Abstract
The interaction of the liquid metal with the plasma confinement magnetic field constitutes a challenge for the design of fusion reactor blankets, due to the arise of MHD effects: increased pressure drops, heat transfer suppression, etc. To overcome these issues, a dielectric fluid can be employed as coolant for the breeding zone. A typical configuration involves pipes transverse to the liquid metal flow direction. This numerical study is conducted to assess the influence of pipe conductivity on the MHD flow and heat transfer. The CFD code ANSYS CFX was employed for this purpose. The fluid is assumed to be bounded by rectangular walls with non-uniform thickness and subject to a skewed magnetic field with the main component aligned with the cylinder axis. The simulations were restricted to Re = (20; 40) and M = (10; 50). Three different scenarios for the obstacle were considered: perfectly insulating, finite conductivity and perfectly conducting. The electrical conductivity was found to affect the channel pressure penalty due to the obstacle insertion only for M = 10 and just for the two limiting cases. A general increment of the heat transfer with M was found due to the tendency of the magnetic field to equalize the flow rate between the sub-channels individuated by the pipe. The best results were obtained with the insulating pipe, due to the reduced electromagnetic drag. The generation of counter-rotating vortices close to the lateral duct walls was observed for M = 50 and perfectly conducting pipe as a result of the modified currents distribution.
Highlights
The flow of an electrically conductive fluid in the presence of an applied magnetic field deviates from the ordinary hydrodynamic behavior due to the arising of induced currents in the fluid bulk, which generate a volumetric Lorentz force that reduces the flow mean velocity and drastically modifies its features
The interaction of the liquid metal with the plasma confinement magnetic field constitutes a challenge for the design of fusion reactor blankets, due to the arise of MHD effects: increased pressure drops, heat transfer suppression, etc
The viscous forces are confined in thin boundary layers close to the walls that, depending on the relative orientation with the magnetic field, can have thickness δ ∝ M −1 or δ ∝ M −1/2
Summary
The flow of an electrically conductive fluid in the presence of an applied magnetic field deviates from the ordinary hydrodynamic behavior due to the arising of induced currents in the fluid bulk, which generate a volumetric Lorentz force that reduces the flow mean velocity and drastically modifies its features. Turbulence suppression and additional pressure drops are some of the effects caused by the transition to a magnetohydrodynamic (MHD) flow regime [1][2]. MHD flows are of interest for many industrial applications, including the design of breeder blankets for nuclear fusion reactors [3]. Since the tritium breeder material is lithium, eutectic alloys like LiPb have been considered in the past for their excellent thermal properties as working fluids. To ensure the required cooling of the breeding zone, one of the strategies adopted is to insert pipes transverse to the main flow direction [4]. The bounded flow past a cyrcular cylinder is a classic case studied in hydrodynamics and recently it has been investigated in a MHD perspective. The blockage ratio (β) and the obstacle offset from the duct centerline (G/d) are the most important geometric parameters and, together
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