Liquid metal flow in a U-bend in a strong uniform magnetic field

Magnetohydrodynamic flows in a U-bend and in a right-angle bend are considered with reference to the toroidal concepts of self-cooled liquid-metal blankets. The ducts composing the bends have rectangular cross-sections. The applied magnetic field is aligned with the toroidal duct and perpendicular to ducts supplying liquid metal. For high Hartmann numbers the flow region is divided into cores and boundary layers of different types. The magnetohydrodynamic equations are reduced to a system of partial differential equations governing wall electric potentials and the core pressure. The system is solved numerically. The results show that the flow is very sensitive to variations of certain parameters, such as the wall conductance ratio and the aspect ratio of the toroidal duct cross-section. Depending on these parameters, the flow exhibits a variety of qualitatively different flow patterns. In particular, structures of helical and vortex type are obtained. A high-velocity jet occurs at the plasma-facing first wall and there is mixing of the fluid in the toroidal duct. These factors lead to desirable heat-transfer conditions.