Numerical Simulation of Thin-Film MHD Flow for Nonuniform Conductivity Walls

Abstract

Liquid metals offer unique properties and their use in a nuclear fusion reactor, both as confined flows and free surface flow, is widely studied in the fusion community. The interaction between this conductive fluid and the tokamak magnetic fields leads to Magnetohydrodynamic (MHD) phenomena that influence the flow features. To properly design components that employ liquid metals, it is necessary to accurately predict these features and, although the efforts made in development, a mature code specifically customized to simulate MHD flows is still unavailable. In this work, the general purpose CFD code ANSYS CFX 18.2 is validated for MHD free surface thin film flow with insulated walls, up to 𝐻𝑎 = 1000 and for several values of the characteristic width/thickness ratio, comparing the results with the theoretical relation available in the literature. For all the cases considered, the maximum integral error is found below 10 %. Successively, the validated code is used to investigate the MHD flow in a chute with a characteristic film ratio equal to 0.1 and for 𝐻𝑎 = 300. Uniform and non-uniform wall electrical conductivity cases are considered with the latter modelled by placing on the side walls and on the back wall localized regions with different conductivity. The electrical conductivity of the back wall is found to have a negligible effect on the global flow when the lateral wall in insulated, similarly to what is observed for the analogous bounded flow. Contrariwise, an electrically conductive lateral wall is found to enhance the free surface jet and to modify the Hartmann layer structure.

Design and Integration of the EU-DEMO Water-Cooled Lead Lithium Breeding Blanket

“…Figure 13 and Figure 14 show the velocity and temperature distribution at Ha = 9159 In broad agreement with the previous studies [27,28], no temperature fluctuations were identified after 100-300 s of transient, and heat transfer was still dominated by conduction Flow repartition is expected to reach up to 300% of the nominal flow (0.155 kg/s) for the terminal ones and as low as 25% for the equatorial ones. These values must be intended as indicative since they are going to be affected by coupling, even if the accurate agreement in terms of overall pressure loss between our model and CFD calculations for the WCLL TBM (see Ref.…”

“…Figure 12 shows the differential pressure between OB BZ cells, which is qualitatively consistent with [26], even if coupling is currently not modeled in R5-MHD. Dedicated CFD analyses have also been conducted to characterize the magnetoconvective regime in the OB equatorial elementary cell considering an idealized pipe layout (straight toroidal tubes) [27]. Compared to previous studies [28,29], the present model aimed to investigate the effect of a skewed magnetic field, more accurate FW thermal boundary conditions and higher magnetic field intensity (≈4 T, Ha = 9159).…”

Magnetohydrodynamics in free surface liquid metal flow relevant to plasma-facing components

“…He used a Galerkin method with two basic functions in the Y-direction, the parabola, and the Hartmann profile, to approximate the velocity profile along the magnetic field lines. Results of Shishko model were confirmed by the fully developed CFD analysis using CFX [52]. In the analytical model we used a drag formula from Shishko paper and applied it at each cross-section for the developing flow on the horizontal plate as shown below:…”

Numerical Simulation of High-Density Ratio Bubble Motion with interIsoFoam

“…Overall, interIsoFoam has proven to be able to correctly simulate the basic characteristics of a flow with a high density ratio, therefore it is an excellent candidate for the future implementation of the MHD equations, following the methodology presented by Zhang et al [41], for the study of the migration of helium bubbles in the blanket [2,3], but also in the framework of the advanced PFCs [17][18][19].…”

“…The possibility of analysing these effects through an MHD solver capable of simulating mixtures of a liquid metal and a gas is, indeed, very important both for the design of the breeding blanket [2,3] and for the plasma-facing components, in which advanced solutions may foresee the employment of liquid metal films, jet curtains and other solutions to protect the solid substrate below from the thermal and radiative load coming from the plasma [17][18][19].…”