rapid calculations of the loop parameters as a function of the applied heat flux. The supplemental ii COMSOL finite-element computations provide detailed 3D velocity and temperature field data but are much more time consuming. Both modelling tools demonstrate an excellent agreement in the computed circulation velocity as well as maximum and minimum temperatures. The performed TCL analysis focuses on flow development in the “hot” and “cold” legs, formation of Dean vortices in corner regions, blocking effect of the immersed samples, and radiative and convective cooling effects under the experiment-relevant conditions for Prandtl number Pr = 0.015, Grashof numbers Gr ∼ 107, and Reynolds numbers Re ∼ 104. The second topic is the optimization studies of the inlet manifold design with gradual expansion. MHD flows in a manifold of a liquid metal blanket can significantly contribute to the blanket pressure drop, which is a feasibility issue for almost all liquid metal blanket concepts. In this topic, optimization studies for a prototypic inlet manifold that feature flow expansion are performed for three expansion angles θ, 45◦, 60◦ and 75◦, expansion ratio of 4, and a wide range of Hartmann (Ha) and Reynolds (Re) numbers: 1000 < Ha < 10000, and 50 < Re < 1000 aiming at the MHD pressure drop reduction and a more uniform flow distribution at the exit of the manifold. The 150 flow cases computed with COMSOL Multiphysics in 3D provide an extended database for the pressure drop coefficient, which is used to construct a correlation for the 3D MHD pressure drop. In addition, many data analyses were performed to characterize the flow inside the manifold and access the most important flow characteristics, such as the recirculation flow bubble that appears when the liquid metal enters the expansion region and the flow development length as a function of Ha,Re and θ. The third topic is the LM MHD flow in blanket supply ducts where high MHD pressure drop is related to a space-varying (fringing) magnetic field. Similar to the manifold cases, high MHD pressure drop is caused by 3D MHD effects, which are studied numerically for a non-conducting rectangular duct for 1000 < Ha < 10000, 1000 < Re < 10000 and four values of the magnetic field gradient in the fringing field region. A total of 80 cases have been computed and the corresponding pressure drop coefficients calculated to deduce a correlation for 3D MHD pressure drop based on linear regression analysis. Strong 3D effects have been observed in almost all computed cases as demonstrated by comparison against the quasi-fully developed MHD flow as well as the transverse pressure difference.