Experimental study of liquid metal magnetohydrodynamic flows near gaps between flow channel inserts

The flow of the electrically conducting lead lithium, foreseen in liquid metal blankets as breeder and coolant, under the influence of the plasma-confining magnetic field induces electric currents that create strong electromagnetic Lorentz forces and high magnetohydrodynamic pressure drop. Electrically insulating flow channel inserts (FCI) may be applied for electrically decoupling the liquid metal flow from the well-conducting channel walls. This reduces currents and associated Lorentz forces that are responsible for the major contribution to pressure drop in the blankets. For fabrication reasons, it is unavoidable that gaps between inserts are present. Gaps will interrupt the electrical insulation, thus providing unwanted local short circuit for electric currents. For experimental investigations of 3D effects at junctions of FCIs, a test section has been manufactured and experiments have been performed in the MEKKA facility at the Karlsruhe Institute of Technology (KIT). The present experimental study shows the benefits of FCIs for pressure drop reduction in fully developed flows and quantifies the deterioration of pressure drop reduction by the presence of uninsulated gaps between FCIs.