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Asymptotic analyses and numerical simulations have been performed to predict liquid metal flow in an electrically conducting circular pipe that exhibits stepwise bends in a strong uniform magnetic field. The present work is motivated by applications in nuclear fusion engineering, where such step-shaped double bends are foreseen in the shield behind the liquid metal test blanket module [1] that will be tested in the International Thermonuclear Experimental Reactor (ITER). Although the geometry is relatively simple, quite complex and unexpected flow patterns are observed, depending on the orientation of the magnetic field. For that reason, the present type of flow constitutes an interesting fundamental problem in magnetohydrodynamics. [ABSTRACT FROM AUTHOR]

Laminar liquid metal flows in straight ducts of square cross-section under strong transverse magnetic fields have been investigated using a numerical code based on finite volume methods. The scope of the simulations is the liquid metal transport in nuclear fusion power reactors, where the orientations of duct walls do not ideally align with the direction of imposed magnetic field. Detailed knowledge about the combined impact of field strength, inclination angle of walls with respect to magnetic field lines, wall thickness, and electric conductivity on the flow of the liquid metal breeder and coolant PbLi is essential for the design of future fusion breeding blankets. Simulations have been performed in the range of fusion relevant parameters and results have been confirmed by asymptotic results for some special cases. [ABSTRACT FROM AUTHOR]

Liquid metal pipe flow entering a strong magnetic field has been investigated experimentally in the MEKKA laboratory at the Karlsruhe Institute of Technology. In the region of the spatially varying magnetic field, the flow becomes three-dimensional due to additional three-dimensional electric currents that are driven by axial potential gradients. The influence of these extra currents on the distribution of pressure and electric potential has been studied for strong magnetic fields. [ABSTRACT FROM AUTHOR]

The transition from laminar to time dependent magnetohydrodynamic duct flows with finite electrically conducting Hartmann walls and insulating side walls is investigated. The linear stability limit is determined based on the procedure presented in [2]. Based on these results, numerical simulations with OpenFOAM are performed for Hartmann numbers 500=Ha=2000, Reynolds numbers 300=Re=12000 and with the wall conductance ratio c=0.03. Simulations show that the so-called Ting&Walker (TW) vortices, which form at the onset of instability above the critical Reynolds number, evolve further with increasing Reynolds number. Jet detachments occur at sufficiently high Re. Onsets of TW-vortices and occurrence of jet detachments in the simulations agree very well with theoretical and experimental results. [ABSTRACT FROM AUTHOR]

In liquid metal blankets for fusion reactors, leakage currents which cross electrically conducting walls and pass from one fluid domain into the adjacent one, have to be taken into account since they influence flow partitioning and pressure drop in parallel ducts. The so-called multi-channel effects depend on the path of leakage currents that is determined by the orientation of common walls with respect to the imposed magnetic field, their electrical conductivity, and by the direction of the flow in neighboring ducts. The present work aims at providing an overview of main phenomena that occur in multiple channel assemblies, where flows are coupled by an exchange of electric currents. [ABSTRACT FROM AUTHOR]

A linear stability analysis has been performed for a liquid-metal flow in a square duct with thin electrically conducting walls in a uniform magnetic field. The analysis uses a vector-streamfunction-vorticity formulation, and the resulting eigenvalue problem is solved by a Chebyshev collocation method as described in previous studies for ideal cases [1, 2]. This method has been extended to apply for magnetohydrodynamic flows in ducts for engineering applications with thin walls of finite electrical conductivity. For strong magnetic fields, i.e. when the Hartmann number Ha is very high, such flows exhibit high velocity jets in narrow side layers of thickness δs ~ Ha-1/2 along walls aligned with the magnetic field. Jets become unstable when the Reynolds number Re is increased beyond a critical value Rec. For Ha ≫ 1 the critical Reynolds numbers apparently approach constant values depending on the conductivity of the duct walls, and an asymptotic dependence is found for the critical wave number as kc ~ 0.5Ha1/2. [ABSTRACT FROM AUTHOR]

For applications in nuclear fusion reactors where magnetic fields are very strong, liquid metal flows in the cores of ducts can often be regarded as inertialess and practically inviscid, while viscous effects are localized in thin boundary layers. The intense electromagnetic Lorentz forces, resulting from the interaction of induced electric currents and imposed magnetic field, tend to remove flow variations along magnetic field lines and they force the fluid to circulate mainly in planes perpendicular to the field. The established quasi-two dimensional magnetohydrodynamic flow can be predicted by means of an approximate model by reducing the basic governing equations to a 2D problem by analytical integration along magnetic field lines. Such models have been applied in the past by numerous authors to investigate duct flow problems and magneto-convection. However, limitations of those Q2D approaches have never been systematically studied. [ABSTRACT FROM AUTHOR]

A linear stability analysis is performed to investigate the onset of convective motions in a flat cavity filled with liquid metal in which a volumetric heat source is distributed uniformly and a horizontal magnetic field is imposed. A quasi-2D mathematical model is derived by integrating the 3D governing equations along the magnetic field direction, which yields a dissipation term in the 2D equations that accounts for 3D viscous effects in thin boundary layers at walls perpendicular to the field. This type of buoyant flow without magnetic field has been investigated by Roberts [1] and the present study extends those results to magnetohydrodynamic conditions. Numerical simulations are performed to support the analytical results and to describe the main convective flow patterns. [ABSTRACT FROM AUTHOR]

The European Community is committed to the development of a DEMOnstration fusion power plant whose operation could start as soon as 2050. The blanket is one of the most critical components in a fusion reactor; three of the four blanket concepts currently under development are based on the use of the liquid eutectic alloy Pb-15.7Li. Since the blanket will operate under the strong magnetic field used to confine the plasma, electromagnetic forces will occur in the PbLi flow, giving rise to magnetohydrodynamic (MHD) phenomena. [ABSTRACT FROM AUTHOR]

In the European concept for a liquid metal test blanket in the International Thermonuclear Experimental Reactor (ITER) lead lithium is foreseen as a breeder material for generating the plasma fuel component tritium. The flow of the electrically conducting liquid breeder in the blanket is strongly affected by the intensity and distribution of the externally applied magnetic field required for plasma confinement. In a series of experiments, MHD flows in a scaled model of the blanket have been investigated. The pressure distribution in the mock-up has been determined, regions in which significant pressure drops occur have been identified and these characteristic contributions have been quantified depending on the flow rates and on the strength and non-uniformity of the magnetic field. Measurements show that the magnitude of the total pressure drop in the mock-up is significantly influenced by the strength of the local magnetic field at the manifolds, while gradients of the field across the entire module have minor effects. [ABSTRACT FROM AUTHOR]