LIQUID-METAL FLOWS IN INSULATING ELEMENTS OF SELF-COOLED BLANKETS

Liquid metal flows in insulating rectangular ducts in strong magnetic fields are considered with reference to poloidal concepts of self-cool ed blankets. Although the major part of the flow in poloidal blanket c oncepts is close to being fully developed, manifolds, expansions, cont ractions, elbows, etc., which are necessary elements in blanket design s, cause three-dimensional effects. The present investigation demonstr ates the flow pattern in basic insulating geometries for actual and mo re advanced liquid metal blanket concepts and discusses the ways to av oid pressure losses caused by flow redistribution. Flows in several ge ometries, such as symmetric and non-symmetric 180 degrees turns with a nd without manifolds, sharp and linear expansions with and without man ifolds, etc., have been considered. They demonstrate the attractivenes s of poloidal concepts of liquid metal blankets, since they guarantee uniform conditions for heat transfer. If changes in the duct cross-sec tion occur in the plane perpendicular to the magnetic field (ideally a coolant should always flow in the radial-poloidal plane), the disturb ances are local and the slug velocity profile is reached roughly at a distance equivalent to one duct width from the manifolds, expansions, etc. The effects of inertia in these flows are unimportant for the det ermination of the pressure drop and velocity profiles in the core of t he flow but may favour heat transfer characteristics via instabilities and strongly anisotropic turbulence.